Wireless from A to Z
A to Z
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A to Z
Nathan J. Muller
New York Chicago San Francisco Lisbon London Madrid
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DOI: 10.1036/0071429182
To my brother Jim
On his retirement from the
South Burlington, Vermont,
Police Department
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Access Points 1
Advanced Mobile Phone Service 6
Air-Ground Radiotelephone Service
Amateur Radio Service 12
Basic Exchange Telephone Radio Service
Bluetooth 18
Bridges 27
Cell Sites 31
Cellular Data Communications 34
Cellular Telephones 36
Cellular Voice Communications 48
Citizens Band Radio Service 55
Code Division Multiple Access 59
Competitive Local Exchange Carriers
Cordless Telecommunications 70
Data Compression 75
Decibel 80
Digitally Enhanced Cordless Telecommunications
Direct Broadcast Satellite 87
Enhanced Data Rates for Global Evolution
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Family Radio Service 97
Federal Communications Commission 99
Fixed Wireless Access 103
Fraud Management Systems 105
Frequency Division Multiple Access 119
Global Maritime Distress and Safety System 123
General Mobile Radio Service 125
General Packet Radio Service 128
Global Positioning System 131
Global System for Mobile (GSM) Telecommunications
Hertz 149
Home Radio-Frequency (RF) Networks
i-Mode 159
Incumbent Local Exchange Carriers 161
Infrared Networking 164
Integrated Digital Enhanced Network 172
Interactive Television 175
Interactive Video and Data Service 181
Interexchange Carriers 183
International Mobile Telecommunications 186
Laser Transmission 195
Local Multipoint Distribution Service
Low-Power FM Radio Service 205
Low-Power Radio Service 208
Maritime Mobile Service 211
Microwave Communications 213
Mobile Telephone Switching Office 217
Multichannel Multipoint Distribution Service 220
Multichannel Video Distribution and Data Service 223
Over-the-Air Service Activation
Paging 229
PCS 1900 238
Peer-to-Peer Networks 243
Personal Access Communications Systems
Personal Air Communications Technology
Personal Communications Services 262
Personal Digital Assistants 266
Personal Handyphone System 273
Private Land Mobile Radio Services 279
Radio Communication Interception 287
Remote Monitoring 290
Repeaters 301
Routers 304
Rural Radiotelephone Service 310
Satellite Communications
Short Messaging Service
Software-Defined Radio
Specialized Mobile Radio
Spectrum Auctions 334
Spectrum Planning 338
Spread-Spectrum Radio
Telegraphy 349
Telemetry 354
Time Division Multiple Access
Ultra Wideband 367
Universal Mobile Telephone Service
Voice Cloning 377
Voice Compression 380
Wired Equivalent Privacy
Wireless E911 392
Wireless Application Protocol 394
Wireless Application Service Providers 401
Wireless Centrex 405
Wireless Communications Services 409
Wireless Fidelity 411
Wireless Internet Access 414
Wireless Internet Service Providers 422
Wireless Internetworking 425
Wireless Intranet Access 430
Wireless IP 434
Wireless LAN Security 437
Wireless LANs 444
Wireless Local Loops 454
Wireless Local Number Portability 464
Wireless Management Tools 465
Wireless Medical Telemetry Service 468
Wireless Messaging 470
Wireless PBX 473
Wireless Telecommunications Bureau 481
Wireless Telecommunications Investment Fraud
Of all the communications services available today, wireless
services are having the most dramatic impact on our personal
and professional lives, enhancing personal productivity,
mobility, and security. With every new wireless product and
service, the boundary between home and office is blurred
further, perhaps to the point that one day they will be indistinguishable. Instead of the flexible work schedule, wireless
products and services give us the capability of being “always
on.” For a growing number of people, a true vacation consists
of shutting down communication with the rest of the world.
The wireless industry worldwide is experiencing rapid
innovation, increased competition, and diversity in service
offerings—all of which have resulted in lower prices for consumers and businesses. Service providers continue to fill in
gaps in their national coverage through mergers, acquisitions, license swaps, and joint ventures. Along with this
process of footprint building, service providers continue to
deploy their networks in an increasing number of markets,
expand their digital networks, and develop pricing plans that
attract new subscribers and stimulate minutes of usage.
Mobile telephony is a particularly vibrant sector, experiencing strong growth and reaching new levels of competitive
development. At year-end 2001, mobile telephony services
generated over $65 billion in revenues in the United States,
increased subscribers from 109.5 million to 128.5 million, and
produced a nationwide penetration rate of over 50 percent.
Broadband PCS carriers and digital SMR providers continue to deploy their networks. According to the Federal
Communications Commission (FCC), 268 million people, or
94 percent of the total U.S. population, live in areas served
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by three or more different operators offering mobile telephone
service. Over 229 million people, or 80 percent of the U.S.
population, live in counties with five or more mobile telephone operators competing to offer service. And 151 million
people, or 53 percent of the population, live in areas in which
six different mobile telephone operators are providing service.
Digital technology is now dominant in the mobile telephone sector. At the end of 2001, digital customers made up
almost 80 percent of the industry total, up from 72 percent
at year-end 2000. In part because of competitive pressures
in the marketplace, the average price of residential mobile
telephone service declined by 5.5 percent during 2001. The
average revenue per minute of mobile telephone use fell 31
percent between 2000 and 2001.
Many mobile telephone carriers are deploying advanced
wireless service network technologies such as cdma2000
1xRTT and General Packet Radio Service (GPRS). These
deployments have contributed to the further convergence of
mobile voice and data. The increased capacity on these digital
networks has permitted operators to offer calling plans with
large buckets of relatively inexpensive minutes, free enhanced
services such as voice mail and caller ID, and wireless data
and mobile Internet offerings.
Once solely a business tool, wireless phones are now a
mass-market consumer device. By some estimates, 3 to 5
percent of customers use their wireless phones as their only
phone. Though relatively few wireless customers have “cut
the cord” in the sense of canceling their wireline telephone
service, there is growing evidence that consumers are substituting wireless service for traditional phone service. It is
also estimated that 20 percent of residential customers have
replaced some wireline phone usage with wireless, and that
11 percent have replaced a significant percentage. And
almost one in five mobile telephony users regard their wireless phone as their primary phone.
Contributing to these trends is the increasing number of
mobile wireless carriers offering service plans designed to
compete directly with wireline local telephone service, many
with virtually unlimited regional calling plans. For $40 to
$50 per month, subscribers get a calling plan that includes
4,000 minutes (usable anytime) and the ability to roam
across several states without extra fees.
Several local carriers have attributed declining access-line
growth rates in part to substitution by wireless. The number
of residential access lines served by BellSouth, SBC, and
Verizon dropped by almost 3 percent during 2001, or more
than 2.5 million lines. Verizon attributes the decline in the
number of access lines in part to the shift to wireless phones.
Nationwide, by year-end 2001, wireless had displaced an
estimated 10 million access lines, primarily by consumers
choosing wireless over installing additional access lines.
Wireless plans are substituting for traditional wireline
long distance as well. Many calling plans offered by national
wireless carriers include free nationwide long distance. For
example, about 20 percent of AT&T’s customers, or 5 million
people, have replaced some wireline long-distance usage with
wireless. AT&T attributes the decline in its long-distance
calling volumes and revenues in part to wireless substitution.
At least one wireless operator, Cingular Wireless, advertises
its nationwide calling plans with the slogan, “Never Pay
Long Distance Again.”
Because of national advertising and the Internet, consumers all over the country are educated about nationwide
rate plans and services enabled by digital technology and
the prices of wireless handsets. No matter where they live,
customers expect and demand the diversity of services at
competitive rates.
Wireless is having an impact in other ways. PDAs, or
handheld devices, began as electronic organizers containing
personal information management (PIM) functions, such
as an address book, calendar, and to-do list that could be
“synched” with PIM software on a user’s desktop computer.
While PDAs still contain these core PIM and software features, handhelds are being repositioned as wireless communication devices instead of simple organizers. All of the PDA
models introduced by the major manufacturers since 2001
allow users some method of connecting to the Internet wirelessly. Some combine the features of mobile phones and PDA
features into so-called “smartphones.”
Compared to traditional mobile handsets, smartphones
generally have larger screens, more advanced graphics and
processing capabilities, more memory, a more user-friendly
operating system, some form of keypad, and the ability to
synch data with and download software from a desktop
computer. Smartphones also integrate traditional mobile
telephone phone number storage and access with a PDA’s
address book so users are not required to store numbers in
two different places.
These smartphones also allow messaging via the Short
Message Service (SMS). SMS provides the ability for users to
send and receive text messages to and from mobile handsets
with maximum message length ranging from 120 to 500
characters. SMS also can be used to deliver a wide range of
information to mobile users, including stock prices, sport
scores, news headlines, weather reports, and horoscopes.
Worldwide, SMS has become increasingly popular, growing
to 250 billion messages sent over wireless networks worldwide in 2001.
Using their existing and next-generation networks, major
mobile telephone service providers offer text-based wireless
web services via mobile telephone handsets at speeds ranging
from approximately 14.4 kbps on 2G networks to 60 kbps on
advanced 2.5/3G wireless networks. During 2001, mobile
telephone providers expanded their data service offerings as
they began to transition their networks to higher speed
technologies. In addition to offering wireless web service on
mobile telephone handsets, several carriers offer wireless
Internet connections via wireless modem cards for PDAs and
laptop computers as well.
Mobile telephone service providers offer wireless web
services that enable customers to surf web sites for news,
stock quotes, traffic reports, weather forecasts, movie listings,
shopping, and other text-based information. To deliver wireless web content to wireless handset users, carriers currently
restrict users to less graphically enriched content. This conserves the resources of the memory-constrained devices.
However, customers who connect to the Internet via a wireless modem card attached to a notebook computer are able to
access the full content of the web.
Many PDAs have the ability to access almost the entire content of the web. For example, Pocket PC PDAs include a PDA
version of Microsoft’s Internet Explorer web browser, which
can access any web site. While many PDAs have the potential
to access web content with their browsing software, they still
require a subscription to a wireless Internet Service Provider
(WISP) in order to connect to the Internet via wireless links.
As workers become increasingly more mobile and remote,
the ability for employees outside the office to access e-mail
messages and files stored electronically on corporate servers
is likely to become an increasingly more important mobile
data application. Analysts claim that giving employees
mobile access to e-mail and to data and applications stored
on corporate servers are two of the most important uses of
PDAs in the enterprise market. Surveys of U.S. firms indicate
that mobile access to e-mail is the top priority.
There are short-range data transmission technologies that
are gaining in popularity: infrared, Bluetooth, and Wireless
Fidelity (Wi-Fi). Infrared is currently used in some PDAs to
allow users to transfer data between two devices. Infrared is
also the technology commonly used in remote controls and
requires line-of-sight transmission. Bluetooth enables multipoint broadcasting applications, and Wi-Fi enables devices to
connect to wireless local area networks (WLANs).
Bluetooth is a technology used to establish wireless connectivity between electronic devices that are up to 30 ft (10 m)
apart. It allows users to send signals and transfer data
among numerous electronic devices, thus creating a personal
area network (PAN). Bluetooth uses unlicensed spectrum
in the 2.4 GHz band and transmits data at speeds close to
1 Mbps. Bluetooth also uses frequency hopping spread spectrum techniques to provide enhanced communications performance and an initial level of transmission security.
Wi-Fi is another wireless networking technology sharing the 2.4 GHz frequency band with Bluetooth. Also called
Wi-Fi, the 802.11b standard is used to connect devices to
WLANs, and allows a maximum throughput of 11 Mbps. The
technology is being used in a number of WLAN settings,
such as college campuses, business parks, office buildings,
and even private homes. It is also being implemented by a
number of vendors in public places such as airports, hotels,
and cafes to give users of notebook computers, handheld
devices, and smartphones wireless Internet access anywhere inside those locations.
Wireless technologies and services have become so popular
worldwide and sufficiently sophisticated and complex as to
merit dozens of books on the topic that are published every
year. This encyclopedia is a quick reference that clearly
explains the essential concepts of wireless, including services,
applications, protocols, network methods, development
tools, administration and management, standards, and regulation. It is designed as a companion to other books you
may want to read about wireless, providing clarification of
concepts that may not be fully covered elsewhere.
The information contained in this book, especially as it
relates to specific vendors and products, is believed to be accurate at the time it was written and is, of course, subject to
change with continued advancements in technology and shifts
in market forces. Mention of specific products and services is
for illustration purposes only and does not constitute an
endorsement of any kind by either the author or the publisher.
Nathan J. Muller
An access point (AP) provides the connection between one or
more wireless client devices and a wired local area network
(LAN). The AP is usually connected to the LAN via a
Category-5 cable connection to a hub or switch. Client
devices communicate with the AP over the wireless link, giving them access to all other devices through the hub or
switch, including a router on the other side of the hub, which
provides Internet access (Figure A-1).
An AP that adheres to the IEEE 802.11b Standard for
operation over the unlicensed 2.4-GHz band supports a wireless link with a data transfer speed of up to 11 Mbps, while
an AP that adheres to the IEEE 802.11a Standard for operation over the unlicensed 5-GHz band supports a wireless link
with a data transfer speed of up to 54 Mbps. Access points
include a number of the following functions and features:
Radio power control for flexibility and ease of networking
Dynamic rate scaling, mobile Internet Protocol (IP) functionality, and advanced transmit/receive technology to
enable multiple access points to serve users on the move
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Access Point
Wireless Clients
Figure A-1 A simple configuration showing the relationship of the access
point to the wired and wireless segments of the network.
Built-in bridging and repeating features to connect buildings miles apart (The use of specialty antennas increases
range. The AP can support simultaneous bridging and
client connections.)
Wired Equivalent Privacy (WEP), which helps protect
data in transit over the wireless link between the client
device and the AP, via 64-, 128-, or 256-bit encryption
Access control list (ACL) and virtual private network
(VPN) compatibility to help guard the network from
Statistics on the quality of the wireless link (Figure A-2)
Configurability using the embedded Web browser
Consumer-level APs stress ease of setup and use (Figure
A-3). Many products are configured with default settings
Figure A-2 The 5-GHz DWL-5000 Access Point from DLink Systems, Inc., keeps the client device notified of the status of the wireless link. In this case, the signal is at
maximum strength and is capable of a data transfer rate of
48 Mbps.
that allow the user to plug in the device and use the wireless
connection immediately. Later, the user can play with the
configuration settings to improve performance and set up
Although APs adhere to the IEEE 802.11 Standards, manufacturers can include some proprietary features that
improve the data transfer speed of the wireless link. For
example, one vendor advertises a “turbo mode” that optionally increases the maximum speed of IEEE 802.11b wireless
links from 11 to 22 Mbps. When this turbo feature is applied
to IEEE 802.11a wireless links, the maximum speed is
increased from 54 to 72 Mbps.
Figure A-3 An example of a consumer AP is this 5-GHz wireless access
point (WAP54A) from Linksys, which features antenna with a range of up
to 328 feet indoors.
Enterprise-level APs provide more management features,
allowing LAN administrators to remotely set up and configure
multiple APs and clients from a central location. For monitoring and managing an entire wireless LAN infrastructure consisting of hundreds or even thousands of access points,
however, a dedicated management system is usually required.
Such systems automatically discover every AP on the network
and provide real-time monitoring of an entire wireless network
spread out over multiple facilities and subnets. These management systems support the Simple Network Management
Protocol (SNMP) and can be tied into higher-level management
platforms such as Hewlett-Packard’s OpenView.
Among the capabilities of these wireless managers is support of remote reboot, group configuration, or group software
uploads for all the wireless infrastructure devices on the network. In addition, the LAN administrator can see how many
client devices are connected to each access point, monitor
those connections to measure link quality, and monitor all
the access points for performance.
Some enterprise APs provide dual-band wireless connections to support both IEEE 802.11a and 802.11b client users
at the same time. This is accomplished by equipping the AP
with two plug-in radio cards—one that supports the 2.4-GHz
frequency specified by the IEEE 802.11b Standard and one
that supports the 5-GHz frequency specified by the IEEE
802.11a Standard.
The choice of a dual-band AP provides organizations with
a migration path to the higher data transfer speeds available
with IEEE 802.11a while continuing to support their existing
investment in IEEE 802.11b infrastructure. Depending on
manufacturer, these dual-band APs are modular so that they
can be upgraded to support future IEEE 802.11 technologies
as they become available, which further protects an organization’s investment in wireless infrastructure.
Access points are the devices that connect wireless client
devices to the wired network. They are available in consumer and commercial versions, with the latter generally
costing more because of more extensive management capabilities and troubleshooting features. They may have more
security features as well and support both the 2.4- and 5GHz frequency bands with separate radio modules that plug
into the same unit.
See also
Wired Equivalent Privacy
Wireless Fidelity
Wireless LANs
Wireless Security
Before the age of digital services, the predominant technology
for analog cellular phone services in North America adhered
to a set of standards for Advanced Mobile Phone Service
(AMPS). Originally, AMPS operated in the 800-MHz frequency band using 30-kHz-wide channels. A variant of AMPS,
known as Narrowband AMPS (NAMPS), uses 10-kHz-wide
channels and consequently has triple the capacity of AMPS.
Although AMPS or a variation of AMPS is still around—
chances are that your cellular phone allows you to switch
between analog and digital mode—its use is rapidly declining
in the face of more sophisticated digital cellular standards.
The mobile telephone service that preceded AMPS was
known as Improved Mobile Telephone Service (IMTS), which
operated in several frequency ranges: 35 to 44 MHz, 152 to
158 MHz, and 454 to 512 MHz. But IMTS suffered from call
setup delay, poor transmission, and limited frequency reuse.
AMPS overcame the limitations of IMTS and set the stage
for the explosive growth of cellular service, which continues
today worldwide. Interestingly, Pacific Bell finally dropped
IMTS in 1995.
Proposed by AT&T in 1971, AMPS is still the standard for
analog cellular networks. It was tested in 1978, and in the
early 1980s cellular systems based on the standards were
installed throughout North America. Although AMPS was
not the first system for wireless telephony, the existence of a
single set of standards enabled the United States to dominate analog cellular throughout the 1980s. Today, Europe
dominates cellular primarily because it is a lower-cost alternative to conventional telephone service.
Analog cellular is delivered from a system of cellular hubs
and base stations with associated radio towers. A mobile
telecommunications switching office (MTSO) authenticates
wireless customers before they make calls, switches calls
between cells as mobile phone users travel across cell boundaries, and places calls from land-based telephones to wireless customers.
AMPS uses a technique called “frequency reuse” to greatly
increase the number of customers that can be served at the
same time. Low-powered mobile phones and radio equipment
at each cell site permit the same radio frequencies to be
reused in different cells, multiplying calling capacity without
creating interference. This spectrum-efficient method contrasts sharply with earlier mobile systems that used a highpowered, centrally located transmitter to communicate with
high-powered mobile equipment installed in vehicles over a
small number of frequencies. Once a channel was occupied
with a call, its frequency could not reused over a wide area.
Despite the success of AMPS, this method of transmission
has its limitations. Analog signals can be intercepted easily
and suffer signal degradation from numerous sources, such
as terrain, weather, and traffic volume. Analog systems also
could not handle the transmission of data very well. A digital version of AMPS—referred to as DAMPS—solves many
of these problems while providing increased capacity and a
greater range of services. Both AMPS and DAMPS operate
in the 800-MHz band and can coexist with each other.
DAMPS is implemented with Time Division Multiple Access
(TDMA) as the underlying technology, which provides 10 to
15 times more channel capacity than AMPS and allows the
introduction of new feature-rich services such as data communications, voice mail, call waiting, call diversion, voice
encryption, and calling-line identification.
A digital control channel available with DAMPS supports
such advanced features as a sleep mode, which increases battery life on newer cellular phones by as much as 10 times over
the current battery capabilities of analog phones. DAMPS
also can be implemented with Code Division Multiple Access
(CDMA) technology to increase channel capacity by as much
as 20 times and provide a comparable range of services and
features. Unlike TDMA, which can be added onto existing
AMPS infrastructure, CDMA requires an entirely new network infrastructure.
DAMPS also allows operators to build overlay networks
using small micro- and picocells, boosting network capacity
still further in high-traffic areas and providing residential
and business in-building coverage. Advanced software in the
networks’ exchanges continuously monitors call quality and
makes adjustments, such as handing calls over to different
cells or radio channels, when necessary. The network management system provides an early warning to the network
operator if the quality of service is deteriorating so that steps
can be taken to head off serious problems. Graphical displays of network configuration and performance statistics
help ensure maximum service quality for subscribers.
In 1983, AMPS was approved by the Federal Communications
Commission (FCC) and first used in Chicago. In order to
encourage competition and keep prices low, the U.S. government required the presence of two carriers in every market,
known as A and B carriers. One of the carriers was normally
the Local Exchange Carrier (LEC); in other words, the local
phone company.
See also
Cellular Data Communications
Cellular Voice Communications
With the Air-Ground Radiotelephone Service, a commercial
mobile radio service (CMRS) provider offers two-way voice,
fax, and data service for hire to subscribers in aircraft—in
flight or on the ground. Service providers must apply for an
FCC license for each and every tower/base site. There are
two versions of this service: one for general aviation and one
for commercial aviation.
General Aviation Air-Ground Service
Air-Ground Radiotelephone Service has been available to
general aviation for more than 30 years. General Aviation
Air-Ground systems may operate in the 454.675- to 454.975MHz and 459.675- to 459.975-MHz bands to provide service
to private aircraft, specifically, small single-engine craft and
corporate jets.
The service is implemented through general aviation
air-ground stations, which comprise a network of independently licensed stations. These stations employ a standardized duplex analog technology called “Air-Ground
Radiotelephone Automated Service” (AGRAS) to provide
telephone service to subscribers flying over the United
States or Canada. Because there are only 12 channels
available for this service, it is not available to passengers
on commercial airline flights.
Commercial Aviation Air-Ground Systems
Commercial Aviation Air-Ground Systems may operate on
10 channel blocks in the 849- to 851-MHz and 894- to 896MHz bands. These nationwide systems employ various analog or digital wireless technologies to provide telephone
service to passengers flying in commercial aircraft over the
United States, Canada, and Mexico. Some systems have
satellite-calling capability as well, where the call is sent to
an earth station instead of the base station.
Passengers use credit cards or prearranged accounts to
make telephone calls from bulkhead-mounted telephones
or, in larger jets, from seatback-mounted telephones. This
service was available from one company on an experimental
basis during the 1980s and began regular competitive operations in the early 1990s. There are currently three operating systems, one of which is GTE Airfone, a subsidiary of
Verizon Communications.
When an Airfone call is placed over North America, information is sent from the phone handset to a receiver in the
plane’s belly and then down to one of the 135 strategically
placed ground radio base stations. From there, it is sent to
one of three main ground switching stations and then over
to the public telephone network to the receiving party’s location. When an Airfone call is placed over water, information
is sent first to an orbiting satellite. From there, the call
transmission path is similar to the North American system,
except that calls are sent to a satellite earth station instead
of a radio base station. Calls can be placed to any domestic
or international location.
To receive calls aboard aircraft, the passenger must
have an activation number. In the case of Airfone, an activation number can be obtained by dialing 0 toll-free
onboard or 1-800-AIRFONE from the ground. For each
flight segment, the activation number will be the same.
However, the passenger must activate the phone for each
flight segment and include his or her seat number. The
person placing the call from the ground dials 1-800-AIRFONE and follows the voice prompts to enter the passenger’s activation number. The passenger is billed for the call
on a calling card or credit card but gets to choose whether
or not to accept the calls.
The following steps are involved in receiving a call:
The phone will ring on the plane, and the screen will indicate a call for the seat location.
The passenger enters a personal identification number
(PIN) to ensure that no one else can answer the call.
The phone number of the calling party will be displayed
on the screen.
If the call is accepted, the passenger is prompted to slide
a calling card or credit card to pay for the call.
Once the call has been accepted, the passenger is automatically connected to the party on the ground.
If the passenger chooses not to accept the call, he or she
follows the screen prompts, and no billing will occur.
Air-to-ground calls are very expensive. The cost to place
domestic calls using GTE’s Airfone Service, for example, is
$2.99 to connect and $3.28 per minute or partial minute,
plus applicable tax. By comparison, AT&T’s Inflight
Calling costs $2.99 to connect plus $2.99 per minute.
These rates apply to all data/fax and voice calls. Even
calls to 800 and 888 numbers—which are normally tollfree on the ground—are charged at the same rate as regular Airfone and Inflight calls. No billing ever occurs for the
ground party. The charges for international calls are
higher; both AT&T and GTE charge $5.00 to connect and
$5.00 per minute. GTE offers satellite service for use over
the ocean and worldwide at $10.00 to connect and $10.00
per minute, but the service is available only on United
FCC rules specifically prohibit the use of cellular transmitters on aircraft, except for aircraft on the ground. This
prohibition was not done to protect the aircraft’s avionics
systems from interference from the cellular transmitter.
Rather, this prohibition was made to protect the cellular
service on the ground from interference. As the altitude of
a cellular handheld transmitter increases, its range also
increases and, consequently, its coverage area. At high
altitudes, such as would be achieved from an in-flight aircraft, the hand-held unit places its signal over several cellular base stations, preventing other cellular users within
range of those base stations from using the same frequency.
This would increase the number of blocked or dropped cellular calls.
See also
Cellular Data Communications
Cellular Voice Communications
Amateur Radio Service is defined by the FCC as “A radio
communication service for the purpose of self-training, intercommunication, and technical investigations carried out by
amateurs; that is, duly authorized persons interested in
radio technique solely with a personal aim and without pecuniary interest.”1
Amateur radio stations are licensed by the FCC and may
engage in domestic and international communications—
both two-way and one-way. Applications for new licenses or
for a change in operator class are filed through a volunteer
examiner-coordinator (VEC). Operators can use their station equipment as soon as they see that information about
their amateur operator/primary station license grant
appears on the amateur service database. New operators
do not need to have the license document in their possession to commence operation of an amateur radio station.
Since amateur stations must share the air waves, each
station licensee and each control operator must cooperate in
selecting transmitting channels and in making the most
effective use of the amateur service frequencies. A specific
transmitting channel is not assigned for the exclusive use of
any amateur station.
1There are two exceptions to this rule. A person may accept compensation when in a
teaching position and the amateur station is used as a part of classroom instruction at
an educational institution. The other exception is when the control operator of a club
station is transmitting telegraphy practice or information bulletins.
Types of Communications
With regard to two-way communications, amateur stations
are authorized to exchange messages with other stations in
the amateur service, except those in any country whose
administration has given notice that it objects to such communications.2 In addition, transmissions to a different country must be made in plain language. Communication is
limited to messages of a technical nature relating to tests
and to remarks of a personal nature for which, by reason of
their unimportance, use of public telecommunications services is not justified.
Amateur radio stations also may engage in one-way communications. For example, they are authorized to transmit
auxiliary, beacon, and distress signals. Specifically, an amateur station may transmit the following types of one-way
Brief transmissions necessary to make adjustments to the
Brief transmissions necessary for establishing two-way
communications with other stations
Transmissions necessary to provide emergency communications
Transmissions necessary for learning or improving proficiency in the use of international Morse code
Transmissions necessary to disseminate an information
bulletin of interest to other amateur radio operators
Prohibited Communications
Although the FCC does not provide a list of communications
that are suitable or unsuitable for the amateur radio service,
2As of mid-2002, no administration in another country had given notice that they
object to communications between the amateur radio stations.
there are several types of amateur-operator communications
that are specifically prohibited, including
Transmissions performed for compensation
Transmissions done for the commercial benefit of the station control operators
Transmissions done for the commercial benefit of the station control operator’s employer
Transmissions intended to facilitate a criminal act
Transmissions that include codes or ciphers intended to
obscure the meaning of the message
Transmissions that include obscene or indecent words or
Transmissions that contain false or deceptive messages,
signals, or identification
Transmissions on a regular basis that could reasonably be
furnished alternatively through other radio services
Broadcasting information intended for the general public is
also prohibited. Amateur stations may not engage in any form
of broadcasting or in any activity related to program production or newsgathering for broadcasting purposes. The one
exception is when communications directly related to the
immediate safety of human life or the protection of property
may be provided by amateur stations to broadcasters for dissemination to the public where no other means of communication is reasonably available before or at the time of the event.
Amateur stations are not afforded privacy protection.
This means that the content of the communications by amateur stations may be intercepted by other parties and
divulged, published, or used for another purpose.
In August 1999, the FCC’s Wireless Telecommunications
Bureau (WTB) began the transition to the Universal Licensing
System (ULS) for all application and licensing activity in the
Amateur Radio Services. As of February 2000, amateur
licensees were required to file using ULS forms, which means
that applications using Forms 610 and 610V are no longer
accepted by the WTB.3 The ULS is an interactive licensing
database developed by the WTB to consolidate and replace 11
existing licensing systems used to process applications and
grant licenses in wireless services. ULS provides numerous
benefits, including fast and easy electronic filing, improved
data accuracy through automated checking of applications,
and enhanced electronic access to licensing information.
See also
Citizens Band Radio Service
For applications that do not need to be filed by a volunteer-examiner coordinator
(VEC), such as renewals and administrative updates. Amateur Service licensees may
still file FCC Form 605 electronically (interactively) or manually, despite the ULS
requirement for other filings.
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Developed in the mid-1980s, Basic Exchange Telephone Radio
Service (BETRS) is a fixed radio service that uses a multiplexed digital radio link as the last segment of the local loop
to provide wireless telephone service to subscribers in remote
areas where it would be impractical to provide wireline telephone service. The wireless link allows up to four subscribers
to use a single radio channel pair simultaneously without
interfering with one another.
Licensed by the Federal Communications Commission
(FCC) under the Rural Radiotelephone Service, BETRS may
be licensed only to state-certified carriers in the area where
the service is provided and is considered a part of the Public
Switched Telephone Network (PSTN) by state regulators.
This service operates in the paired 152/158- and 454/459MHz bands and on 10 channel blocks in the 816- to 820-MHz
and 861- to 865-MHz bands. These channels are also allocated for paging services. Since BETRS primarily serves
rural areas in the western part of the United States, it typically does not conflict geographically with paging services.
When there is a conflict, the FCC provides a remedy.
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
Rural Radiotelephone Service and BETRS providers
obtain site licenses and operate facilities on a secondary
basis. This means that if any geographic area licensee subsequently notifies the Rural Radiotelephone Service or
BETRS licensee that a facility must be shut down because it
may cause interference to the paging licensee’s existing or
planned facilities, the Rural Radiotelephone Service or
BETRS licensee must discontinue use of the particular channel at that site no later than 6 months after such notice.
BETRS primarily serves rural, mountainous, and sparsely
populated areas that might not otherwise receive basic telephone service. Although the industry has raised concerns
that auctioning spectrum for BETRS would have the effect
of raising the cost of the service, which could deprive these
areas of basic telephone service, the FCC does not distinguish BETRS from other services that use radio spectrum to
provide commercial communication services.
See also
Rural Radiotelephone Service
Bluetooth is an omnidirectional wireless technology that provides limited-range voice and data transmission over the unlicensed 2.4-GHz frequency band, allowing connections with a
wide variety of fixed and portable devices that normally would
have to be cabled together. Up to eight devices—one master
and seven slaves—can communicate with one another in a socalled piconet at distances of up to 30 feet. Table B-1 summarizes the performance characteristics of Bluetooth products
that operate at 1 Mbps in the 2.4-GHz range.
Among the many things users can do with Bluetooth is swap
data and synchronize files merely by having the devices
come within range of one another. Images captured with a
digital camera, for example, can be dropped off at a personal
computer (PC) for editing or a color printer for output on
photo-quality paper—all without having to connect cables,
load files, open applications, or click buttons.
The technology is a combination of circuit switching and
packet switching, making it suitable for voice as well as
data. Instead of fumbling with a cell phone while driving, for
example, the user can wear a lightweight headset to answer
a call and engage in a conversation even if the phone is
tucked away in a briefcase or purse.
While useful in minimizing the need for cables, wireless
local area networks (LANs) are not intended for interconnecting the range of mobile devices people carry around
everyday between home and office. For this, Bluetooth is
needed. And in the office, a Bluetooth portable device can be
Performance Characteristics of Bluetooth Products
Connection type
Transmission power
Aggregate data rate
Supported stations
Voice channels
Data security
Spread spectrum (frequency hopping)
2.4-GHz ISM (industrial, scientific, and
medical) band
1 milliwatt (mW)
1 Mbps using frequency hopping
Up to 30 feet (9 meters)
Up to eight devices per piconet
Up to three synchronous channels
For authentication, a 128-bit key; for
encryption, the key size is configurable
between 8 and 128 bits
Each device has a 48-bit Media Access
Control (MAC) address that is used to
establish a connection with another
in motion while connected to the LAN access point as long as
the user stays within the 30-foot range.
Bluetooth can be combined with other technologies to
offer wholly new capabilities, such as automatically lowering the ring volume of cell phones or shutting them off as
users enter quiet zones such as churches, restaurants, theaters, and classrooms. On leaving the quiet zone, the cell
phones are returned to their original settings.
The devices within a piconet play one of two roles: that of
master or slave. The master is the device in a piconet whose
clock and hopping sequence are used to synchronize all other
devices (i.e., slaves) in the piconet. The unit that carries out
the paging procedure and establishes a connection is by
default the master of the connection. The slaves are the
units within a piconet that are synchronized to the master
via its clock and hopping sequence.
The Bluetooth topology is best described as a multiplepiconet structure. Since Bluetooth supports both point-topoint and point-to-multipoint connections, several piconets
can be established and linked together in a topology called a
“scatternet” whenever the need arises (Figure B-1).
Piconets are uncoordinated, with frequency hopping
occurring independently. Several piconets can be established
and linked together ad hoc, where each piconet is identified
by a different frequency-hopping sequence. All users participating on the same piconet are synchronized to this hopping
sequence. Although synchronization of different piconets is
not permitted in the unlicensed ISM band, Bluetooth units
may participate in different piconets through Time Division
Multiplexing (TDM). This enables a unit to sequentially participate in different piconets by being active in only one
piconet at a time.
With its service discovery protocol, Bluetooth enables a
much broader vision of networking, including the creation of
Single Slave
Figure B-1 Possible topologies of networked Bluetooth devices, where
each is either a master or slave.
personal area networks, where all the devices in a person’s
life can communicate and work together. Technical safeguards ensure that a cluster of Bluetooth devices in public
places, such as an airport lounge or train terminal, would
not suddenly start talking to one another.
Two types of links have been defined for Bluetooth in support of voice and data applications: an asynchronous connectionless (ACL) link and a synchronous connection-oriented
(SCO) link. ACL links support data traffic on a best-effort
basis. The information carried can be user data or control
data. SCO links support real-time voice and multimedia
traffic using reserved bandwidth. Both data and voice are
carried in the form of packets, and Bluetooth devices can
support active ACL and SCO links at the same time.
ACL links support symmetric or asymmetric packetswitched point-to-multipoint connections, which are typically
used for data. For symmetric connections, the maximum data
rate is 433.9 kbps in both directions, send and receive. For
asymmetric connections, the maximum data rate is 723.2
kbps in one direction and 57.6 kbps in the reverse direction.
If errors are detected at the receiving device, a notification is
sent in the header of the return packet so that only lost or corrupt packets need to be retransmitted.
SCO links provide symmetric circuit-switched point-topoint connections, which are typically used for voice. Three
synchronous channels of 64 kbps each are available for voice.
The channels are derived through the use of either Pulse
Code Modulation (PCM) or Continuous Variable Slope Delta
(CVSD) Modulation. PCM is the standard for encoding
speech in analog form into the digital format of ones and
zeros. CVSD is another standard for analog-to-digital encoding but offers more immunity to interference and therefore
is better suited than PCM for voice communication over a
wireless link. Bluetooth supports both PCM and CVSD; the
appropriate voice-coding scheme is selected after negotiations between the link managers of each Bluetooth device
before the call takes place.
Voice and data are sent as packets. Communication is
handled with Time Division Duplexing (TDD), which divides
the channel into time slots, each 625 microseconds (µs) in
length. The time slots are numbered according to the clock of
the piconet master. In the time slots, master and slave can
transmit packets. In the TDD scheme, master and slave
alternatively transmit (Figure B-2). The master starts its
transmission in even-numbered time slots only, and the
slave starts its transmission in odd-numbered time slots
only. The start of the packet is aligned with the slot start.
Packets transmitted by the master or the slave may extend
over as many as five time slots.
With TDD, bandwidth can be allocated on an as-needed
basis, changing the makeup of the traffic flow as demand
warrants. For example, if the user wants to download a large
data file, as much bandwidth as is needed will be allocated
Time Slot 0
Time Slot 1
Time Slot 2
625 µs
Figure B-2 With the TDD scheme used in Bluetooth, packets are sent
over time slots of 625 microseconds (µs) in length between the master and
slave units within a piconet.
to the transfer. Then, at the next moment, if a file is being
uploaded, that same amount of bandwidth can be allocated
to that transfer.
No matter what the application—voice or data—making
connections between Bluetooth devices is as easy as powering them up. In fact, one advantage of Bluetooth is that it
does not need to be set up—it is always on, running in the
background, and looking for other devices that it can communicate with.
When Bluetooth devices come within range of one
another, they engage in a service discovery procedure, which
entails the exchange of messages to become aware of each
other’s service and feature capabilities. Having located
available services within the vicinity, the user may select
from any of them. After that, a connection between two or
more Bluetooth devices can be established.
The radio link itself is very robust, using frequencyhopping spread-spectrum technology to overcome interference and fading. Spread spectrum is a digital coding technique in which the signal is taken apart or “spread” so that
it sounds more like noise as it is sent through the air. With
the addition of frequency hopping—having the signals skip
from one frequency to another—wireless transmissions are
made even more secure. Bluetooth specifies a rate of 1600
hops per second among 79 frequencies. Since only the sender
and receiver know the hopping sequence for coding and
decoding the signal, eavesdropping is virtually impossible.
For enhanced security, Bluetooth also supports device
authentication and encryption.
Other frequency-hopping transmitters in the vicinity will
be using different hopping patterns and much slower hop
rates than Bluetooth devices. Although the chance of
Bluetooth devices interfering with non-Bluetooth devices
that share the same 2.4-GHz band is minimal, should nonBluetooth transmitters and Bluetooth transmitters coincidentally attempt to use the same frequency at the same
moment, the data packets transmitted by one or both devices
will become garbled in the collision, and a retransmission of
the affected data packets will be required. A new data packet
will be sent again on the next hopping cycle of each transmitter. Voice packets, because of their sensitivity to delay,
are never retransmitted.
Points of Convergence
In some ways, Bluetooth competes with infrared, and in
other ways, the two technologies are complementary. With
both infrared and Bluetooth, data exchange is considered to
be a fundamental function. Data exchange can be as simple
as transferring business card information from a mobile
phone to a palmtop or as sophisticated as synchronizing personal information between a palmtop and desktop PC. In
fact, both technologies can support many of the same applications, raising the question: Why would users need both
The answer lies in the fact that each technology has its
advantages and disadvantages. The very scenarios that leave
infrared falling short are the ones where Bluetooth excels,
and vice versa. Take the electronic exchange of business card
information between two devices. This application usually
will take place in a conference room or exhibit floor where a
number of other devices may be attempting to do the same
thing. This is the situation where infrared excels. The shortrange and narrow angle of infrared—30 degrees or less—
allow each user to aim his or her device at the intended
recipient with point-and-shoot ease. Close proximity to
another person is natural in a business card exchange situation, as is pointing one device at another. The limited range
and angle of infrared allow other users to perform a similar
activity with ample security and no interference.
In the same situation, a Bluetooth device would not perform as well as an infrared device. With its omnidirectional
capability, the Bluetooth device must first discover the
intended recipient. The user cannot simply point at the
intended recipient—a Bluetooth device must perform a discovery operation that probably will reveal several other
Bluetooth devices within range, so close proximity offers no
advantage here. The user will be forced to select from a list
of discovered devices and apply a security mechanism to prevent unauthorized access. All this makes the use of
Bluetooth for business card exchange an awkward and needlessly time-consuming process.
However, in other data-exchange situations, Bluetooth
might be the preferred choice. Bluetooth’s ability to penetrate solid objects and its ability to communicate with other
devices in a piconet allow for data-exchange opportunities
that are very difficult or impossible with infrared. For example, Bluetooth allows a user to synchronize a mobile phone
with a notebook computer without taking the phone out of a
jacket pocket or purse. This would allow the user to type a
new address at the computer and move it to the mobile
phone’s directory without unpacking the phone and setting
up a cable connection between the two devices. The omnidirectional capability of Bluetooth allows synchronization to
occur instantly, assuming that the phone and computer are
within 30 feet of each other.
Using Bluetooth for synchronization does not require that
the phone remain in a fixed location. If a phone is carried
about in a briefcase, the synchronization can occur while the
user moves around. This is not possible with infrared because
the signal is not able to penetrate solid objects, and the
devices must be within a few feet of each other. Furthermore,
the use of infrared requires that both devices remain stationary while the synchronization occurs.
When it comes to data transfers, infrared does offer a big
speed advantage over Bluetooth. While Bluetooth moves data
between devices at an aggregate rate of 1 Mbps, infrared
offers 4 Mbps of data throughput. A higher-speed version of
infrared is now available that can transmit data between
devices at up to 16 Mbps—a four times improvement over the
previous version. The higher speed is achieved with the Very
Fast Infrared (VFIR) Protocol, which is designed to address
the new demands of transferring large image files between
digital cameras, scanners, and PCs. Even when Bluetooth is
enhanced for higher data rates in the future, infrared is likely
to maintain its speed advantage for many years to come.
Bluetooth complements infrared’s point-and-shoot ease of
use with omnidirectional signaling, longer-distance communications, and capacity to penetrate walls. For some users,
having both Bluetooth and infrared will provide the optimal
short-range wireless solution. For others, the choice of
adding Bluetooth or infrared will be based on the applications and intended usage.
Communicator platforms of the future will combine a number
of technologies and features in one device, including mobile
Internet browsing, messaging, imaging, location-based applications and services, mobile telephony, personal information
management, and enterprise applications. Bluetooth will be a
key component of these platforms. Since Bluetooth radio
transceivers operate in the globally available ISM (industrial, scientific, and medical) radio band of 2.4 GHz, products
do not require an operator license from a regulatory agency,
such as the FCC in the United States. The use of a generally
available frequency band means that Bluetooth-enabled
devices can be used virtually anywhere in the world and link
up with one another for ad hoc networking when they come
within range.
See also
Infrared Networking
Spread Spectrum Radio
Bridges are used to extend or interconnect LAN segments,
whether the segments consist of wired or wireless links. At
one level, they are used to create an extended network that
greatly expands the number of devices and services available to each user. At another level, bridges can be used for
segmenting LANs into smaller subnets to improve performance, control access, and facilitate fault isolation and testing without impacting the overall user population.
The bridge does this by monitoring all traffic on the subnets that it links. It reads both the source and destination
addresses of all the packets sent through it. If the bridge
encounters a source address that is not already contained in
its address table, it assumes that a new device has been
added to the local network. The bridge then adds the new
address to its table.
In examining all packets for their source and destination
addresses, bridges build a table containing all local addresses.
The table is updated as new packets are encountered and as
addresses that have not been used for a specified period of time
are deleted. This self-learning capability permits bridges to
keep up with changes on the network without requiring that
their tables be updated manually.
The bridge isolates traffic by examining the destination
address of each packet. If the destination address matches
any of the source addresses in its table, the packet is not
allowed to pass over the bridge because the traffic is local.
If the destination address does not match any of the source
addresses in the table, the packet is discarded onto an
adjacent network. This filtering process is repeated at
each bridge on the internetwork until the packet eventually reaches its destination. Not only does this process
prevent unnecessary traffic from leaking onto the internetwork, it acts as a simple security mechanism that can
screen unauthorized packets from accessing various corporate resources.
Bridges also can be used to interconnect LANs that use
different media, such as twisted-pair, coaxial, and fiberoptic cabling and various types of wireless links. In office
environments that use wireless communications technologies such as spread spectrum and infrared, bridges can
function as an access point to wired LANs (Figure B-3). On
the widea area network (WAN), bridges even switch traffic
to a secondary port if the primary port fails. For example,
a full-time wireless bridging system can establish a
modem connection on the public network if the primary
wire or wireless link is lost because of environmental
In reference to the Open Systems Interconnection (OSI)
model, a bridge operates at Layer 2; specifically, it operates at the Media Access Control (MAC) sublayer of the
Data Link Layer. It routes by means of the Logical Link
Control (LLC), the upper sublayer of the Data Link Layer
(Figure B-4).
Because the bridge connects LANs at a relatively low
level, throughput often exceeds 30,000 packets per second
Figure B-3 For the home or small office network, the Instant
Wireless Ethernet Bridge from Linksys extends wireless connectivity to any Ethernet-ready network device, such as a printer,
scanner, or desktop or notebook PC.
(pps). Multiprotocol routers and gateways, which provide
LAN interconnection over the WAN, operate at higher levels
of the OSI model and provide more functionality. In performing more protocol conversions and delivering more functionality, routers and gateways are generally more
processing-intensive and, consequently, slower than bridges.
Source Station
Destination Station
Data Link
Data Link
Data Link
Data Link
Figure B-4 Bridge functionality in reference to the OSI model
See also
Access Points
A cellular system operates by dividing a large geographic service area into cells (Figure C-1) and assigning the same frequencies to multiple, nonadjacent cells. This is known in the
industry as “frequency reuse.” As a subscriber travels across
the service area, the call is transferred (handed off) from one
cell to another without noticeable interruption. All the base stations in a cellular system, including radio towers, are connected
to a mobile telephone switching office (MTSO) by landline or
microwave links. The MTSO controls the switching between
the Public Switched Telephone Network (PSTN) and the cell
site for all wireline-to-mobile and mobile-to-wireline calls.
Site Planning
There is a huge investment at stake when determining the
location of a cell site. The radio tower alone can cost from
$250,000 to $1 million. Thus, before a cell site is installed, a
number of studies are performed to justify the cost and calculate the return on investment (ROI). A demographics study, for
example, helps forecast the potential subscriber base in the
area planned for the cell site. The study begins with the total
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
Figure C-1 In a cellular network, the signal coverage of each tower is limited so that the same frequencies can be assigned to multiple nonadjacent
cells. This increases the total call-handling capacity
of the network while conserving spectrum.
population, broken down by sex, age, race, types of households,
occupancy rates, and income levels. Much of this information
is gleaned from data compiled by the U.S. Census Bureau.
By generating a topography map, engineers are able to
determine if there will be any obvious interference issues. The
goal is to discover problems that would impair the performance of the wireless cell site solution or wireless link.
Sometimes a 50-foot portable crank-up tower is used to create
a temporary cell site. Together with vehicles containing both
access points and subscriber units, tests are run to find out
what may interfere with the signal and demonstrate a realtime cell site coverage area.
After determining any interference issues and the best
strategic location for the cell site, a full site survey is done to
establish the final plans for cell site deployment. This
includes having all the information about the types of mounts
needed as well as having potential interference-filtering
measures defined. Certified network engineers then determine the best base station configuration and orientation. If
no problems are encountered, a tower can be up and running
within 6 weeks.
The Telecommunications Act of 1996 specifically leaves in
place the authority that local zoning authorities have over the
placement of cell towers. It does prohibit the denial of facilities siting based on radio frequency (RF) emissions if the
licensee has complied with the Federal Communications
Commission’s (FCC’s) regulations concerning RF emissions. It
also requires that denials be based on a reasoned approach
and prohibits discrimination and outright bans on construction, placement, and modification of wireless facilities.
The FCC mandates that service providers build out their
systems so that adequate service is provided to the public. In
addition, all antenna structures used for communications
must be approved by the FCC, which determines if there is
a reasonable possibility that the structure may constitute a
menace to air navigation. The tower height and its proximity to an airport or flight path will be considered when making this determination. If such a determination is made, the
FCC will specify appropriate painting and lighting requirements. Thus the FCC does not mandate where towers must
be placed, but it may prohibit the placement of a tower in a
particular location without adequate lighting and marking.
Low-powered transmitters are an inherent characteristic of
cellular radio and broadband personal communication services (PCS). As these systems mature and more subscribers
are added, the effective radiated power of the cell site transmitters is reduced so that frequencies can be reused at closer
intervals, thereby increasing subscriber capacity. There are
more than 50,000 cell sites operating within the United
States and its possessions and territories. Therefore, due to
the nature of frequency reuse and the consumer demand for
services, cellular and PCS providers must build numerous
base sites. The sheer number of towers has caused municipalities to impose new requirements on service providers,
such as requiring them to disguise new towers to look like
trees, which can add $150,000 to the cost of a tower.
See also
Cellular Data Communications
Cellular Voice Communications
Mobile Telephone Switching Office
Personal Communications Services
One of the oldest services for sending data over a cellular
communications network is known as “Cellular Digital
Packet Data” (CDPD), which provides a way of passing
Internet Protocol (IP) data packets over analog cellular voice
networks at speeds of up to 19.2 kbps. Although CDPD
employs digital modulation and signal processing techniques, the underlying service is still analog. The medium
used to transport data consists of the idle radio channels typically used for Advanced Mobile Phone System (AMPS) cellular service.
Channel hopping automatically searches out idle channel
times between cellular voice calls. Packets of data select
available cellular channels and go out in short bursts without
interfering with voice communications. Alternatively, cellular carriers also may dedicate voice channels for CDPD traf-
fic to meet high traffic demand. This situation is common in
dense urban environments where cellular traffic is heaviest.
Once the user logs onto the network, the connection stays
in place to send or receive data. In accordance with the IP,
the data are packaged into discrete packets of information
for transmission over the CDPD network, which consists of
routers and digital radios installed in current cell sites. In
addition to addressing information, each IP packet includes
information that allows the data to be reassembled in the
proper order via the Transmission Control Protocol (TCP) at
the receiving end. The transmissions are encrypted over the
air link for security purposes.
Although CDPD piggybacks on top of the cellular voice
infrastructure, it does not suffer from the 3-kHz limit on
voice transmissions. Instead, it uses the entire 30-kHz RF
channel during idle times between voice calls. Using the
entire channel contributes to CDPD’s faster data transmission rate. Forward error correction ensures a high level of
wireless communications accuracy. With encryption and
authentication procedures built into the specification,
CDPD offers more robust security than any other native
wireless data transmission method. As with wireline networks, CDPD users also can customize their own end-toend security.
To take advantage of CDPD, the user must have an integrated mobile device that operates as a fully functional cellular phone and Internet appliance. For example, the
AT&T PocketNet Phone contains both a circuit-switched
cellular modem and a CDPD modem to provide users with
fast and convenient access to two-way wireless messaging
services and Internet information. GTE provides a similar
service through its Wireless Data Services. Both companies have negotiated intercarrier agreements that enable
their customers to enjoy seamless CDPD service in virtually all markets across the country. AT&T’s Wireless IP
service, for example, is available in 3000 cities in the
United States.
Among the applications for CDPD are access to the
Internet for e-mail and to retrieve certain Web-based content.
AT&T PocketNet Phone users, for example, have access to
two-way messaging, airline flight information, financial
information, show times, restaurant reviews, and door-todoor travel directions. AT&T provides unlimited access to featured sites on the wireless Internet, which means that there
are no per-minute charges for surfing wireless Web sites.
Companies also can use CDPD to monitor alarms
remotely, send/receive faxes, verify credit cards, and dispatch
vehicles. Although CDPD services might prove too expensive
for heavy database access, the use of intelligent agents can
cut costs by minimizing connection time. Intelligent agents
gather requested information and report back only the
results the next time the user logs onto the network.
Wireless IP is an appealing method of transporting data over
cellular voice networks because it is flexible, fast, widely available, and compatible with a vast installed base of computers
and has security features not offered with other wireless data
services. One caveat: The carrier’s wireless data network is
different from its wireless voice network. Therefore, users of
AT&T Digital PocketNet service, for example, will not be able
to access that service everywhere voice calls can be made. It is
important to look at coverage maps and compare service plans
before subscribing to this type of service.
See also
Wireless IP
Bell Labs built the first cellular telephone in 1924 (Figure
C-2). After decades of development, cellular telephones have
Figure C-2 The first cellular telephone, developed by Bell Labs in 1924.
emerged as a “must have” item among mobile professionals
and consumers alike, growing in popularity every year since
they became commercially available in 1983. Their widespread use for both voice and data communications has
resulted from significant progress made in their functionality, portability, the availability of network services, and the
declining cost for equipment and services.
System Components
There are several categories of cellular telephone. Mobile
units are mounted in a vehicle. Transportable units can be
easily moved from one vehicle to another. Pocket phones,
weighing in at less than 4 ounces, can be conveniently carried in a jacket pocket or purse. There are even cellular
telephones that can be worn. Regardless of how they are
packaged, cellular telephones consist of the same basic
Handset/Keypad The handset and keypad provide the inter-
face between the user and the system. This is the only component of the system with which, under normal operation,
the user needs to be concerned. Any basic or enhanced system
features are accessible via the keypad, and once a connection
is established, this component provides similar handset functionality to that of any conventional telephone. Until a connection is established, however, the operation of the handset
differs greatly from that of a conventional telephone.
Instead of initiating a call by first obtaining a dial tone
from the network switching system, the user enters the
dialed number into the unit and presses the “Send” function
key. This process conserves the resources of the cellular system, since only a limited number of talk paths are available
at any given time. The “Clear” key enables the user to correct misdialed digits.
Once the network has processed the call request, the user
will hear conventional call-progress signals such as a busy
signal or ringing. From this point on, the handset operates
in the customary manner. To disconnect a call, the “End”
function key is pressed on the keypad. The handset contains
a small illuminated display that shows dialed digits and provides a navigational aid to other features. The keypad
enables storage of numbers for future use and provides
access to other enhanced features, which may vary according
to manufacturer.
Logic/Control The logic/control functions of the phone
include the numeric assignment module (NAM) for programmable assignment of the unit’s telephone number by
the service provider and the electronic serial number of the
unit, which is a fixed number unique to each telephone.
When a customer signs up for service, the carrier makes a
record of both numbers. When the unit is in service, the cellular network interrogates the phone for both of these numbers in order to validate that the calling/called cellular
telephone is that of an authentic subscriber.
The logic/control component of the phone also serves to
interact with the cellular network protocols. Among other
things, these protocols determine what control channel the
unit should monitor for paging signals and what voice channels the unit should use for a specific connection. The
logic/control component is also used to monitor the control
signals of cell sites so that the phone and network can coordinate transitions to adjacent cells as conditions warrant.
Transmitter/Receiver The transmitter/receiver component of
the cell phone is under the command of the logic/control unit.
Powerful 3-watt telephones are typically of the vehiclemounted or transportable type, and their transmitters are
understandably larger and heavier than those contained
within lighter-weight handheld cellular units. These more
powerful transmitters require significantly more input
wattage than hand-held units that transmit at power levels
of only a fraction of a watt, and they use the main battery
within a vehicle or a relatively heavy rechargeable battery to
do so. Special circuitry within the phone enables the transmitter and receiver to use a single antenna for full-duplex
Antenna The antenna for a cellular telephone can consist of
a flexible rubber antenna mounted on a hand-held phone, an
extendible antenna on a pocket phone, or the familiar curly
stub seen attached to the rear window of many automobiles.
Antennas and the cables used to connect them to radio
transmitters must have electrical performance characteristics that are matched to the transmitting circuitry, frequency, and power levels. Use of antennas and cables that
are not optimized for use by these phones can result in poor
performance. Improper cable, damaged cable, or faulty connections can render the cell phone inoperative.
Power Sources Cell phones are powered by a rechargeable
battery. Nickel-cadmium (NiCd) batteries are the oldest and
cheapest power source available for cellular phones. Newer
nickel–metal hydride (NiMH) batteries provide extend talk
time compared to lower-cost conventional NiCd units. They
provide the same voltage as NiCd batteries but offer at least
30 percent more talk time than NiCd batteries and take
approximately 20 percent longer to charge.
Lithium ion batteries offer increased power capacity and
are lighter in weight than similar-size NiCd and NiMH batteries. These batteries are optimized for the particular
model of cellular phone, which helps ensure maximum
charging capability and long life.
Newer cellular phones may operate with optional highenergy AA alkaline batteries that can provide up to 3 hours
of talk time or 30 hours of standby time. These batteries take
advantage of lithium–iron disulfide technology, which
results in 34 percent lighter weight than standard AA 1.5volt batteries (15 versus 23 grams per battery) and 10-year
storage life—double that of standard AA alkaline batteries.
Vehicle-mounted cell phones can be optionally powered
via the vehicle’s 12-volt dc battery by using a battery eliminator that plugs into the dashboard’s cigarette lighter. This
saves useful battery life by drawing power from the vehicle’s
battery and comes in handy when the phone’s battery has
run down. A battery eliminator will not recharge the phone’s
battery, however. Recharging the battery can only be done
with a special charger.
Lead-acid batteries are used to power transportable cellular phones when the user wishes to operate the phone away
from a vehicle. The phone and battery are usually carried in
a vinyl pouch.
Features and Options
Cellular telephones offer many features and options, including
Voice activation Sometimes called “hands-free operation,”
this feature allows the user to establish and answer calls by
issuing verbal commands. This safety feature enables a driver to control the unit without becoming visually distracted.
Memory functions These allow storage of frequently called
numbers to simplify dialing. Units may offer as few as 10
memory locations or in excess of 100, depending on model
and manufacturer.
Multimode This allows the phone to be used with multiple
carriers. The phone can be used to access digital service
where it is available and then switch to an analog service of
another wireless carrier when roaming.
Multiband This allows the phone to be used with multiple networks using different frequency bands. For example, the cell phone can be used to access the 1900-MHz
band when it is available and then switch to the 800MHz band when roaming.
Visual status display This conveys information on numbers dialed, state of battery charge, call duration, roaming
indication, and signal strength. Cell phones differ widely
in the number of characters and lines of alphanumeric
information they can display. The use of icons enhances
ease of use by visually identifying the phone’s features.
Programmable ring tones Some cellular phones allow the
user to select the phone’s ring tone. Multiple ring tones
can be selected, each assigned to a different caller. A variety of ring tones may be downloaded from the Web.
Silent call alert Features include visual or vibrating notification in lieu of an audible ring tone. This can be particularly useful in locations where the sound of a ringing
phone would constitute an annoyance.
Security features These include password access via the
keypad to prevent unauthorized use of the cell phone as
well as features to help prevent access to the phone’s telephone number in the event of theft.
Voice messaging This allows the phone to act as an
answering machine. A limited amount of recording time
(about 4 minutes) is available on some cell phones.
However, carriers also offer voice-messaging services that
are not dependent on the phone’s memory capacity. While
the phone is in standby mode, callers can leave messages
on the integral answering device. While the phone is off,
callers can leave messages on the carrier’s voice-mail system. Users are not billed for airtime charges when retrieving their messages.
Call restriction This enables the user to allow use of the
phone by others to call selected numbers, local numbers,
or emergency numbers without permitting them to dial
the world at large and rack up airtime charges.
Call timers These provide the user with information as to
the length of the current call and a running total of airtime for all calls. These features make it easier for users
to keep track of call charges.
User-defined ring tones These offer users the option to
compose or download ring tones of their choice to replace
the standard ring tone that comes with the cell phone.
Data transfer kit For cell phones that are equipped with a
serial interface, there is software for the desktop PC that
allows users to enter directory information via keyboard
rather than the cell phone keypad. The information is
transferred via the kit’s serial cable. Through the software
and cable connection, information can be synchronized
between the PC and cell phone, ensuring that both devices
have the most recent copy of the same information.
Location-Reporting Technology
Mobile phone companies are under orders from the FCC to
incorporate location-reporting technology into cellular
phones. Dubbed E-911, or enhanced 911, the initiative is
meant to provide law enforcement and emergency services
personnel with a way to find people calling 911 from mobile
phones when callers do not know where they are or are
unable to say. Since no carrier was able to make an October
2001 deadline to fully implement E-911, the FCC issued
waivers permitting carriers to add location-detection services to new phones over time so that 95 percent of all mobile
phones will be compliant with E-911 rules by 2005.
One way manufacturers can address this requirement is by
providing cell phones with a Global Positioning System (GPS)
capability in which cell phone towers help GPS satellites fix a
cell phone caller’s position. Special software installed in the
base station hardware serves location information to cell
phones, which is picked up at the public safety answering
point (PSAP). However, subscribers would need to purchase a
new GPS-equipped handset, since this method would not allow
legacy handsets to use the location-determination system.
Another location-determination technique is called “Time
Difference of Arrival” (TDOA), which works by measuring
the exact time of arrival of a handset radio signal at three or
more separate cell sites. Because radio waves travel at a
fixed known rate (the speed of light), by calculating the difference in arrival time at pairs of cell sites, it is possible to
calculate hyperbolas on which the transmitting device is
located. The TDOA technique makes use of existing receive
antennas at the cell sites. This location technique works
with any handset, including legacy units, and only requires
modifications to the network.
Internet-Enabled Mobile Phones
Internet-enabled mobile phones potentially represent an
important communications milestone, providing users with
access to Web content and applications, including the ability
to participate in electronic commerce transactions. The
Wireless Application Protocol (WAP), an internationally
accepted specification, allows wireless devices to retrieve
content from the Internet, such as general news, weather,
airline schedules, traffic reports, restaurant guides, sports
scores, and stock prices.
Users also can personalize these services by creating a
profile that might request updated stock quotes every halfhour or specify tastes in music and food. A user also could set
up predefined locations, such as home, main office, or transit, so that the information is relevant for that time and location. With access to real-time traffic information, for
example, users can obtain route guidance on their cell phone
screens via the Internet. Up-to-the-minute road conditions
are displayed directly on the cell phone screen. Street-bystreet guidance is provided for navigating by car, subway, or
simply walking, taking into account traffic congestion to
work out the best itinerary. Such services can even locate
and guide users to the nearest facilities, such as free parking
lots or open gas stations, using either an address entered on
the phone keypad or information supplied by an automatic
location identification (ALI) service.
One vendor that has been particularly active in developing WAP-compliant Internet-enabled mobile phones is
Nokia, the world’s biggest maker of mobile phones. The
company’s Model 7110 works only on GSM 900 and GSM
1800 in Europe and Asia but is indicative of the types of new
mobile phones that about 70 other manufacturers are targeting at the world’s 200 million cellular subscribers. It displays Internet-based information on the same screen used
for voice functions. It also supports Short Messaging
Service (SMS) and e-mail and includes a calendar and
phonebook as well.
The phone’s memory also can save up to 500 messages—
SMS or e-mail—sorted in various folders such as the inbox,
outbox, or user-defined folders. The phonebook has enough
memory for up to 1000 names, with up to five phone and fax
numbers and two addresses for each entry. The user can
mark each number and name with a different icon to signify
home or office phone, fax number, or e-mail address, for
example. The phone’s built-in calendar can be viewed by day,
week, or month, showing details of the user’s schedule and
calendar notes for the day. The week view shows icons for the
jobs the user has to do each day. Up to 660 notes in the calendar can be stored in the phone’s memory.
Nokia has developed several innovative features to make
it faster and easier to access Internet information using a
mobile phone:
Large display The screen has 65 rows of 96 pixels (Figure
C-3), allowing it to show large and small fonts, bold or regular, as well as full graphics.
Microbrowser Like a browser on the Internet, the microbrowser feature enables the user to find information by
entering a few words to launch a search. When a site of
interest is found, its address can be saved in a “favorites”
folder or input using the keypad.
Navi Roller This built-in mouse looks like a roller (Figure
C-4) that is manipulated up and down with a finger to
scroll and select items from an application menu. In each
situation, the Navi Roller knows what to do when it is
clicked—select, save, or send.
Predictive text input As the user presses various keys to
spell words, a built-in dictionary continually compares
the word in progress with the words in the database. It
selects the most likely word to minimize the need to continue spelling out the word. If there are several word possibilities, the user selects the right one using the Navi
Figure C-3 Display screen of the Nokia 7110.
Figure C-4 Close-up of the Navi Roller on the Nokia 7110.
Roller. New names and words can be input into the
phone’s dictionary.
However, the Nokia phone cannot be used to access just
any Web site. It can access only Web sites that have been
developed using WAP-compliant tools. The WAP standard
includes its own Wireless Markup Language (WML), which
is a simple version of the HyperText Markup Language
(HTML) that is used widely for developing Web content. The
strength of WAP is that it is supported by multiple airlink
standards and, in true Internet tradition, allows content
publishers and application developers to be unconcerned
about the specific delivery mechanism.
Third-Generation Phones
The world is moving toward third-generation (3G) mobile
communications systems that are capable of bringing highquality mobile multimedia services to a mass market.
The International Telecommunication Union (ITU) has
put together a 3G framework known as International
Mobile Telecommunications-2000 (IMT-2000). This framework encompasses a small number of frequency bands,
available on a globally harmonized basis, that make use of
existing national and regional mobile and mobile-satellite
frequency allocations.
Along the way toward 3G is a 2.5G service known as
General Packet Radio Service (GPRS), which offers true
packet data connectivity to cell phone users. GPRS leverages
Internet Protocol (IP) technologies, adding convenience and
immediacy to mobile data services. GPRS is ideal for wireless data applications with bursty data, especially WAPbased information retrieval and database access.
GPRS enables wireless users to have an “always on” data
connection, as well as high data transfer speeds. Although
GPRS offers potential data transfer rates of up to 115 kbps,
subscribers will only really notice faster service at the initial
connection. The faster speed is in the connect time. At present, users connect at a maximum of 19.2 kbps.
GPRS packet-based service should cost users less than
circuit-switched services, since communication channels are
shared rather than dedicated only to one user at a time. It
also should be easier to make applications available to
mobile users because the faster data rate means that middleware currently needed to adapt applications to the slower
speed of wireless systems will no longer be needed. To take
advantage of GPRS, however, mobile users will have to buy
new cell phones that specifically support the data service.
Cellular phones are getting more intelligent, as evidenced by
the combination of cellular phone, personal digital assistant
(PDA), Web browser, and always-on GPRS connection into
one unit. These devices not only support data communications, they also support voice messaging, e-mail, fax, and
micropayments over the Internet as well. Third-party software provides the operating system and such applications as
calendaring, card file, and to-do lists. With more cellular
phones supporting data communications, cellular phones
are available that provide connectivity to PC desktops and
databases via Bluetooth, infrared, or serial RS-232 connections. Information can even be synchronized between cell
phones and desktop computers to ensure that the user is
always accessing the most up-to-date information.
See also
Cellular Data Communications
Cellular Voice Communications
Global Positioning System
Personal Communications Services
Cellular telephony provides communications service to automobiles and hand-held portable phones and interconnects
with the Public Switched Telephone Network (PSTN) using
radio transmissions based on a system of cells and base station antennas.
AT&T’s Bell Laboratories developed the cellular concept
in 1947, but it was not until 1974 that the FCC set aside
radio spectrum between 800 and 900 MHz for cellular radio
systems. The first cellular demonstration system was
installed in Chicago in 1978, and 3 years later the FCC formally authorized 666 channels for cellular radio signals and
established cellular geographic servicing areas (CGSAs) to
cover the nation’s major metropolitan centers.
At the same time, the FCC created a regulatory scheme
for cellular service that specified that two competing cellular
companies would be licensed in each market. For each city,
one license would be reserved for the local telephone company (a wireline company), and the other license would be
granted to another qualified applicant. When the number of
applicants became prohibitively large, the FCC amended its
licensing rule and specified the use of lotteries to select
applicants for all but the top 30 markets.
Cellular service—whether analog or digital—is now available virtually everywhere in the United States and from
many more service providers in each market. According the
FCC, 259 million people, or almost 91 percent of the total
U.S. population, have access to three or more different operators [cellular, broadband personal communications services
(PCS), and/or digital specialized mobile radio (SMR)
providers] offering mobile telephone service in the counties
in which they live. Over 214 million people, or 75 percent of
the U.S. population, live in areas with five or more mobile
telephone operators competing to offer service. And 133 million people, or 47 percent of the population, can choose from
at least six different mobile telephone operators.
If a subscriber uses the cell phone outside the home service area, this is traveling, and an extra charge is applied to
the call. When the cell phone is used outside the service
provider’s network, this is roaming. In this case, if the service provider has agreements with other carriers, the traveling rate is applied to each call. Where digital service is not
available and the service provider has agreements with conventional analog service providers, subscribers can use their
cell phones in analog mode, in which case airtime and longdistance charges are applied to each call.
Cellular telephones were targeted originally at mobile professionals, allowing them to optimize their schedules by
turning nonproductive driving and out-of-the-office time
into productive and often profitable work time. Cellular
solutions not only facilitate routine telephone communications, they also increase revenue potential for people in professions that have high-return opportunities as a direct
result of being able to respond promptly to important calls.
Today, cellular service is also targeted at consumers, giving
them the convenience of anytime, anywhere calling plus the
security of instant access to service in times of emergency. As
of mid-2001, more than half of U.S. households subscribed to
wireless phone service, and a majority of them had two or more
mobile phones. Over 15 percent of cellular subscribers use the
service for more than half of their long-distance calls, while
about 10 percent use it for more than half their local calls.
Developing countries that do not have an advanced communications infrastructure are increasingly turning to cellular technology so that they can take part in the global
economy without having to go through the resource-intensive
step of installing copper wire or optical fiber. Explosive
growth is occurring in India and China. Even among industrialized countries, there is continued high growth in cellular
usage. In Japan, the number of cell phones now exceeds the
number of analog fixed-line phones.
Technology Components
Cellular networks rely on relatively short-range transmitter/receiver (transceiver) base stations that serve small sections (or cells) of a larger service area. Mobile telephone
users communicate by acquiring a frequency or time slot in
the cell in which they are located. A master switching center
called the “mobile transport serving office” (MTSO) links
calls between users in different cells and acts as a gateway
to the PSTN. Figure C-5 illustrates the link from the MTSO
to the base stations in each cell. The MTSO also has links to
local telephone central offices so that cellular users can communicate with users of conventional phones.
Cell Sites Cell boundaries are neither uniform nor constant.
The usage density in the area, as well as the landscape, the
presence of major sources of interference (e.g., power lines,
buildings), and the location of competing carrier cells, contributes to the definition of cell size. Cellular boundaries
change continuously, with no limit to the number of frequencies available for transmission of cellular calls in an
area. As the density of cellular usage increases, individual
Mobile Transport Serving Office
Central Office
Figure C-5 A typical cellular network configuration.
cells are split to expand capacity. By dividing a service area
into small cells with limited-range transceivers, each cellular system can reuse the same frequencies many times.
Technologies such as Code Division Multiple Access (CDMA)
and Expanded Time Division Multiple Access (E-TDMA)
promise further capacity gains in the future.
Master Switching Center In a typical cellular network, the
master-switching center operates similar to a telephone central office and provides links to other offices. The switching
center supports trunk lines to the base stations that establish the cells in the service area. Each base station supports
a specific number of simultaneous calls—from 3 to 15,
depending on the underlying technology (i.e., CDMA,
TDMA, or some derivative).
Transmission Channels Most cellular systems provide two
types of channels: a control channel and a traffic channel.
The base station and mobile station use the control channel
to support incoming and outgoing calls, monitor signal quality, and register when a user moves into a new zone. The
traffic channel is used only when the station is off-hook and
actually involved in a call.
The control and traffic channels are divided into time slots.
When the user initiates access to the control channel to place
a call, the mobile station randomly selects a subslot in a general-use time slot to reach the system; the system then
assigns a time slot to the traffic channel. For an incoming call
to a mobile station, the base station initiates conversations on
the control channel by addressing the mobile station in a time
slot, which at the same time reserves that time slot for the station’s reply. If a user’s call attempt collides with another user’s
call attempt, both instruments automatically reselect a subslot and try again. After repeated collisions, if no time slots
are available within a predetermined time, the system rejects
service requests for incoming and outgoing calls.
When a mobile telephone user places a call, the cell in
which the user is traveling allocates a slot for the call. The
call slot allows the user access through the base station to
the master switching center, essentially providing an extension on which the call can be placed. The master switching
center, through an element of the user-to-base-station connection, continuously monitors the quality of the call signal
and transfers the call to another base station when the signal quality reaches an unacceptable level due to the distance
traveled by the user, obstructions, and/or interference. If the
user travels outside the system altogether, the master
switching center terminates the call as soon as the signal
quality deteriorates to an unacceptable level.
Cellular Telephones Cellular telephones incorporate a com-
bination of multiaccess digital communications technology
and traditional telephone technology and are designed to
appear to the user as familiar residential or business telephone equipment. Manufacturers use miniaturization and
digital signal processing technology to make cellular phones
feature rich yet compact and economical.
Cellular instruments consist of a transceiver, an analog/digital converter, and a supervisory/control system that
manages calls and coordinates service with both the base
station and the master switching center. Cellular telephones
can be powered from a variety of sources, including vehicle
batteries, ac adapters, and rechargeable battery sets.
Traditional cellular instrument types include hand-held,
transportable, and car telephones. However, advances in cellular technology are creating additional types of telephones,
including modular and pocket phones. The trend in cellular
instruments is toward multipurpose transportable telephones.
There are dual-mode cellular phones that can be used with
in-building wireless Private Branch Exchanges (PBXs) as
well as with the outside cellular service. The handset registers itself with an in-building base station and takes its commands from the wireless PBX. For out-of-building calling, the
handset registers with the nearest cell site transceiver. Aside
from convenience, an added benefit of the dual-mode phone is
that calls made off the corporate premises can be aggregated
with business calls made at home or on the road for the purpose of achieving a discounted rate on all calls.
Network Optimization
Network optimization is a high priority for wireless carriers. A
single cell site, including electronics and tower, can cost as
much as $600,000 to build. With skyrocketing growth for wireless voice and data access in recent years, wireless service
providers want to get the most efficient use out of their current
networks and target upgrades appropriately to meet customer
demand. The use of network-optimization tools translates into
lower wireless service costs and better coverage.
Such tools measure cell site footprints, service areas within
those footprints, and frequency assignments—all with the
purpose of identifying the disruptive interference that cell
sites receive from adjoining sites. By taking steps to limit
interference between cells, wireless providers can maximize
the bandwidth devoted to moving traffic. In addition to monitoring the cell sites, these network-optimization tools monitor
the strength of radio frequency (RF) signals emanating from
cell sites as well as how calls are handed off among cell sites.
The FCC sets rules, regulations, and policies to, among other
Grant licenses for frequencies and license renewals
Rule on assignments and transfers of control of licenses
Govern the interconnection of cellular networks with
other wireless and wireline carriers
Establish access and universal service funding provisions
Impose fines and forfeitures for violations of any of the
FCC rules
Regulate the technical standards of cellular networks
In addition, the FCC and many states have established
universal service programs to ensure affordable, quality
telecommunications services for all Americans. Contributions
to these programs by cellular/PCS service providers are typically a percentage of end-user revenues.
The FCC currently prohibits a single entity from having a
combined attributable interest (20 percent or greater interest in any license) in broadband PCS, cellular, and specialized mobile radio licenses totaling more than 45 MHz in any
geographic area, except that in rural service areas no
licensee may have an attributable interest in more than 55
MHz of Commercial Mobile Radio Service (CMRS) spectrum.
The FCC must approve any substantial changes in ownership or control of a cellular/PCS license. Noncontrolling
interests in an entity that holds a license or operates cellu-
lar/PCS networks generally may be bought or sold without
prior FCC approval. In addition, the FCC now requires only
postconsummation notification of certain pro forma assignments or transfers of control.
All licenses are granted for 10-year terms. Licenses may
be revoked if any FCC rules are violated. Licenses may be
renewed for additional 10-year terms. Renewal applications
are not subject to spectrum auctions. Third parties, however,
may oppose renewal applications.
No other technology has taken the world by storm quite like
cellular except, perhaps, the Internet. Cellular systems have
expanded beyond providing voice communication to supporting more sophisticated applications, such as Internet access
for electronic mail and accessing Web content. New Internetenabled cellular phones feature larger displays that help
make them all-purpose communications appliances. It has
reached the point where cellular service is as necessary for
the average consumer as for mobile professionals.
See also
Calling Party Pays
Cellular Data Communications
Cellular Telephones
Code Division Multiple Access
Personal Communications Service
Time Division Multiple Access
Citizens Band (CB) Radio Service is a two-way voice communication service for use in personal and business activities.
The service uses 40 channels in the assigned frequency range
of 26.965 to 27.405 MHz, and the effective communication
distance is 1 to 5 miles. An FCC license is not required to use
this service. CB Rule 3 provides users with all the authority
they need to operate a CB unit in places where the FCC regulates radio communications, as long as an unmodified FCCaccepted CB unit is used. An FCC-accepted unit has an
identifying label placed on it by the manufacturer. There is
no age or citizenship requirement for using this service.1
CB users may use an on-the-air pseudonym or “handle” of
their own choosing and may operate their CB units within the
territorial limits of the 50 states, the District of Columbia, and
the Caribbean and Pacific insular areas. Users also may operate their CB units on or over any other area of the world,
except within the territorial limits of areas where radio communications are regulated by another agency of the United
States or within the territorial limits of any foreign government. In addition, users can use their CB units in Canada,
subject to the rules of the Canadian Department of
The power output of the CB unit may not be raised, since
raising the level of radio noise would be unfair to the other
users sharing a channel. Users also must not attach a linear
amplifier or any other type of power amplifier to their CB unit
or modify the unit internally. Doing so cancels its type acceptance, and the user forfeits his or her authorization to use it.
There are no height restrictions for antennas mounted on
vehicles or for hand-held units. For structures, the highest
point of the antenna must not be more than 20 feet above the
highest point of the building or tree on which it is mounted
or 60 feet above the ground. There are lower height limits if
the antenna structure is located within 2 miles of an airport.
No CB channel is assigned to any specific individual or
organization. Any of the 40 CB channels can be used on a
1The only caveat to CB Rule 3 in this regard is that the user cannot be a foreign government, a representative of a foreign government, or a federal government agency. Of
course, if the FCC has issued a cease and desist order, that person cannot be a CB user.
“take turns” basis. Since CB channels are shared, cooperation among users is essential; communications should be
short, with conversations never more than 5 minutes continuously. Users should wait at least 1 minute before starting another communication. Channel 9 should only be used
for emergency communications or for traveler assistance.
“Ten-codes” is abbreviations of common questions and answers
used on all types of radio communication. Professional CB
users use these codes to send their message quickly and easily.
Additionally, ten-codes can be readily understood by users
when poor reception or language barriers must be overcome.
Although the FCC authorizes CB operators to use ten-codes, it
does not regulate their meaning. The most commonly used
ten-codes are listed below in Table C-1.
Initially, users were required to obtain a CB radio license
and call letters from the FCC before they could go on the air.
However, the FCC became so inundated with requests for
CB radio licenses that it finally abandoned formal licensing
and allowed operators to buy CB radio equipment and go on
the air without any license or call letters. Although no
license is required to operate a CB radio, the FCC’s rules for
CB radio operation are still in effect and must be followed.
These rules cover CB radio equipment, the ban on linear
amplifiers, and the types of communications permitted on
the air. Manufacturers are required to provide a copy of the
operating rules with each CB set.
See also
Family Radio Service
General Mobile Radio Service
Common Ten-Codes Used by CB Operators
10-1 = Receiving poorly
10-2 = Receiving well
10-3 = Stop transmitting
10-4 = Message received
10-5 = Relay message to _________
10-6 = Busy, please stand by
10-7 = Out of service, leaving the
10-8 = In service, subject to call
10-9 = Repeat message
10-10 = Transmission complete,
standing by
10-11 = Talking too rapidly
10-12 = Visitors present
10-13 = Advise weather/ road
10-16 = Make pickup at _________
10-17 = Urgent business
10-18 = Anything for us?
10-19 = Nothing for you, return to
10-20 = My location is _________
10-21 = Call by telephone
10-22 = Report in person to
10-23 = Stand by
10-24 = Completed last assignment
10-25 = Can you contact _________
10-26 = Disregard last information
10-27 = I am moving to channel
10-28 = Identify your station
10-29 = Time is up for contact
10-30 = Does not conform to FCC
10-32 = I will give you a radio
10-33 = Emergency traffic
10-34 = Trouble at this station
10-35 = Confidential information
10-36 = Correct time is
10-37 = Wrecker needed at
10-38 = Ambulance needed at
10-39 = Your message delivered
10-41 = Please turn to channel
10-42 = Traffic accident at
10-43 = Traffic tie-up at
10-44 = I have a message for you
10-45 = All units within range
please report
10-50 = Break channel
10-60 = What is next message
10-62 = Unable to copy, use phone
10-63 = Net directed to
10-64 = Net clear
10-65 = Awaiting next
10-67 = All units comply
10-70 = Fire at _________
10-71 = Proceed with transmission
in sequence
10-77 = Negative contact
10-81 = Reserve hotel room for
10-82 = Reserve room for _________
10-84 = My telephone number is
10-85 = My address is _________
10-91 = Talk closer to the microphone
10-93 = Check my frequency on
this channel
10-94 = Please give me a long count
(1 to 10)
10-99 = Mission completed, all
units secure
10-200 = Police needed at ________
Low-Power Radio Service
Wireless Medical Telemetry Service
Code Division Multiple Access (CDMA) is a spread-spectrum
technology that is used for implementing cellular telephone
service. Spread spectrum is a family of digital communication
techniques originally used in military communications and
control applications. Spread spectrum uses carrier waves that
consume a much wider bandwidth than that required for simple point-to-point communication at the same data rate. This
results in the carrier wave looking more like random noise than
real communication between a sender and receiver. Originally,
there were two motivations for implementing spread spectrum:
to resist enemy efforts to jam vital communications and to hide
the fact that communication was even taking place.
For cellular telephony, spread-spectrum technology underlies CDMA, which is a digital multiple access technique specified by the Telecommunications Industry Association (TIA)
as IS-95. Commercial applications of CDMA became possible
because of two key developments. One was the availability of
low-cost, high-density digital integrated circuits, which
reduce the size, weight, and cost of the mobile phones. The
other was the realization that optimal multiple access communication depends on the ability of all mobile phones to regulate their transmitter power to the lowest level that will
achieve adequate signal quality.
CDMA changes the nature of the mobile phone from a predominately analog device to a predominately digital device.
CDMA receivers do not eliminate analog processing entirely,
but they separate communication channels by means of a
pseudorandom modulation that is applied and removed in
the digital domain, not on the basis of frequency. This allows
multiple users to occupy the same frequency band; this frequency reuse results in high spectral efficiency.
TDMA systems commonly start with a slice of spectrum,
referred to as a “carrier.” Each carrier is then divided into
time slots. Only one subscriber at a time is assigned to each
time slot or channel. No other conversations can access this
channel until the subscriber’s call is finished or until that
original call is handed off to a different channel by the system. For example, TDMA systems, designed to coexist with
AMPS systems, divide 30 kHz of spectrum into three channels. By comparison, GSM systems create eight timedivision channels in 200-kHz-wide carriers.
Wideband Usage
With CDMA systems, multiple conversations simultaneously share the available spectrum in both the time and frequency dimensions. The available spectrum is not
“channelized” in frequency or time as in Frequency Division
Multiple Access (FDMA) or TDMA systems, respectively.
Instead, the individual conversations are distinguished
through coding; that is, at the transmitter, each conversation is processed with a unique spreading code that is used
to distribute the signal over the available bandwidth. The
receiver uses the unique code to accept the energy associated
with a particular code. The other signals present are each
identified by a different code and simply produce background noise. In this way, many conversations can be carried
simultaneously within the same block of spectrum.
The following analogy is used commonly to explain how
CDMA technology works. Four speakers are simultaneously
giving a presentation, and they each speak a different native
language: Spanish, Korean, English, and Chinese (Figure C6). If English is your native language, you only understand
the words of the English speaker and tune out the Spanish,
Korean, and Chinese speakers. You hear only what you know
and recognize. The rest sounds like background noise. The
same is true for CDMA. Each conversation is specially
encoded and decoded for a particular user. Multiple users
How are you?
ni hao!
Como estan
hasip nikka!
Figure C-6 In this analogy of CDMA functionality, each conversation is
specially encoded and decoded for each particular user. Thus the Englishspeaking person will only hear another English-speaking person and tune
out the other languages, which are heard as background noise.
share the same frequency band at the same time, yet each
user hears only the conversation he or she can interpret.
CDMA assigns each subscriber a unique code to put multiple users on the same wideband channel at the same time.
These codes are used to distinguish between the various conversations. The result of this access method is increased callhandling capacity.
One of the unique aspects of CDMA is that while there are
ultimate limits to the number of phone calls that a system
can handle, this is not a fixed number. Rather, the capacity
of the system depends on how coverage, quality, and capacity are balanced to arrive at the desired level of system performance. Since these parameters are tightly intertwined,
operators cannot have the best of all worlds: 3 times wider
coverage, 40 times capacity, and high-quality sound. For
example, the 13-kbps vocoder provides better sound quality
but reduces system capacity compared with an 8-kbps
vocoder. Higher capacity might be achieved through some
degree of degradation in coverage and/or quality.
System Features
CDMA has been adapted for use in cellular communications
with the addition of several system features that enhance
efficiency and lower costs.
Mobile Station Sign-on On power-on, the mobile station
already knows the assigned frequency for CDMA service in
the local area and will tune to that frequency and search for
pilot signals. Multiple pilot signals typically will be found,
each with a different time offset. This time offset distinguishes one base station from another. The mobile station
will pick the strongest pilot and establish a frequency reference and a time reference from that signal. Once the mobile
station becomes synchronized with the base station’s system
time, it can then register. Registration is the process by
which the mobile station tells the system that it is available
for calls and notifies the system of its location.
Call Processing The user makes a call by entering the digits
on the mobile station keypad and hitting the “Send” button. If
multiple mobile stations attempt a link on the access channel
at precisely the same moment, a collision occurs. If the base
station does not acknowledge the access attempt, the mobile
station will wait a random time and try again. On making contact, the base station assigns a traffic channel, whereupon
basic information is exchanged, including the mobile station’s
serial number. At this point, the conversation mode is started.
As a mobile station moves from one cell to the next, another
cell’s pilot signal will be detected that is strong enough for it
to use. The mobile station will then request a “soft handoff,”
during which it is actually receiving both signals via different
correlative elements in the receiver circuitry. Eventually, the
signal from the first cell will diminish, and the mobile station
will request from the second cell that the soft handoff be terminated. A base station does not hand off the call to another
base station until it detects acceptable signal strength.
This soft handoff technique is a significant improvement
over the handoff procedure used in analog FM cellular systems, where the communication link with the old cell site is
momentarily disconnected before the link to the new site is
established. For a short time, the mobile station is not connected to either cell site, during which the subscriber hears
background noise or nothing at all. Sometimes the mobile
stations Ping-Pong between two cell sites as the links are
handed back and forth between the approaching and
retreating cell sites. Other times, the calls are simply
dropped. Because a mobile station in the CDMA system has
more than one modulator, it can communicate with multiple
cells simultaneously to implement the soft handoff.
At the end of a call placed over the CDMA system, the
channel will be freed and may be reused. When the mobile
station is turned off, it will generate a power-down registration signal that tells the system that it is no longer available
for incoming calls.
Voice Detection and Encoding With voice activity detection,
the transmitter is activated only when the user is speaking.
This reduces interference levels—and, consequently, the
amount of bandwidth consumed—when the user is not
speaking. Through interference averaging, the capacity of
the system is increased. This allows systems to be designed
for the average rather than the worst interference case.
However, the IS-95 CDMA standard requires that no interfering signal be received that is significantly stronger than
the desired signal, since it would then jam the weaker signal. This has been called the “near-far problem” and means
that high cell capacity does not necessarily translate into
high overall system capacity.
The speech coder used in CDMA operates at a variable
rate. When the subscriber is talking, the speech coder operates at the full rate; when the subscriber is not talking, the
speech coder operates at only one-eighth the full rate. Two
intermediate rates are also defined to capture the transitions
and eliminate the effect of sudden rate changes. Since the
variable-rate operation of the speech coder reduces the average bit rate of the conversations, system capacity is increased.
Privacy Increased privacy is inherent in CDMA technology.
CDMA phone calls will be secure from the casual eavesdropper
because, unlike a conversation carried over an analog system,
a simple radio receiver will not be able to pick out individual
digital conversations from the overall RF radiation in a frequency band.
A CDMA call starts with a standard rate of 9.6 kbps. This
is then spread to a transmitted rate of about 1.25 Mbps.
“Spreading” means that digital codes are applied to the data
bits associated with users in a cell. These data bits are transmitted along with the signals of all the other users in that
cell. When the signal is received, the codes are removed from
the desired signal, separating the users and returning the
call to the original rate of 9.6 kbps.
Because of the wide bandwidth of a spread-spectrum signal, it is very difficult to identify individual conversations for
eavesdropping. Since a wideband spread-spectrum signal is
very hard to detect, it appears as nothing more than a slight
rise in the “noise floor” or interference level. With analog
technologies, the power of the signal is concentrated in a
narrower band, which makes it easier to detect with a radio
receiver tuned to that set of frequencies.
The use of wideband spread-spectrum signals also offers
more protection against cloning, an illegal practice whereby
a mobile phone’s electronic serial number is taken over the
air and programmed into another phone. All calls made from
a cloned phone are “free” because they are billed to the original subscriber.
Power Control CDMA systems rely on strict control of power at
the mobile station to overcome the so-called near-far problem.
If the signal from a near mobile station is received at the cell
site receiver with too much power, the cell site receiver will
become overloaded and prevent it from picking up the signals
from mobile stations located farther away. The goal of CDMA
is to have the signals of all mobile stations arrive at the base
station with exactly the same power level. The closer the
mobile station is to the cell site receiver, the lower is the power
necessary for transmission; the farther away the mobile station, the greater is the power necessary for transmission.
Two forms of adaptive power control are employed in
CDMA systems: open loop and closed loop. Open-loop power
control is based on the similarity of loss in the forward and
reverse paths. The received power at the mobile station is
used as a reference. If it is low, the mobile station is assumed
to be far from the base station and transmits with high
power. If it is high, the mobile station is assumed to be near
the base station and transmits with low power. The sum of
the two power levels is a constant.
Closed-loop power control is used to force the power from
the mobile station to deviate from the open-loop setting. This
is achieved by an active feedback system from the base station to the mobile station. Power control bits are sent every
1.25 millisecond (ms) to direct the mobile station to increase
or decrease its transmitted power by 1 decibel (dB). Lack of
power control to at least this accuracy greatly reduces the
capacity of CDMA systems.
With these adaptive power-control techniques, the mobile
station transmits only enough power to maintain a link. This
results in an average power requirement that is much lower
than that for analog systems, which do not usually employ
such techniques. CDMA’s lower power requirement translates into smaller, lightweight, longer-life batteries—approximately 5 hours of talk time and over 2 days of standby
time—and makes possible smaller, lower-cost hand-held
computers and hybrid computer-communications devices.
CDMA phones can easily weigh in at less than 8 ounces.
Spatial Diversity Among the various forms of diversity is
that of spatial diversity, which is employed in CDMA, as well
as in other multiple access techniques, including FDMA and
TDMA. Spatial diversity helps to maintain the signal during
the call handoff process when a user moves from one cell to
the next. This process entails antennas in two different cell
sites maintaining links with one mobile station. The mobile
station has multiple correlative receiver elements that are
assigned to each incoming signal and can add these.
CDMA uses at least four of these correlators: three that
can be assigned to the link and one that searches for alternate paths. The cell sites send the received data, along with
a quality index, to the MTSO, where a choice is made regarding the better of the two signals.
Not all these features are unique to CDMA; some can be
exploited by TDMA-based systems as well, such as spatial
diversity and power control. These already exist in all TDMA
standards today, while soft handoff is implemented in the
European Digital Enhanced Cordless Telecommunications
(DECT) standard, which is based on TDMA.
There are still conflicting performance claims for TDMA and
CDMA. Since both TDMA and CDMA have become TIA standards—IS-54 and IS-95, respectively—vendors are now aiming their full marketing efforts toward the cellular carriers.
Proponents of each technology have the research to back up
their claims of superior performance. Of the two, CDMA suffered a credibility problem early on because its advocates
made grandiose performance claims for CDMA that could not
be verified in the real-world operating environment. In some
circles, this credibility problem lingers today. Of note, however, is that both technologies have been successful in the
marketplace, each having been selected by many cellular carriers around the world. Both are capable of supporting emerging PCS networks and providing such services as wireless
Internet access, Short messaging Service, voice mail, facsimile, paging, and video. Although TDMA-based Global System
for Mobile (GSM) telecommunications is the dominant standard in the global wireless market, the use of CDMA is growing rapidly. GSM’s head start in the market gives it a much
larger presence and practically guarantees that GSM will continue to lead the digital cellular market for the next 5 years.
See also
Digital Enhanced Cordless Telecommunications
Frequency Division Multiple Access
Spread Spectrum Radio
Time Division Multiple Access
Competitive Local Exchange Carriers (CLECs) offer voice,
data services, and value-added services at significantly
lower prices than the Incumbent Local Exchange Carriers
(ILECs), enabling residential and business users to save
money on such things as local calls, call-handling features,
lines, and Internet access. Typically, CLECs offer service in
major cities, where traffic volumes are greatest and, consequently, users are hardest hit with high local exchange
charges from the incumbent carrier. Some CLECs call themselves integrated communications providers (ICPs) because
their networks are designed from the outset to support voice
and data services as well as Internet access. Others call
themselves Data Local Exchange Carriers (DLECs) because
they specialize in data services such as Digital Subscriber
Line (DSL), which is used primarily for Internet access.
As of 2002, the ILECs still controlled 97 percent of the market for local services, according to the FCC, which means that
the CLECs are trying to sustain themselves on the remaining
3 percent as they attempt to take market share from the
ILECs. To deal with this situation, the CLECs have adopted
different strategies based on resale and facilities ownership.
Resale versus Ownership
CLECs may compete in the market for local services by setting up their own networks or by reselling lines and services
purchased from the ILEC. They may have hybrid arrangements for a time, which are part resale and part facilities
ownership. Most CLECs prefer to have their own networks
because the profit margins are higher than for resale.
However, many CLECs start out in new markets as
resellers. This enables them to establish a local presence,
build brand awareness, and begin building a customer base
while they assemble their own facilities-based network.
Although this strategy is used by many CLECs, many fail
to carry it out properly. They get into financial trouble by using
their capital to expand resale arrangements to capture even
more market share instead of using that capital to quickly
build their own networks and migrate customers to the highmargin facilities. Depending on the service, it could take a carrier 3 to 4 years to break even on a pure resale customer versus
only 6 to 9 months on a pure facilities-based customer. With
capital markets drying up for telecom companies and customers deferring product and services purchases, prolonged
dependence on resale could set the stage for bankruptcy.
CLECs employ different technologies for competing in the
local services market. Some set up their own Class 5 central
office switches, enabling them to offer “dial tone” and the
usual voice services, including Integrated Services Digital
Network (ISDN) and features such as caller ID and voice
messaging. The larger CLECs build their own fiber rings to
serve their metropolitan customers with high-speed data
services. Some CLECs have chosen to specialize in broadband data services by leveraging existing copper-based local
loops, offering DSL services for Internet access. Others
bypass the local loop entirely through the use of broadband
wireless technologies, such as Local Multipoint Distribution
Service (LMDS), enabling them to feed customer traffic to
their nationwide fiber backbone networks without the
incumbent carrier’s involvement.
Despite the risks, some CLECs view resale as a viable
long-term strategy. It not only allows them to enter into new
markets more quickly than if they had initially deployed
their own network, it also reduces initial capital requirements in each market, allowing them to focus capital
resources initially on the critical areas of sales, marketing,
and operations support systems (OSS). In addition, the
strategy allows them to avoid deployment of conventional
circuit switches and maintain design flexibility for the next
generation of telecommunications technology.
Unfortunately, the resale strategy also results in lower
margins for services than for facilities-based services. This
means that the CLEC must pass much of its customer revenues back to the ILEC to pay the monthly fees for access
lines. When investors stopped stressing market growth
over profits in 2000, these CLECs found that capital was
hard to get. By then, many had no money to invest in their
own facilities where margins are greater. Most financial
analysts doubt that CLECs can rely strictly on resale and
survive. Although the ILECs have a vested interest in survival of some resale CLECs in order to receive regulatory
approval to provide in-region long distance, once that
approval is gained, some analysts believe that the ILECs
may have no further interest in cooperating with the
With the Telecommunications Act of 1996, CLECs and other
types of carriers are allowed to compete in the offering of
local exchange services and must be able to obtain the same
service and feature connections as the ILECs have for themselves—and on an unbundled basis. If the ILEC does not
meet the requirements of a 14-point checklist to open up its
network in this and other ways, it cannot get permission
from the FCC to compete in the market for long-distance
See also
Federal Communications Commission
Incumbent Local Exchange Carriers
Interexchange Carriers
The familiar cordless telephone, introduced in the early
1980s, has become a key factor in reshaping voice communications. Since people cannot be tied to their desks, as much
as 70 percent of business calls do not reach the right person
on the first attempt. This situation has seen dramatic
improvement with cordless technology, which makes phones
as mobile as their users. Now almost 30 percent of business
calls reach the right person on the first attempt.
Cordless versus Cellular
Although cellular phones and cordless phones are both wireless, they have come to assume quite distinct and separate
applications based on their areas of use and the differing
technologies developed to meet user requirements. Cellular
and cordless are implemented with their own standardsbased technologies.
Briefly, cellular telephones are intended for off-site use.
The systems are designed for a relatively low density of
users. In this environment, macrocellular technology provides wide area coverage and the ability to make calls while
traveling at high speeds. Cordless telephones, on the other
hand, are designed for users whose movements are within a
well-defined area, such as an office building. The cordless
user makes calls from a portable handset linked by radio signals to a fixed base station (Figure C-7). The base station is
connected either directly or indirectly to the public network.
Telephone Network
Figure C-7 The familiar cordless telephone found in many homes.
Cordless Standards
The cordless system standards are referred to as CT0, CT1,
CT2, CT3, and DECT, with “CT” standing for Cordless
Telecommunications. CT0 and CT1 were the technologies for
first-generation analog cordless telephones. Comprising
base station, charger, and handset and intended primarily
for residential use, they had a range of 100 to 200 meters.
They used analog radio transmission on two separate channels, one to transmit and one to receive. The potential disadvantage of CT0 and CT1 systems is that the limited
number of frequencies can result in interference between
handsets, even with the relatively low density of residential
Also targeted at the residential user, CT2 represented an
improved version of CT0 and CT1. Using Frequency Division
Multiple Access (FDMA), the CT2 system splits the available
bandwidth into radio channels in the assigned frequency
domain. In the initial call setup, the handset scans the available channels and locks onto an unoccupied channel for the
duration of the call. Using Time Division Duplexing (TDD),
the call is split into time blocks that alternate between
transmitting and receiving.
The Digital Enhanced Cordless Telecommunications
(DECT) standard started as a European standard for cordless communications, with applications that included residential telephones and wireless Private Branch Exchange
(PBX) and wireless local loop (WLL) access to the public network. Primarily, DECT was designed to solve the problem of
providing cordless telephones in high-density, high-traffic
office and other business environments.
CT3, on the other hand, is a technology developed by
Ericsson in advance of the final agreement on the DECT
standard and is designed specifically for the wireless PBX
application. Since DECT is essentially based on CT3 technology, the two standards are very similar. Both enable the
user to make and receive calls when within the range of a
base station. Depending on the specific operating conditions,
this amounts to a distance of between 164 feet (50 meters)
and 820 feet (250 meters) from the base station. To provide
service throughout the site, multiple base stations are set up
to create a picocellular network. Signal handoff between the
cells is supported by one or more radio exchange units,
which are ultimately connected to the host PBX.
Both DECT and CT3 have been designed to cope with the
highest-density telephone environments, such as city office
districts, where user densities can reach 50,000 per block. A
feature called Continuous Dynamic Channel Selection (CDCS)
ensures seamless handoff between cells, which is particularly
important in a picocellular environment where several handoffs may be necessary, even during a short call. The digital
radio links are encrypted to provide absolute call privacy.
The two standards, DECT and CT3, are based on multicarrier Time Division Multiple Access/Time Division Duplexing
(TMDA/TDD). They do not use the same operating frequencies, though, and consequently have different overall bit rates
and call-carrying capacity.
It is the difference in frequencies that governs the commercial availability of DECT and CT3 around the world.
Europe is committed to implementing the DECT standard
within the frequency range of 1.8 to 1.9 GHz. Other countries, however, have made frequencies in the 800- to 1000MHz band available for wireless PBXs, thereby paving the
way for the introduction of CT3.
Many of the problems arising from the nonavailability of
staff to a wired PBX can be avoided with cordless telephones.
They are ideal for people who by the very nature of their
work can be difficult to locate (e.g., maintenance engineers,
warehouse staff, messengers, etc.) and for places on a company’s premises that cannot be effectively covered by a wired
PBX (e.g., warehouses, factories, refineries, exhibition halls,
dispatch points, etc.).
A key advantage of cordless telecommunications is that it
can simply be integrated into the corporate telecom system
with add-on products and without the need to replace existing
equipment. Another advantage of cordless telecommunications is that the amount of telephone wiring is dramatically
reduced. Since companies typically spend between 10 and 20
percent of the original cost of their PBX on wiring the system,
the use of cordless technology can have a significant impact on
costs. There is also considerable benefit in terms of administration. For example, when moving offices, employees need
not change extension numbers, and the PBX does not have to
be reprogrammed to reflect the change.
See also
Cellular Voice Communications
Cellular Data Communications
Digital Enhanced Cordless Telecommunications
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Data compression is a standard feature of most bridges and
routers, as well as modems, especially those used for transferring bulky files over wireless links. Compression improves
throughput by capitalizing on the redundancies found in the
data to reduce frame size and thereby allow more data to be
transmitted over a link. An algorithm detects repeating characters or strings of characters and represents them as a symbol or token. At the receiving end, the process works in reverse
to restore the original data.
There are many different algorithms available to compress data, which are designed for specific types of data
sources and the redundancies found in them but do a poor
job when applied to other sources of data. For example, the
Moving Pictures Experts Group (MPEG) compression standards were designed to take advantage of the relatively
small difference from one frame to another in a video
stream and so do an excellent job of compressing motion pictures. On the other hand, MPEG would not be effective if
applied to still images. For this data source, the Joint
Photographic Experts Group (JPEG) compression standards would be applied.
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
JPEG is “lossy,” meaning that the decompressed image is
not quite the same as the original compressed image—there
is some degradation. JPEG is designed to exploit known limitations of the human eye, notably that small color details
are not perceived as well as small details of light and dark.
JPEG eliminates the unnecessary details to greatly reduce
the size of image files, allowing them to be transmitted
faster and take up less space in a storage server.
On wide area network (WAN) links, the compression ratio
tends to differ by application. The compression ratio can be
as high as 6 to 1 when the traffic consists of heavy-duty file
transfers. The compression ratio is less than 4 to 1 when the
traffic is mostly database queries. When there are only “keep
alive” signals or sporadic query traffic on a T1 line, the compression ratio can dip below 2 to 1.
Encrypted data exhibit little or no compression because
the encryption process expands the data and uses more
bandwidth. However, if data expansion is detected and compression is withheld until the encrypted data are completely
transmitted, the need for more bandwidth can be avoided.
Types of Data Compression
There are several different data-compression methods in use
today over WANs—among them are Transmission Control
Protocol/Internet Protocol (TCP/IP) header compression,
link compression, and multichannel payload compression. Depending on the method used, there can be a significant tradeoff between lower bandwidth consumption and
increased packet delay.
TCP/IP Header Compression With TCP/IP header compres-
sion, the packet headers are compressed, but the data payload remains unchanged. Since the TCP/IP header must be
replaced at each node for IP routing to be possible, this compression method requires hop-by-hop compression and
decompression processing. This adds delay to each com-
pressed/decompressed packet and puts an added burden on
the router’s CPU at each network node.
TCP/IP header compression was designed for use on slow
serial links of 32 kbps or less and to produce a significant performance impact. It needs highly interactive traffic with small
packet sizes. In such traffic, the ratio of Layer 3 and 4 headers to payload is relatively high, so just shrinking the headers
can result in a substantial performance improvement.
Payload Compression Payload compression entails the
compression of the payload of a Layer 2 WAN protocol,
such as the Point-to-Point Protocol (PPP), Frame Relay,
High-Level Data Link Control (HDLC), X.25, and Link
Access Procedure–Balanced (LAPB). The Layer 2 packet
header is not compressed, but the entire contents of the
payload, including higher-layer protocol headers (i.e.,
TCP/IP), are compressed. They are compressed using the
industry standard Lemple-Ziv algorithm or some variation
of that algorithm.
Layer 2 payload compression applies the compression
algorithm to the entire frame payload, including the TCP/IP
headers. This method of compression is used on links operating at speeds from 56 to 1.544 Mbps and is useful on all
traffic types as long as the traffic has not been compressed
previously by a higher-layer application. TCP/IP header
compression and Layer 2 payload compression, however,
should not be applied at the same time because it is redundant and wasteful and could result in the link not coming up
to not passing IP traffic.
Link Compression With link compression, the entire frame—
both protocol header and payload—is compressed. This form
of compression is typically used in local area network
(LAN)–only or legacy-only environments. However, this
method requires error-correction and packet-sequencing
software, which adds to the processing overhead already
introduced by link compression and results in increased
packet delays. Also, like TCP/IP header compression, link
compression requires hop-by-hop compression and decompression, so processor loading and packet delays occur at
each router node the data traverses.
With link compression, a single data compression vocabulary dictionary or history buffer is maintained for all virtual circuits compressed over the WAN link. This buffer holds a
running history about what data have been transmitted to help
make future transmissions more efficient. To obtain optimal
compression ratios, the history buffer must be large, requiring
a significant amount of memory. The vocabulary dictionary
resets at the end of each frame. This technique offers lower
compression ratios than multichannel, multihistory buffer
(vocabulary) data-compression methods. This is particularly
true when transmitting mixed LAN and serial protocol traffic
over the WAN link and frame sizes are 2 kilobytes or less. This
translates into higher costs, but if more memory is added to get
better ratios, this increases the upfront cost of the solution.
Mixed-Channel Payload Data Compression By using sepa-
rate history buffers or vocabularies for each virtual circuit,
multichannel payload data compression can yield higher
compression ratios that require much less memory than
other data-compression methods. This is particularly true in
cases where mixed LAN and serial protocol traffic traverses
the network. Higher compression ratios translate into lower
WAN bandwidth requirements and greater cost savings.
But performance varies because vendors define payload
data compression differently. Some consider it to be compression of everything that follows the IP header. However,
the IP header can be a significant number of bytes. For overall compression to be effective, header compression must be
applied. This adds to the processing burden of the CPU and
increases packet delays.
External Data Compression Solutions Bridges and routers
can perform data compression with optional software or add-
on hardware modules. While compression can be implemented via software, hardware-based compression off-loads
the bridge/router’s main processor to deliver even higher levels of throughput. With a data-compression module, the compression process can occur without as much processing delay
as a software solution.
The use of a separate digital signal processor (DSP) for
data compression, instead of the software-only approach,
enables the bridge/router to perform all its core functions
without any performance penalty. This parallel-processing
approach minimizes the packet delay that can occur when
the router’s CPU is forced to handle all these tasks by itself.
If there is no vacant slot in the bridge/router for the addition of a data-compression module, there are two alternatives: the software-only approach or an external compression
device. The software-only approach could bog down the overall performance of the router, since its processor would be
used to implement compression in addition to core functions.
Although an external data compression device would not bog
down the router’s core functions, it means that one more
device must be provisioned and managed at each remote site.
Data compression will become increasingly important to
most organizations as the volume of data traffic at branch
locations begins to exceed the capacity of the wide area links
and as wireless services become available in the 2.4- and 5GHz range. Multichannel payload solutions provide the
highest compression ratios and reduce the number of packets transmitted across the network. Reducing packet latency
can be effectively achieved via a dedicated processor like a
DSP and by employing end-to-end compression techniques
rather than node-to-node compression/decompression. All
these factors contribute to reducing bandwidth and equipment costs as well as improving the network response time
for user applications.
See also
Voice Compression
Decibel (dB) is a unit of measurement expressing gain or
loss. It is used to measure such things as sound, electrical or
mechanical power, and voltage. In the telecommunications
industry, the decibel is used to conveniently express the gain
or loss in transmission systems, whether the medium is copper, optical fiber, or wireless.
The decibel is actually the relationship of some reference
point and another point that is above or below the reference
point. The base reference point is 0 dB, and subsequent measurements are relative to that reference point. There are a
number of decibel notations, each indicating the context of
the measurement, such as
dBi is the antenna gain in dB relative to an isotropic
dBm is the power in dB relative to 1 milliwatt.
dBW is the power in dB relative to 1 watt.
dBmV is referenced to 1 millivolt. It is often used as a
measure of signal levels (or noise) on a network.
The dB scale related to power is different from the dB
scale related to voltage. In power measurements, the power
level doubles every 3 dB, instead of every 6 dB as in voltage.
Likewise, the dB scale related to audio output is different
from the dB scales relating to voltage and power.
Audio Intensity
Since the range of audio intensities that the human ear can
detect is so large, the scale frequently used to measure them is
a scale based on multiples of 10. This type of scale is sometimes
referred to as a “logarithmic scale.” The threshold of hearing is
assigned a sound level of 0 dB. A sound that is 10 times more
intense is assigned a sound level of 10 dB. A sound that is 10
times more intense (10 × 10) is assigned a sound level of 20 dB.
A sound that is 10 times more intense (10 × 10 × 10) is assigned
a sound level of 30 dB. A sound that is 10 times more intense
(10 × 10 × 10 × 10) is assigned a sound level of 40 dB. Table D1 lists some common and not so common sounds with an estimate of their intensity and decibel level.
There are a variety of test instruments available to handle
virtually any measurement requirement, including analog
impulse meters to measure quick bursts of sound. These
devices typically have output jacks for connections to charting devices that plot continuous noise levels across a roll of
paper. Digital devices output measurements to light-emitting
Decibel Levels of Selected Sounds
Threshold of hearing (TOH)
Rustling leaves
Normal conversation
Busy street traffic
Vacuum cleaner
Heavy truck traffic
Walkman at maximum level
Power tools
Threshold of pain to the ear
Airport runway
Sonic boom
Perforation of eardrum
12 feet from a battleship
cannon muzzle
No. of Times
Greater than
Threshold of Hearing
diode (LED) screens. Band filters allow selection of narrow
frequency ranges to isolate specific noises for measurement.
Optional calibrators are available for in-field adjustments.
See also
The Digital Enhanced Cordless Telecommunications (DECT)
standard defines a protocol for secure digital telecommunications and is intended to offer an economical alternative to
existing cordless and wireless solutions. DECT uses Time
Division Multiple Access (TDMA) technology to provide ten
1.75-MHz channels in the frequency band between 1.88 and
1.90 GHz. Each channel can carry up to 12 simultaneous twoway conversations. Speech quality is comparable to conventional land-based phone lines. Frequency bands have been
made available for DECT in more than 100 countries.
Whereas conventional analog cordless phones have a
range of about 100 meters, the DECT version can operate
reliably up to 300 meters. What started out as a European
standard for replacing analog cordless phones has been continually refined by the European Telecommunication
Standards Institute (ETSI) to become a worldwide standard
that provides a platform for wireless local loops (WLL), wireless LANs, and more recently, wireless Internet access. In
addition, DECT services are compatible with GSM and
ISDN, and dual-mode DECT/GSM handsets are available.
A key advantage of DECT is dynamic reconfiguration,
which means that implementation does not require advance
load, frequency, or cell planning. Other wireless architectures require a predetermined frequency-allocation plan.
Conventional analog cellular networks, for example, are
organized as cells in honeycomb fashion. To avoid conflict
from adjacent cells, each base station is allotted only a fraction of the allowable frequencies. Changing a particular station’s frequency band to accommodate the addition of more
base stations to increase network capacity entails an often
difficult and expensive hardware upgrade. However
sparsely the base stations are constructed at the start of an
installation, all possible base stations must be assigned frequencies before any physical systems are put into place.
In a DECT system, planning for uncertain future growth
is unnecessary. This is because a DECT base station can
dynamically assign a call to any available frequency channel
in its band. The 12 conversations occurring at any one time
can take place on any of the 10 channels in any combination.
The handset initiating a call identifies an open frequency
and time slot on the nearest base station and grabs it. DECT
systems also can reconfigure themselves on the fly to cope
with changing traffic patterns. Therefore, adding a base station requires no modification of existing base stations and no
prior planning of channel allocations.
Compared to conventional analog systems, DECT systems do not suffer from interference or cross-talk. Neither
different mobile units nor adjacent DECT cells can pose
interference problems because DECT manages the availability of frequencies and time slots dynamically. This
dynamic reconfiguration capability makes DECT useful also
as a platform for WLLs. DECT allows the deployment of a
few base stations to meet initial service demand, with the
easy addition of more base stations as traffic levels grow.
Voice compression [i.e., Adaptive Differential Pulse Code
Modulation (ADPCM)] and the higher levels of the DECT
protocol are not implemented at the base stations but are
handled separately by a concentrator. The concentrator
routes calls between the WLL network and the public switch
telephone network (PSTN). This distributed architecture
frees up base station processing power so that it can better
handle the up to 12 concurrent transmission and reception
For high-end residential and small-business users, DECT
permits wireless versions of conventional PBX equipment,
supporting standard functions such as incoming and outgoing calls, call hold, call forwarding, and voice mail without
having to install new wiring. In this application, DECT
dynamic reconfiguration means that implementation does
not require advance load, frequency, or cell planning. Users
can begin with a small system and then simply add components as needs change.
The DECT/GSM Interworking Profile allows a single
handset to address both DECT systems and conventional
cellular networks. This allows users to take advantage of the
virtually free wireless PBX service within a corporate facility and then seamlessly switch over to GSM when the handset passes out of range of the PBX base station. When the
call is handled by GSM, appropriate cellular charges accrue
to the user. If the call cannot get through on either type of
network, it is diverted to a voice mailbox.
Wireless Local Loops
Although residential cordless communication represents the
largest current market for DECT-based products, other
applications look promising for the future. In developing
countries, where lack of a universal wired telecommunications infrastructure can limit economic growth, DECT permits the creation of a wireless local loop (WLL), thereby
avoiding the considerable time and expense required to lay
wire lines. WLLs can be implemented in several ways, which
are summarized in Figure D-1.
In a small cell installation in densely populated urban or
downtown areas, the existing telephone network can be used
as a backbone that connects the base stations for each DECT
Fiber to
the Curb
Figure D-1 DECT supports the deployment of wireless local loops that
offer a high degree of configuration flexibility and cost savings over conventional wireless and wireline solutions.
cell. These DECT base stations may be installed on telephone poles or other facilities. Customer boxes (i.e., transceivers) installed on the outsides of houses and office
buildings connect common phone, fax, and modem jacks
inside. Through the transceivers, customers use their telephone, fax, and modem equipment to communicate with the
base stations outside. In addition, customers can use DECTcompliant mobile phones, which can receive and transmit
calls to the same base station.
In larger cell installations, such as suburban or rural
areas, fiberoptic lines may provide the backbone that connects local relay stations to the nearest base station. These
relay stations transmit and receive data to and from customer boxes. In these installations, the customer box must
have a direct line of sight to the relay station.
Network feeds over long distances may be accomplished via
microwave links, which is more economical than having to
install new copper or fiber lines. Large cells can be converted
easily into smaller cells by installing additional base units or
relay stations. Since DECT system has a self-organizing air
interface, no top-down frequency planning is necessary, as
is the case with other wireless connection techniques such
as GSM or its derivative Digital Cellular System 1800
(DCS 1800).
While most WLL installations focus on regular telephone
and fax services, DECT paves the way for enhanced services.
Multiple channels can be bundled to provide wider bandwidth,
which can be tailored for each customer and billed accordingly.
Among other things, this allows the mapping of ISDN services
all the way through the network to the mobile unit.
Wireless LANs
In many data applications with low bit rate requirements,
DECT can be a cost-effective solution. One example is
remote wireless access to corporate LANs. By bundling
channels, full-duplex transmission of up to 480 kbps per frequency carrier is theoretically possible. For multiple data
links, a DECT base station can be complemented by additional DECT base stations controlled by a DECT server. This
forms a multicell system for higher traffic requirements.
With a transparent interface to ISDN, data access and videoconferencing through wireless links can be realized. Such
installations also may include such services as voice mail,
automatic call back, answering and messaging services,
data on demand, and Internet access.
DECT is a radio access technology. As such, it has been
designed and specified to work with many other types of networks, including the PSTN, ISDN, GSM, and the Internet,
as well as LANs and telephone systems in office buildings
and homes. DECT modules incorporated into building control and security systems provide intelligent systems that
allow automatic control and alerting to augment or replace
today’s customized telemetry and wired systems. DECT also
may find its way into the home, providing automatic security
alerting in the event of unauthorized entry, fire, or flood;
remote telephone control of appliances; and return channels
for interactive television. While DECT is an international
standard, it has been adapted only recently for use in North
America, where it operates in the unlicensed 2.4-GHz ISM
(industrial, scientific, and medical) band. The standard in
North America is known as Worldwide Digital Cordless
Telephone (WDCT), which is based on DECT.
See also
Global System for Mobile (GSM) Telecommunications
Wireless LANs
Wireless Local Loops
Direct broadcast satellite (DBS) operators use satellites to
transmit video programming to subscribers, who must buy
or rent a small parabolic dish antenna and pay a subscription fee to receive the programming service. DBS meets consumer demand for entertainment programming, Internet
connectivity, and multimedia applications. DBS offers more
programming choices for consumers and a platform for the
development of new services, including video on demand,
interactive TV, Internet messaging services, and personalized on-demand stock quotes. Much of the growing popularity of DBS is attributable to the programming choices
available to consumers as well as the picture quality provided by digital technology. And like cable television systems, DBS offers programming in the high-definition
television (HDTV) format.
One of the most popular DBS services is DirecTV, a unit of
Hughes Electronics, which markets the service worldwide.
First introduced in the United States in 1994, DirecTV offers
over 225 channels and has over 10 million customers. The
satellite service requires the user to have an 18-inch dish, a
digital set-top decoder box, and a remote control. The system
features an on-screen guide that lets users scan and select
programming choices using the remote. Customers also can
use the remote control to instantly order pay-per-view
movies, as well as set parental controls and spending limits.
The DirecTV installation includes an access card, which
provides security and encryption information and allows
customers to control the use of the system. The access card
also enables DirecTV to capture billing information. A standard telephone connection is also used to download billing
information from the decoder box to the DirecTV billing center. This telephone line link enables DirecTV subscribers to
order pay-per-view transmission as desired.
DirecTV allows users to integrate local broadcast channels
with satellite-based transmissions. In markets where broadcast or cable systems are in place, users can maintain a basic
cable subscription or connect a broadcast antenna to the
DirecTV digital receiver to receive local and network broadcasts. A switch built into the remote control enables consumers
to instantly switch between DirecTV and local stations.
HDTV programming from DirecTV is delivered from its
119° west longitude orbital slot location. To receive HDTV
programming, consumers must have an HDTV set with a
built-in DirecTV receiver or a DirecTV-enabled HDTV settop converter box. A small elliptical satellite dish is needed
to receive HDTV programming from the 119° orbital slot
location, as well as core DirecTV programming from the 101°
orbital location.
Internet access is provided via two services. The older service is DirecPC, a product that uses DirecTV technology in
conjunction with a PC to deliver high-bandwidth, satellitebased access to the Internet. The DirecPC package includes
a satellite dish and an expansion card designed for a PC’s
input-output (I/O) bus. This receiver card transmits data
from the Internet to the computer at 400 kbps, a rate 14
times faster than that of a 28.8-kbps modem connection.
Users connect to the Internet service provider (ISP)
through a modem connection, but the ISP is responsible for
routing data through the satellite uplink and transmitting
the data to the receiver card and into the computer (Figure
D-2). The service also provides users with the option to “narrowcast” software from the head end of a network to branch
users during off-peak hours. Additionally, DirecPC transmits television broadcasts from major networks, such as
CNN and ESPN, to the user’s computer system.
The company’s newer service, DirecWAY, offers a two-way
broadband connection that offers 400 kbps on the downlink
and about 150 kbps on the uplink, which eliminates the need
for a modem and separate phone line. A new dish antenna provides access to the Internet and cable programming. A business-class DirecWAY service is also available. Multiple-seat
account options (2 seats is the entry-level service; 5-, 10-, and
20-seat options are available), LAN software routing, and firewall security are offered as part of the business class service.
Requested data
sent to user at up
to 400 Kbps
DirecPC Satellite
NOC sends data
to DirecPC Satellite
Figure D-2
Local ISP
Typical DBS configuration for Internet access.
Center (NOC)
DBS operates in the Ku band, the group of frequencies from
12 to 18 GHz. TV shows and movies are stored on tape or in
digital form at a video server, while live events are broadcast
directly to a satellite (Figure D-3). Stored programs are sent
to the uplink (ground-to-satellite) center manually via tape
or electronically from the video server over fiberoptic cable.
Live events also pass through the uplink center. There, all
programs—whether live or stored—are digitized (or redigitized) and compressed before they are uplinked to the satellites. All DBS systems use the MPEG-2 compression scheme
because it supports a wide range of compression ratios and
data rates. It is capable of delivering a clean, high-resolution
video signal and CD-quality sound. The satellites broadcast
over 200 channels simultaneously via the downlink. The
home satellite dish picks up all the channels and sends them
via a cable to a set-top decoder. The set-top decoder tunes
one channel, decodes the video, and sends an analog signal
to the TV.
High-speed Link
(Live event)
Video Camera
Set-top decoder
Uplink Center
Tape Unit
or Video Server
(Recorded events)
Figure D-3
Typical DBS configuration for television programming.
Service Providers
More than 1 million U.S. residents have installed small TV
satellite dishes to receive programming via satellite services. At this writing, there are four direct broadcast satellite systems in operation: PrimeStar, EchoStar, Digital
Satellite Service (DSS), and AlphStar. DirectTV uses DSS
and PrimeStar.
Ordering PrimeStar service is similar to ordering cable:
After the order is placed, a technician installs the dish and
activates programming. DSS, EchoStar, and AlphaStar services also give users the option of installing the dish themselves. The dish must be placed so that it can capture a clean
signal from the nearest satellite—usually on the roof, facing
south. To activate service, the user calls the programming
provider to obtain a unique satellite dish address.
The key component of the DBS system is the dish antenna,
which comes in various sizes. Dish size depends on the
strength of the satellite signal; the stronger the signal, the
smaller the dish can be. Users select the dish according to
their geographic proximity to the satellite source. This also
explains why it is necessary to install the dish so that it
points in a specific direction. If the satellite sits on the southern horizon, the dish must be pointed south.
The user also needs a receiver-decoder unit, which tunes
in one channel from the multitude of channels it receives
from the dish. The decoder then decompresses and decodes
the video signal in real time so that the programs can be
watched on the television set. These set-top units also may
include a phone-line connection for pay-per-view ordering
and Internet access. Taping DBS programs requires the settop unit to be tuned to the correct channel. To make recording easier, some receiver-decoders include an event scheduler
and an on-screen programming guide.
As with most audio-video components, DBS units come
with a remote control. Some manufacturers offer a universal
remote that also can be used to operate the TV and VCR.
The accessories available for DBS systems deal with secondary and tertiary installations. Users can buy additional
receiver-decoder units or multiroom distribution kits, which
use either cable or radio frequencies to transmit the signals
from the original set-top unit to other rooms. Some kits
enable the VCR to be plugged into the distributor.
Each of the four DBS systems currently available provides
similar core services. The differences lie mainly in the availability of premium movie channels, audio channels, pay-perview events, Internet services, and custom features.
With more than 200 channels to choose from, the onscreen programming guide can become an important factor
when selecting a service. Most guides enable users to sort
the available programming based on content area—such
as sports, movies, comedies—or list favorite channels at
the top of the menu. Depending on the equipment selected,
users can even store the favorite-channel profiles of multiple family members.
Parental lockout enables adults to block specific channels
or programming with a specific content rating or to set a
maximum pay-per-view spending limit. Channel-blocking
options are protected by passwords; with multiprofile units,
parents can customize the system for each child.
The addition of digital television recording systems such
as TiVo allows viewers to easily find and schedule their
favorite television shows automatically and digitally record
or store up to 35 hours of video content without the use of
videotape. Such systems provide the ability to pause,
rewind, replay, and slow motion live shows. An advanced
programming guide allows viewers to check program listings
up to 14 days in advance.
Despite increases in the number of subscribers to DBS
systems in recent years, CATV systems remain the dominant supplier in what is called the “multichannel video
program distribution” (MVPD) market. The FCC has regulatory authority over DBS and is charged with implementing the Satellite Home Viewer Improvement Act of
1999 (SHVIA).
This law provides that after December 31, 2001, each
satellite carrier providing television broadcast signals to
subscribers within the local market of a television broadcast
station of a primary transmission made by that station shall
carry on request the signals of all television broadcast stations located within that local market.
Until January 1, 2002, satellite carriers were granted a
royalty-free copyright license to retransmit broadcast signals on a station-by-station basis, subject to obtaining a
broadcaster’s retransmission consent. This transition period
was intended to provide the satellite industry with time to
begin providing local signals into local markets—in effect,
providing local-into-local satellite service.
While DBS competes well against cable television in terms
of television programming, it may not be able to compete
with cable on the data front. In contrast with the finite
bandwidth available to wireless and satellite systems, the
terrestrial broadband pipe technologies available to cable
systems offer bandwidth that is virtually limitless for
almost all current practical purposes. Duplication of this
pipe requires an investment of tens of billions of dollars and
therefore would be impractical. Realizing this, DBS services
limit downlink throughput per subscriber at about 400 kbps
and reserve the right to limit bandwidth-hogging activities,
such as audio and video streaming, and automatic file
exchange applications. These restrictions are justified as
being necessary to preserve an adequate level of service for
all subscribers.
See also
Satellite Communications
It is expected that packet data will dominate circuit-switched
data in the future, primarily to give users high-speed
Internet access from mobile phones and other handheld
devices. One of the key enabling technologies that will allow
this to happen is known as Enhanced Data Rates for Global
Evolution (EDGE), which combines multiple 30-kHz time
slots available under Time Division Multiple Access (TDMA)
to provide data rates of up to 384 kbps.
An interim technology is known as General Packet Radio
Service (GPRS), which combines TDMA time slots to provide data rates of up to 115 kbps. EDGE technology builds
on GPRS, offering enhanced modulation that adapts to
radio circumstances, thereby offering the highest data rates
in good propagation conditions while ensuring wider area
coverage at lower data speeds per time slot. Typical applications for this type of service include multimedia messaging, Web browsing, enhanced short messages, wireless
imaging with instant pictures, video services, document and
information sharing, surveillance, voice over the Internet,
and broadcasting.
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Europe is ahead of the United States in the deployment of
EDGE technology on their GSM networks. Instead of the
advertised speed of 384 kbps, however, the actual speed may
not even reach half that. Where EDGE is already deployed in
the United Kingdom, for example, the top speed is 160 kbps.
Nevertheless, EDGE (and GPRS) offers a 2.5G migration
path to the global standard Universal Mobile Telecommunications System (UMTS), which is considered a third-generation
(3G) wireless communications platform that will be capable of
supporting speeds of up to 2.4 Mbps.
The introduction of GPRS and then EDGE as an overlay to
existing TDMA networks builds on the operator’s existing
investment in infrastructure. EDGE provides a boost to data
speeds using existing TDMA networks, allowing the operator to offer personal multimedia applications before the
introduction of UMTS. As wireless data become available to
all subscribers and they demand a full set of high-speed services and shorter response times, EDGE will provide an
operator with a competitive advantage. EDGE also enables
data capacity to be deployed when and where demand warrants, minimizing the investment required.
See also
General Packet Radio Service
Global System for Mobile Telecommunications
Time Division Multiple Access
Universal Mobile Telecommunications System
Family Radio Service (FRS) is one of the Citizens Band
Radio Services. It is for family, friends, and associates to
communicate among themselves within their neighborhood
and while on group outings. Users may select any of the 14
FRS channels on a “take turns” basis. No FRS channel is
assigned to any specific individual or organization.
Although manufacturers advertise a range of up to 2
miles, users can expect a communication range of less than
1 mile. Although FRS may be used for business-related communications, it cannot be connected to the public switched
telephone network (PSTN) and used for telephone calls.
License documents are neither needed nor issued. FRS
Rule 1 provides all the authority necessary to operate
an FRS unit (Figure F-1) in places where the Federal
Communications Commission (FCC) regulates radio communications as long as an unmodified FCC-certified FRS
unit is only used. An FCC-certified FRS unit has an identifying label placed on it by the manufacturer. There is no age
or citizenship requirement.
FRS units may be operated within the territorial limits of
the 50 United States, the District of Columbia, and the
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Figure F-1 Motorola’s TalkAbout 280 SLK is a
palm-size FRS unit that is small enough to carry
in a shirt pocket. The 6-ounce radio runs on three
AA batteries.
Caribbean and Pacific insular areas. Such units also may be
operated on or over any other area of the world, except
within the territorial limits of areas where radio communications are regulated by another agency of the United States
or within the territorial limits of any foreign government.
Users cannot make any internal modification to an FRS
unit. Any internal modification cancels the FCC certification
and voids the user’s authority to operate the unit over the
FRS. In addition, users may not attach any antenna, power
amplifier, or other apparatus to an FRS unit that has not
been FCC certified as part of that FRS unit. There are no
exceptions to this rule, and attaching any such apparatus to
an FRS unit cancels the FCC certification and voids everyone’s authority to operate the unit over the FRS.
Family Radio Service is used for conducting two-way voice
communications with another person. One-way transmission
may be used only to establish communications with another
person, send an emergency message, provide traveler assis-
tance, make a voice page, or conduct a brief test. Operators
must, at all times and on all channels, give priority to emergency communication messages concerning the immediate
safety of life or the immediate protection of property.
See also
Citizens Band Radio Service
General Mobile Radio Service
Low-Power Radio Service
The Federal Communications Commission (FCC) is an independent federal agency in the United States that is responsible directly to Congress. Established by the Communications
Act of 1934, the FCC is charged with regulating interstate
and international communications by radio, television, wire,
satellite, and cable. Its jurisdiction covers the 50 states and
territories, the District of Columbia, and U.S. possessions.
The FCC is directed by five commissioners appointed by
the President and confirmed by the Senate for 5-year terms,
except when filling an unexpired term. The President designates one of the commissioners to serve as chairman, who
presides over all FCC meetings. The commissioners hold
regular open and closed agenda meetings and special meetings. By law, the FCC must hold at least one open meeting
per month. It also may act between meetings by “circulation,” a procedure whereby a document is submitted to each
commissioner individually for consideration and official
Certain other functions are delegated to staff units and
bureaus and to committees of the commissioners. The chairman coordinates and organizes the work of the FCC and represents the agency in legislative matters and in relations
with other government departments and agencies.
Operating Bureaus
At the staff level, the FCC comprises seven operating bureaus
and 10 staff offices. Most issues considered by the FCC are
developed by the bureaus and offices, which are organized by
substantive area (Figure F-2):
The Common Carrier Bureau handles domestic wireline
The Wireless Telecommunications Bureau oversees wireless services such as private radio, cellular telephone, personal communications service (PCS), and pagers.
The Cable Services Bureau regulates cable television and
related services.
The International Bureau regulates international and satellite communications.
The Enforcement Bureau enforces the Communications
Act, as well as the FCC’s rules, orders, and authorizations.
Office of
Inspector General
Office of
Engineering &
Office of
Office of
Law Judges
Figure F-2
Office of
Office of
Plans &
Office of
Office of
Office of
Legislative &
Office of
Enforcement International
Organizational chart of the Federal Communications
The Mass Media Bureau regulates AM and FM radio and
television broadcast stations, as well as multipoint distribution (i.e., cable and satellite) and instructional television fixed services.
The Consumer Information Bureau communicates information to the public regarding FCC policies, programs,
and activities. This bureau is also charged with overseeing disability mandates.
Other Offices
In addition, the FCC includes the following other offices:
The Office of Plans and Policy serves as the FCC’s chief
economic policy advisor.
The Office of the General Counsel reviews legal issues
and defends FCC actions in court.
The Office of the Managing Director manages the internal
administration of the FCC.
The Office of Legislative and Intergovernmental Affairs
coordinates FCC activities with other branches of
The Office of the Inspector General reviews FCC activities.
The Office of Communications Business Opportunities
provides assistance to small businesses in the communications industry.
The Office of Engineering and Technology allocates spectrum for nongovernment use and provides expert advice
on technical issues before the FCC.
The Office of Administrative Law Judges adjudicates
The Office of Workplace Diversity ensures equal employment opportunities within the FCC.
The Office of Media Relations informs the news media of
FCC decisions and serves as the FCC’s main point of contact with the media.
Reorganization Plan
In mid-1999, the FCC unveiled a 5-year restructuring plan
that will enable it to better meet the fast-changing needs of
the communications business. The plan eliminates unnecessary rules in areas where competition has emerged and reorganizes the FCC along functional rather than technological
lines. The plan’s success hinges on thriving competition,
enough to reduce the need for the FCC to regulate directly.
Under the plan, the FCC is making the transition from an
industry regulator to a market facilitator.
The plan addresses the disintegration of boundaries
between wire, wireless, satellite, broadcast, and cable communications—categories around which the FCC is currently
The internal bureaus are now grouped around functions
such as licensing and competition rather than by technology.
The plan consolidates enforcement and consumer information into two separate bureaus of the FCC rather than having those functions spread across the agency.
The plan has streamlined and speeded up the FCC’s services, for example, by instituting agency-wide electronic filing and automated licensing systems. Other goals include
reducing backlog and making greater use of alternative
dispute-resolution mechanisms. The plan also makes it
faster and easier for consumers to interact with the agency.
Under the reorganization plan, the FCC keeps many of its
existing priorities, such as protecting consumers from fraud
and keeping phone rates affordable for the poor.
The top-down regulatory model of the industrial age is as out
of place in today’s digital economy as the rotary telephone.
As competition and convergence develop, the FCC must
streamline its operations and continue to eliminate regulatory burdens. However, despite the FCC’s planned reorgani-
zation from “regulator” to “facilitator,” the commission will
still have to contend with a set of core functions that are not
normally addressed by market forces. These core functions
include universal service, consumer protection and information, enforcement and promotion of procompetition goals
domestically and worldwide, and spectrum management.
See also
Wireless Telecommunications Bureau
Fixed wireless access technology provides a wireless link to
the public switched telephone network (PSTN) as an alternative to traditional wire-based local telephone service. Since
calls and other information (e.g., data, images) are transmitted through the air rather than through conventional cables
and wires, the cost of providing and maintaining telephone
poles and cables is avoided. Unlike cellular technologies,
which provide services to mobile users, fixed wireless services require a rooftop antenna to an office building or home
that is lined up with a service provider’s hub antenna.
Fixed wireless access systems come in two varieties: narrowband and broadband. A narrowband fixed wireless access
service can provide bandwidth up to 128 kbps, which can
support one voice conversation and a data session such as
Internet access or fax transmission. A broadband fixed wireless access service can provide bandwidth in the multimegabit-per-second range, which is enough to support
telephone calls, television programming, and broadband
Internet access.
A narrowband fixed wireless service requires a wireless
access unit that is installed on the exterior of a home or business (Figure F-3) to allow customers to originate and receive
calls with no change to their existing analog telephones.
Access 128 Kbps
Fiber Link
Figure F-3 Fixed wireless access configuration.
This transceiver is positioned to provide an unobstructed
view to the nearest base station receiver. Voice and data calls
are transmitted from the transceiver at the customer’s location to the base station equipment, which relays the call
through the carrier’s existing network facilities to the appropriate destination. No investment in special phones or facsimile machines is required; customers use all their existing
Narrowband fixed wireless systems use the licensed 3.5GHz radio band with 100-MHz spacing between uplink and
downlink frequencies. Subscribers receive network access
over a radio link within a range of 200 meters (600 feet) to
40 kilometers (25 miles) of the carrier’s hub antenna. About
2000 subscribers can be supported per cell site.
Broadband fixed wireless access systems are based on
microwave technology. Multichannel Multipoint Distribution
Service (MMDS) operates in the licensed 2- to 3-GHz frequency range, while Local Multipoint Distribution Service
(LMDS) operates in the licensed 28- to 31-GHz frequency
range. Both services are used by Competitive Local Exchange
Carriers (CLECs) primarily to offer broadband Internet
access. These technologies are used to bring data traffic to
the fiberoptic networks of Interexchange Carriers (IXCs)
and nationwide CLECs, bypassing the local loops of the
Incumbent Local Exchange Carriers (ILECs).
Fixed wireless access technology originated out of the need to
contain carriers’ operating costs in rural areas, where pole and
cable installation and maintenance are more expensive than
in urban and suburban areas. However, wireless access technology also can be used in urban areas to bypass the local
exchange carrier for long-distance calls. Since the IXC or
CLEC avoids having to pay the ILEC’s local loop interconnection charges, the savings can be passed back to the customer.
This arrangement is also referred to as a “wireless local loop.”
See also
Cellular Voice Communications
Local Multipoint Distribution Service
Multichannel Multipoint Distribution Service
Despite advances in technology, mobile phone fraud continues
to be an ongoing problem. Fraud management systems that
incorporate mechanisms to integrate service usage data are
becoming a necessary weapon among wireless carriers. The
challenge is to monitor and profile the activity using hard
data and to be alert to the ever-changing nature of fraud. To
combat cell phone fraud, a number of systems have been
implemented that can discourage cell phone cloning and stop
thieves from obtaining free access to cellular networks.
Personal Identification Numbers
Some service providers offer their subscribers a free fraud
protection feature (FPF) to help protect against unauthorized use of their cell phones. Like an ATM bank card, FPF
uses a private combination, or personal identification number (PIN), that only the subscriber knows. The PIN code does
not interfere with regular phone usage. Even if pirates capture the phone’s signal, they would not be able to use it without the PIN code.
For example, the subscriber locks the phone account by
pressing *56 + PIN + SEND. This blocks all outgoing calls,
except for 911 (emergency) and the carrier’s customer care
number. While the account is locked, calls can still be
received, and voice mail will continue to take messages.
When the subscriber wants to make a call, the account is
unlocked by pressing *56 + 0 + PIN + SEND. Both the lock
and unlock sequences can be programmed directly into the
mobile phone’s speed-dial option.
There are database applications available that help service providers make better use of PINs to detect potentially
fraudulent calls and prevent their completion. One of these
products comes from Sanders Telecommunications Systems,
a Lockheed Martin company. The company’s MicroProfile
software enables the carrier to determine when a call is
being placed to a number outside the subscriber’s normal
calling pattern. Combined with another product, an intelligent network-based application called Intelligent PIN, the
MicroProfile software requires that the caller provide a PIN
only for out-of-profile calls. By establishing and maintaining
calling profiles of subscribers, out-of-profile call requests can
be identified in real time, whereupon PINs can be requested
to ensure that only legitimate calls are allowed to be placed.
With this system, unauthorized calls and lost revenues
resulting from phone cloning or other illegal means can be
reduced significantly. MicroProfile also provides the ability
to monitor and analyze call histories to detect patterns of
fraud and identify their origins. Since more than 90 percent
of mobile calls will be within an established profile and,
therefore, will not require routine PIN use, this method of
fraud prevention poses little or no inconvenience to users.
Other fraud detection schemes are able to detect when
more than one phone with the same personality is attempting to access the system. On detection, the subscriber is
requested to enter a PIN prior to all new call attempts until
further investigation.
There are also fraud detection schemes that can be controlled by subscribers. For example, the subscriber can enter
numbers on a targeted list comprised of 900 numbers or
international area codes that require a PIN when dialed. If
the PIN entry fails, the subscriber record is marked as
fraudulent and requires a PIN for all future calls until further investigation.
Call Pattern Analysis
Cloned phones can be identified with a technology called
“call pattern analysis.” When a subscriber’s phone deviates
from its normal activity, it trips an alarm at the service
provider’s fraud management system. There it is put into a
queue, where a fraud analyst ascertains whether the customer has been victimized and then remedies the situation
by dropping the connection.
Coral Systems offers an innovative software solution
designed to help wireless carriers worldwide to fight the
ongoing fraud problem. The company’s FraudBuster system
is designed specifically to detect and manage fraud in multiple wireless systems. Through its support of wireless standards including Advanced Mobile Phone Service (AMPS),
Code Division Multiple Access (CDMA), and Global System
for Mobile (GSM), FraudBuster targets the most pervasive
types of fraud, including cloned phones and subscription
fraud. Through the development of personalized customer
profiles based on the subscriber’s typical calling patterns,
FraudBuster can immediately identify suspicious usage.
After primary detection, a member of the carrier’s fraud
investigation team is immediately alerted, supplied with
detailed information on the calls in question, and provided
with recommended actions to address the alleged fraud
(Figure F-4).
Authentication works by automatically sending a series of
encoded passwords over the airwaves between the cellular
telephone and the cellular network to validate a customer
each time a call is placed or received. Authentication uses a
complex security feature that contains a secret code and special number based on an algorithm shared only by the cellular telephone and the wireless network. Whenever a
customer places or receives a call, the wireless system asks
the cellular telephone to prove its identity through a question-and-answer process. This process occurs without delaying the time it takes to connect a legitimate cellular call.
There is no charge for this service.
Authentication uses advanced encryption technology that
makes it almost impossible for a subscriber’s mobile phone
number to be cloned. It involves the exchange of a secret code
based on an intricate algorithm between the phone and the
Real-time call
details records
Individual user
Time and
Credit limit
Call pattern
Called party
Individual user
profile analysis
Figure F-4 Coral System’s FraudBuster software creates individual user
profiles on a real-time basis to allow for per-subscriber monitoring. The profiles are updated, referenced, and analyzed on a call-by-call basis. When a
suspicious deviation is detected, a fraud investigator is immediately alerted
and provided with a detailed accounting of events that triggered the alert.
switch. These algorithms are so complex that service providers
say that they will remain impenetrable for at least 20 years.
Authentication technology identifies cloned phone numbers immediately, before costly communications can take
place. The digital network and the authentication-ready
phones operating on it carry matching information. When a
user initiates a call, the network challenges the phone to verify itself by performing a mathematical equation only that
specific phone can solve. An authenticatable phone will
match the challenge, confirming that it and the corresponding phone number are being used by a legitimate customer.
If it does not match, the network determines that the phone
number is being used illegally, and service to that phone is
terminated. All this takes place in a fraction of a second.
Prior to authentication, a PIN had to be entered before the
call was connected. All that the user needs now is an authentication-ready phone to take advantage of the service, which
is usually offered free. Where authentication service is available, subscribers no longer need to use a PIN to make calls,
except when roaming in areas where authentication is not
yet available.
PINs have become an effective fraud prevention tool. If
a subscriber’s phone gets cloned anyway, a simple call to
the service provider to obtain a new PIN is the extent of the
customer’s inconvenience—there is no need to change
phone numbers, which also obviates the need for new business cards and letterheads. The subscriber does not even
need to come into the service center. But PINs are far from
bulletproof, and cloners have proven particularly adept at
cracking most security systems carriers have deployed.
Still, PINs have decreased cellular phone fraud by as much
as 70 percent.
Radio frequency Fingerprinting
Radio frequency fingerprinting is a step up from the use of
PINs. With digital analysis technology that recognizes the
unique characteristics of radio signals emitted by mobile
phones, a fingerprint can be made that can distinguish individual phones within a fraction of a second after an attempt
to place a call is made. Once the fraudulent call is detected, it
is immediately disconnected. The technology works so well
that it has cut down on fraudulent calls by as much as 85 percent in certain high-fraud markets, including Los Angeles
and New York.
Voice Verification
Most fraud prevention technologies—such as PINs, call pattern analysis, authentication, and radio frequency fingerprinting—are only partially effective. Rather than verifying the
caller, they merely authenticate a piece of information (PIN,
ESN/MIN), a piece of equipment (RF fingerprinting, authentication), or the subscriber’s call patterns (call pattern analysis).
Voice verification systems are based on the uniqueness of
each person’s voice and the reliability of the technology that
can distinguish one voice from another by comparing a digitized sample of a person’s voice with a stored model or
“voice print.”
One of the most advanced voice verification systems comes
from T-NETIX, Inc. The company uses a combination of decision-tree and neural network technologies to implement what
it calls a “neural tree network”. The neural tree is comprised
of nodes, or neurons, that are discriminantly trained through
multiple repeated utterances of a subscriber-selected password or a small sample of speech. Discriminant training contrasts the acoustic features of the speaker being enrolled to
features of the speakers already enrolled in the service.
During the verification process, each neuron must decide
whether the acoustic features of the spoken input are more
like those of the person whose identity is claimed or more like
those of other speakers in the system. The neural tree network technology permits this complex decision-making, or
discriminant, process to be completed in a relatively short
period of time in contrast to other technologies. In effect,
yes/no decisions are reached at each neuron of the neural tree,
and a conclusion is reached after moving through five or six
branches of the tree. The relative simplicity of the neural network decision-path design facilitates rapid analysis of spoken
input with no upward limit on the number of enrollees.
The technology is also robust in its ability to determine and
isolate channel environmental conditions. The front-end
analysis recognizes and normalizes conditions such as background noise, channel differences, and microphone variances.
The mobile service subscriber goes through an enrollment
process consisting of the following steps:
To access the enrollment system, the subscriber inputs his
or her identity using a PIN.
The voice response unit prompts the subscriber to speak
the password a few times (typically three or four). The
speaker verification technology averages the voice samples to obtain a more robust voice model for the subscriber.
The technology then analyzes the characteristics of the
subscriber’s statement of the password and characterizes
its tonal aspects. The process also results in characterization and isolation of the channel environment (i.e., line
type, hand-set type).
The system segments the voice utterance into its subword
units in order to examine the utterance in greater detail.
Models for the voice segments are created and compared
with other samples stored in the database to train the system to distinguish between individuals with similar voice
Finally, the system loads the subscriber’s voice model into
the voice identification database, indexing it to the subscriber’s numeric identifier.
The voice verification system can reside on a public or private network as an intelligent peripheral or can be placed as
an adjunct serving a Private Branch Exchange (PBX) or
Automatic Call Distributor (ACD). In a mobile environment, the system can be an adjunct to a Mobile Switching
Center (MSC).
Data Mining
Another method of fraud detection entails the use of datamining software that examines billing records and picks up
patterns that reveal the behavior of cloning fraud.
Two major patterns are associated with cloning fraud.
One is called the “time overlap pattern,” which means that a
phone is involved in two or more independent calls simultaneously. The other is called the “velocity pattern,” which
originates from the assumption that a handset cannot initiate or receive another call from a location far away from its
previous call in a short time. If this happens, there is a high
probability that a clone phone is being used somewhere.
The cloning information is passed to the service provider’s
billing and management system, and countermeasures will
be executed to prevent further damages. Cloning history
data are also kept in the database and can be queried by service representatives via a wide area network (WAN).
Real-Time Usage Reporting
Several software vendors offer products that provide realtime collection of data from cellular switches that can be
used for identifying fraudulent use. Subscriber Computing’s
FraudWatch Pro software, for example, provides workable
cases of fraud rather than just alarms. With this system,
analysts have the ability to select the types of fraud that
they work, such as subscription fraud or cloning. Based on
an analysis of call detail records (CDR) received from home
switches and roaming CDR data feeds, the system detects
fraudulent activities and provides prioritized cases to the
analyst for action. The system provides investigative tools
that allow the analyst to ascertain whether fraudulent activ-
ity has indeed occurred. The cases are continuously prioritized according to fraud certainty factors or the probability
of fraud occurring.
FraudWatch Pro receives CDR records directly from the
switches and from roaming CDR exchanges as quickly as
the data become available to the service provider. Profiles
are created that contain details about the specific daily
activity of a given subscriber. The subscriber profile contains about 40 single and multidimensional data “buckets”
that are updated in real time. Analysts have a Graphical
User Interface (GUI) that allows them to query the database to search for a wide range of behavior patterns as well
as address queries about specific individuals. The system
stores up to 12 months of summary statistics as well as up
to 6 months of daily call detail records.
The software also provides support for the investigative
analysis of additional dialed digit relationships. This
allows the relationships among clones and their dialed digits to be graphically displayed as a means to help build
prosecutable cases.
Smart Cards
While it is easy to intercept information from mobile
phones used on analog networks, it is much harder to do so
on such digital networks as the North American Personal
Communication Services (PCS) and the European Global
System for Mobile (GSM) telecommunications. This is so
because the signals are encrypted, making them much
more difficult to intercept without expensive equipment
and a higher degree of technical expertise.
Although signal encryption during airtime is a standard
feature of GSM networks, a network operator can choose not
to implement it. In this case, when a handset is turned on to
access the host base station for services, the subscriber is
vulnerable to the same eavesdropping attacks as with analog systems.
GSM signal encryption is done via a programmable smart
card—the Subscriber Identification Module (SIM), which
slips into a slot built into the handset. Each customer has a
personal smart card holding personal details (short codes,
frequently called numbers, etc.) as well as an international
mobile subscriber identity (IMSI)—equivalent to Mobile
Identification Number (MIN) for analog systems—and an
authentication key on the microprocessor. Plugging the
smart card into another phone will allow that phone to be
used as if it were the customer’s own. This is convenient in
that the subscriber needs only to carry the SIM while traveling and plug it into a rental phone at the destination location where the difference in frequency would preclude use of
the owner’s phone.
However, it is still possible for a technically savvy fraudster to access a microprocessor’s firmware for identification
details and to reprogram them into other SIM cards.
Counterfeiting SIM cards for GSM phones can be accomplished by programming computer chips using a laptop computer and other peripheral equipment. Although cloning
fraud is possible, the technical expertise required is such
that fewer people will be able to engage in this activity. And
the nature of the process is such that it cannot be done on a
massive scale cost-effectively.
While cloning may have hit a higher technological barrier
on GSM and PCS networks, other types of fraud, such as
technical fraud in international roaming markets and subscription fraud, are on the rise. With GSM networks, there is
little protection from the theft of authentication keys. In
fact, the use of mobile communications services by a growing
subscriber base across an expanding network of roaming
partners has created opportunities to defraud the digital
networks to a degree not envisioned by participants in the
early design phases of the technology.
The weak link in GSM networks is the challenge and
response technique incorporated into the authentication
process that allows the SIM to verify its IMSI by demon-
strating knowledge of the authentication algorithm and the
unique key, referred to as the Ki. The home system sends a
random challenge to the handset, and only that handset can
encrypt the challenge using both the algorithm and the Ki
resident within the SIM assigned to that subscriber. Using
the stored algorithm, the SIM generates the correct response
back to the home system. In this scenario, the single point of
failure is the authentication center in the home system.
Authentication should prevent fraudulent access to the
wireless service, and the authentication center itself can be
secured against internal and external theft of the IMSI and
Ki sets. However, even this solution has its share of problems. For example, when high call volumes and nonsignaling traffic threaten to overburden the system—as when
subscribers roam to international locations where the potential of intersystem bottlenecks is greatest—network administrators can reconfigure their systems to reuse the results
of previous authentications or bypass the authentication
process entirely to reduce the traffic back to the home system. As traffic increases, network administrators come
under increasing pressure to alter or dispense with authentication out of the need to keep congestion down, customers
happy, and revenues up. Unfortunately, tampering with
authentication creates opportunities for fraud, which also
can result in customer churn and lost revenues. The solution
is to increase network capacity, which also costs money and
can lead to customer churn if prices are increased.
Fraud Management Procedures
In addition to implementing new technologies to combat the
fraudulent use of cellular phones, carriers and retail agents
have implemented new fraud management procedures to
help prevent the opportunity for abuse.
Service Providers Revenue losses to mobile phone fraud are
so great that many service providers have an internal unit
that is responsible for advising the company on ways to minimize opportunities for fraud, investigating instances of
fraud and working with law enforcement authorities to prosecute criminals, and to educate corporate mobile phone
users about ways to prevent fraud.
The following procedures, when adopted by service
providers, can minimize opportunities for fraud:
Check clearance. Allow a new customer to access the network only after the check has been cleared. In the United
States, the Federal Reserve requires three business days
to clear personal checks.
Credit card verification. Allow a new customer to access
the network only after the credit card has been verified.
This can be done in a few minutes via card readers connected to the card issuer’s regional database.
Welcome call. Verify a new customer’s identity before paying
out a bonus or commission to the salesperson or licensed
dealer. Call the customer on a fixed line to verify name and
address, and confirm other details on the application
form—such as mother’s maiden name or spouse’s initials.
Ask for the name and address of the employer; if in doubt,
call the workplace to verify employment information.
Welcome letter. Send a letter to the customer in an envelope
that does not give the appearance of being junk mail. In
order to activate service, the recipient must call the customer service toll-free phone number specified in the letter.
Commission withholding. Implement a 3-month withholding period for connection commissions to dealers. If a
new subscriber fails to make the first payment within
that period, the sale should be declared invalid and the
connection commission canceled.
Premium services bar. Only provide those services which
a new subscriber has asked for. International calling and
premium rate services would be automatically barred by
default when the phone is given to the customer.
Early invoicing. Send the first phone bill out early to minimize airtime fraud or expose commission fraud.
Credit alert. Generate a report of phones with a high-volume of calls. A complex algorithm is used to detect fraudulent activity based on customer profiling, how long the
phone has been connected, average monthly spend, and
period of inactivity followed by hectic usage.
Nonphone alert. This is a commission fraud involving a
bogus phone, or the phone was never switched on. If the
phone was switched on only two or three times over a
period, the customer should be contacted as a precaution.
Subscribers Businesses and government agencies are very
susceptible to cellular fraud. Not only do employees have no
personal stake in taking basic antitheft precautions, but the
phone bills of many organizations are so massive that fraudulent calls are difficult, if not impossible, identify. Most
fraudulent phone calls are paid for by unknowing victims,
often traveling executives who pass the invoices on to their
companies without inspecting them. Nevertheless, organizations (and consumers) can minimize mobile phone fraud by
taking the following precautions:
If available, purchase phones equipped with authentication technology, which uses secret codes that are never
transmitted across the airwaves.
Ask the mobile service for a PIN that must be entered
before a call can go through. Given the infrequency of its
transmission, this code is not easily intercepted, and
without it, cell phones cannot be cloned.
If not needed, ask the service provider to shut off access to
international service. This would prevent anyone from
making illegal calls to other countries, where many fraudulent calls are directed.
If possible, use a beeper to screen incoming calls. With
the phone is turned off, it will not be transmitting its
identifying numbers, thereby minimizing vulnerability
to fraud. Since call retrieval usually entails air time
charges, it is more economical to use the beeper as a
screening device for calls that do not demand immediate
Do not lend the cell phone to anyone, and put it in a safe
place when it is not in use. Even if the cell phone is
insured against theft, most subscriber agreements limit
coverage to one incident, after which the user must pay
for a replacement phone.
When leaving cars unattended, remove the handset and
antenna to prevent mobile phone thieves from targeting
the vehicle.
Never leave the subscriber agreement or contract out in
plain view; it usually contains such sensitive information
as Social Security Number, drivers license number, credit
card number, mobile number, and electronic serial number.
Report all problems to the service provider immediately,
especially if there is trouble placing calls. This may indicate that someone may have cloned the phone and is using
it at that time. Other warning signs include difficulty
retrieving voice-mail messages, excessive hangups, and
callers receiving busy signals or wrong numbers.
While there is great progress in cracking down on mobile
phone fraud in the United States and Europe, other countries are experiencing an increase in this kind of criminal
activity. According to some experts, the international arena
looms as the next frontier for mobile phone fraud, particularly in locations where U.S.-based multinationals are setting up shop and buying this kind of service. Foreign
governments have just not been aggressive in finding and
prosecuting this kind of criminal, they note. In some countries such as China, there are even operations dedicated to
building cell phones that get illegally programmed and then
sold on the black market.
Scanning the airwaves for cell phone identification numbers and programming them into clones has been made more
difficult with sophisticated authentication processes and
digital networks that support encryption. GSM will change
the nature of fraud in the future. The authentication mechanism implemented with the SIM is forcing many would-be
criminals to turn their attention to subscription fraud,
which is still time-consuming to track down, even for the
largest service providers.
Mobile phone fraud is an extension of “phone phreaking,” the
name given to a method of payphone fraud that originated in
the 1960s and employed an electronic box held over the
speaker. When a user is asked to insert money, the electronic
box plays a rapid sequence of tones that fool the billing computer into thinking that money has been inserted. Since then,
criminals and hackers have devoted time and money to develop
and refine their techniques, applying them to mobile phones as
well. The growing popularity and spread of the Internet to distribute tips and tricks to defraud carriers makes mobile phone
fraud a billion-dollar international activity. Not only is mobile
phone fraud lucrative, the stolen handsets have also provided
anonymity to callers engaged in criminal activities. Apart from
the called numbers, often no other evidence is left behind. The
calls are charged to the legitimate subscribers’ accounts.
See also
Wireless Security
Three multiple access schemes are in use today, providing the
foundation for mobile communications systems (Figure F-5):
Frequency Division Multiple Access (FDMA), which
serves the calls with different frequency channels
Time Division Multiple Access (TDMA), which serves the
calls with different time slots
Code Division Multiple Access (CDMA), which serves the
calls with different code sequences
All three technologies are widely used in cellular networks. FDMA is still used on some first-generation cellular
analog networks, such as Advanced Mobile Phone Service
(AMPS)1 and TACS (Total Access Communications System).1
TDMA is used on second-generation digital cellular networks, such as North American Digital Cellular and Global
System for Mobile (GSM) communications. CDMA is also
used on second-generation digital cellular networks, such as
PCS 1900. Both TDMA and CDMA have been enhanced to
support emerging third-generation networks.
Of the three, FDMA is the simplest and still the most
widespread technology in use today for mobile communications. For example, FDMA is used in the CT2 system for
Figure F-5 Simple comparison of Frequency Division Multiple Access
(FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple
Access (CDMA).
There is a digital version of AMPS called D-AMPS (Digital-Advanced Mobile Phone
Service). D-AMPS adds Time Division Multiple Access (TDMA) to AMPS to get three
subchannels for each AMPS channel, tripling the number of calls that can be handled
on a channel.
cordless telecommunications. The familiar cordless phone
used in the home is representative of this type of system. It
creates capacity by splitting bandwidth into radio channels
in the frequency domain. In the initial call setup, the handset scans the available channels and locks onto an unoccupied channel for the duration of the call.
The traditional analog cellular systems, such as those
based on AMPS, also use FDMA to derive the channel. In the
case of AMPS, the channel is a 30-kHz “slice” of spectrum.
Only one subscriber at a time is assigned to the channel. No
other conversations can access the channel until the subscriber’s call is finished, or until the call is handed off to a
different channel in an adjacent cell.
The analog operating environment poses several problems. One is that the wireless devices are often in motion.
Current analog technology does not deal with call handoffs
very well, as evidenced by the high incidence of dropped calls.
This environment is particularly harsh for data, which is less
tolerant of transmission problems than voice. Whereas
momentary signal fade, for instance, is a nuisance in voice
communications, it may cause a data connection to drop.
Another problem with analog systems is their limited
capacity. To increase the capacity of analog cellular systems,
the 30-kHz channel can be divided into three narrower channels of 10 kHz each. This is the basis of the narrowband
AMPS (N-AMPS) standard. However, this band-splitting
technique incurs significant base station costs, and its limited growth potential makes it suitable only as a short-term
While cell subdivision often is used to increase capacity,
this solution has its limits. Since adjacent cells cannot use
the same frequencies without risking interference, a limited
number of frequencies are being reused at closer distances,
which makes it increasingly difficult to maintain the quality
of communications. Subdividing cells also increases the
amount of overhead signaling that must be used to set up
and manage the calls, which can overburden switch
resources. In addition, property or rights of way for cell sites
are difficult to obtain in metropolitan areas where traffic volume is highest and future substantial growth is anticipated.
These and other limitations of analog FM radio technology have led to the development of second-generation cellular systems based on digital radio technology and advanced
networking principles. Providing reliable service in this
dynamic environment requires digital radio systems that
employ advanced signal processing technologies for modulation, error correction, and diversity. These capabilities are
provided by TDMA and CDMA.
FM systems have supported cellular service for nearly 20
years, during which demand has finally caught up with the
available capacity. Now first-generation cellular systems
based on analog FM radio technology are rapidly being
phased out in favor of digital systems that offer higher
capacity, better voice quality, and advanced call handling
features. TDMA- and CDMA-based systems are contending
for acceptance among analog cellular carriers worldwide.
See also
Code Division Multiple Access
Cordless Telecommunications
Time Division Multiple Access
The Global Maritime Distress and Safety System (GMDSS)
is an internationally recognized distress and radio communication safety system for ships that replaced the previous
ship-to-ship safety system that relied on manual Morse code
operating on 500 kHz and voice radiotelephony on Channel
16 and on 2182 kHz.
The GMDSS is an automated ship-to-shore system using
satellites and digital selective calling technology. The GMDSS
is mandated for ships internationally by the International
Maritime Organization (IMO) Safety of Life at Sea Convention
(SOLAS), 1974, as amended in 1988, and carries the force of an
international treaty. The procedures governing use are contained in the International Telecommunications Union (ITU)
recommendations and in the International Radio Regulations
and also carry the force of an international treaty.
There are many advantages of the GMDSS over the previous system, including
Provides worldwide ship-to-shore alerting; it is not
dependent on passing ships.
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Simplifies radio operations; alerts may be sent by “two simple actions.”
Ensures redundancy of communications; it requires two
separate systems for alerting.
Enhances search and rescue; operations are coordinated
from shore centers.
Minimizes unanticipated emergencies at sea; maritime
safety broadcasts are included.
Eliminates reliance on a single person for communications; it requires at least two licensed GMDSS radio operators and typically two maintenance methods to ensure
distress communications capability at all times.
Radio officers (trained in manual Morse code) are not part
of the GMDSS regulations or system. In lieu of a single radio
officer, the GMDSS regulations require at least two GMDSS
radio operators and a GMDSS maintainer if the ship elects
at-sea repair as one of its maintenance options.
The Federal Communications Commission (FCC) requires
two licensed radio operators to be aboard all GMDSS-certified
ships, one of which must be dedicated to communications during a distress situation. The radio operators must be holders
of a GMDSS Radio Operator’s License. The GMDSS radio
operator is an individual licensed to handle radio communications aboard ships in compliance with the GMDSS regulations, including basic equipment and antenna adjustments.
The GMDSS radio operator need not be a radio officer.
Another IMO convention requires all masters and mates
to hold the GMDSS Radio Operator’s License and attend a
two-week training course and demonstrate competency with
operation of the GMDSS equipment. These requirements
also would carry to any person employed specifically to act
as a dedicated radio operator if the ship elected to carry such
a position.
The international GMDSS regulations apply to “compulsory” ships, including
Cargo ships of 300 gross tons and over when traveling on
international voyages or in the open sea
All passenger ships carrying more than 12 passengers
when traveling on international voyages or in the open sea
Fishing vessels to which GMDSS previously applied are
under a waiver until a date to be announced in the future. The
waiver is conditioned on the requirement that, for the duration
of the waiver, fishing vessels of 300 gross tons or greater continue to carry a 406-MHz receiver and survival craft equipment
including at least three portable VHF radiotelephones and two
9-GHz radar transponders. The GMDSS regulations do not
apply to vessels operating exclusively on the Great Lakes.
GMDSS was mandated by international treaty obligations.
In 1988, the International Maritime Organization (IMO), an
organization of the United Nations, amended the Safety of
Life at Sea (SOLAS) Convention to implement the GMDSS
worldwide. The United States has been a strong advocate of
the GMDSS internationally. In January 1992, the FCC
adopted the GMDSS regulations for U.S. compulsory vessels. The only way to ensure compliance with GMDSS
requirements is to use equipment that has been specifically
approved by the FCC for GMDSS use.
See also
Wireless E911
General Mobile Radio Service (GMRS) is one of several personal radio services; specifically, it is a personal two-way
ultra-high-frequency (UHF) voice communication service
that can be used to facilitate the activities of an individual’s
immediate family members. This FCC-licensed service has a
communications range of 5 to 25 miles and cannot be used to
make telephone calls.
A GMRS system consists of station operators, a mobile station (often composed of several mobile units), and sometimes
one or more land stations. The classes of land stations are base
station, mobile relay station (also known as a “repeater”), and
control stations. A small base station is one that has an antenna
no more than 20 feet above the ground or above the tree on
which it is mounted and transmits with no more than 5 watts.
Users communicate with a GMRS radio unit (Figure G-1)
over the general area of their residence in an urban or rural
Figure G-1 Motorola’s TalkAbout
Distance DPS is a hand-held GMRS
radio that weighs 11.7 ounces and runs
on a rechargeable NiCad battery or 6
AA batteries. A GMRS license, issued
by the FCC, and a fee are required for
use of this radio.
area. This area must be within the territorial limits of the 50
United States, the District of Columbia, and the Caribbean
and Pacific insular areas. In transient use, mobile station
units from one GMRS system may communicate through a
mobile relay station in another GMRS system with the permission of its licensee.
There are 23 GMRS channels. None of the GMRS channels are assigned for the exclusive use of any system.
License applicants and licensees must cooperate in the selection and use of the channels in order to make the most effective use of them and to reduce the possibility of interference.
Any mobile station or small base station in a GMRS system operating in the simplex mode may transmit voice-type
emissions with no more than 5 watts on the following 462MHz channels: 462.5625, 462.5875, 462.6125, 462.6375,
462.6625, 462.6875, and 462.7125 MHz. These channels are
shared with the Family Radio Service (FRS).
Any mobile station in a GMRS system may transmit on
the 467.675-MHz channel to communicate through a mobile
relay station transmitting on the 462.675-MHz channel. The
communications must be for the purpose of soliciting or rendering assistance to a traveler or for communicating in an
emergency pertaining to the immediate safety of life or the
immediate protection of property.
Each GMRS system license assigns one or two of eight
possible channels or channel pairs (one 462-MHz channel
and one 467-MHz channel spaced 5 MHz apart) as
requested by the applicant. Applicants for GMRS system
licenses are advised to investigate or monitor to determine
the best available channel(s) before making their selection. Each applicant must select the channel(s) or channel
pair(s) for the stations in the proposed system from the following list:
For a base station, mobile relay station, fixed station, or
mobile station: 462.550, 462.575, 462.600, 462.625, 462.650,
462.675, 462.700, and 462.725 MHz.
For a mobile station, control station, or fixed station in
a duplex system: 467.550, 467.575, 467.600, 467.625,
467.650, 467.675, 467.700, and 467.725 MHz.
GMRS system station operators must cooperate in sharing the assigned channel with station operators in other
GMRS systems by monitoring the channel before initiating
transmissions, waiting until communications in progress
are completed before initiating transmissions, engaging in
only permissible communications, and limiting transmissions to the minimum practical transmission time.
Any individual 18 years of age or older who is not a representative of a foreign government is eligible to apply for a
GMRS system license. There is a filing fee for new licenses
and license renewals. For general information regarding the
fee and filing requirements, contact the FCC’s Consumer
Center toll free at 1-888-225-5322.
See also
Citizens Band Radio Service
Family Radio Service
Low-Power Radio Service
Many carriers will take an interim step to third generation
(3G), referred to as 2.5G, that uses the Internet Protocol (IP) to
provide fast access to data networks via General Packet Radio
Service (GPRS) technology. Compared to circuit-switched data
(CSD), which operates at up to 14.4 kbps and high-speed circuit-switched data (HSCSD), which operates at up to 43.2
kbps, GPRS uses packet-switching technology to transmit
short bursts of data over an IP-based network to deliver speeds
of up to 144 kbps over an “always on” wireless connection.
True 3G networks based on enhanced data rates for GSM
evolution (EDGE) technology deliver data at speeds of up to
384 kbps. EDGE is a step beyond GPRS that will allow up to
three times higher throughput compared to GSM/GPRS
using the same bandwidth. Carriers in the United States
have been moving toward 3G for several years by overlaying
various technologies onto their existing networks to enhance
their data-handling capabilities.
For carriers with TDMA-based networks, the first step to
offering true 3G services is to deploy Global Systems for
Mobile communications (GSM) and then GPRS. The GPRS
enhancement to GSM can support peak network speeds of
wireless data transmissions between 64 and 170 kbps depending on the various claims of hardware vendors. The new
GSM/GPRS network does not replace existing TDMA networks; carriers will continue supporting these networks long
into the future to service their voice customers. Eventually, all
TDMA customers will be migrated to GSM/GPRS.
Once the GSM/GPRS overlay is in place in a market, the
carriers can upgrade their networks with EDGE-compliant
software to boost data transmission rates to as much as 384
kbps and begin the availability of true 3G services.
Carriers whose wireless networks are based on CDMA
will take a different technology path to 3G, going through
CDMA2000, before eventually arriving at Wideband Code
Division Multiple Access (W-CDMA). Both EDGE and WCDMA offer a migration path to the global standard
Universal Mobile Telecommunications System (UMTS).
Coverage for 2.5/3G services is still ramping up, despite
the impressive figures thrown out by individual carriers.
The next step is for service providers to engage in more
roaming arrangements, which is a way to save costs, reduce
time to market, and add value to attract more customers.
The data speed of 2.5/3G services is determined by many
factors, including the equipment and software in the wireless
network, the distance of the user from the nearest base station, and how fast the user may be moving. The claimed
speed of the service is rarely, if ever, achieved in the realworld operating environment.
The pricing plans and price points differ by carrier, from a
simple add-on to existing digital voice plans for a basic data
service, to tiered pricing plans based on actual data usage.
Depending on the applications, users can opt for 2.5/3G
cell phones with multimedia messaging capabilities.
Alternatively, users with heavy messaging and file transfer
requirements may opt for PC cards for notebooks and personal digital assistants (PDAs).
The choice of 2.5G platform depends on whether the carrier has a TDMA- or CDMA-based network. Both technologies are capable of eventual migration to full 3G and at a
higher level will be able to interoperate in compliance with
the global IMT-2000 initiative.
Some service providers intend to support Wireless
Fidelity (Wi-Fi), as well as GPRS. Wi-Fi networks are based
on the IEEE 802.11b Standard for Ethernet, which operates
in the unlicensed 2.4-GHz band to provide a maximum
stated speed of 11 Mbps. In actual operation, however, Wi-Fi
offers between 5 and 6 Mbps. Some carriers are looking at
ways to offer both Wi-Fi and 3G from the same device to
meet the diverse needs of customers.
The existing GPRS and upcoming EDGE networks provide wide area coverage for applications where customers
want constant access to such as e-mail and calendar,
whereas Wi-Fi networks will be available in convenient locations where customers are likely to spend time accessing
larger data files.
The United States lags behind the rest of the world when it
comes to wireless technologies for a number of reasons. The
telecommunications infrastructure in the United States is
more developed than in many European and Asian countries. As a result, the demand for wireless devices has been
lower in the United States because consumers have other
low-cost options. Also, the United States has a number of
competing technical standards for digital services, while
European and Asian countries are predominately centered
on GSM. In the United States, carriers have only recently
adopted GSM. Now that carriers in the United States have
mapped out their migration strategies, they have been busy
positioning their networks to 2.5G, investing billions of dollars for infrastructure upgrades, with billions more committed to go the rest of the way to 3G. In the process, they are
betting they can attract millions of new customers who will
want high-speed wireless data on their mobile phones, notebooks, and PDAs.
See also
Code Division Multiple Access
Enhanced Data Rates for Global Evolution
Global System for Mobile Telecommunications
Time Division Multiple Access
Universal Mobile Telecommunications System
The Global Positioning System (GPS) is a network of 24
Navstar1 satellites orbiting Earth at 11,000 miles up.
Established by the U.S. Defense Department for military
applications, access to GPS is now free to all users, including
those in other countries. The system’s positioning and timing
data are used for a variety of applications, including air, land,
1Originally, NAVSTAR was an acronym for Navigation System with Timing and
and sea navigation; vehicle and vessel tracking; surveying and
mapping; and asset and natural resource management. With
military accuracy restrictions lifted in May 2000, the GPS can
now pinpoint the exact location of people as they move about
with their receivers powered on. This development has ushered in a wave of new commercial applications for GPS.
GPS Components
The first GPS satellite was launched in 1978. The first 10
satellites were developmental satellites. From 1989 to 1993,
23 production satellites were launched. The launch of the
twenty-fourth satellite in 1994 completed the $13 billion
constellation. The satellites are positioned so that signals
from 6 of them can be received nearly 100 percent of the time
at any point on earth.
The GPS consists of satellites, receivers, and ground control systems. The satellites transmit signals (1575.42 MHz)
that can be detected by GPS receivers on the ground. These
receivers can be portable or mounted in ships, planes, or cars
to provide exact position information, regardless of weather
conditions. They detect, decode, and process GPS satellite
signals to give the precise position of the user.
The GPS control or ground segment consists of five
unmanned monitor stations located in Hawaii, Kwajalein
in the Pacific Ocean, Diego Garcia in the Indian Ocean,
Ascension Island in the Atlantic Ocean, and Colorado Springs,
Colorado. There is also a master ground station at Falcon Air
Force Base in Colorado Springs, Colorado, and four large
ground antenna stations that broadcast signals to the satellites. The stations also track and monitor the GPS satellites.
System Operation
With GPS, signals from several satellites are triangulated to
identify the exact position of the user. To triangulate, GPS
measures distance using the travel time of a radio message
from the satellite to a ground receiver. To measure travel time,
GPS uses very accurate clocks in the satellites. Once the distance to a satellite is known, knowledge of the satellite’s location in space is used to complete the calculation. GPS receivers
on the ground have an “almanac” stored in their computer
memory that indicates where each satellite will be in the sky
at any given time. GPS receivers calculate for ionosphere and
atmosphere delays to further tune the position measurement.
To make sure both satellite and receiver are synchronized,
each satellite has four atomic clocks that keep time to within 3
nanoseconds, or 3 billionths of a second. For cost savings, the
clocks in the ground receivers are not that accurate. To compensate, an extra satellite range measurement is taken.
Trigonometry says that if three perfect measurements locate a
point in three-dimensional space, then a fourth measurement
can eliminate any timing offset. This fourth measurement
compensates for the receiver’s imperfect synchronization.
The ground unit receives the satellite signals, which
travel at the speed of light. Even at this speed, the signals
take a measurable amount of time to reach the receiver. The
difference between when the signals are sent and the time
they are received, multiplied by the speed of light, enables
the receiver to calculate the distance to the satellite. To measure precise latitude, longitude, and altitude, the receiver
measures the time it took for the signals from several satellites to get to the receiver (Figure G-2).
GPS uses a system of coordinates called the Worldwide
Geodetic System 1984 (WGS-84). This is similar to the latitude
and longitude lines that are commonly seen on large wall maps
used in schools. The WGS-84 system provides a built-in, standardized frame of reference, enabling receivers from any vendor to provide exactly the same positioning information.
GPS Applications
The GPS system has amply proven itself in military applications, most notably in Operation Desert Storm where U.S.
Navstar Satellites
GPS-equipped Vehicles
Figure G-2 Signals from four satellites, captured by a vehicle’s onboard
GPS receiver, are used to determine precise location information.
and allied troops faced a vast, featureless desert. Without a
reliable navigation system, sophisticated troop maneuvers
could not have been performed. This could have prolonged
the operation well beyond the 100 hours it actually took.
With GPS, troops were able to go places and maneuver in
sandstorms or at night when even the troops who were native
to the area could not. Initially, more than 1000 portable commercial receivers were purchased for their use. The demand
was so great that before the end of the conflict, more than
9000 commercial receivers were in use in the Gulf region.
They were carried by ground troops and attached to vehicles,
helicopters, and aircraft instrument panels. GPS receivers
were used in several aircraft, including F-16 fighters, KC-135
tankers, and B-52s. Navy ships used GPS receivers for rendezvous, minesweeping, and aircraft operations.
While the GPS system was developed originally to meet
the needs of the military community, new ways to use its
capabilities are continually being found, from the exotic to
the mundane. Among the former is the use of GPS for
wildlife management. Endangered species such as Montana
elk and Mojave Desert tortoises have been fitted with tiny
GPS receivers to help determine population distribution patterns and possible sources of disease. In Africa, GPS
receivers are used to monitor the migration patterns of large
herds for a variety of research purposes.
Handheld GPS receivers are now used routinely in field
applications that require precise information gathering,
including field surveying by utility companies, mapping by
oil and gas explorers, and resource planning by timber
GPS-equipped balloons are used to monitor holes in the
ozone layer over the polar ice caps. Air quality is being monitored using GPS receivers. Buoys tracking major oil spills
transmit data using GPS. Archaeologists and explorers are
using the system to mark remote land and ocean sites until
they can return with proper equipment and funding.
Vehicle tracking is one of the fastest-growing GPS applications. GPS-equipped fleet vehicles, public transportation
systems, delivery trucks, and courier services use receivers
to monitor their locations at all times.
GPS data are especially useful to consumers when they
are linked with digital mapping. Accordingly, some automobile manufacturers are offering moving-map displays guided
by GPS receivers as an option on new vehicles. The displays
can even be removed and taken into a home to plan a trip.
Some GPS-equipped vehicles give directions to drivers on
display screens and through synthesized voice instructions.
These features enable drivers to get where they want to go
more rapidly and safely than has ever been possible before.
GPS receivers are also included in newer mobile phones, and
add-on receivers are available for hand-held computers,
such as the Palm III (Figure G-3).
Figure G-3 Palm III users can clip on Rand
McNally’s StreetFinder GPS receiver, turning
the unit into a portable navigational tool.
Customized maps from the StreetFinder software can be downloaded to the Palm III, along
with address-to-address directions accessible via
the Internet. With trip information stored on the
Palm III, the GPS receiver enables the user to
track travel progress and manage itinerary
changes en route.
GPS is also helping save lives. Many police, fire, and emergency medical service units are using GPS receivers to determine the police car, fire truck, or ambulance nearest to an
emergency, enabling the quickest possible response in life-ordeath situations.
When GPS data are used in conjunction with geographic
data collection systems, it is possible to instantaneously
arrive at submeter positions together with feature descriptions to compile highly accurate geographic information systems (GIS). When used by cities and towns, for example,
GPS can help in the management of the geographic assets
summarized in Table G-1.
Some government agencies, academic institutions, and
private companies are using GPS to determine the location
of a multitude of features, including point features such as
pollutant discharges and water supply wells, line features
such as roads and streams, and area features such as waste
lagoons and property boundaries. Before GPS, such features
had to be located with surveying equipment, aerial photographs, or satellite imagery. With GPS, the precise location of these and other features can be determined with a
hand-held GPS receiver.
GPS and Cellular
GPS technology is even being used in conjunction with cellular technology to provide value-added services. With the
push of a button on a cellular telephone, automobile drivers and operators of commercial vehicles in some areas
can talk to a service provider and simultaneously signal
their position, emergency status, or equipment failure
information to auto clubs, security services, or central dispatch services.
TABLE G-1 Types of Geographic Assets That Can Be Managed with the
Aid of the Global Positioning System (GPS)
Point Features
Line Features
Area Features
Manhole covers
Fire hydrants
Light poles
Storm drains
Fitness trails
Sewer lines
Water lines
Bus routes
Planning zones
Recycling centers
This is possible with Motorola’s Cellular Positioning and
Emergency Messaging Unit, for example, which offers
mobile security and tracking to those who drive automobiles
and/or operate fleets. The system is designed for sale to systems integrators that configure consumer and commercial
systems that operate via cellular telephony. The Cellular
Positioning and Emergency Messaging Unit communicates
GPS-determined vehicle position and status, making it
suited for use in systems that support roadside assistance
providers, home security monitoring firms, cellular carriers,
rental car companies, commercial fleet operators, and auto
manufacturers seeking a competitive advantage.
As an option, the OnStar system is available for select
vehicles manufactured by General Motors, which uses a
GPS receiver in conjunction with analog cellular phone technology to provide a variety of travel assistance services,
including emergency response. At the push of a button, a cellular call is placed to an OnStar operator. Although digital
technology is more advanced, OnStar uses analog cellular
because it has the broadest geographic coverage in the
United States. Over 90 percent of the country is covered by
the analog system, whereas digital coverage is less than 30
percent. OnStar has worked to “clear” the OnStar emergency button call through all analog cellular phone companies so that it will go through no matter which carrier is used
locally. GPS comes into play by providing the OnStar operator with the precise location of the vehicle.
Because of its accuracy, GPS is rapidly becoming the location
data-collection method of choice for a variety of commercial,
government, and military applications. GPS certainly has
become an important and cost-effective method for locating
terrestrial features too numerous or too dynamic to be
mapped by traditional methods. Although originally funded
by the U.S. Defense Department, access to the GPS network
is free to all users in any country. This has encouraged applications development and created an entirely new consumer
market, particularly in the area of vehicular location and
highway navigation.
See also
Satellite Communications
Global System for Mobile (GSM) telecommunications—formerly known as Groupe Spéciale Mobile, for the group that
started developing the standard in 1982—was designed
from the beginning as an international digital cellular service.
It was intended that GSM subscribers should be able to cross
national borders and find that their mobile services crossed
with them. Today, GSM is well established in most countries,
with the highest concentration of service providers and users
in Europe.
Originally, the 900-MHz band was reserved for GSM services. Since GSM first entered commercial service in 1992, it
has been adapted to work at 1800 MHz for the Personal
Communications Networks (PCN) in Europe and at 1900
MHz for Personal Communications Services (PCS) in the
United States.
GSM Services
GSM telecommunication services are divided into teleservices, bearer services, and supplementary services.
Teleservices The most basic teleservice supported by GSM is
telephony. There is an emergency service in which the nearest emergency service provider is notified by dialing three
digits (similar to 911). Group 3 fax, an analog method
described in ITU–T Recommendation T.30, is also supported
by GSM through the use of an appropriate fax adapter.
Bearer Services A unique feature of GSM compared to older
analog systems is the Short Message Service (SMS). SMS is
a bidirectional service for sending short alphanumeric messages (up to 160 bytes) in a store-and-forward manner. For
point-to-point SMS, a message can be sent to another subscriber to the service, and an acknowledgment of receipt is
provided to the sender. SMS also can be used in cell broadcast mode for sending messages such as traffic updates or
news updates. Messages can be stored in a smart card called
the “Subscriber Identity Module” (SIM) for later retrieval.
Since GSM is based on digital technology, it allows synchronous and asynchronous data to be transported as a
bearer service to or from an Integrated Services Digital
Network (ISDN) terminal. The data rates supported by GSM
are 300, 600, 1200, 2400, and 9600 bps. Data can use either
the transparent service, which has a fixed delay but no guarantee of data integrity, or a nontransparent service, which
guarantees data integrity through an automatic repeat
request (ARQ) mechanism but with variable delay.
GSM has much more potential in terms of supporting
data. The GSM standard for high-speed circuit-switched
data (HSCSD) enables mobile phones to support data rates
of up to 38.4 kbps, compared with 9.6 kbps for regular GSM
networks. Transmission speeds of up to 171.2 kbps are available with mobile phones that support the GSM standard for
General Packet Radio Service (GPRS). The high bandwidth
is achieved by using eight timeslots, or voice channels,
simultaneously. GPRS facilitates several new applications,
such as Web browsing over the Internet.
Both HSCSD and GPRS are steps toward the third generation (3G) of mobile technology, called International Mobile
Telecommunications (IMT), a framework for advanced mobile
telephony that seeks to harmonize all national and regional
standards for global interoperability, which is in various
phases of implementation around the world. IMT includes
standards that eventually will allow mobile phones to operate
at up to 2 Mbps, enabling broadband applications such as
Supplementary Services Supplementary services are pro-
vided on top of teleservices or bearer services and include
such features as caller identification, call forwarding, call
waiting, and multiparty conversations. There is also a lockout feature that prevents the dialing of certain types of calls,
such as international calls.
Network Architecture
A GSM network consists of the following elements: mobile
station, base station subsystem, and mobile services switching center (MSC). Each GSM network also has an operations
and maintenance center that oversees the proper operation
and setup of the network. There are two air interfaces: the
Um interface is a radio link over which the mobile station
and the base station subsystem communicate; the A interface is a radio link over which the base station subsystem
communicates with the MSC.
The Mobile Station The mobile station (MS) consists of the
radio transceiver, display and digital signal processors, and
the SIM. The SIM provides personal mobility so that the subscriber can have access to all services regardless of the terminal’s location or the specific terminal used. By removing
the SIM from one GSM cellular phone and inserting it into
another GSM cellular phone, the user is able to receive calls
at that phone, make calls from that phone, or receive other
subscribed services. The SIM card may be protected against
unauthorized use by a password or personal identification
number (PIN).
An International Mobile Equipment Identity (IMEI) number uniquely identifies each mobile station. The SIM card
contains an International Mobile Subscriber Identity (IMSI)
number identifying the subscriber, a secret key for authentication, and other user information. Since the IMEI and IMSI
are independent, this arrangement provides users with a
high degree of security.
The SIM comes in two form factors: credit-card size (ISO
format) or postage-stamp size (plug-in format). Both sizes
are offered together to fit any kind of cell phone the user happens to have (Figure G-4). There is also a micro SIM adapter
(MSA) that allows the user to change back from the plug-in
format SIM card into an ISO format card.
The SIM cards also allow services to be individually tailored and updated over the air and activated without requiring the user to find a point-of-sale location in order to carry
out the update. SIM cards’ remote control and modification
possibilities allow the carriers to offer their subscribers such
new, interactive services as remote phonebook loading and
remote recharging of prepaid SIMs. The cards also can contain company/private or parent/children subscriptions with
separate PIN codes that can be changed over the air.
Figure G-4 SIM issued to subscribers of
Vodafone, the largest cellular service provider
in the United Kingdom. Within the larger card
is a detachable postage-stamp-sized SIM. Both
use the same gold contact points.
Base Station Subsystem The base station subsystem consists
of two parts: the base transceiver station (BTS) and the base
station controller (BSC). These communicate across the
A–bis interface, enabling operation between components
made by different suppliers.
The base transceiver station contains the radio transceivers that define a cell and handles the radio link protocols
with the mobile stations. In a large urban area, there typically will be a number of BTSs to support a large subscriber
base of mobile service users.
The base station controller provides the connection
between the mobile stations and the mobile service switching
center (MSC). It manages the radio resources for the BTSs,
handling such functions as radio channel setup, frequency
hopping, and handoffs. The BSC also translates the 13-kbps
voice channel used over the radio link to the standard 64-kbps
channel used by the land-based Public Switched Telephone
Network (PSTN) or ISDN.
Mobile Services Switching Center The mobile services
switching center (MSC) acts like an ordinary switching node
on the PSTN or ISDN and provides all the functionality
needed to handle a mobile subscriber, such as registration,
authentication, location updating, handoffs, and call routing
to a roaming subscriber. These services are provided in conjunction with several other components, which together form
the network subsystem. The MSC provides the connection to
the public network (PSTN or ISDN) and signaling between
various network elements that use Signaling System 7 (SS7).
The MSC contains no information about particular mobile
stations. This information is stored in two location registers
that are essentially databases. The Home Location Register
(HLR) and Visitor Location Register (VLR), together with
the MSC, provide the call routing and roaming (national and
international) capabilities of GSM.
The HLR contains administrative information for each subscriber registered in the corresponding GSM network, along
with the current location of the mobile device. The current
location of the mobile device is in the form of a Mobile Station
Roaming Number (MSRN), which is a regular ISDN number
used to route a call to the MSC where the mobile device is currently located. Only one HLR is needed per GSM network,
although it may be implemented as a distributed database.
The Visitor Location Register (VLR) contains selected
administrative information from the HLR that is necessary
for call control and provision of the subscribed services for
each mobile device currently located in the geographic area
controlled by the VLR.
There are two other registers that are used for authentication and security purposes. The Equipment Identity
Register (EIR) is a database that contains a list of all valid
mobile equipment on the network, where each mobile station is identified by its IMEI. An IMEI is marked as invalid
if it has been reported stolen or is not type approved. The
authentication center is a protected database that stores a
copy of the secret key stored in each subscriber’s SIM card,
which is used for authentication.
Channel Derivation and Types
Since radio spectrum is a limited resource shared by all
users, a method must be devised to divide up the bandwidth
among as many users as possible. The method used by GSM
is a combination of Time and Frequency Division Multiple
Access (TDMA/FDMA).
The FDMA part involves the division by frequency of the
total 25-MHz bandwidth into 124 carrier frequencies of 200kHz bandwidth. One or more carrier frequencies are then
assigned to each base station. Each of these carrier frequencies is then divided in time, using a TDMA scheme, into eight
time slots. One time slot is used for transmission by the
mobile device and one for reception. They are separated in
time so that the mobile unit does not receive and transmit at
the same time.
Within the framework of TDMA, two types of channels are
provided: traffic channels and control channels. Traffic channels carry voice and data between users, while the control
channels carry information that is used by the network for
supervision and management.
Among the control channels are the following:
Fast Associated Control Channel (FACCH). Robs slots
from traffic channels to transmit power control and call
handoff messages.
Broadcast Control Channel (BCCH). Continually broadcasts on the downlink, information including base station
identity, frequency allocations, and frequency hopping
Stand-Alone Dedicated Control Channel (SDCCH). Used
for registration, authentication, call setup, and location
Common Control Channel (CCCH) Comprises three control channels used during call origination and call paging.
Random Access Channel (RACH). Used to request access
to the network.
Paging Channel (PCH). Used to alert the mobile station of
an incoming call.
Authentication and Security
Since radio signals can be accessed by virtually anyone,
authentication of users to prove their identity is a very important feature of a mobile network. Authentication involves two
functional entities, the SIM card in the mobile unit and the
authentication center (AC). Each subscriber is given a secret
key, one copy of which is stored in the SIM card and the other
in the AC. During authentication, the AC generates a random
number that it sends to the mobile unit. Both the mobile unit
and the AC then use the random number, in conjunction with
the subscriber’s secret key and an encryption algorithm called
A3, to generate a number that is sent back to the AC. If the
number sent by the mobile unit is the same as the one calculated by the AC, the subscriber is authenticated.
The calculated number is also used, together with a
TDMA frame number and another encryption algorithm
called A5, to encrypt the data sent over the radio link, preventing others from listening in. Encryption provides an
added measure of security, since the signal is already coded,
interleaved, and transmitted in a TDMA manner, thus providing protection from all but the most technically astute
Another level of security is performed on the mobile
equipment, as opposed to the mobile subscriber. As noted, a
unique IMEI number is used to identify each GSM terminal.
A list of IMEIs in the network is stored in the EIR. The status returned in response to an IMEI query to the EIR is one
of the following:
White listed. Indicates that the terminal is allowed to connect to the network.
Gray listed. Indicates that the terminal is under observation from the network for possible problems.
Black listed. Indicates that the terminal either has been
reported as stolen or is not type approved (i.e., not the correct type of terminal for a GSM network). Such terminals
are not allowed to connect to the network.
By mid-2001, there were 404 GSM networks in operation in
171 countries, providing mobile telephone service to 538 million subscribers. GSM accounts for 70 percent of the world’s
digital market and 65 percent of the world’s wireless market.
One new subscriber signs up for service every second of the
day and night. GSM in North America has some 11 million
customers across the United States and Canada. GSM ser-
vice is available in 6500 cities in 48 states, the District of
Columbia, and six Canadian provinces. According to the
North American GSM Alliance, GSM coverage reaches more
than half the Canadian population and two-thirds of the
U.S. population.
See also
Digital Enhanced Cordless Telecommunications
International Mobile Telecommunications
PCS 1900
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The term hertz is a measure of frequency, or the speed of
transmission. The frequency of electromagnetic waves generated by radio transmitters is measured in cycles per second (cps), but this designation was officially changed to
hertz (Hz) in 1960.
An electromagnetic wave is composed of complete
cycles. The number of cycles that occur each second gives
radio waves their frequency, while the peak-to-peak distance of the waveform gives the amplitude of the signal
(Figure H-1).
The frequency of standard speech is between 3000 cycles
per second, or 3 kilohertz (kHz), and 4000 cycles per second,
or 4 kHz. Some radio waves may have frequencies of many
millions of hertz (megahertz, or MHz), and even billions of
hertz (gigahertz, or GHz). Table H-1 provides the range of frequencies and their band classification.
The term hertz was adopted in 1960 by an international
group of scientists and engineers at the General Conference
of Weights and Measures in honor of Heinrich R. Hertz
(1857–1894), a German physicist (Figure H-2). Hertz is best
known for proving the existence of electromagnetic waves,
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1 Second
Figure H-1 Each cycle per second equates to 1 hertz (Hz). In this case, 3
cycles occur in 1 second, which equates to 3 Hz.
TABLE H-1 List of Frequency Ranges and Corresponding Band
Less than 30 kHz
30 to 300 kHz
300 kHz to 3 MHz
3 to 30 MHz
30 to 300 MHz
300 MHz to 3 GHz
3 to 30 GHz
More than 30 GHz
Band Classification
Very low frequency (VLF)
Low frequency (LF)
Medium frequency (MF)
High frequency (HF)
Very high frequency (VHF)
Ultrahigh frequency (UHF)
Superhigh frequency (SHF)
Extremely high frequency (EHF)
which had been predicted by British scientist James Clerk
Maxwell in 1864.
Hertz used a rapidly oscillating electric spark to produce
UHF waves. These waves caused similar electrical oscillations in a distant wire loop. The discovery of electromagnetic
waves and how they could be manipulated paved the way for
the development of radio, microwave, radar, and other forms
of wireless communication.
Figure H-2 German physicist Heinrich R.
Hertz (1857–1894) proved the existence of electromagnetic waves, which led to the development
of radio, microwave, radar, and other forms of
wireless communication.
As interest in electromagnetic waves grew in the nineteenth century, a physical model to describe it was proposed. It was suggested that electromagnetic waves,
including light, were like sound waves but that they propagated through some previously unknown medium called
the “luminiferous ether” that filled all unoccupied space
throughout the universe. The experiments of Albert A.
Michelson and Edward W. Morley in 1887 proved that the
ether did not exist. Albert Einstein’s theory of relativity,
proposed in 1905, eliminated the need for a light-transmitting
medium, so today the term ether is used only in a historical context, as in the term Ethernet.
See also
One method of implementing a wireless network in the home
is to use products that adhere to the standards of the Home
Radio Frequency Working Group. HomeRF is positioned as
a global extension of Digitally Enhanced Cordless Telephony
(DECT), the popular cordless phone standard that allows
different brands to work together so that certified handsets
from one vendor can communicate with base stations from
another. DECT has been largely confined to Europe because
its native 1.9-GHz frequency band requires a license elsewhere, but HomeRF extends DECT to other regions by using
the license-free 2.4-GHz frequency band. It also adds functionality by blending several industry standards, including
IEEE 802.11 frequency hopping for data and DECT for voice.
This convergence makes HomeRF useful for broadband
As more PCs, peripherals, and intelligent devices are
installed in the home, and as network connections proliferate, users are faced with new opportunities for accessing
information as well as challenges for sharing resources. For
example, users want to
Access information delivered via the Internet from anywhere in the home
Share files between PCs and share access to peripherals
no matter where they are located within the home
Control electrical systems and appliances whether in,
around, or away from home
Effectively manage communications channels for phone,
fax, and Internet usage
Each of these capabilities requires a common connection
between the various devices and networks found in the
home. However, in order to truly be effective, any home network must meet certain criteria:
It must not require additional home wiring. Most existing
homes are not wired for networking, and retrofitting them
would too labor-intensive and expensive. A wireless solution is a viable alternative.
The wireless connections must be immune to interference,
especially with the growing number of wireless devices
and appliances emitting RF noise in the home.
The range of the wireless connection must be adequate to
allow devices to communicate from anywhere within and
around a typical family home.
The network must be safe and protected from unwanted
security breaches.
It must be easy to install, configure, and operate for nontechnical users. Most home users do not have the expertise
to handle complex network installation and configuration
The entire system must be easily and spontaneously
accessible—anytime and from anywhere in or even away
from the home.
These issues have been addressed by a consortium of vendors called the Home Radio Frequency Working Group
(HomeRF WG), which has developed a platform for a broad
range of interoperable consumer devices. Its specification,
called the Shared Wireless Access Protocol (SWAP), is an
open standard that allows PCs, peripherals, cordless telephones, and other consumer electronic devices to communicate and interoperate with one another without the
complexity and expense associated with installing new wires.
The SWAP is designed to carry both voice and data traffic and to interoperate with the Public Switched Telephone
Network (PSTN) and the Internet. It operates in the 2.4GHz ISM (industrial, scientific, medical) band and uses
frequency-hopping spread-spectrum radio for security and
reliability. The SWAP technology was derived from extensions of DECT and wireless local area network (LAN) technologies to enable a new class of home cordless services. It
supports both a Time Division Multiple Access (TDMA)
service to provide delivery of interactive voice and other
time-critical services, and a Carrier Sense Multiple
Access/Collision Avoidance (CSMA-CA) service for delivery
of high-speed packet data. Table H-2 summarizes the main
characteristics of HomeRF.
The SWAP specification provides the basis for a broad range
of new home networking applications, including
TABLE H-2 HomeRF Characteristics
Frequency-hopping network
Frequency range
Transmission power
Data rate
Total network devices
Voice connections
Data security
Data compression
48-bit network ID
Source: HomeRF Working Group.
50 hops/second
2.4-GHz ISM band
100 mW
1.6 Mbps with HomeRF 1.0; 10 Mbps
with HomeRF 2.0; 25 Mbps with
HomeRF 3.0 (future)
Covers up to 150 feet for typical home
and yard
Up to 127
Up to 4 active handsets
Blowfish encryption algorithm (over 1
trillion codes)
LZRW3-A algorithm
Enables concurrent operation of multiple colocated networks
Shared access to the Internet from anywhere in the home,
allowing a user to browse the Web from a laptop on the
deck or have stock quotes delivered to a PC in the den.
Automatic intelligent routing of incoming telephone calls
to one or more cordless handsets, fax machines, or voicemail boxes of individual family members.
Cordless handset access to an integrated message system
to review stored voice mail, faxes, and electronic mail.
Personal intelligent agents running on the PC for each
family member, accessed by speaking into cordless handsets. This new voice interface would allow users to access
and control their PCs and all the resources on the home
wireless network spontaneously, from anywhere within
the home, using natural language commands.
Wireless LANs allowing users to share files and peripherals between one or more PCs, no matter where they are
located within the home.
Spontaneous control of security and electrical, heating,
and air-conditioning systems from anywhere in or around
the home.
Multiuser computer games playable in the same room or
in multiple rooms throughout the home.
Network Topology
The SWAP system can operate either as an ad-hoc network
or as a managed network under the control of a connection
point. In an ad-hoc network, where only data communication
is supported, all stations are equal, and control of the network is distributed between the stations. For time-critical
communications such as interactive voice, a connection point
is required to coordinate the system. The connection point,
which provides the gateway to the public switched telephone
network (PSTN), can be connected to a PC via a standard
interface such as the Universal Serial Bus (USB) that will
enable enhanced voice and data services. The SWAP system
also can use the connection point to support power management for prolonged battery life by scheduling device wakeup
and polling.
The network can accommodate a maximum of 127 nodes.
The nodes are of four basic types:
Connection point that supports voice and data services
Voice terminal that only uses the TDMA service to communicate with a base station
Data node that uses the CSMA-CA service to communicate with a base station and other data nodes
Integrated node thath can use both TDMA and CSMA/CA
HomeRF uses intelligent hopping algorithms that detect
wideband static interference from microwave ovens, cordless
phones, baby monitors, and other wireless LAN systems.
Once detected, the HomeRF hop set adapts so that no two
consecutive hops occur within this interference range. This
means that, with very high probability, a packet lost due to
interference will get through when it retries on the next hop.
While these algorithms benefit data applications, they are
especially important for voice, which requires extremely low
bit error rates and low latency.
Future Plans
Work has already begun on the future HomeRF 2.1 specification, which will add features designed to reinforce its
advantages for voice. Planned enhancements also will allow
HomeRF to complement other wireless standards, including
IEEE 802.11, also known as Wi-Fi.
HomeRF 2.0 already supports up to eight phone lines,
eight registered handsets, and four active handsets with
voice quality and range comparable to leading 2.4-GHz phone
systems. With this many lines, each family member can have
a personal phone number. HomeRF 2.1 plans to increase the
number of active handsets with the same or better voice quality, thus supporting the needs of small businesses.
The 150-foot range of HomeRF already covers most homes
and into the yard. HomeRF 2.1 will extend this range for
larger homes and businesses by using wireless repeaters
that are similar to enterprise access points but without the
need to connect each one to Ethernet. HomeRF frequency
hopping technology also avoids the complexity of assigning
RF channels to multiple access points (or repeaters) and
offers easy and effective security and interference immunity.
This is especially important since households and small
businesses do not usually have network administrators.
To allow individuals to roam across very large homes and
fairly large offices while talking on the phone and without
loosing their voice connection, HomeRF 2.1 also will support
voice roaming with soft handoff between repeaters.
HomeRF 2.0 supports Ethernet speeds up to 10 Mbps
with fallback speeds and backward compatibility to earlier
versions of HomeRF. Performance can be further enhanced
to about 20 Mbps. The HomeRF WG is evaluating the need
for such enhancements at 2.4 GHz in light of its planned
support of 5 GHz.
A proposed change to Federal Communications Commission
(FCC) Part 15 rules governing the 2.4-GHz ISM band will
allow adaptive frequency hopping. While not legal today,
these proposed techniques allow hoppers such as Bluetooth
and HomeRF to recognize and avoid interference from static
frequency technologies such as Wi-Fi. Since HomeRF
already adjusts its hopping pattern based on interference to
ensure that two consecutive hops do not land on interference, supporting this FCC proposal seems trivial.
The HomeRF WG believes in the peaceful coexistence of 2.4
and 5 GHz since each frequency band and technology has specific strengths that complement each other. Rather than draft
a specification for 5 GHz, the group simply endorses IEEE
802.11a (also known as Wi-Fi5) for high-bandwidth applications such as high-definition video streaming and MPEG2 compression. It plans to write application briefs describing how to
bridge between 2.4- and 5-GHz technologies, including how to
handle differences in quality of service (QoS). This information,
while written for IEEE 802.11a, also can apply to HiperLAN-2,
IEEE 802.11h, and proprietary IEEE 802.11a extensions.
Some analysts expect IEEE 802.11a to eventually take
over as the wireless standard for enterprise offices, gain
needed QoS support from IEEE 802.11e, and start a slow
migration into homes. It already supports 54 Mbps, and proprietary extensions increase performance to about 100
Mbps. But because of the higher frequencies used, IEEE
802.11a has disadvantages in cost, power consumption,
range, and signal attenuation through materials. A combination of HomeRF and IEEE 802.11a brings together the
strengths of both technologies.
Home users have a need for a wireless network that is easy
to use, cost-effective, spontaneously accessible, and can carry
voice and data communications. Certified HomeRF products
are available today from consumer brands such as Compaq,
Intel, Motorola, Proxim, and Siemens through retail, online,
and service provider channels. They come in a variety of form
factors such as USB and PC card adapters, residential gateways, and a growing variety of devices that embed HomeRF.
See also
Digitally Enhanced Cordless Telephony
Spread Spectrum Radio
Wireless Fidelity
i-Mode means “information mode” and refers to a type of
Internet-enabled mobile phone service that is currently
available in Japan from NTT DoCoMo, the world’s largest
cellular provider. With the push of a button, i-mode connects
users to a wide range of online services, many of which are
interactive, including mobile banking, news and stock
updates, telephone directory service, restaurant guide, and
ticket reservations. The i-mode phones also feature the
Secure Sockets Layer (SSL) protocol, which provides encryption for the safe transmission of personal information such
as credit card and bank account numbers.
All services are linked directly to the DoCoMo i-mode portal
Web site. Content can be accessed virtually instantly simply by
pushing the cell phone’s dedicated i-mode button. Once connected, users also can access hundreds of other i-mode sites via
standard Web addresses. Since i-mode is based on packet data
transmission technology, users are charged only for how much
information they retrieve, not by how long they are online.
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Customers can access many different kinds of content,
including news, travel, information, database services, and
entertainment. In addition, i-mode can be used to exchange
e-mail with computers, personal digital assistants (PDAs),
and other i-mode cellular phones. In Japan, the e-mail
address is simply the cellular phone number followed by
@docomo.ne.jp. And since i-mode is always active, e-mails
are displayed automatically when they arrive.
Initially, the transmission speed was only 9.6 kbps, but
this increased to 28.8 kbps in mid-2002. The next phase in
development is underway with the company’s introduction
of first third-generation (3G) wireless service, which delivers data between 64 and 384 kbps. At these rates, it is possible to deliver music or video over wireless networks.
Restaurant location programs also are able to deliver threedimensional maps of the restaurant that describe the
The i-mode service was launched in February 1999, and by
mid-2002, the number of subscribers exceeded 30 million.
Over 800 companies provide information services through imode. In addition, there are over 38,000 i-mode Web sites
that offer content to mobile phone users. This makes i-mode
a worthy contender to the Wireless Application Protocol
(WAP), which is used by almost 22 million users worldwide.
The primary reason for i-mode’s growing success is its simplicity. Unlike the WAP, which provides access to Web content
from cell phones in the United States, content providers catering to the i-mode market can use standard HyperText Markup
Language (HTML) to develop their Web sites. The Web sites are
linked to DoCoMo’s i-mode portal, where users go automatically
on hitting the cell phone’s dedicated i-mode button. An i-mode
cell phone typically weighs less than 4 ounces, has a comparatively large liquid-crystal display, and features a four-point navigation button that moves a pointer on the display.
The i-mode platform also supports Java technology. Java
supports stand-alone applications that can be downloaded
and stored, eliminating the need to continually connect to a
Web site to play video games, for example. Java also supports
agent-type applications for constantly changing information,
such as stock quotes, weather forecasts, and sports scores,
that can be updated automatically at set times by the agent.
i-Mode services are now available in the United States. AT&T
Wireless’ mMode service is based on the i-mode technology
developed by Japan’s NTT DoCoMo. mMode provides consumers with a variety of communication, information, and
entertainment services. The services include e-mail, news,
weather, sports, and games. Pricing is based on volume of
data, with plans starting at $2.99 per month. The service
works over the General Packet Radio Service (GPRS) network of AT&T Wireless using cell phones that are specifically
designed to support i-mode. Other thin application environments include Binary Runtime Environment for Wireless
BREW) from Qualcomm, Java 2 Micro Edition (J2ME) from
Sun Microsystems, and the WAP from the WAP Forum.
See also
General Packet Radio Service
Wireless Application Protocol
Incumbent Local Exchange Carriers (ILECs) is a term that
refers to the 22 former Bell Operating Companies (BOCs)
divested from AT&T in 1984, as well as Cincinnati Bell,
Southern New England Telephone (SNET), and the larger
independent telephone companies of GTE and United
Telecommunications. In addition, some 1300 smaller telephone companies are also in operation, serving mostly rural
areas. These, too, are considered incumbents, but the small
markets they serve do not attract much competition.
After being spun off by AT&T in 1984, the BOCs were
assigned to seven regional holding companies: Ameritech, Bell
Atlantic, BellSouth, Nynex, Pacific Telesis, Southwestern
Bell Communications (SBC), and US West. Over the years,
some of these regional companies merged to the point that
today only four are left. Bell Atlantic and Nynex were the first
to merge in 1994. Bell Atlantic also completed a $53 billion
merger with GTE in mid-1999 and changed its name to
Verizon. SBC Communications merged with Pacific Telesis in
1997 and then Ameritech in 1999. It also acquired Southern
New England Telephone (SNET).
Regulatory Approval
All the mergers passed regulatory approval at the state and
national level. The Federal Communications Commission
(FCC) approves mergers with input from the Department of
Justice (DoJ). In the case of the SBC-Ameritech merger, the
FCC imposed 28 conditions on SBC in exchange for approving the transaction.
The approval package contained a sweeping array of conditions designed to make SBC-Ameritech’s markets the
most open in the nation, boosting local competition by providing competitors with the nation’s steepest discounts for
resold local service and full access to operating support systems (OSS).
It also required SBC to accelerate by 6 months its entry
into new markets, forcing the company to compete in 30 new
markets within 30 months after completion of the merger.
The FCC’s rationale was that increased competition in outof-region territories would help offset reduced competition in
the SBC-Ameritech service areas.
The conditions also required stringent performance monitoring, reporting, and enforcement provisions that could trigger more than $2 billion in fines if these goals were not met.
Fortunately for SBC, the agreement required it to serve only
three customers in each out-of-region market. According to
SBC, it will not begin to seriously market its out-of-region services until it has obtained approval to offer long-distance services in its 13 home states.
The monopoly status of the ILECs officially ended with passage of the Telecommunications Act of 1996. Not only can
other types of carriers enter the market for local services in
competition with them, but also their regional parent companies can compete in each other’s territories. Through
mergers, the reasoning went, the combined companies can
enter out-of-region markets on a broad scale quickly and efficiently enough to become effective national competitors.
Unfortunately, this has not occurred on a significant
scale. In fact, the lack of out-of-region competition among
the Baby Bells means that consumers and businesses do
not have as much choice in service providers, especially
now that many Competitive Local Exchange Carriers
(CLECs) are being hit hard by financial problems and the
lack of venture capital. The ILECs are more concerned with
being able to qualify for long-distance services in their own
markets so that they can bundle local and long-distance
services and Internet access—a package few, if any, competitors would be able to match.
See also
Competitive Local Exchange Carriers
Interexchange Carriers
Local Exchange Carriers
Infrared (IR) technology is used to implement wireless local
area networks (LANs) as well as the wireless interface to
connect laptops and other portable machines to the desktop
computer equipped with an IR transceiver. IR LANs are proprietary in nature, so users must rely on a single vendor for
all the equipment. However, the IR interface for connecting
portable devices with the desktop computer is standardized
by the Infrared Data Association (IrDA).
Infrared LANs
IR LANs typically use the wavelength band between 780 and
950 nanometers (nm). This is due primarily to the ready
availability of inexpensive, reliable system components.
There are two categories of IR systems that are commonly
used for wireless LANs. One is directed IR, which uses a
very narrow laser beam to transmit data over one to three
miles. This approach may be used for connecting LANs in
different buildings. Although transmissions over laser beam
are virtually immune to electromechanical interference and
would be extremely difficult to intercept, such systems are
not widely used because their performance can be impaired
by atmospheric conditions, which can vary daily. Such
effects as absorption, scattering, and shimmer can reduce
the amount of light energy that is picked up by the receiver,
causing the data to be lost or corrupted.
The other category is nondirected IR, which uses a less
focused approach. Instead of a narrow beam to convey the
signal, the light energy is spread out and bounced off narrowly defined target areas or larger surfaces such as office
walls and ceilings.
Nondirected IR links may be further categorized as either
line of sight or diffuse (Figure I-1). Line-of-sight links
require a clear path between transmitter and receiver but
generally offer higher performance.
Line of Sight
Figure I-1 Line-of-sight versus diffuse configurations for infrared links.
The line-of-sight limitation may be overcome by incorporating a recovery mechanism in the IR LAN that is managed
and implemented by a separate device called a “multiple
access unit” (MAU) to which the workstations are connected.
When a line-of-sight signal between two stations is temporarily blocked, the MAU’s internal optical link control circuitry automatically changes the link’s path to get around
the obstruction. When the original path is cleared, the MAU
restores the link over that path. No data are lost during this
recovery process.
Diffuse links rely on light bounced off reflective surfaces.
Because it is difficult to block all the light reflected from
large surface areas, diffuse links are generally more robust
than line-of-sight links. The disadvantage of diffused IR is
that a great deal of energy is lost, and consequently, the data
rates and operating distances are much lower.
System Components
Light-emitting diodes (LEDs) or laser diodes (LDs) are used
for transmitters. LEDs are less efficient than LDs, typically
exhibiting only 10 to 20 percent electrooptical power conversion efficiency, while LDs offer an electrooptical conversion
efficiency of 30 to 70 percent. However, LEDs are much less
expensive than LDs, which is why most commercial systems
use them.
Two types of low-capacitance silicon photodiodes are used
for receivers: positive-intrinsic-negative (PIN) and avalanche.
The simpler and less expensive PIN photodiode is typically
used in receivers that operate in environments with bright
illumination, whereas the more complex and more expensive
avalanche photodiode is used in receivers that must operate
in environments where background illumination is weak. The
difference in the two types of photodiodes is their sensitivity.
The PIN photodiode produces an electric current in proportion to the amount of light energy projected onto it.
Although the avalanche photodiode requires more complex
receiver circuitry, it operates in much the same way as the
PIN diode, except that when light is projected onto it, there
is a slight amplification of the light energy. This makes it
more appropriate for weakly illuminated environments. The
avalanche photodiode also offers a faster response time than
the PIN photodiode.
Operating Performance
Current applications of IR technology yield performance
that matches or exceeds the data rate of wire-based LANs:
10 Mbps for Ethernet and 16 Mbps for Token Ring. However,
IR technology has a much higher performance potential—
transmission systems operating at 50 and 100 Mbps have
already been demonstrated.
Because of its limited range and inability to penetrate walls,
nondirected IR can be easily secured against eavesdropping.
Even signals that go out windows are useless to eavesdroppers
because they do not travel far and may be distorted by impurities in the glass as well as by the glass’s placement angle.
IR offers high immunity from electromagnetic interference, which makes it suitable for operation in harsh environments like factory floors. Because of its limited range and
inability to penetrate walls, several IR LANs may operate in
different areas of the same building without interfering with
each other. Since there is less chance of multipath fading
(large fluctuations in received signal amplitude and phase),
IR links are highly robust.
Many indoor environments have incandescent or fluorescent lighting that induces noise in IR receivers. This is overcome by using directional IR transceivers with special filters
to reject background light.
Media Access Control
IR supports both contention-based and deterministic media
access control techniques, making it suitable for Ethernet as
well as Token Ring LANs.
To implement Ethernet’s contention protocol, carriersense multiple access (CSMA), each computer’s IR transceiver is typically aimed at the ceiling. Light bounces off the
reflector in all directions to let each user receive data from
other users (Figure I-2). CSMA ensures that only one station
can transmit data at a time. Only the stations to which packets are addressed can actually receive them.
Figure I-2 Ethernet implementation using diffuse IR.
Deterministic media access control relies on token passing
to ensure that all stations in turn get an equal chance to
transmit data. This technique is used in Token Ring LANs,
where each station uses a pair of highly directive (line-ofsight) IR transceivers. The outgoing transducer is pointed at
the incoming transducer of a station down line, thus forming
a closed ring with the wireless IR links among the computers
(Figure I-3). With this configuration, much higher data rates
can be achieved because of the gain associated with the directive IR signals. This approach improves overall throughput,
since fewer bit errors will occur, which minimizes the need for
Infrared Computer Connectivity
Most notebook computers and personal digital assistants
(PDAs) have IR ports. Every major mobile phone brand has
Figure I-3 Token Ring implementation using line-of-sight IR.
at least one IR-enabled handset, and even wristwatches are
beginning to incorporate IR data ports. IR products for computer connectivity conform to the standards developed by
the Infrared Data Association (IrDA). The standard protocols include Serial Infrared (SIR) at 115 kbps, Fast Infrared
(FIR) at 4 Mbps, and Very Fast Infrared (VFIR) at 16 Mbps.
The complete IrDA protocol suite contains the following
mandatory protocols and optional protocols.
Mandatory protocols:
Infrared Physical Layer Specifies IR transmitter and
receiver optical link, modulation and demodulation
schemes, and frame formats.
Infrared Link Access Protocol (IrLAP) Has responsibility for link initiation, device address discovery, address
conflict resolution, and connection startup. It also
ensures reliable data delivery and provides disconnection services.
Infrared Link Management Protocol (IrLMP) Allows multiple software applications to operate independently and
concurrently, sharing a single IrLAP session between a
portable PC and network access device.
Information Access Service (IAS) Used along with IrLMP
and IrLAP, this protocol resolves queries and responses
between a client and server to determine the services each
device supports.
Optional protocols:
Infrared Transport Protocol (IrTTP) or Tiny TP Has
responsibility for data flow control and packet segmentation and reassembly.
IrLAN Defines how a network connection is established
over an IrDA link.
IrCOM Provides COM (serial and parallel) port emulation
for legacy COM applications, printing, and modem
IrOBEX Provides object exchange services similar to the
HyperText Transfer Protocol (HTTP) used to move information around the Web.
IrDA Lite Provides methods of reducing the size of IrDA code
while maintaining compatibility with full implementations.
IrTran-P Provides image exchange for digital image capture devices/cameras.
IrMC Specifies how mobile telephony and communication
devices can exchange information. This includes phonebook, calendar, and message data.
In addition, there is a protocol called IrDA Control that
allows cordless peripherals such as keyboards, mice, game
pads, joysticks, and pointing devices to interact with many
types of intelligent host devices. Host devices include PCs,
home appliances, game machines, and television/Web settop boxes.
An extension called Very Fast IR (VFIR) provides a maximum transfer rate of 16 Mbps, a fourfold increase in speed
from the previous maximum data rate of 4 Mbps. The extension provides users with faster throughput without an
increase in cost and is backward compatible with equipment
employing the previous data rate. The higher speed is
intended to address the new demands of transferring large
image files between digital cameras, scanners, and PCs.
Table I-1 summarizes the performance characteristics of the
IrDA’s IR standard.
The IrDA has developed a “point and pay” global wireless
point-of-sale (POS) payment standard for hand-held devices,
called Infrared Financial Messaging (IrFM). In an electronic
wallet application, consumers use their IR-enabled PDAs to
make purchases at the point of sale. Users “beam” their
financial information to pay for a purchase and receive a digital receipt. The IrFM protocol defines payment usage models, profiles, architecture, and protocol layers to enable
hardware, software, and systems designers to develop IrFMcompliant products and ensure interoperability and compat-
TABLE I-1 Performance Characteristics of the Infrared Data
Association’s Infrared Standard
Connection type
Transmission power
Data rate
Supported devices
Data security
Infrared, narrow beam (30º angle or less)
Optical, 850 nanometers (nm)
100 milliwatts (mW)
Up to 16 Mbps using Very Fast Infrared
Up to 3 feet (1 meter)
The short range and narrow angle of the IR
beam provide a simple form of security; otherwise, there are no security capabilities at
the link level.
Each device has a 32-bit physical ID that is
used to establish a connection with another
ibility globally. IrFM uses IrDA’s Object Exchange (OBEX)
protocol to facilitate interoperability between devices.
The Infrared Data Association has formed a Special
Interest Group (SIG) to produce a standard for interappliance MP3 data exchange using IR technology. The popularity
of MP3-capable appliances begs for a standard connection
between the MP3 players, computers, and the network,
allowing consumers to easily move music from device to
device without a cable or docking port. The hand-held player
should be able to transfer a song into a car stereo or home
entertainment system. The MP3 SIG is identifying concerns
specific to transferring MP3 data and building solutions into
the protocol. Among the issues that must be addressed is how
to identify copyrighted content and describe distribution
restrictions to handle the MP3 content appropriately.
IR’s primary impact will take the form of benefits for mobile
professional users. It enables simple point-and-shoot
connectivity to standard networks, which streamlines users’
workflow and allows them to reap more of the productivity
gains promised by portable computing. IrDA technology is
supported in over 100 million electronic devices, including
desktop, notebook, and palm PCs; printers; digital cameras;
public phones/kiosks; cellular phones; pagers; PDAs; electronic books; electronic wallets; and other mobile devices.
When used on a LAN, IR technology also confers substantial benefits to network administrators. IR is easy to install
and configure, requires no maintenance, and imposes no
remote-access tracking hassles. It does not disrupt other
network operations, and it provides data security. And
because it makes connectivity so easy, it encourages the use
of high-productivity network and groupware applications on
portables, thus helping administrators amortize the costs of
these packages across a larger user base.
See also
Spread Spectrum Radio
Wireless LANs
Introduced in 1994 by Motorola, Integrated Digital Enhanced
Network (iDEN) is a wireless network technology designed
for vertical market mobile business applications. iDEN operates in the 800-MHz, 900-MHz, and 1.5-GHz bands and is
based on Time Division Multiple Access (TDMA) and Global
System for Mobile (GSM) architectures. It uses Motorola’s
Vector Sum Excited Linear Predictors (VSELP) voice encoder
for compression and quadrature amplitude modulation
(QAM) to deliver 64 kbps over a 25-kHz channel.
iDEN is promoted as being “four-in-one,” allowing users
to take advantage of two-way digital radio, digital wireless
phone, alphanumeric messaging, and data, fax, and Internet
capabilities with one pocket-sized digital handset. This eliminates the need to carry around multiple communication
devices and the time-consuming task of synchronizing them.
The iDEN phones are full-featured business phones that
provide features such as call forwarding, call hold, automatic answer, and speakerphone. Using the group call feature, users can communicate with one or hundreds of people
with the push of a single button without having to set up a
conference call or waste time with costly individual calls.
The data-ready phones also provide fax and e-mail capabilities and access to the Internet.
Motorola iDEN phones incorporate a number of valuable
messaging services, including voice messaging, text messaging, and alphanumeric paging. This gives the user the ability to receive messages even when the phone is turned off.
Some iDEN phones are voice-activated and allow the user to
record voice memos for playback later.
The newest phones, such as the i90c, feature J2ME technology, enabling users to download interactive content and
applications—from business tools to graphically rich games.
Users select “Java Apps” from the phone’s main menu, and
the applications execute directly on the handset instead of
on a server within the network, as is the case with applications based on the complementary Wireless Application
Protocol (WAP).
Call Setup
When a mobile radio places a call on an iDEN system, it goes
through a series of system handshakes to establish the call
as follows:
When the mobile radio is powered up, it scans and locks
onto a control channel.
The mobile radio registers on the system.
When it initiates a call, the mobile radio places a service
request on the control channel.
The fixed end system assigns the mobile radio to the dedicated control channel.
The mobile radio uses the dedicated control channel to
transmit the information required by the fixed end system to complete the call.
The fixed end system assigns the mobile radio to a traffic
channel that is used for communication of voice or data.
Each time the mobile radio initiates or receives a call, it
measures the strength of the received signal. Based on this
measurement and the power control constant defined on the
control channel, it adjusts its transmit power level to a level
just high enough to ensure clear reception of its signal by the
intended recipients.
Future Directions
In keeping with the industry trend of upgrading wireless
networks to third-generation (3G) technologies, Nextel and
Motorola are working to double the voice capacity of iDEN
and implement data compression on the network.
The two most important factors driving carriers to
upgrade to 3G technologies are the need to increase voice
capacity and deliver packet data service at acceptable
speeds. After considering its various technology and strategic options, Nextel decided to leverage its existing infrastructure by making enhancements to its iDEN network
rather than overlay a standards-based technology onto the
proprietary Motorola iDEN platform.
Nextel also expects to provide a two- to fivefold increase in
the end-user experience of most Web-enabled and general
office data applications. While 2.5G technologies like
General Packet Radio Service (GPRS) are capable of achieving up to 115 or 144 kbps with extensions to TDMA or
CDMA, respectively, Nextel expects to achieve data speeds
up to 60 to 70 kbps with the addition of data compression.
iDEN is designed to give the mobile user quick access to
information without having to carry around several devices.
Currently, iDEN systems work in more than a dozen countries, but only two service providers in the United States use
iDEN in their wireless networks: Nextel and Southern
See also
Code Division Multiple Access
General Packet Radio Service
Global System for Mobile Telecommunications
Time Division Multiple Access
Although the concept of interactive television (ITV) has been
around for more than two decades, the market is still emerging in fits and starts, with no clear business model in sight.
The term ITV refers to a set of real and potential capabilities
that are designed to improve the television viewing experience. But platform makers, application developers, content
providers, and the major networks differ in their opinions of
what capabilities will accomplish this.
Numerous entrants have appeared on the scene with
offerings that incorporate a hodge-podge of different functions. Despite the feverish pace of innovation, a consensus
seems to be forming that ITV, at a minimum, should include
Internet-on-the-TV-set, video-on-demand services, interactive program guides, and a consumer electronic device that
permits viewers to interact with their television sets. What
remains to be seen is whether any particular enhancement
or combination of potential ITV features will succeed in the
To date, many attempts at ITV have failed either because
of lack of consumer interest or limits of the technology.
Nevertheless, there seems to be industry-wide interest in
pursuing interactive TV, due in large part to technical
advancements that make all things possible. And then there
is the persistent conviction that consumers now have a
greater interest and appreciation for interactive services in
general, which equates to “pent-up demand.”
One of the largest players in the ITV market is Microsoft,
which has garnered close to 1 million subscribers for its
WebTV interactive service. WebTV provides consumers with
an interactive electronic program guide, interactive content,
Internet access, e-mail, chat, and Microsoft’s own instant
messenger. But after 5 years, WebTV’s growth has flattened
out, indicating that something is wrong. The service was
expected to have 1 million subscribers by year-end 1998 and
eventually become as ubiquitous as the VCR. As of mid2001, WebTV still had about the same number of subscribers, despite several major upgrades.
Interactive Applications
There is already a level of “enhanced” television possible
through the traditional set-top box. Viewers can order payper-view movies, read messages from their service provider,
and search through the evening’s programming guide for
their favorite sitcom. With the addition of another device
and a subscription fee, viewers can access the Internet from
their televisions, as with WebTV. And with still another
device and subscription fee, a VCR-like device searches and
records television programs automatically for playback at a
convenient time, as with TiVo’s offering. Moving from
enhanced television to interactive television promises to
offer more interesting applications.
Among the possible ITV applications are home shopping,
bank account access, e-mail, advertised product information,
voting in viewer surveys, and playing along with game
shows. Another application for ITV is the delivery of
enhanced content. While watching a sports program, for
example, viewers can call up more information about the
game, buy merchandise, or click on pop-up advertisements
of interest (Figure I-4).
Telephone calls can be made through the television as
well. Subscribers can use a television set-top box equipped
with a speakerphone and voice over Internet Protocol (VoIP)
software to make telephone calls through a graphical dial
pad that appears on the screen. Notification of incoming
calls is displayed on the screen, and the viewer can decide to
take the call or let it go to a voice mailbox.
Online gaming in Europe and the United States is
expected to fuel growth of the ITV industry. The apparent
appeal of ITV games is that they allow television viewers to
participate in contests linked to popular TV shows or a series
Figure I-4 With interactive television, viewers can call up more information about a sports program, shop for merchandise, or click on advertisements of interest.
they watch on a regular basis. Revenues can be generated
through advertisers or by charging users a nominal fee to
enter these contests in the hope of winning prizes or participating in live shows.
Advertisers are intrigued with the information-gathering
potential of ITV technology, gleaned from testing television
programs, hosts or trailers, and advertising spots. A viewer
panel would receive questions and provide answers directly
onto their television screens. A special set-top box connects
the television via the Internet to a research database. This
method allows for better representation, faster response and
processing of results, and lowers the costs of collecting this
kind of information. With the results, advertisers could target their messages more effectively.
Market Complexity
The complicated nature of the ITV market, in which different cable operators use different set-top boxes with different
operating systems, has hindered market growth so far. In
addition, cable carriers, advertisers, and the TV networks
seem to be having difficulty figuring out how to make ITV
pay off. This is reminiscent of the dot-com market a few
years ago, where companies could not quite figure out how to
make money on the services they put up on the Web.
Even the top players in the ITV market remain uncertain
about it. This was illustrated in mid-2001, when AT&T
scaled back its plans for the service. Microsoft had pumped
$5 billion into AT&T’s cable operation in 1999 with the hope
of creating an ITV service for about 10 million users. Things
never really progressed beyond the planning stage, as
Microsoft experienced delays in getting the operating system ready for its ITV systems based on Motorola’s DCT5000
set-top box.
Meanwhile, AT&T did additional research and concluded
that the average consumer did not consider surfing the Web
as a priority for ITV, which is Microsoft’s strong point.
Instead, consumers expressed the desire for video on demand
(VoD) and personal video recorders that automatically save
TV shows to a hard drive. AT&T then scaled back its service
model and considered software from other vendors before
launching its ITV service.
Potential Market Barriers
A possible clue about the difficulties that await ITV comes
from the lackluster performance of WebTV. Microsoft
acquired the Internet-on-TV service in 1997, and since then,
the number of subscribers to the service reportedly has
reached a peak of about 1 million.
Some of WebTV’s lack of success has been blamed on poor
corporate vision. But the cost of innovation may have played
a part as well. Adding more functionality forces higher prices
for equipment and service, which is not a good thing to do
when market growth is on the decline and the economy is
One source of trouble for ITV companies has been how to
keep costs low enough to be attractive. Industry surveys
reveal that less than 3 percent of consumers would pay more
than $300 for a set-top box that supports time-shifting and
personalized TV services, as well as several other leading
ITV applications. Only 6 percent of all consumers would pay
more than $9 per month to subscribe to a service that offers
such capabilities. With this much consumer resistance,
there is not much hope of ITV achieving widespread success
anytime soon, and key players in the market will continue to
Among the over-40 population, ITV comes under more
severe scrutiny from the content perspective. To this market
segment, ITV does not appear to improve content—it is perceived merely as a way to throw more of the same low-quality stuff at viewers while asking them to pay more for it.
There will be a limited number of venues where ITV will
succeed. Interactive-friendly areas include sports, game
shows, and news, but interactivity in drama and sitcom
venues will be more difficult to penetrate. If it turns out that
ITV just offers more ways for advertisers to improve the targeting of their messages, however interactive, market penetration will be limited.
This also raises the privacy issue, even among young people, who are more likely to be receptive to ITV. The ITV service providers will count on subscriber revenues as well as
advertising dollars. Privacy advocates are concerned that
ITV combines the worst aspects of the Internet and mass
media because the new systems are being designed to track
not only every activity of users as they surf the Net but also
the programs and commercials they watch. They fear that if
ITV systems are to realize their promise as the “advertising
nirvana” for marketers, privacy necessarily must collapse as
ITV becomes a spy in the home, collecting information on
age, discretionary income, and parental status, along with
psychographic and demographic data, that will be analyzed
and made available to marketers, advertisers, programmers, and others.
Even the more recent reports on the ITV market have not
factored in the dismal state of the global economy and the
consequent decline in discretionary income for new and
novel forms of entertainment. The interactive TV industry is
not immune to general economic conditions, and the computer and telecommunications markets have been hit the
hardest throughout 2001 and 2002.
Consumer demand for ITV has proved to be too complex for
any one product or service to appeal to everyone. The players in this market are realizing that certain consumer segments have very different preferences and attitudes toward
ITV. The challenges for these companies is to understand
how consumers differ, why these differences exist, and how
they can determine the success of a given product or service.
Failure to do so will inhibit market growth, despite all the
optimistic revenue projections and technologies that seemingly can fulfill any request for entertainment and information—passively or interactively.
See also
High-Definition Television
Interactive Video and Data Service
Interactive Video and Data Service (IVDS) is a point-to-multipoint, multipoint-to-point, short-distance communication
service that operates in the 218- to 218.5-MHz and 218.5- to
219-MHz frequency bands. In September 1993, the FCC
assigned the licenses for IVDS by lottery in the top 10 markets. The following year, two licenses per market were
offered for auction at the same time, with the highest bidder
given a choice between the two available licenses, and the
second highest bidder winning the remaining license. More
than 95 percent of all IVDS licenses were won by small businesses or businesses owned by members of minority groups
or women. Additional auctions, ending in 1997, were held for
the available spectrum in other markets.
As envisioned, an IVDS licensee would be able to use IVDS to
transmit information and product and service offerings to its
subscribers and receive interactive responses. Potential applications included ordering goods or services offered by television services, viewer polling, remote meter reading, vending
inventory control, and cable television theft deterrence. An
IVDS licensee was able to develop other applications without
specific approval from the FCC. An IVDS channel, however,
was insufficient for the transmission of conventional fullmotion video.
Initially, mobile operation of IVDS was not permitted. In
1996, however, the FCC amended its rules to permit IVDS
licensees to provide mobile service to subscribers. This
action authorized mobile operation of response transmitter
units (subscriber units) operated with an effective radiated
power of 100 milliwatts or less. The FCC found that this
change would increase the flexibility of IVDS licensees to
meet the communications needs of the public without
increasing the likelihood of interference with TV channel 13,
which was of concern at the time.
According to the FCC’s rules at the time IVDS spectrum
was awarded, licenses cancel automatically if a licensee does
not make its service available to at least 30 percent of the population or land area within the service area within 3 years of
grant of the system license. Each IVDS system licensee had to
file a progress report at the conclusion of 3- and 5-year benchmark periods to inform the FCC of the construction status of
the system. This arrangement was intended to reduce the
attractiveness of licenses to parties interested in them only as
a speculative vehicle.
The spectrum for IVDS was initially allocated in 1992 to provide interactive capabilities to television viewers. This did
not occur largely because the enabling technology was too
expensive and market demand too low or nonexistent. IVDS
is now known as 218- to 219-MHz service. In September
1999, the FCC revised its rules for the 218- to 219-MHz service to maximize the efficient and effective use of this frequency band. The FCC simply reclassified service from a
strictly private radio service—one that is used to support the
internal communications requirements of the licensee—to a
service that can be used in both common carrier and private
operations. Licensees are now free to design any service
offering that meets market demand. In addition, licensees
now have up to 10 years from the date of the license grant to
build out their service without meeting the 3- and 5-year
construction benchmarks.
See also
Interactive Television
Local Multipoint Distribution Service
Multichannel Multipoint Distribution Service
Interexchange Carriers (IXCs), otherwise known as “longdistance carriers,” include the big three—AT&T, Worldcom,
and Sprint—all of which also operate wireless networks and
are migrating them to 3G capabilities.
In addition to providing long-distance telephone service
over wired and wireless networks, the IXCs offer business services like Integrated Services Digital Network (ISDN), Frame
Relay, leased lines, and a variety of other digital services.
Many IXCs are also Internet service providers (ISPs), which
offer Internet access services, virtual private networks, electronic mail, Web hosting, and other Internet-related services.
Traditionally limited to providing service between local access
and transport areas (LATAs), the Telecommunications Act of
1996 allows IXCs to offer local exchange services in competition with the Incumbent Local Exchange Carriers
(ILECs). But because the ILECs charge too much for local
loop connections and services and do not deliver them in a
consistently timely manner, the larger IXCs have implemented technologies that allow them to bypass the local
exchange. Among the methods IXCs use to bypass the local
exchange include CATV networks and broadband wireless
technologies, such as Local Multipoint Distribution
Service (LMDS) and Multichannel Multipoint Distribution
Service (MMDS).
With regard to cable, AT&T, for example, has acquired the
nation’s two largest cable companies, TCI and MediaOne, to
bring local telephone services to consumers, in addition to
television programming and broadband Internet access. As
these bundled services are introduced in each market, they
are provided to consumers at an attractive price with the
added convenience of a single monthly bill. Sprint uses
MMDS to offer Internet access to consumers and businesses
that are out of range for Digital Subscriber Line (DSL) services. XO Communications, a nationwide integrated communications provider (ICP) uses LMDS to reach beyond its
metropolitan fiber loops to reach buildings that are out of the
central business districts.
Long-Distance Market
In January 2001, the FCC released the results of a study on
the long-distance telecommunications industry. Among the
findings from the report:
In 1999, the long-distance market had more than $108 billion in revenues, compared to $105 billion in 1998. In
1999, long-distance carriers accounted for over $99 billion
and local telephone companies accounted for the remaining $9 billion.
Interstate long-distance revenues increased by 12.8 percent in 1999 compared to 1.5 percent the year before.
Since 1984, international revenues have grown more than
fivefold from less than $4 billion in 1984 to over $20 billion in 1999. The number of calls has increased from about
half a billion in 1984 to almost 8 billion in 1999.
In 1984, AT&T’s market share was about 90 percent of the
toll revenues reported by long-distance carriers. By 1999,
AT&T’s market share had declined to about 40 percent,
WorldCom’s share was 25 percent, Sprint’s was 10 percent, and more than 700 other long-distance carriers had
the remaining quarter of the market.
According to a sampling of residential telephone bills, in
1999 the average household spent $64 monthly on telecommunications. Of this amount, $21 was for services provided
by long-distance carriers, $34 for services by local exchange
carriers, and the remainder for services by wireless carriers.
According to the same sampling of residential telephone
bills, 38 percent of toll calls in 1999 were interstate and
accounted for 50 percent of toll minutes. Also, 33 percent of
residential long-distance minutes were on weekdays, 30
percent on weekday evenings, and 37 percent on weekends.
Growing competition in long-distance services has eroded
AT&T’s market share from its former monopoly level to about
40 percent. With this competition has come increasing availability of low-cost calling plans for a broad range of consumers. As a result, average revenue per minute earned by
carriers has been declining steadily for several years, while
long-distance usage has increased substantially to make up
for that revenue shortfall. As more ILECs get permission from
the FCC to enter the in-region long-distance market, IXCs
will come under increasing competitive pressure because the
ILECs will be able to bundle local and long-distance calling
and Internet access into attractively priced service packages.
See also
Competitive Local Exchange Carriers
Incumbent Local Exchange Carriers
The International Telecommunication Union (ITU) has put
together a framework for 3G mobile communications systems
that are capable of bringing high-quality mobile multimedia
services to a worldwide mass market based on a set of
standardized interfaces. Known as International Mobile
Telecommunications-2000 (IMT-2000), this framework encompasses a small number of frequency bands, available on a globally harmonized basis, that make use of existing national and
regional mobile and mobile-satellite frequency allocations.
IMT-2000 is the largest telecommunications project ever
attempted, involving regulators, operators, manufacturers,
media, and information technology (IT) players from all
regions of the world as they attempt to position themselves
to serve the needs of an estimated 2 billion mobile users
worldwide by 2010. Originally conceived in the early 1990s
when mobile telecommunications provided only voice and
low-speed circuit-switched data, the IMT-2000 concept has
adapted to the changing telecommunication environment as
its development progressed. In particular, the advent of
Internet, intranet, e-mail, e-commerce, and video services
has significantly raised user expectations of the responsiveness of the network and the terminals and, therefore, the
bandwidth of the mobile channel.
Spanning the Generations
Over the years, mobile telecommunications systems have
been implemented with great success all over the world.
Many are still first-generation systems—analog cellular systems such as the Advanced Mobile Phone System (AMPS),
Nordic Mobile Telephone (NMT), and the Total Access
Communication System (TACS). Most systems are now in
the second generation, which is digital in nature. Examples
of digital cellular systems include Global System for Mobile
(GSM) communications, Digital AMPS (DAMPS), and
Japanese Digital Cellular (JDC). Although both first- and
second-generation systems were designed primarily for
speech, they offer low-bit-rate data services as well.
However, there is little or no compatibility between the different systems, even within the same generation.
The spectrum limitations and various technical deficiencies
of second-generation systems and the potential fragmentation
problems they could cause in the future led to research on the
development and standardization of a global 3G platform. The
ITU and regional standards bodies came up with a “family of
systems” concept that would be capable of unifying the various
technologies at a higher level to provide users with global
roaming and voice-data convergence, leading to enhanced services and support for innovative multimedia applications.
The result of this activity is IMT-2000, a modular concept
that takes full account of the trends toward convergence of
fixed and mobile networks and voice and data services. The
3G platform represents an evolution and extension of current GSM systems and services available today, optimized
for high-speed packet data-rate applications, including highspeed wireless Internet services, videoconferencing, and a
host of other data-related applications.
Vendor compliance with IMT-2000 enables a number of
sophisticated applications to be developed. For example, a
mobile phone with color display screen and integrated 3G
communications module becomes a general-purpose communications and computing device for broadband Internet
access, voice, videotelephony, and videoconferencing (Figure
I-5). These applications can be used by mobile professionals
on the road, in the office, or at home. The number of Internet
Protocol (IP) networks and applications is growing fast.
Most obvious is the Internet, but private IP networks (i.e.,
intranets and extranets) show similar or even higher rates of
growth and usage. With an estimated billion Internet users
worldwide expected in 2010, there exists tremendous pentup demand for 3G capabilities.
Figure I-5 This prototype of a 3G mobile phone from
Nokia supports digital mobile multimedia communications, including videotelephony. Using the camera eye in
the top right corner of the phone, along with the thumbnail screen below it, the local user can line up his or her
image so that it can appear properly centered on the
remote user’s phone.
3G networks will become the most flexible means of broadband access because they allow for mobile, office, and residential use in a wide range of public and nonpublic networks.
Such networks can support both IP and non-IP traffic in a
variety of transmission modes, including packet (i.e., IP), circuit-switched (i.e., PSTN), and virtual circuit (i.e., ATM).
Goals of IMT-2000
Under the IMT-2000 model, mobile telephony will no longer
be based on a range of market-specific products but will be
founded on common standardized flexible platforms that
will meet the basic needs of major public, private, fixed, and
mobile markets around the world. This approach should
result in a longer product life cycle for core network and
transmission components and offer increased flexibility and
cost-effectiveness for network operators, service providers,
and manufacturers.
In developing the family of systems that would be capable
of meeting the future communications demands of mobile
users, the architects of IMT-2000 identified several key
issues that would have to be addressed to ensure the success
of the third-generation of mobile systems.
High Speed Any new system must be able to support high-
speed broadband services, such as fast Internet access or
multimedia-type applications. Users will expect to be able to
access their favorite services just as easily from their mobile
equipment as they can from their wire line equipment.
Flexibility The next generation of integrated systems must
be as flexible as possible, supporting new kinds of services
such as universal personal numbering and satellite telephony while providing for seamless roaming to and from
IMT-2000-compatible terrestrial wireless networks. These
and other features will greatly extend the reach of mobile
systems, benefiting consumers and operators alike.
Affordability The system must be as affordable as today’s
mobile communications services, if not more so. Economies
of scale achievable with a single global standard will drive
down the price to users.
Compatibility Any new-generation system has to offer an
effective evolutionary path for existing networks. While the
advent of digital systems in the early 1990s often prompted
the shutting down of first-generation analog networks, the
enormous investments that have been made in developing
the world’s 2G cellular networks over the last decade make
a similar scenario for adoption of 3G systems untenable.
Differentiation In coordinating the design of the IMT-2000
framework, the ITU was mindful of the need to preserve a
competitive domain for manufacturers to foster incentive
and stimulate innovation. Accordingly, the aim of IMT-2000
standards is not to stifle the evolution of better technologies
or innovative approaches but to accommodate them.
Spectrum Allocations
The 2500- to 2690-MHz band was identified by the 2000
World Radio Conference (WRC-2000) as candidate spectrum
for 3G systems, along with the 806- to 960-MHz and 1710- to
1885-MHz bands. The WRC-2000 results allow countries
flexibility in deciding how to implement 3G systems. The
conference recognized, however, that in many countries the
frequency bands identified for 3G systems might already be
in use by equally vital services.
In the United States, the 2500- to 2690-MHz band is
currently used by the Instructional Television Fixed
Service (ITFS) and the Multipoint Distribution Service
(MDS), which are experiencing and are expected to see
significant future growth, particularly in the provision of
new broadband fixed access to the Internet. Given the
ubiquitous nature of ITFS/MDS, the FCC found that sharing of this spectrum for 3G does not appear feasible.
Further, the FCC found that reallocating a portion of the
2500- to 2690-MHz band from incumbent services for new
3G mobile wireless services would raise significant technical and economic difficulties.
The 1710- to 1755-MHz band is now used by federal government operations and is scheduled for transfer to the private sector on a mixed-use basis by 2004. The 2110- to
2150-MHz and 2160- to 2165-MHz bands are currently used
by the private sector for fixed microwave services. The FCC
identified these bands several years ago for reallocation to
emerging technologies.
The 1710- to 1850-MHz band would be the preferred
choice for 3G services. This would partially harmonize U.S.
spectrum allocations with those in use or planned internationally. Harmonization would permit economies of scale
and reduce costs in manufacturing equipment, as well as
facilitate international roaming.
Parts of the 1710- to 1850-MHz band also could be used to
harmonize with 2G GSM systems, which are currently used
extensively throughout the world and are expected to transition eventually to 3G systems. Other parts of the 1710- to
1850-MHz band could be paired with the 2110- to 2150-MHz
band to achieve partial harmonization with spectrum recently
auctioned in Europe and elsewhere for 3G systems.
Although decisions have not yet been finalized on allocating these bands to 3G wireless communications at this writing, it looks as if there is general agreement that this is the
direction that will be pursued. In addition, the FCC is committed to making spectrum available for new advanced wireless services in the United States, as is the World Radio
Conference at the international level.
Radio Interface Technology
A key ingredient of the IMT-2000 framework is the air interface technology for 3G systems. For the radio interface technology, the ITU considered 15 submissions from organizations
and regional bodies around the world. These proposals were
examined by special independent evaluation groups, which
submitted their final evaluation reports to the ITU in
September 1998. The final selection of key characteristics for
the IMT-2000 radio interfaces occurred in March 1999, which
led to the development of more detailed ITU specifications for
The decision of the ITU was to provide essentially a single
flexible standard with a choice of multiple access methods,
which include CDMA, TDMA, and combined TDMA/CDMA—
all potentially in combination with Space Division Multiple
Access—to meet the many different mobile operational environments around the world. Although 2G mobile systems
involve both TDMA and CDMA technologies, very little use is
currently being made of SDMA. However, the ITU expects the
advent of adaptive antenna technology linked to systems
designed to optimize performance in the space dimension to
significantly enhance the performance of future systems.
The IMT-2000 key characteristics are organized, for both
the terrestrial and satellite components, into the radio frequency (RF) part (front end), where impacts are primarily on
the hardware part of the mobile terminal, and the baseband
part, largely defined in software. In addition to RF and baseband, the satellite key characteristics also cover the architecture and the system aspects. According to the ITU, the
use of common components for the RF part of the terminals,
together with flexible capabilities that are primarily software defined in baseband processing, should provide the
mobile terminal functionality to cover the various radio
interfaces needed in the twenty-first century as well as provide economies of scale in their production.
U.S. proposals submitted to the ITU for consideration as the
radio interface technology in the IMT-2000 framework
included wideband versions of CDMA, of which there are
three competing standards in North America: wideband
cdmaOne, WIMS W-CDMA, and WCDMA/NA. All three have
been developed from 2G digital wireless technologies and are
evolving to 3G technologies. Early on,WIMS W-CDMA and
WCDMA/NA, however, were merged into a single proposed
standard and, along with wideband cdmaOne, were submitted to the ITU for inclusion into its IMT-2000 family-ofsystems concept for globally interconnected and interoperable
3G networks. Also submitted to the ITU was a separate proposal for a TDMA-based radio interface. Eventually, all these
proposals were accepted by the ITU and included in the IMT2000 family of standards.
IMT-2000 addresses the key needs of the increasingly
global economy—specifically, cross-national interoperability, global roaming, high-speed transmission for multimedia
applications and Internet access, and customizable personal services. The markets for all of these exist now and
will grow by leaps and bounds through the next millenium.
IMT-2000 puts into place standards that permit orderly
migration from current 2G networks to 3G networks while
providing a growth path to accommodate more advanced
mobile services.
See also
Code Division Multiple Access
Global System for Mobile (GSM) Telecommunications
Time Division Multiple Access
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A relatively new category of wireless communication uses
laser, sometimes called “free-space optics,” operating in the
near-infrared region of the light spectrum. Utilizing coherent
laser light, these wireless line-of-sight links are used in campus environments and urban areas where the installation of
cable is impractical and the performance of leased lines is too
slow. Laser links between sites can be operated at the full
local area network (LAN) channel speed. And unlike
microwave transmission, laser transmission does not require
a Federal Communications Commission (FCC) license, and
data traveling by laser beam cannot be intercepted.
Performance Impairments
The lasers at each location are aligned with a simple bar
graph and tone lock procedure. Fiberoptic repeaters are used
to connect the LANs to the laser units. Alternatively, a bridge
equipped with a fiberoptic to attachment unit interface (AUI)
transceiver may be used. Connections to and from the laser
are made using standard fiberoptic cable, protecting data
from radio frequency interference (RFI) and electromagnetic
interference (EMI). Monitors can be attached to the laser
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units to provide operational status, such as signal strength,
and to implement local and remote loop-back diagnostics.
The reason that laser products are not used very often for
business applications is that transmission is affected by
atmospheric conditions that produce such effects as absorption, scattering, and shimmer. All three can reduce the
amount of light energy that is picked up by the receiver and
corrupt the data being sent.
Absorption refers to the ability of various frequencies to
pass through the air. Absorption is determined largely by the
water vapor and carbon dioxide content of the air along the
transmission path, which, in turn, depends on humidity and
altitude. The gases that form in the atmosphere have many
resonance bands that allow specific frequencies of light to
pass. These transmission windows occur at various wavelengths, such as the visible light range. Another window
occurs at the near-infrared wavelength of approximately 820
nanometers (nm). Laser products tuned to this window are
not greatly affected by absorption.
Scattering has a much greater effect on laser transmission than absorption. The atmospheric scattering of light is
a function of its wavelength and the number and size of scattering particles in the air. The optical visibility along the
transmission path is directly related to the number and size
of these particles. Fog and smog are the main conditions that
tend to limit visibility for optical-infrared transmission, followed by snow and rain.
Shimmer is caused by localized differences in the air’s
index of refraction. This is caused by a combination of factors, including time of day (daytime heat), terrain, cloud
cover, wind, and the height of the optical path above the
source of shimmer. These conditions cause fluctuations in
the received signal level by directing some of the light out of
its intended path. Beam fluctuations may degrade system
performance by producing short-term signal amplitudes
that approach threshold values. Signal fades below these
threshold values result in error bursts.
Vendors have taken steps to mitigate the effects of absorption, scatter, and shimmer. For example, such techniques as
frequency modulation (FM) in the transmitter and an automatic gain control (AGC) in the receiver can minimize the
effects of shimmer. Also, selecting an optical path several
meters above heat sources can greatly reduce the effects of
shimmer. However, all of these distorting conditions can vary
greatly within a short time span or persist for long periods,
requiring onsite expertise to constantly fine-tune the system.
Many businesses simply cannot risk frequent or extended
periods of downtime while the necessary compensating
adjustments are being made. As if all this were not enough,
there are other potential problems to contend with, such as
thermal window coatings and the laser beam’s angle of incidence, both of which can disrupt transmission. These problems are being overcome with newer lasers that operate in
the 1550-nanometer (nm) wavelength. A 1550-nanometer
delivery system is powerful enough to go through windows,
can deliver signals under the fog blanket, and is safe enough
that it does not blind the casual viewer who happens to look
into the beam. Up to 1 Gbps of bandwidth is available with
these systems—the equivalent bandwidth capacity of 660 T1
lines (Figure L-1).
There is also a distance limitation associated with laser.
The link generally cannot exceed 1.5 kilometers (km), and 1
kilometer is preferred. With 1550-nanometer systems, the
practical distance of the link is only 500 meters.
Despite its limitations, laser, or free-space optics, can provide
a valuable last link between the fiber network and the end
user—including as a backup to more conventional methods,
such as fiber. Free-space optics, unlike other transmission
technologies, are not tied to standards or standards development. Vendors simply attach their equipment into existing
fiber-based networks and then use any laser transmission
Figure L-1 Terabeam Magna,
a free-space optics system from
TeraBeam Corp.
methods they like. This encourages innovation, differentiation, and speed of deployment.
See also
Infrared Networking
Local Multipoint Distribution Service (LMDS) is a two-way
millimeter microwave technology that operates in the 27- to
31-GHz range. This broadband service allows communications providers to offer a variety of high-bandwidth services
to homes and businesses, including broadband Internet
access. LMDS offers greater bandwidth capabilities than a
predecessor technology called “Multichannel Multipoint
Distribution Service” (MMDS) but has a maximum range of
only 7.5 miles from the carrier’s hub to the customer
premises. This range can be extended, however, through the
use of optical fiber links.
LMDS provides enormous bandwidth—enough to support
16,000 voice conversations plus 200 channels of television
programming. Figure L-2 contrasts LMDS with the bandwidth available over other wireless services.
Competitive Local Exchange Carriers (CLECs) can deploy
LMDS to completely bypass the local loops of the Incumbent
Local Exchange Carriers (ILECs), eliminating access
charges and avoiding service-provisioning delays. Since the
service entails setting up equipment between the provider’s
PCS (A-C Block)
Digital Audio Radio Service
PCS (D-F Block)
Emergency Medical Radio
Figure L-2 Local Multipoint Distribution Service (LMDS) operates in the
27- to 31-GHz range and offers 1150 MHz of bandwidth capacity, which is
over two times more than all other auctioned spectrum combined.
hub location and customer buildings for the microwave link,
LMDS costs far less to deploy than installing new fiber. This
allows CLECs to very economically bring customer traffic
onto their existing metropolitan fiber networks and, from
there, to a national backbone network.
The strategy among many CLECs is to offer LMDS to owners of multitenant office buildings and then install cable to
each tenant who subscribes to the service. The cabling goes to
an on-premises switch, which is run to the antenna on the
building’s roof. That antenna is aimed at the service provider’s
antenna at its hub location. The line-of-sight wireless link
between the two antennas offers a broadband “pipe” for multiple voice, data, and video applications. Subscribers can use
LMDS for a variety of high-bandwidth applications, including
television broadcast, videoconferencing, LAN interconnection,
broadband Internet access, and telemedicine.
LMDS operation requires a clear line of sight between the carrier’s hub station antenna and the antenna at each customer
location. The maximum range between the two is 7.5 miles.
However, LMDS is also capable of operating without having a
direct line-of-sight with the receiver. This feature, highly
desirable in built-up urban areas, may be achieved by bouncing signals off buildings so that they get around obstructions.
At the receiving location, the data packets arriving at different times are held in queue for resequencing before they are
passed to the application. This scheme does not work well for
voice, however, because the delay resulting from queuing and
resequencing disrupts two-way conversation.
At the carrier’s hub location there is a roof-mounted multisectored antenna (Figure L-3). Each sector of the antenna
receives/transmits signals between itself and a specific customer location. This antenna is very small, some measuring
only 12 inches in diameter. The hub antenna brings the multiplexed traffic down to an indoor switch (Figure L-4) that
processes the data into 53-byte Asynchronous Transfer Mode
(ATM) “cells” for transmission over the carrier’s fiber network. These individually addressed cells are converted back
to their native format before going off the carrier’s network to
their proper destinations—the Internet, Public Switched
Telephone Network (PSTN), or customer’s remote location.
At each customer’s location, there is a rooftop antenna
that sends/receives multiplexed traffic. This traffic passes
through an indoor network interface unit (NIU) that provides the gateway between the RF (radio frequency) components and the in-building equipment, such as a LAN hub,
Private Branch Exchange (PBX), or videoconferencing system. The NIU includes an up/down converter that changes
the frequency of the microwave signals to a lower intermediate frequency (IF) that the electronics in the office equipment can manipulate more easily (and inexpensively).
Spectrum Auctions
In May 1999, the FCC held the last auction for LMDS spectrum. Over 100 companies qualified for the auctions, bidding
against each other for licenses in select basic trading areas
Figure L-3 A multisectored
antenna at the carrier’s hub location transmits/receives traffic
between the antennas at each
customer location.
Figure L-4 A microwave transceiver (top right) handles multiple point-topoint downstream and upstream channels to customers. The transceiver is
connected via coaxial cables to an indoor switch (bottom left) that provides
the connectivity to the carrier’s fiber network. The traffic is conveyed over
the fiber network in the form of 53-byte ATM cells. (Source: Wavtrace, Inc.)
(BTAs). The FCC auctioned two types of licenses in each market: An “A-block” license permits the holder to provision 1150
MHz of spectrum for distribution among its customers, while
a “B-block” license permits the holder to provision 150 MHz.
Most of the A-block licenses in the largest BTAs were won by
major CLECs, while the B-block licenses were taken by
smaller companies, Internet service providers (ISPs), universities, and government agencies. The licenses are granted for
a 10-year period, after which the FCC can take them back if
the holder does not have service up and running.
Development History
Bernard Bossard is generally recognized as the inventor of
LMDS. Bossard, who had worked with microwaves for the
military, believed that he could make point-to-multipoint
video work in the 28-GHz band. Not interested in sending
high-powered, low-frequency signals over long distances,
Bossard focused instead on sending low-powered, high-frequency signals over a short distance. The result was LMDS.
In 1986, he received funding and formed CellularVision with
his financial backers. CellularVision then spun off the technical rights to the technology into a separate subsidiary,
CT&T, that licenses it to other companies.
CellularVision was awarded a pioneer’s preference license
by the FCC for its role in developing LMDS. CellularVision
began operating a commercial LMDS in metropolitan New
York, providing video programming to subscribers in the
Brighton Beach area. In 1998, CellularVision changed its
name to SPEEDUS.COM. The company has a network operations center and recently has been expanding the number
of operating cells in the New York area and now claims more
than 12,000 residential and business subscribers.
SPEED service is delivered via 14 fully functional Internet
broadcast stations in operation under SPEEDUS.COM’s
FCC license covering metropolitan New York. SPEED subscribers are able to browse the Web using the company’s
SPEED modem capable of downstream speeds of up to 48
Mbps, which is 31 times faster than a full T1 line.
In the SPEEDUS.COM system, cable programming is
downlinked from satellites to the company’s head-end facility, where local broadcast transmissions are also received. At
the company’s master control room, the programming signals
are then amplified, sequenced, scrambled, and up-converted
to 28 GHz. The SPEED.COM transmitters and repeaters
then broadcast a polarized FM signal in the 28-GHz band
over a radius of up to 3 miles to subscribers and to adjacent
cells for transmission. A 6-inch-square, highly directional,
flat-plate, window- , roof- , or wall-mounted antenna receives
the scrambled signal and delivers it to the addressable settop converter, which decodes the signals. The subscriber
receives 49 channels of high-quality video and audio programming, including pay-per-view and premium channels.
Over 100 companies own licenses for LMDS. XO Communications (formerly known as Nextlink) is one of the
largest single holders of LMDS licenses in the United States,
having invested over $800 million in such systems, largely
through the acquisition of other companies that held LMDS
licenses. XO is a CLEC and is using LMDS to feed traffic to
its fiber networks. Its approach to building out a city is to
install fiber. In areas where that will take too long or where
permits are too hard to come by, XO will use, in this order,
LMDS, Digital Subscriber Line (DSL), and ILEC facilities.
Potential Problems
A potential problem for LMDS users is that the signals can be
disrupted by heavy rainfall and dense fog—even foliage can
block a signal. In metropolitan areas where new construction is
a fact of life, a line-of-sight transmission path can disappear virtually overnight. For these reasons, many information technology (IT) executives are leery of trusting mission-critical applications to this wireless technology. Service providers downplay
this situation by claiming that LMDS is just one local access
option and that fiber links are the way to go for mission-critical
applications. In fact, some LMDS providers offer fiber as a
backup in case the microwave links experience interference.
There is controversy in the industry about the economics of
the point-to-multipoint architecture of LMDS, with some
experts claiming that the business model of going after lowusage customers is fundamentally flawed and will never justify
the service provider’s cost of equipment, installation, and provisioning. With an overabundance of fiber in the ground and
metropolitan area Gigabit Ethernet services coming online at a
competitive price, the time for LMDS may have come and gone.
In addition, newer wireless technologies like free-air laser hold
a significant speed advantage over LMDS, as does submillimeter transmission in the 60- and 95-GHz bands.
Another problem that has beset LMDS is that the major
license holders have gotten caught up in financial problems,
some declaring Chapter 11 bankruptcy. These carriers built
their networks quickly, incurring massive debt, without lining up customers fast enough. This strategy worked well as
long as the capital markets were willing to continue funding
these companies. But once the capital markets dried up in
2000, so did the wireless providers’ coffers and their immediate prospects. The uncertain future of these financially
strapped carriers has discouraged many companies from
even trying LMDS.
Fiberoptics is the primary transmission medium for broadband connectivity today. However, of the estimated 4.6 million commercial buildings in the United States, 99 percent
are not served by fiber. Businesses are at a competitive disadvantage in today’s information-intensive world unless they
have access to broadband access services, including highspeed Internet access. These businesses, including many
data-intensive high-technology companies, can be served
adequately with LMDS. Despite the financial problems of
LMDS providers, the technology has the potential to become
a significant portion of the global access market, which will
include a mix of many technologies, including DSL, cable
modems, broadband satellite, and fiberoptic systems.
See also
Microwave Communications
Multichannel Multipoint Distribution Service
The FCC in January 2000 created two new classes of noncommercial radio stations, referred to as “low-power frequencymodulated (LPFM) radio services.” LPFM radio services are
designed to serve very localized communities or underrepresented groups within communities.
The LP100 service operates in the power range of 50 to
100 watts and has a service radius of about 3.5 miles. The
LP10 service operates in the power range of 1 to 10 watts
and has a service radius of about 1 to 2 miles. In conjunction
with the new radio services, the FCC adopted interference
protection requirements based on distance separation
between stations. This is intended to preserve the integrity
of existing FM radio stations and safeguard their ability to
transition to digital transmission capabilities.
The FCC put into place minimum distance separations as
the best practical means of preventing interference between
low-power radio and full-power FM stations. It requires minimum distances between stations using the same or first
adjacent channels. However, third adjacent channel and possibly second adjacent channel separations may not be necessary in view of the low power levels of LPFM radio.
License Requirements
Eligible LPFM licensees can be noncommercial government
or private educational organizations, associations, or entities;
nonprofit entities with educational purposes; or government
or nonprofit entities providing local public safety or transportation services. However, LPFM licenses will be awarded
throughout the FM radio band and will not be limited to the
channels reserved for use by noncommercial educational
radio stations.
To further its goals of diversity and creating opportunities
for new voices, no existing broadcaster or other media entity
can have an ownership interest or enter into any program or
operating agreement with any LPFM station. In addition, to
encourage locally originated programming, LPFM stations
will be prohibited from operating as translators.
To foster local ownership and diversity, during the first 2
years of LPFM license eligibility, licensees will be limited to
local entities certifying that they are physically headquartered, have a campus, or have 75 percent of their board members residing within 10 miles of the station they seek to
operate. During this time, no entity may own more than one
LPFM station in any given community. After 2 years from the
date the first applications are accepted, in order to bring into
use whatever low-power stations remain available but unapplied for, applications will be accepted from nonlocal entities.
For the first 2 years, no entity will be permitted to operate
more than one LPFM station nationwide. After the second
year, eligible entities will be able to own up to five stations
nationwide, and after 2 more years, up to 10 nationwide.
LPFM stations are licensed for 8-year renewable terms.
These licenses are not transferable. Licensees receive fourletter call signs with the letters LP appended.
In the event multiple applications are received for the
same LPFM license, the FCC will implement a selection
process that awards applicants one point each for
Certifying an established community presence of at least
2 years prior to the application
Pledging to operate at least 12 hours daily
Pledging to air at least 8 hours of locally originated programming daily
If applicants have the same number of points, time-sharing proposals will be used as a tiebreaker. Where ties have
not been resolved, a group of up to eight mutually exclusive
applicants will be awarded successive license terms of at
least 1 year for a total of 8 years. These 8-year licenses will
not be renewable.
LPFM stations will be required to broadcast a minimum of
36 hours per week, the same requirement imposed on fullpower noncommercial educational licensees. They will be subject to statutory rules, such as sponsorship identification,
political programming, prohibitions of airing obscene or indecent programming, and requirements to provide periodic call
sign announcements. They also will be required to participate
in the national Emergency Alert System.
According to the FCC, the new LPFM service will enhance
community-oriented radio broadcasting. During the proceedings leading up to the new classes of radio service, broad
national interest in LPFM service was demonstrated by the
thousands of comments received from state and local government entities, religious groups, students, labor unions, community organizations, musicians, and others supporting the
introduction of a new LPFM service. The FCC expects that
the local nature of the LPFM service, coupled with the eligibility and selection criteria, will ensure that LPFM licensees
will meet the needs and interests of their communities.
See also
Federal Communications Commission
Spectrum Auctions
Low-Power Radio Service (LPRS) is one of the Citizens’ Band
(CB) Radio Services. It is a one-way short-distance very-highfrequency (VHF) communication service providing auditory
assistance to persons with disabilities, persons who require
language translation, and persons in educational settings. It
also provides health care assistance to the ill, law enforcement tracking services in cooperation with a law enforcement
agency, and point-to-point network control communications
for Automated Marine Telecommunications System (AMTS)
coast stations. In all applications, two-way voice communications are prohibited.
A license from the FCC is not needed to use most LPRS
transmitters. To operate an LPRS transmitter for AMTS
purposes, however, the user must hold an AMTS license.
Otherwise, provided the user is not a representative of a foreign government, anyone can operate an FCC type-accepted
LPRS transmitter for voice, data, or tracking signals.
An LPRS transmitter may be operated within the territorial limits of the 50 United States, the District of Columbia,
and the Caribbean and Pacific insular areas. It also may be
operated on or over any other area of the world, except
within the territorial limits of areas where radio communications are regulated by another agency of the United States
or within the territorial limits of any foreign government.
The transmitting antenna must not exceed 30.5 meters (100
feet) above ground level. This height limitation does not
apply, however, to LPRS transmitter units located indoors or
where the antenna is an integral part of the unit.
There are 260 channels available for LPRS. These channels are available on a shared basis only and are not
assigned for the exclusive use of any entity. Certain channels
(19, 20, 50, and 151 to 160) are reserved for law enforcement
tracking purposes. Further, AMTS-related transmissions
are limited to the upper portion of the band (216.750 to
217.000 MHz).
Users must cooperate in the selection and use of channels
in order to reduce interference and make the most effective
use of the authorized facilities. Channels must be selected in
an effort to avoid interference with other LPRS transmissions. This means that if users are experiencing interference
on a particular channel, they should change to another channel until a clear one is found.
Finally, operation is subject to the conditions that no
harmful interference is caused to the U.S. Navy’s SPASUR
radar system (216.88 to 217.08 MHz) or to a Channel 13 television station.
LPRS can operate anywhere CB station operation is permitted. An LPRS station is not required to transmit a station
identification announcement. The LPRS transmitting device
may not interfere with TV reception or federal government
radar and must accept any interference received, including
interference that may cause undesired operation. On
request, system equipment must be available for inspection
by an authorized FCC representative.
See also
Citizens Band Radio Service
Family Radio Service
General Mobile Radio Service
The Maritime, or Marine, Radio Services have evolved from
the earliest practical uses of radio. In 1900, just 6 years after
Marconi demonstrated his “wireless” radio, devices were
being installed aboard ships to enable them to receive storm
warnings transmitted from stations on shore. Today, the
same principle applies in using both shipboard and land stations in the marine services to safeguard life and property at
sea. Both types of stations are also used to aid marine navigation, commerce, and personal business, but such uses are
secondary to safety, which has international priority.
The Marine Radio Services include the Maritime Mobile
Service, the Maritime Mobile-Satellite Service, the Port
Operations Service, the Ship Movement Service, the Maritime
Fixed Service, and the Maritime Radiodetermination Service.
Maritime Mobile Service is an internationally allocated
radio service providing for safety of life and property at
sea and on inland waterways.
Maritime Mobile-Satellite Service provides frequencies
for public correspondence between ships and public coast
stations as well as between aircraft and public coast stations and coast earth stations. The transmission of public
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correspondence from aircraft must not cause interference
to maritime communications.
Port Operations Service provides frequencies for intership communications related to port operations in coastal
harbors, allowing the vessel traffic to be managed more
efficiently while protecting the marine environment from
vessel collisions and groundings.
Ship Movement Service provides frequencies for communications relating to the operational handling of the
movement and the safety of ships and, in emergency, to
the safety of persons.
Maritime Fixed Service provides frequencies for communications equipment installed on oil drilling platforms,
lighthouses, and maritime colleges.
Maritime Radiodetermination Service provides frequencies for determining position, velocity, and other characteristics of vessels.
Together, shipboard and land stations in the Marine Services
are meant to serve the needs of the entire maritime community. The Federal Communications Commission (FCC) regulates these services both for ships of U.S. registry that sail in
international and foreign waters and for all marine activities
in U.S. territory. For this and other reasons, the rules make
a distinction between compulsory users of marine radio for
safety at sea and noncompulsory uses for purposes other
than safety. In addition, rules concerning domestic marine
communications are matched to requirements of the U.S.
Coast Guard, which monitors marine distress frequencies
continuously to protect life and property in U.S. waters.
See also
Global Maritime Distress and Safety System
A microwave is a short radio wave that varies from 1 millimeter to 30 centimeters in length. Because microwaves can
pass through the ionosphere, which blocks or reflects longer
radio waves, microwaves are well suited for satellite communications. This reliability also makes microwave well suited
to terrestrial communications as well, such as those delivered by Local Multipoint Distribution Service (LMDS) and
Multichannel Multipoint Distribution Service (MMDS).
Much of the microwave technology in use today for pointto-point communications was derived from radar developed
during World War II. Initially, microwave systems carried
multiplexed speech signals over common carrier and military communications networks; but today they are used to
handle all types of information—voice, data, facsimile, and
video—in either an analog or digital format.
The first microwave transmission occurred in 1933, when
European engineers succeeded in communicating reliably
across the English Channel—a distance of about 12 miles
(20 kilometers). In 1947, the first commercial microwave
network in the United States came online. Built by Bell
Laboratories, this was a New York to Boston system consisting of 10 relay stations carrying television signals and multiplexed voice conversations.
A year later, New York was linked to San Francisco via
109 microwave relay stations. By the 1950s, transcontinental microwave networks were routinely handling over 2000
voice channels on hops averaging 25 miles (41.5 kilometers)
in length. By the 1970s, just about every single telephone
call, television show, telegram, or data message that crossed
the country spent some time on a microwave link.
Over the years, microwave systems have matured to the
point that they have become major components of
the nation’s Public Switched Telephone Network (PSTN)
and an essential technology with which private organizations can satisfy internal communications requirements.
Microwave systems can even exceed the 99.99 percent reliability standard set by the telephone companies for their
phone lines.
Microwave Applications
Early technology limited the operations of microwave systems to radio spectrum in the 1-GHz range, but because of
improvements in solid-state technology, today’s government
systems are transmitting in the 153-GHz region, while commercial systems are transmitting in the 40-GHz region with
FCC approval. The 64- to 71-GHz band is reserved for intersatellite links. These frequency bands offer short-range
wireless radio systems the means to provide communications capacities approaching those now achievable only with
coaxial cable and optical fiber.
These spectrum allocations offer a variety of possibilities,
such as use in short-range, high-capacity wireless systems
that support educational and medical applications, and
wireless access to libraries or other information databases.
In addition to telecommunication service providers, shorthaul microwave equipment is used routinely by hotel chains,
CATV operators, and government agencies.
Corporations are making greater use of short-haul
microwave, especially for extending the reach of local area
networks (LANs) in places where the cost of local T1 lines
is prohibitive. Common carriers use microwave systems
for backup in the event of fiber cuts and in terrain where
laying fiber is not economically feasible. Cellular service
providers use microwave to interconnect cell sites with
each other as well as to the regular telephone net-work.
Some interexchange carriers (and corporations) even
use short-haul microwave to bypass Incumbent Local
Exchange Carriers (ILECs) to avoid lengthy service provisioning delays and to avoid paying hefty local access
Network Configurations
There are more than 25,000 microwave networks in the
United States alone. There are basically two microwave network configurations: point-to-point and point-to-multipoint.
The first type meets a variety of low- and medium-density
communications requirements, ranging from simple links to
more complex extended networks, such as
Sub-T1/E1 data links
Ethernet/Token Ring LAN extensions
Low-density digital backbone for wide area mobile radio
and paging services
PBX/OPX/FX voice, fax, and data extensions
Facility-to-facility bulk data transfer
Point-to-multipoint microwave systems provide communications between a central command and control site and
remote data units. A typical radio communications system
provides connections between the master control point and
remote data collection and control sites. Repeater configurations are also possible. The basic equipment requirements
for a point-to-multipoint system include
Antennas For the master, an omnidirectional antenna; for
the remotes, a highly directional antenna aimed at the
master station’s location.
Tower (or other structure, such as a mast) To support the
antenna and transmission line.
Transmission line Low-loss coaxial cable connecting the
antenna and the radio.
Master station radio Interfaces with the central computer; it transmits and receives data from the remote
radio sites and can request diagnostic information from
the remote transceivers. The master radio also can serve
as a repeater.
Remote radio transceiver Interfaces to the remote data
unit; receives and transmits to the master radio.
Management station A computer that can be connected to
the master station’s diagnostic system either directly or
remotely for control and collection of diagnostic information from master and remote radios.
Wireless Cable
Traditionally, cable system operators have used microwave
transmission systems to link cable networks. These Cable
Antenna Relay Services (CARS) have experienced declining
usage as cable operators have deployed more optical fiber
in their transmission systems. However, improvements in
microwave technology and the opening of new frequencies for
commercial use have contributed to the resurgence in shorthaul microwave. In the broadcast industry, short-haul
microwave is often referred to as “wireless cable,” which comes
in the form of Local Multipoint Distribution Service (LMDS)
and Multichannel Multipoint Distribution Service (MMDS).
These wireless cable technologies have two key advantages. One is availability—with an FCC license, they can be
made available in areas of scattered population and other
areas where it is too expensive to build a traditional cable
station. The other is affordability—because of the lower
costs of building a wireless cable station, savings can be
passed on to subscribers.
The radio spectrum is the part of the natural spectrum of
electromagnetic radiation lying between the frequency limits of 9 kHz and 400 GHz. In the United States, regulatory
responsibly for the radio spectrum is divided between the
FCC and the National Telecommunications and Information
Administration (NTIA).
The FCC, which is an independent regulatory agency,
administers spectrum for non-federal government use, and
the NTIA, which is an operating unit of the Department
of Commerce, administers spectrum for federal government use. Within the FCC, the Office of Engineering and
Technology (OET) provides advice on technical and policy
issues pertaining to spectrum allocation and use. This office
manages the spectrum and provides leadership to create new
opportunities for competitive technologies and services for
the American public.
Microwave is now almost exclusively a short-haul transmission medium, while optical fiber and satellite have become
the long-haul transmission media of choice. Short-haul
microwave is now one of the most agile and adaptable transmission media available, with the capability of supporting
data, voice, and video. It is also used to back up fiberoptic
facilities and to provide communications services in locations where it is not economically feasible to install fiber.
See also
Local Multipoint Distribution Service
Multichannel Multipoint Distribution Service
Satellite Communications
The Mobile Telephone Switching Office (MTSO) acts like an
ordinary switching node on the Public Switched Telephone
Network (PSTN) or Integrated Services Digital Network
(ISDN) and provides all the functionality needed to handle
a mobile subscriber, such as registration, authentication,
location updating, handoffs, and call routing to a roaming
All cell phones have special codes associated with them:
Electronic Serial Number (ESN) A unique 32-bit number
programmed into the phone when it is manufactured.
Mobile Identification Number (MIN) A 10-digit number
derived from the mobile phone number.
System Identification Code (SID) A unique 5-digit number
that is assigned to each carrier by the FCC.
While the ESN is considered a permanent part of the phone,
both the MIN and SID codes are programmed into the phone
on purchase and activation with a service plan.
When the mobile phone is powered up, it listens for the
network operator’s SID on the control channel. The control
channel is a special frequency that the phone and base station use to talk to one another about such functions as call
setup and channel changing. If the phone cannot find any
control channels to listen to, it assumes that it is out of range
and displays a “no service” message.
When it receives the SID, the phone compares it to the
SID programmed into the phone. If the SIDs match, the phone
knows that the cell it is communicating with is part of its
home system.
Along with the SID, the phone also transmits a registration request. The MTSO then knows the location of the
phone, which is recorded in a database so that it knows
which cell to target when it wants to ring that phone for an
incoming call.
When the MTSO gets the call, it looks up the location of
the phone in its database. The MTSO picks a frequency
pair the phone will use in that cell to take the call. The
MTSO communicates with the phone over the control
channel to tell it which frequencies to use, and once the
phone and the tower switch on those frequencies, the call
is connected.
As the mobile phone moves toward the edge of a cell, that
cell’s base station notices that its signal strength is diminishing. Meanwhile, the base station in the cell the mobile
phone is moving toward is listening and measuring signal
strength on all frequencies and sees that the approaching
phone’s signal strength increasing. The two base stations
coordinate with each other through the MTSO, and at some
point, the phone gets a signal on a control channel telling it
to change frequencies. This handoff switches the phone to
the new cell.
If the SID on the control channel does not match the SID
programmed into the mobile phone, then the phone assumes
that it is roaming. The MTSO of the cell that the phone is
roaming in contacts the MTSO of its home system, which
then checks its database to confirm that the SID is valid. The
home system verifies the phone to the local MTSO, which
then tracks it while it is moving through its cells.
The local wireless cellular network consists of a Mobile
Telephone Switching Office (MTSO) with cell sites scattered
throughout a geographic serving region. T-carrier or fiber
lines are typically leased from the local carrier to interconnect the cell sites with the MTSO. These lines also provide
the MTSO with connectivity to a local central office switch so
that calls can be completed between the wireless network
and the PSTN.
See also
Cell Sites
Cellular Voice Communication
Cellular Data Communication
Cellular Telephones
Multichannel Multipoint Distribution Service (MMDS) is a
microwave technology that traces its origins to 1972 when it
was introduced to provide an analog service called Multipoint
Distribution Service (MDS). For many years, MMDS was
used for one-way broadcast of television programming, but in
early 1999, the FCC opened up this spectrum to allow for twoway transmissions, making it useful for delivering telecommunication services, including high-speed Internet access to
homes and businesses.
This technology, which has now been updated to digital,
operates in the 2- to 3-GHz range, enabling large amounts of
data to be carried over the air from the operator’s antenna
towers to small receiving dishes installed at each customer
location. The useful signal range of MMDS is about 30 miles,
which beats Local Multipoint Distribution Service (LMDS)
at 7.5 miles and Digital Subscriber Line (DSL) at 18,000
feet. Furthermore, MMDS is easier and less costly to install
than cable service.
With MMDS, a complete package of TV programs can be
transmitted to homes and businesses. Since MMDS operates
within the frequency range of 2 to 3 GHz, which is much
lower than LMDS at 28 to 31 GHz, it can support only up to
24 stations. However, operating at a lower frequency range
means that the signals are not as susceptible to interference
as those using LMDS technology.
Most of the time the operator receives TV programming
via a satellite downlink. Large satellite antennas installed
at the head end collect these signals and feed them into
encoders that compress and encrypt the programming. The
encoded video and audio signals are modulated, via amplitude modulation (AM) and frequency modulation (FM),
respectively, to an intermediate frequency (IF) signal. These
IF signals are up-converted to MMDS frequencies and then
amplified and combined for delivery to a coaxial cable, which
is connected to the transmitting antenna. The antenna can
have an omnidirectional or sectional pattern.
The small antennas at each subscriber location receive
the signals and pass them via a cable to a set-top box connected to the television. If the service also supports highspeed Internet access, a cable also goes to a special modem
connected to the subscriber’s PC. MMDS sends data as fast
as 10 Mbps downstream (toward the computer). Typically,
service providers offer downstream rates of 512 kbps to 2.0
Mbps, with burst rates up to 5 Mbps whenever spare bandwidth becomes available.
Originally, there was a line-of-sight limitation with MMDS
technology. But this has been overcome with a complementary technology called Vector Orthogonal Frequency Division
Multiplexing (VOFDM). Because MMDS does not require an
unobstructed line of sight between antennas, signals bouncing off objects en route to their destination require a mechanism for being reassembled in their proper order at the
receiving site. VOFDM handles this function by leveraging
multipath signals, which normally degrade transmissions. It
does this by combining multiple signals at the receiving end
to enhance or recreate the transmitted signals. This
increases the overall wireless system performance, link quality, and availability. It also increases service providers’ market coverage through non-line-of-sight transmission.
Channel Derivation
MMDS equipment can be categorized into two types based
on the duplexing technology used: Frequency Division
Duplexing (FDD) or Time Division Duplexing (TDD).
Systems based on FDD are a good solution for voice and bidirectional data because forward and reverse use separate and
equally large frequency bands. However, the fixed nature of
this scheme limits overall efficiency when used for Internet
access. This is so because Internet traffic tends to be “bursty”
and asymmetric. Instead of preassigning bandwidth with
FDD, Internet traffic is best supported by a more flexible
bandwidth allocation scheme.
This is where TDD comes in; it is more efficient because
each radio channel is divided into multiple time slots
through Time Division Multiple Access (TDMA) technology,
which enables multiple channels to be supported. Because
TDD has flexible timeslot allocations, it is better suited for
data delivery—specifically Internet traffic. TDD enables service providers to vary uplink and downlink ratios as they add
customers and services. Many more users can be supported
by the allocation of bandwidth on a nonpredefined basis.
MMDS is being used to fill the gaps in market segments
where cable modems and DSL cannot be deployed because of
distance limitations and cost concerns. Like these technologies, MMDS provides data services and enhanced video services such as video on demand, as well as Internet access.
MMDS will be another access method to complement a carrier’s existing cable and DSL infrastructure, or it can be used
alone for direct competition. With VOFDM technology,
MMDS is becoming a workable option that can be deployed
cost-effectively to reach urban businesses that do have lineof-sight access and in suburban and rural markets for small
businesses and telecommuters.
See also
Cable Television Networks
Digital Subscriber Line Technologies
Local Multipoint Distribution Service
Microwave Communications
Multichannel Video Distribution and Data Service (MVDDS)
supports broadband communication services that include
local television programming and high-speed Internet access
in the 12-GHz band. This is the same band used by Direct
Broadcast Satellite (DBS).
The FCC adopted MVDDS service and technical rules
that permit MVDDS operators to share the 12-GHz band
with DBS on a coprimary basis subject to the condition that
they do not cause impermissible interference to the DBS service. Specifically, the FCC adopted equivalent power flux
density (EPFD) limits for MVDDS to protect DBS subscribers from interference. MVDDS operators are required
to ensure that the adopted EPFD limits are not exceeded at
any existing DBS customer location. If the EPFD limits are
exceeded, the MVDDS operator will be required to discontinue service until the limits can be met. MVDDS power flux
density limits, MVDDS spacing rules, and coordination
requirements are intended to facilitate mutual sharing of
the 12-GHz band. A “safety valve” allows individual DBS
licensees or distributors to present evidence that the appropriate EPFD for a given service area should be different from
the EPFD applicable in that zone.
With MVDDS, the FCC adopted a geographic licensing
scheme and, in the event mutually exclusive applications
are filed, will assign licenses via competitive bidding. A
licensing system based on component economic areas
(CEAs) will be used with one spectrum block of 500 MHz
available per CEA.
In setting up the rules for MVDDS, the FCC restricted
dominant cable operators from acquiring an interest in an
MVDDS license for a service area where significant overlap
is present. There is no restriction on DBS providers from
acquiring MVDDS licenses.
MVDDS providers will share the 12-GHz band with incumbent Direct Broadcast Satellite (DBS) providers on a coprimary, non-harmful interference basis. The objective of this
arrangement is to accommodate the introduction of innovative services and to facilitate the sharing and efficient use of
spectrum. Furthermore, the FCC believes that this service
will facilitate the delivery of communications services, such
as video and broadband services, to various populations,
including those deemed to be unserved or underserved.
See also
Direct Broadcast Satellite
Federal Communications Commission
Interactive Video and Data Service
Over-the-air service activation, sometimes called “over-theair service provisioning,” allows a potential wireless, both
cellular and personal communications services (PCS), service subscriber to activate new wireless service without the
intervention of a third party (e.g., authorized dealer). The
use of special software enables wireless service providers to
offer over-the-air service provisioning capabilities—including initial activation—plus provisioning of other innovative
wireless features, such as paging and voice mail. The process
is made secure by restricting the phone’s initial use to activation only. Once subscribers have the phone in hand, they
can immediately dial a customer service representative who
can activate the phone and accept account information.
Over-the-air activation also enables the service provider
to activate a potential service subscriber’s unit by downloading over the air the required parameters, such phone
number and features, into the unit. The service subscriber
does not have to bring the unit into a dealer or service agent.
This allows service providers the capability to start marketing subscriber units through nontraditional mass-market
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retailers who do not have the personnel to individually program subscriber units.
Another capability of over-the-air service activation is the
ability to load an authentication key into a subscriber unit
securely. Authentication is the process by which information
is exchanged between a subscriber unit and the network for
the purpose of confirming and validating the identity of the
subscriber unit. The over-the-air service activation feature
incorporates an authentication key exchange agreement
algorithm. This algorithm enhances security for the subscriber and reduces the potential for fraudulent use of cellular service.
New customers simply place a call to the cellular operator,
and the information is transferred automatically to the cellular phone over the cellular airwaves. This method of activation enables cellular operators to explore new distribution
channels for subscriber units and substantially reduce distribution and service provisioning costs.
These features operate over a digital control channel
(DCC). In addition to over-the-air programming, the DCC
supports such advanced services as calling line ID, message
waiting indication, and Short Message Service (SMS). It also
offers tiered services, allowing operators to tailor pricing
packages for residential and business customers based on
location and usage. Sleep mode, another DCC feature,
improves handset battery life by allowing mobile phones to
“sleep” while idle to conserve power. DCC also improves network performance and supports advanced voice coder technology for improved audio quality.
In 1995, Code Division Multiple Access (CDMA) became the
first digital cellular technology to offer instant activation to
customers based on specifications defined by the CDMA
Development Group (CDG) in 1994. In the future, cellular
operators will look to leverage this capability to offer more
value-added services, providing them with the latest applications software coming directly from the network.
See also
Cellular Telephones
Code Division Multiple Access
Mobile Telephone Switching Office
Time Division Multiple Access
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Paging is a wireless service that provides one- or two-way messaging to give mobile users continuous accessibility to family,
friends, and business colleagues while they are away from
their telephones. Typically, the mobile user carries a palmsized device (the pager or some other portable device with a
paging capability) that has a unique identification number.
The calling party inputs this number, usually through the
Public Switched Telephone Network (PSTN), to the paging
system, which then signals the pager to alert the called party.
Alternatively, callback numbers and short-text messages
can be sent to pagers via messaging software installed on a
PC or input into forms accessed on the Web for delivery via an
Internet gateway. Regardless of delivery method, the called
party receives an audio or visual notification of the call, which
includes a display of the phone number to call back. If the
pager has an alphanumeric capability, messages may be displayed on the pager’s screen.
Origin of the Pager
The pioneer of wireless telecommunications is Al Gross
(Figure P-1). In 1938, the Canadian inventor developed the
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walkie-talkie. In 1948, he pioneered Citizens’ Band (CB)
radio. In 1949, he invented the pager from radio technology he used for blowing up bridges via remote control during World War II. His first attempt to sell pagers to doctors
and nurses in 1960 failed because nurses did not want to
disturb patients and doctors did not want to disturb their
golf games.
Gross’s ideas were so far advanced that most of his
patents expired before the technology could catch up to
make his inventions a reality. As a result, he did not make
much money. Had he been born 35 years later, he could have
capitalized on his ideas to become far wealthier than Bill
Gates at Microsoft.
Figure P-1 Wireless pioneer Al Gross (1918–2000)
invented many of the concepts used today in cordless
and cellular telephony for
which he held many patents.
Paging Applications
There are many applications for paging. Among the most
popular are
Mobile messaging Allows messages to be sent to mobile
workers. They can respond with confirmation or a request
for additional instructions.
Data dispatch Allows managers to schedule work appointments for mobile workers. When they activate their pagers
each morning, their itinerary will be waiting for them.
Single-key callback Allows the user to read a message and
respond instantly with a predefined stored message that
is selected with a single key.
Some message paging services work with text messaging
software programs, allowing users to send messages from
their desktop or notebook computers to individuals or groups.
This kind of software also keeps a log of all messaging activity.
This method also offers privacy, since messages do not have to
go through an operator before delivery to the recipient.
Types of Paging Services
Several types of paging services are available.
Selective Operator-Assisted Voice Paging Early paging sys-
tems were nonselective and operator-assisted. Operators at
a central control facility received voice input messages,
which were taped as they came in. After an interval of
time—15 minutes or so—these messages were then broadcast and received by all the paging system subscribers.
This meant that subscribers had to tune in at appointed
times and listen to all messages broadcast to see if there
were any messages for them. Not only did this method
waste airtime, it also was inconvenient and labor-intensive
and offered no privacy.
These disadvantages were overcome with the introduction of address encoders at the central control facility and
associated decoders in the pagers. Each pager was given a
unique address code. Messages intended for a particular
called party were input to the system preceded by this
address. In this way, only the party addressed was alerted to
switch on his or her pager to retrieve messages.
With selective paging, tone-only alert paging became possible. The called party was alerted by a beep tone to call the
operator or a prearranged home or office number to have the
message read back.
Automatic Paging Traditionally, an operator was always
needed either to send the paging signal or to play back or relay
messages for the called party. With automatic paging, a telephone number is assigned to each pager, and the paging terminal can automatically signal for voice input, if any, from the
calling party, after which it will automatically page the called
party with the address code and relay the input voice message.
Tone and Numeric Paging Voice messages take up a lot of
airtime, and as the paging market expands, frequency overcrowding becomes a potentially serious problem. Tone-only
alert paging saves on airtime usage but has the disadvantage that the alerted subscriber knows only that he or she
has to call certain prearranged numbers, depending on the
kind of alert tone received.
With the introduction of numeric display pagers in the
mid-1980s, the alert tone is followed by a display of a telephone number to call back or a coded message. This method
resulted in great savings in airtime usage because it was no
longer necessary to add a voice message after the alert tone.
This is still the most popular form of paging.
Alphanumeric Paging Alphanumeric pagers display text or
numeric messages entered by the calling party or operator
using a modem-equipped computer or a custom page-entry
device designed to enter short-text messages. Although
alphanumeric pagers have captured a relatively small market in recent years, the introduction of value-added services
that include news, stock quotes, sports scores, traffic bulletins, and other specialized information services has heated
up the market for such devices.
Ideographic Paging Pagers capable of displaying different
ideographic languages—Chinese, Japanese, and others—
are also available. The particular language supported is
determined by the firmware (computer program) installed in
the pager and in the page-entry device. The pager is similar
to that used in alphanumeric display paging.
Paging System Components
The key components of a paging system include an input
source, the existing wireline telephone network, the paging encoding and transmitter control equipment, and the
pager itself.
Input Source A page can be entered from a phone, a com-
puter with modem, or other type of desktop page-entry
device; a personal digital assistant (PDA); or an operator
who takes a phone-in message and enters it on behalf of the
caller. Various forms posted on the Web also can be used to
input messages to pagers.
The Web form of WorldCom (Figure P-2), for example, allows
users to send a text message consisting of a maximum of 240
characters to subscribers of its One-Way Alphanumeric service
and 500 characters to subscribers of its Enhanced One-Way,
Interactive (two-way), and QuickReply Interactive services. In
addition, users can send a text message consisting of a maximum of 200 characters to subscribers of MobileComm. The
form even provides a means to check the character count before
the message is sent.
Figure P-2 WorldCom offers a Web pager that lets anyone send a message to anyone else who has a WorldCom, SkyTel, or MobileComm pager.
Telephone Network Regardless of exactly how the message is
entered, it eventually passes through the PSTN to the paging
terminal for encoding and transmission through the wireless
paging system. Typically, the encoder accepts the incoming
page, checks the validity of the pager number, looks up the
directory or database for the subscriber’s pager address, and
converts the address and message into the appropriate paging signaling protocol. The encoded paging signal is then sent
to the transmitters (base stations), through the paging transmission control systems, and broadcast across the coverage
area on the specified frequency.
Encoder Encoding devices convert pager numbers into pager
codes that can be transmitted. There are two ways in which
encoding devices accept pager numbers: manually and automatically. In manual encoding, a paging system operator
enters pager numbers and messages via a keypad connected
to the encoder. In automatic encoding, a caller dials up an
automatic paging terminal and uses the phone keypads to
enter pager numbers. Regardless of the method used, the
encoding device then generates the paging code for the numbers entered and sends the code to the paging base station
for wireless transmission.
Base Station Transmitters The base station transmitters
send page codes on an assigned radio frequency. Most base
stations are specifically designed for paging, but those
designed for two-way voice can be used as well.
Pagers Pagers are essentially FM receivers tuned to the
same radio frequency as the paging base station. A decoder
unit built into each pager recognizes the unique code
assigned to the pager and rejects all other codes for selective
alerting. However, pagers can be assigned the same code for
group paging. There are also pagers that can be assigned
multiple page codes, typically up to a maximum of four,
allowing the same pager to be used for a mix of individual
and group paging functions.
Despite all the enhancements built into pagers and paging services in recent years, the market is slowing down.
Alphanumeric services—which provide word messages
instead of just phone numbers—have failed to attract a wide
audience largely because paging subscribers still need a
phone to respond to messages. Some providers have tried to
offer services that would allow callers to leave voice messages on pagers, but this too has failed to catch on.
Consequently, about four out of five of today’s paging customers still rely on cheap numeric services.
Two-way paging networks may be the industry’s last hope
for survival. They allow a pager—which comes equipped with
a minikeyboard—to “talk” to another pager (Figure P-3) or
with a telephone, e-mail address, or fax machine. Some two-
Figure P-3 With Motorola’s PageWriter
2000, users can send text messages to other
two-way pagers and alphanumeric pagers
directly or through e-mail.
way services allow consumers to reply to messages with predetermined responses.
Signaling Protocols
In a paging system, the paging terminal, after accepting an
incoming page and validating it, will encode the pager
address and message into the appropriate paging signaling
protocol. The signaling protocol allows individual pagers to
be uniquely identified/alerted and to be provided with the
additional voice message or display message, if any.
Various signaling protocols are used for the different paging service types, such as tone-only or tone and voice. Most
paging networks are able to support many different paging
formats over a single frequency. Many paging formats are
manufacturer-specific and often proprietary, but there are
public-domain protocols, such as the Post Office Code
Standardization Advisory Group (POCSAG), that allow different manufacturers to produce compatible pagers.
POCSAG is a public-domain digital format adopted by
many pager manufacturers around the world. It can accommodate 2 million codes (pagers), each capable of supporting
up to four addresses for such paging functions as tone-only,
tone and voice, and numeric display. POCSAG operates at
data rates of up to 2400 bps. At this rate, to send a single
tone-only page requires only 13 milliseconds. This is about
100 times faster than two-tone paging.
With the explosion of wireless technology and dramatic
growth in the paging industry in many markets, existing networks are becoming more and more overcrowded. In addition,
RF spectrum is not readily available because of demands by
other wireless applications. In response to this problem,
Motorola has developed a one-way messaging protocol called
Flex (feature-rich long-life environment for executing) messaging applications that is intended to transform and broaden
paging from traditional low-end numeric services into a range
of PCS/PCN and other wireless applications.
PCS 1900
Relative to POCSAG, Flex can transmit messages at up to
6400 bps and permit up to 600,000 numeric pagers on a single frequency compared to POCSAG’s 2400-bps transmission
rate and 300,000 users per frequency. In addition, Flex provides enhanced bit error correction and much higher protection against the signal fades common in FM simulcast paging
systems. The combination of increased bit error correction
and improved fade protection increases the probability of
receiving a message intact, especially longer alphanumeric
messages and data files that will be sent over PCS/PCN.
Motorola also has developed ReFlex, a two-way protocol
that will allow users to reply to messages, and InFlexion, a
protocol that will enable high-speed voice messaging and
data services at up to 112 kbps.
The hardware and software used in radio paging systems
have evolved from simple operator-assisted systems to terminals that are fully computerized, with such features as
message handling, scheduled delivery, user-friendly prompts
to guide callers to a variety of functions, and automatic reception of messages. After tremendous growth in the last decade,
from 10 million subscribers in 1990 to 60 million today, the
paging industry has slowed down markedly—in large part
because of cutthroat competition and increasing use of digital mobile phones.
See also
Electronic Mail
Personal Communication Services
PCS 1900
PCS 1900 is the American National Standards Institute (ANSI)
radio standard for 1900-MHz Personal Communication Service
PCS 1900
(PCS) in the United States. Also known as GSM 1900, it is compatible with the Global System for Mobile (GSM) communications, an international standard adopted by 404 networks
supporting 538 million subscribers in 171 countries as of mid2001. Network operators aligned to the GSM standard have 35
percent of the world’s wireless market.
PCS 1900 can be implemented with either Time Division
Multiple Access (TDMA) or Code Division Multiple Access
(CDMA) technology. TDMA-based technology enjoys an initial cost advantage over rival technology CDMA equipment
because suppliers making TDMA infrastructure equipment
and handsets have already reached economies of scale. In
contrast, CDMA equipment is still in its first generation and
therefore is generally more expensive.
The CDMA (IS-95) standard has been chosen by about
half of all the PCS licensees in the United States, giving it
the lead in the total number of potential subscribers.
However, the first operational PCS networks have been
using PCS 1900 as their standard mainly because of the
maturity of the GSM-based technology.
Although similar in appearance to analog cellular service, PCS 1900 is based on digital technology. As such, PCS
1900 provides better voice quality, broader coverage, and a
richer feature set. In addition to improved voice quality,
fax and data transmissions are more reliable. Laptop computer users can connect to the handset with a Personal
Computer Memory Card International Association (PCMCIA) card and send fax and data transmissions at higher
speeds with less chance of error.
The PCS 1900 system architecture consists of the following
major components:
Switching system Controls call processing and subscriberrelated functions.
Base station Performs radio-related functions.
PCS 1900
Mobile station The end-user device that supports voice
and data communications as well as short message services.
Operation and support system (OSS) Supports the operation and maintenance activities of the network.
The switching system for PCS 1900 service contains the
following functional elements (Figure P-4):
Mobile Switching Center (MSC) Performs the telephony
switching functions for the network. It controls calls to and
from other telephone and data communications networks
such as Public Switched Telephone Networks (PSTN),
Integrated Services Digital Networks (ISDN), Public Land
Mobile Radio Services (PLMRS) networks, Public Data
Networks (PDN), and various private networks.
Visitor Location Register (VLR) A database that contains
all temporary subscriber information needed by the MSC
to serve visiting subscribers.
Home Location Register (HLR) A database for storing and
managing subscriptions. It contains all permanent subscriber information, including the subscriber’s service
profile, location information, and activity status.
Authentication Center (AC) Provides authentication and
encryption parameters that verify the user’s identity
and ensure the confidentiality of each call. This functionality protects network operators from common types
of fraud found in the cellular industry today.
Message Center (MC) Supports numerous types of messaging services, for example, voice mail, facsimile, and e-mail.
Advanced Services and Features
Like GSM, PCS 1900’s digital orientation makes possible
several advanced services and features that are not effi-
PCS 1900
Telephone and Data
Support System
Figure P-4
PCS 1900 switching system architecture.
ciently and economically supported in analog cellular networks. Among them are
Short Message Service Enables alphanumeric messages
up to 160 characters to be sent to and from PCS
1900–compatible handsets. Short Message Service applications include two-way point-to-point messaging, confirmed message delivery, cell-based messaging, and
voice-mail alert. These messaging and paging capabilities
create a broad array of potential new revenue-generating
opportunities for carriers.
Voice Mail The PCS 1900 network provides one central
voice-mail box for both wired and wireless service. In
addition, the voice-mail alert feature ensures that subscribers do not miss important messages.
Personal Call Management Offers subscribers a single
telephone number for all their physical telecommunication devices. For example, a single number can be
assigned for home and mobile use or office and mobile use.
This allows subscribers to receive all calls regardless of
their physical location.
PCS 1900
Data Applications Wireless data applications that can be
supported by PCS 1900 networks include Internet access,
electronic commerce, and fax transmission.
Smart Cards
The PCS 1900 standard supports the smart card, which provides similar features as GSM’s Subscriber Identity Module
(SIM). The size of a credit card, smart cards contain embedded computer chips with user-profile information. By removing the smart card from one PCS 1900 phone and inserting it
into another PCS 1900 phone, the user is able to receive calls
at that phone, make calls from that phone, or receive other
subscribed services such as wireless Internet access. The
handsets cannot be used to place calls (except 911 emergency
calls) until the subscriber inserts the smart card and enters
a personal identification number (PIN).
The profile information stored in the smart card also
enables international roaming. When traveling in the
United States, international GSM customers will be able to
rent handsets, insert their SIM, and access their services as
if they are back home. By the same token, when U.S. subscribers travel internationally to cities with compatible networks and mutual roaming agreements, they only need to
take their smart card with them to access the services they
subscribed to back home via the local GSM network.
Like SIMs, smart cards also provide storage for features
such as frequently called numbers and short messages.
Smart cards also include the AT command-set extensions,
which integrate computing applications with cellular data
communications. In the future, smart cards and PCS 1900
technology also will link subscribers to applications in electronic commerce, banking, and health care.
PCS 1900 is a frequency-adapted version of GSM that operates at 1800 MHz in Europe and elsewhere. While GSM
looks to be a perennial third in North America digital markets, this is mainly because the technology has not been
adopted for use in cellular 800-MHz frequencies. Otherwise,
PCS 1900 and GSM are similar in all other respects, including the network architecture and types of services supported. An advantage U.S. carriers have in supporting the
PCS 1900 standard is that it is interoperable with the worldwide GSM standard, which means that users can roam globally. GSM phones are available in either dual-band
(900/1900 MHz) or triband (900/1800/1900 MHz) models,
enabling their use in countries with different frequency
bands for GSM services.
See also
Global System for Mobile (GSM) Telecommunications
Personal Communication Services
In a peer-to-peer network, computers are linked together for
resource sharing. If there are only two computers to link
together, networking can be done with a Category 5
crossover cable that plugs into the RJ45 jack of the network
interface card (NIC) on each computer. If the computers do
not have NICs, they can be connected with either a serial or
parallel cable. Once connected, the two computers function
as if they were on a local area network (LAN), and each computer can access the resources of the other. If three or more
computers must be connected, a wiring hub is required.
The peer network can be extended to portable devices,
including desktop and notebook computers and personal digital assistants (PDAs), through the use of wireless access points.
The access point connects to the LAN through a hub or switch
via Category 5 cabling, just like any other device on the wired
network. The access point establishes the wireless link to one
or more client devices, which are equipped with a wireless card.
The wireless devices operate in either the 2.4-GHz band for 11
Mbps or the 5-GHz band for 54 Mbps. Newer access points have
slots for wireless cards of both frequency bands, allowing users
to protect investments in 2.4-GHz equipment while migrating
to the higher speeds offered by 5-GHz equipment.
Regardless of exactly how the computers are interconnected, wired or wireless, each is an equal or “peer” and can
share the files and peripherals of the others. For a small
business doing routine word processing, spreadsheets, and
accounting, this type of network is the low-cost solution to
sharing resources like files, applications, and peripherals.
Multiple computers can even share an external cable or
Digital Subscriber Line (DSL) modem, allowing them to
access the Internet at the same time.
Networking with Windows
Windows 95/98 and Windows NT/2000 are often used for peerto-peer networking. In addition to peer-to-peer network access,
both provide network administration features and memory
management facilities, support the same networking protocols—including the Transmission Control Protocol/Internet
Protocol (TCP/IP) for accessing intranets, virtual private networks (VPNs), and the public Internet—and provide such
options as dial-up networking and fax routing.
One difference between the two operating systems is that
in Windows 95/98 the networking configuration must be
established manually, whereas in Windows NT/2000 the networking configuration is part of the initial program installation, on the assumption that NT/2000 will be used in a
network. Although Windows 95/98 is good for peer-to-peer
networking, Windows NT/2000 is more suited for larger
client-server networks.
Windows supports Ethernet, Token Ring, Asynchronous
Transfer Mode (ATM), and Fiber Distributed Data Interface
(FDDI) data-frame types. Ethernet is typically the least
expensive network to implement. The NICs can cost as little
as $20 each, and a five-port hub can cost as little as $40.
Category 5 cabling usually costs less than 50 cents per foot in
100-foot lengths with the RJ45 connectors already attached
at each end. Snap-together wall plate kits cost about $6 each.
If wireless connections are part of the peer network, the wireless NICs cost between $170 and $300, depending on whether
the 2.4- or 5-GHz band is used. Access points can cost as little as $199 for 2.4-GHz units and $299 for 5-GHz units.
Enterprise class versions cost quite a bit more.
Configuration Details
When setting up a peer-to-peer network with Windows
95/98, each computer must be configured individually. After
installing an NIC and booting the computer, Windows will
recognize the new hardware and automatically install the
appropriate network-card drivers. If the drivers are not
already available on the system, Windows will prompt the
user to insert the manufacturer’s disk containing the drivers, and they will be installed automatically (Figure P-5).
Next, the user must select the client type. If a Microsoft
peer-to-peer network is being created, the user must add
“Client for Microsoft Networks” as the primary network logon
(see Figure P-5). Since the main advantage of networking
computers is resource sharing, it is important to enable the
sharing of both printers and files. The user does this by clicking on the “File and Print Sharing” button and choosing one
or both of these capabilities (see Figure P-5). Through file and
printer sharing, each workstation becomes a potential server.
Identification and security are the next steps in the configuration process. From the “Identification” tab of the dialog box, the user must select a unique name for the computer
and the workgroup to which it belongs, as well as a brief
description of the computer (Figure P-6). When others use
Network Neighborhood to browse the network, they will see
the menu trees of all active computers on the network.
Figure P-5 To verify that the right drivers have been
installed, the user opens the Network Control Panel to check
the list of installed components. In this case, a Linksys
LNEPCI II Ethernet Adapter has been installed.
From the “Access Control” tab of the dialog box, the user
selects the security type. For a small peer-to-peer network,
share-level access is adequate (Figure P-7). This allows
printers, hard drives, directories, and other resources to be
shared and enables the user to establish password access for
each of these resources. In addition, read-only access allows
users to view (not modify) a file or directory.
To allow a printer to be shared, for example, the user
right-clicks on the printer icon in the Control Panel and
selects “Sharing” from the drop-down list (Figure P-8). Next,
the user clicks on the “Shared As” radio button and enters a
unique name for the printer (Figure P-9). If desired, this
Figure P-6 A unique name for the computer, the workgroup to which it belongs, and a brief description of the computer identify it to other users when they access Network
Neighborhood to browse the network.
resource can be given a password as well. When another
computer tries to access the printer, the user will be
prompted to enter a password. If a password is not necessary, the password field is left blank.
Another security option in the “Access Control” tab is
user-level access, which is used to limit resource access by
user name. This function eliminates the need to remember
passwords for each shared resource. Each user simply logs
onto the network with a unique name and password; the network administrator governs who can do what on the network. However, this requires the computers to be part of a
larger network with a central server—perhaps running
Figure P-7 Choosing share-level access allows the user to
password-protect each shared resource.
Windows NT/2000 server—that maintains the accesscontrol list for the whole network. Since Windows 95/98 and
Windows NT/2000 workstations support the same protocols,
Windows 95/98 computers can participate in a Windows
NT/2000 server domain.
Peer services can be combined with standard client-server
networking. For example, if a Windows 95/98 computer is a
member of a Windows NT/2000 network and has a color printer
to share, the resource “owner” can share that printer with other
computers on the network. The server’s access-control list
determines who is eligible to share resources.
Once the networking infrastructure is in place, the NIC of
each computer is individually connected to a hub with
Figure P-8
A printer can be configured for sharing.
Category 5 cable or wirelessly via the access point. This
cable has connectors on each end that insert into the RJ45
jacks of the hub and NICs. For small networks, the hub usually
will be manageable with the Simple Network Management
Protocol (SNMP), so no additional software is installed. Once
the computers are properly configured and connected to the
hub, the network is operational.
Peer-to-peer networking is an inexpensive way for small companies and households to share resources among a small
Figure P-9
A printer can be password-protected if necessary.
group of computers. This type of network provides most of the
same functions as the traditional client-server network,
including the ability to run network versions of popular software packages. Peer-to-peer networks also are easy to
install. Under ideal conditions, installation of the cards, software, hub, and cabling for five users would take only a few
hours. Wireless links provide the advantage of mobility
within the home or office, allowing a notebook to be used in
any room.
See also
Wireless Fidelity
Wireless LANs
Personal Access Communications Systems (PACS) is a standard adopted by ANSI for Personal Communication Services
(PCS). Adopted in June 1995, PACS provides an approach for
implementing PCS in North America that is fully compatible
with the local exchange telephone network and interoperable with existing cellular systems. Based on the Personal
Handyphone System (PHS) developed in Japan and the
Wireless Access Communications System (WACS) developed
by Bellcore (now known as Telcordia Technologies), PACS is
designed to support mobile and fixed applications in the
1900-MHz frequency range. It promises low installation and
operating costs while providing very-high-quality voice and
data services. In the United States, trials of PACS equipment began in 1995, and equipment rollout began in 1996.
Most of the standards—including up-banded versions of
CDMA, TDMA, and GSM—look like cellular systems in that
they have high transmit powers and receivers designed for
the large delay spreads of the macrocellular environment
and typically use low-bit-rate voice coders (vocoders). PACS
fills the niche between these classes of systems, providing
high-quality services, high data capability, and high user
density in indoor and outdoor microcellular environments.
PACS equipment is simpler and less costly than macrocellular systems yet more robust than indoor systems.
PACS capabilities include pedestrian- and vehicularspeed mobility, data services, and licensed and unlicensed
spectrum systems, as well as simplified network provisioning, maintenance, and administration. The key features of
PACS are summarized as follows:
Voice and data services are comparable in quality, reliability, and security with wire-line alternatives.
Systems are optimized to provide service to the in-building,
pedestrian, and city traffic operating environments.
It is most cost-effective to serve high-density traffic areas.
Small, inexpensive line-powered radios provide for unobtrusive pole or wall mounting.
There is low-complexity per-circuit signal processing.
Low transmit power and efficient sleep mode require only
small batteries to power portable subscriber units for
hours of talk time and multiple days of standby time.
Like the Personal Handyphone System (PHS), PACS uses
32-kbps Adaptive Differential Pulse Code Modulation
(ADPCM) waveform encoding, which provides near landline
voice quality. ADPCM has demonstrated a high degree of tolerance to the cascading of vocoders, as experienced when a
mobile subscriber calls a voice-mail system and the mailbox
owner retrieves the message from a mobile phone. With other
mobile technologies, the playback quality is noticeably diminished. With PACS, it is very clear. Similarly, the compounding
of delays in mobile to PCS through satellite calls—a routine
situation in Alaska and in many developing countries—can be
troublesome. PACS provides extremely low delay.
The low complexity and transmit power of PACS yield
limited cell sizes, which makes it well suited for urban and
suburban applications where user density is high. Antennas
can be installed inconspicuously, piggybacking on existing
structures. This avoids the high costs and delays associated
with obtaining permits for the construction of high towers.
Wireless local loop, pedestrian venues, commuting routes,
and indoor wireless are typical PACS applications.
Additionally, PACS is designed to offer high-capacity, superior voice quality and Integrated Services Digital Network
(ISDN) data services. Interoperability with ISDN is provided by aggregating two 32-kbps time slots to form a single
higher-speed 64-kbps channel. A 64-kbps channel also can
support 28.8-kbps voice-band data using existing modems.
PACS also can be used for providing wireless access to the
Internet. The packet data communications capabilities defined
in the PACS standards, together with the ability to aggregate
multiple 32-kbps channels, make it possible for users to access
the Internet from their PCs equipped with suitable wireless
modems at speeds of up to 200 kbps. When using the packet
mode of PACS for Internet traffic, radio channels are not dedicated to users while they are on active Internet sessions, which
can be very long. Rather, radio resources are used only when
data are actually being sent or received, resulting in very efficient operation and minimally impacting the capacity of the
PACS network to support voice communications.
PACS was designed to support the full range of advanced
intelligent network (AIN) services, including custom calling
features and personal mobility. As new AIN features are
developed, the PACS-compliant technology will evolve to
facilitate incorporation of the new services.
The market for PCS is very competitive. Already PCS is
exerting downward price pressure on traditional analog cellular services where the two compete side by side. PACS
enables PCS operators to differentiate their offerings
through digital voice clarity, high-bit-rate data communications, and advanced intelligent network services—all in a
lightweight handset. Moreover, the cost savings and ease of
use associated with PACS make it very economical for residential and business environments compared to competitive
high-powered wide area systems.
See also
Personal Handyphone System
Personal Communication Services
Voice Compression
Wireless Communications Services
Personal Air Communications Technology (pACT) is a wireless two-way messaging and paging technology that is
offered as an alternative to wireless Internet Protocol (IP),
also known as Cellular Digital Packet Data (CDPD).
The pACT specification, released in 1995, was developed to
enable compact, inexpensive devices to access low-cost, highcapacity network infrastructures. The protocol enhances
one-way paging, response paging, two-way paging, voice
paging, telemetry, and two-way messaging applications. The
pACT protocol thus addresses the demands of a growing
market for narrowband PCS. Despite huge investments in
spectrum for narrowband PCS, some U.S. paging carriers
are already running short of bandwidth. This situation has
prompted them to look for ways to add capacity to their networks. In major U.S. cities, the solution has been to make
better use of existing spectrum.
pACT supports two-way messaging and paging applications while still retaining all the strengths of one-way paging services, including long battery life, good in-building
reception, and ubiquitous coverage. pACT also provides carriers with the ability to substantially increase system capacity by more efficiently utilizing spectrum, thereby allowing
for more cost-effective paging and messaging services. Its
cellular-like network design enables carriers to take advantage of capacity gains through frequency reuse, a fundamental difference from other two-way systems.
The difference between wireless IP and pACT is that the
former is TCP/IP-centric, whereas the latter is User
Datagram Protocol/Internet Protocol (UDP/IP)–centric. While
wireless IP compresses the standard 40-byte TCP/IP header
to an average of 3 bytes to conserve bandwidth, pACT compresses the header to only 1 byte. The greater compression is
important for providing a short alphanumeric messaging service, especially when the message body is roughly the same
size as the header. Consequently, the maximum number of
subscribers that can be supported by the system is constrained not by protocol efficiency but by service traffic.
Two-way wireless messaging is working its way into a myriad
of user applications where one-way messaging is no longer
adequate. These are applications where time is of the essence,
and guaranteed message delivery is critical. pACT uses the
same upper layers of the protocol stack as wireless IP, making
it suitable for a broad range of messaging applications, including two-way-paging, e-mail, fleet dispatch, telemetry, transaction processing (e.g., point-of-sale credit card authorizations),
and voice messaging. Since pACT is based on the IP, it provides wireless network users with access to other IP-based networks such as corporate local area networks (LANs) and the
Internet from remote locations.
Network Capacity Narrowband PCS and two-way protocols
such as pACT give the paging industry new ways to increase
the capacity of one-way paging systems, which introduce
opportunities for providing new and enhanced services. Like
traditional mobile telephony systems, pACT increases
capacity by reusing frequencies—theoretically providing
unlimited capacity. Given higher airlink speeds (8 kbps) and
knowing a subscriber’s exact location, operators can increase
capacity in a large zone by 100 to 200 times and even more
in networks that are made up of several zones.
While one-way paging over a two-way network offers no
real benefits to subscribers, the benefits to operators are
substantial. First, two-way networks enable paging devices
to acknowledge that a message has been received. With this
capability, operators can offer subscribers guaranteed delivery, which can result in competitive advantage.
The second benefit to operators is that they do not have
to broadcast a message via every transmitter in the network
to reach an intended recipient. With a two-way network,
the exact location of each subscriber device is known
because the devices register automatically as they move
through the network. Since messages are sent solely via
the transmitter that is closest to the subscriber, a great
deal of network capacity is freed. This means that all other
transmitters in the network can be used simultaneously to
serve other subscribers.
Service Enhancement The two-way pACT architecture
affects more than capacity: It also enables providers to
enhance services, as well as to provide completely new services and applications. For example, paging devices that
contain a transmitter are able to send information back to
the network, to someone else in the network, or to any other
network. The two-way paging and messaging paradigm provides five levels of acknowledgment:
System acknowledgment The paging device acknowledges
receipt of an error-free message. A transparent Link
Layer acknowledgment between the device and the network enables guaranteed delivery service. The network
stores and retransmits messages at periodic intervals
that pagers have not acknowledged.
Message read When a recipient reads a message, the paging device transmits a “message read” acknowledgment
back to the host system or to the originator of the message.
Canned messages The paging device contains several
ready-to-use responses such as “Yes” or “No” that recipients can use when they reply to an inquiry.
Multiple choice The originator of a message defines several possible responses to accompany his or her message.
To reply, the recipient selects the most appropriate
Editing capabilities Some devices may be used to create
messages. Editing capabilities vary from device to device.
Some devices are managed by a few simple keys and pro-
vide only minor editing capabilities, while others such as
portable computers may contain full-feature keyboards.
Like wireless IP, pACT provides secure service—including encryption and authentication—to ensure that messages
are delivered solely to intended subscribers.
System Overview
The pACT system is built from several flexible modules that
can be combined and configured in different ways to meet specific operator demands (Figure P-10). Because the pACT network is based on the IP, operators and application providers
can take full advantage of existing applications, application
programming interfaces (APIs), and other development tools.
With pACT, a single 50-kHz channel may accommodate up to
IP, X.25
Frame relay
Figure P-10 The message center, which is the gateway or interface to the
pACT network, permits several interfaces and applications, such as Internet
applications, to be implemented. A pACT network may be configured in several ways using message centers and subnetworks of various sizes.
three individual radiofrequency (RF) carriers. Each base station is assigned a particular 12.5-kHz channel.
pACT Data Base Stations The pACT data base stations
(PDBS) are located at the cell site and relay data between
subscriber devices and the serving pACT data intermediate
system (PDIS). Typically, the PDBSs are connected to the
serving PDIS switch via a Frame Relay network. Cellular
radio system design and roaming techniques enable pACT to
determine which base station is closest to a subscriber
device each time communication takes place between the
device and the network. The mobile terminals determine cell
handoff based on signal-strength measurements implemented by the base stations.
pACT Data Intermediate System The PDIS acts as the cen-
tral switching site, routing data to and from the appropriate
base stations. It also maintains routing information for each
subscriber device in the network.
There are two versions of the PDIS: the home PDIS and
the serving PDIS. Besides switching data packets, the home
PDIS maintains a location directory and provides a forwarding service and subscriber authentication. Every subscriber
is registered in a home PDIS database. The serving PDIS
provides message forwarding, a registration directory, and
readdress services. Other services or functions are multicast, broadcast, unicast, airlink encryption, header compression (to minimize airlink use), data segmentation, frame
sequencing, and network management.
The serving PDIS is connected to the home PDIS switch.
If necessary, the two switches may be located on the same
hardware platform. Various configurations of computer
processor power and memory are available for the PDIS,
depending on requirements for computing capacity and on
how the requirements relate to traffic load and the number
of subscribers in the network. More computing capacity may
be added easily if necessary.
Message Center The fixed entry point into the pACT network
is provided by one or more message centers (MCs) that initiate, provision, and connect pACT services to private and
public networks, including corporate intranets and the
PSTN, respectively.
Every message passes through the message center, whose
functionality and applications vary according to network
operator requirements. The core of the message center is the
message store, which handles virtually any data type and
makes APIs accessible for building various applications, such
as interactive voice response (IVR) and voice or fax mail.
The message store also provides functions for operation
and maintenance, system monitoring, and event/alarm handling. Any of the message center’s databases can be queried
via the Structured Query Language (SQL). The message
center also supports virtually any protocol. Typical protocols
are the IP, Telocator Alphanumeric Protocol (TAP), Telocator
Network Paging Protocol (TNPP), and X.400 (the ITU-T
standard for message handling services).
Network Management System
The pACT network management system (NMS) gives operators full control of every component in a pACT network.
Through the NMS, each base station is provided with a set
of radio resource management (RRM) parameters that are
used to control traffic and maintain links to the network, as
well as to give instructions to mobile terminals that access
the channel.
The NMS supports the Common Management Information
Protocol (CMIP) and the Simple Network Management Protocol
(SNMP). The NMS contains a database component that permanently stores parameters, configuration data, and historical
records of traps and performance data. A pACT network may
contain more than one NMS, allowing responsibility to be
passed across time zones to other operators, ensuring 24-hour
monitoring and control.
Customer Activation System The pACT Customer Activation
System (CAS) enables customer service representatives to
manage customer accounts and to dynamically activate
pACT-related services for customers. Customer accounts are
of two types: individual and business, where individual
accounts are for single subscribers and business accounts
are for multiple subscribers.
pACT End System (Mobile Terminals) Mobile terminals
range from simple pagers to sophisticated two-way messaging devices such as PDAs or palmtop computers with wireless modems. When not being used to send messages, mobile
terminals periodically check the designated forward channel
for incoming messages; otherwise, they are usually in sleep
mode to conserve battery life.
pACT System Protocol Stack The pACT protocol stack is
based on the concepts and principles of the ITU-X.200 and
ITU-X.210 reference models, as well as service conventions
for Open Systems Interconnection (OSI). The Limited Size
Messaging (LSM) protocol provides the functionality of a
simple e-mail application protocol, such as the Simple Mail
Transfer Protocol (SMTP), but is optimized for low-bandwidth channels so that unnecessary overhead over the airlink is minimized. In addition, the LSM protocol provides a
platform for providing true two-way messaging and data
communication services. Examples of services are embedded response messaging for simple pager devices, true twoway e-mail connectivity, and multicast and broadcast
pACT’s subnetwork convergence layer provides a new
approach to encryption. To ensure that airlink bandwidth is
not spent on resynchronizing the encryption engines, pACT
devices may employ a technique that automatically resyn-
chronizes the engines, even when the underlying layers fail
to deliver a packet. This technique is important because it
provides a mechanism by which multicast and broadcast services may be encrypted.
The CDPD Link Layer is optimized for duplex, whereas
pACT uses two-way simplex. The pACT Mobile Data Link
Layer Protocol (MDLP) is an enhanced version of the link
access procedure on the D-channel (LAPD) (i.e., ITU Q.920)
that allows subscriber devices to adopt strategies for automatically resetting the link and saving power.
pACT Airlink Interface The pACT backbone network is sim-
ilar to a CDPD network. The main differences between the
two involve functionality—mostly for extending battery life
in subscriber devices—and features such as group messaging, broadcast, and unicast. The pACT protocol shortens and
reduces the number of transmissions and contains an efficient sleep mode for conserving battery power.
As an alternative to wireless IP, also known as CDPD,
Personal Air Communications Technology (pACT) supports
various paging and messaging applications while providing
more efficient use of limited spectrum. This allows wireless
carriers to stay competitive, even when they cannot easily
add more capacity to their networks. Since pACT is based on
the IP, wireless network users can access other IP-based networks such as corporate LANs and the Internet from remote
locations. With integral authentication and encryption, data
are protected as they traverse the pACT network.
See also
Cellular Data Communications
Personal Communications Services (PCS) is a set of wireless
communication services personalized to the individual.
Subscribers can tailor their service package to include only
the services they want, which may include stock quotes,
sports scores, headline news, voice mail, e-mail and fax notification, and caller ID. The service offers full roaming capability, allowing anywhere-to-anywhere communication.
Unlike many existing cellular networks, PCS is a completely digital service. The digital nature of PCS allows
antennas, receivers, and transmitters to be smaller. It also
allows for the simultaneous transmission/reception of data
and voice with no performance penalty. Eventually, PCS will
overtake analog cellular technology as the preferred method
of wireless communication.
Several technologies are being used to implement PCS.
In Europe, the underlying digital technology for Personal
Communication Networks (PCNs) is Global System for
Mobile (GSM) Telecommunications, where it has been
assigned the 1800-MHz frequency band. GSM has been
adapted for operation at 1900 MHz for PCS in the United
States (i.e., PCS 1900). Other versions of GSM are
employed to provide PCS services in other countries, such
as the Personal Handyphone System (PHS) in Japan.
Many service providers in the United States have standardized their PCS networks on Code Division Multiple
Access (CDMA) or Time Division Multiple Access (TDMA)
digital technology.
The PCS Network
A typical PCS network operates around a system of microcells—smaller versions of a cellular network’s cell sites—
each equipped with a base station transceiver. The microcell
transceivers require less power to operate but cover a more
limited range. The base stations used in the microcells can
even be placed indoors, allowing seamless coverage as the
subscriber walks into and out of buildings.
Similar to packet radio networks today, terminal devices
stay connected to the network even when not in use, allowing
the network to locate an individual within the network via
the nearest microcell and routing calls and messages directly
to the subscriber’s location. For a “follow me” service, which
incorporates more than one device, a subscriber may be
required to turn on a pager, for example, to receive messages
on that device. If the subscriber receives a phone call while
the pager is on, the network may store the call, take a message, or send the call to a personal voice-mail system and
simultaneously page the subscriber. In this way, PCS allows
the concept of universal messaging to be fully realized.
Currently, cellular switching systems operate separately
from the Public Switched Telephone Network (PSTN). When
cellular subscribers call a landline phone (and vice versa), the
two systems are interconnected to complete the communications circuit. Many PCS services are supported on the same
switches that handle calls over the wire-line network, with
the only distinction between a wireless and wire-line call
being the medium at each end of the circuit. In some places,
wireless PCS and cable television (CATV) are already integrated in a unified CDMA-based architecture called “PCS
over cable.” The use of CATV allows PCS to reach more
potential subscribers with a lower startup costs for service
Broadband and Narrowband
There are two technically distinct types of PCS: narrowband
and broadband, each of which operates on a specific part of
the radio spectrum and has unique characteristics.
Narrowband PCS is intended for two-way paging and
other types of communications that handle small bursts of
data. These services have been assigned to the 900-MHz frequency range, specifically, 901 to 912, 930 to 931, and 940 to
941 MHz. Broadband PCS is intended for more sophisticated
data services. These types of services have been assigned a
frequency range of 1850 to 1990 MHz.
Narrowband PCS and broadband PCS license ownerships
have been determined by public auctions conducted by the
Federal Communications Commission (FCC). PCS service
areas are divided into 51 regional service areas, which are
subdivided into a total of 492 metropolitan areas. There is
competition in each service area by at least two service
providers. There are 10 national service providers plus 6
regional providers in each of 5 multistate regions called
“major trading areas.”
An unlicensed portion of the PCS spectrum has been allocated from 1890 to 1930 MHz. This service is designed to
allow unlicensed operation of short-distance—typically
indoor or campus-oriented environments—voice and data
services provided by wireless LANs and wireless Public
Branch Exchanges (PBXs).
One of the largest PCS networks is operated by Sprint PCS.
At year end 2001, the company’s CDMA-based wireless network served close to 13 million customers, making it the fourth
largest wireless carrier. In addition to offering voice services
from 300 major metropolitan markets, including more than
4000 cities and communities in the United States, the company
leads the wireless industry in the number of wireless Web users
on its Internet-ready phones and devices (Figure P-11).
In addition, users may shop online at Amazon.com from
their Internet-ready Sprint PCS phones. The service supports two-way transactional electronic commerce services to
provide users with easy and convenient shopping on the
Internet. Users also easily access the Sprint PCS Wireless
Web to check e-mail, news, stock portfolios, or flight schedules. The service offers the ability to customize and receive
important news, receive e-mail and information updates
from Yahoo, as well as dial into a corporate intranet or the
Internet using a Sprint PCS phone in place of a modem connected to a laptop, PDA, or other handheld computing device.
P-11 Sprint
Wireless Web subscribers can
access more than 1.3 billion
pages of Web content via integrated search technology from
Google, which automatically
converts HyperText Markup
Language (HTML) pages into a
format optimized for Wireless
Application Protocol (WAP)
phones. This is in addition to 2.2
million Web pages that are
already WAP-formatted.
Migration to 3G
PCS service providers are in the process of migrating their
wireless networks to the global third generation (3G) framework. In the case of PCS based on CDMA, this entails a multiphase rollout of new technology that will increase the
network’s capacity for both voice and data.
The first phase of deployment will be to migrate to a Code
Division Multiple Access 2000 (CDMA 2000) network, which
will double the PCS network’s capacity for voice communications, increase data transmission speeds from 14.4 to 144
kbps, and lower handset battery consumption. In early 2003,
PCS service providers will move to the second stage of their
transition to 3G and offer data speeds of up to 384 kbps. By
late 2003, data transmission speeds will reach up to 2.4
Mbps, and in early 2004, transmission speeds for voice and
data are expected to hit between 3 and 5 Mbps.
The popularity of PCS is bringing about a variety of new
mobile and portable devices such as small, lightweight telephone handsets that work at home, in the office, or on the
street; advanced “smart” paging devices; and wireless electronic mail and other Internet-based services. PCS services
are available in all regions of the United States. Most of the
smaller PCS networks are now interconnected to the nationwide PCS networks, providing users with extensive roaming
coverage without having to switch to analog cellular on a
dual-mode handset. At this writing, momentum toward 3G
networks has stalled. Questions about how much demand
there is for 3G services and delays in 3G network implementations are causing many PCS service providers to
rethink their transition timetable.
See also
Cellular Voice Communications
Code Division Multiple Access
Global System for Mobile (GSM) Telecommunications
PCS 1900
Personal Handyphone System
Personal digital assistants (PDAs) are hand-held computers
equipped with operating system and applications software.
PDAs can be equipped with communications capabilities for
short-text messaging, e-mail, news updates, Web surfing,
voice mail, and Internet telephony. Today’s PDAs also can act
as MP3 players, voice recorders, and digital cameras with the
addition of multimedia modules. Some PDAs can even
accommodate a module that provides location information
via the Global Positioning System (GPS). PDAs are intended
for mobile users who require instant access to information
regardless of their location at any given time (Figure P-12).
The Newton MessagePad, introduced by Apple Computer
in 1993, was the first true PDA. Trumpeted as a major milestone of the information age, the MessagePad was soon
joined by similar products from such companies as HewlettPackard, Motorola, Sharp, and Sony.
These early hand-held devices were hampered by poor performance, excessive weight, and unstable software. Without a
wireless communications infrastructure, there was no com-
Figure P-12 Palm Computing offers one of the most popular lines of PDAs. This Palm V, shown with cradle charger
and HotSync serial cable, weighs in at only 4 ounces.
pelling advantage of owning a PDA. With the performance limitations largely corrected and the emergence of new wireless
PCS—plus continuing advances in operating systems, connectivity options, and battery technology—PDAs are now well on
the way toward fulfilling their potential.
Real estate agents, medical professionals, field service technicians, and delivery people are just a few of the people using
PDAs. Real estate agents can use PDAs to conveniently
browse through property listings at client locations. Health
care professionals can use PDAs to improve their ability to
access, collect, and record patient information at the point of
care. Numerous retailers and distributors can collect inventory data on the store and warehouse floor and later export
tose data into a spreadsheet on a PC. Insurance agents,
auditors, and inspectors can use PDAs to record data in the
field and then instantly transfer those data to PCs and databases at the home office.
For professionals who tote around a laptop computer to
give presentations with Microsoft PowerPoint, there is a module for the Springboard Visor that connects the device directly
to digital projectors (or other VGA displays) with an interface
cable. The user downloads the presentation material from a
PC to the Visor and then taps an icon displayed on the Visor
screen to start the 1024 × 768 resolution color presentation.
The user can even control the presentation from anywhere in
the room using the product’s infrared remote control.
PDA Components
Aside from the case, PDA components include a screen, keypad, or other type of input device; an operating system;
memory; and battery. Many PDAs can be outfitted with
fax/modem cards and a docking station to facilitate direct
connection to a PC or LAN for data transfers and file synchronization. Some PDAs, such as Palm Computing’s Palm
VII, have a wireless capability that allows information
retrieval from the Internet. Of course, PDAs run numerous
applications to help users stay organized and productive.
Some PDAs have integral 56-kbps modems and serial ports
that allow them to be attached via cable to other devices.
A unique PDA is Handspring’s Visor, which uses the
Palm OS operating system. What makes the Visor unique
is that it is expandable via an external expansion slot
called a Springboard. In addition to backup storage and
flash storage modules, the slot lets users add software and
hardware modules that completely change the function of
the Visor. Springboard modules allow the Visor to become
an MP3 player, pager, modem, GPS receiver, e-book, or
video game device.
Display The biggest limitation of PDAs is the size of their
screens. Visibility is greatly improved through the use of
nonglare screens and backlighting, which aid viewing and
entering information in any lighting condition. In a dim
indoor environment, backlighting is a virtual necessity, but
it drains the battery faster. Some PDAs offer user-controllable
backlighting, while others let the user set a timer that shuts
off the screen automatically after the unit has been idle for a
specified period of time. Both features greatly extend battery
life. Other PDAs, such as the Visor Prism, feature an
active-matrix backlit display capable of displaying over
65,000 colors.
Keyboard Some PDAs have on-screen keyboards, but they
are too small to permit touch typing. The use of a stylus
speeds up text input and makes task selection easier. Of
course, the instrument can be used for handwritten notes.
The PDA’s handwriting-recognition capability enables the
notes to be stored as text for use by various applications,
such as a date book, address book, and to-do list. As an
option, foldout full-size keyboards are available that
attach to the PDA. They weigh only 8 ounces, making it
much easier to respond to e-mail, compose memos, and
take notes without having to lug around a laptop.
Operating Systems A PDA’s operating system provides the
foundation on which applications run. The operating system
may offer handwriting recognition, for example, and include
solutions for organizing and communicating information via
fax or electronic mail, as well as the ability to integrate with
Windows and Mac OS-based computers in enterprise environments. The operating system also may include built-in
support for a range of modems and third-party paging and
cellular communication solutions. Because memory is limited in a PDA, usually between 2 and 64 MB, the operating
system and the applications that run on it must be compact.
Some operating systems come with useful utilities. There
are utilities that set up direct connections between the PDA
and desktop applications to transfer files between them via
a cable or infrared connection. A synchronization utility
ensures that the user is working from the latest version of a
file. Some operating systems offer tools called “intelligent
agents” that automate routine tasks. An intelligent agent
can be programmed to set up a connection to the Internet, for
example, and check for e-mail. To activate this process, the
user might only have to touch an icon on the PDA’s screen
with a pen.
There are two major operating systems in use today—
Microsoft’s Pocket PC platform and the Palm OS. Pocket
PC’s predecessor, Windows CE, was too difficult to use and
not powerful enough to draw users away from the popular
Palm OS. But the Pocket PC’s redesigned interface overcomes most of Windows CE’s previous problems.
The Pocket PC platform is a version of Windows that preserves the familiarity of the Windows-based desktop and
integrates seamlessly with Outlook, Word, and Excel. The
platform includes a version of Internet Explorer for brows-
ing the Web over a wireless connection or ordinary phone
line and Windows Media Player for listening to digital music
and watching digital videos. It also includes Microsoft
Reader for reading e-books downloaded from the Internet.
Palm OS is a more efficient operating system than Pocket
PC. Consequently, it requires less processing power and less
memory than equivalent products using the Pocket PC operating system.
Memory Although PDAs come with a base of applications
built into ROM—usually a file manager, word processor, and
scheduler—users can install other applications as well. New
applications and data are stored in RAM. At a minimum,
PDAs come with only 2 MB, while others offer up to 64 MB.
When equipped with 2 MB of memory, the PDA can store
approximately 6000 addresses, 5 years of appointments,
1500 to-do items, and 1500 memos. Some PDAs have a PC
card (formerly PCMCIA) slot that can accommodate storage
cards that are purchased separately.
Even though many Pocket PC products come in higher
memory configurations, an 8-MB Palm OS product can store
as much or even more information than a 16-MB Pocket PC
product with little performance degradation. The better performance is due to the efficiencies of the Palm OS, which
uses less memory and processing power than equivalent
products based on Pocket PC. Since greater memory capacity increases the overall price of the product, vendors like
Handspring believe that 8 MB offers the most utility at the
most competitive price.
Power Many PDAs use ordinary AAA alkaline batteries.
Manufacturers claim a battery life of 45 hours when users
search for data 5 minutes out of every hour the unit is turned
on. Of course, using the backlight display will drain the batteries much faster. Using the backlight will reduce battery
life by about 22 percent. Other power sources commonly
used with PDAs include an ac adapter and rechargeable
lithium-ion battery.
The rechargeable battery offers more flexible power management in a smaller space. The components that operate the
color screen increase the power draw from the battery. With
AAA batteries, the user would have to replace them rather
frequently. The rechargeable battery solution enhances the
user’s experience by providing full power in a pocket-sized
package. Lithium-ion rechargeable batteries offer 2 hours of
continuous use.
Fax/Modems Some PDAs come with an external fax/modem
to support basic messaging needs when hooked up to a telephone line. Others offer a PC card slot (formerly PCMCIA)
that can accept not only fax/modems but also storage cards.
With fax/modems, PDA users can receive a fax from their
office, annotate it, and fax it back with comments written on
it in “electronic ink.”
There are wireless Ethernet modules available that allow
the user to roam about the workplace or campus with secure
connections, peer-to-peer links between devices, and highspeed access to the Internet, e-mail, and network resources.
Transmissions of up to 11 Mbps are possible, but actual
throughput is determined by the speed of the PDA’s processor.
The modules adhere to the IEEE 802.11b high-rate standard
for wireless LANs and support 40- or 128-bit Wired-Equivalent
Privacy (WEP) encryption. Transmission ranges of up to 1000
feet (300 meters) in open environments and 300 feet (90
meters) in office environments are supported.
Cradle A cradle allows the PDA to connect to a desktop PC
via a standard serial cable or USB cable. The user simply
drops the PDA into the cradle and presses a button to automatically synchronize desktop files with those held in the
PDA. An alternative to cable is an infrared (IR) connection.
With an IR-enabled PDA, users not only can swap and synchronize files with a PC but also can beam business cards,
phone lists, memos, and add-on applications to other IRenabled PDAs. IR-enabled PDAs also can use third-party
beaming applications with IR-enabled phones, printers, and
other devices.
Improvements in technology and the availability of wireless
communications services, including PCS, overcome many of
the limitations of early PDA products, making today’s handheld devices very attractive to mobile professionals. In the
process, PDAs are finding acceptance beyond vertical markets and finally becoming popular among consumers, particularly those looking for an alternative to notebook computers
and younger people who want a versatile device from which
they also can play MP3 music files and games as well as
read e-books.
See also
Cellular Telephones
Global System for Mobile (GSM) Telecommunications
Personal Communication Services
Personal Handyphone System
The Personal Handyphone System (PHS) is a wireless technology that offers high-quality, low-cost mobile telephone
services using a fully digital system operating in the 1.9GHz range. Originally developed by NTT, the Japanese
telecommunications giant, PHS is based on the Global
System for Mobile (GSM) Telecommunications standard.
PHS made its debut in Japan in July 1995, where service
was initially offered in metropolitan Tokyo and Sapporo.
Although PHS was originally developed in Japan, it is now
considered a pan-Asian standard.
Advantages over Cellular
PHS phones (Handyphones) operate at 1.9 GHz, whereas
cellular phones operate at 800 MHz. To achieve high voice
quality, PHS uses a portion of its capacity to support a highperformance voice-encoding algorithm called Adaptive
Differential Pulse Code Modulation (ADPCM). With this
algorithm, PHS can support a much higher data throughput
(32 kbps) than a cellular-based system, enabling PHS to support fax and voice-mail services and emerging multimedia
applications such as high-speed Internet access and photo
and video transmission.
PHS supports the handoff of calls from one microcell to
the next during roaming. However, PHS goes a step farther
than cellular by giving users the flexibility to make calls at
home (just like conventional cordless phones), at school, in
the office, while riding the subway, or while roaming through
the streets. PHS also gives subscribers more security and
complete privacy. And unlike cellular phones, PHS phones
cannot be cloned for fraudulent use.
Another key advantage of PHS over cellular is cost—PHS
can provide mobile communications more economically that
cellular. Through its efficient microcell architecture and use
of the public network, startup and expansion costs for operators are minimized. As a result, total per-subscriber costs
tend to be much lower than with traditional cellular networks. Because PHS is a “low tier” microcellular wireless
network, it offers far greater capacity per dollar of infrastructure than existing cellular networks, which results in
lower calling rates. In Japan, the cost of a 3-minute call
using a PHS handset is comparable to the cost of making
that same call on a public phone.
Not only are PHS handsets extremely small and lightweight—almost half the size and weight of cellular hand-
sets—but the battery life of PHS handsets is superior to that
offered by cellular handsets. PHS phones output 10 to 20 milliwatts, whereas most cellular phones output between 1 and
5 watts. Whereas the typical cellular handset has a battery
life of 3 hours talk time, the typical PHS handset has a battery life of 6 hours talk time. Whereas the typical cellular
handset has a battery life of 50 hours in standby mode, the
typical PHS handset has a battery life of 200 hours in
standby mode (more than a week). The low-power operation
of PHS handsets is achieved through strict built-in power
management and “sleep” functions in individual circuits.
There are a number of applications of PHS technology. In the
area of mobile telecommunications, users can establish communications through public cell stations, which are installed
throughout a serving area. PHS phones also can be used
with a home base station as a residential cordless telephone
at the Public Switched Telephone Network (PSTN) tariff.
When used in the local loop, PHS provides the means to
access the PSTN in areas where conventional local loops—
consisting of copper wire, optical fiber, or coaxial cable—are
impractical or not available.
PHS also can be adopted as a digital cordless PBX for
office use, providing readily expandable, seamless communications throughout a large office building or campus. Users
carry PHS handsets with them and are no longer chained to
their desks by their communications systems. As a digital
system, PHS provides a level of voice quality not normally
associated with a cordless telephone. In addition, the digital
signal employed by PHS provides security for corporate communications, and the system’s microcell architecture can be
reconfigured easily to accommodate increases or decreases
in the number of users. Another benefit of PHS is the ease
and minimal expense with which the entire network can be
dismantled and set up again in another facility if, for example, a business decides to relocate its offices.
For personal use as a cordless telephone at home, PHS is
a low-cost mobile solution that allows the customer to use a
single handset at home and out of doors with a digital signal
that provides improved voice quality for a cordless phone
and enough capacity for data and fax transmissions that are
increasingly a part of users’ home communications.
Network Architecture
The PHS radio interface offers four-channel Time Division
Multiple Access with Time Division Duplexing (TDMA/TDD),
which provides one control channel and three traffic channels
for each cell station.
The base station allocates channels dynamically and is
not constrained by a frequency reuse scheme, thus deriving
the maximum advantage of carrier-switched TDMA. This
means that PHS handsets communicating to a base station
may all be on different carrier frequencies.
The PHS system uses a microcell configuration that creates a radio zone with a 100- to 300-meter diameter. The base
stations themselves are spaced a maximum of 500 meters
apart. In urban areas, the microcell configuration is capable
of supporting several million subscribers. This configuration
also makes possible smaller and lighter handsets and the
more efficient reuse of radio spectrum to conserve frequency
bands. In turn, this permits very low transmitter power consumption and, as a result, much longer handset talk times
and standby times than are possible with cellular handsets.
A drawback of the lower operating power level is the
smaller radius that a PHS base station can cover: only 100
to 300 meters, versus at least 1500 meters for cellular base
stations. The extra power of cellular systems improves penetration of the signals into buildings, whereas PHS may
require an extra base station inside some buildings. Another
drawback of PHS is that the quality of reception can dimin-
ish significantly when mobile users are traveling at a rate
greater than 15 miles per hour.
Since PHS uses the public network rather than dedicated
facilities between microcells, the only service startup requirements are handsets, cell stations, a PHS server, and a database of services to support PHS network operation. With no
separate transmission network needed for connecting cell stations and for call routing, carriers can introduce PHS service
with little initial capital investment.
Service Features
PHS is a feature-rich service, giving Handyphone users
access to a variety of call-handling features, including
Call forwarding To a fixed line, to another PHS phone, or
to a voice mail box.
Call waiting Alerts the subscriber of an incoming call.
Call hold Enables the subscriber to alternate between two
Call barring Restricts any incoming local or international
Calling line identification (CLI) Displays the number of
the incoming call, informing the subscriber of the caller’s
Voice mail The subscriber receives recorded messages,
even when the phone is busy or turned off.
Text messaging Enables the subscriber to send and
receive text messages through the PHS phone.
International roaming Enables subscribers to use their
PHS phones in another country but be billed by the service provider in their home country.
Depending on the implementation progress of the service
provider, the following value-added data services also may
be available to Handyphone users:
Virtual fax Enables subscribers to retrieve fax messages
anywhere, have fax messages sent to a Handyphone, or
have them redirected to any fax machine.
Fax By attaching the Handyphone to a laptop or desktop
computer, subscribers can send and receive faxes anywhere.
E-mail/Internet access Allows subscribers to retrieve email from the Internet through the Handyphone.
Conference calls Enables subscribers to talk to as many as
four other parties at the same time.
News, sports scores, and stock quotes Enables subscribers
to obtain a variety of information on a real-time basis.
Many other types of services can be implemented over
PHS. There is already the world’s first consumer-oriented
videophone service in Japan. Kyocera Corp. offers a mobile
phone able to transmit a caller’s image and voice simultaneously. Two color images are transmitted per second
through a camera mounted on the top of the handset. The
recipient can view the caller via a 2-inch active matrix liquid-crystal display (LCD). Since the transmission technology sends data at only 32 kbps, however, this makes for
jerky video images.
While 32-kbps channels are now available in Japan,
research is now under way to achieve a transmission rate of
64 kbps through the combined use of two channels. With
this much capacity, PHS can be extended to a variety of
other services in the future, including better-quality video.
In combination with a small, lightweight portable data terminal, PHS also may be used to realize the concept of
“mobile network computing,” whereby users would access
application software stored on the Internet. With the limited memory and disk storage capacity of the PHS terminals, the applications and associated programs would stay
on the Internet, preventing the PHS devices from becoming
See also
Cellular Data Communications
Cellular Voice Communications
Global System for Mobile (GSM) Telecommunications
Personal Access Communications Systems
Personal Communication Services
Personal Digital Assistants
Since the 1920s, Private Land Mobile Radio Services
(PLMRS) have been meeting the internal communication
needs of private companies, state and local governments,
and other organizations. These services provide voice and
data communications that allow users to control their business operations and production processes, protect worker
and public safety, and respond quickly in times of natural
disaster or other emergencies.
In 1934, shortly after its establishment, the Federal
Communications Commission (FCC) identified four private
land mobile services—Emergency Service, Geophysical
Service; Mobile Press Service, and Temporary Service, which
applied to frequencies used by the motion picture industry.
Over the years, the FCC refined these categories. Until
1997, PLMRS consisted of 20 services spread among six
service categories: Public Safety, Special Emergency,
Industrial, Land Transportation, Radiolocation, and Transportation Infrastructure. In that year, the FCC did away
with 20 discrete radio services and the six service categories
and replaced them with two frequency pools: the Public
Safety Pool and the Industrial/Business Pool. Table P-1
Radio Services in the Two Frequency Pools
Public Safety Pool
Local Government Radio Service
Police Radio Service
Fire Radio Service
Highway Maintenance Radio
Forestry-Conservation Radio
Emergency Medical Radio Service
Special Emergency Radio Service
Industrial/Business Pool
Power Radio Service
Petroleum Radio Service
Forest Products Radio Service
Film and Video Production Radio
Relay Press Radio Service
Special Industrial Radio Service
Business Radio Service
Manufacturers Radio Service
Telephone Maintenance Radio
Motor Carrier Radio Service
Railroad Radio Service
Taxicab Radio Service
Automobile Emergency Radio
summarizes the reorganization of the 20 radio services into
the two frequency pools.
Public Safety Radio Pool
The Public Safety Radio Pool was created in 1997. It covers
the licensing of the radio communications of state and local
governmental entities and the following categories of activities: medical services, rescue organizations, veterinarians,
persons with disabilities, disaster-relief organizations,
school buses, beach patrols, establishments in isolated
places, communications standby facilities, and emergency
repair of public communications facilities.
The FCC has established an 800-MHz National Plan that
specifies special policies and procedures governing the
Public Safety Pool. The principal spectrum resource for the
National Plan is the 821- to 824-MHz and the 866- to 869MHz bands. The National Plan establishes planning regions
covering all parts of the United States, Puerto Rico, and the
U.S. Virgin Islands. The license application to provide service must be approved by the appropriate regional planning
committee before frequency assignments will be made in
these bands.
Industrial/Business Pool
The Industrial/Business Pool consists of a number of frequencies that were previously allotted to the Industrial or
Land Transportation Radio Services, including the Business
Radio Service. Anyone eligible in one of these radio services
is eligible in the new Industrial/Business Pool for any frequency in that pool. In this regard, the FCC has adopted the
eligibility criteria from the old Business Radio Service. The
Industrial/Business Radio Pool covers the licensing of the
radio communications of entities engaged in commercial
activities; engaged in clergy activities; operating educational, philanthropic, or ecclesiastical institutions; or operating hospitals, clinics, or medical associations.
General Access Pool
Prior to 1977, channels in the 470- to 512-MHz band were
allocated to seven frequency pools based on category of eligibility. The FCC eliminated the separate allocation to these
pools and created a General Access Pool to permit greater
flexibility and foster more effective and efficient use of the
470- to 512-MHz band. Frequencies in the 470- to 512-MHz
band are shared with UHF TV Channels 14 to 20 and are
available in only 11 cities, listed in Table P-2.
All unassigned channels, including those which subsequently become unassigned, are considered to be in the
General Access Pool and available to all eligible parties on a
first-come, first-served basis. If a channel is assigned in an
area, however, subsequent authorizations on that channel
will only be granted to users from the same category.
Cities with General Access Pool Frequencies
Urban Areas
Frequencies (MHz)
Boston, MA
Chicago, IL
Dallas/Fort Worth, TX
Houston, TX
Los Angeles, CA
Miami, FL
New York/Northeast NJ
Philadelphia, PA
Pittsburgh, PA
San Francisco/Oakland, CA
Washington, DC/MD/VA
Applications for PLMRS
PLMRS are used by organizations that are engaged in a
wide variety of activities. Police, fire, ambulance, and emergency relief organizations such as the Red Cross use private
wireless systems to dispatch help when emergency calls
come in or disaster strikes. Utility companies, railroad and
other transportation providers, and other infrastructurerelated companies use their systems to provide vital day-today control of their systems (including monitoring and
control and routine maintenance and repair), as well as to
respond to emergencies and disasters—often working with
public safety agencies. A wide variety of businesses, including
package delivery companies, plumbers, airlines, taxis, manufacturers, and even the American Automobile Association
(AAA), rely on private wireless systems to monitor, control,
and coordinate their production processes, personnel, and
Although commercial services can serve some of the needs
of these organizations, private users generally believe that
their own systems provide them with capabilities, features,
and efficiencies that commercial services cannot. Some of
the requirements and features that PLMRS users believe
make their systems unique include
Immediate access to a radio channel (no dialing required)
Coverage in areas where commercial systems cannot provide service
Peak usage patterns that could overwhelm commercial
High reliability
Priority access, especially in emergencies
Specialized equipment required by the job
Radio Trunking
In a conventional radio system, a radio can access only one
channel at a time. If that channel is in use, the user must
either wait for the channel to become idle or manually
search for a free channel. A trunked radio system differs
from a conventional system by having the ability to automatically search all available channels for one that is clear.
The FCC has recognized two types of trunking: centralized
and decentralized. A centralized trunked system uses one or
more control channels to transmit channel-assignment information to the mobile radios. In a decentralized trunked system, the mobile radios scan the available channels and find
one that is clear.
The rules require that licensees take reasonable precautions to avoid causing harmful interference, including monitoring the transmitting frequency for communications in
progress. This requirement is met in decentralized trunked
systems because each mobile unit monitors each channel
and finds a clear one on which to transmit. In a centralized
trunked radio system, radios typically monitor the control
channel(s), not the specific transmit frequencies. Therefore,
this form of trunking generally has not been allowed in the
shared bands below 800 MHz.
Under certain conditions, however, the FCC allows some
licensees to implement centralized trunked radio systems in
the shared bands below 800 MHz. Centralized trunking may
be authorized if the licensee has an exclusive service area
and uses the 470- to 512-MHz band only. If the licensee does
not have an exclusive service area, it must obtain consent
from all licensees who have cochannel and/or adjacent channel stations.
Private radio systems serve a great variety of communication needs that common carriers and other commercial service providers traditionally have not been able or willing to
fulfill. Companies large and small use their private systems
to support their business operations, safety, and emergency
needs. The one characteristic that all these uses share—and
that differentiates private wireless use from commercial
use—is that private wireless licensees use radio as a tool to
accomplish their missions in the most effective and efficient
ways possible.
Private radio users employ wireless communications as
they would any other tool or machine—radio contributes to
their production of some other good or service. For commercial wireless service providers, by contrast, the services
offered over the radio system are the end products. Cellular,
PCS, and Specialized Mobile Radio (SMR) providers sell service or capacity on wireless systems, permitting a wide
range of mobile and portable communications that extend
the national communications infrastructure. This difference
in purpose is significant because it determines how the services are regulated.
See also
Cellular Data Communications
Cellular Voice Communications
Federal Communications Commission
Personal Communication Services
Specialized Mobile Radio
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As the term implies, radio communication interception is the
capture of radio signals by a scanning device for the purpose
of eavesdropping on a voice call or learning the contents of
data messages. When it comes to the interception of radio
communications, the Federal Communications Commission
(FCC) has the authority to interpret Section 705 of the
Communications Act, 47 U.S.C. Section 605, which deals
with “Unauthorized Publication of Communications.”
Although the act of intercepting radio communications
may violate other federal or state statutes, this provision
generally does not prohibit the mere interception of radio
communications. For example, if someone happens to overhear a conversation on a neighbor’s cordless telephone, this
is not a violation of the Communications Act. Similarly, if
someone listens to radio transmissions on a scanner, such
as emergency service reports, this is not a violation of
Section 705.
A violation of Section 705 would occur, however, if a person
were to divulge or publish what he or she hears or use it for
his or her own or someone else’s benefit. An example of using
an intercepted call for a beneficial use in violation of Section
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
705 would be someone listening to accident reports on a
police channel and then driving or sending one of his or her
own tow trucks to the reported accident scene in order to
obtain business.
The Communications Act does allow for the divulgence of
certain types of radio transmissions. The statute specifies
that there are no restrictions on the divulgence or use of
radio communications that have been transmitted for the
use of the general public, such as transmissions of a local
radio or television broadcast station. Likewise, there are no
restrictions on divulging or using radio transmissions originating from ships, aircraft, vehicles, or persons in distress.
Transmissions by amateur radio or citizens’ band radio operators are also exempt from interception restrictions.
In addition, courts have held that the act of viewing a
transmission (such as a pay television signal) that the
viewer was not authorized to receive is a “publication” violating Section 705. This section also has special provisions
governing the interception of satellite television programming transmitted to cable operators. The section prohibits
the interception of satellite cable programming for private
home viewing whether the programming is scrambled or not
scrambled but is sold through a marketing system. In these
circumstances, authorization must be obtained from the programming provider to legally intercept the transmission.
The act also contains provisions that affect the manufacture of equipment used for listening or receiving radio
transmissions, such as scanners. Section 302(d) of the
Communications Act, 47 U.S.C. Section 302(d), prohibits
the FCC from authorizing scanning equipment that is capable of receiving transmissions in the frequencies allocated to
domestic cellular services, that is capable of readily being
altered by the user to intercept cellular communications, or
that may be equipped with decoders that convert digital
transmissions to analog voice audio. And since April 26,
1994 (47 CFR 15.121), such receivers may not be manufactured in the United States or imported for use in the United
States. FCC regulations also prohibit the sale or lease of
such scanning equipment (47 CFR 2.803).
Government Interception
While intercepting radio communications for beneficial
purposes is illegal in the United States, the federal government systematically engages in such monitoring for the
purpose of learning industrial secrets. Under a program
known as “Echelon,” a satellite interception system, private
and commercial communications are monitored around the
world. The program is run by five nations—the United
States, the United Kingdom, Canada, Australia, and New
Zealand. France and Russia are also known to have systems
of their own.
Business is often subject to surveillance involving economic data, such as details of developments in individual
sectors of the economy, developments in commodity markets,
or compliance with economic embargoes. Although this is
ostensibly the purpose behind Echelon, some countries claim
that it is also used for industrial espionage; specifically for
spying on foreign businesses with the aim of securing a competitive advantage for firms in the home country. While it is
often maintained that Echelon has been used in this way, no
such case has been substantiated.
The FCC receives many inquiries regarding the interception
and recording of telephone conversations. To the extent that
these conversations are radio transmissions, there would be no
violation of Section 705 if no divulgence or beneficial use of the
conversation takes place. Again, however, the mere interception of some telephone-related radio transmissions—whether
cellular, cordless, or landline conversations—may constitute a
criminal violation of other federal or state statutes.
See also
Federal Communications Commission
Fraud Management
Wired Equivalent Privacy
Wireless Security
The common platform from which to monitor multivendor wireless and wired networks is the Simple Network Management
Protocol’s (SNMP’s) Remote Monitoring (RMON) Management
Information Base (MIB). Although a variety of SNMP MIBs collect performance statistics to provide a snapshot of events,
RMON enhances this monitoring capability by keeping a past
record of events that can be used for fault diagnosis, performance tuning, and network planning. RMON works on wired,
wireless and hybrid networks.
Hardware- and/or software-based RMON-compliant devices
(i.e., probes) placed on each network segment monitor all data
packets sent and received. The probes view every packet and
produce summary information on various types of packets,
such as undersized packets, and events, such as packet collisions. The probes also can capture packets according to predefined criteria set by the network manager or test technician. At
any time, the RMON probe can be queried for this information
by a network management application or an SNMP-based
management console so that detailed analysis can be performed in an effort to pinpoint where and why an error
The original Remote Network Monitoring MIB defined a
framework for the remote monitoring of Ethernet. Subsequent
RMON MIBs have extended this framework to Token Ring and
other types of networks. A map of the RMON MIB for Ethernet
and Token Ring is shown in Figure R-1.
Ring Station Control
Ring Station
Ring Station
Ethernet Statistics
Token Ring
MAC Layer Statistics
Source Routing
Token Ring
Token Ring
MAC Layer
Ring Station
Ring Station
Traffic Matrix
Host Top N
Token Ring
Figure R-1 A map of SNMP’s remote monitoring management information base—RMON MIB.
RMON Applications
A management application that views the internetwork, for
example, gathers data from RMON agents running on each
segment in the network. The data are integrated and correlated to provide various internetwork views that provide
end-to-end visibility of network traffic, both local area network (LAN) and wide area network (WAN). The operator can
switch between a variety of views.
For example, the operator can switch between a Media
Access Control (MAC) view (which shows traffic going through
routers and gateways) and a network view (which shows endto-end traffic) or can apply filters to see only traffic of a given
protocol or suite of protocols. These traffic matrices provide the
information necessary to configure or partition the internetwork to optimize LAN and WAN utilization.
In selecting the MAC level view, for example, the network
map shows each node of a segment separately, indicating
intrasegment node-to-node data traffic. It also shows total
intersegment data traffic from routers and gateways. This
combination allows the operator to see consolidated internetwork traffic and how each end node contributes to it.
In selecting the network level view, the network map
shows end-to-end data traffic between nodes across segments. By connecting source and ultimate destination without clouding the view with routers and gateways, the
operator can immediately identify specific areas contributing to an unbalanced traffic load.
Another type of application allows the network manager
to consolidate and present multiple segment information,
configure RMON alarms, and provide complete Token Ring
RMON information, as well as perform baseline measurements and long-term reporting. Alarms can be set on any
RMON variable. Notification via traps can be sent to multiple management stations. Baseline statistics allow longterm trend analysis of network traffic patterns that can be
used to plan for network growth.
Ethernet Object Groups
The RMON specification consists of nine Ethernet/Token
Ring groups and ten specific Token Ring RMON extensions
(see Figure R-1).
Ethernet Statistics Group The Statistics Group provides seg-
ment-level statistics (Figure R-2). These statistics show
packets, octets (or bytes), broadcasts, multicasts, and collisions on the local segment, as well as the number of occurrences of packets dropped by the agent. Each statistic is
maintained in its own 32-bit cumulative counter. Real-time
packet size distribution is also provided.
Figure R-2 The Ethernet Statistics window accessed from Enterasys
Networks’ NetSight Element Manager. This window would be used to view a
detailed statistical breakdown of traffic on the monitored Ethernet network
segment. The data provided apply only to the interface or network segment.
Ethernet History Group With the exception of packet size
distribution, which is provided only on a real-time basis, the
History Group provides historical views of the statistics provided in the Statistics Group. The History Group can
respond to user-defined sampling intervals and bucket counters, allowing for some customization in trend analysis.
The RMON MIB comes with two defaults for trend analysis. The first provides for 50 buckets (or samples) of 30-second sampling intervals over a period of 25 minutes. The
second provides for 50 buckets of 30-minute sampling intervals over a period of 25 hours. Users can modify either of
these or add additional intervals to meet specific requirements for historical analysis. The sampling interval can
range from 1 second to 1 hour.
Host Table Group The RMON MIB specifies a host table that
includes node traffic statistics: packets sent and received,
octets sent and received, as well as broadcasts, multicasts,
and errored packets sent. In the host table, the classification
“errors sent” is the combination of packet undersizes, fragments, cyclic redundancy check (CRC)/alignment errors, collisions, and oversizes sent by each node.
The RMON MIB also includes a host timetable that shows
the relative order in which the agent discovered each host.
This feature is not only useful for network management
purposes but also assists in uploading those nodes to the
management station of which it is not yet aware. This
reduces unnecessary SNMP traffic on the network.
Host Top N Group The Host Top N Group extends the host
table by providing sorted host statistics, such as the top 10
nodes sending packets or an ordered list of all nodes according to the errors sent over the last 24 hours. The data selected
and the duration of the study are both defined at the network
management station. The number of studies that can be run
depends on the resources of the monitoring device.
When a set of statistics is selected for study, only the
selected statistics are maintained in the Host Top N counters; other statistics over the same time intervals are not
available for later study. This processing—performed
remotely in the RMON MIB agent—reduces SNMP traffic on
the network and the processing load on the management
station, which would otherwise need to use SNMP to
retrieve the entire host table for local processing.
Alarms Group The Alarms Group provides a general mechanism for setting thresholds and sampling intervals to generate events on any counter or integer maintained by the
agent, such as segment statistics, node traffic statistics
defined in the host table, or any user-defined packet match
counter defined in the Filters Group. Both rising and
falling thresholds can be set, each of which can indicate
network faults. Thresholds can be established for both the
absolute value of a statistic and its delta value, enabling
the manager to be notified of rapid spikes or drops in a
monitored value.
Filters Group The Filters Group provides a generic filtering
engine that implements all packet capture functions and
events. The packet capture buffer is filled with only those
packets that match the user-specified filtering criteria.
Filtering conditions can be combined using the Boolean
parameters “and” or “not.” Multiple filters are combined
with the Boolean “or” parameter.
Packet Capture Group The types of packets collected
depend on the Filter Group. The Packet Capture Group
allows the user to create multiple capture buffers and to
control whether the trace buffers will wrap (overwrite)
when full or stop capturing. The user may expand or contract the size of the buffer to fit immediate needs for packet
capturing rather than permanently commit memory that
will not always be needed.
Notifications (Events) Group In a distributed management
environment, the RMON MIB agent can deliver traps to multiple management stations that share a single community
name destination specified for the trap. In addition to the
three traps already mentioned—rising threshold and falling
threshold (see Alarms Group) and packet match (see Packet
Capture Group)—seven additional traps can be specified:
coldStart This trap indicates that the sending protocol
entity is reinitializing itself such that the agent’s configuration or the protocol entity implementation may be altered.
warmStart This trap indicates that the sending protocol
entity is reinitializing itself such that neither the agent configuration nor the protocol entity implementation is altered.
linkDown This trap indicates that the sending protocol
entity recognizes a failure in one of the communication
links represented in the agent’s configuration.
linkUp This trap indicates that the sending protocol
entity recognizes that one of the communication links represented in the agent’s configuration has come up.
authenticationFailure This trap indicates that the sending
protocol entity is the addressee of a protocol message that
is not properly authenticated. While implementations of
the SNMP must be capable of generating this trap, they
also must be capable of suppressing the emission of such
traps via an implementation-specific mechanism.
egpNeighborLoss This trap indicates that an External
Gateway Protocol (EGP) neighbor for whom the sending
protocol entity was an EGP peer has been marked down
and the peer relationship is no longer valid.
enterpriseSpecific This trap indicates that the sending
protocol entity recognizes that some enterprise-specific
event has occurred.
The Notifications (Events) Group allows users to specify
the number of events that can be sent to the monitor log.
From the log, any specified event can be sent to the management station. The log includes the time of day for each
event and a description of the event written by the vendor of
the monitor. The log overwrites when full, so events may be
lost if not uploaded to the management station periodically.
Traffic Matrix Group The RMON MIB includes a traffic
matrix at the MAC layer. A traffic matrix shows the amount
of traffic and number of errors between pairs of nodes—one
source and one destination address per pair. For each pair, the
RMON MIB maintains counters for the number of packets,
number of octets, and error packets between the nodes. Users
can sort this information by source or destination address.
Applying remote monitoring and statistics-gathering
capabilities to the Ethernet environment offers a number of
benefits. The availability of critical networks is maximized,
since remote capabilities allow for a more timely resolution
of the problem. With the capability to resolve problems
remotely, operations staff can avoid costly travel to troubleshoot problems on site. With the capability to analyze
data collected at specific intervals over a long period of time,
intermittent problems can be tracked down that would normally go undetected and unresolved.
Token Ring Extensions
As noted, the first version of RMON defined media-specific
objects for Ethernet only. Later, media-specific objects for
Token Ring were added.
Token Ring MAC-Layer Statistics This extension provides
statistics, diagnostics, and event notification associated with
MAC traffic on the local ring. Statistics include the number
of beacons, purges, and IEEE 803.5 MAC management packets and events; MAC packets; MAC octets; and ring soft
error totals.
Token Ring Promiscuous Statistics This extension collects
utilization statistics of all user data traffic (non-MAC) on the
local ring. Statistics include the number of data packets and
octets, broadcast and multicast packets, and data frame size
Token Ring MAC-Layer History This extension offers histor-
ical views of MAC-layer statistics based on user-defined
sample intervals, which can be set from 1 second to 1 hour to
allow short- or long-term historical analysis.
Token Ring Promiscuous History This extension offers histori-
cal views of promiscuous (i.e., unfiltered) statistics based on
user-defined sample intervals, which can be set from 1 second
to 1 hour to allow short-term or long-term historical analysis.
Ring Station Control Table This extension lists status infor-
mation for each ring being monitored. Statistics include ring
state, active monitor, hard error beacon fault domain, and
number of active stations.
Ring Station Table This extension provides diagnostics and
status information for each station on the ring. The type of
information collected includes station MAC address, status,
and isolating and nonisolating soft error diagnostics.
Source Routing Statistics The extension for source routing
statistics is used for monitoring the efficiency of source-routing processes by keeping track of the number of data packets
routed into, out of, and through each ring segment. Traffic
distribution by hop count provides an indication of how much
bandwidth is being consumed by traffic-routing functions.
Ring Station Configuration Control The extension for station
configuration control provides a description of the network’s
physical configuration. A media fault is reported as a “fault
domain,” an area that isolates the problem to two adjacent
nodes and the wiring between them. The network administrator can discover the exact location of the problem—the fault
domain—by referring to the network map. Some faults result
from changes to the physical ring—including each time a station inserts or removes itself from the network. This type of
fault is discovered through a comparison of the start of symptoms and the timing of the physical changes.
The RMON MIB not only keeps track of the status of each
station but also reports the condition of each ring being monitored by a RMON agent. On large Token Ring networks with
several rings, the health of each ring segment and the number of active and inactive stations on each ring can be monitored simultaneously. Network administrators can be alerted
to the location of the fault domain should any ring go into a
beaconing (fault) condition. Network managers also can be
alerted to any changes in backbone ring configuration that
could indicate loss of connectivity to an interconnect device
such as a bridge or to a shared resource such as a server.
Ring Station Configuration The ring station group collects
Token Ring–specific errors. Statistics are kept on all significant MAC-level events to assist in fault isolation, including
ring purges, beacons, claim tokens, and such error conditions as burst errors, lost frames, congestion errors, frame
copied errors, and soft errors.
Ring Station Order Each station can be placed on the network
map in a specified order relative to the other stations on the
ring. This extension provides a list of stations attached to
the ring in logical ring order. It lists only stations that comply
with IEEE 802.5 active monitoring ring poll or IBM trace tool
present advertisement conventions.
The RMON MIB is basically a MAC-level standard. Its visibility does not extend beyond the router port, meaning that it
cannot see beyond individual LAN segments. As such, it does
not provide visibility into conversations across the network
or connectivity between the various network segments.
Given the trends toward remote access and distributed workgroups, which generate a lot of intersegment traffic, visibility
across the enterprise is an important capability to have.
RMON II extends the packet capture and decoding capabilities of the original RMON MIB to Layers 3 through 7 of
the Open Systems Interconnection (OSI) reference model.
This allows traffic to be monitored via network-layer
addresses—which lets RMON “see” beyond the router to the
internetwork—and distinguish between applications.
Analysis tools that support the network layer can sort traffic by protocol rather than just report on aggregate traffic.
This means that network managers will be able to determine,
for example, the percent of Internet Protocol (IP) versus
Internet Packet Exchange (IPX) traffic traversing the network. In addition, these higher-level monitoring tools can
map end-to-end traffic, giving network managers the ability
to trace communications between two hosts—or nodes—even
if the two are located on different LAN segments. RMON II
functions that will allow this level of visibility include
Protocol directory table Provides a list of all the different
protocols a RMON II probe can interpret.
Protocol distribution table Permits tracking of the number of bytes and packets on any given segment that have
been sent from each of the protocols supported. This information is useful for displaying traffic types by percentage
in graphical form.
Address mapping Permits identification of traffic-generating nodes, or hosts, by Ethernet or Token Ring address
in addition to MAC address. It also discovers switch or
hub ports to which the hosts are attached. This is helpful
in node discovery and network topology applications for
pinpointing the specific paths of network traffic.
Network-layer host table Permits tracking of bytes, packets, and errors by host according to individual networklayer protocol.
Network-layer matrix table Permits tracking, by networklayer address, of the number of packets sent between
pairs of hosts.
Application-layer host table Permits tracking of bytes,
packets, and errors by host and according to application.
Application-layer matrix table Permits tracking of conversations between pairs of hosts by application.
History group Permits filtering and storing of statistics
according to user-defined parameters and time intervals.
Configuration group Defines standard configuration
parameters for probes that includes such parameters as
network address, serial line information, and SNMP trap
destination information.
RMON II is focused more on helping network managers
understand traffic flow for the purpose of capacity planning
rather than for the purpose of physical troubleshooting. The
capability to identify traffic levels and statistics by application has the potential to greatly reduce the time it takes to
troubleshoot certain problems. Without tools that can pinpoint which software application is responsible for gobbling
up a disproportionate share of the available bandwidth, network managers can only guess. Often it is easier just to
upgrade a server or a buy more bandwidth, which inflates
operating costs and shrinks budgets.
Applying remote monitoring and statistics-gathering
capabilities to Ethernet and Token Ring environments via
the RMON MIB offers a number of benefits. The availability of critical wireless and wired networks is maximized,
since remote capabilities allow for timely problem resolution. With the capability to resolve problems remotely,
operations staff can avoid costly travel to troubleshoot
problems on site. With the capability to analyze data collected at specific intervals over a long period of time, intermittent problems can be tracked down that normally
would go undetected and unresolved. And with RMON II,
these capabilities are enhanced and extended up to the
applications level across the enterprise.
See also
Wireless Management Tools
A repeater is a device that extends the inherent distance limitations of various transmission media, including wireless
links, by boosting signal power so that it stays at the same
level regardless of the distance it must travel. As such, the
repeater operates at the lowest level of the Open Systems
Interconnection (OSI) reference model—the Physical Layer
(Figure R-3).
Repeaters are necessary because signal strength weakens
with distance: The longer the path a signal must travel, the
weaker it gets. This condition is known as “signal attenuation.” On a telephone call, a weak signal will cause low volume, interfering with the parties’ ability to hear each other.
In cellular networks, when a mobile user moves beyond the
range of a cell site, the signal fades to the point of disconnecting the call. In the LAN environment, a weak signal can
result in corrupt data, which can substantially reduce
throughput by forcing retransmissions when errors are
detected. When the signal level drops low enough, the
chances of interference from external noise increase, rendering the signal unusable.
Repeaters also can be used to link different types of network media—fiber to coaxial cable, for example. Often LANs
are interconnected in a campus environment by means of
repeaters that form the LANs into connected network segSource Station
Destination Station
Data Link
Data Link
Figure R-3 Repeaters operate at the Physical Layer of the OSI reference
ments. The segments may employ different transmission
media—thick or thin coaxial cable, twisted-pair wiring, or
optical fiber. The cost of media converters is significantly
less than full repeaters and can be used whenever media distance limitations will not be exceeded in the network.
Hubs or switches usually are equipped with appropriate
modules that perform the repeater and media conversion
functions on sprawling LANs. But the use of hubs or switches
also can eliminate the need for repeaters, since most cable segments in office buildings will not run more than 100 feet (about
30 meters), which is well within the distance limitation of most
LAN standards, including 1000BaseT Gigabit Ethernet running over Category 5 cable.
Often the terms repeater and regenerator are used interchangeably, but there is a subtle difference between the two.
In an analog system, a repeater boosts the desired signal
strength but also boosts the noise level as well. Consequently,
the signal-to-noise ratio on the output side of the repeater
remains the same as on the input side. This means that once
noise is introduced into the desired signal, it is impossible to
get the signal back into its original form again on the output
side of the repeater.
In a digital system, regenerators are used instead of
repeaters. The regenerator determines whether the information-carrying bits are 1s or 0s on the basis of the
received signal on the input side. Once the decision of 1 or
0 is made, a fresh signal representing that bit is transmitted on the output side of the regenerator. Because the quality of the output signal is a perfect replication of the input
signal, it is possible to maintain a very high level of performance over a range of transmission impairments. Noise,
for instance, is filtered out because it is not represented as
a 1 or 0.
Stand-alone repeaters have transceiver interface modules
that provide connections to various media. There are
fiberoptic transceivers, coaxial transceivers, and twistedpair transceivers. Some repeaters contain the intelligence
to detect packet collisions and will not repeat collision
fragments to other cable segments. Some repeaters also
can “deinsert” themselves from a hub or switch when there
are excessive errors on the cable segment, and they can
submit performance information to a central management
See also
Access Points
Wireless LANs
A router operates at Layer 3 of the Open Systems
Interconnection (OSI) reference model, the Network Layer.
The device distinguishes among network layer protocols—
such as IP, IPX, and AppleTalk—and makes intelligent packet
delivery decisions using an appropriate routing protocol. Used
on wired and wireless networks, routers can be used to segment a network with the goals of limiting broadcast traffic
and providing security, control, and redundant paths.
A router also can provide multiple types of interfaces,
including those for T1, Frame Relay, Integrated Services
Digital Network (ISDN), Asynchronous Transfer Mode
(ATM), cable networks, and Digital Subscriber Line (DSL)
services, among others. Some routers can perform simple
packet filtering to control the kind of traffic that is allowed to
pass through them, providing a rudimentary firewall service.
Larger routers can perform advanced firewall functions.
A router is similar to a bridge in that both provide filtering and bridging functions across the network. But while
bridges operate at the Physical and Data Link Layers of the
OSI reference model, routers join LANs at the Network
Layer (Figure R-4). Routers convert LAN protocols into
WAN protocols and perform the process in reverse at the
remote location. They may be deployed in mesh as well as
point-to-point networks and, in certain situations, can be
used in combination with bridges.
Although routers include the functionality of bridges, they
differ from bridges in the following ways: They generally offer
more embedded intelligence and, consequently, more sophisticated network management and traffic control capabilities
than bridges. Another distinction—perhaps the most significant one—between a router and a bridge is that a bridge delivers packets of data on a “best effort” basis, specifically, by
discarding packets it does not recognize onto an adjacent network. Through a continual process of discarding unfamiliar
packets, data get to theirs proper destination—on a network
Source Station
Destination Station
7 Application
Application 7
6 Presentation
Presentation 6
Network Layer
Data Link
Data Link
Data Link
Data Link
Token Ring
Figure- R-4 Routers operate at the Network Layer of the OSI reference
where the bridge recognizes the packets as belonging to a
device attached to its network. By contrast, a router takes
a more intelligent approach to getting packets to their destination—by selecting the most economical path (i.e., least number of hops) on the basis of its knowledge of the overall network
topology, as defined by its internal routing table. Routers also
have flow-control and error-protection capabilities.
Types of Routing
There are two types of routing: static and dynamic. In static
routing, the network manager configures the routing table
to set fixed paths between two routers. Unless reconfigured,
the paths on the network never change. Although a static
router will recognize that a link has gone down and issue an
alarm, it will not automatically reroute traffic. A dynamic
router, on the other hand, reconfigures the routing table
automatically and recalculates the most efficient path in
terms of load, line delay, or bandwidth.
In wired networks, some routers balance the traffic load
across multiple access links, providing an N × T1 inverse multiplexer function. This allows multiple T1 access lines operating at 1.544 Mbps each to be used as a single
higher-bandwidth facility. If one of the links fails, the other
links remain in place to handle the offered traffic. As soon as
the failed link is restored to service, traffic is spread across the
entire group of lines as in the original configuration.
Routing Protocols
Each router on the network keeps a routing table and moves
data along the network from one router to the next using
such protocols as the Open Shortest Path First (OSPF) protocol and the Routing Information Protocol (RIP).
Although still supported by many vendors, RIP does not
perform well in today’s increasingly complex networks. As
the network expands, routing updates grow larger under
RIP and consume more bandwidth to route the information.
When a link fails, the RIP update procedure slows route discovery, increases network traffic and bandwidth usage, and
may cause temporary looping of data traffic. Also, RIP cannot base route selection on such factors as delay and bandwidth, and its line-selection facility is capable of choosing
only one path to each destination.
The newer routing standard, OSPF, overcomes the limitations of RIP and even provides capabilities not found in RIP.
The update procedure of OSPF requires that each router on
the network transmit a packet with a description of its local
links to all other routers. On receiving each packet, the other
routers acknowledge it, and in the process, distributed routing tables are built from the collected descriptions. Since
these description packets are relatively small, they produce
a minimum of overhead. When a link fails, updated information floods the network, allowing all the routers to simultaneously calculate new tables.
Types of Routers
Multiprotocol nodal, or hub, routers are used for building
highly meshed internetworks. In addition to allowing several protocols to share the same logical network, these
devices pick the shortest path to the end node, balance the
load across multiple physical links, reroute traffic around
points of failure or congestion, and implement flow control
in conjunction with the end nodes. They also provide the
means to tie remote branch offices into the corporate backbone, which might use such WAN services as Transmission
Control Protocol/Internet Protocol (TCP/IP), T1, ISDN,
and ATM.
Access routers are typically used at branch offices. These
are usually fixed-configuration devices available in
Ethernet and Token Ring versions that support a limited
number of protocols and physical interfaces. They provide
connectivity to high-end multiprotocol routers, allowing
large and small nodes to be managed as a single logical
enterprise network. Although low-cost, plug-and-play
bridges can meet the need for branch office connectivity,
low-end routers can offer more intelligence and configuration flexibility at comparable cost.
The newest access routers are multiservice devices that are
designed to handle a mix of data, voice, and video traffic. They
support a variety of WAN connections through built-in interfaces that include dual ISDN Basic Rate Interface (BRI) interfaces, dual analog ports, T1/Frame Relay ports, and an ISDN
interface for videoconferencing. Such routers can run software that provides Internet Protocol Secure (IPSec) virtual
private network (VPN), firewall, and encryption services.
Midrange routers provide network connectivity between
corporate locations in support of workgroups or the corporate
intranet, for example. These routers can be stand-alone
devices or packaged as modules that occupy slots in an intelligent wiring hub or LAN switch. In fact, this type of router is
often used to provide connectivity between multiple wiring
hubs or LAN switches over high-speed LAN backbones such
as ATM, Fiber Distributed Data Interface (FDDI), and Fast
There is a consumer class of routers for 2.4-GHz Wireless
Fidelity (Wi-Fi) networks that are capable of providing
shared access to the Internet over such broadband technologies as cable and DSL. The EtherFast Wireless AP +
Cable/DSL Router from Linksys, for example, connects a
wireless network to a high-speed broadband Internet connection and a 10/100 Fast Ethernet backbone (Figure R-5).
Configurable through any networked PC’s Web browser, the
router can be set up for Network Address Translation (NAT),
allowing it to act as an externally recognized Internet device
with its own IP address for the home LAN. The Linksys
device is also equipped with a four-port Ethernet switch. The
combination of wireless router and switch technology eliminates the need to buy an additional hub or switch and
extends the range of the wireless network.
Figure R-5 The EtherFast Wireless AP +
Cable/DSL Router from Linksys
Whether used on a wired or wireless network or a hybrid network, routers fulfill a vital role in implementing complex mesh
networks such as the Internet and private intranets using
Layer 3 protocols, usually IP. They also have become an economical means of tying branch offices into the enterprise network and providing PCs tied together on a home network with
shared access to broadband Internet services such as cable and
DSL. Like other interconnection devices, enterprise-class
routers are manageable via SNMP, as well as the proprietary
management systems of vendors. Just as bridging and routing
functions made their way into a single device, routing and
switching functions are being combined in the same way.
See also
Access Points
Rural Radiotelephone Service is a fixed wireless service that
allows common carriers to provide telephone service to the
homes of subscribers living in extremely remote rural areas,
where it is not feasible to provide telephone service by wire
or other means. Rural Radiotelephone Stations, operating in
the paired 152- to 158-MHz and 454- to 459-MHz bands,
employ standard duplex analog technology to provide telephone service to subscribers’ homes.
The quality of conventional rural radiotelephone service is
similar to that of precellular mobile telephone service. Several
subscribers may have to share a radio-channel pair (similar to
party-line service), each waiting until the channel pair is not
in use by the others before making or receiving a call.
Rural Radiotelephone Service is generally considered by
state regulators to be a separate service that is interconnected to the Public Switched Telephone Network (PSTN).
This service has been available to rural subscribers for more
than 25 years.
Carriers must apply to the FCC for permission to offer Rural
Radiotelephone Service. Among other things, each application
for a central office station must contain an exhibit showing
that it is impractical to provide the required communication
service by means of landline facilities.
See also
Air-Ground Radiotelephone Service
Basic Exchange Telephone Radio Service
Fixed Wireless Access
The idea of using satellites as relay stations for an international microwave radiotelephone system goes back to 1945
when Arthur C. Clarke (Figure S-1) proposed the scheme in a
British technical journal. Clarke, then a young scientist and
officer of the Royal Air Force, later became a leading science
fiction writer and coauthor of the motion picture 2001: A Space
Odyssey. However, it was not until 1957 that the first satellite
was put into orbit. Although just a beacon whose primary purpose was to announce its presence in the sky, the successful
orbital deployment of the 185-pound Russian Sputnik sparked
a technological revolution in communications that continues to
this day. There are now over 2560 satellites in orbit, along with
over 6000 pieces of debris tracked by the National Aeronautics
and Space Administration (NASA).
The United States launched the first communication
satellites in the early 1960s. Echo 1 and Echo 2 were little
more than metallic balloons that simply reflected microwave
signals from point A to point B. These passive satellites
could not amplify the signals. Reception was often poor and
the range of transmission limited. Ground stations had to
track them across the sky, and communication between two
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Figure S-1 Arthur C. Clarke
articulated his vision of satellites in
a British technical journal in 1945.
ground stations was only possible for a few hours a day when
both had visibility with the satellite at the same time. Later,
geostationary satellites overcame this problem. Such systems were high enough in orbit to move with the earth’s rotation, in effect giving them fixed positions so that they could
provide communications coverage to specific areas.
Satellites are now categorized by type of orbit and area of
coverage as follows:
Geostationary-earth-orbit (GEO) satellites orbit the equator in a fixed position about 23,000 miles above the earth.
Three GEO satellites can cover most of the planet, with
each unit capable of handling 20,000 voice calls simultaneously. Because of their large coverage “footprint,” these
satellites are ideal for radio and television broadcasting and
long distance domestic and international communications.
Middle-earth-orbit (MEO) satellites circle the earth at
about 6000 miles up. It takes about 12 satellites to provide global coverage. The lower orbit reduces power
requirements and transmission delays that can affect signal quality and service interaction.
Low-earth-orbit (LEO) satellites circle the earth only
600 miles up (Figure S-2). As many as 200 satellites may
be required to provide global coverage. Since their low
altitude means that they have nonstationary orbits and
they pass over a stationary caller rather quickly, calls
must be handed off from one satellite to the next to keep
the session alive. The omnidirectional antennas of these
devices do not have to be pointed at a specific satellite.
There is also very little propagation delay. And the low
altitude of these satellites means that earthbound transceivers can be packaged as low-powered, inexpensive
hand-held devices.
The International Telecommunication Union (ITU)
is responsible for all frequency/orbit assignments. Through
its International Bureau, the Federal Communications Commission (FCC) regulates all satellite service rates, competition
among carriers, and international telecommunications traffic
Telephone Network
Telephone Network
Figure S-2 Low-earth-orbit satellites hold out the promise of ubiquitous
personal communications services, including telephone, pager, and two-way
messaging services worldwide.
in the United States, ensuring that U.S. satellite operators
conform to ITU frequency and orbit assignments. The FCC
also issues licenses to domestic satellite service providers.
Satellite Technology
Each satellite carries transponders, which are devices that
receive radio signals at one frequency and convert them to
another for transmission. The uplink and downlink frequencies are separated to minimize interference between transmitted and received signals.
Satellite channels allow one sending station to broadcast
transmissions to one or more receiving stations simultaneously. In a typical scenario, the communications channel
starts at a host computer, which is connected through a traditional telephone company medium to the central office
(i.e., master earth station or hub) of the satellite communications vendor. The data from this and other local loops are
multiplexed into a fiberoptic or microwave signal and sent
to the satellite vendor’s earth station. This signal becomes
part of a composite transmission that is sent by the earth
station to the satellite (uplink) and then transmitted by the
satellite to the receiving earth stations (downlink). At the
receiving earth station, the data are transferred by a
fiberoptic or microwave link to the satellite carrier’s central office. The composite signal is then separated into individual communications channels that are distributed over
the Public Switched Telephone Network (PSTN) to their
Satellite communication is very reliable for data transmission. The bit error rate (BER) for a typical satellite channel is in the range of 1 error in 1 billion bits transmitted.
However, a potential problem with satellite communication
is delay. Round-trip satellite transmission takes approximately 500 milliseconds, which can hamper voice communications and create significant problems for real-time
interactive data transmissions. For voice communications,
digital echo cancelers can correct voice echo problems caused
by the transmission delay.
A number of techniques are employed to nullify the
effects of delay during data transmissions via satellite.
One technique employed by Mentat, Inc., increases the
performance of Internet and intranet access over satellites
by transparently replacing the Transmission Control
Protocol (TCP) over the satellite link with a protocol optimized for satellite conditions. The company’s SkyX
Gateway intercepts the TCP connection from the client
and converts the data to a proprietary protocol for transmission over the satellite. The gateway on the opposite
side of the satellite link translates the data back to TCP for
communication with the server (Figure S-3). The result is
vastly improved performance while the process remains
transparent to the end user and fully compatible with the
Internet infrastructure. No changes are required to the client
or server, and all applications continue to function without
SkyX Gateway
SkyX Gateway
Web Server
Protocol Translation Module
Protocol Translation Module
IP Protocol
Protocol IP
To Gateway
To Client
To Satellite
To Satellite
To Server
To Gateway
SkyX Protocol
Figure S-3 Mentat’s SkyX Gateway overcomes the effects of delay on
Internet/intranet access by replacing TCP on the client side of the link with
a proprietary protocol optimized for the satellite environment and then converting it back to TCP on the server side of the satellite link.
Very Small Aperture Terminals (VSATs)
VSAT networks have evolved to become mainstream communication networking solutions that are affordable to both large
and small companies. Today’s VSAT is a flexible, softwareintensive system built around standard communications protocols. With a satellite as the serving office and using
radiofrequency (RF) electronics instead of copper or fiber
cables, these systems can be truly considered packet-switching
systems in the sky.
VSATs can be configured for broadcast (one-way) or interactive (two-way) communications. The typical star topology
provides a flexible and economical means of communications
with multiple remote or mobile sites. Applications include
broadcasting database information, insurance agent support, reservations systems, retail point-of-sale credit card
checking, and interactive inventory data sharing.
Today’s VSATs are used for supporting high-speed message broadcasting, image delivery, integrated data and voice,
and mobile communications. VSATs are used increasingly for
supporting local area network (LAN)–to-LAN connectivity
and LAN-to–wide area network (WAN) bridging, as well as
for providing route and media diversity for disaster recovery.
To make VSAT technology more affordable, VSAT
providers offer compact hubs and submeter antennas that
provide additional functionality at approximately 33 percent
less than the cost of full-size systems. Newer submeter
antennas are even supporting direct digital TV broadcasts to
the home.
Network Management
The performance of the VSAT network is monitored increasingly at the hub location by the network control system. A
failure anywhere on the network automatically alerts the
network control operator, who can reconfigure capacity
among individual VSAT systems. In the case of signal fade
due to adverse weather conditions, for example, the hub
detects the weak signal—or the absence of a signal—and
alerts the network operations staff so that corrective action
can be taken.
Today’s network management systems indicate whether
power failures are local or remote. They also increasingly
locate the source of communications problems and determine whether the trouble is with the software or hardware.
Such capabilities often eliminate the expense of dispatching
technicians to remote locations. And when technicians must
be dispatched, the diagnostic capabilities of the network
management system can ensure that service personnel have
the appropriate replacement parts, test gear, software
patch, and documentation with them to solve the problem in
a single service call.
Overall link performance is determined by the BER, network availability, and response time. Because of the huge
amount of information transmitted by the hub station,
uplink performance requirements are more stringent. A
combination of uplink and downlink availability, coupled
with BER and response time, provides the network control
operator with overall network performance information on a
continuous basis.
The VSAT’s management system provides an interface to
the major enterprise management platforms for single-point
monitoring and control and offers a full range of accounting,
maintenance, and data flow statistics, including those for
inbound versus outbound data flow, peak periods, and total
traffic volume by node. Also provided are capabilities for
identifying fault conditions, performing diagnostics, and initiating service restoration procedures.
Communications Protocols
Within the VSAT network there are three categories of
protocols—those associated with the backbone network,
those of the host computer, and those concerned with
transponder access. The scope and functionality of protocol
handling differ markedly among VSAT network providers.
The backbone network protocol is responsible for flow
control, retransmissions of bad packets, and running concurrent multiple sessions. The backbone network protocol
could be associated with either the host or the communications link. The host protocol is related to the user application interface, which provides a compatible translation
between the backbone protocol and the host communications protocol. Several host protocols are used in VSAT networks, including SNA/SDLC, 3270 Base Station Controller
(BSC), Poll Select, and HASP. Multiple protocols can be
used at the same VSAT location.
Transponder access protocols are used to assign transponder resources to various VSATs on the network. The three
key transponder access protocols that are used on VSAT networks include Frequency Division Multiple Access (FDMA),
Time Division Multiple Access (TDMA), and Code Division
Multiple Access (CDMA).
Frequency Division Multiple Access With FDMA, the radiofre-
quency is partitioned so that bandwidth can be allocated to
each VSAT on the network. This permits multiple VSATs to
simultaneously use their portion of the frequency spectrum.
Time Division Multiple Access With TDMA, each VSAT
accesses the hub via the satellite by the bursting of digital
information onto its assigned radiofrequency carrier. Each
VSAT bursts at its assigned time relative to the other VSATs
on the network. Dividing access in this way—by time slots—
is inherently wasteful because bandwidth is available to the
VSAT in fixed increments whether or not it is needed. To
improve the efficiency of TDMA, other techniques are applied
to ensure that all the available bandwidth is used, regardless
of whether the application contains bursty or streaming data.
A reservation technique can even be applied to ensure that
bandwidth is available for priority applications.
Code Division Multiple Access With CDMA, all VSATs share
the assigned frequency spectrum and also can transmit
simultaneously. This is possible through the use of spreadspectrum technology, which employs a wideband channel as
opposed to the narrowband channels employed by other multiple access techniques such as FDMA and TDMA. Over the
wideband channel, each transmission is assigned a unique
code—a long row of numbers resembling a combination to a
lock. The outbound data streams are coded so that they can
be identified and received only by the station(s) having that
code. This technique is also used in mobile communications
as a means of cutting down interference and increasing
available channel capacity by as much as 20 times.
Mobile Satellite Communications
Mobile satellite communications are used by the airline,
maritime, and shipping industries. Among the key providers
of mobile satellite communications services are Inmarsat,
Intelsat, and Comsat. All began as government entities but,
through global privatization efforts, have become private
corporations that compete for market share.
Inmarsat The International Maritime Satellite Organization
(Inmarsat) was formed in the late 1970s as a maritime-focused
intergovernmental organization. Inmarsat completed its transition to a limited company in 1999 and now serves a broad
range of markets. Today, Inmarsat delivers its solutions—
including telex, voice, data, and video transmission—through
a global distribution network of approximately 200 distributors and other service providers operating in over 150 countries to end users in the maritime, land, and aeronautical
sectors. At year end 2000, approximately 212,000 terminals
were registered to access Inmarsat services.
Inmarsat’s primary satellite constellation consists of four
Inmarsat-3 satellites in geostationary orbit. Between them,
the global beams of the satellites provide overlapping coverage
of the whole surface of the earth, apart from the poles. The
Inmarsat-3 satellites are backed up by a fifth Inmarsat-3 and
four previous-generation Inmarsat-2s, also in geostationary
orbit. A key advantage of the Inmarsat-3s over their predecessors is their ability to generate a number of spot beams as well
as single large global beams. Spot beams concentrate extra
power in areas of high demand and make it possible to supply
standard services to smaller, simpler terminals.
Among Imarsat’s newest services is Swift64, which uses
its Global Area Network platform to offer airlines and users
of corporate jets the ability to operate an Integrated
Services Digital Network (ISDN) connection of up to 64
kbps or a Mobile Packet Data connection using the existing
Inmarsat antenna already installed on almost 80 percent of
modern long-haul jets, as well as over 1000 corporate jets.
With Swift64, airlines will be able to provide passengers
with an ISDN 64-kbps bearer channel that is billed according to connection time. Mobile Packet Data, on the other
hand, offers an “always on” connection that is billed according to the number of packets sent. These services enable
users to surf the Web and send and receive e-mails and documents across all the continents of the world outside the
north and south poles.
Intelsat Another provider on international mobile satellite
communications services is Intelsat, which has the widest
distribution network of any satellite communications company. Operating since 1964, Intelsat has a global fleet of 21
satellites from which it offers wholesale Internet, broadcast,
telephony, and corporate network solutions to leading service providers in more than 200 countries and territories
worldwide. Seven more satellites will be put into operation
in the next 2 years to broaden coverage and add capacity. In
mid-2001, Intelsat completed its transformation from a
treaty-based organization to a privately held company with
over 200 shareholders composed of companies from more
than 145 countries.
Comsat In the United States, the government-sponsored
satellite company was Comsat, which had been the only
authorized U.S. organization that could directly access the
Intelsat system. Lockheed Martin’s acquisition of Comsat in
August 2000 ended the 38-year history of quasi-government
backing for Comsat. The federal government created the
company in 1962 to prevent AT&T, then a telephone monopoly, from extending its monopoly to the satellite communications sector. Comsat became a publicly traded company
the next year, but Congress ordered that no single investor
could own a majority stake in the company because it was
the only American firm with access to Intelsat. Congress
eliminated the exclusive right to access Intelsat as part of
the agreement that allowed Lockheed Martin to purchase
Satellites provide a reliable, economical way of providing
communications to remote locations and supporting mobile
telecommunications. Taking into account the large number of
satellites that can be employed, along with their corresponding
radiofrequency assignments, it is clear that satellite communications systems offer ample room for expansion. Conversion of
satellite transmissions from analog to digital and use of more
sophisticated multiplexing techniques will further increase
satellite transmission capacity. Other technological advances
are focusing on the higher frequency bands—applying them in
ways that decrease signal degradation.
See also
Direct Broadcast Satellite
Global Positioning System
Microwave Communications
Short Messaging Service (SMS) is the ability to send and
receive text messages between mobile telephones over cellular networks. Once used exclusively by carriers to push notifications of new voice messages down to smart cell phones,
SMS is now on a fast track to universal adoption by the cellular subscribers around the world, who have adopted it as a
two-way personal messaging medium.
Created as part of the Global System for Mobile (GSM)
Phase 1 standard, the first short message was sent in
December 1992 from a PC to a mobile phone on the Vodafone
GSM network in the United Kingdom. With SMS, subscribers can send up to 160 characters of text when Latin
alphabets are used and 70 characters when non-Latin alphabets such as Arabic and Chinese are used. The text can consist of words or numbers or an alphanumeric combination.
The success of SMS can be attributed to certain unique
features, such as message storage if the recipient is not
available, confirmation of short message delivery, and
simultaneous transmission with GSM voice, data, and fax
services. The person receiving the message also will know
the phone number of the sender and the time at which the
message was sent. While its principal use is still for personal messaging, SMS is also being used for receiving
weather reports and traffic information, mobile shopping,
banking, and stock trading. SMS is being enhanced to support the delivery of long-text messages, images, and video
as well.
Although the prospects for SMS in the United States look
promising, its rollout has been hampered by interoperability
problems between different carriers. While all European
carriers have standardized on GSM, carriers in the United
States use several competing technologies. As a result,
AT&T’s message service will only work between other AT&T
wireless customers or other carriers using its TDMA transmission technology. Likewise, Sprint PCS message-service
customers would be able to communicate only with other
Sprint PCS customers or other carriers using its CDMA
transmission technology. Fortunately, gateway systems are
being deployed that permit messages to be transmitted
between customers on different carrier networks.
Most premises-based mobile-access gateways and servers
already provide interfaces to SMS. A growing number of service providers offer SMS backbone-routing services to bridge
otherwise-incompatible SMS carrier services. For example,
TeleCommunication Systems introduced technology that
allows intercarrier text messaging through use of a customer’s phone number. InfoSpace added wireless network
SMS interoperability to its technology platform that already
enables Internet content and mobile-commerce services via
several wireless carriers. Software developed by InphoMatch
enables AT&T Wireless customers to send text messages to
other wireless carriers’ customers.
The growth prospects for SMS look so good that traditional paging services may one day disappear. Motorola has
already announced that it is pulling out of the market for
traditional paging infrastructure and handsets in favor of
developing two-way technologies for use in wireless phones.
The company’s Wireless Messaging Division will now focus
on providing SMS products for use on networks for GSM,
General Packet Radio Services (GPRS), and CDMA protocols. At the same time, Motorola announced that it is discontinuing products that support the ReFlex protocol, which
Motorola developed in the 1990s for traditional two-way
paging carriers such as Skytel and Arch Wireless.
AT&T Wireless was the first national carrier to bring SMS
to the United States and is the current market leader. AT&T
claims to handle 35 million text messages a month. Two plans
are available for the two-way text-messaging service. The first
has no monthly charge, and the user pays $0.10 per message
sent. The second has a monthly charge of $4.99 per month with
100 included outgoing messages and $0.10 per message thereafter. Both plans offer unlimited incoming messages and allow
messages to be sent to subscribers of other carriers at no additional charge.
The service also offers features that let users reply, forward, store, and retrieve messages right from their phone.
Messages of up to 150 characters can be sent between compatible phones and to Internet e-mail addresses—including
e-mail addresses for pagers, handheld devices, or Webenabled phones. Among the mobile phones offered by
AT&T Wireless that are compatible with its 2-Way Text
Messaging service are the Nokia 5165, 3360, and 8260
(Figure S-4).
Since November 2001, AT&T Wireless customers have
had the ability to send text messages to virtually any wireless phone regardless of the carrier simply by knowing the
Figure S-4 Among the mobile phones offered
by AT&T Wireless that are compatible with its 2Way Text Messaging service is the Nokia 3360.
recipient’s phone number. The intercarrier text messaging
capability is available to postpaid and prepaid subscribers in
all the company’s TDMA and GSM markets. InphoMatch, a
wireless messaging solution provider, supplies the software
for the intercarrier messaging services. InphoMatch’s routing system sends messages between and across U.S. carriers
simply by using a wireless phone number while remaining
transparent to the customer.
Other service providers in the United States now offer
SMS. The two-way text messaging service of Cingular is
Interactive Messaging, which allows up to 150 characters.
Users send text messages via the 10-digit mobile number of
the recipient, regardless of which wireless service the recipient happens to have. Sprint PCS offers an SMS-based service called Short Mail, which allows users to send messages
of up to 100 characters from one Sprint PCS phone to
another. Verizon Wireless offers its SMS-based service,
called Mobile Messenger, which allows users to send short
text messages of up to 160 characters between handsets or
any Internet e-mail system. Voicestream’s two-way messaging service is called Ping Pong. It allows text messages of up
to 140 characters to be sent and received between wireless
devices using only an e-mail address.
In the same way instant messaging (IM) on the Internet has
become a standard method of communication among U.S.
teenagers, SMS will provide a choice that will grow the total
messaging market and, in some cases, replace voice traffic
and IM. Desktop-to-desktop IM is not conducive to mobility.
Even desktop-to-mobile IM inhibits mobility because a cellular subscriber using a limited screen and keyboard cannot
keep up with messaging traffic generated from a fully featured desktop. Unlike SMS, IM clients operating on wireless devices have proven complex, cumbersome, and
difficult to use.
See also
Wireless Messaging
Software-defined radios can be reprogrammed quickly to
transmit and receive on multiple frequencies in different
transmission formats. This reprogramming capability could
change the way users traditionally communicate across wireless services and promote more efficient use of radio spectrum. In a software-defined radio, functions that were
formerly carried out solely in hardware, such as generation of
the transmitted radio signal and tuning of the received radio
signal, are performed by software. Because these functions
are carried out in software, the radio is programmable, allowing it to transmit and receive over a wide range of frequencies
and to emulate virtually any desired transmission format.
The concept of software-defined radio originated with the
military, where it was used quickly for electronic warfare
applications. Now the cellular/wireless industries in the
United States and Europe have begun work to adapt the
technology to commercial communications services in the
hope of realizing its long-term economic benefits. If all goes
according to plan, future radio services will provide seamless
access across cordless telephone, wireless local loop,
Personal Communications Services (PCS), mobile cellular,
and satellite modes of communication, including integrated
data and paging.
Generations of Radio Systems
First-generation hardware-based radio systems are built to
receive a specific modulation scheme. A handset would be
built to work over a specific type of analog network or a specific type of digital network. The handset worked on one network or the other, but not both, and it could certainly not
cross between analog and digital domains.
Second-generation radio systems also are based in hardware. Miniaturization enables two sets of components to be
packaged into a single, compact handset. This enables the
unit to operate in dual mode—for example, switching
between Advanced Mobile Phone Service (AMPS) or TDMA
modulation as necessary. Such handsets are implemented
using snap-in components: Two existing chip sets—one for
AMPS and one for TDMA, for example—are used together.
Building such handsets typically costs only 25 to 50 percent
more than a single-mode handset but offers network operators and users far more flexibility.
Handsets that work across four or more modes/bands
entail far more complexity and processing power and call for
a different architecture altogether. The architecture is based
in software and programmable digital signal processors
(DSPs). This architecture is referred to as “software-defined
radio” or just “software radio.” It represents the third generation of radio systems.
As new technologies are placed onto existing networks
and wireless standards become more fragmented—particularly in the United States—the need for a single radio unit
that can operate in different modes and bands becomes more
urgent. A software radio handset could, for example, operate
in a GSM-based PCS network, a legacy AMPS network, and
a future satellite mobile network.
As noted, a software radio is one in which channel modulation waveforms are defined in software. Waveforms are generated as sampled digital signals, converted from digital to
analog via a wideband digital-to-analog converter (DAC),
and then up-converted from an intermediate frequency (IF)
to the desired radiofrequency (RF).
In similar fashion, the receiver employs a wideband
analog-to-digital converter (ADC) that captures all the channels of the software radio node. The receiver then extracts,
down-converts, and demodulates the channel waveform
using the software loaded on a general-purpose processor.
As competing technologies for wireless networks emerged in
the early 1990s, it became apparent that subscribers would
have to make a choice: The newer digital technologies
offered more advanced features, but coverage would be
spotty for some years to come. The older analog technologies
offered wider coverage but did not support the advanced features. A compromise was offered in the form of wireless multimode/multiband systems that offered subscribers the best
of both worlds.
At the same time, wireless multimode/multiband systems
allow operators to economically grow their networks to support new services where the demand is highest. With multimode/multiband handsets, subscribers can access new digital
services as they become available while retaining the capability to communicate over existing analog networks. The wireless system gives users access to digital channels wherever
digital service is available while providing a transparent
handoff when users roam between cells alternately served by
various digital and analog technologies. As long as subscribers
stay within cells served by advanced digital technologies, they
will continue to enjoy the advantages provided by these technologies. When they reach a cell that is supported by analog
technology, they will have access only to the features supported by that technology. The intelligent roaming capability
of multimode/multiband systems automatically chooses the
best system for the subscriber to use at any given time.
Third-generation radio systems are frequency-agile and
extend this flexibility even further by supporting more modes
and bands. It is important to remember, however, that software radio systems may never catch up to encompass all the
modes and bands that are available today and that may
become available in the future. Users will always be confronted by choices. Making the right choice will depend on
calling patterns, the features associated with the different
technologies and standards, and the type of systems in use at
international locations visited most frequently.
Multimode and multiband handsets have been available
from several manufacturers since 1995. These handsets support more than one technology for their mode of operation
and more than one frequency band.
An example of a multimode wireless system is one that
supports both AMPS and Narrowband AMPS (N-AMPS).
Narrowband AMPS is a system-overlay technology that
offers enhanced digital-like features, such as Digital
Messaging Service, to phones operating in a traditional
analog-based AMPS network. Among the vendors offering
dual-mode AMPS/N-AMPS handsets is Nokia, the world’s
second-largest manufacturer of cellular phones.
An example of a multiband wireless system is one that
supports GSM at both 900 and 1800 MHz in Europe. Among
the vendors offering dual-band GSM handsets is Motorola.
The company’s International 8800 Cellular Telephone allows
GSM 1800 subscribers to roam on either their home or GSM
900 networks (where roaming agreements are in place)
using a single cellular telephone.
Of course, handsets can be both multimode and multiband. Ericsson, for example, offers dual-band/dual-mode
handsets that support communication over both 800-MHz
AMPS/Digital AMPS (D-AMPS) and 1900-MHz D-AMPS
networks. Subscribers on a D-AMPS 1900 channel can hand
off both to and from a D-AMPS channel on 800 MHz as well
as to and from an analog AMPS channel.
Multimode and multiband wireless systems allow operators
to expand their networks to support new services where they
are needed most, expanding to full coverage at a pace that
makes economic sense. From the subscribers’ perspective,
multimode and multiband wireless systems allow them to take
advantage of new digital services that are initially deployed in
large cities while still being able to communicate in areas
served by the older analog technologies.
With its multimode capabilities, the wireless system preferentially selects a digital channel wherever digital service
is available. If the subscriber roams out of the cell served by
digital technology—from one served by CDMA to one served
by AMPS, for example—a handoff occurs transparently. As
long as subscribers stay within CDMA cells, they will continue to enjoy the advantages the technology provides, such
as better voice quality and soft handoff, which virtually eliminates dropped calls. When subscribers reach a cell that supports only AMPS, voice quality diminishes and the chances
for dropped calls increases.
However, these multimode/multiband handsets are not
software-programmable. They rely instead on packaging
dual sets of hardware in the same handset. Miniaturization
of the various components makes this both practical and economical, but this approach has its limitations when the
number of modes and frequencies that must be supported
goes beyond two or three. Beyond that point, a totally new
approach is required that relies more on programmable
Despite the promising concept of software-defined radios,
the rollout of consumer products that use the technology has
been slow. In September 2001, the FCC adopted rule
changes to accommodate the authorization and deployment
of software-defined radios. Under the previous rules, if a
manufacturer wanted to make changes to the frequency,
power, or type of modulation for an approved transmitter, a
new approval was required, and the equipment had to be
relabeled with a new identification number. Because
software-defined radios have the capability of being repro-
grammed in the field, these requirements could be overly
burdensome and hinder the deployment of software-defined
radios to consumers.
Under the new rules, software modifications in a
software-defined radio can be made through a “permissive
change” that has a streamlined filing process. The FCC
identification number will not have to be changed, so equipment in the field will not have to be relabeled. These permissive changes can be obtained only by the original
grantee of the equipment authorization. To allow for
changes to equipment by other parties such as software
developers, the FCC will permit an optional “electronic
label” for software-defined radios, in which the FCC identification number could be displayed on a liquid-crystal display (LCD) or similar screen. It will allow another party to
obtain an equipment approval in its name and become the
party responsible for compliance instead of the original
The FCC also requires that a grantee take adequate steps
to prevent unauthorized software modifications to radios,
but it declined to set specific security requirements at this
time. This will allow manufacturers flexibility to develop
innovative equipment while at the same time provide for
oversight of the adequacy of such steps through the equipment authorization process.
Software radio architectures not only reduce the complexity
and expense of serving a diverse customer base, they also
simplify the integration and management of rapidly emerging standards. With software-based radio systems, access
points, cell sites, and wireless data network hubs can be
reprogrammed to meet changing standards requirements
instead of replacing them or maintaining them in parallel
with a newer infrastructure.
From the perspective of users, the same hardware would
continue to be used—only the software gets upgraded. This
could signal the end of outdated cellular telephones.
Consumers will be able to upgrade their phones with new
applications—much as they would purchase new programs
to add new capabilities to their computers. Although the
benefits are clear, commercial software-defined radio systems are still a few years away. Until they become available,
users will have to make do with the current generation of
multimode/multiband handsets.
See also
Cellular Telephones
Specialized Mobile Radio (SMR) is used to provide two-way
radio dispatch service for the public safety, construction, and
transportation industries. In 1979, the FCC established
SMR service in the 800-MHz band and, in 1986, established SMR service in the 900-MHz band. Although SMR is
used primarily for voice communications, such systems also
support data and facsimile services. Generally, SMR systems provide dispatch services for companies with multiple
vehicles using the “push to talk” method of communication.
A traditional SMR system consists of one or more base
station transmitters, one or more antennas, and mobile
radio units obtained from the SMR operator for a fee or purchased from a retail source.
SMR has limited roaming capabilities, but its range may
be extended through interconnection with the Public
Switched Telephone Network (PSTN), as if the user were a
cellular subscriber. Both types of services operate over different assigned frequencies within the range of 800 to 900
MHz. Cellular services are assigned to bands between 824
and 849 MHz and 869 and 894 MHz.
SMR networks traditionally used one large transmitter
to cover a wide geographic area. This limited the number of
subscribers because only one subscriber could talk on one
frequency at any given moment. The number of frequencies
allocated to SMR is smaller than for cellular, and there have
been several operators in each market. Because dispatch
messages are short, SMR services were able to work reasonably well.
Types of Systems
The 800-MHz SMR systems operate on two 25-kHz channels
paired, while the 900-MHz systems operate on two 12.5-kHz
channels paired. Because of the different sizes of the channel bandwidths allocated for 800- and 900-MHz systems, the
radio equipment used for 800-MHz SMR is not compatible
with the equipment used for 900-MHz SMR systems.
SMR systems consist of two distinct types: conventional
and trunked systems. A conventional system allows an end
user the use of only one channel. If someone else is already
using that end user’s assigned channel, that user must wait
until the channel is available.
In contrast, a trunked system combines channels and contains processing capabilities that automatically search for
an open channel. This search capability allows more users to
be served at any one time. A majority of the current SMR
systems are trunked systems.
In 1993, Congress reclassified most SMR licensees as
Commercial Radio Service (CMRS) providers and established
the authority to use competitive bidding to issue new licenses.
With the development of digital systems, the SMR marketplace now offers new services such as acknowledgment paging
and inventory tracking, credit card authorization, automatic
vehicle location, fleet management, inventory tracking,
remote database access, and voice mail.
See also
Cellular Voice Communications
In recent years, the FCC has assigned licenses for wireless
spectrum by putting it up for auction. The idea behind the
auction process is that is encourages companies to roll out
new services as soon as possible to recover their investments
in the licenses. In getting spectrum into the hands of those
who initially value it the most, competitive bidding also
facilitates efficient spectrum aggregation rather than fragmented secondary markets.
In the past, the FCC often relied on comparative hearings,
in which the qualifications of competing applicants were
examined to award licenses in cases where two or more
applicants filed applications for the same spectrum in the
same market. This process was time-consuming and
resource-intensive. The FCC also used lotteries to award
licenses, but this created an incentive for companies to
acquire licenses on a speculative basis and resell them.
Of the three methods of assigning spectrum, competitive
bidding has proved to be the most effective way to ensure
that licenses are assigned quickly and to the companies that
value them the most while recovering the value of the spectrum resource for the public.1 In addition, auctions avoid the
perception of the government making decisions that are
biased toward or against individual industry players. The
rules and procedures of the auctions are clearly established,
and the outcomes are definitive.
The revenues generated from spectrum auctions go to the U.S. Treasury, not the FCC.
Auction Process
The FCC’s auctions of electromagnetic spectrum assign
licenses using a unique methodology called “electronic
simultaneous multiple-round auctions.” This methodology is
similar to a traditional auction, except that instead of
licenses being sold one at a time, a large set of related
licenses is auctioned simultaneously and bidders can bid on
any license offered. The auction closes when all bidding
activity has stopped on all licenses.
Another characteristic of the auction process is that it is
automated. When the FCC began to design auctions for the
airwaves, it became apparent that manual auction methods
could not adequately allocate large numbers of licenses
when thousands of interdependent licenses were being auctioned to hundreds of bidders at the same time. The FCC’s
Automated Auction System (AAS) provides the necessary
tools to conduct large auctions very efficiently. The system
accommodates the needs of bidders by allowing them to bid
from their offices using a PC and a modem through a private
and secure wide area network (WAN). The system also can
accommodate on-site bidders and telephonic bidding.
Bidders and other interested parties are able to track the
progress of the auctions through the Auction Tracking Tool
(ATT), a stand-alone application that allows a user to track
detailed information on an auction. During an auction, the
FCC releases result files after every round, with details on all
the activity that occurred in that round. Users can use the
ATT to import these round result files into a master database
file and then view a number of different tables containing a
large amount of data in a spreadsheet view. Users can sort,
filter, and query the tables to track the activity of an auction
in virtually any way they desire. There are also canned tables
containing simple summary data to allow more casual
observers to track the progress of the auction in general.
The FCC also provides the capability to plot maps of auction
winners, high bidders by round, and more general auction
activity. Through a Geographic Information System (GIS),
interested parties can use a Web browser–based application to
construct queries against the database for a particular auction
and have the results displayed in a map format. The GIS presents its query results primarily in maps, which the user can
export to easily transportable graphical formats. The GIS also
allows the user to display data in tabular format. Currently,
there are three queries that can be executed against any closed
or open auction in the GIS:
Market analysis by number of bids Allows users to see
which licenses received a bid in a given round and how
many bids each market received.
Round results summary Provides a high-level summary of
activity for the selected round, depicting markers for
which a new high bid was received, markets for which a
bid was withdrawn, and markets that had no new activity.
Bidder activity Allows users to query the database to generate a map showing all the licenses for which a particular area has a high bid in a given round.
Companies interested in participating in spectrum auctions must submit an electronic application to the FCC disclosing their ownership structure and identifying the
markets/licenses on which they intend to bid. Approximately
2 weeks after the filing deadline and 2 weeks before the start
of the auction, potential bidders must submit a refundable
deposit that is used to purchase the bidding units required
to place bids in the auction. This deposit is not refundable
after the auction closes.
At a minimum, an applicant’s total up-front payment
must be enough to establish eligibility to bid on at least one
of the licenses applied for, or else the applicant will not be
eligible to participate in the auction. In calculating the upfront payment amount, an applicant should determine the
maximum number of bidding units it may wish to bid on in
any single round and submit a payment that covers that
number of bidding units. Bidders have to check their calcu-
lations carefully because there is no provision for increasing a bidder’s maximum eligibility after the up-front payment deadline.
About 10 days before the auction, qualified bidders
receive their confidential bidding access codes, Automated
Auction System software, telephonic bidding phone number,
and other documents necessary to participate in the auction.
Five days before the start of the auction, the FCC sponsors a
mock auction that allows bidders to work with the software,
become comfortable with the rules and the conduct of a
simultaneous multipleround auction, and familiarize themselves with the telephonic bidding process.
When the auction starts, it continues until all bidding
activity has stopped on all licenses. To ensure the competitiveness and integrity of the auction process, the rules prohibit applicants for the same geographic license area from
communicating with each other during the auction about
bids, bidding strategies, or settlements.
The winning bidders for spectrum in each market are
awarded licenses. Within 10 business days, each winning
bidder must submit sufficient funds (in addition to its upfront payment) to bring its total amount of money on deposit
to 20 percent of its net winning bids (actual bids less any
applicable bidding credits). Up-front payments are applied
first to satisfy the penalty for any withdrawn bid before
being applied toward down payments.
If a company fails to pay on time, the FCC takes back the
licenses and holds them for a future auction. The licenses are
granted for a 10-year period, after which the FCC can take
them back if the holder fails to provide service over that
The FCC’s simultaneous multiple-round auction methodology
and the AAS software have generated interest worldwide. The
FCC has demonstrated the system to representatives of many
countries, including Argentina, Brazil, Canada, Hungary,
Peru, Russia, South Africa, and Vietnam. Mexico licensed the
FCC’s copyrighted system and has used it successfully in a
spectrum auction. In addition, in 1997, the FCC was awarded
a bronze medal from the Smithsonian Institution for recognition of the visionary use of information technology.
See also
Federal Communications Commission
Spectrum Planning
Radio spectrum is managed as a scarce natural resource in the
United States. It is scarce because at any given time and place
one use of a portion of the spectrum precludes any other use
of that portion. In the broadcasting service alone, the broadcaster must know where the station’s signal can be received
in order to meet the needs of advertisers. Interference is
unacceptable because it unnaturally limits the broadcaster’s
market. Similarly, a taxi company or a police department
must be able to reliably determine their coverage areas and
know that they will be able to operate without interference in
that area. Consequently, for the public good, the use of the
radio spectrum is regulated, access is controlled, and rules for
its implementation are enforced because of the possibility for
interference between uncoordinated uses.
Spectrum planning in the United States is the shared
responsibility of the National Telecommunications and
Information Administration (NTIA) and the Federal
Communications Commission (FCC). The NTIA is an agency
within the U.S. Department of Commerce and is responsible
for ensuring the spectrum requirements of federal government users. The FCC is an independent regulatory agency
headed by five members who are appointed for 5-year terms
by the President, with the advice and consent of the Senate.
It is responsible for ensuring the spectrum needs of commercial operators and that the public interest is served by a
competitive environment.
Both the NTIA and the FCC work with other executive
branch agencies to allocate portions of the spectrum for specific radio services. Any spectrum shared by federal and nonfederal users is jointly managed by the NTIA and the FCC.
Because 93.1 percent of the spectrum below 30 GHz is
shared, with only 5.5 and 1.4 percent allocated, respectively,
to the private sector and the government on exclusive bases,
effective coordination between the NTIA and the FCC is
The NTIA and the FCC establish their individual spectrum
requirements and then coordinate these requirements with
one another through the Interdepartment Radio Advisory
Committee (IRAC). If difficulties arise in the coordination
process, the IRAC typically facilitates the negotiation efforts.
The current approach to wireless spectrum allocation is
viewed by experts as seriously fractured and in need of revision, given the rapid evolution of technology. While progress
has been made in the FCC’s methods of assigning spectrum,
primarily through auctions, allocation policy has not kept
pace with the increasing demand, with the result that the
allocation system is not moving spectrum to its best uses in
a timely manner.
To assist it in identifying and evaluating changes in spectrum policy that will increase the public benefits derived
from the use of the radio spectrum, the FCC has established
a Spectrum Policy Task Force. The responsibilities of the
task force are to provide specific recommendations to the
FCC for ways in which to evolve the current “command and
control” approach to spectrum policy into a more integrated,
market-oriented approach that provides greater regulatory
certainty while minimizing regulatory intervention. The
task force also assists the FCC in addressing ubiquitous
spectrum issues, including interference protection, spectral
efficiency, effective public safety communications, and implications of international spectrum policies.
Congress also can influence spectrum allocations through
legislation. Once spectrum is allocated, the frequencies
become available for managed federal use under the authority of NTIA and for state and local government and commercial use under the authority of the FCC.
Federal courts also have something to say about spectrum
matters—specifically about FCC enforcement. For example,
NextWave Telecom, a small wireless carrier embroiled in
bankruptcy, won back the rights to airwave licenses worth
billions of dollars when a U.S. Appeals Court ruled in mid2001 that the FCC had stripped the company’s spectrum
improperly when it defaulted on its payments. The 90
licenses at issue, which NextWave picked up in a 1996 spectrum auction for more than $4.7 billion, provide as much as
30 MHz in major cities. Ultimately, NextWave sold the
licenses to AT&T, Cingular, Verizon, and VoiceStream for
$16 billion, with NextWave getting $5 billion and the U.S.
Treasury getting $11 billion.
International spectrum allocations typically influence
allocation decisions within the United States; however, the
interests of the federal government and commercial spectrum users usually take precedence. Therefore, domestic
and international spectrum allocations do not always coincide, as in the case of third-generation (3G) networks, which
use different frequency bands—one set for the United States
and a different set for the rest of the world.
Radio spectrum is managed as a scarce natural resource. It
is scarce because at any given time and place one use of a
portion of the spectrum precludes any other use of that portion. In the broadcasting service alone, the broadcaster must
know where the station’s signal can be received in order to
meet the needs of advertisers. Interference is unacceptable
because it unnaturally limits the broadcaster’s market.
Similarly, a taxi company or a police department must be
able to reliably determine its coverage area and know that it
will be able to operate without interference in that area.
Consequently, for the public good, the use of the radio spectrum is regulated, access is controlled, and rules for its use
are enforced because of the possibility for interference
between uncoordinated uses.
See also
Federal Communications Commission
Spectrum Auctions
Spread spectrum is a digital coding technique in which the
signal is taken apart or “spread” so that it sounds more like
noise to the casual listener, allowing many more users to
share the available bandwidth while affording each conversation a high degree of privacy. Actress Hedy Lamarr (Figure
S-5) and composer George Antheil share the patent for
spread-spectrum technology. Their patent for a “Secret
Communication System,” issued in 1942, was based on the
frequency-hopping concept, with the keys on a piano representing the different frequencies and frequency shifts.2
Lamarr had become intrigued with radio-controlled missiles and the problem of how easy it was to jam the guidance signal. She realized that if the signal jumped from
2In 1942, the technology did not exist for a practical implementation of spread spectrum. When the transistor finally did become available, the Navy used the idea in
secure military communications. When transistors became really cheap, the idea was
used in cellular phone technology to keep conversations private. By the time the Navy
used the idea, the original patent had expired, and Lamarr and Antheil never received
any royalty payments for their idea.
Figure S-5 Actress Hedy Lamarr (1914–2000), codeveloper of spread-spectrum technology.
frequency to frequency quickly—like changing stations on
a radio—and both sender and receiver changed in the same
order at the same time, then the signal could never be
blocked without knowing exactly how and when the frequency changed. Although the frequency-hopping idea
could not be implemented at that time because of technology limitations, it eventually became the basis for cellular
communication based on Code Division Multiple Access
(CDMA) and wireless Ethernet LANs based on infrared
Frequency Assignment
Spread spectrum uses the industrial, scientific, and medical
(ISM) bands of the electromagnetic spectrum. The ISM bands
include the frequency ranges at 902 to 928 MHz and 2.4 to
2.484 GHz, which do not require a site license from the FCC.
Spread spectrum is a highly robust wireless data transmission technology that offers substantial performance
advantages over conventional narrowband radio systems. As
noted, the digital coding technique used in spread spectrum
takes the signal apart and spreads it over the available
bandwidth, making it appear as random noise. The coding
operation increases the number of bits transmitted and
expands the bandwidth used. Noise has a flat, uniform spectrum with no coherent peaks and generally can be removed
by filtering. The spread signal has a much lower power density but the same total power.
This low power density, spread over the expanded transmitter bandwidth, provides resistance to a variety of conditions that can plague narrowband radio systems, including
Interference A condition in which a transmission is being
disrupted by external sources, such as the noise emitted
by various electromechanical devices, or internal sources
such as cross-talk.
Jamming A condition in which a stronger signal overwhelms a weaker signal, causing a disruption to data
Multipath A condition in which the original signal is distorted after being reflected off a solid object.
Interception A condition in which unauthorized users capture signals in an attempt to determine its content.
Non-spread-spectrum narrowband radio systems transmit and receive on a specific frequency that is just wide
enough to pass the information, whether voice or data. In
assigning users different channel frequencies, confining the
signals to specified bandwidth limits, and restricting the
power that can be used to modulate the signals, undesirable
cross-talk—interference between different users—can be
avoided. These rules are necessary because any increase in
the modulation rate widens the radio signal bandwidth,
which increases the chance for cross-talk.
The main advantage of spread-spectrum radio waves is
that the signals can be manipulated to propagate fairly well
through the air, despite electromagnetic interference, to virtually eliminate cross-talk. In spread-spectrum modulation,
a signal’s power is spread over a larger band of frequencies.
This results in a more robust signal that is less susceptible
to interference from similar radio-based systems, since,
although they too are spreading their signals, they use different spreading algorithms.
Spread spectrum is a digital coding technique in which a
narrowband signal is taken apart and “spread” over a spectrum of frequencies (Figure S-6). The coding operation
increases the number of bits transmitted and expands the
amount of bandwidth used. With the signal’s power spread
over a larger band of frequencies, the result is a more robust
signal that is less susceptible to impairment from electromechanical noise and other sources of interference. It also
makes voice and data communications more secure.
Using the same spreading code as the transmitter, the
receiver correlates and collapses the spread signal back down
to its original form. The result is a highly robust wireless data
transmission technology that offers substantial performance
advantages over conventional narrowband radio systems.
There are two spreading techniques in common use today:
direct sequence and frequency hopping.
Direct Sequence In direct sequence spreading—the most com-
mon implementation of spread-spectrum technology—the
Narrowband Waveform
Noise Level
Spread Waveform
Figure S-6 Spread spectrum transmits the entire signal over a bandwidth that is much greater than that required for standard narrowband
transmission. Increasing the frequency range allows more signal components to be transmitted, which results in a more accurate reconstruction of
the original signal at the receiving device.
radio energy is spread across a larger portion of the band than
is actually necessary for the data. Each data bit is broken into
multiple subbits called “chips.” The higher modulation rate is
achieved by multiplying the digital signal with a chip
sequence. If the chip sequence is 10, for example, and it is
applied to a signal carrying data at 300 kbps, then the resulting bandwidth will be 10 times wider. The amount of spreading depends on the ratio of chips to each bit of information.
Because data modulation widens the radio carrier to
increasingly larger bandwidths as the data rate increases,
this chip rate of 10 times the data rate spreads the radio carrier to 10 times wider than it would otherwise be for data
alone. The rationale behind this technique is that a spreadspectrum signal with a unique spread code cannot create the
exact spectral characteristics as another spread-coded signal.
Using the same code as the transmitter, the receiver can correlate and collapse the spread signal back down to its original form, while other receivers using different codes cannot.
This feature of spread spectrum makes it possible to build
and operate multiple networks in the same location. When
each network is assigned its own unique spreading code, all
transmissions can use the same frequency range yet remain
independent of each other. The transmissions of one network
appear to the other as random noise and are filtered out
because the spreading codes do not match.
This spreading technique would appear to result in a
weaker signal-to-noise ratio, since the spreading process
lowers the signal power at any one frequency. Normally, a
low signal-to-noise ratio would result in damaged data packets that would require retransmission. However, the processing gain of the despreading correlator recovers the loss
in power when the signal is collapsed back down to the original data bandwidth but is not strengthened beyond what
would have been received had the signal not been spread.
The FCC has set rules for direct sequence transmitters.
Each signal must have 10 or more chips. This rule limits the
practical raw data throughput of transmitters to 2 Mbps in
the 902-MHz band and 8 Mbps in the 2.4-GHz band. The
number of chips is directly related to a signal’s immunity to
interference. In an area with a lot of radio interference,
users will have to give up throughput to successfully limit
Frequency Hopping In frequency hopping, the transmitter
jumps from one frequency to the next at a specific hopping
rate in accordance with a pseudo-random code sequence. The
order of frequencies selected by the transmitter is taken
from a predetermined set as dictated by the code sequence.
For example, the transmitter may have a hopping pattern of
going from Channel 3 to Channel 12 to Channel 6 to Channel
11 to Channel 5, and so on (Figure S-7). The receiver tracks
these changes. Since only the intended receiver is aware of
One Frequency Hop
Channel = 500 KHz
Channel 3
Channel 12
Channel 6
Channel 11
Channel 5
903 MHz
904 MHz
905 MHz
Figure S-7 Frequency-hopping spread spectrum.
906 MHz
907 MHz
the transmitter’s hopping pattern, then only that receiver
can make sense of the data being transmitted.
Other frequency-hopping transmitters will be using different hopping patterns that usually will be on noninterfering
frequencies. Should different transmitters coincidentally
attempt to use the same frequency and the data of one or both
become garbled at that point, retransmission of the affected
data packets is required. Those data packets will be sent
again on the next hopping frequency of each transmitter.
The FCC mandates that frequency-hopped systems must
not spend more than 0.4 second on any one channel each 20
seconds, or 30 seconds in the 2.4-GHz band. Furthermore,
they must hop through at least 50 channels in the 900-MHz
band or 75 channels in the 2.4-GHz band. These rules reduce
the chance of repeated packet collisions in areas with multiple transmitters.
Direct sequence spread spectrum offers better performance,
but frequency-hopping spread spectrum is more resistant to
interference and is preferable in environments with electromechanical noise and more stringent security requirements.
Direct sequence is more expensive than frequency hopping
and uses more power. Although spread spectrum generally
provides more secure data transmission than conventional
narrowband radio systems, this does not mean the transmissions are immune from interception and decoding by
knowledgeable intruders with sophisticated tapping equipment. For this reason, many vendors provide optional
encryption for added security.
See also
Code Division Multiple Access
Frequency Division Multiple Access
Time Division Multiple Access
Telegraphy is a form of data communication that is based on
the use of a signal code. The word telegraphy comes from
Greek tele meaning “distant” and graphein meaning “to
write”—writing at a distance.
The inventor of the first electric telegraph was Samuel
Finley Breese Morse, an American inventor and painter
(Figure T-1). On a trip home from Italy, Morse became
acquainted with the many attempts to create usable
telegraphs for long-distance telecommunications. He was
fascinated by this problem and studied books on physics for
2 years to acquire the necessary scientific knowledge.
Early Attempts
Morse focused his research on the characteristics of electromagnets, whereby they became magnets only while the current flows. The intermittence of the current produced two
states—magnet and no magnet—from which he developed a
code for representing characters, which eventually became
known as Morse Code. (The International Morse Code is a
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
Figure T-1
c. 1865.
Samuel Finley Breese Morse (1791–1872),
system of dots and dashes that can be used to send messages
by a flash lamp, telegraph key, or other rhythmic device such
as a tapping finger.)
His first attempts at building a telegraph failed, but he
eventually succeeded with the help of some friends who were
more technically knowledgeable. The signaling device was
very simple. It consisted of a transmitter containing a battery and a key, a small buzzer as a receiver, and a pair of
wires connecting the two. Later, Morse improved it by
adding a second switch and a second buzzer to enable transmission in the opposite direction as well.
In 1837, Morse succeeded in a public demonstration of his
first telegraph. Although he received a patent for the device
in 1838, he worked for 6 more years in his studio at New York
University to perfect his invention. Finally, on May 24,1844,
with a $30,000 grant from Congress, Morse unveiled the
results of his work. Over a line strung from Washington,
D.C., to Baltimore, Morse tapped out the message, “What
hath God wrought.” The message reached Morse’s collaborator, Alfred Lewis Vail, in Baltimore, who immediately sent it
back to Morse.
With the success of the telegraph assured, the line
was expanded to Philadelphia, New York, Boston, and
other major cities and towns. The telegraph lines tended to
follow the rights-of-way of railroads, and as the railroads expanded westward, the nation’s communications network
expanded as well.
Morse Code
Morse Code uses a system of dots and dashes that are tapped
out by an operator using a telegraph key. (It also can be used
to communicate via radio and flash lamp.) Various combinations of dots and dashes represent characters, numbers, and
symbols separated by spaces. The Morse Code for letters,
numbers, and symbols used in the United States is described
in Table T-1.
Morse Code is the basis of today’s digital communication.
Although it has virtually disappeared in the world of professional communication, it is still used in the world of amateur
radio (HAM) and is kept alive by history buffs. There are
even pages on the Web that teach telegraphy and perform
translations of text into Morse Code.
Wireless Telegraphy
An Italian inventor and electrical engineer, Guglielmo
Marconi (1874–1937), pioneered the use of wireless telegraphy. Telegraph signals previously had been sent through
electrical wires. In experiments he conducted in 1894,
Morse Code
Marconi (Figure T-2) demonstrated that telegraph signals
also could be sent through the air.
A few years earlier, Heinrich Hertz had produced and
detected the waves across his laboratory. Marconi’s achievement was in producing and detecting the waves over long
distances, laying the groundwork for what today we know as
radio. So-called Hertzian waves were produced by sparks in
one circuit and detected in another circuit a few meters
away. By continuously refining his techniques, Marconi
could soon detect signals over several kilometers, demon-
Figure T-2 Guglielmo Marconi, at 22 years of age, behind
his first patented wireless receiver (1896).
strating that Hertzian waves could be used as a medium for
The results of these experiments led Marconi to approach
the Italian Ministry of Posts and Telegraphs for permission
to set up the first wireless telegraph service. He was unsuccessful, but in 1896, his cousin, Henry Jameson-Davis,
arranged an introduction to Nyilliam Preece, engineer-inchief of the British Post Office. Encouraging demonstrations
in London and on Salisbury Plain followed, and in 1897,
Marconi obtained a patent and established the Wireless
Telegraph and Signal Company, Ltd, which opened the
world’s first radio factory at Chelmsford, England, in 1898.
Experiments and demonstrations continued. Queen
Victoria at Osborne House received bulletins by radio about
the health of the Prince of Wales, convalescing on the royal
yacht off Cowes. Radio transmission was pushed to greater
and greater lengths, and by 1899, Marconi had sent a signal
9 miles across the Bristol Channel and then 31 miles across
the English Channel to France. Most people believed that
the curvature of the earth would prevent sending a signal
much farther than 200 miles, so when Marconi was able to
transmit across the Atlantic in 1901, it opened the door to a
rapidly developing wireless industry. Commercial broadcasting was still in the future—the British Broadcasting
Company (BBC) was established in 1922—but Marconi had
achieved his aim of turning Hertz’s laboratory demonstration into a practical means of communication.
By Morse’s death in 1872, the telegraph was being used
worldwide and would pave the way for the invention of the
telephone. Western Union had the monopoly on commercial
telegraph service but spurned Alexander Graham Bell, who
approached the company with an improvement that would
convey voice over the same wires. Bell had to form his own
company, American Bell Telephone Company, to offer a commercial voice communication service. Since then, voice and
data technologies have progressed through separate evolutionary paths. Only in recent years has voice-data integration been pursued as a means of containing the cost of
telecommunication services.
See also
Cellular Telephones
Telemetry is the monitoring and control of remote devices
from a central location via wire-line or wireless links.
Applications include utility meter reading, load management, environmental monitoring, vending machine management, and security alarm monitoring. Companies are
deploying telemetry systems to reduce the cost of manually
reading and checking remote devices. For example, vending
machines need not be visited daily to check for proper operation or out-of-stock conditions. Instead, this information
can be reported via modem to a central control station so
that a repair technician or supply person can be dispatched
as appropriate. Such telemetry systems greatly reduce service costs.
When telemetry applications use wireless technology,
additional benefits accrue. The use of wireless technology
enables systems to be located virtually anywhere without
depending on the telephone company for line installation.
For instance, a kiosk equipped with a wireless modem can be
located anywhere in a shopping mall without incurring line
installation costs. Via wireless modems, data are collected
from all the area kiosks at the end of the day for batch processing at a data center. The kiosk also runs continuous
diagnostics to ensure proper operation. If a malfunction
occurs, problems are reported via the wireless link to a central control facility, which can diagnose and fix the problem
remotely or dispatch a technician if necessary.
Security Application
A number of wireless security systems are available for commercial and residential use (Figure T-3). Wireless technology
provides installation flexibility, since sensors can be placed
anywhere without proximity to phone jacks. A number of
sensors are available to detect such things as temperature,
frequency, or motion. The system can be programmed to
automatically call monitoring station personnel, police, or
designated friends and neighbors when an alert is triggered.
Such systems can be set to randomly turn lights on and off
at designated times to give the appearance of occupancy.
Depending on vendor, the system may even perform continuous diagnostics to report low battery power or tampering.
In a typical implementation, the security system console
monitors the sensors placed at various potential points of
entry. The console expects the sensor to send a confirmation
Central Office
Service Unit (HUB)
Local Loop
Central Office
Intelligent Home
Loop Back
Line Testing
NI = Network Interface
TIU = Telemetry Interface Unit
Figure T-3 Telemetry applications for residential users.
signal at preset intervals, say, every 90 seconds. If the console does not get the signal, it knows that something is
wrong. For example, a sensor attached to a corner of the window or other glass panel is specially tuned to vibrations
caused by breaking glass. When it detects the glass breaking, the sensor opens its contact and sends a wireless signal
to an audio alarm located on the premises, at a police station, or at a private security firm.
The use of wireless technology for security applications
actually can improve service reliability. A security service
that does not require a dedicated phone line is not susceptible to intentional or accidental outages when phone lines are
down or there is bad weather. Wireless links offer more
immunity to such problems.
Traffic Monitoring
Another common application of wireless technology is its use
in traffic monitoring. For example, throughout the traffic
signal control industry there has been a serious effort to find
a substitute for the underground hard-wired inductive loop
that is in common use today to detect the presence of vehicles at stoplights. Although the vehicle detection loop is
inherently simple, it has many disadvantages:
Slot cutting for loop and lead-in wire is time-consuming
and expensive.
Traffic is disrupted during installation.
Reliability depends on geographic conditions.
Maintenance costs are high, especially in cold climates.
A wireless proximity detector can overcome these problems. Its signals activate traffic lights in the prescribed
sequence. The proximity detector, usually mounted on a
nearby pole, focuses the wireless signal very narrowly on the
road to represent a standard loop. The microprocessor-based
detector provides real-time information while screening out
such environmental variations as temperature, humidity,
and barometric pressure. By tuning out environmental variations, the detectors provide consistent output. This
increases the reliability of traffic control systems. Using a
laptop computer with a Windows-compatible setup package,
information can be exchanged with the detector via an
infrared link. From the laptop, the pole-mounted detector
can be set up remotely, calibrated, and put through various
diagnostic routines to verify proper operation.
Role of Cellular Carriers
Cellular carriers are well positioned to offer wireless telemetry services. The cellular telephone system has a total of 832
channels, half of which are assigned to each of the two competing cellular carriers in each market. Each cellular carrier
uses 21 of its 416 channels as control channels. Each control
channel set consists of a Forward Control Channel (FOCC)
and a Reverse Control Channel (RECC).
The FOCC is used to send general information from the
cellular base station to the cellular telephone. The RECC is
used to send information from the cellular telephone to the
base station. The control channels are used to initiate a cellular telephone call. Once the call is initiated, the cellular
system directs the cellular telephone to a voice channel.
After the cellular telephone has established service on a
voice channel, it never goes back to a control channel. All
information concerning handoff to other voice channels and
termination of the telephone call is handled via communication over the voice channels.
This leaves the control channels free to provide other services such as telemetry, which is achieved by connecting a
gateway to a port at the local mobile switching center (MSC)
or regional facility. The gateway can process the telemetry
messages according to the specific needs of the applications.
For instance, if telemetry is used to convey a message
from an alarm panel, the gateway will process the message
on a real-time, immediate basis and pass the message to the
central alarm monitoring service. On the other hand, if a soft
drink vending company uses telemetry to poll its machines
at night for their stock status, the gateway will accumulate
all the data from the individual vending machines and
process them in batch mode so that the management reports
can be ready for review the next morning.
Individual applications can have different responses from
the same telemetry radio. While the vending machine uses
batch processing for its stock status, it could have an alarm
message conveyed to the vending company on an immediate
basis, indicating a malfunction. A similar scenario is applicable for utility meter reading. Normal meter readings can be
obtained on a batch basis during the night and delivered to
the utility company the following morning. However, realtime meter readings can be made any time during the day
for customers who desire to close out or open service and
require an immediate, current meter reading. Telemetry can
even be used to turn on or turn off utility service remotely by
the customer service representative.
Web-Enabled Telemetry
The next big market for telemetry systems is for those which
distribute data through the Internet for access by a Web
browser, which lowers the cost of implementing telemetry
applications. A growing number of companies offer Webenabled telemetry solutions for such applications as ground
station telemetry processing as well as remote and wide area
With such systems, a host device acts as a network server
that plugs into the local area network (LAN) with standard
Category 5 cabling and RJ-45 connectors. The host device is
connected to remote units over phone lines or wireless links
to the Internet. Data are sent and received between the host
and remote units in standard Transmission Control
Protocol/Internet Protocol (TCP/IP) packets. Client computers connected anywhere on the LAN or the Internet can use
a standard Web browser to display the collected data with no
requirement for additional software. In some cases, integrated Java applets provide real-time telemetry display.
With accumulated data published as Web pages over an
Ethernet LAN or over the Internet, it possible to monitor and
control a process through a browser from anywhere in the
world. For example, using a remote unit attached to a heater
with a wireless link to an access point, an engineer can monitor the temperature, change set points or alarm points, turn
the heater on and off, or make other modifications from anywhere on the local network, or anywhere on the Internet,
simply by using a Web browser. The remote unit also can
send an e-mail message to the engineer alerting him or her to
an alarm condition or updating the status of the remote
device. Leveraging the technology of the Internet even further, the engineer could receive a message from the remote
unit on an Internet-capable pager or cell phone.
Through the Web browser an administrator can set monitoring and measurement parameters from any computer on
the network and configure and change all communication
parameters of the remote units in the field. Access to configurations and data is protected through passwords. Selectable
local disk archiving protects data for future reference should
the primary storage disk fail.
Telemetry services, once implemented by large companies
over private networks, are becoming more widely available
for a variety of mainstream business and consumer applications. Wireless technology permits more flexibility in the
implementation of telemetry systems and can save on line
installation costs. Telemetry systems are inherently more
reliable when wireless links are used to convey status and
control information, since they are less susceptible to outages due to tampering and severe weather. As data communications technology advances and companies continue to
exploit the global ubiquity of the Internet, telemetry solutions will become more pervasive.
See also
Access Points
Cellular Data Communications
Time Division Multiple Access (TDMA) technology is used in
digital cellular telephone communication. It divides each cellular channel into three time slots to increase the amount of
conversations that can be carried. TDMA improves the bandwidth utilization and overall system capacity offered by older
FM radio systems by dividing the 30-kHz channel into three
narrower channels of 10 kHz each. Newer forms of TDMA
allow even more users to be supported by the same channel.
TDMA systems have been providing commercial digital
cellular service since mid-1992. Versions of the technology
are used to provide Digital American Mobile Phone Service
(D-AMPS), Global System for Mobile (GSM) communications, Personal Digital Cellular (PDC), and Digital
Enhanced Cordless Telecommunications (DECT). Originally,
the TDMA specification was described in EIA/TIA Interim
Standard 54 (IS-54). An evolved version of that standard is
IS-136, which is used in the United States for both cellular
and Personal Communications Services (PCS) in the 850MHz and 1.9-GHz frequency bands, respectively. The difference is that IS-136 makes use of a control channel to provide
advanced call features and messaging services.
Time Slots
As noted, TDMA divides the original 30-kHz channel into
three time slots. Users are assigned their own time slot into
which voice or data are inserted for transmission via synchronized timed bursts. The bursts are reassembled at the
receiving end and appear to provide continuous, smooth
communication because the process is very fast. The digital
bit streams that correspond to the three distinct voice conversations are encoded, interleaved, and transmitted using
a digital modulation scheme called Differential Quadrature
Phase-Shift Keying (DQPSK). Together these manipulations
reduce the effects of most common radio transmission
If one side of the conversation is silent, however, the time
slot goes unused. Enhancements to TDMA use dynamic time
slot allocation to avoid the wasted bandwidth when one side
of the conversation is silent. This technique almost doubles
the bandwidth efficiency of TDMA over the original analog
systems. Frequency reuse further enhances network capacity. In nonadjacent cells, the same frequency sets are used as
in other cells, but the cells with the same frequency sets are
spaced many miles apart to reduce interference (Figure T-4).
In a TDMA system, the digitized voice conversations are separated in time, with the bit stream organized into frames,
Figure T-4 Each number represents a different
set of channels or paired frequencies used by a
cell. A cellular system separates each cell that
shares the same channel set, which minimizes
interference while allowing the same frequencies
to be used in another part of the system.
typically on the order of several milliseconds. A 6-millisecond
frame, for example, is divided into six 1-millisecond time
slots, with each time slot assigned to a specific user. Each
time slot consists of a header and a packet of user data for
the call assigned to it (Figure T-5). The header generally contains synchronization and addressing information for the
user data.
If the data in the header become corrupted as a result of a
transmission problem—signal fade, for example—the entire
slot can be wasted, in which case no more data will be transmitted for that call until the next frame. The loss of an entire
data packet is called “frame erasure.” If the transmission problem is prolonged (i.e., deep fade), several frames in sequence
can be lost, causing clipped speech or forcing the retransmis-
6 ms
(30 KHz Channel)
1 ms
1 ms
1 ms
1 ms
1 ms
1 ms
Packet of User Data
Figure T-5 Six TDMA time slots.
sion of data. Most transmission problems, however, will not be
severe enough to cause frame erasure. Instead, only a few bits
in the header and user data will become corrupted, a condition
referred to as “single-bit errors.”
Network Functions
The IS-54 standard defines the TDMA radio interface
between the mobile station and the cell site radio. The radio
downlink from the cell site to the mobile phone and the radio
uplink from the mobile phone to the cell site are functionally
similar. The TDMA cell site radio is responsible for speech
coding, channel coding, signaling, modulation/demodulation, channel equalization, signal strength measurement,
and communication with the cell site controller.
The TDMA system’s speech encoder uses a linear predictive
coding technique and transfers Pulse Code Modulated (PCM)
speech at 64 kbps to and from the network. The channel coder
performs channel encoding and decoding, error correction,
and bit interleaving and deinterleaving. It processes speech
and signaling information, builds the time slots for the channels, and communicates with the main controller, modulator,
and demodulator.
The modulator receives the coded information and signaling bits for each time slot from the channel coders. It performs
DQPSK modulation to produce the necessary digital components of the transmitter waveform. These waveform samples
are converted from digital to analog signals. The analog signals are then sent to the transceiver, which transmits and
receives digitally modulated radiofrequency (RF) control and
information signals to and from the cellular phones.
The modulator/equalizer receives signals from the transceiver. It performs filtering, automatic gain control, receive
signal strength estimation, adaptive equalization, and
demodulation. The demodulated data for each of the time
slots is then sent to the channel coder for decoding.
Newer voice coding technology is available that produces
near-landline speech quality in wireless networks based on
the IS-136 TDMA standard. One technology uses an algebraic code excited linear predictive (ACELP) algorithm, an
enhanced internationally accepted code for dividing waves of
sound into binary bits of data. The ACELP coders can be
integrated easily into current wireless base station radios as
well as new telephones. ACELP-capable phones enable users
to take advantage of the improved digital clarity over both
North American frequency bands—850 MHz for cellular and
1.9 GHz for PCS.
Call Handoff
Receive signal strength estimation is used in the call handoff process. The traditional handoff process involves the cell
site currently serving the call, the switch, and the neighboring cells that potentially can continue the call. The neighboring cells measure the signal strength of the potential call
to be handed off and report that measurement to the serving
cell, which uses it to determine which neighboring cell can
best handle the call. TDMA systems, on the other hand,
reduce the time needed and the overhead required to complete the handoff by assigning some of this signal strength
data gathering to the cellular phone, relieving the neighboring cells of this task and reducing the handoff interval.
Digital Control Channel
Digital Control Channel (DCCH), described in IS-136, gives
TDMA features that can be added to the existing platform
through software updates. Among these new features are
Over-the-air activation Allows new subscribers to activate
cellular or PCS service with just a phone call to the service provider’s customer service center.
Messaging Allows users to receive visual messages up to
the maximum length allowed by industry standards (200
alphanumeric characters). Transmission of messages permits a mobile unit to function as a pager.
Sleep mode Extends the battery life of mobile phones and
allows subscribers to leave their portables powered on
throughout the day, ready to receive calls.
Fraud prevention The cellular system is capable of identifying legitimate mobile phones and blocking access to
invalid ones.
A number of other advanced features also can be supported over the DCCH, such as voice encryption and secure
data transmission, caller ID, and voice mail notification.
Many vendors and service providers have committed to supporting either TDMA or CDMA. Those who have committed
to CDMA claim that they did so because they consider
TDMA to be too limited in meeting the requirements of the
next generation of cellular systems. Although TDMA provides service providers with a significant increase in capacity over AMPS, the standard was written to fit into the
existing AMPS channel structure for easy migration.
Proponents of TDMA, however, note that the inherent
compatibility between AMPS and TDMA, coupled with the
deployment of dual-mode/dual-band terminals, offers full
mobility to subscribers with seamless handoff between PCS
and cellular networks. They also note that the technology is
operational in many of the world’s largest wireless networks
and is providing reliable, high-quality service without additional development or redesign. These TDMA systems can be
easily and cost-effectively integrated with existing wireless and
landline systems, and the technology is evolving to meet the
quality and service requirements of the global third-generation
(3G) wireless infrastructure.
See also
Code Division Multiple Access
Frequency Division Multiple Access
Ultra wideband (UWB) offers the promise of new radar and
imaging services that can save lives by helping to rescue
hostages, locate disaster victims trapped under the rubble of
a collapsed building, detect hidden flaws in the construction
of highways or airport runways, secure homes and businesses, and possibly even provide short-range high-speed
Internet access to the classroom. UWB devices operate by
employing very narrow or short-duration pulses that result
in very large or wideband transmission bandwidths. Its
ultrawide disbursement of ultra-low power bursts presents
novel interference questions that must be addressed, including how to ensure that existing services are not adversely
impacted—especially those services which support public
safety—and whether widespread deployment would have
any appreciable effect on the noise floor. With appropriate
technical standards, however, UWB devices can operate
using spectrum occupied by existing radio services without
causing interference, thereby permitting scarce spectrum
resources to be used more efficiently.
In early 2002, the Federal Communications Commission
(FCC) issued standards designed to ensure that existing and
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planned radio services, particularly safety services, are adequately protected from UWB users. The FCC will enforce the
rules and act quickly on any reports of interference. The
standards are based in large measure on standards that the
National Telecommunications and Information administration (NTIA) believes are necessary to protect against interference to vital federal government operations.
On an ongoing basis, the FCC intends to review the standards for UWB devices, explore more flexible standards,
and address the operation of additional types of UWB operations and technology. Since there is no production UWB
equipment available at this writing and there is little operational experience with the impact of UWB on other radio
services, the FCC chose to err on the side of conservatism in
setting emission limits when there are unresolved interference issues.
The FCC establishes different technical standards and
operating restrictions for three types of UWB devices based
on their potential to cause interference. These three types
of UWB devices are imaging systems, including groundpenetrating radars (GPRs), wall, through-wall, medical
imaging, and surveillance devices; vehicular radar systems; and communications and measurement systems.
Imaging systems Provides for the operation of GPRs and
other imaging devices subject to certain frequency and
power limitations. The operators of imaging devices must
be eligible for licensing, except that medical imaging
devices may be operated by a licensed health care practitioner. At the request of NTIA, the FCC will notify or coordinate with NTIA prior to the operation of all imaging
systems. Imaging systems include
Ground-penetrating radar systems GPRs must be operated below 960 MHz or in the frequency band 3.1 to
10.6 GHz. GPRs operate only when in contact with or
within close proximity of the ground for the purpose of
detecting or obtaining the images of buried objects.
The energy from the GPR is intentionally directed
down into the ground for this purpose. Operation is
restricted to law enforcement, fire and rescue organizations, scientific research institutions, commercial
mining companies, and construction companies.
Wall-imaging systems Wall-imaging systems must be
operated below 960 MHz or in the frequency band 3.1
to 10.6 GHz. Wall-imaging systems are designed to
detect the location of objects contained within a “wall,”
such as a concrete structure, the side of a bridge, or the
wall of a mine. Operation is restricted to law enforcement, fire and rescue organizations, scientific research
institutions, commercial mining companies, and construction companies.
Through-wall imaging systems These systems must be
operated below 960 MHz or in the frequency band 1.99 to
10.6 GHz. Through-wall imaging systems detect the location or movement of persons or objects that are on the
other side of a structure such as a wall. Operation is limited to law enforcement and fire and rescue organizations.
Medical systems These devices must be operated in the
frequency band 3.1 to 10.6 GHz. A medical imaging system may be used for a variety of health applications to
“see” inside the body of a person or animal. Operation
must be at the direction of or under the supervision of
a licensed health care practitioner.
Surveillance systems Although technically these devices
are not imaging systems, for regulatory purposes they
are treated in the same way as through-wall imaging
and are permitted to operate in the frequency band
1.99 to 10.6 GHz. Surveillance systems operate as
“security fences” by establishing a stationary radio frequency (RF) perimeter field and detecting the intrusion
of persons or objects in that field. Operation is limited
to law enforcement, fire and rescue organizations, public utilities, and industrial entities.
Vehicular radar systems Provides for the operation of
vehicular radar systems in the 24-GHz band using directional antennas on terrestrial transportation vehicles provided the center frequency of the emission and the
frequency at which the highest radiated emission occurs
are greater than 24.075 GHz. These devices are able to
detect the location and movement of objects near a vehicle, enabling features such as near collision avoidance,
improved airbag activation, and suspension systems that
better respond to road conditions.
Communications and measurement systems Provides for
use of a wide variety of other UWB devices, such as highspeed home and business networking devices as well as
storage tank measurement devices under Part 15 of the
FCC’s rules subject to certain frequency and power limitations. The devices must operate in the frequency band
3.1 to 10.6 GHz. The equipment must be designed to
ensure that operation can only occur indoors, or it must
consist of handheld devices that may be employed for such
activities as peer-to-peer operation.
UWB technologies are destined to play a significant public
safety role. UWB devices will save the lives of firefighters
and police officers, prevent automobile accidents, assist
search-and-rescue crews in seeing through the rubble of disaster sites, enable broadband connections between home
electronics, and allow new forms of communications in the
years ahead. The U.S. government already uses UWB extensively to make soldiers, airport runways, and highway
bridges safer. But opinion differs greatly on the interference
effect of the widespread use of UWB technologies by the public. If interference does occur, it conceivably could affect critical government and nongovernment spectrum users.
National defense and several safety-of-life systems depend
on bands that have the potential to be impacted by UWB
devices. For this reason, the FCC and NTIA will cooperate in
managing the use of UWB technology.
See also
Federal Communications Commission
Spectrum Planning
One of the major new third-generation (3G) mobile systems
being developed within the global IMT-2000 framework is the
Universal Mobile Telecommunications System (UMTS), which
has been standardized by the European Telecommunications
Standards Institute (ETSI). UMTS makes use of UMTS
Terrestrial Radio Access (UTRA) as the basis for a global terrestrial radio access network. Europe and Japan are implementing UTRA in the paired bands 1920–1980 MHz and
2110–2170 MHz. Europe also has decided to implement UTRA
in the unpaired bands 1900–1920 MHz and 2010–2025 MHz.
UMTS combines key elements of Time Division Multiple
Access (TDMA)—about 80 percent of today’s digital mobile
market is TDMA-based—and Code Division Multiple Access
(CDMA) technologies with an integrated satellite component
to deliver wideband multimedia capabilities over mobile communications networks. The transmission rate capability of
UTRA will provide at least 144 kbps for full-mobility applications in all environments, 384 kbps for limited-mobility
applications in the macro- and microcellular environments,
and 2.048 Mbps for low-mobility applications particularly in
the micro- and picocellular environments. The 2.048-Mbps
rate also may be available for short-range or packet applications in the macrocellular environment.
Because the UMTS incorporates the best elements of
TDMA and CDMA, this 3G system provides a glimpse of
how future wireless networks will be deployed and what
possible services may be offered within the IMT-2000 family of systems.
UMTS Objectives
UMTS makes possible a wide variety of mobile services ranging from messaging to speech, data and video communications,
Internet and intranet access, and high-bit-rate communication up to 2 Mbps. As such, UMTS is expected to take mobile
communications well beyond the current range of wireline and
wireless telephony, providing a platform that will be ready for
implementation and operation in the year 2002.
UMTS is intended to provide globally available, personalized, and high-quality mobile communication services. Its
objectives include
Integration of residential, office, and cellular services into
a single system, requiring one user terminal.
Speech and service quality at least comparable to current
fixed networks.
Service capability up to multimedia.
Separation of service provisioning and network operation.
Number portability independent of network or service
The capacity and capability to serve over 50 percent of the
Seamless and global radio coverage and radio bearer
capabilities up to 144 kbps and further to 2 Mbps.
Radio resource flexibility to allow for competition within
a frequency band.
UMTS separates the roles of service provider, network operator, subscriber, and user. This separation of roles makes pos-
sible innovative new services without requiring additional
network investment from service providers. Each UMTS user
has a unique network-independent identification number,
and several users and terminals can be associated with the
same subscription, enabling one subscription and bill per
household to include all members of the family as users with
their own terminals. This arrangement would give children
access to various communications services under their parents’ account. This application also would be attractive for
businesses that require cost-efficient system operation—
from subscriber/user management down to radio system—as
well as adequate subscriber control over the user services.
UMTS supports the creation of a flexible service rather than
standardizing the implementations of services in detail. The
provision of services is left to service providers and network
operators to decide according to the market demand. The subscriber—or the user when authorized by the subscriber—
selects services into individual user service profiles, either
with the subscription or interactively with the terminal.
UMTS supports its services with networking, broadcasting, directory, localization, and other system facilities, giving
UMTS a clear competitive edge over mobile speech and
restricted data services of earlier-generation networks.
Being adept at providing new services, UMTS is also competitive in the cost of speech services and as a platform for
new applications.
UMTS offers a high-quality radio connection that is capable of supporting several alternative speech codecs at 2 to 64
kbps, as well as image, video, and data codecs. Also supported
are advanced data protocols covering a large portion of those
used in Integrated Services Digital Network (ISDN). The concept includes variable and high bit rates up to 2 Mbps.
Functional Model
The UMTS functional model relies on distributed databases and processing, leaving room for service innovations
without the need to alter implemented UMTS networks or
existing UMTS terminals. This service-oriented model provides three main functions: management and operation of
services, mobility and connection control, and network
Management and operation of services A service data function (SDF) handles storage and access to service-related
data. A service control function (SCF) contains overall service and mobility control logic and service-related data
processing. A service switching function (SSF) invokes
service logic—to request routing information, for example. A call control function (CCF) analyzes and processes
service requests in addition to establishing, maintaining,
and releasing calls.
Mobility and connection control Drawing on the contents
of distributed databases, UMTS will provide for the realtime matching of user service profiles to the available network services, radio capabilities, and terminal functions.
This function will handle mobile subscriber registration,
authentication, location updating, handoffs, and call routing to a roaming subscriber.
Network management Under UMTS, the administration
and processing of subscriber data, maintenance of the network, and charging, billing, and traffic statistics will
remain within the traditional telecommunications management network (TMN).
TMN consists of a series of interrelated national and
international standards and agreements that provide for
the surveillance and control of telecommunications service provider networks on a worldwide scale. The result is
the ability to achieve higher service quality, reduced costs,
and faster product integration. TMN is also applicable in
wireless communications, CATV networks, private overlay networks, and other large-scale, high-bandwidth communications networks. With regard to UTMS (and other
3G wireless networks), TMN will be enhanced to accommodate new requirements. In areas such as service profile
management, routing, and radio resource management
between UMTS services, networks, and terminal capabilities, new TMN elements will be developed.
Bearer Services
Under UMTS, four kinds of bearer services will be provided
to support virtually any current and future application:
Class A This bearer service offers constant-bit-rate (CBR)
connections for isochronous (real-time) speech transmission. This service provides a steady supply of bandwidth
to ensure the highest quality speech.
Class B This bearer service offers variable-bit-rate
connections that are suited for bursty traffic, such as
transaction-processing applications.
Class C This bearer service is a connection-oriented
packet protocol that can be used support time-sensitive
legacy data applications such as those based on IBM’s
Systems Network Architecture (SNA).
Class D This is a connectionless packet bearer service.
This is suitable for accessing data on the public Internet
or private intranets.
By harnessing the best in cellular, terrestrial, and satellite
wideband technology, UMTS will guarantee access to all
communications, from simple voice telephony to high-speed,
high-quality multimedia services. It will deliver information
directly to users and provide them with access to new and
innovative services and applications. It will offer mobile personalized communications to the mass market regardless of
location, network, or terminal used. Users will be provided
with adaptive multimode/multiband phones or terminals with
a flexible air interface to enable global roaming across locations and with backward compatibility with second-generation
(2G) systems.
See also
Cellular Telephones
International Mobile Telecommunications
Voice cloning is a technology that promises human-sounding
synthetic speech that can be used to support existing applications and encourage the development of new applications,
particularly for use in mobile phone voice mail, announcement messages, and voice-activated features. Although synthesized speech systems go back to 1939, today’s technology
offers voice quality that is so realistic that it justifies being
called “cloning.”
Voice cloning is based on technology developed by AT&T
Labs and has two components. The first is a text-to-speech
engine that turns written words into natural-sounding
speech. The second includes a library of voices and the ability to custom-develop a voice, perhaps duplicating a celebrity
spokesperson. The English-speaking voice, male or female,
can be used to read text on a computer, cell phone, or personal digital assistant (PDA). The technology can even be
added to a car’s computer system to recite driving directions,
provide city and restaurant guides, and report on the performance of key subsystems.
The speech software is so good at reproducing the sounds,
inflections, and intonations of a human voice that it can
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
recreate voices and even bring the voices of long-dead
celebrities back to life. The software, which turns printed
text into synthesized speech, makes it possible for a company to use recordings of a person’s voice to utter new things
that the person never actually said. The software, called
Natural Voices, is not flawless—the synthesized speech may
contain a few robotic tones and unnatural inflections—but
this is the first text-to-speech software to raise the specter of
voice cloning, replicating a person’s voice so perfectly that
the human ear cannot tell the difference.
The product itself is provided as a text-to-speech server
engine and client software development kit (SDK) that is an
integrated collection of C++ classes to help developers integrate text to speech into their applications. The SDK
includes a sample application that can be used to explore
potential uses of the SDK and text-to-speech server. Both the
text-to-speech server engine and SDK run on popular computer and development platforms, including Linux, Solaris,
and Windows NT and 2000. An installation package installs
the AT&T Labs Natural Voices TTS engine, documentation,
tools, class libraries, sample applications, and demo applications onto the target system.
AT&T Labs also offers a custom voice product that entails
a person going to a studio where staff record 10 to 40 hours
of readings. Texts range from business and news reports to
outright babble. The recordings are then chopped into the
smallest number of units possible and sorted into databases.
When the software processes text, it retrieves the sounds
and reassembles them to form new sentences. In the case of
long-dead celebrities, archival recordings can be used in the
same way.
Potential customers for the software, which is priced in the
thousands of dollars, include telephone call centers, companies that make software that reads digital files aloud, and
makers of automated voice devices. Businesses could use the
software to
Create new revenue-generating applications and services
for cell phone users.
Improve customer relationships by putting a pleasantsounding voice interface on applications, products, or services.
Realize mobility and “access anywhere/anytime/any
device” strategies by making computer-based information
accessible by voice.
Facilitate international expansion plans through a wide
variety of text-to-speech languages.
Third-party developers can use voice cloning technology
to add significant enhancements to existing applications and
services, drive new revenue opportunities, and add “stickiness” to applications or services. Voice on an e-commerce
Web site, for example, can make content easily accessible to
the visually impaired, which would keep them coming back
for future purchases.
The software also can be used by publishers of video
games and books on tape. In the near future, people will
want high-end speech technology that enables them to interact at length with their cell phones and Palm organizers
instead of typing entries and squinting at a tiny screen.
Ownership Issues
Voice cloning technology raises ownership issues. For example, who owns the rights to a celebrity’s voice? This and
related issues can be addressed in contracts that include
voice-licensing clauses. Current technical limitations may
alleviate any worries that a person’s voice could be cloned
without permission.
Although the technology is not yet good enough to carry out
fraud, synthesized voices eventually may be capable of tricking
people into thinking that they are getting phone calls from people they know—such as a politician during an election campaign. Politicians already make use of machines that perfectly
mimic their signatures and handwritten postscript messages,
making it appear that they are sending personal letters to constituents. In the not too distant future, we can expect voice
cloning to add another personal touch to campaigning.
What is unique about voice cloning is the ability to recreate
custom voices. AT&T has previously licensed speech technology, such as SpeechWorks, to other companies but contends that the latest version represents a huge technological
leap forward. Despite the technical breakthroughs by AT&T
Labs, many engineers are skeptical that a completely simulated voice can be indistinguishable from that of a human.
With the pressure on to perfect the technology, however, it is
too soon to rule out this possibility. Already industry analysts are predicting that the market for text-to-speech software will reach more than $1 billion in the next 5 years,
providing ample incentive to fine-tune the technology.
See also
Voice Compression
Voice compression entails the application of various algorithms to the voice stream to reduce bandwidth requirements while preserving the quality or audibility of the voice
transmission. Numerous compression standards for voice
have emerged over the years that allow businesses to
achieve substantial savings on leased lines with only a modest cost for additional hardware. Using these standards, the
normal 64-kbps voice channel can be reduced to 32, 16, or 8
kbps, or even as little as 6.3 and 5.3 kbps, for sending voice
over the Internet or cellular phone networks. As the compression ratio increases, however, voice quality diminishes.
In the 1960s, the CCITT standardized the use of Pulse
Code Modulation (PCM) as the internationally accepted coding standard (G.711) for toll-quality voice transmission.
Under this standard, a single voice channel requires 64 kbps
when transmitted over the telephone network, which is
based on Time Division Multiplexing (TDM). The 64-kbps
PCM time slot—or payload bit rate—forms the basic building block for today’s public telephone services and equipment, such that 24 time slots or channels of 64 kbps each
that can be supported on a T1 line.
Pulse Code Modulation
A voice signal takes the shape of a wave, with the top and the
bottom of the wave constituting the signal’s frequency level,
or amplitude. The voice is converted into digital form by an
encoding technique called Pulse Code Modulation (PCM).
Under PCM, voice signals are sampled at the minimum rate
of two times the highest voice frequency level of 4000 Hertz
(Hz), which equates to 8000 times per second. The amplitudes of the samples are encoded into binary form using
enough bits per sample to maintain a high signal-to-noise
ratio. For quality reproduction, the required digital transmission speed for 4-kHz voice signals works out to 8000 samples per second × 8 bits per sample = 64,000 bps (64 kbps).
The conversion of analog voice signals to and from digital is
performed by a coder-decoder, or codec, which is a key component of D4 channel banks and multiplexers. The codec translates amplitudes into binary values and performs mu-law
quantizing. The mu-law process (North America only) is an
encoding-decoding scheme for improving the signal-to-noise
ratio. This is similar in concept to Dolby noise reduction,
which ensures quality sound reproduction.
Other components in the channel bank or multiplexer
interleave the digital signals representing as many as 24
channels to form a 1.544-Mbps bit stream (including 8 kbps
for control) suitable for transmission over a T1 line. PCM
exhibits high quality, is robust enough for switching through
the public network without suffering noticeable degradation, and is simple to implement. But PCM allows for only 24
voice channels over a T1 line. Digital compression techniques can be applied to multiply the number of channels on
a T1 line, several of which are described in Table V-1.
Compression Basics
Among the most popular compression methods is Adaptive
Differential Pulse Code Modulation (ADPCM), which has
Description of Commonly Used Digital Compression
Digital Encoding
Pulse Code
Modulation (PCM)
Adaptive Differential
Pulse Code Modulation
Low Delay Code
Excited Linear
Prediction (LDCELP)
Conjugate Structure
Algebraic Code
Excited Linear
Prediction (CSACELP)
Multipulse Maximum
Likelihood Quantization
Algebraic Code Excited
Linear Prediction (ACELP)
Bit Rate,
Opinion Score
40, 32, 24, 16
Note: The mean opinion score (MOS) is the accepted measure of voice quality, determined
through a statistical sample of user opinions.
been a worldwide standard since 1984. It is used primarily
on private T-carrier networks to double the channel capacity
of the available bandwidth from 24 to 48 channels, but it can
be applied to microwave and satellite links as well.
ADPCM is also used on some cellular networks such as
those based on the Personal Handyphone System (PHS) and
Personal Air Communications Systems (PACS). Both employ
32-kbps ADPCM waveform encoding, which provides near
landline voice quality. ADPCM has demonstrated a high
degree of tolerance to the cascading of voice encoders
(vocoders), as experienced when a mobile subscriber calls a
voice-mail system and the mailbox owner retrieves the message from a mobile phone. With other mobile technologies,
the playback quality is noticeably diminished, but with PHS
and PACS, it is very clear.
The ADPCM device accepts the 8000-sample-per-second
rate of PCM and uses a special algorithm to reduce the 8-bit
samples to 4-bit words. These 4-bit words, however, no
longer represent sample amplitudes but only the difference
between successive samples. This is all that is necessary for
a like device at the other end of the line to reconstruct the
original amplitudes.
Integral to the ADPCM device is circuitry called the “adaptive predictor” that predicts the value of the next signal based
only on the level of the previously sampled signal. Since the
human voice does not usually change significantly from one
sampling interval to the next, prediction accuracy can be very
high. A feedback loop used by the predictor ensures that voice
variations are followed with minimal deviation.
Consequently, the high accuracy of the prediction means
that the difference in the predicted and actual signal is very
small and can be encoded with only 4 bits rather than the 8
bits used in PCM. In the event that successive samples vary
widely, the algorithm adapts by increasing the range represented by the 4 bits. However, this adaptation will decrease
the signal-to-noise ratio and reduce the accuracy of voice frequency reproduction.
At the other end of the digital facility is another compression device (Figure V-1), in which an identical predictor performs the process in reverse to reinsert the predicted signal
and restore the original 8-bit code.
By halving the number of bits to accurately encode a voice
signal, T1 transmission capacity is doubled from the original
24 channels to 48 channels, providing the user with a 2 for 1
cost savings on monthly charges for leased T1 lines.
It is also possible for ADPCM to compress voice to 16
kbps by encoding voice signals with only 2 bits instead of 4
1,344 Channels via T3
192 Channels via T2
96 Channels via T1C
48 Channels via T1
Local Coder
Remote Decoder
Figure V-1 Some basic network configurations employing Adaptive
Differential Pulse Code Modulation (ADPCM) to double the number of
channels on the available bandwidth of various digital facilities.
bits, as discussed above. This 4 to 1 level of compression
provides 96 channels on a T1 line without significantly
reducing signal quality.
Although other compression techniques are available for
use on wire and wireless networks, ADPCM offers several
advantages. ADPCM holds up well in the multinode environment, where it may undergo compression and decompression several times before arriving at its final
destination. And unlike many other compression methods,
ADPCM does not distort the distinguishing characteristics
of a person’s voice during transmission.
Variable-Rate ADPCM
Some vendors have designed ADPCM processors that not
only compress voice but also accommodate 64-kbps passthrough as well. The use of very compact codes allows several different algorithms to be handled by the same ADPCM
processor. The selection of algorithm is controlled in software and is done by the network manager. Variable-rate
ADPCM offers several advantages.
Compressed voice is more susceptible to distortion than
uncompressed voice—16 kbps more so than 32 kbps. When
line conditions deteriorate to the point where voice compression is not possible without seriously disrupting communications, a lesser compression ratio may be invoked to
compensate for the distortion. If line conditions do not permit
compression even at 32 kbps, 64-kbps pass-through may be
invoked to maintain quality voice communication. Of course,
channel availability is greatly reduced, but the ability to communicate with the outside world becomes the overriding concern at this point rather than the number of channels.
Variable-rate ADPCM provides opportunities to allocate
channel quality according to the needs of different classes of
users. For example, all intracompany voice links may operate at 16 kbps, while those used to communicate externally
may be configured to operate at 32 kbps.
The number of channels may be increased temporarily by
compressing voice to 16 kbps instead of 32 kbps until new
facilities can be ordered, installed, and put into service. As
new links are added to keep up with the demand for more
channels, the other links may be returned to operation at 32
kbps. Variable-rate ADPCM, then, offers much more channel
configuration flexibility than products that offer voice compression at only 32 kbps.
Other Compression Techniques
Other compression schemes can be used over T-carrier facilities, such as Continuously Variable Slope Delta (CVSD)
modulation and Time Assigned Speech Interpolation (TASI).
CVSD The higher the sampling rate, the smaller is the
average difference between amplitudes. At a high enough
sampling rate—32,000 times a second in the case of 32kbps voice—the average difference is small enough to be
represented by only 1 bit. This is the concept behind CVSD
modulation, where the 1 bit represents the change in the
slope of the analog curve. Successive 1s or 0s indicate that
the slope should get steeper and steeper. This technique
can result in very good voice quality if the sampling rate is
fast enough.
Like ADPCM, CVSD will yield 48 voice channels at 32
kbps on a T1 line. But CVSD is more flexible than ADPCM
in that it can provide 64 voice channels at 24 kbps or 96 voice
channels at 16 kbps. This is so because the single-bit words
are sampled at the signaling rate. Thus, to achieve 64 voice
channels, the sampling rate is 24,000 times a second, while
96 voice channels takes only 16,000 samples per second. In
reducing the sampling rate to obtain more channels, however, the average difference between amplitudes becomes
greater. And since the greater difference between amplitudes is still represented by only 1 bit, there is a noticeable
drop in voice quality. Thus the flexibility of CVSD comes at
the expense of quality. It is even possible for CVSD to provide 192 voice channels at 8 kbps.
TASI Since people are not normally able to talk and listen
simultaneously, network efficiency at best is only 50 percent.
And since all human speech contains pauses that constitute
wasted time, network efficiency is further reduced by as
much as 10 percent, putting maximum network efficiency at
only 40 percent.
Statistical voice compression techniques, such as Time
Assignment Speech Interpolation (TASI), take advantage of
this quiet time by interleaving various other conversation
segments together over the same channel. TASI-based systems actually seek out and detect the active speech on any
line and assign only active talkers to the T1 facility. Thus
TASI makes more efficient utilization of “time” to double T1
capacity. At the distant end, the TASI system sorts out and
reassembles the interwoven conversations on the line to
which they were originally intended.
The drawback to statistical compression methods is that
they have trouble maintaining consistent quality. This is so
because such techniques require a high number of channels,
at least 100, from which a good statistical probability of
usable quiet periods may be gleaned. However, with as few as
72 channels, a channel gain ratio of 1.5 to 1 may be achieved.
If the number of input channels is too few, a condition known
as “clipping” may occur, in which speech signals are deformed
by the cutting off of initial or final syllables.
A related problem with statistical compression techniques
is freeze-out, which usually occurs when all trunks are in use
during periods of heavy traffic. In such cases, a sudden burst
in speech can completely overwhelm the total available
bandwidth, resulting in loss of entire strings of syllables.
Another liability inherent in statistical compression techniques, even for large T1 users, is that they are not suitable
for transmissions having too few quiet periods, such as when
facsimile and music on-hold is used. Statistical compression
techniques, then, work better in large configurations than in
small ones.
Adding lines and equipment is one way that organizations
can keep pace with increases in traffic. But even when funds
are immediately available for such network upgrades, communications managers must contend with the delays inherent in ordering, installing, and putting new facilities into
service. To accommodate the demand for bandwidth in a
timely manner, communications managers can apply an
appropriate level of voice compression to obtain more channels out of the available bandwidth. Depending on the compression technique selected, there need not be a noticeable
decrease in voice quality.
See also
Data Compression
Personal Access Communications Systems
Personal Handyphone System
Wired Equivalent Privacy (WEP) is the security protocol
specified in the IEEE 802.11b Standard for Wireless Fidelity
(Wi-Fi) networks. A key point of vulnerability exists on the
wireless link between client devices and access points. Here,
WEP provides a level of security and privacy ostensibly comparable to what is expected of a wired local area network
(LAN). Since it was not intended as an end-to-end security
solution, however, users must implement additional safeguards to fully protect their information.
WEP relies on a secret key that is shared between a
mobile station such as a notebook equipped with a wireless
Ethernet card and an access point that provides a wired connection to the LAN. The secret key is used to encrypt packets before they are transmitted, and an integrity check is
used to ensure that packets are not modified in transit.
The IEEE standard does not discuss how the shared key
is established. In practice, most installations use a single
key that is shared between all mobile stations and access
points. Commercial products offer more sophisticated key
management techniques that can be used to help defend
against hacker attacks, but products for the residential market generally lack these features because they require a
more technical understanding of security concepts.
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
WEP uses the RC4 encryption algorithm, which is known
as a “stream cipher.” A stream cipher operates by expanding
a short key into an infinite pseudo-random key stream. The
sending device implements the XOR (exclusive or) operation
on the key stream with the plaintext to produce ciphertext.
The receiving device has a copy of the same key and uses it
to generate an identical key stream. By implementing XOR
on the key stream with the ciphertext, the original plaintext
is recovered.
Researchers from the University of California at Berkeley
have found that this mode of operation makes stream
ciphers vulnerable to several attacks. If an attacker flips a
bit in the ciphertext, then on decryption the corresponding
bit in the plaintext will be flipped. Also, if an eavesdropper
intercepts two ciphertexts encrypted with the same key
stream, it is possible to obtain the XOR of the two plaintexts.
According to the Berkeley researchers, knowledge of this
XOR can enable statistical attacks to recover the plaintexts.
The statistical attacks become increasingly effective as more
ciphertexts using the same key stream become known. Once
one of the plaintexts becomes known, it is a relatively simple
matter to recover all of the others. These attack methods
work equally well on both 64- and 128-bit versions of WEP.
WEP has defenses against both of these attacks. To
ensure that a packet has not been modified in transit, it uses
an integrity check (IC) field in the packet. To avoid encrypting two ciphertexts with the same key stream, an initialization vector (IV) is used to augment the shared secret key and
produce a different RC4 key for each packet. The IV is also
included in the packet. However, the Berkeley researchers
contend that both these measures are implemented incorrectly, resulting in poor security.
The integrity check field is implemented as a CRC-32
checksum, which is part of the encrypted payload of the
packet. However, CRC-32 is linear, which means that it is
possible to compute the bit difference of two CRCs based on
the bit difference of the messages over which they are taken.
In other words, flipping bit X in the message results in a
deterministic set of bits in the CRC that must be flipped to
produce a correct checksum on the modified message.
Because flipping bits carries through after an RC4 decryption, this allows the attacker to flip arbitrary bits in an
encrypted message and correctly adjust the checksum so
that the resulting message appears valid.
Vendors that offer business-class products that use WEP
for security on wireless links have dealt with these problems
by adding features to WEP. Cisco Systems, for example,
offers Dynamic WEP Key Management, which allows network administrators to set time increments in which WEP
keys are exchanged per user per session. Increasing the frequency in which keys are exchanged helps systems mitigate
the possibility of successful attacks.
Although WEP will be refined continually to increase the
security of wireless links, even Cisco recognizes that no single security scheme works for all customers. Accordingly, in
addition to WEP, Cisco also offers virtual private network
(VPN), firewall, and other features to enhance the end-toend security of corporate networks.
WEP seeks to establish a similar level of protection as that
offered by the wired network’s physical security measures by
encrypting data transmitted over the wireless LAN. Data
encryption protects the vulnerable wireless link between
clients and access points. Once this measure has been taken,
other typical LAN security mechanisms such as password
protection, end-to-end encryption, VPNs, client firewall software, and authentication can be put in place to further
ensure privacy.
See also
Access Points
Wireless Fidelity
Wireless LAN Security
The number 911 is the designated universal emergency
number in North America for both wireline and wireless
telephone service. Dialing 911 puts the caller in immediate
contact with a public safety answering point (PSAP) operator who arranges for the dispatch of appropriate emergency
services—ambulance, fire, police, rescue—based on the
nature of the reported problem. Since its inception in 1968,
this concept has amply demonstrated its value by saving
countless lives in thousands of cities and towns across the
United States and Canada.
In a series of orders since 1996, the Federal Communications Commission (FCC) has taken action to improve the
quality and reliability of 911 emergency services for wireless
phone users by adopting rules to govern the availability of
basic 911 services and the implementation of enhanced 911
(E911) for wireless services. To further these goals, the
agency has required wireless carriers to implement E911
service, subject to certain conditions and schedules. The
wireless 911 rules apply to all cellular, broadband Personal
Communications Service (PCS) and certain Specialized
Mobile Radio (SMR) service providers.
These carriers are required to provide to the PSAP the
telephone number of the originator of a 911 call and the location of the cell site or base station receiving a 911 call. This
information assists in the provision of timely emergency
responses both by providing some information about the
general location from which the call is being received and by
permitting emergency call takers to reestablish a connection
with the caller if the call is disconnected.
All mobile phones manufactured for sale in the United
States after February 13, 2000, that are capable of operating
in an analog mode, including dual-mode and multimode
handsets, must include a special method for processing 911
calls. When a 911 call is made, the handset must override
any programming that determines the handling of ordinary
calls and must permit the call to be handled by any available
carrier, regardless of whether the carrier is the customer’s
preferred service provider.
As of October 2001, wireless carriers were required to
begin providing automatic location identification (ALI) as
part of E911 service implementation, according to the following schedule:
1. Begin selling and activating ALI-capable handsets no
later than October 1, 2001.
2. Ensure that at least 25 percent of all new handsets activated are ALI-capable no later than December 31, 2001.
3. Ensure that at least 50 percent of all new handsets activated are ALI-capable no later than June 30, 2002.
4. Ensure that 100 percent of all new digital handset activated are ALI-capable no later than December 31, 2002
and thereafter.
5. By December 31, 2005, achieve 95 percent penetration of
ALI-capable handsets among its subscribers.
Originally, the FCC envisioned that carriers would need
to deploy network-based technologies to provide ALI.
However, there have been significant advances in location
technologies that employ new or upgraded handsets and
that are based on the Global Positioning System (GPS).
These methods are approved for implementing enhanced
911 services as well.
Emergency 911 services have become valuable tools in rendering prompt and appropriate assistance to people in critical need. Most states have laws that mandate prompt action
on all calls received by a PSAP operator. Unfortunately, 911
systems are so taken for granted that many calls are not for
emergencies at all, and expensive resources end up being
expended needlessly on trivial pursuits. PSAP operators
now receive calls on such matters as garbage collection
dates, late mail delivery, a leaky faucet or heater the landlord won’t fix, directions to stores and restaurants, and
whether or not to see a lawyer for this or that problem. The
911 systems in some communities have become so bogged
down with nonemergency calls that the subject is frequently
addressed by public awareness campaigns in the print and
broadcast media.
See also
Global Positioning System
Personal Communications Service
Specialized Mobile Radio
The Wireless Application Protocol (WAP) is a specification
developed by the WAP Forum for sending and reading
Internet content and messages on small wireless devices,
such as cellular phones equipped with text displays.
Common WAP-enabled information services are news, stock
quotes, weather reports, flight schedules, and corporate
announcements. Special Web pages called “WAP portals” are
specifically formatted to offer information and services.
CNN and Reuters are among the content providers that offer
news for delivery to cell phones, wireless personal digital
assistants (PDAs), and handheld computers. Electronic commerce and e-mail are among the WAP-enabled services that
can be accessed from these devices as well.
Typically, these devices will have very small screens, so
content must be delivered in a “no frills” format. In addition,
the bandwidth constraints of today’s cellular services mean
that the content must be optimized for delivery to handheld
devices. To get the information in this form, Web sites are
built with a light version of the HyperText Markup Language
(HTML) called the Wireless Markup Language (WML).
The strength of WAP is that it spans multiple air link
standards and, in the true Internet tradition, allows content
publishers and application developers to be unconcerned
about the specific delivery mechanism. Like the Internet,
the WAP architecture is defined primarily in terms of network protocols, content formats, and shared services. This
approach leads to a flexible client-server architecture that
can be implemented in a variety of ways but which also provides interoperability and portability at the network interfaces. The WAP protocol stack is depicted in Figure W-1.
WAP solves the problem of using Internet standards such
as HTML, HyperText Transfer Protocol (HTTP), TLS, and
Transmission Control Protocol (TCP) over mobile networks.
These protocols are inefficient, requiring large amounts of
mainly text-based data to be sent. Web content written with
HTML generally cannot be displayed in an effective way on
the small-sized screens of pocket-sized mobile phones and
pagers, and navigation around and between screens is not
easy with one hand.
Furthermore, HTTP and TCP are not optimized for the
intermittent coverage, long latencies, and limited bandwidth associated with wireless networks. HTTP sends its
headers and commands in an inefficient text format instead
of compressed binary format. Wireless services using these
protocols are often slow, costly, and difficult to use. The TLS
security standard, too, is problematic, since many messages
need to be exchanged between client and server. With wireless transmission latencies, this back-and-forth traffic flow
results in a very slow response for the user.
WAP has been optimized to solve all these problems. It
makes use of binary transmission for greater compression of
data and is optimized for long latency and low to medium
bandwidth. WAP sessions cope with intermittent coverage
and can operate over a wide variety of wireless transports
using the Internet Protocol (IP) where possible and other
Wireless Application
Environment (WAE)
Wireless Session
Protocol (WSP)
Wireless Transaction
Protocol (WTP)
Wireless Transport
Layer Security (WTLS)
Datagrams (UDP/IP)
Wireless Bearers:
Figure W-1 The Wireless Application Protocol (WAP) stack.
optimized protocols where IP is impossible. The WML used
for WAP content makes optimal use of small screens, allows
easy navigation with one hand without a full keyboard, and
has built-in scalability from two-line text displays through to
the full graphic screens on smart phones and communicators.
WAP Applications Environment
WAP applications are built within the Wireless Application
Environment (WAE), which closely follows the Web content
delivery model, but with the addition of gateway functions.
Figure W-2 contrasts the conventional Web model with the
WAE model. All content is specified in formats that are similar to the standard Internet formats and is transported using
standard protocols on the Web while using an optimized
CGI Scripts,
Java, etc.
Response (Content)
and Decoders
Encoded Response
CGI Scripts,
Java, etc.
Response (Content)
Figure W-2 The standard Web content delivery model (top) and the
Wireless Application Environment mode (bottom).
HTTP-like protocol in the wireless domain (i.e., WAP). The
architecture is designed for the memory and CPU processing
constraints that are found in mobile terminals. Support for
low-bandwidth and high-latency networks is also included in
the architecture as well. Where existing standards were not
appropriate due to the unique requirements of small wireless
devices, WAE has modified the standards without losing the
benefits of Internet technology.
The major elements of the WAE model include
WAE user agents These client-side software components provide specific functionality to the end user. An example of a
user agent is a browser that displays content downloaded
from the Web. In this case, the user agent interprets network
content referenced by a Uniform Resource Locator (URL).
WAE includes user agents for the two primary standard content types: encoded WML and compiled WML Script.
Content generators Applications or services on servers
may take the form of Common Gateway Interface (CGI)
scripts that produce standard content formats in response
to requests from user agents in the mobile terminal. WAE
does not specify any particular content generator, since
many more are expected to become available in the future.
Standard content encoding A well-defined content encoding, allowing a WAE user agent (e.g., a browser) to conveniently navigate Web content. Standard content encoding
includes compressed encoding for WML, bytecode encoding for WMLScript, standard image formats, a multipart
container format, and adopted business and calendar
data formats (i.e., vCard and vCalendar).
Wireless Telephony Application (WTA) This collection of
telephony specific extensions provides call and feature
control mechanisms, allowing users to access and interact with mobile telephones for phonebooks and calendar
WMLScript is a lightweight procedural scripting language based on JavaScript. It enhances the standard brows-
ing and presentation facilities of WML with behavioral capabilities. For example, an application programmer can use
WMLScript to check the validity of user input before it is
sent to the network server, provide users with access to
device facilities and peripherals, and interact with the user
without a round-trip to the network server (e.g., display an
error message).
WAP 2.0
The latest version of the Wireless Application Protocol is
WAP 2.0, which continues the convergence of WAP with the
evolving Internet, merging the work of the WAP Forum, the
World Wide Web Consortium (W3C), and the Internet
Engineering Task Force (IETF) and enabling more rapid
development of new mobile Internet applications.
New technologies of WAP 2.0 that will improve the user
experience are data synchronization, multimedia messaging
service (MMS), persistent storage interface, provisioning,
and pictograms. Additionally, WTA, Push, and User Agent
Profile (UAPROF) use more advanced features in WAP 2.0
than in previous versions.
Data synchronization adopts the SyncML protocol to
ensure a common solution framework with a multitude of
devices. The SyncML messages are supported over both
the Wireless Session Protocol (WSP) and the HTTP/1.1
Multimedia messaging service provides the framework to
develop applications that support feature-rich messaging
solutions, permitting delivery of varied types of content in
order to tailor the user experience.
Persistent storage interface provides a set of storage services that allows the user to organize, access, store, and
retrieve data on wireless devices.
Provisioning permits the network operator to manage the
devices on its network with a common set of tools.
Pictogram permits the use of a set of tiny images, allowing
users to quickly convey concepts in a small amount of space
while transcending traditional language boundaries.
Wireless Telephony Application provides a range of
advanced telephony services within the application environment, enabling a host of call handling functions such
as making and answering calls, placing them on hold, and
redirecting them even while performing data-centric
tasks. The availability of these services enables operators
to offer customers a unique user interface to control complex network features, such as call forwarding options.
Push technology allows trusted application servers to
proactively send personalized content to the end user,
such as a sales offer for a product a person might be interested in buying, a new e-mail notification, or a locationdependent promotion. Push technology complements the
traditional “pull” model of the Internet, where users
request specific information from a Web site.
User agent profile enables application servers to send the
appropriate content to the user and to recognize the capabilities of devices, such as screen size and color, to maximize performance potential, bringing the user increased
WAP 2.0 is a next-generation specification that addresses
the needs of all players in the wireless industry who plan on
incorporating the platform-agnostic specification in their
products and services to grow the wireless market by offering value-added features.
WAP is an open global specification that empowers mobile
users with wireless devices to easily access and interact
with information and services instantly. It is designed to
work with most wireless networks, including Bluetooth,
DECT, and GRPS. It can be built to run on any operating
system, including PalmOS, EPOC, Windows CE, FLEXOS,
OS/9, and JavaOS. WAP offers the additional advantage of
providing service interoperability between different device
See also
Cellular Data Communications
Infrared Networking
Wireless IP
Application service providers (ASPs) host business-class
applications in their data centers and make them available
to customers on a subscription basis over the network.1
Among the business functions commonly outsourced in this
way are customer relationship management (CRM), financial management, human resources, procurement, and
enterprise resource planning (ERP). The ASP owns the
applications, and subscribers are charged a fixed monthly
fee for use of the applications over secure network connections. Wireless ASPs (WASPs) provide hosted wireless applications so that companies will not have to build their own
sophisticated wireless infrastructures.
The difference between Web hosting or e-commerce hosting and the kind of hosting
performed by ASPs is that in the former case the customer owns the applications and
merely runs them on the shared or dedicated servers of an Internet service provider
(ISP). In the latter case the ASP has strategic alliances with third-party software
providers for licensed use of the applications over the network. The ASP pays fees to
the software firms based on factors such as the number and type of customers’ users.
An ASP enables customers to avoid many of the significant
and unpredictable ongoing application management challenges and costs. Following the implementation of software
applications, performed for a fixed fee or on a time and materials basis, customers pay a monthly service fee based largely
on the number of applications used, total users, the level of
service required, and other factors. By providing application
implementation, integration, management, and various
upgrade services and related hardware and network infrastructure, the ASP reduces information technology (IT) burdens of its customers, enabling them to focus on their core
businesses and react quickly to dynamic market conditions.
Traditionally, organizations have installed, operated, and
maintained enterprise software applications internally. The
implementation of enterprise software applications often
takes twice as long as planned. Moreover, the ongoing costs of
operating these applications, including patching, upgrading,
training, and management expenses, are often significant,
unpredictable, and inconsistent and may increase over time.
The emergence of the Internet, the increased communications
bandwidth, and the rewriting of enterprise software to be
delivered over IP networks are transforming the way enterprise software applications are being provided to companies.
Instead of in-house installations, these applications are
beginning to be hosted by third parties, in which the hosting
company maintains the applications on an off-site server,
typically in a data center, and delivers the applications to
customers over the Internet as a service. In addition, competitive pressures have led to a renewed focus on core competencies, with many businesses concluding that building
and maintaining IT capabilities across their entire set of
applications are not core competencies. In response to these
factors, companies are adopting hosted applications rather
than managing them in-house.
An ASP typically can complete a standard implementation of its services in 2 to 14 weeks. This allows customers to
avoid the longer implementation times frequently experi-
enced with installing and integrating customized, sophisticated applications. This enables customers to achieve the
desired benefits quickly by reducing the time required to
establish or augment IT capabilities with wire or wireless
infrastructures of their own.
To address this market, many types of companies are setting themselves up as ASPs in this relatively new market,
including long-distance carriers, telephone companies, computer firms, Internet service providers (ISPs), software vendors, integrators, and business management consultants.
Intel Corp., for example, has built data centers around the
world to be ready to host electronic business sites for millions
of businesses that will embrace the Internet within 5 years.
Another ASP, Corio, enables businesses to obtain best-ofbreed applications at an affordable cost. Corio is responsible
for maintaining and managing the applications and ensuring their availability to its customers from its data centers.
For a fixed monthly fee for the suite of integrated business
applications and services, businesses can achieve a 70 percent reduction on average of total cost of ownership (TCO) in
the first year versus traditional models and a 30 to 50 percent TCO reduction over a 5-year period.
Among the WASPs are Etrieve and Wireless Knowledge.
Etrieve combines the reach of wireless, information processing technology, and voice recognition to provide mobile professionals with the right information, at the right time, in
the right format. As an extension of the desktop, Etrieve
enables mobile professionals to manage their critical office
information—e-mail, calendar, and address book—by voice,
by text, and by importance. Wireless Knowledge, a subsidiary of Qualcomm, provides mobile access to Microsoft
Exchange or Lotus Domino groupware.
Past Attempts
Application outsourcing has been around for nearly 30 years
under the concept of the service bureau. In the service
bureau arrangement, business users rented applications
running the gamut from rudimentary data processing to
high-end proprietary payroll. Companies such as EDS and
IBM hosted the applications at centralized sites for a
monthly fee and typically provided access via low-speed
private-line connections.
In an early 1990s incarnation of the service-bureau
model, AT&T rolled out hosted Lotus Notes and Novell
NetWare services, complete with 24 × 7 monitoring and management. Users typically accessed the applications over a
Frame Relay service or dedicated private lines. AT&T’s
Notes hosting effort failed and was discontinued in early
1996. The carrier lacked the expertise needed to provide
application-focused services and did not offer broad enough
access to these applications. The lesson: Large telecommunications companies are focused on building networks,
which is quite different from implementing and managing
enterprise applications.
In 1998, there emerged renewed interest in this type of service with a new twist—that of providing an array of standardized services to numerous business customers. Economies of
scale could be achieved in this “one to many” model by cost
reductions incurred in service delivery; specifically by relying
on managed IP networks. Further cost reductions could be
achieved by developing implementation templates, innovative
application management tools, and integration models that
can be used for numerous applications across a variety of companies and industries.
To help sell the benefits of applications outsourcing, 25
companies have formed the Applications Service Provider
Industry Consortium. The consortium includes a wide range
of companies, including AT&T on the service-provider side.
Compaq Computer, IBM, and Sun Microsystems are representative of the systems and software vendors. Interconnect
companies such as Cisco Systems are also members. The
consortium’s goals include education, common definitions,
research, standards, and best practices.
Several trends have come together to rekindle the market
for applications outsourcing. The rise of the Internet as an
essential business tool, the increasing complexity of enterprise software programs, and the shortage of IT expertise
have created a ready environment for carriers and other
companies entering the applications hosting business. The
economics of outsourcing are compelling, and new companies are being created to deal with customers’ emerging outsourcing requirements. As wireless technologies become
popular, WASPs have emerged to bring applications to
mobile devices, saving companies the trouble and expense of
doing it themselves.
See also
Wireless Internet Service Providers
Centrex—short for “central office exchange”—is a service
that handles business calls at the telephone company’s
switch rather than through a customer-owned, premisesbased Private Branch Exchange (PBX). Centrex provides a
full complement of station features, remote switching, and
network interfaces that provides an economical alternative
to owning a PBX. Centrex offers remote options for businesses with multiple locations, providing features that
appear to users and the outside world as if the remote sites
and the host switch are one system. Centrex-capable
switches now support wireless links, which extends the
boundaries of business services.
Centrex users have access to direct inward dialing (DID)
features, as well as station identification on outgoing calls.
Each station has a unique line appearance in the central
office, in a manner similar to residential telecommunications
subscriber connections. A Centrex call to an outside line exits
the switch in the same manner as a toll call exits a local
exchange. Users dial a four- or five-digit number without a
prefix to call internal extensions and dial a prefix (usually 9)
to access outside numbers.
The telephone company operates, administers, and maintains all Centrex switching equipment for the customers. It
also supplies the necessary operating power for the switching equipment, including backup power to ensure uninterrupted service during commercial power failures.
Centrex may be offered under different brand names.
BellSouth calls it Essex, and SBC Communications calls it
Plexar, while Verizon calls it CentraNet. Centrex is also
offered through resellers that buy Centrex lines in bulk from
the local exchange carrier. Using its own or commercially
purchased software, the reseller packages an offering of
Centrex and perhaps other basic and enhanced telecommunications services to meet the needs of a particular business.
The customer gets a single bill for all local, long-distance,
800, 900, and calling-card services at a fee that is less than
the customer would otherwise pay.
Centrex Features
Centrex service offerings typically include direct inward dialing (DID), direct outward dialing (DOD), and automatic identification of outward dialed calls (AIOD). Advanced digital
Centrex service provides all the basic and enhanced features
of the latest PBXs in the areas of voice communications, data
communications, networking, and Integrated Services
Digital Network (ISDN) access. Commonly available features
include voice mail, electronic mail, message center support,
and modem pooling.
For large networks, the Centrex switch can act as a tandem
switch, linking a company’s PBXs through an electronic
tandem network. Centrex is also compatible with most private switched network applications, including the Federal
Telecommunications System (FTS) and the Defense Switched
Network (DSN).
Many organizations subscribe to Centrex service primarily because of its networking capabilities, particularly for
setting up a virtual citywide network without major cost or
management concerns. With city-wide Centrex, a business
can set up a network of business locations with a uniform
dialing plan, a single published telephone number, centralized attendant service, and full feature transparency for
only an incremental cost per month over what a single
Centrex site would cost.
Wireless Service
A number of value-added services are available through
wireless Centrex. Pacific Bell’s Wireless Centrex, for example, combines an existing Centrex service with Ericsson’s
Freeset Business Wireless Telephone system to create a private wireless environment at a company’s business location
without incurring expensive cellular airtime charges. At the
corporate facility multiple, overlapping cells cover assigned
areas. The number of cells required is determined by traffic
density at a given location.
An on-premises system called the “radio exchange” handles such functions as powering, control, and facilities for
connection to Centrex. Base stations relay calls from the
radio exchange to the portable telephones. Each base station
provides multiple simultaneous speech channels. The coverage of each base station depends on the character of the environment, but it is typically between 8000 and 15,000 square
feet. Portable telephones contain the intelligence needed to
accommodate roaming and cell-to-cell handover.
When the radio exchange receives an incoming call, it
transmits the identification signal of a portable telephone to
all base stations. Because the portable telephone communicates with the nearest base station, even in standby mode, it
receives the signal and starts ringing. When the call is
answered, the portable telephone selects the channel with
the best quality transmission.
Pacific Bell’s Wireless Centrex service gives business
users full wireless mobility plus the following options:
Account codes
Authorization codes
Automatic callback
Automatic recall
Call diversion/call forwarding
Call diversion override
Call hold
Call transfer
Call waiting
Call pickup
Speed calling
Call park
Conference/three-way calling
Remote access to network services
Distinctive/priority ringing
Do not disturb
External call forwarding
Executive intrusion/executive busy override
Individual abbreviated dialing/single digit dialing
Speed dialing
Last number redial
Loudspeaker paging
Message waiting indication
Remote access to subscriber features
Select call forwarding
Centrex offers high-quality, dependable, feature-rich telephone service that supports a variety of applications. For
many organizations, Centrex offers distinct advantages over
on-premises PBX or key/hybrid systems. Centrex can save
money over the short term because there is no outlay of cash
for an on-premises system. If the service is leased on a
month-to-month basis, there is little commitment and no
penalty for discontinuing the service. A company can pick up
and move without worrying about reinstalling the system,
which may not be right for the new location. With wireless
capabilities, businesses get the advantage of mobility without the expense of investing in wireless infrastructure of
their own.
See also
Wireless PBX
Wireless Communications Services (WCS) is a category of service that operates in the 2.3-GHz band of the electromagnetic
spectrum from 2305 to 2320 MHz and 2345 to 2360 MHz. The
FCC issued licenses for WCS as the result of a spectrum auction held in April 1997. Licensees are permitted—within their
assigned spectrum and geographic areas—to provide any
fixed, mobile, radiolocation, or broadcast-satellite service.
One use for the WCS spectrum is for services that adhere to
the Personal Access Communications System (PACS) standard. This standard is applied to consumer-oriented products,
such as personal cordless devices.
There are two 10-MHz WCS licenses for each of 52 major
economic areas (MAEs) and two 5-MHz WCS licenses for
each of 12 regional economic area groupings (REAGs).
WCS licensees are permitted to partition their service
areas into smaller geographic service areas and to disaggregate their spectrum into smaller blocks without limitation.
Licenses are good for a term of 10 years and are renewable
just like PCS and cellular licensees. In addition, WCS
licensees will be required to provide “substantial service”
within their 10-year license term.
WCS is implemented through small relay stations, which
may interface with the Public Switched Telephone Network
(PSTN). Where WCS poses interference problems with existing Multipoint Distribution Service (MDS) or Instructional
Television Fixed Service (ITFS) operations, the WCS licensees
must bear the full financial obligation for the remedy. WCS
licensees must notify potentially affected MDS/ITFS licensees
at least 30 days before commencing operations from any new
WCS transmission site or increasing power from an existing
site of the technical parameters of the WCS transmission
facility. The FCC expects WCS and MDS/ITFS licensees to
coordinate voluntarily and in good faith to avoid interference
problems, which will result in the greatest operational flexibility in each of these types of operations.
In establishing WCS, the FCC believed that the flexible use of
the 2305- to 2320-MHz and 2345- to 2360-MHz frequency
bands would help ensure that new technologies are developed
and deployed, such as a wireless system tailored to provide
portable Internet access over wide areas at data rates comparable to an ISDN-type connection. Because the technical
characteristics of such a system would differ significantly
from those for some other systems that might use this band
(e.g., PCS), the FCC neither restricted the services provided
in this band nor dictated technical standards for operation
beyond those required to avoid interference and protect the
public interest. In fact, WCS licensees are not constrained to
a single use of this spectrum and, therefore, may offer a mix
of services and technologies to their customers.
See also
Personal Access Communications Systems
Spectrum Auctions
Wireless Fidelity (Wi-Fi) refers to a type of Ethernet specified under the IEEE 802.11a and IEEE 802.11b Standards
for LANs operating in the 5- and 2.4-GHz unlicensed frequency bands respectively. Wi-Fi is equally suited to residential users and businesses, and equipment is available
that allows both bands to be used to support separate networks simultaneously.
The IEEE 802.11 Standard makes the wireless network a
straightforward extension of the wired network. This has
allowed for a very uncomplicated implementation of wireless
communication with obvious benefits—they can be installed
using the existing network infrastructure with minimal
retraining or system changes. Notebook users can roam
throughout their sites while remaining in contact with the
network via strategically placed access points that are
plugged into the wired network.
Wireless users can run the same network applications
they use on an Ethernet LAN. Wireless adapter cards used
on laptop and desktop systems support the same protocols as
Ethernet adapter cards. For most users, there is no noticeable functional difference between a wired Ethernet desktop
computer and a wireless computer equipped with a wireless
adapter other than the added benefit of the ability to roam
within the wireless cell. Under many circumstances, it may
be desirable for mobile network devices to link to a conventional Ethernet LAN in order to use servers, printers, or an
Internet connection supplied through the wired LAN. A wireless access point (AP) is a device used to provide this link.
The IEEE 802.11b Standard designates devices that operate in the 2.4-GHz band to provide a data rate of up to 11
Mbps at a range of up to 300 feet (100 meters) using directsequence spread-spectrum technology. Some vendors have
implemented proprietary extensions to the IEEE 802.11b
Standard, allowing applications to burst beyond 11 Mbps to
reach as much as 22 Mbps. Users can share files and applications, exchange e-mail, access printers, share access to the
Internet, and perform any other task as if they were directly
cabled to the network.
The IEEE 802.11a Standard designates devices that operate in the 5-GHz band to provide a data rate of up to 54 Mbps
at a range of up to 900 feet (300 meters). Sometimes called
“Wi-Fi5,” this amount of bandwidth allows users to transfer
large files quickly or even watch a movie in MPEG format
over the network without noticeable delays. This technology
works by transmitting high-speed digital data over a radio
wave using Orthogonal Frequency Division Multiplexing
(OFDM) technology.
OFDM works by splitting the radio signal into multiple
smaller subsignals that are then transmitted simultaneously at different frequencies to the receiver. OFDM
reduces the amount of interference in signal transmissions, which results in a high-quality connection. Wi-Fi5
products automatically sense the best possible connection
speed to ensure the greatest speed and range possible with
the technology. Some vendors have implemented proprietary extensions to the IEEE 802.11a Standard allowing
applications to burst beyond 54 Mbps to reach as much as
72 Mbps.
IEEE 802.11 wireless networks can be implemented in
infrastructure mode or ad-hoc mode. In infrastructure
mode—referred to in the IEEE specification as the “basic
service set”—each wireless client computer associates with
an AP via a radio link. The AP connects to the 10/100-Mbps
Ethernet enterprise network using a standard Ethernet
cable and provides the wireless client computer with access
to the wired Ethernet network. Ad-hoc mode is the peer-topeer network mode, which is suitable for very small instal-
lations. Ad-hoc mode is referred to in the IEEE 802.11b specification as the “independent basic service set.”
Security for Wi-Fi networks is handled by the IEEE standard called Wired Equivalent Privacy (WEP), which is available in 64- and 128-bit versions. The more bits in the
encryption key, the more difficult it is for hackers to decode
the data. It was originally believed that 128-bit encryption
would be virtually impossible to break due to the large number of possible encryption keys. However, hackers have since
developed methods to break 128-bit WEP without having to
try each key combination, proving that this system is not
totally secure. These methods are based on the ability to
gather enough packets off the network using special eavesdropping equipment to then determine the encryption key.
Although WEP can be broken, it does take considerable
effort and expertise to do so. To help thwart hackers, WEP
should be enabled and the keys rotated on a frequent basis.
The wireless LAN industry has recognized that WEP is
not as secure as once thought and is responding by developing another standard, known as IEEE 802.11i, that will
allow WEP to use the Advanced Encryption Algorithm (AES)
to make the encryption key even more difficult to determine.
AES replaces the older 56-bit Digital Encryption Standard
(DES), which had been in use since the 1970s. AES can be
implemented in 128- , 192- , and 256-bit versions. Assuming
a computer with enough processing power to test 255 keys
per second, it would take 149 trillion years to crack AES.
Wi-Fi is a certification of interoperability for IEEE 802.11b
systems awarded by the Wireless Ethernet Compatibility
Alliance (WECA), now known as the Wi-Fi Alliance. The WiFi seal indicates that a device has passed independent tests
and will reliably interoperate with all other Wi-Fi certified
equipment. Customers benefit from this standard by avoiding
becoming locked into one vendor’s solution—they can pur-
chase Wi-Fi certified access points and client devices from different vendors and still expect them to work together.
See also
Access Points
Wired Equivalent Privacy
Wireless Internet Service Providers
Wireless LANs
Wireless Security
In most organizations today, Internet access via the LAN is
the norm. Workers share applications, data, and services
through their hub- or switch-based LAN connection. When
they require Internet access to do research on the Web or
send e-mail to someone on another network, for example, the
traffic goes through a router connected to the hub or switch
and then out to the ISP via a dedicated, “always on” connection such as a Digital Subscriber Line (DSL) or T1 link or
even cable. Telecommuters may have to rely on dialup services that offer no more than 56 kbps.
However, there are two trends that make the case for
wireless Internet access. One trend has to do with the workforce itself; more and more workers are becoming mobile and
require a flexible method of Internet access from wherever
they happen to be. This greatly improves flexibility in that
the user does not have to find an available phone line in
order to dial into the Internet. Wireless access to the
Internet also increases productivity in that the user can
accomplish work-related tasks at the most opportune time,
even while traveling or taking a “vacation.”
Second, more companies require high-speed Internet
access and cannot always get ISDN, DSL, or cable in their
areas or afford the price of one or more T1 lines. Larger companies that require broadband Internet access in the multimegabit range via T3 or OC-3 may not be able to wait for
fiber installation to their locations. These companies are
looking to fixed wireless providers for fast installation as
well as cheap bandwidth. Whereas a new fiber build may
take months to complete under a best-case scenario, wireless
broadband connectivity from the customer premises to the
service provider’s hub antenna can be accomplished in a
matter of days.
Business users have a growing number of wireless
Internet access services to choose from, and vendors and service providers are emphasizing technologies designed to let
users take the Internet with them wherever they go.
Already, wireless offerings run the gamut from Wireless
Application Protocol (WAP)–enabled mobile phones to
broadband architectures that offer fixed wireless access to
IP-based networks at megabit-per-second speeds. In addition, Internet connectivity is now available with all major
mobile phone protocols, including Code Division Multiple
Access (CDMA), Time Division Multiple Access (TDMA), and
Global System for Mobile (GSM) telecommunications.
Wireless Access Methods
There are several methods to wirelessly access the
Internet, including analog cellular and cellular digital
packet data networks, packet radio services, and satellite.
Cellular Networks Analog cellular phone subscribers can
send files and e-mail wirelessly via the Internet by hooking
up a modem to their phones. Of course, this method of access
requires that the user have a cell phone in the first place, as
well as an adapter cable to connect the phone to the modem.
Cellular modems work anywhere a cell phone does. The
problem is that they work only as well as the cell phone
does at any given moment. Checking e-mail on the Internet
can be slow, and connection quality varies from network to
To access Web content on the Internet, however, really
requires a digital cellular service [also called Personal
Communication Service (PCS)] and a special phone equipped
with a liquid-crystal display (LCD) screen. AT&T’s PocketNet
phone, for example, lets users access the Internet in areas
served by its Cellular Digital Packet Data (CDPD) network.
With this type of cellular service, standard analog cell
phones will not work; a digital CDPD phone is required. An
alternative is to use a dual-mode phone that operates in standard analog cellular mode for voice conversations and CDPD
mode for access to the Internet at 19.2 kbps. AT&T’s
PocketNet service includes a personal information manager
(PIM) that contains an address book, calendar, and to-do list
that are maintained on AT&T’s Web site and accessed through
the phone. The personal address book is tied to the PocketNet
phone’s “easy dialing” feature for fast, convenient calling.
Another feature offered by CDPD is mobility management, which routes messages to users regardless of the location or the technology. Gateways provide the cellular
network with the capability to recognize when subscribers
move out of the CDPD coverage area and transfer messages
to them via circuit-switched cellular.
Packet Radio Networks An example of a radio network is
provided by the Ricochet service developed by Metricom,
now a subsidiary of Aerie Networks, that provides network
solutions and wireless data communications for industrial
and PC applications. The Ricochet service comprises radios,
wired access points (AP), and network interconnection facilities (NIF) that enable data to be sent across a network of
intelligent radio nodes at speeds of over 176 kbps, with
bursts of up to 400 kbps.
The network uses frequency-hopping spread-spectrum
packet radios. A large number of these low-power radios are
installed throughout a geographic region in a mesh topology,
usually placed on top of streetlights or utility poles. These
radio receivers, about the size of a shoebox, are also referred
to as “microcell radios.” Only a small amount of power is
required for the radio, which is received by connecting a special adapter to the streetlight. No special wiring is required.
These radios are placed about every quarter to a half mile
and take only about 5 minutes each to install. Using 162 frequency-hopping channels in a random pattern accommodates many users at the same time, along with providing a
high degree of security.
Distributed among the radios are APs, which are used to
route the wireless packets on to the wired backbone.
Gathering and converting the packets so that they can be
transmitted to the wired backbone is accomplished via a T1based Frame Relay connection. The packets can then be sent
to another AP, the Internet, or the appropriate service
provider. If the packet is sent to another WAP, it is being
used as an alternate route through the mesh. The number of
paths a packet can take through the network enhances
speed throughput, since network blockage is not as frequent
and many possible repeaters exist for the packet.
The Ricochet modem weighs only 8 ounces and thus is
very portable. It can be plugged into the serial port of a computer and can be connected to online services and networks
just like a standard phone modem. The modem works with
most communications software, as well as with Intel-based
and Macintosh hardware platforms and operating systems.
Ricochet’s wired backbone is based on standard Internet
Protocol (IP) technology, routing data via a metropolitan service area. If a data packet has to move across the country,
Ricochet’s NIF system is used. The NIF functions as a router,
collecting packets from the WAPs and using leased lines to
connect with NIFs situated in the different metropolitan
areas. A name server is part of the Ricochet network backbone, providing security by validating all connection requests.
Metricom had been testing a new wireless data technology
that would have provided data rates equal to that provided
by wired ISDN 128-kbps service. This technology, called
Ricochet II, uses two bands of unlicensed spectrum: the 900MHz band and the 2.4-GHz band. The new network is compatible with the company’s existing Ricochet network and
modems. After investing $1.3 billion in infrastructure,
Metricom declared bankruptcy and discontinued operations
in August 2001. Under new management, the company is in
the process of reactivating the existing network and expanding Ricochet to areas where high-speed broadband access is
currently unavailable.
The outlook for Ricochet is unclear. Newer, cheaper Wi-Fi
networks are being set up that greatly surpasses the speed
of Ricochet. In fact, a new type of wireless Internet service
provider (WISP) has emerged, such as Boingo Wireless,
which uses the 2.4-GHz frequency band to offer data rates of
up to 11 Mbps in public places.
Fixed Wireless Access As an alternative to traditional wire-
based local telephone service, fixed wireless access technology provides a wireless link to the Public Switched Telephone
Network (PSTN). Unlike cellular technologies, however,
which provide services to mobile users, fixed wireless services require a rooftop antenna to an office building or home
that has a line of sight with a service provider’s hub antenna.
Fixed wireless access systems come in two varieties: narrowband and broadband. A narrowband fixed wireless access
service can provide bandwidth up to 128 kbps, which can support one voice conversation and a data session such as Internet
access or fax transmission. A broadband fixed wireless access
service can provide bandwidth in the multimegabit-per-second
range, which is enough to support telephone calls, television
programming, and broadband Internet access.
A narrowband fixed wireless service requires a wireless
access unit that is installed on the exterior of a home or business to allow customers to originate and receive calls with no
change to their existing analog telephones. Voice and data
calls are transmitted from the transceiver at the customer’s
location to the base station equipment, which relays the call
through carrier’s existing network facilities to the appropriate destination. No investment in special phones or facsimile machines is required; customers use all their existing
Narrowband fixed wireless systems use the licensed 3.5GHz radio band with 100-MHz spacing between uplink and
downlink frequencies. Subscribers receive network access
over a radio link within a range of 200 meters (600 feet) to
40 kilometers (25 miles) of the carrier’s hub antenna. About
2000 subscribers can be supported per cell site.
Broadband fixed wireless access systems are based on
microwave technology. Multichannel Multipoint Distribution
Service (MMDS) operates in the licensed 2- to 3-GHz frequency range, while Local Multipoint Distribution Service
(LMDS) operates in the licensed 28- to 31-GHz frequency
range. Both services are used by Competitive Local exchange
Carriers (CLECs) primarily to offer broadband Internet
access. These technologies are used to bring data traffic to the
fiberoptic networks of Interexchange Carriers (IXCs) and
nationwide CLECs, bypassing the local loops of the Incumbent
Local Exchange Carriers (ILECs).
Fixed wireless access technology originated out of the
need to contain carriers’ operating costs in rural areas,
where pole and cable installation and maintenance are more
expensive than in urban and suburban areas. However,
wireless access technology also can be used in urban areas to
bypass the local exchange carrier for long-distance calls.
Since the IXC or CLEC avoids having to pay the ILEC’s local
loop interconnection charges, the savings can be passed back
to the customer. This arrangement is also referred to as a
“wireless local loop.”
Satellite Services Satellites are another solution for the
rapidly growing demand to transmit Internet and other networking traffic because they offer reliable connections to virtually anywhere in the world.
CyberStar, for example, offers a portfolio of business services, including a global broadband IP multicasting service
that allows business users to send high-bandwidth voice,
video, and data files to branch offices. By integrating IP,
applications, video and audio streaming, IP multicast,
Webcasting, and high-speed delivery onto an independent,
satellite-based platform, CyberStar gives the IT manager a
scalable broadband network.
The satellite service enhances, not replaces, existing
enterprise communications infrastructures. The CyberStar
system is intended as an overlay that fits with whatever
companies are currently running. They can keep missioncritical applications on the current network and run dataintensive and media-rich applications over a reliable and
cost-efficient satellite network.
Customers pay for the bandwidth they use rather than
signing up for a flat-rate service. Pricing is based on the
amount of traffic that is sent each month and the number of
sites that are receiving that traffic. Customers are charged
initial installation costs per site, which includes antennas,
satellite receiver cards, and service activation fees.
Other satellite service providers also support Internet
traffic. For homes and businesses, Hughes Network Systems
(HNS) has given has been offering its one-way DirecPC
Internet access service for several years as well as a newer
one- and two-way broadband service, called DirecWAY,
which offers 400 kbps.
In the near future, low-earth-orbit (LEO) satellites such
as Teledesic will provide Internet access and support other
broadband applications with bandwidth on demand ranging
from 64 kbps to multimegabit-per-second speeds.
Service Caveats
The biggest and most obvious concern to those interested in
wireless technology is that it is more expensive than its
wired counterpart and requires an investment in special
equipment. As portability becomes more of a factor with
regard to Internet access, corporations will become more
willing to pay the higher cost of wireless technology. As history has shown, once prices drop due to corporate participation, consumers also will be able to reap the benefits of
wireless technology.
Another concern is how network managers are going to
integrate the wireless and wired worlds. This involves not
only two skill sets, but also two network management systems and two separate application development paths.
Nevertheless, wireless technology is becoming more
accepted because it can now be economically integrated
with wired networks. This can be done with wireless LAN
access points that are connected to the hub or switch with
Category 5 cable.
Performance is another issue that needs to be improved in
wireless Internet access, particularly for real-time applications. The perception is that a wireless connection should
have the same throughput and latency as a wired connection, but this is usually not possible. This tends to give the
notion that there is not a reasonable response time for interactive applications with wireless connections. While good
response time can be had with fixed wireless systems that
use MMDS and LMDS, these technologies have other issues
that bear consideration, such as limited distance and a lineof-sight requirement. These technologies also falter during
heavy rain, dense fog, and dust storms. While the service is
out periodically, wired links for backup may be required.
As noted, there are some wireless Internet access
providers that are starting to use the 2.4-GHz ISM (industrial, scientific, medical) frequency band to offer commercial
Wi-Fi services. But this is unlicensed spectrum, which
means that there is no guarantee against interference.
MMDS and LMDS, on the other hand, are services provided
over licensed spectrum. Since the FCC controls the use of
this spectrum, business users can expect interference-free
wireless connections for Internet access.
There are a variety of technologies available for wireless
Internet access. Although wide-scale deployment of wireless
Internet access services is still somewhere in the future, the
long-term prospects for those services may be brighter than
ever, due in large part to the number of carriers getting
involved with the various technologies and the increasing
investments being made toward further development. In
many parts of the United States, there is the growing realization that obtaining broadband Internet access through
cable and DSL will not be available anytime soon, if ever.
Wireless technologies have an important role to play on filling this niche.
See also
Cellular Data Communications
Direct Broadcast Satellite
Fixed Wireless Access
Local Multipoint Distribution Service
Multichannel Multipoint Distribution Service
Wireless Fidelity
Wireless Internet Service Providers
Wireless Local Loops
Wireless Internet service providers (WISPs) use Wi-Fi technology to offer access to the Internet at speeds of up to 11
Mbps when users are in range of an antenna. Based on the
IEEE 802.11b Standard, Wi-Fi technology is used by WISPs
to provide wireless Internet access at airports, hotels, convention centers, coffee shops, and other public places. Users
download free software from the WISP’s Web page and use it
to find an available signal (Figure W-3). On powering up a
notebook computer equipped with a Wi-Fi-compatible IEEE
802.11b card, the software searches all available networks
and establishes a wireless connection within seconds.
Service Plans
There are usually several service plans to chose from,
according to the number of days the user expects to be
10-day connect package A package of 10 connect days a
month, which includes unlimited access in a WISP’s service location for up to 24 hours. The user can even disconnect and reconnect within each 24-hour period from the
same location with no additional charge. Each additional
connect day is charged separately.
Figure W-3 Free software from wireless Internet service providers
(WISPs) such as Boingo Wireless lets users know when they are in range of
a high-speed wireless signal so that they can make a connection.
Unlimited usage Unlimited usage allows the user to stay
connected to the wireless network all day every day for a
fixed monthly charge.
Pay-as-you-go For users who are not sure how much they
will use the service, they can sign up for the service and
pay a daily charge instead of a monthly fee. A connect day
includes unlimited access in a WISP’s service location for
up to 24-hours. The user can disconnect and reconnect
within each 24-hour period from the same location with
no additional charge.
In addition to being able to connect to hundreds of hot spot
locations, a monthly service plan also may include
Wi-Fi “sniffer” software that checks the airwaves for
available wireless networks.
Location directory to find service locations.
Web-based account management, allowing the user to
manage his or her own account. Online and 800 number
customer support is available.
Save and manage security keys and network settings.
Built-in personal virtual private network (VPN) to ensure
secure connections to corporate networks.
Wi-Fi services are also offered by traditional ISPs such as
Earthlink, giving customers another way to access their services while at public places where they can use the precious
little time they have catching up on e-mail or connecting to
the Internet.
Some cellular service providers are offering wireless data
access via an integrated GPRS/EDGE/IEEE 802.11b service
offering. By combining the benefits of their existing 2.5/3G
and Wi-Fi networks, they expect to give customers what they
want most from wireless data services: ubiquitous coverage
and high speed. Customers will have seamless service
between the two wireless networks via a combo PC card for
notebook computers that provides access to both GPRS/EDGE
and IEEE 802.11b networks, giving them the ability to move
between the two environments without having to change
cards. The existing GPRS and upcoming EDGE networks provide wide area coverage for applications where customers
need constant access to such applications as e-mail and calendar, whereas Wi-Fi networks available in convenient public
locations allow them to spend time accessing larger data files
and multimedia messages or browse the Web.
See also
Enhanced Data Rates for Global Evolution
General Packet Radio Service
Wireless Fidelity
Corporations are making greater use of wireless technologies for extending the reach of LANs where a wired infrastructure is absent, impractical, or too costly to install.
Wireless bridges and routers can extend data communications between buildings in a campus environment or
between buildings in a metropolitan area. A variety of technologies may be used for extending the reach of LANs to
remote locations, including microwave, laser, and spread
spectrum. All rely on directional antennas at each end and a
clear line of site between locations.
Wireless Bridges
Short-haul microwave bridges, for example, provide an economical alternative to leased lines or underground cabling.
Because they operate over very short distances—less than a
mile—and are less crowded, they are less stringently regulated and have the additional advantage of not requiring an
FCC license.
The range of a bridge is determined by the type of directional antenna. A four-element antenna, for example, provides a wireless connection of up to 1 mile. A ten-element
antenna provides a wireless connection of up to 3 miles.
Directional antennas require a clear line of sight. To
ensure accurate alignment of the directional antennas at
each end, menu-driven diagnostic software is used. Once the
antennas are aligned and the system ID and channel are
selected with the aid of configuration software, the system is
operational. Front-panel light-emitting diodes (LEDs) provide a visual indication of link status and traffic activity. The
bridge unit has a diagnostic port, allowing performance
monitoring and troubleshooting through a locally attached
terminal or remote computer connected via modem.
Because they are fully compatible with the IEEE 802.3
Ethernet Standard, microwave bridges support all Ethernet
functionality and applications without the need for any special software or network configuration changes. For Ethernet
connections, the interface between the microwave equipment
and the network is virtually identical to that between the
LAN and any cable medium, where retiming devices and
transceivers at each end of the cable combine to extend the
Ethernet cable segments. Typically, microwave bridges support all Ethernet media types via AUI connectors for thick
Ethernet (10Base5), 10Base2 connectors for thin Ethernet,
and twisted-pair connectors for 10BaseT Ethernet. These connections allow microwave bridges to function as an access
point to wired LANs.
Like conventional Ethernet bridges, microwave bridges
perform packet forwarding and filtering to reduce the
amount of traffic over the wireless segment. The microwave
bridges contain Ethernet address filter tables that help to
reduce the level of traffic through the system by passing only
the Ethernet packets bound for an inter- or intrabuilding
destination over the wireless link. Since the bridges are
“self-learning,” the filter tables are automatically filled with
Ethernet addresses as the bridge learns which devices reside
on its side of the link. In this way, Ethernet packets not destined for a remote address remain local. The table is dynamically updated to account for equipment added or deleted
from the network. The size of the filter table can be 1000
entries or more depending on vendor.
With additional hardware, microwave bridges have the
added advantage of pulling double duty as a backup to local
T1/E1 facilities. When a facility degrades to a preestablished
error-rate threshold or is knocked out of service entirely, the
traffic can be switched over to a wireless link to avoid loss of
data. When line quality improves or the facility is restored to
service, the traffic is switched from the wireless link to the
wireline link.
Wireless Routers
Wireless remote access routers scale wireless connect geographically disbursed LANs by creating a wireless wide area
network (WAN) over which network traffic is routed at distances of 30 miles or more using microwave, laser, or spreadspectrum technology.
Applications of wireless routers include remote-site LAN
connectivity and network service distribution. Organizations
with remote offices such as banks, health care entities, government agencies, schools, and other service organizations
can connect their distributed computing resources with wireless routers. Industrial and manufacturing companies can
reliably and cost-effectively connect factories, warehouses,
and research facilities. Network service providers can distribute Internet, Very Small Aperture Terminal (VSAT), and
other network services to their customers. Performance is
comparable to commonly used wired WAN connections,
approaching T1 speeds with a 1.3-Mbps data rate.
Unlike wireless bridges, which simply connect LAN segments into a single logical network, wireless routers function
at the network layer with IP/IPX routing, permitting the network designer to build large, high-performance, manageable
networks. Wireless routers are capable of supporting star,
mesh, and point-to-point topologies that are implemented
with efficient Media Access Control (MAC) protocols. These
topologies can even be combined in an internetwork.
A polled protocol (star topology) provides efficient shared
access to the channel even under heavy loading (Figure W-4).
In the star topology, remote stations interconnect with the
central base station and with other remote stations through
the base station. Only one location needs line of site to the
remotes. Networks and workstations at each location tie into
a common internetwork. The maximum range between the
central base station and remote stations is approximately 15
For small-scale networks, a CSMA/CA protocol supports a mesh topology (Figure W-5). In the mesh topology,
Base Station
Figure W-4 Star topology of a router-based wireless WAN.
each site must be line of sight to every other. The
CSMA/CA protocol ensures efficient sharing of the radio
channel. The range with omnidirectional antennas is up
to 3.5 miles.
The point-to-point topology is useful where there are only
a few sites (Figure W-6). A router also can function as a
repeater link between sites. The single-hop node-to-node
range is up to 30 miles depending on such factors as terrain
and antennas, with a multiple hop range extending on the
order of a hundred miles. Clusters of nodes also can be connected using a point-to-point protocol when building largescale internetworks.
Interconnecting LANs with bridges and routers that use
wireless technologies is an economical alternative to leased
lines and carrier-provided services. Installation, setup, and
maintenance are fairly easy with the graphical management
tools provided by vendors.
Base Station
Figure W-5 Mesh topology of a router-based wireless WAN.
Figure W-6
A point-to-point topology of a router-based wireless WAN.
See also
Access Points
Wireless Management Tools
For many businesses today, mobile staff require immediate
access to up-to-date company information without having to
physically plug into a LAN to access the corporate intranet.
The advantages of a wireless connection are obvious: Newly
gathered information can be entered directly into the corporate information system, and in the opposite direction, the
most current information, such as product inventory, documentation, and pricing, can be retrieved immediately from
the corporate information system—regardless of the
employee’s location in a building or campus, which may
change continuously throughout the day.
An intranet is a private, secure version of the public
Internet that enables employees to access corporate databases, applications, and services over a TCP/IP network
through a Web browser. These resources reside on local or
remote servers that can be accessed when users log onto the
corporate network with their user name and password.
After the authentication process, users click the Web
browser icon displayed on the desktop, which opens the
home page of the intranet. From there they can go to department Web pages to obtain specific information, access a
directory to find the address of another employee, go to the
order entry system to add a customer order, check the inventory database for product availability, or launch a query to
the decision support system (DSS) that returns a breakdown of sales by region.
Virtual Private Networks
Using a portable wireless device, such as a laptop or PDA
equipped with a Web browser, gives employees instant
access to resources on the corporate intranet to do their job,
including messaging applications and productivity tools. For
remote users on the move, connectivity to the corporate
intranet can be accomplished through a commercial wireless
service that provides a means of accessing a company’s VPN
gateway, where authentication and encryption are applied to
ensure secure wireless access to intranet resources.
WAP Portals
For employees in the field, such as salespeople and maintenance crews, service providers offer wireless connectivity to
corporate VPN gateways that are cabled to a LAN that provides intranet access. But because of bandwidth constraints on
wireless WANs, data reduction techniques must be used to
facilitate information retrieval from the intranet. Overcoming
this throughput limitation can be accomplished by formatting
selected intranet content in an abbreviated form using the
Wireless Markup Language (WML), which can be accessed
even by such memory-constrained devices as PDAs and
Internet-enabled cell phones. The WML-formated content can
be accessed via the company’s Wireless Application Protocol
(WAP) portal.
By installing IEEE 802.11b (Wi-Fi) wireless access points
throughout the building and equipping laptop computers
with wireless network cards, companies can provide employees with wireless connectivity to the LAN at speeds of up to
11 Mbps over the unlicensed 2.4-GHz frequency band. The
laptops communicate wirelessly with the access point, which
is wired to the LAN hub with Category 5 cable. Once employees turn on their laptops, log onto the network, and pass
authentication, they can do anything their colleagues can do
with their wired desktop computers, including access the
intranet with a Web browser.
Another way to access the corporate intranet is via a
Bluetooth-enabled access point cabled to the LAN. Like WiFi, Bluetooth operates in the 2.4-GHz band but at the comparatively slow rate of 30 to 400 kbps across a range of only
30 feet. Bluetooth supports “piconets” that link laptops,
PDAs, mobile phones, and other devices on an as-needed
basis. It improves on infrared in that it does not require a
line of sight between the devices and has greater range than
infrared’s 3 to 10 feet.
While Bluetooth does not have the power and range of a
full-fledged LAN, its master-slave architecture does permit
the devices to face different piconets, in effect, extending the
range of the signals beyond 30 feet.
Like Wi-Fi, Bluetooth uses spread-spectrum technology,
but since it is a frequency hopper, there is little chance that
2.4-GHz Wi-Fi devices will interfere with Bluetooth. The
Bluetooth standard specifies a very fast frequency hop
rate—1600 times a second among 79 frequencies—so it will
be the first to sense problems and act to steer clear of interference from other 2.4-GHz devices.
Packaged Solutions
Packaged wireless intranet solutions are becoming available. Accessible through cell phones and PDAs such as
Palm’s products, these solutions lets users access their
intranets to collaborate on projects, documents, schedules,
and contacts. Users automatically receive a company Web
mail address when the system administrator provides them
with access to the corporate intranet. This allows users to
send and receive e-mail and includes functionality that
enables employees to create folders and rules, attach files,
filter e-mail, send sort messages, and import contacts from
the contact manager.
Portal vendors offer wireless services that let mobile
users have unlimited access to enterprise information portals and resources. Plumtree, for example, offers its Wireless
Device Server, an add-on to its Internet Device Server portal
package that enables wireless access to portal e-mail,
intranet databases, the Web, and other resources. Wireless
Device Server lowers the cost of wireless, enabling a corporate intranet by automatically detecting devices and presenting content in the appropriate WML or HTML format.
This dispenses with the need for a company to maintain separate sites for different devices.
For building intranet content intended specifically for
wireless access, companies can even turn to their database vendor. Oracle, for example, offers a wireless edition
of its Oracle 9i Application Server that provides tools for
creating wireless Internet/intranet content, services, and
As wireless technologies and services become more ubiquitous, vendors are addressing mobile users’ needs for
products that allow them to access resources on their company’s intranet. Among other things, these products adapt
Web-based applications to handheld devices, manage wireless connectivity, and deliver end-to-end security.
See also
Access Points
Wireless Fidelity
Wireless Internets
For a long time, the term wireless IP was interchangeable
with Cellular Digital Packet Data (CDPD), which supports
data over analog cellular networks at 19.2 kbps. As cellular
technologies progressed, however, describing wireless IP
merely as CDPD is wholly inadequate. Today, wireless IP
refers to a new class of wireless data platform that enables
wireless carriers for the first time to offer premium-pay,
business-quality IP services such as mobile VPNs, enhanced
security, location-based services in General Packet Radio
Service (GPRS)/Enhanced Data for Global Evolution
(EDGE), Universal Mobile Telecommunication System
(UMTS) core networks, and Code Division Multiple Access
(CDMA) 3G networks.
Wireless IP switches enable mobile operators to bring the
service richness of data services to the mobile environment,
offering a whole new class of mobile data services that
promise to increase mobile worker productivity. These
switches also seamlessly transport user traffic from the
mobile data network onto public data networks such as the
Internet. In this role, wireless IP switches perform the function of the Packet Data Serving Node/Home Agent
(PDSN/HA) that supports CDMA 2000 wireless networks
and a Gateway GPRS Support Node (GGSN), which supports GPRS and UMTS.
The tunnel switching capability of these new switches
supports mobile VPNs in both GPRS and CDMA 3G environments. Once traffic is offered to the network from a customer location, the wireless IP switch can mediate between
the different tunnel types and decide whether or not to convert them into other tunnel types and provide access to private networks or terminate the tunnel and provide plain
Internet access.
Advanced IP address management is available for mobile
customers who want to access the private network from wireless carrier radio access network. The wireless IP switch uses
network address translation (NAT) and port address translation (PAT) to switch that private address to a public address.
Under the administrative control of the service provider, a
customer is allowed access to certain actions (i.e., monitor,
configure, change, create, etc.) to customize its services.
Wireless IP switches offer compression support, which is
essential to mobile VPNs and Point-to-Point Protocol (PPP)
performance because bandwidth is usually limited.
Compression reduces traffic volume, which helps boost
access performance while reducing packet fragmentation,
thus decreasing delay time.
To ensure that priority applications get the treatment
they deserve, wireless IP switches provide class of service
(CoS) and quality of service (QoS) on IP networks, as well as
Multiprotocol Label Switching (MPLS) path mapping and
differentiated services marking.
End-to-end security is important for establishing user
confidence in network-based intranets and extranets.
Wireless IP switches are capable of supporting triple-DES
(3DES) encryption for tens of thousands of flows simultaneously while maintaining full line rate throughput without
any delays.
Virtual routing is the ability to create individual
instances of routers for customers and providers. This functionality greatly simplifies the routing configuration for the
service provider because the service provider obtains access
to all these customers through a single router interface.
With the virtual router capability and the ability to interconnect virtual routers within the chassis configuration of
the wireless IP switch, a user can create very complex wireless IP core network topologies within the same platform.
Security is handled by the wireless IP switch’s policydriven stateful firewall, which provides granular firewall
policies with “follow me” characteristics. Thus, wherever a
customer accesses the network, the wireless IP switch will
gather and implement the specific policies associated with
that user. The wireless IP switch also supports other firewall
capabilities, including intrusion detection and denial of service protection.
The wireless IP switch’s element management system
(EMS) allows subscribers to select their service providers as
well as their services from a Web browser. This reduces service provider operations costs, reduces service turn-on times,
and improves end-customer satisfaction by allowing subscribers to provision their own services.
With policy-based provisioning, the wireless IP switch
delivers individualized services based on directory profiles.
This eliminates the need for tedious manual router configuration and provides single-point IP service delivery and control while decreasing the number of devices to manage and
reducing the cost of operations. Policies follow users
throughout network.
Businesses have long been skeptical of using IP for critical
and real-time applications and have been wary about the
security of IP-based networks as well, especially over wireless networks. Vendors such as Lucent and Nortel, however,
have taken all these concerns into account with their wireless IP switches. With flexible configuration options for service modules, interface cards, switch fabrics, and control
modules, today’s wireless IP switches provide a wide range
of service choices. High service availability is ensured with
redundant power supplies, switch fabrics, service modules,
and processors. Instant failover functionality is designed
into the hardware so that if a primary component fails, the
backup component takes over immediately without any
interruption of service. Interface cards support high-availability features such as port failover, rerouting, and SONET
automatic protection switching (APS). Software provides
full-service failover of virtual routers (including forwarding
tables), firewall, QoS, and VPN policies.
See also
Cellular Data Communications
Wireless links are inherently less secure than copper or fiber
media. In copper media, the wires are twisted together to
minimize the amount of signal radiation that can be picked
up by eavesdroppers. Some types of copper media used in
data centers include shielding, which prevents any signal
radiation. In fiber media, the difference in the density of the
core and surrounding cladding prevents light from radiating
away and being picked up by eavesdroppers. Of course, it is
still possible to intercept communications over copper and
fiber media, but it is much easier to do so when the communication occurs over unprotected wireless links.
The biggest threat to the security of a wireless LAN is the
failure to use any form of security in the belief that the information traversing the wireless link is not important enough
to safeguard. But leaving the wireless link unprotected can
have unintended consequences. For example, a hacker might
not be interested in intercepting a telecommuter’s communications at all but may see the wireless link as an opportunity
to access a VPN connection to the telecommuter’s corporate
network, where sensitive information is stored on application
servers and distributed databases. Some companies are diligent in this regard and do not allow telecommuters to use
wireless technologies at home, considering it a willful security breach if they do so.
With Wi-Fi systems, the first line of defense in securing a
wireless link is to enable Wired Equivalent Privacy (WEP).
This will deter the casual intruder, but experienced hackers
have been known to break into WEP-enabled systems in 15
minutes or less. Although WEP is being improved continually, additional measures must be taken to strengthen security. The Wi-Fi Alliance recommends one or more of the
Turn WEP on and manage the WEP key by changing the
default key and, subsequently, changing the WEP key
daily to weekly.
Turn windows sharing off on sensitive files and directories.
Protect access to drives and folders with passwords.
Change the default Service Set Identifier (SSID) that
comes with the product.
Use session keys if available in the product.
Use MAC address filtering if available in the product.
Use a VPN system. Although it would require a VPN
server, the VPN client is already included in many operating systems such as Windows 98 Second Edition,
Windows 2000, and Windows XP.
These steps alone, however, are not enough to completely
protect the wireless network. The SSID, for example, is a
two-edged sword. This is a plaintext identifier of no more
than 32 characters that gets attached to the header of packets sent over a wireless LAN. The SSID differentiates one
wireless LAN from another, so all access points and all
devices attempting to connect to a specific WLAN must use
the same SSID, as if it were a password. A device will not
be permitted to join a wireless LAN unless it can provide
the unique SSID. But because hacker tools can sniff the
SSID in plaintext from a packet, it does not really enhance
network security.
Encryption Enhancements
As noted, Wi-Fi systems implement an encryption scheme
known as WEP that protects data transmitted through the
air, making it difficult (but no impossible) for wireless stations that do not operate on the same encryption key to
obtain the transmitted data. The IEEE 802.11 Standard
defines the encryption key to be 64 bits in length, 40 bits of
which can be defined by the user as the selected secret key.
The other 24 bits are generated by the system and change on
each successive transmission to make sure that the actual
encryption key changes constantly. This cryptography
scheme is known as RC4.
Some vendors have added to this standard encryption
scheme the option to use longer encryption keys. For example, they may use 128-bit keys, 104 bits of which are the
user-defined secret key. The longer the key, the more time it
takes for a hacker to obtain the key using brute force methods. To prevent comprising the encryption key if the notebook’s PC card is stolen, some Wi-Fi vendors even avoid
storing the keys in the wireless PC card’s flash ROM (readonly memory).
Without the correct encryption key, a wireless client station cannot communicate with an access point and, therefore, cannot get onto the network, much less monitor the
traffic from a neighboring station.
But not even these safeguards are entirely hacker-proof.
There are now tools freely available on the Internet specifically designed for WEP key hacking, eliminating the need to
use brute-force methods. These tools exploit weaknesses in
the key-scheduling algorithm of RC4. Once the tool captures
the data traffic, the key can be derived from it.
The weakness of WEP lies in the predictability of the socalled initialization vector, which is the 24 bits of the encryption key generated by the system that changes on each
successive transmission—ostensibly to improve security.
But some values of this initialization vector can be predicted
for generating “weak keys” that can be used to gain access to
the wireless network. All IEEE 802.11–compliant wireless
networks are vulnerable to this kind of attack, since they all
implement WEP security in a similar manner.
Authentication via RADIUS
Some access points have the added capability to restrict
access to the network to those stations whose MAC address
is included in a Remote Authentication Dial-In User Service
(RADIUS) database. To enable this feature, the access points
need to be configured to communicate to the RADIUS server
each time a wireless station makes the initial contact.
To add to the availability of the service, the access points
can connect to two servers, a primary and a backup, in case
the primary is down. The network administrator builds the
database at the RADIUS server by including the MAC
addresses of all the stations that are allowed access to the
network. Stations with MAC addresses that do not appear in
this table are not granted access, and the traffic generated
by these stations will be filtered out.
To ensure the effectiveness of RADIUS, the network
administrator must make sure that all access points are configured to use the RADIUS database for MAC address
authentication. To do so, the database has to be populated
with the MAC addresses of PC cards. New cards have to be
added to the database, and cards that have been reported as
stolen or no longer in use must be removed from the database.
Key Change Administration
Regular key changes are important to maintain the integrity
of the security system. Some Wi-Fi systems allow for the use
of multiple keys in support of dynamic key rollover. Multiple
keys active at the same time can cover the period required
for all users to rotate to a new key.
To support frequent key change procedures, vendors offer
software tools that allow changing the WEP encryption keys
remotely. In other words, a network or security administrator is able to transmit a new WEP key or set of keys to client
stations and to have them active the next time the PC card
driver is loaded. The end-user will not be aware that this key
change has taken place and does not even know the exact
value of the WEP key.
To allow visitors and guests to use a network where
RADIUS-based MAC authentication and WEP encryption are
effective, local procedures can be implemented where IT staff
can loan PC cards with MAC addresses that are registered in
the RADIUS database. These adapters stay on the premises,
and a procedure is implemented to enforce the return of the
PC card by the guest/visitor to the IT staff. PC cards should be
used that do not hold the WEP key in ROM; that way, if a card
is not returned, network security is not compromised.
However, if a laptop used for wireless LAN communication is stolen, a key change must be implemented immediately. This is so because if the key is not stored in the PC
card’s ROM, then it is maintained in the registry of the operating system. In changing the keys as soon as the theft is
reported, the risk of unauthorized access to the wireless network is minimized.
Closed Systems
Wi-Fi access points have the capability to filter wireless
client stations on the network name, which is a parameter
that the wireless client needs to supply in order to attach to
a wireless network. If a wireless client station is not configured with the correct network name, this station will not be
able to attach to the access point.
However, the Wi-Fi standard does allow wireless clients
to attach to any network if no value for this parameter is
entered. This is called an “empty string,” and it is typically
used to access a public access point, such as those available
Starbucks cafés. To ensure a reasonable level of security, some
products like Agere’s ORiNOCO systems are equipped with a
so-called closed system option, which is a user-selectable
option to reject wireless stations that try to attach to the network using the empty string option. With “Closed System”
selected, wireless clients that are not configured with the correct network name cannot access the network.
To protect communications over wireless LANs requires the
use of more advanced security techniques, such as a firewall.
Firewalls can be standalone devices that are dedicated to
safeguarding the enterprise network. Similar functionality
can be added to wireless routers, in which case the security
features are programmed through the router’s operating
system. Internet appliances can have firewall capabilities as
well, such a DSL routers and cable modems. In addition,
there is client software that can be loaded into notebooks
and desktop computers that gives users personal control
over security (Figure W-7).
A packet-filtering firewall examines all the packets
passed to it and then forwards them or drops them based on
predefined rules (Figure W-8). The network administrator
can control how packet filtering is performed, permitting or
denying connections using criteria based on the source and
destination host or network and the type of network service.
By itself, WEP is offers no guarantee of security against
hackers. A combination of steps must be taken to create the
highest degree of security for a wireless network, including
the proper selection of equipment, the implementation of
Figure W-7 Firewall software for individual computers allows
users to control their own level of security. Shown is ZoneAlarm from
Zone Labs, which is available free at the company’s Web site for personal use.
RADIUS, and the use of firewalls. With the right security
provisions in place, wireless systems will have equal or more
privacy than can be expected from existing wired stations. It
is essential, however, that proper operational procedures be
defined to implement and activate the security options and
that there be corporate enforcement of these procedures.
Packet-filter Gateways
Packet Received
Next Rule
Data Link
Pass the
Drop the Packet
Figure W-8 Operation of a packet-filtering firewall: (1) inbound/outbound
packets are examined for compliance with company-defined security rules;
(2) packets found to be in compliance are allowed to pass into the network;
(3) packets that are not in compliance are dropped.
See also
Wired Equivalent Privacy
Wireless Fidelity
A wireless local area network (WLAN) is a data communications system implemented as an extension—or as an alternative—to a wired LAN. Using a variety of technologies
including narrowband radio, spread spectrum, and infrared,
wireless LANs transmit and receive data through the air,
minimizing the need for wired connections.
Wireless LANs have become popular in a number of vertical
markets, including health care, retail, manufacturing, and
warehousing. These industries have profited from the productivity gains of using handheld terminals and notebook computers to transmit real-time information to centralized hosts
for processing. Wireless LANs allow users to go where wires
cannot always go. Specific uses of wireless LANs include
Hospital staff members can become more productive when
using handheld or notebook computers with a wireless LAN
capability to deliver patient information, regardless of their
Consulting or accounting audit teams, small workgroups, or
temporary office staff can use wireless LANs to quickly set
up for ad-hoc projects and become immediately productive.
Network managers in dynamic enterprise environments
can minimize the overhead cost of moves, adds, and
changes with wireless LANs, since the need to install or
extend wiring is eliminated.
Warehouse workers can use wireless LANs to exchange
information with central databases, thereby increasing
Branch office workers can minimize setup requirements
by installing preconfigured wireless LANs.
Wireless LANs are an alternative to cabling multiple computers in the home.
While the initial investment required for wireless LAN
hardware can be higher than the cost of conventional LAN
hardware, overall installation expenses and life-cycle costs
can be significantly lower. Long-term cost savings are greatest in dynamic environments requiring frequent moves,
adds, and changes. Wireless LANs can be configured in a
variety of topologies to meet the needs of specific applications and installations. They can grow by adding access
points and extension points to accommodate virtually any
number of users.
There are several technologies to choose from when selecting
a wireless LAN solution, each with advantages and limitations. Most wireless LANs use spread spectrum, a wideband
radio frequency technique developed by the military for use
in reliable, secure, mission-critical communications systems. To achieve these advantages, the signal is spread out
over the available bandwidth and resembles background
noise that is virtually immune from interception.
There are two types of spread-spectrum radio: frequency
hopping and direct sequence. Frequency-hopping spread
spectrum (FHSS) uses a narrowband carrier that changes
frequency in a pattern known only to the transmitter and
receiver. Properly synchronized, the net effect is to maintain
a single logical channel. To an unintended receiver, FHSS
appears to be short-duration impulse noise.
Direct-sequence spread spectrum (DSSS) generates a
redundant bit pattern for each bit to be transmitted and
requires more bandwidth for implementation. This bit pattern, called a “chip” (or “chipping code”), is used by the
receiver to recover the original signal. Even if one or more
bits in the chip are damaged during transmission, statistical
techniques embedded in the radio can recover the original
data without the need for retransmission. To an unintended
receiver, DSSS appears as low-power wideband noise.
Another technology used for wireless LANs is infrared (IR),
which uses very high frequencies that are just below visible
light in the electromagnetic spectrum. Like light, IR cannot
penetrate opaque objects—to reach the target system, the
waves carrying data are sent in either directed (line-of-sight)
or diffuse (reflected) fashion. Inexpensive directed systems
provide very limited range of not more than 3 feet and typically
are used for personal area networks but occasionally are used
in specific wireless LAN applications. High-performance
directed IR is impractical for mobile users and therefore is
used only to implement fixed subnetworks. Diffuse IR wireless
LAN systems do not require line-of-sight transmission, but
cells are limited to individual rooms. As with spread-spectrum
LANs, IR LANs can be extended by connecting the wireless
access points to a conventional wired LAN.
As noted, wireless LANs use electromagnetic waves (radio or
infrared) to communicate information from one point to
another without relying on a wired connection. Radio waves
are often referred to as “radio carriers” because they simply
perform the function of delivering energy to a remote
receiver. The data being transmitted are superimposed on
the radio carrier so that they can be extracted accurately at
the receiving end. This process is generally referred to as
“carrier modulation.” Once data are modulated onto the
radio carrier, the radio signal occupies more than a single
frequency, since the frequency or bit rate of the modulating
information adds to the carrier.
Multiple radio carriers can exist in the same space at the
same time without interfering with each other if the radio
waves are transmitted on different frequencies. To extract
data, a radio receiver tunes into one radio frequency while
rejecting all other frequencies.
In a typical wireless LAN configuration, a transmitter/
receiver (transceiver) device, called an “access point,” connects to the wired network from a fixed location using standard cabling. At a minimum, the access point receives, buffers
and transmits data between the wireless LAN and the wired
network infrastructure. A single access point can support a
small group of users and can function within a range of less
than 100 to several hundred feet. The access point (or the
antenna attached to the access point) is usually mounted high
but may be mounted essentially anywhere that is practical as
long as the desired radio coverage is obtained.
Users access the wireless LAN through wireless LAN
adapters. These adapters provide an interface between the
client network operating system (NOS) and the airwaves via
an antenna. The nature of the wireless connection is transparent to the NOS.
Wireless LANs can be simple or complex. The simplest
configuration consists of two PCs equipped with wireless
adapter cards, which form a network whenever they are
within range of one another (Figure W-9). This peer-topeer network requires no administration. In this case,
each client would only have access to the resources of the
other client and not to a central server.
Installing an access point can extend the operating range
of the wireless network, effectively doubling the range at
which the devices can communicate. Since the access point
is connected to the wired network, each client would have
access to the server’s resources as well as to other clients
(Figure W-10). Each access point can support many clients—
the specific number depends on the nature of the transmissions involved. In some cases, a single access point can
support up to 50 clients.
Depending on the manufacturer and the frequency band
used in its products, access points have an operating range of
about 500 feet indoors and 1000 feet outdoors. In a very large
Figure W-9 A wireless peer-to-peer network created between two notebook computers equipped with external wireless adapters.
Access Point
Switch or Hub
Figure W-10
A wireless client connected to the wired LAN via an access
facility such as a warehouse or on a college campus, it probably will be necessary to install more than one access point
(Figure W-11). Access point positioning is determined by a site
survey. The goal is to blanket the coverage area with overlapping coverage cells so that clients can roam throughout the
area without ever losing network contact. Access points hand
the client off from one to another in a way that is invisible to
the client, ensuring uninterrupted connectivity.
To solve particular problems of topology, the network
designer might choose to use extension points (EPs) to augment
the network of access points (Figure W-12). These devices look
and function like access points (APs), but they are not tethered
to the wired network, as are APs. EPs function as repeaters by
boosting signal strength to extend the range of the network by
relaying signals from a client to an AP or another EP.
Another component of wireless LANs is the directional
antenna. If a wireless LAN in one building must be connected
to a wireless LAN in another building a mile away, one solution might be to install a directional antenna on the two
buildings—each antenna targeting the other and connected
to its own wired network via an access point (Figure W-13).
Switch or Hub
Figure W-11 Multiple access points extend wireless coverage and enable
Switch or Hub
Figure W-12 Use of an extension point to extend the reach of a wireless
Switch or
Switch or
Wireless Link
Directional Antenna
Building A
Building B
Figure W-13 A directional antenna can be used to interconnect wireless
LANs in different buildings.
Wireless LAN Standards
There are several wireless LAN standards, each suited for a
particular environment: IEEE 802.11a and 802.11b, HomeRF,
and Bluetooth.
For the residential and office environments, the IEEE
802.11a offers a data transfer rate of up to 11 Mbps at a range
of up to 300 feet from the base station. It operates in the 2.4GHz band and transmits via the direct-sequence spread-spectrum method. Multiple base stations can be linked to increase
that distance as needed, with support for multiple clients per
access point. IEEE 802.11a specifies the 5-GHz frequency
band, offering a data transfer rate of up to 54 Mbps.
The HomeRF 2.0 Standard draws from IEEE 802.11b and
Digital Enhanced Cordless Telecommunication (DECT), a popular standard for portable phones worldwide. Operating in the
2.4-GHz band, HomeRF was designed from the ground up for
the home market for both voice and data. It offers throughput
rates comparable to IEEE 802.11b and supports the same
kinds of terminal devices in both point-to-point and multipoint
configurations. HomeRF transmits at up to 10 Mbps over a
range of about 150 feet from the base station, which makes it
suitable for the average home. HomeRF transmits using
spread-spectrum frequency hopping; that is, it hops around
constantly within its prescribed bandwidth. When it encounters interference, like a microwave oven or an adjacent wireless LAN, it adapts by moving to another frequency.
The key advantage that HomeRF has over IEEE 802.11b
in the home environment is its superior ability to adapt to
interference from devices like portable phones and
microwaves. As a frequency hopper, it coexists well with
other frequency-hopping devices that proliferate in the
home. Another advantage of HomeRF is that it continuously
reserves a chunk of bandwidth via “isochronous channels”
for voice services. Speech quality is high; there is no clipping
while the protocol deals with interference.
The IEEE 802.11b Standard does not include frequency
hopping. In response to interference, IEEE 802.11b simply
retransmits or waits for the higher-level TCP/IP protocol to
sort out signal from noise. This works well for data but can
result in voice transmissions sounding choppy. Voice and data
are treated the same way, converting voice into data packets
but offering no priority to voice. This results in unacceptable
voice quality. Another problem with IEEE 802.11b is that its
Wired Equivalent Protocol (WEP) encryption, designed to
safeguard privacy, has had problems living up to its claim.
Bluetooth also operates in the 2.4-GHz band but was not
created originally to support wireless LANs; it was intended as
a replacement for cable between desktop computers, peripherals, and handheld devices. Operating at the comparatively
slow rate of 30 to 400 kbps across a range of only 30 feet,
Bluetooth supports “piconets” that link laptops, PDAs, mobile
phones, and other portable devices on an as-needed basis. It
improves on infrared in that it does not require a line of sight
between the devices and has greater range than infrared’s 3 to
10 feet. Bluetooth also supports voice channels.
While Bluetooth does not have the power and range of a
full-fledged LAN, its master-slave architecture does permit
the devices to face different piconets, in effect, extending the
range of the signals beyond 30 feet. Like HomeRF, Bluetooth
is a frequency hopper, so devices that use these two standards
can coexist by hopping out of each other’s way. Bluetooth has
the faster hop rate, so it will be the first to sense problems and
act to steer clear of interference from HomeRF devices.
The three standards each have particular strengths that
make them ideal for certain situations, as well as specific
shortcomings that render them inadequate for use beyond
their intended purpose:
While suited for the office environment, IEEE 802.11b is
not designed to provide adequate interference adaptation
and voice quality for the home. Data collisions force
packet retransmissions, which is fine for file transfers
and print jobs but not for voice or multimedia that cannot
tolerate the resulting delay.
HomeRF delivers an adequate range for the home market
but not for many small businesses. It is better suited than
IEEE 802.11b for streaming multimedia and telephony,
applications that may become more important for home
users as convergence devices become popular.
Bluetooth does not provide the bandwidth and range
required for wireless LAN applications but instead is
suited for desktop cable replacement and ad-hoc networking for both voice and data within the narrow 30-foot
range of a piconet.
Wireless LAN technology is continually improving. The
IEEE 802.11b Standard developers seek to improve encryption (IEEE 802.11i) and make the standard more multimedia
friendly (IEEE 802.11e). Dozens of vendors are shipping
IEEE 802.11b products, and the standard’s proliferation in
corporate and public environments is a distinct advantage.
An office worker who already has an IEEE 802.11b–equipped
notebook will not likely want to invest in a different network
for the home.
Furthermore, the multimedia and telephony applications
HomeRF advocates tout have not yet arrived to make the
technology a compelling choice. Although HomeRF currently
beats IEEE 802.11b in terms of security, this is not a big issue
in the home. For these and other reasons, industry analysts
predict that IEEE 802.11b will soon overtake HomeRF in the
consumer marketplace, especially since the price difference
between the two has just about reached parity.
Once expensive, slow, and proprietary, wireless LAN products are now reasonably fast, standardized, and priced for
mainstream business and consumer use. Wireless LAN configurations range from simple peer-to-peer topologies to
complex networks offering distributed data connectivity and
roaming. To solve problems of vendor interoperability, the
Wi-Fi Alliance offers a certification program that tests vendor-submitted products. Those that pass WECA’s battery of
tests receive the right to bear the Wireless Fidelity (Wi-Fi)
logo of interoperability.
See also
Digital Enhanced Cordless Telecommunication
Home RF
Infrared Networking
Spread-Spectrum Radio
Wireless Fidelity
Wireless Management Tools
A wireless local loop (WLL) is a generic term for an access
system that uses wireless links rather than conventional
copper wires to connect subscribers to the local telephone
company’s switch. Wireless local loop—also known as “fixed
wireless access” (FWA) or “simply fixed radio”—entails the
use of analog or digital radio technology to provide telephone, facsimile, and data services to business and residential subscribers.
WLL systems provide rapid deployment of basic phone
service in areas where the terrain or telecommunications
development makes installation of traditional wireline service too expensive. WLL systems can be easily integrated
into the wireline Public Switched Telephone Network
(PSTN) and usually can be deployed within a month of
equipment delivery, far more quickly than traditional wireline installations, which can take several months for initial
deployment and years to grow capacity to meet the continually growing demand for communication services.
WLL solutions include analog systems for medium- to
low-density and rural applications. For high-density, highgrowth urban and suburban locations, there are WLL solutions based on Code Division Multiple Access (CDMA). Time
Division Multiple Access (TDMA) and Global System for
Mobile (GSM) telecommunications) systems are also offered.
In addition to being able to provide higher voice quality than
analog systems, digital WLL systems are able to support
higher-speed fax and data services.
WLL technology is also generally compatible with existing operations support systems (OSS), as well as existing
transmission and distribution systems. WLL systems are
scalable, enabling operators to leverage their previous infrastructure investments as the system grows.
WLL subscribers receive phone service through a radio
unit linked to the PSTN via a local base station. The radio
unit consists of a transceiver, power supply, and antenna. It
operates off ac or dc power and may be mounted indoors or
outdoors, and it usually includes battery backup for use during line power outages. On the customer side, the radio unit
connects to the premises wiring, enabling the customer to
use existing phones, modems, fax machines, and answering
devices (Figure W-14).
The WLL subscriber has access to all the usual voice and
data features, such as caller ID, call forwarding, call waiting, three-way calling, and distinctive ringing. Some radio
units provide multiple channels, which are equivalent to
having multiple lines. The radio unit offers service operators
Customer Premises
Cell Site
Fixed Wireless Terminal
Answering Machine
Figure W-14 The fixed wireless terminal is installed at the customer location. It connects several standard terminal devices (telephone, answering
machine, fax, computer) to the nearest cell site base transceiver station (BTS).
the advantage of over-the-air programming and activation to
minimize service calls and network management costs.
The radio unit contains a coding and decoding unit that converts conventional speech into a digital format during voice
transmission and back into a nondigital format for reception.
Many TDMA-based WLL systems use the 8-kbps Enhanced
Variable Rate Coder (EVRC), a Telecommunications Industry
Association (TIA) standard (IS-127). EVRC provides benefits
to both network operators and subscribers.
For operators, the high-quality voice reproduction of the
EVRC does not sacrifice the capacity of a network or the coverage area of a cell site. An 8-kbps EVRC system, using the
same number of cell sites, provides network operators with
greater than 100 percent additional capacity than the 13kbps voice coders that are deployed in CDMA-based WLL
systems. In fact, an 8-kbps EVRC system requires at least 50
percent fewer cell sites than a comparable 13-kbps system to
provide similar coverage and in-building penetration.
For subscribers, the 8-kbps EVRC uses a state-of-the-art
background noise suppression algorithm to improve the
quality of speech in noisy environments typical of urban
streets, where there is heavy pedestrian and vehicular traffic. This also is an advantage compared with traditional
landline phone systems, which do not have equivalent noise
suppression capabilities.
Depending on vendor, the radio unit also may include
special processors to enhance call privacy on analog WLL
systems. Voice privacy is enhanced through the use of a
digital signal processor (DSP)–based speech coder, an echo
canceler, a data encryption algorithm, and an error-detection/
correction mechanism. To prevent eavesdropping, the lowbit-rate encoded speech data are encrypted using a private
key algorithm, which is randomly generated during a call.
The key is used by the DSPs at both ends of the communications link to decrypt the received signal. The use of DSPs
in the radio units of analog WLL systems also improves fax
and data transmission.
WLL Architectures
WLL systems come in several architectures: a PSTN-based
direct connect network, a Mobile Telephone Switching
Office/Mobile Switching Center (MTSO/MSC)–based network, and proprietary networks.
PSTN-Based Direct Connect
There are several key components of the PSTN direct connect network:
The PSTN-to-radio interconnect system, which provides
the concentration interface between the WLL and the
wireline network.
The system controller (SC), which provides radio channel
control functions and serves as a performance monitoring
concentration point for all cell sites.
The base transceiver station (BTS), which is the cell-site
equipment that performs the radio transmit and receive
The fixed wireless terminal (FWT), which is a fixed radio
telephone unit that interfaces to a standard telephone set,
acting as the transmitter and receiver between the telephone and the base station.
The operations and maintenance center (OMC), which is
responsible for the daily management of the radio network and provides the database and statistics for network
management and planning.
An MTSO/MSC-based network contains virtually the same
components as the PSTN direct connect network, except that
the MTSO/MSC replaces the PSTN-to-radio interconnect system. The key components of an MTSO/MSC-based network are
Mobile telephone switching office/mobile switching center
(MTSO/MSC), which performs the billing and database
functions and provides a T1/E1 interface to the PSTN.
Cell-site equipment, including the base transceiver station (BTS).
Fixed wireless terminal (FWT).
Operations and maintenance center (OMC).
For digital systems such as GSM and CDMA, the radio
control function is performed at the base station controller
(BSC) for GSM or the centralized base site controller (CBSC)
for CDMA.
In GSM systems, there is a base station system controller
(BSSC), which includes the base station controller (BSC)
and the transcoder. The BSC manages a group of BTSs, acts
as the digital processing interface between the BTSs and the
MTSO/MSC, and performs GSM-defined call processing.
In CDMA systems, there is a centralized base site controller (CBSC), which consists of the mobility manager
(MM) and the transcoder subsystems. The MM provides
both mobile and fixed call processing control and performance monitoring for all cell sites as well as subscriber data
to the switch.
As in PSTN-based networks, the FWT in MTSO/MSCbased networks is a fixed radio telephone unit that interfaces to a standard telephone set acting as the transmitter
and receiver between the telephone and the base station.
Operations and maintenance functions are performed at
the OMC. As in PSTN-based networks, the OMC in
MTSO/MSC-based networks is responsible for the day-to-day
management of the radio network and provides the database
and statistics for network management and planning.
The PSTN direct connect network is appropriate when
there is capacity on the existing local or central office switch.
In this case, the switch continues to provide the billing and
database functions, the numbering plan, and progress tones.
The MTSO/MSC architecture is appropriate for adding a
fixed subscriber capability to an already existing cellular
mobile network or for offering both fixed and mobile services
over the same network.
Proprietary Networks
While MTSO/MSC-based and PSTN direct connect networks
are implemented using existing cellular technologies, proprietary WLL solutions are designed specifically as a
replacement for wireline local loops. One of these proprietary solutions is Nortel’s Proximity I, which is used in the
United Kingdom to provide wireline-equivalent services in
the 3.5-GHz band. The TDMA-based system was designed in
conjunction with U.K. public operator Ionica, which is the
source of the I designation. The I series provides telecommunications service from any host network switch, providing toll-quality voice, data, and fax services. The system is
switch-independent and is transparent to dual-tone multifrequency (DTMF) tones and switch features.
The Proximity I system architecture consists of the following main elements:
Residential service system (RSS), which is installed at the
customer premises and provides a wireless link to the
base station.
Base station, which provides the connection between the
customer’s RSS and the PSTN.
Operations, administration, and maintenance system,
which provides such functions as radio link performance
management and billing.
Residential Service System (RSS) The RSS offers two lines,
which can be assigned for both residential and home office
use or for two customers in the same 2-kilometer area. Once
an RSS is installed, the performance of the wireless link is
virtually indistinguishable from a traditional wired link.
The wireless link is able to handle high-speed fax and data
via standard modems, as well as voice. The system supports
subscriber features such as call transfer, intercom, conference call, and call pickup.
The RSS has several components: a transceiver unit, residential junction unit (RJU), network interface unit, and
power supply. The transceiver unit consists of an integral 30-
centimeter octogonal array antenna with a radio transceiver
encased within a weatherproof enclosure. The enclosure is
mounted on the customer premises and points toward the
local base station.
The RJU goes inside the house, where it interfaces with
existing wiring and telephone equipment. The Proximity I
system supports two 32-kbps links for every house, enabling
subscribers to have a voice conversation and data connection
for fax or Internet access at the same time. At this writing,
work is under way to develop systems that can handle ISDN
speeds of 64 kbps and beyond. Further developments will
result in RSSs that can handle more lines per unit for
medium-sized businesses or apartment blocks.
The network interface unit (NIU), mounted internally or
externally, is a cable junction box that accepts connections
from customer premises wiring. The unit also provides
access for service provider diagnostics and contains lightening protection circuitry.
The power unit is usually mounted internally and connects to the local power supply (110/220 V ac). The power
unit provides the dc supply to the transceiver unit. A
rechargeable battery takes over in the event of a power failure and is capable of providing 12 hours of standby and 30
minutes of talk time.
Base Station The base station contains the radio frequency
(RF) equipment for the microwave link between the customer’s RSS and the PSTN, along with subsystems for call
signal processing, frequency reference, and network management. This connection is via radio to the RSS and by
microwave radio, optical fiber, or wireline to the local
exchange. The base station is modular and can be configured
to meet a range of subscriber densities and traffic requirements. The base station has several components: transceiver
microwave unit, cabinet, power supply, and network management module.
The base station’s dual antenna transceiver microwave unit
provides frequency conversion and amplification functions.
Each unit provides three RF channels, the frequency of which
can be set remotely. The unit can be configured for a maximum
of 18 RF channels. The antennas are available in omnidirectional or sectored configurations, depending on population
densities and geographic coverage. An omnidirectional system
can support 600 or more customers, while a trisectored
antenna can serve more than 2000 customers. Base stations in
rural areas can be sited up to 20 kilometers from a subscriber’s
The base station can be configured with either an internal or
external cabinet. The internal cabinet is for location in an
equipment room, while the external cabinet is weather-sealed
and vandal-proofed for outside locations. Both types of cabinets
house the integrated transceiver system, transmission equipment, optional power system, and batteries. A separate power
cabinet provides dc power to the base station from the local
110/220 V ac source. This cabinet may include battery backup,
with battery management capability and a power distribution
panel that provides power for technicians’ test equipment.
The network management module is the base station
polls individual RSS units to flag potential service degradation. Reports include link bit error rate (BER), signal-tonoise ratio, power supply failure, and the status of the
customer standby battery.
The connection from the base stations to the local
exchange on the PSTN is via the V5.2 open-standard interface. In addition to facilitating interconnections between
multivendor systems, this interface enables operators to
take full advantage of Proximity I’s ability to maximize spectrum utilization through allocation of finite spectrum on a
dynamic per-call basis rather than on a per-customer basis.
Concentration allows the same finite spectrum to be shared
across a much larger number of customers, producing large
savings in infrastructure, installation, and operations costs
for the network operator.
Operations, Administration and Maintenance OA&M
functions are implemented through an element manager
accessed through a field engineering terminal. In Nortel’s
Proximity I, the element manager is built around HewlettPackard’s OpenView. Communications with the network of
base stations and customer equipment is done through the
Airside Management Protocol, which is based on the OSI
Common Management Information Protocol (CMIP). The
field engineering terminal can operate in a remote operations center but is intended primarily for use by on-site
maintenance engineers who are responsible for the proper
operation of the base stations.
All the applications software in the customer premises
equipment is downloadable from the element manager. This
software provides the algorithms that convert analog voice
signals into 32-kbps digital ADPCM, which provides toll quality voice transmission. Other applications software includes
algorithms for controlling the draw of battery-delivered power
in the event of a 110/220 V ac power failure.
Via the Air Interface Protocol, the customer equipment is
able to provide the element manager with information about
its current status and performance, the most useful of which
are measurements taken during the transmission of speech.
This allows the management system to flag performance
degradation for corrective action.
Wireless local loops eliminate the need for laying cables and
hard-wired connections between the local switch and the
subscriber’s premises, resulting in faster service startup and
lower installation and maintenance costs. And because the
subscriber locations are fixed and not mobile, the initial
deployment of radio base stations need only provide coverage to areas where immediate demand for service is apparent. Once the WLL system is in place, new customers can be
added quickly and easily. Such systems support standard
analog as well as digital services and provide the capability
to support the evolution to new and enhanced services as the
needs of the market evolve.
See also
Fixed Wireless Access
Wireless Centrex
Local number portability (LNP) refers to the ability of individuals, businesses, and organizations to retain their existing
telephone number(s)—and the same quality of service—when
switching to a new local service provider. The concept applies
to cellular and other wireless services as well.
The provision of number portability is an obligation that
the Telecommunications Act of 1996 imposes on all Local
Exchange Carriers (LECs) as a means of fostering a procompetitive, deregulatory national policy framework. By
enabling customers to switch to a new service provider without forcing them to change telephone numbers, LNP permits
consumers to select a local telephone company based on service, quality, and price rather than on their desire to keep a
particular telephone number. Accordingly, all wireline carriers were required to support LNP in 1999.
However, cellular and other wireless carriers were not
required to provide telephone number portability at the
same time as wireline service providers because of additional technical and competitive burdens but were required
to do so by November 2002. But in mid-2002, the FCC
extended for 1 year the compliance deadline for wireless carriers to achieve LNP to November 2003.
The decision was prompted by a request from Verizon
Wireless to the FCC to eliminate the requirement altogether.
Much of the wireless industry supported the petition.
Carriers had argued that offering number portability would
cost them $1 billion in 2003 and that customers are not wedded to their telephone number, citing the FCC’s own statistics, which showed a 30 percent turnover rate among cellular
subscribers. Four of the five FCC commissioners denied the
petition of Verizon Wireless, voting instead to extend the
compliance deadline by another year.
Wireless LNP is the ability of a user to keep the same phone
number when changing service providers. It is generally
available now when a customer switches wireline carriers.
The FCC and state regulatory agencies contend that allowing consumers to keep their telephone numbers helps mitigate another big problem facing U.S. consumers—the
shortage of telephone numbers. LNP is viewed as a way to
protect this dwindling resource without having to add more
digits to dial.
See also
Federal Communications Commission
The setup and management of wireless LANs is typically
done with Windows-based tools. ORiNOCO Software Tools
from Agere Systems, for example, is a Windows-based site
survey tool to facilitate remote management, configuration,
and diagnosis of spread-spectrum wireless LANs, specifically Wi-Fi–certified access points and adapters that operate
in the 2.4-GHz frequency band.
The tool suite makes it easy for system administrators to
monitor the quality of communications at multiple locations in
a wireless network (Figure W-15), including access points and
clients. It also can be used to verify building coverage, identify
coverage patterns, select alternate frequencies, locate and
tune around RF interference, and customize network access
security. The tool suite offers the following basic functions:
Figure W-15 ORiNOCO Software Tools from Agere Systems, formerly
Lucent’s WaveMANAGER, provides an administrative graphical user interface
through which wireless LANs can be configured, managed, and troubleshooted.
Communications indicator located on the Windows taskbar
and providing mobile users graphical, real-time information on the level of communication quality between a wireless station (client) and the nearest access point.
Link test diagnostics the verify the communications path
between neighboring client stations as well as between a
client station and access points within a wireless cell. With
this feature, signal quality, signal-to-noise ratio, and the
number of successfully received packets can be displayed.
Site monitor that ensures optimal placement of access
points. While carrying a wireless-equipped notebook computer through the facility, the site monitor graphically
displays changing communication quality levels with the
various access points installed in the building. This tool
makes it easy to locate radio dead spots or sources of
Frequency select manages RF channel selection. It enables
the user to choose from up to eight different channels in
the 2.4-GHz frequency band.
Access control table manager enables the system administrator to provide extra levels of security by restricting
access to individual computers in a facility.
Authentication is a MAC address–based authentication
scheme using a centrally-maintained RADIUS-based
database that records the users who are permitted to have
access to the network. Using a MAC address–based
authentication also can help prevent unauthorized access
of the corporate network by visitors with their own
portable wireless devices. If a laptop or desktop computer
is stolen or misplaced, the unit’s MAC address can be
deleted easily and quickly.
For centralized management, the ORiNOCO management
tools can be integrated with an HP OpenView-based enterprise network management system. Unlike most other wireless networks that require each access point’s parameters to
be individually updated, a single ORiNOCO HPOV management station can configure an entire wireless network.
In addition to Windows-based tools for managing wireless
LANs, the Simple Network Management Protocol (SNMP) is
available for managing the wireless internetwork end to
end. The same SNMP tools used to manage the rest of the
enterprise network can be used to support management of
the bridges and routers on the wireless WAN. The result is a
manageable network with reach extending to metropolitan,
suburban, rural, remote, and isolated areas.
SNMP is usually implemented using a proxy agent supplied by the vendor. This is an application that continually
polls the managed devices for changes in alarm and status
information and updates its locally stored management information base (MIB). Events such as major and minor alarms
cause the device to generate enterprise specific traps directed
to the network management system (NMS). General alarm
and status information stored in the MIB is made available to
the NMS in response to SNMP’s Get and GetNext requests.
As enterprises and service providers build out their wireless
LAN networks and systems, they require tools that help IT
managers recognize and troubleshoot network problems
before they are reported. This can be accomplished with
wireless LAN management tools that provide real-time
monitoring of an entire WLAN network spread out over multiple facilities and subnets and enable an IT manager to control, update, and configure the entire wireless network from
a single user interface.
See also
Access Points
Wireless Fidelity
Wireless Security
Wireless Medical Telemetry Service (WMTS) allows operation of potentially lifesaving equipment over the air on an
interference-protected basis. Medical transmissions can be
unidirectional or bidirectional, but they cannot include a
voice or video component. In June 2000, the FCC allocated
spectrum and established rules for this service. To minimize
regulatory procedures and facilitate deployment, WMTS
operators are licensed by rule, like Citizens’ Band radio operators. Although the FCC does not issue a formal license,
operators must adhere to the rules for this service.
Medical telemetry equipment is used in hospitals and
health care facilities to transmit patient measurement data
to a nearby receiver, which may permit greater patient
mobility and increased comfort. Examples of medical
telemetry equipment include heart, blood pressure, and respiration monitors. The use of these devices can allow
patients to move around early in their recovery while still
being monitored for adverse symptoms. With such devices,
one health care worker can monitor several patients
remotely, which could reduce health care costs.
The frequency allocation for WMTS provides spectrum
where the equipment can operate on a primary basis,
increasing the reliability of this important service. The FCC
allocated 14 MHz of spectrum for use by medical telemetry
equipment in the 608- to 614-MHz, 1395- to 1400-MHz, and
1429- to 1432-MHz frequency bands. This allocation was
based on a needs assessment conducted by the American
Hospital Association (AHA).
The 608- to 614-MHz band, which corresponds to TV
Channel 37, had been reserved for radioastronomy uses.
With its action in mid-2000, the FCC elevated medical
telemetry to a coprimary status with radioastronomy in this
band. The 1395- to 1400-MHz and 1429- to 1432-MHz bands
are former government bands reallocated for nongovernment use by the Omnibus Budget Reconciliation Act of 1993.
Allocating two separate bands facilitates two-way communications and gives medical telemetry greater flexibility.
Despite existing constraints in these bands—primarily
that the entire allocation is unlikely to be available in any
individual market—this allocation is flexible enough to
allow spectrum to be available for medical telemetry services
in all locations while protecting radioastronomy and government operations currently operating in the allocated spectrum. The FCC believed, however, that the benefits of a
primary allocation dedicated to this service compensates for
the reduced availability of spectrum.
Medical telemetry devices once operated on a secondary
basis to TV broadcasting; that is, they had to tolerate any
interference that may have been caused by local television
stations’ broadcast signals. Users and manufacturers of
medical telemetry devices had been able to avoid interference by using TV channels that were vacant locally. In other
words, the medical devices used frequencies that local TV
stations did not. As these vacant channels started to become
used and medical telemetry services expanded, the risk of
interference increased. With its own frequency allocations
from the FCC, medical telemetry services and equipment
now operate more reliably without the risk of interference.
See also
Citizens’ Band Radio Service
Wireless E911
Although “beepers” had been in existence since the 1960s
and pagers since the 1980s, true wireless messaging made
its debut in 1992 with EMBARC (Electronic Mail
Broadcast to A Roaming Computer), built by Motorola as a
nationwide one-way message service aimed at mobile executives and field-office workers who required access to email. EMBARC, now defunct, was based on the 931-MHz
paging technology Motorola acquired when it purchased
Contemporary Communications, Inc., in 1990. At its
zenith, EMBARC provided coverage spanning 250 cities in
the United States and Canada.
Users were able to send messages from any e-mail system
that had an EMBARC interface. Typically, the user accessed
EMBARC on a PC and addressed a message to one or more
recipients. The message was then sent through an X.400 gateway to a central switch, which stored and translated it for
satellite transmission. The message traveled from the satellite to one or more regional transmission sites that rebroadcast it at 931 MHz to a Motorola NewsStream receiver, which
interfaced with a mobile computer via the standard RS-232C
serial port. The data transmission rate was 300 bps.
EMBARC was designed from the start as an advanced
messaging network, but after pouring tens of millions of dollars into EMBARC, in mid-1996 Motorola sold the service to
ProNet, a large regional paging company. ProNet then
merged with Teletouch Communications, another regional
paging carrier.
E-mail over Paging Nets
Wireless messaging took another leap forward in 1996 with
the ability of pagers to accept e-mail messages. Not only
could traditional paging services support e-mail, the messages also could originate from Internet e-mail clients on
desktop computers. An Internet gateway allows customers
to receive e-mail messages sent across the Internet. Senders
use an address consisting of the Pager Identification
Number (PIN) assigned to the intended text pager followed
by the domain of the paging service, such as SkyTel. For the
PIN 1234567, for example, the e-mail address of a SkyTel
subscriber would be
[email protected]
SkyTel’s support for paging from public X.400 networks
and the connected corporate e-mail systems means that email users around the world can send a message to SkyTel
text pagers in the same manner they would to other e-mail
recipients. Most paging service providers have Web pages
that allow anyone to send e-mail messages of not more than
260 characters to their subscribers.
Integrated Applications
A newer messaging solution integrates various messaging formats and various communications technologies into a single
package that can be especially useful to mobile professionals.
Depending on service plan, the following capabilities are
Send and receive e-mail worldwide via the Internet
Send faxes worldwide
Convert text to speech to send telephone messages from a
Receive text messages from a 24-hour, operator-assisted
message center
Send messages to any alphanumeric pager in the United
Receive notification of incoming messages to a computer
on an alphanumeric pager in the United States
Filter and automatically forward messages to another email address
Send and receive file attachments
Customize faxes from a personal library of electronically
stored documents
For the ultimate in messaging, there is even software
available that enables users to send e-mail messages out
over the Internet for receipt on all of a person’s communications devices simultaneously, including cell phone, pager,
wireless PDA, and notebook computer.
Not too many years ago, e-mail was considered a fad. Now
there is great appreciation for e-mail and its role in support-
ing daily business operations. Wireless services extend the
reach of e-mail even further, since they do not rely as much
on the existing wireline infrastructure. In turn, this has
given the distributed workforce the highest degree of mobility, enabling them to conduct business and stay in touch with
coworkers without regard for location, distance from the
office, or proximity to a telephone. The evolution of wireless
messaging continues, with Short Messaging Services (SMS)
available with most cellular services today, rendering paging
virtually obsolete. And with third-generation (3G) networks
coming online, there will be enough bandwidth to support
multimedia messaging.
See also
Cellular Telephones
Short Messaging Services
With office workers spending increasing amounts of time
away from their desks—supervising various projects, working at temporary assignments, attending meetings, and just
walking corridors—there is a growing need for wireless technology to help them stay in touch with colleagues, customers, and suppliers. The idea behind the wireless PBX is
to facilitate communication within the office environment,
enabling employees to be as productive with a wireless
handset as they would if they were sitting at their desk.
Typically, a wireless switch connects directly to an existing
PBX, key telephone system, or Centrex service, converting an
office building into an intracompany microcellular system.
This arrangement provides wireless telephone, paging, and
e-mail services to mobile employees within the workplace
through the use of pocket-sized portable phones, similar to
those used for cellular service. Almost any organization can
benefit from improved communications offered by a wireless
PBX system, including
Manufacturing Roving plant managers or factory supervisors do not have to leave their inspection or supervisory
tasks to take important calls.
Retail Customers can contact in-store managers directly,
eliminating noisy paging systems.
Hospitality Hotel event staff can stay informed of guest’s
needs and respond immediately.
Security Guards can relay emergency information quickly
and clearly, directly to the control room or police department, without trying to reach a desktop phone.
Business Visiting vendors or customers have immediate
use of preassigned phones without having to take over
employee offices to use a phone.
Government In-demand office managers can be available
at all times for instant decision making.
A wireless PBX is especially appropriate in such areas as
education and health care or any operation with multiple
buildings in a campus environment. In the health care
industry, for example, a typical environment for a wireless
PBX would be a hospital where staff members typically are
away from their workstations one-third of the workday.
System Components
Many of the wireless office systems on the market today are
actually adjunct systems that interfaces to an existing PBX
that provides user features and access to wireline telephones
and outside trunk carrier facilities. The advantages of this
approach include cost savings in terms of hardware, space
requirements, and power. A wireless PBX typically consists
of several discrete components (Figure W-16).
Adjunct Switch The adjunct contains the CPU and control
logic. Its function is to manage the calls sent and received
between the base stations. The adjunct is a standalone unit
that can be wall-mounted for easy installation and maintenance. It can be collocated with the PBX or connected to the
PBX via twisted-pair or optical fiber from several thousand
feet away. Optional battery backup is usually available, permitting uninterrupted operation should a power failure
occur. System control, management, and administration
Remote Location
Distribution Hub
Use of the
same telephone
Figure W-16 A typical wireless PBX system in the corporate environment. In this case, workers can roam between the office and home using the
same handset. When the handset moves within range of the local cellular
service provider, the signal is handed off from the wireless PBX to the cellular carrier’s nearest base station.
functions are provided through an attached terminal that is
password-protected to guard against unauthorized access.
As portable telephones and base stations are added to
accommodate growth, line cards are added to the PBX, and
radio cards are added to the adjunct switch to handle the
increasing traffic load. Each adjunct is capable of supporting
several hundred portable telephones. Additional adjuncts
can be added as necessary to support future growth.
Base Stations The antenna-equipped base stations, which
are about the size of smoke detectors, are typically mounted
on the ceiling and are connected by twisted-pair wiring to
the wireless PBX. They send and receive calls between the
portable telephones and the adjunct unit. As the user moves
from one cell to another, the base station hands off the call to
the nearest base station with an idle channel. When the next
base station grabs the signal, the channel of the former base
station becomes idle and is free to handle another call.
To facilitate the handoff process, each base station may be
equipped with dual antennas (antenna diversity). This
improves signal detection, enabling the handoff to occur in a
timely manner. This is accomplished by the base station sampling the reception on each of its antennas and switching to
the one that offers the best reception. This process is continuous, ensuring the best voice quality throughout the duration
of the call. Some vendors offer optional external antennas for
outdoor coverage or directional coverage indoors.
Wireless PBX systems are easily expanded—portable
telephones and base stations are added as needed.
Substantial savings can accrue over time through the elimination of traditional phone moves, adds, and changes. There
also is significant savings in cabling, since there is less need
to rewire offices and other locations for desktop telephones.
Telephone Handset Each portable phone has a unique iden-
tification number that must be registered with the adjunct
switch. This allows only authorized users to access the com-
munications system. The portable phone can be configured
to have the same number as the user’s desk phone so that
when a call comes in, both phones ring. The user can even
start a conversation on one phone and switch to the other. If
the portable and desktop phones have different numbers,
each can be programmed by the user to forward incoming
calls to the other.
Since the adjunct switch becomes an integrated part of
the company’s existing telephone system, users have access
to all its features through their portable phones. Users can
even set up conference calls, forward calls, and transfer
calls. If the handset is equipped with an LCD, the unit also
can be used to retrieve e-mail messages, faxes, and pages. An
alphanumeric display shows the name and number of the
person or company calling.
The portable phone offers a number of other features,
Private directory of stored phone numbers for quick dialing
Multilevel last number redial
Audio volume, ring volume, and ring tone control
Visual message-waiting indicator
Silent vibrating alert
Electronic lock for preventing outgoing calls
In-range/out-of-range notifications
Low battery notification
When the portable phone is not being used, a desktop
unit houses the phone and charges both an internal and a
spare battery. A LED indicates when the battery is fully
charged. Recharging takes only a few hours and varies
according to the type of battery used: Nickel cadmium
(NiCd) takes about 21⁄2 hours, while nickel metal hydride
(NiMH) and the newer lithium ion (Li-Ion) batteries take
about 11⁄2 hours. Li-Ion batteries offer longer life and are
lighter weight than NiCd and NiMH batteries. Some vendors
offer an intelligent battery charging capability that protects
the battery from overcharging.
Distribution Hub Distribution hubs are used in large instal-
lations to extend and manage communications among the
base units in remote locations that are ordinarily out of
range of the adjunct unit. They also allow high-traffic locations to be divided into smaller cells, called “microcells,” with
each cell containing multiple base stations. This arrangement makes more channels available to handle more calls.
The distribution units are connected to the adjunct unit
with twisted-pair wiring or optical fiber. Optical fiber is an
ideal medium for an in-building wireless network because
its low attenuation over distance (approximately 1 decibel
per kilometer) allows high-quality coverage even in large
buildings and campus environments. Fiber is also immune
to electromagnetic interference, allowing it to work effectively alongside other electronic equipment in installations
such as factories and warehouses.
Frequency Bands Wireless PBXs operate in a variety of fre-
quency bands, including the unlicensed 1910- to 1930-MHz
Personal Communications Services (PCS) band. The term
unlicensed refers to the spectrum that is used with equipment that can be bought and deployed without FCC
approval because it is not part of the public radio spectrum.
In other words, since wireless PBX operates over a dedicated
frequency band for communications within a very narrow
geographic area, it has little chance of interfering with other
wireless services in the surrounding area. The individual
channels supported by the wireless PBX system are spaced
far enough apart to prevent interference with one another.
The Telecommunications Industry Association (TIA) and the
American National Standards Institute (ANSI) have defined
a North American standard that ensures interoperability
between portable phones and wireless PBXs from different
vendors. The TIA TR41.6.1 subcommittee based its development of the standard, called Personal Wireless Telecommunications (PWT), on the Digital European Cordless
Telecommunications (DECT) standard. Portable phones that
support PWT, formerly known as the Wireless Customer
Premises Equipment standard, will interoperate with PWTcompliant wireless PBXs from any vendor.
For a wireless handset to communicate with any wireless PBX, manufacturers of both devices must agree on
how the signal should be handled. As part of the PWT standard, the Customer Premises Access Profile defines the
features that each side of the air interface must support to
provide full, multivendor interoperability for voice services. As with most standards, vendors can add proprietary
extensions to support additional features and differentiate
their products.
The air interface is a layered protocol, similar to
the International Organization for Standardization’s
(ISO’s) Open Systems Interconnection (OSI) architecture.
Accordingly, the air interface is composed of four protocol
Physical Layer Specifies radio characteristics such as
channel frequencies and widths, the modulation scheme,
and power and sensitivity levels. This layer also specifies
the framing, so each handset can translate the bits it
Media Access Control (MAC) Layer Specifies the procedures by which the portable phone and the base station,
or antenna, negotiate the selection of the radio channels.
Data Link Control (DLC) Layer Specifies how frames are
transmitted and sequenced between the handset and the
base station.
Network Layer Specifies messages that identify and
authenticate the handset to the wireless PBX.
Call Handoff Scenario
By examining the handoff from one base station to another,
the operation of these protocols can be illustrated. A handoff
occurs when the mobile user walks out of the range of one
base station and into the zone or cell of another base station.
When the handset detects a change of signal strength from
strong to weak, it will attempt to get acceptable signal
strength from another channel offered by the same base station. If there is a better channel available, an exchange of
messages at the MAC level occurs, which allows the conversation to continue without interruption. This channel
change takes place without notification to the DLC layer.
If an acceptable channel is not available to the current base
station, the handset searches for another base station. An
exchange of messages at the DLC and MAC layers secures a
data link via a radio channel to the new base station while the
call through the original base station continues. When the data
link to the second base station is established, the handset drops
the old channel and begins processing the frames received
through the new one. This process occurs without the network
layer being notified. This means the caller and the wireless
PBX are not aware that a handoff has happened.
Businesses everywhere have put a high priority on increasing the productivity of their workforce, even while they continue to cut back on staff. In order to improve profitability,
serve customers, and grow market share, organizations
must find ways to do more—cheaper, faster, and better. Most
companies are focused on increasing efficiency and productivity while reducing time to market and improving customer service. This puts workers between a rock and a hard
place: They must be mobile, away from their desks and
offices, but not far from their telephones. Wireless PBX technology meets both demands.
See also
Wireless Centrex
Wireless LANs
The Wireless Telecommunications Bureau (WTB) handles
all domestic wireless telecommunications programs and
policies for the FCC—except those involving satellite communications or broadcasting—including licensing, enforcement, and regulatory functions. Wireless communications
services under the purview of the WTB include Amateur,
Cellular, Paging, and Broadband PCS.
The amateur and amateur-satellite services are for qualified persons of any age who are interested in radio technique
solely with a personal aim and without pecuniary interest.
These services present an opportunity for self-training,
intercommunication, and technical investigations.
Radiotelephone service, commonly referred to as “cellular” or “mobile telephone service,” uses spectrum to provide
a mobile telecommunications service for hire to the general
public using cellular systems. Cellular licensees may operate using either analog or digital networks or both. Cellular
licensees that operate digital networks also may offer
advanced two-way data services.
Commercial paging is provided for profit, interconnected
to the public switched network, and available to the public.
Commercial paging may operate in the 35- , 43- , 152- , 158-,
454- , 929- (exclusive channels only), and 931-MHz bands.
Response paging channels allow paging operators to provide
two-way or response paging services.
Paging systems are traditionally one-way signaling systems. Paging services, grouped by output, include tone,
tone/voice, numeric, and alphanumeric. Present systems are
of two basic types: a wide-area general-use type providing
subscription service to the public and in-building, private
paging systems limited to a commercial building or the general area of a manufacturing plant. Currently, neither of
these paging systems can initiate an answer without calling
through a landline telephone.
Personal Communications Service (PCS) spectrum is
used for a variety of mobile and fixed radio services, also
called “wireless services.” Mobile broadband PCS services
include both voice and advanced two-way data capabilities
that are generally available on small, mobile multifunction
devices. Many broadband PCS licensees offer these services
in competition with existing cellular and Specialized Mobile
Radio (SMR) licensees. Examples of service providers holding a significant amount of broadband PCS spectrum include
AT&T Wireless and Sprint PCS.
The goals of the Wireless Telecommunications Bureau are to
Foster competition among different services
Promote universal service and service to individuals with
Maximize efficient use of spectrum
Develop a framework for analyzing market conditions for
wireless services
Minimize regulation where appropriate
Facilitate innovative service and product offerings, particularly by small businesses and new entrants
Serve WTB customers efficiently, including improving
licensing, eliminating backlogs, disseminating information, and making staff accessible.
Enhance consumer outreach and protection and improve
the enforcement process
In addition, the WTB is responsible for implementing the
competitive bidding process for spectrum auctions, authority
for which was given to the FCC by the 1993 Omnibus Budget
Reconciliation Act.
The WTB also had responsibility for public safety radio communications, but following the September 11 terrorist
attacks of 2001, the FCC established the National
Coordination Committee (NCC) to satisfy public safety communications needs into the twenty-first century and provide
the capability for a nationwide public safety interoperability
communications system.
See also
Federal Communications Commission
Spectrum Auctions
Spectrum Planning
The FCC offers guidelines to help protect potential investors
in wireless telecommunications services from being
defrauded by unscrupulous promoters. According to the FCC,
there has been a surge in the number of reported cases of
fraud in emerging telecommunications services such as
Paging, Specialized Mobile Radio (SMR), Wireless Cable,
Interactive Video and Data Services (IVDS), Personal
Communications Service (PCS), and Cellular Radio Telephone
in underserved areas.
As the FCC warns, telecommunications is an undeniably
alluring, fast-paced, multi-billion dollar industry. “Combine
that with brain-numbingly complex technologies, and it creates the perfect environment for scam artists. The problem
for the potential investor is differentiating opportunity from
Separating truth from fiction in these sophisticated scams
is not easy. However, the experience gained by the Federal
Trade Commission (FTC) and other agencies prosecuting
these types of scams suggests some common warning signs
that should alert consumers that the investment proposal
might not be legitimate.
Common Warning Signs
Cold calls and infomercials If the first contact with the
telemarketer is an unsolicited call from a salesperson, be
skeptical. Another favorite tactic for luring investors is
via television or radio infomercials.
High profits, low risk Scam artists are clever liars. If the
sales representative promises high profits with little or no
risk, chances are the deal is phony.
Urgency Beware of promoters who say that it is urgent to
invest now. Swindlers do not want people to have time to
think things over. Some may even apply pressure to
promptly send money by courier or wireless transfer.
IRA funds Many scam artists claim that their investments have been approved for use in Investment
Retirement Accounts (IRAs). In reality, there is no formal
government approval process for certifying the appropriateness of funds for IRA status.
Avoiding Fraud
Be skeptical The best protection against being scammed is
skepticism. Investigate thoroughly any representations
from salespersons before sending any money because, if
duped, it is unlikely that any of it will be recovered. Make
sure to fully understand the telemarketers’ answers to
questions. Continually assess whether their answers are
High risk A venture that seeks to obtain immediate,
short-term profits from ownership of an FCC-licensed or
-authorized service is a high-risk enterprise. Investors
can and do lose money. In evaluating risk tolerance,
would-be investors should consider whether they can
afford to lose the entire investment.
Ask questions Do not rely solely on the representations of
the salesperson. Obtain advice from others: friends and
family, an attorney, an accountant, an investment advisor,
appropriate industry trade groups, the Better Business
Bureau, state commission on corporations, state attorney
general, or other business professionals. Be suspicious of
representations that the investment is not subject to registration with or regulated by such federal agencies as the
Security and Exchange Commission (SEC) or the FTC.
Administrative costs Fraudulent telemarketers often take
most of the money they solicit from consumers as commissions, promotions, and management and administrative costs. A shockingly small amount of anyone’s
investment actually goes into ownership interest.
Auctions If the license is subject to an auction, be sure that
The auction is scheduled by the FCC.
The telecommunications service of interest is included
in that auction.
The investment will be maintained pending the auction.
The venture is a “qualified bidder” in the auction.
If the venture wins a license, there will be funds and
expertise available to the venture to construct and
operate the system.
If the venture does not win a license, know how much,
if any, of the investment will be returned.
License speculation Be skeptical of any representation
that the venture will quickly sell the license or authorization to another company for a huge profit. Sales of systems typically involve a long and complex process. The
FCC has regulations that prohibit some services from
being sold until the system has been constructed and is
Construction requirements Construction of advance
telecommunications systems may cost tens of thousands
or even millions of dollars beyond the initial investment.
Know exactly where that money is coming from.
Ultimately, the responsibility to construct and operate the
system falls on the licensee. Some licenses are subject to
construction deadlines. Failure to comply with these
deadlines may result in the automatic cancellation of the
The burden is entirely on the investor to investigate the
technology, the potential of wireless licenses to produce revenues, and the condition of the marketplace. License holders
are responsible for being familiar with FCC rules and regulations. The FCC does not approve any individual investment proposal, nor does it provide a warranty with respect
to any authorization. Receiving an authorization for a wireless license from the FCC is not a guarantee of success in the
See also
Federal Communications Commission
Wireless Telecommunications Bureau
ATM Adaptation Layer
Automated Auction System
Automated Bit Access Test System
Accunet Bandwidth Manager (AT&T)
Available Bit Rate
Access Control
Address Copied
Alternating Current
Authentication Center
Automatic Call Distributor
Algebraic Code Excited Linear Predictive
Access Control Point
Access Control List
Asynchronous Connectionless (link)
Asynchronous Communications Server
Advanced Communication Technology
Satellite (NASA)
Americans with Disabilities Act
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Alternate Destination Call Routing (AT&T)
Add-Drop Multiplexer
Advanced Digital Network (Pacific Bell)
Adaptive Differential Pulse Code Modulation
Asymmetric Digital Subscriber Line
Advanced Encryption Algorithm
Apple File Protocol
Automatic Gain Control
Agent Applet (IBM Corp.)
Air-Ground Radiotelephone Automated
Automatic Identification of Outward Dialed
Advanced Intelligent Network
Automatic Location Identification or
Antilocking Mechanism
Amplitude Modulation
Advanced Mobile Phone Service
Automated Marine Telecommunications
Automatic Number Identification
Automatic Network Routing (IBM Corp.)
American National Standards Institute
ADSL Network Terminator
America Online
Access Point
Access Protection Capability (AT&T)
Application Programming Interface
Advanced Program-to-Program
Communications (IBM Corp.)
Advanced Peer-to-Peer Network (IBM Corp.)
Automatic Protection Switching
Attached Resource Computer Network
(Datapoint Corp.)
Adaptive Rate Based (IBM Corp.)
Association of Radio Industries and
Businesses (Japan)
Address Resolution Protocol
Advanced Research Projects Agency
Automatic Repeat Request
Action Request System (Remedy Systems, Inc.)
Autonomous System
American Standard Code for Information
Application-Specific Integrated Circuit
Abstract Syntax Notation 1
Alternate Signaling Transport Network
American Telephone & Telegraph
Asynchronous Time Division Multiplexing
Alliance for Telecommunications Industry
Solutions (formerly, ECSA)
Asynchronous Transfer Mode
Automated Teller Machine
Advanced Television Systems Committee
Auction Tracking Tool
Attachment Unit Interface
Administrative View Module
American Wire Gauge
Abstract Window Toolkit
Binary Eight Zero Substitution
Bandwidth Allocation Control Protocol
Bulletin Board System
Broadcast Control Channel
Broadband Digital Cross-Connect System
Backward Explicit Congestion Notification
Bell Communications Research, Inc.
Bit Error Rate
Bit Error Rate Tester
Basic Exchange Telephone Radio Service
Binary File Transfer
Border Gateway Protocol
Busy Hour Call Attempts
Busy Hour Call Rate
Backward Indicator Bit
Basic Input-Output System
Block Multiplexer Channel (IBM Corp.)
Bandwidth Management Service–Extended
Bell Operating Company
Bandwidth on Demand Interoperability Group
Boot Protocol
Bridge Protocol Data Unit
Bits per Second
Bipolar Violation
Binary Runtime Environment for Wireless
Basic Rate Interface (ISDN)
Basis Serving Arrangement
Base Station Controller
Binary Synchronous Communications
Basic Service Element
Backward Sequence Number
Base Station System Controller
Base Station Transceiver
Both-Way Trunk
Business Trading Area
Base Transceiver Station
Communications Assistant
Computer-Aided Design
Common Air Interface
Computer-Aided Manufacturing
Campus Area Network
Carrierless Amplitude/Phase (Modulation)
Competitive Access Provider
Cable Antenna Relay Services
Customer Activation System
Computer-Aided Software Engineering
Computed Axial Tomography
Cable Television
Cell Broadcast
Citizens’ Band
Constant Bit Rate
Centralized Base Site Controller
Clear Channel Capability
Common Control Channel
Call Control Function
Consultative Committee for International
Telegraphy and Telephony
Customer-Controlled Reconfiguration
Common Channel Signaling
Common Channel Signaling Network
Common Channel Signaling System 6
Compact Disc
Compact Disc–Recordable
Compact Disc–Read Only Memory
Continuous Dynamic Channel Selection
Copper Distributed Data Interface
CDMA Development Group
Code Division Multiple Access
Cellular Digital Messaging Protocol
Community Dial Office
Cellular Digital Packet Data
Call Detail Record or Recording
Component Economic Area
Comparably Efficient Interconnection
Central Office Exchange
Circular Error Probable
Conference of European Posts and
Common Gateway Interface
Cellular Geographic Servicing Areas
Challenge Handshake Authentication Protocol
Common Intermediate Format
Common Information Model
Computer Interface to Message Distribution
(Nokia Telecommunications)
Committed Information Rate
Cordless Local Area Network
Custom Local Area Signaling Services
Competitive Local Exchange Carrier
Calling Line Identification
Connectionless Network Protocol
Cell Loss Priority
Circuit-Switched Mobile-End System
Circuit-Switched Mobile Data Intermediate
Cable Microcell Integrator
Common Management Information Protocol
Common Management Information Services
Commercial Mobile Radio Service
Clearlink Network Control System (AT&T
Calling Number Identification Presentation
Customer Network Reconfiguration
Complementary Network Service
Central Office
Component Object Model (Microsoft Corp.)
Communications Satellite Corp.
Common Object Request Broker
Class of Service
Central Office Terminal
Coordination Processor
Customer Premises Equipment
Contention, Priority-Oriented Demand
Cycles per Second (Hertz)
Central Processing Unit
Carriage Return
Cyclic Redundancy Check
Cisco Resource Manager (Cisco Systems)
Customer Relationship Management
Cell Station
Circuit-Switched Cellular Digital Packet Data
Carrier Serving Area
Conjugate Structure Algebraic Code Excited
Linear Prediction
Circuit-Switched Cellular
Circuit-Switched CDPD Control Protocol
Circuit-Switched Data
Communications Services Management
Carrier Sense Multiple Access with Collision
Carrier Sense Multiple Access with Collision
Customer Service Representative
Channel Service Unit
Cordless Telecommunications
Computer-Telephony Integration
Closed User Groups
Continuously Variable Slope Delta
Digital Advanced Mobile Phone Service
Destination Address
Digital-to-Analog Converter
Digital Access and Cross-Connect System
Demand Access Protocol
Dual Attached Station
Direct Access Storage Device (IBM Corp.)
Digital Audio Tape
Database Management System
Direct Broadcast Satellite
Dial Backup Unit
Direct Current
Digital Control Channel
Digital Control Channel
Data Communications Equipment
Distributed Computing Environment
Data Communication Function
Digital Cross-Connect System
Digital Data Fast (Motorola)
Digital Data Services
Digital Data Service with Secondary Channel
Debt-Equity (Ratio)
Digital Enhanced (formerly, European)
Cordless Telecommunication
Data Encryption Standard
Data Facility Storage Management
Subsystem (IBM Corp.)
Dynamic Host Configuration Protocol
Direct Inward Dialing
Digital Interface Frame
Domestic and International Satellite
Consolidation Orders (FCC)
Digital Loop Carrier System
Data Link Layer
Dynamic Link Library (Microsoft Corp.)
Data Link Switching (IBM Corp.)
Digital Line Unit
Distributed Management
Distributed Management Environment
Desktop Management Interface
Discrete Multitone
Desktop Management Task Force
Domain Name Service
Department of Defense (U.S.)
Direct Outward Dialing
Disk Operating System
Department of Transportation (U.S.)
Data over Voice
Distributed Queue Dual Bus
Differential Quadrature Phase-Shift Keying
Dynamic Random Access Memory
Digital Signal–Level 0 (64 kbps)
Digital Signal–Level 1 (1.544 Mbps)
Digital Signal–Level 1C (3.152 Mbps)
Digital Signal–Level 2 (6.312 Mbps)
Digital Signal–Level 3 (44.736 Mbps)
Digital Signal–Level 4 (274.176 Mbps)
Digital Speech Interpolation
Digital Subscriber Line
Digital Sense Multiple Access
Defense Switched Network
Digital Signal Processor
Decision Support System
Direct Sequence Spread Spectrum
Data Service Unit
Digital Systems Cross-Connect 1
Data Terminal Equipment
Dual Tone Multifrequency
Dedicated Token Ring
Data Transfer Unit
Digital Television
Discontinuous Transmission
Discrete Wavelet Multitone
Data Exchange Interface
Enhanced Advanced Mobile Phone Service
Electronic Mail
Expanded Time Division Multiple Access
Enterprise Command Center (Bay Networks)
Exchange Carriers Standards Association
Ending Delimiter
Enhanced Data Rates for Global Evolution
Electronic Data Interchange
Enhanced Diversity Routing Option (AT&T)
Electronically Erasable Programmable ReadOnly Memory
Electronically Erasable Read-Only Memory
Enhanced Full Rate Codec
Electronic Funds Transfer
External Gateway Protocol
Extremely High Frequency (More than 30 GHz)
Electronic Industries Association
Equipment Identity Register
Extended Industry Standard Architecture
Electronic Messaging Association
Electronic Mail Broadcast to a Roaming
Electromechanical Inteference
Element Management System
Embedded Overhead Channel
End of Transmission
Extension Point
Equivalent Power Flux Density
Enhanced Radio Messaging System
Effective Radiated Power
Enterprise Resource Planning
Enterprise System Connection (IBM Corp.)
Electronic Software Distribution
Extended Super Frame
Enhanced Specialized Mobile Radio
Enhanced Short Message Service
Extended Simple Mail Transfer Protocol
Electronic Serial Number
End System Query
Enhanced Cellular Throughput
European Telecommunication Standards
Enhanced Variable Rate Coder
Fourth-Generation Language
Foreign Agent
Fast Associated Control Channel
Financial Accounting Standards Board
Fraud Analysis and Surveillance Center
File Allocation Table
Frame Control
Fibre Channel
Federal Communications Commission (U.S.)
Frame Check Sequence
Fiber Distributed Data Interface
Federal Deposit Insurance Corporation
Facilities Data Link
Forward Explicit Congestion Notification
Front-End Processor
Frequency Hopping Spread Spectrum
Forward Indicator Bit
Forwarding Information Base
Fast Infrared
Fiber in the Loop
Frequency Modulation
Forward Control Channel
Fax on Demand
Fraud Protection Feature
Field Programmable Gate Array
Frame Relay Access Device
Family Radio Service
Frame Status
Forward Sequence Number
Film Super-Twisted Nematic
File Transfer, Access, and Management
Fractional T1
File Transfer Protocol
Federal Telecommunications System
Fiber to the Building
Fiber to the Curb
Fiber to the Home
Fixed Wireless Access
Fixed Wireless Terminal
Foreign Exchange (Line)
General Accounting Office (U.S.)
General Agreement on Tariffs and Trade
Ground Control Station
Generic Digital Services
Geostationary Earth Orbit
Generic Flow Control
Gateway GPRS Support Node
Gigahertz (Billions of Cycles per Second)
Geographic Information Systems
Global Maritime Distress and Safety System
General Mobile Radio Service
Gaussian Minimum Shift Keying
General Purpose Interface
General Packet Radio Services
Global Positioning System
General Services Administration
Global System for Mobile
Telecommunications (formerly Groupe
Spéciale Mobile)
Graphical User Interface
High-Capacity ISDN Channel Operating at
384 kbps
High-Capacity ISDN Channel Operating at
1.536 Mbps
Home Agent
High-Level Data Link Control
Handheld Device Markup Language
High-Bit-Rate Digital Subscriber Line
High Definition Television
Header Error Check
High Frequency (1.8–30 MHz)
Hybrid Fiber/Coax
Head-End Interface Converter
Home Location Register
HyperMedia Management Protocol
HyperMedia Management Schema
HyperMedia Object Manager
High-Speed Circuit-Switched Data
HyperText Markup Language
HyperText Transfer Protocol
Heating, Ventilation, and Air
Hertz (Cycles per Second)
Internet Architecture Board
Internet Assigned Numbers Authority
Inter Access Point Protocol
Integrated Circuit
Integrity Check
Interexchange Carrier Interface
Internet Control Message Protocol
Integrated Communications Provider
Intelligent Call Routing
Intelligent Calling System
International Direct Dialing Designator
Integrated Digital Enhanced Network
Inter-Domain Policy Routing
International Electrotechnical Commission
Institute of Electrical and Electronic
Internet Engineering Steering Group
Internet Engineering Task Force
Intermediate Frequency
Interior Gateway Protocol
Intercast Industry Group
Internet Inter-ORB Protocol
Incumbent Local Exchange Carrier
Instant Messaging
Internet Mail Access Protocol
International Mobile Equipment Identity
International Maritime Organization
Information Management System/Virtual
Storage (IBM Corp.)
International Mobile Subscriber Identity
Improved Mobile Telephone Service
Intelligent Network
International Maritime Satellite
Integrated Network Management System
Interactive Television
Interoffice Channel
Internet Protocol
Internet Protocol Version 4 (Current)
Internet Protocol Version 6 (Future)
Integrated Packet Handler
Intelligent Peripheral Interface
Intelligent Peripheral Node
Internet Protocol Secure
Internet Packet Exchange
Interdepartment Radio Advisory Committee
Internet Relay Chat
Infrared Data Association
Infrared Data Association Serial Infrared
Infrared Financial Messaging
Infrared Local Area Network
Infrared Link Access Protocol
Infrared Link Management Protocol
Infrared Physical Layer
Infrared Tiny Transport Protocol
Interrupt Request
Infrared Transport Protocol
Information System
Industry Standard
Intraautonomous System to
Intraautonomous System
Industry Standard Architecture
ISDN Subscriber Digital Line
Integrated Services Digital Network
Industrial, Scientific, and Medical
(Frequency Bands)
International Organization for
Internet Society
Internet Service Provider
Inter-Switching Systems Interface
Information Technology
Instructional Television Fixed Service
Intelligent Text Retrieval
Internet Telephony Server (Lucent
International Telecommunications
Union–Telecommunications Standardization
Sector (formerly CCITT)
Initialization Vector
Interactive Video and Data Service
Interactive Voice Response
Interexchange Carrier
Java 2 Micro Edition
Java Database Connectivity
Japanese Digital Cellular
Java Development Kit
Joint Electronic Payments Initiative
Just in Time
Java Management Application Programming
Joint Photographic Experts Group
Joint Technical Committee
Java Virtual Machine
k (kilo)
One Thousand (e.g., kbps)
Key Service Unit
Key Telephone System
Kilohertz (Thousands of Cycles per Second)
Layer 2 Forwarding
Layer 2 Tunneling Protocol
Local Area Network
Link Access Procedure–Balanced
Link Access Procedure on the D-Channel
Local Area Transport (Digital Equipment
Local Access and Transport Area
Line Build Out
Liquid-Crystal Display
Local Channel Number
Link Control Protocol
Laser Diode
Lightweight Directory Access Protocol
Low Delay Code Excited Linear Prediction
Local Exchange Carrier
Light-Emitting Diode
Low Earth Orbit
Line Feed
Low Frequency (30–300 kHz)
Length Indicator
Lithium Ion
Logical Link Control
Local Multipoint Distribution System
Location and Monitoring Service
Local Number Portability
Low-Power Frequency-Modulated
Low-Power Radio Service
Large-Scale Integration
Limited-Size Messaging
Line Trunk Group
Logical Unit (IBM Corp.)
M (Mega)
One Million (e.g., Mbps)
Mobile End System
Media Access Control
Moves, Adds, Changes
Major Economic Area
Metropolitan Area Network
Messaging Applications Programming
Interface (Microsft Corp.)
Multistation Access Unit
Mediation Device
Mobile Data–Intermediate System
Mobile Database System
Mobile Data Initiative
Mobile Data-Link Layer Protocol
Multipoint Distribution Service
Middle Earth Orbit
Master Earth Station
Mediation Function
Mobile Host
Megahertz (Millions of Cycles per Second)
Management Information Base
Mobile Identification Number
Millions of Instructions per Second
Management Information Services
Mobility Manager
Multichannel, Multipoint Distribution
Maritime Mobile Service
Multimedia Messaging Service
Mobile Network Location Protocol
Mobile Network Registration Protocol
Mobile Originating
Moving Pictures Experts Group
Multiprotocol Label Switching
Multipulse Maximum Likelihood
Message Register
Millisecond (Thousandths of a Second)
Mobile Station
Mobile Switching Center
Mobile Station Roaming Number
Mobile Satellite Service
Mobile Terminating
Mean Time Between Failure
Mobile Telephone Switching Office
Mobile Transport Serving Office
Multicast Virtual Circuit
Microwave Video Distribution System
Multichannel Video Distribution and Data
Multichannel Video Program Distribution
Mobile Exchange Unit
Narrowband Advanced Mobile Phone Service
Narrowband Personal Communications
Numeric Assignment Module
Network Access Point
National Aeronautics and Space
Administration (U.S.)
Network Address Translation
Navigation System with Timing and Ranging
National Coordination Committee
Network Element
Network Equipment Identifier
Network Basic Input-Output System
Network File System (or Server)
Network Interface Card
Nickel Cadmium
Network Interconnect Facility (Metricom,
Nickel-Metal Hydride
National Institute of Standards and
Network Interface Unit
Network Manager
Network Management System
Nordic Mobile Telephone (Ericsson)
Network Operations Center
Network Operating System
Narrowband Personal Communication
National Security Agency (U.S.)
National Science Foundation (U.S.)
National Telecommunications and
Information Administration (U.S.)
National Television Standards Committee
Operations, Administration, Management
Operations, Administration, Maintenance,
and Provisioning
Object Exchange
Optical Carrier
Original Equipment Manufacturer
Office of Engineering and Technology (FCC)
Orthogonal Frequency Division Multiplexing
Operations and Maintenance Center
Operating System
Open Systems Interconnection
Open Shortest Path First
Personal Access Communications System
Personal Air Communications Technology
Password Authentication Protocol
Port Address Translation
Private Branch Exchange
Personal Computer
Printed Circuit Board
Paging Channel
Pulse Code Modulation
Personal Computer Memory Card
International Association
Personal Communications Networks
Personal Communications Services
Private Communication Technology
Personal Digital Assistant
pACT Database Station
pACT Data Intermediate System
Packet Data Network
Packet Data Serving Node
Payload Data Unit
Pretty Good Privacy
Personal Handyphone System
Physical Layer
PHS Internet Access Forum (Japan)
Personal Information Manager
Personal Identification Number
Private Land Mobile Radio Services
Post Office Code Standardization Advisory
Point of Presence
Plain Old Telephone Service
Point-to-Point Protocol
Packets per Second
Primary Rate Interface (ISDN)
Public Safety Answering Point
Packet Switched Network
Public Switched Telephone Network
Payload Type
Post Telephone & Telegraph
Public Utility Commission
Permanent Virtual Circuit
Personal Wireless Telecommunications
Quality Assurance
Quality of Service
Quadrature Phase Shift Keying
Random Access Channel
Remote Antenna Driver
Remote Authentication Dial-In User Service
Random Access Memory
Remote Antenna Signal Processor
Radio Determination Satellite Service
Regional Economic Area Grouping
Reverse Control Channel
Routing Field
Radio frequency Interference
Routing Information Protocol
Remote Monitoring
Return on Investment
Radio Resource Management
Residential Service System (Nortel)
Remote Terminal
Radio Technical Commission for Maritime
Services Special Committee
Source Address
Slow Associated Control Channel
Satellite Access Node
System Controller
Satellite Control Center
Service Control Function
Synchronous Connection Oriented
Starting Delimiter
Service Data Function
Symmetric Digital Subscriber Line
Secure Electronic Transaction
Start Frame Delimiter
Super High Frequency (3–30 GHz)
Satellite Home Viewer Improvement Act
Secure HyperText Transfer Protocol
Special Interest Group
System Identification
Service Set Identifier
Subscriber Identification Module
Specialized Mobile Radio
Service Management System
Short Message Service
Short Message Service Service Center
Short Message Service/Cell Broadcast
Short Message Service/Point-to-Point
Simple Mail Transfer Protocol
Simple Network Management Protocol
Small Office/Home Office
Safety of Life at Sea
Structured Query Language
Switching System
Signaling System No. 7
Service Switching Function
Secure Sockets Layer
Transmission Service at the DS1 Rate of
1.544 Mbps
Transmission Service at the DS3 Rate of
44.736 Mbps
Technical Advisor
Technical Advisory
Total Access Communications System
Telocator Alphanumeric Protocol
Time Assigned Speech Interpolation
Terabyte (Trillion Bytes)
Terabits per Second
Total Cost of Ownership
Transmission Control Protocol
Time Division Duplexing
Time Division Multiplexer
Time Division Multiple Access
Time Division Multiple Access with Time
Division Duplexing
Time Difference of Arrival
Time Domain Reflectometer
Transcend Enterprise Manager (3Com Corp.)
Trivial File Transfer Protocol
Telecommunications Industry Association
Tag Information Base
Telecommunications Management Network
Telocator Network Paging Protocol
User Agent Profile
Universal Asynchronous
Unspecified Bit Rate
User Datagram Protocol
User Datagram Protocol/Internet Protocol
Ultra High Frequency (238 MHz to 1.3 GHz)
Universal Licensing System
Universal Messaging System
Universal Mobile Telephone Service
Universal Mobile Telecommunications
United Nations
User-Network Interface
Uninterruptible Power Supply
Uniform Resource Locator
Ultra Small Aperture Terminal
Unshielded Twisted-Pair
Ultra Wide Band
Virtual Circuit
Volunteer Examiner-Coordinator
Voice Frequency
Very Fast Infrared
Very High Frequency (50–146 MHz)
Very Low Frequency (Less than 30 kHz)
Visitor Location Register
Very Large Scale Integration
Video on Demand
Virtual Private Network
Very Small Aperture Terminal
World Wide Web Consortium
Wireless Access Communications System
Wireless Application Environment
Wide Area Network
Wireless Access Point
Wireless Application Protocol
Wireless Application Service Provider
Web-Based Management
Wideband Code Division Multiple Access
Wireless Communications Service
Worldwide Digital Cordless Telephone
Wireless Ethernet Compatibility Alliance
Wired Equivalent Privacy
Weighted Fair Queuing (Cisco Systems)
Worldwide Geodetic System
Wireless Fidelity
Wireless Internet Service Provider
Wireless Local Area Network
Wireless Local Loop
Wireless Markup Language
Wireless Medical Telemetry Service
World Radio Conference
Wireless Session Protocol
Wireless Telephony Application
Wireless Telecommunications Bureau
World Wide Web
Exclusive Or
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Boldface page range indicates a main entry.
“A-block” licenses, 202
AAS (see Automated Auction System)
Absorption, 196
AC (see Authentication center)
Access control table manager, 467
Access points (AP), 1–6, 447–450
ACD (Automatic Call Distributor), 112
ACELP (algebraic code excited linear
predictive) algorithm, 264
ACL (see Asynchronous connectionless
Adaptive Differential Pulse Code
Modulation (ADPCM):
DECT, 83
PACS, 252
PHS, 274
voice compression, 382–385
WLL, 463
Advanced Encryption Algorithm
(AES), 413
Advanced intelligent networks
(AINs), 253
Advanced Mobile Phone Service
(AMPS), 6–8
cellular data communications, 34
FDMA, 120, 121
fraud management systems, 107
IMT, 186
software-defined radio, 327, 329, 330
TDMA, 366
AES (Advanced Encryption
Algorithm), 413
AGRAS (Air-Ground Radiotelephone
Automated Service), 9
AINs (advanced intelligent
networks), 253
AIOD (automatic identification of
outward dialed calls), 406
Air-Ground Radiotelephone
Automated Service (AGRAS), 9
Air-Ground Radiotelephone Service,
commercial aviation, 9–11
general aviation, 9
Alarms Group, 294–295
Algebraic code excited linear predictive
(ACELP) algorithm, 264
ALI (see Automatic location
Alphanumeric paging, 232–233
AlphStar, 91
AM (amplified modulation), 220
Amateur radio (HAM), 351
Amateur Radio Service, 12–15
Amazon.com, 264
American Bell Telephone
Company, 354
American National Standards
Institute (ANSI), 238, 251, 478
Ameritech, 162
Amplified modulation (AM), 220
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
AMPS (see Advanced Mobile Phone
AMTS (see Automated Marine
Telecommunications System)
ANSI (see American National
Standards Institute)
Antennas, microwave, 215
Antheil, George, 341
AP (see Access points)
Application service providers, wireless,
Applications Service Provider
Industry Consortium, 404
Arch Wireless, 323
ARQ (automatic repeat request), 140
Asynchronous connectionless (ACL)
links, 21–22
Asynchronous Transfer Mode (ATM):
LMDS, 201
routers, 304, 307
AT&T, 11, 35–36, 161–162, 178, 179,
183–185, 321–324, 340, 377, 378,
380, 404, 416
ATT (Auction Tracking Tool), 335
Attachment unit interfaces (AUIs), 195
Auction Tracking Tool (ATT), 335
AUIs (attachment unit
interfaces), 195
fraud management systems,
GMS, 145–146
wireless LAN security, 440
wireless management tools, 467
Authentication center (AC),
145–146, 240
Automated Auction System (AAS),
335, 337–338
Automated Marine
Telecommunications System
(AMTS), 208–209
Automatic Call Distributor
(ACD), 112
Automatic identification of outward
dialed calls (AIOD), 406
Automatic location identification
(ALI), 44, 393
Automatic paging, 232
Automatic repeat request (ARQ), 140
“B-block” licenses, 202
Base station controllers (BSCs), 143
Base station transceiver stations
(BTSs), 143
Base station transmitters, 235
Basic Exchange Telephone Radio
Service (BETRS), 17–18
Basic trading areas (BTAs), 201–202
BBC (British Broadcasting
Company), 354
BCCH (Broadcast Control
Channel), 145
Bearer services, 140–141, 375
Bell, Alexander Graham, 354
Bell Atlantic, 162
Bell Labs, 36, 48, 213
Bell Operating Companies (BOCs),
Bellcore, 251
BellSouth, 162, 406
BER (bit error rate), 314
BETRS (see Basic Exchange
Telephone Radio Service)
Bit error rate (BER), 314
Bluetooth, 18–27
applications, 19–20
points of convergence, 24–26
technology, 21–24
topologies, 20–21
wireless Intranet access, 432
WLANs, 452–453
BOCs (see Bell Operating Companies)
Boingo Wireless, 418, 423
Bossard, Bernard, 202–203
Bridges, 27–30
laser transmission, 195
routers, 305–306
British Broadcasting Company
(BBC), 354
Broadband communication
services, 223
Broadband fixed wireless access,
103–105, 418, 419
Broadband PCS, 264
Broadcast Control Channel
(BCCH), 145
BSCs (base station controllers), 143
BTAs (see Basic trading areas)
BTSs (base station transceiver
stations), 143
Business Radio Service, 281
Cable Antenna Relay Services
(CARS), 216
Cable networks, 304
Cable Services Bureau (FCC), 100
Cable television (CATV):
DBS, 93
PCS, 263
Call detail records (CDRs), 112–113
Call handoff, 364–365
Call pattern analysis, 107–108
Call processing, 62–63
Carrier Sense Multiple Access
(CSMA), 167
Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA):
HomeRF, 154, 156
wireless Internetworking, 428–429
CARS (Cable Antenna Relay
Services), 216
CAS (Customer Activation
System), 260
Category 5 cabling:
peer-to-peer networks, 243, 245, 249
telemetry, 359
wireless Internet access, 421
wireless Intranet access, 432
CATV (see Cable television)
CB Radio Service (see Citizens Band
Radio Service)
CBR (constant-bit-rate), 375
CCCH (Common Control
Channel), 145
CDCS (Continuous Dynamic Channel
Selection), 72
CDMA (see Code Division Multiple
CDPD (see Cellular Digital
Packet Data)
CEAs (component economic areas), 223
Cell sites, 31–34
cellular voice communications,
regulation, 33
site planning, 31–33
Cellular carriers, 357–358
Cellular data communications, 34–36
Cellular Digital Packet Data (CDPD):
cellular data communications,
wireless Internet access, 416
wireless IP, 434
Cellular networks, 6, 415–416
Cellular Positioning and Emergency
Messaging Unit, 138
Cellular technology:
cell sites, 31–34
data communications, 34–36
telephones, 36–48
voice communications, 48–55
Cellular telephones, 36–48
CDMA, 59
cellular voice communications,
features and options, 40–42
GPS, 127–138
Internet-enabled, 43–48
location-reporting technology, 42–43
MTSO, 217–219
system components, 37–40
third-generation, 46–47
voice communications, 48–55
WTB, 481
Cellular voice communications, 48–55
applications, 49–50
network optimization, 53–54
regulation, 54–55
technology components, 50–53
CellularVision, 203
Central office exchange (Centrex),
wireless, 405–409
Centralized trunked system, 283–284
Centrex (see Central office exchange)
“Chipping code,” 446
Cincinnati Bell, 161
Cingular, 325, 340
Circuit-switched data (CSD), 128
Cisco Systems, 391, 404
Citizens Band (CB) Radio
Service, 55–59
FRS, 97
Al Gross, 230
LPRS, 208
Clarke, Arthur C., 311, 312
Class A bearer service, 375
Class B bearer service, 375
Class C bearer service, 375
Class D bearer service, 375
CLECs (see Competitive Local
Exchange Carriers)
Closed systems, 441–442
CMIP (Common Management
Information Protocol), 259
CMRS (see Commercial Mobile Radio
CNN (TV network), 394
Code Division Multiple Access
(CDMA), 59–67
AMPS, 7–8
cellular voice communications, 51
FDMA, 120, 122
fraud management systems, 107
GPRS, 130
iDEN, 174
IMT, 192
over-the-air activation, 226
PCS, 265–266
PCS 1900, 239
satellite technology, 319
SMS, 323
software-defined radio, 330
spread-spectrum radio, 342
system features, 62–66
TDMA, 365
UMTS, 371
wideband usage, 60–61
WLL, 455, 457
Commercial Aviation Air-Ground
Systems, 9–11
Commercial Mobile Radio Service
(CMRS), 8, 54, 333
Common Carrier Bureau (FCC), 100
Common Control Channel
(CCCH), 145
Common Management Information
Protocol (CMIP), 259
Communications and measurement
systems, 370
Communications indicator, 466
Compaq Computer, 404
Competitive Local Exchange Carriers
(CLECs), 67–70
fixed wireless access, 104–105
Competitive Local Exchange Carriers
(CLECs) (Cont.):
ILECs, 163
LMDS, 199–200, 202
wireless Internet access, 419
Component economic areas
(CEAs), 223
data, 75–80
voice, 380–388, 382–385
wireless IP, 435
Comsat, 321
Connectivity, IR, 168–171
Constant-bit-rate (CBR), 375
Consumer Information Bureau
(FCC), 101
Continuous Dynamic Channel
Selection (CDCS), 72
Continuously Variable Slope Delta
(CVSD), 22, 386–387
Coral Systems, 107
Cordless telecommunications (CT),
cellular vs., 70–71
DECT, 82–87
standards, 71–73
Corio, 403
CRC-32 checksum, 390–391
CSD (circuit-switched data), 128
CSMA/CA (see Carrier Sense Multiple
Access with Collision Avoidance)
CSMA (Carrier Sense Multiple
Access), 167
CT (see Cordless telecommunications)
CT0, 71
CT1, 71
CT2, 71, 120–121
CT3, 71, 72
Customer Activation System
(CAS), 260
CVSD (see Continuously Variable
Slope Delta)
CyberStar, 420
D-AMPS (see Digital American
Mobile Phone Service)
DACs (digital-to-analog
converters), 327
DAMPS (see Digital Advanced Mobile
Phone Service)
Data compression, 75–80
DBS, 90
external data compression, 78–79
link compression, 77–78
mixed-channel payload data
compression, 78
payload compression, 77
TCP/IP header compression, 76–77
Data dispatch, 231
Data mining, 112
DB (see Decibel)
DBS (see Direct Broadcast Satellite)
DCC (see Digital Control Channel)
DCCH (see Digital Control Channel)
DCS 1800 (Digital Cellular System
1800), 86
Decentralized trunked system,
Decibel (dB), 80–82
DECT (see Digital Enhanced Cordless
DECT/GSM Interworking Profile, 84
Defense Switched Network (DSN), 407
DES (see Digital Encryption
Destination Address (DA), 27–28
DID (see Direct inward dialing)
Differential Quadrature Phase-Shift
Keying (DQPSK), 361, 364
Digital Advanced Mobile Phone
Service (DAMPS), 7–8
IMT, 187
Digital American Mobile Phone
Service (D-AMPS), 360
Digital Cellular System 1800 (DCS
1800), 86
Digital Control Channel (DCCH),
226, 365
Digital Encryption Standard
(DES), 413
Digital Enhanced Cordless
Telecommunications (DECT):
cordless telecommunications, 71, 72
TDMA, 360
wireless PBX, 479
WLANs, 451
Digital Messaging Service, 329
Digital Satellite Service (DSS), 91
Digital signal processor (DSP):
data compression, 79
software-defined radio, 327
WLL, 457
Digital Subscriber Line (DSL):
IXCs, 184
MMDS, 220
peer-to-peer networks, 244
routers, 304
Digital-to-analog converters (DACs),
Digitally Enhanced Cordless
(DECT), 82–87
advantages, 82–84
HomeRF, 152
WLAN, 86
WLL, 84–86
DirecPC, 88, 420
Direct Broadcast Satellite
(DBS), 87–94
equipment, 91–92
MVDDS, 224, 225
operation, 90
programming, 92
regulation, 93
service providers, 91
Direct inward dialing (DID), 405, 406
Direct outward dialing (DOD), 406
Direct-sequence spread spectrum
(DSSS), 446
Direct sequence spreading, 344–346
Directional antenna, 450, 451
DirecTV, 87–88
DirecWAY, 89
Dish antenna, 91
DoCoMo, 159–161
DOD (direct outward dialing), 406
DoJ (U.S. Department of Justice), 162
DQPSK (see Differential Quadrature
Phase-Shift Keying)
DSL (see Digital Subscriber Line)
DSN (see Defense Switched Network)
DSP (see Digital signal processor)
DSS (Digital Satellite Service), 91
DSSS (direct-sequence spread
spectrum), 446
Dynamic WEP Key Management, 391
E911 (see Enhanced 911)
Internet-enabled mobile phones, 44
PHS, 278
wireless messaging, 470–473
E-TDMA (Expanded Time Division
Multiple Access), 51
Eavesdropping, 287, 390
“Echelon,” 289
Echo (satellites), 311
EchoStar, 91
EDGE (see Enhanced Data Rates for
Global Evolution)
EDS (company), 404
EIR (see Equipment Identity
Electromagnetic interference
(EMI), 195
Electronic Mail Broadcast to A
Roaming Computer (EMBARC),
Electronic Serial Number (ESN), 218
EMBARC (see Electronic Mail
Broadcast to A Roaming
Emergency services, 392–394
EMI (electromagnetic
interference), 195
Encoding devices, 235
data compression, 76
fraud management systems, 108
GSM, 145–146
WEP, 389–391
Wi-Fi, 413
wireless IP, 435
wireless LAN security, 439–440
Enforcement Bureau (FCC), 100
Enhanced 911 (E911), 42–43, 392–394
Enhanced Data Rates for Global
Evolution (EDGE), 95–96, 129
Enhanced Variable Rate Coder
(EVRC), 457
EPFD (see Equivalent power flux
EPFD (equivalent power flux
density), 223
EPs (see Extension points)
Equipment Identity Register (EIR),
144, 146
Equivalent power flux density
(EPFD), 223
Ericsson, 329, 407
ESN (Electronic Serial Number), 218
HomeRF, 157
IR, 166, 167
microwave communications, 215
peer-to-peer networks, 244–245
repeaters, 303
routers, 307
Wi-Fi, 411, 412
wireless Internetworking, 426–427
Ethernet History Group, 293
Ethernet Object Groups, 292–297
Ethernet Statistics Group, 292–293
Etrieve, 403
European Telecommunication
Standards Institute (ETSI):
DECT, 82
UMTS, 371
EVRC (Enhanced Variable Rate
Coder), 457
Expanded Time Division Multiple
Access (E-TDMA), 51
Extension points (EPs), 448, 450
External data compression, 78–79
FACCH (Fast Associated Control
Channel), 145
Family Radio Service (FRS),
97–99, 127
Fast Associated Control Channel
(FACCH), 145
Fast Infrared (FIR) protocol, 169
PDAs, 272
PHS, 278
FCC (see Federal Communications
FDD (see Frequency Division
FDMA (see Frequency Division
Multiple Access)
Federal Communications Commission
(FCC), 99–103
Amateur Radio Service, 12–15
BETRS, 17, 18
Bluetooth, 27
CB Radio, 56, 57
cell sites, 33
cellar voice communications, 48, 49,
CLECs, 67, 69
DBS, 93
FRS, 97–98
GMDSS, 124
GMRS, 126, 128
HomeRF, 157
ILECs, 162
IMT, 190–191
IVDS, 181–183
IXCs, 184–185
laser transmission, 195
LMDS, 201–202
location-reporting technology, 42–43
LPFM, 205–208
LPRS, 208–210
Maritime Mobile Service, 212
microwave communications, 214,
MVDDS, 223–224
operating bureaus, 100–101
other offices, 101
PCS, 264
PLMRS, 279–281, 282, 284
radio communication interception,
reorganization plan, 102
Rural Radiotelephone Service, 310
satellite communications, 313–314
SMR, 332
software-defined radio, 330–331
spectrum auctions, 334–338
spectrum planning, 338–340
spread-spectrum radio, 346, 348
UWB, 367–368, 370, 371
WCS, 409–410
wireless E911, 392, 393
wireless Internet access, 421
wireless investment fraud, 483–486
wireless LNP, 464–465
WMTS, 468–470
WTB, 481, 483
Federal Telecommunications System
(FTS), 406–407
Federal Trade Commission (FTC),
FHSS (see Frequency-hopping spread
Fiberoptics, 195
Filters Group, 295
FIR (Fast Infrared) protocol, 169
wireless IP, 436
wireless LAN security, 442–444
Fixed wireless access (FWA), 103–105
Internet, 418–419
WLL, 455, 456
FM (frequency modulation), 220
Forward Control Channel
(FOCC), 357
FPF (free fraud protection
feature), 106
Frame erasure, 362
Frame relay, 77, 304, 308
Framing, 361–363
Fraud management systems, 105–119
authentication, 108–109
call pattern analysis, 107–108
data mining, 112
PINs, 106–107
procedures, 115–119
radiofrequency fingerprinting,
real-time usage reporting,
service providers, 115–117
smart cards, 113–115
subscribers, 117–118
voice verification, 110–112
FraudBuster, 107–108
FraudWatch Pro, 112–113
Free fraud protection feature
(FPF), 106
Frequency Division Duplexing (FDD),
Frequency Division Multiple Access
(FDMA), 60, 119–122
cordless, 71
GSM, 144
satellite technology, 318
Frequency hopping, 346–348
Frequency-hopping spread spectrum
(FHSS), 445–446
Frequency modulation (FM), 220
Frequency reuse, 7
Frequency select, 467
FRS (see Family Radio Service)
FTC (see Federal Trade Commission)
FTS (see Federal Telecommunications
FWA (see Fixed wireless access)
3G mobile communications systems
(see Third-generation mobile
communications systems)
General Access Pool, 281–282
General Aviation Air-Ground
systems, 9
General Mobile Radio Service
(GMRS), 125–128
General Motors, 138
General Packet Radio Service
(GPRS), 47, 128–131
EDGE, 95, 96
GSM, 140
i-Mode, 161
iDEN, 174
SMS, 323
GEO (geostationary-earth-orbit)
satellites, 312
Geographic Information System
(GIS), 137, 335–336
Geostationary-earth-orbit (GEO)
satellites, 312
GIS (see Geographic Information
Global Maritime Distress and Safety
System (GMDSS), 123–125
Global Positioning System (GPS), 43,
applications, 133–137
and cellular, 137–138
components, 132
PDAs, 267
system operation, 132–133
wireless E911, 393
Global System for Mobile (GSM)
telecommunications, 139–147
authentication and security, 145–146
Global System for Mobile (GSM)
telecommunications (Cont.):
CDMA, 66–67
channel derivation and types,
FDMA, 120
fraud management systems, 107,
GPRS, 129, 131
iDEN, 172
IMT, 186–187
ITM, 187
network architecture, 141–144
PCS 1900, 239, 242–243, 262
PHS, 273
services, 139–141
SMS, 322, 323, 325
software-defined radio, 329
TDMA, 360
WLL, 455
GMDSS (see Global Maritime
Distress and Safety System)
GMRS (see General Mobile Radio
Google, 265
GPRS (see General Packet Radio
GPRs (see Ground-penetrating radar
GPS (see Global Positioning System)
Graphical User Interfaces (GUIs), 113
Gross, Al, 229–230
Ground-penetrating radar systems
(GPRs), 368–369
GSM 1900, 239
GSM telecommunications (see Global
System for Mobile
GTE, 161, 162
GTE Airfone, 10, 11
GUIs (Graphical User Interfaces), 113
HAM (amateur) radio, 351
“Hands-free operation,” 40
Handyphones (see Personal
Handyphone System)
HDLC (High-Level Data Link
Control), 77
HDTV (see High-definition television)
Hertz, Heinrich R., 149, 151, 352
Hertz (Hz), 149–152
High-definition television (HDTV),
87, 88
High-Level Data Link Control
(HDLC), 77
High-speed circuit-switched data
GPRS, 128
GSM, 140
HLR (see Home Location Register)
HNS (see Hughes Network Systems)
Home Location Register (HLR):
GSM, 143–144
PCS 1900, 240
Home Radio Frequency Working Group
(HomeRFWG), 152, 153, 157–158
Home RadioFrequency (HomeRF)
Networks, 152–158
applications, 154–155
future, 156–158
network topology, 155–156
WLANs, 451–454
HomeRF (see Home RadioFrequency
HomeRFWG, Home Radio Frequency
Working Group
Host Table Group, 293–294
Host Top N Group, 294
HSCSD (see High-speed circuitswitched data)
HTML (see HyperText Markup
HTTP (see HyperText Transfer
Hubs, wireless PBX, 478
Hughes Network Systems (HNS), 420
HyperText Markup Language
(HTML), 46
i-Mode, 160
WAP, 395
HyperText Transfer Protocol (HTTP),
395, 398
Hz (see Hertz)
i-Mode (see Information mode)
IBM, 375, 404
iDEN (see Integrated Digital
Enhanced Network)
Ideographic paging, 233
IEEE 802.11 standards (Wi-Fi), 272,
access points, 3, 5
GPRS, 130
HomeRF, 152, 156–158
WEP, 389
wireless Intranet access, 432
wireless LAN security, 439, 440
WISPs, 422–425
WLANs, 450–451, 451–454
IETF (Internet Engineering Task
Force), 399
IF (see Intermediate frequency)
ILECs (see Incumbent Local
Exchange Carriers)
IM (instant messaging), 325
Imaging systems, 368
IMEI (see International Mobile
Equipment Identity)
IMO (see International Maritime
IMSI (see International mobile
subscriber identity)
IMT (see International Mobile
IMT-2000 (see International Mobile
Incumbent Local Exchange Carriers
(ILECs), 161–163
CLECs, 67–69
IXCs, 183–185
LMDS, 199
microwave communications, 214
wireless Internet access, 419
Industrial, scientific, and medical
(ISM) bands, 343, 421
Industrial/Business Pool, 281
Industrial espionage, 289
Industrial or Land Transportation
Radio Services, 281
Information mode (i-Mode), 159–161
Infrared Data Association (IrDA),
Infrared Financial Messaging (IrFM),
Infrared (IR) networking, 164–172
Infrared (IR) networking (Cont.):
computer connectivity, 168–171
LANs, 164–165
MAC, 167–168
operating performance, 166–167
PDA, 272–273
system components, 165–166
WLANs, 446
Inmarsat (see International Maritime
Satellite Organization)
InphoMatch, 325
Instant messaging (IM), 325
Instant Wireless Ethernet Bridge, 29
Instructional Television Fixed Service
(ITFS), 190
Integrated Digital Enhanced Network
(iDEN), 172–175
call setup, 173–174
future, 174
Integrated Services Digital Network
CLECs, 68
GSM, 140, 143
IXCs, 183
MTSO, 217
PACS, 252
PCS 1900, 240
routers, 304, 307, 308
satellite technology, 320
UMTS, 373
wireless Centrex, 406
Integrity check (IC) field, 390–391
Intel Corp., 403
Intelsat, 320
Interactive Messaging, 325
Interactive television (ITV), 175–181
applications, 176–178
market complexity, 178–179
potential market barriers, 179–180
Interactive Video and Data Service
(IVDS), 181–183
Interception, 343
Interdepartment Radio Advisory
Committee (IRAC), 339
Interexchange Carriers (IXCs),
bypass, 183–184
fixed wireless access, 105
long-distance market, 184–185
Interexchange Carriers (IXCs) (Cont.):
wireless Internet access, 419
Interference, 343
Intermediate frequency (IF), 221, 328
International Bureau (FCC), 100
International Maritime Organization
(IMO), 123–125
International Maritime Satellite
Organization (Inmarsat),
International Mobile Equipment
Identity (IMEI):
GSM, 142, 144, 146
International mobile subscriber
dentity (IMSI):
fraud management systems, 114
GSM, 142
International Mobile
Telecommunications-2000 (IMT2000), 46
goals, 188–190
IMT, 186–193
radio interface technology, 191–192
UMTS, 372
International Mobile
Telecommunications (IMT),
generations, 186–188
goals of IMT-2000, 188–190
GSM, 140–141
radio interface technology, 191–192
spectrum allocations, 190–191
International Morse Code, 349–350
International Telecommunication
Union (ITU), 46
GMDSS, 123
IMT, 186, 187, 190–192
satellite communications, 313
i-Mode, 159–161
MVDDS, 223
PACS, 253
PHS, 278
WAP, 394, 395
wireless, 414–422
Internet-enabled mobile phones,
Internet Engineering Task Force
(IETF), 399
Internet Protocol (IP):
cellular data communications, 35
GPRS, 128–129
IMT, 187–188
WAP, 395, 397
Internet service providers (ISPs):
DBS, 89
IXCs, 183
Ionica, 460
IP (see Internet Protocol)
IR networking (see Infrared
IRAC (Interdepartment Radio
Advisory Committee), 339
IrDA (see Infrared Data Association)
IrFM (see Infrared Financial
IS-54 Standard, 361, 363
IS-95 Standard, 59, 239
IS-127 Standard, 457
ISDN (see Integrated Services Digital
ISM bands (see Industrial, scientific,
and medical bands)
ISPs (see Internet service providers)
ITFS (Instructional Television Fixed
Service), 190
ITU (see International
Telecommunication Union)
ITV (see Interactive television)
IXCs (see Interexchange Carriers)
Jamming, 343
Japanese Digital Cellular (JDC), 187
Java, 161
JDC (Japanese Digital Cellular), 187
J2ME technology, 173
Joint Photographic Experts Group
(JPEG), 75–76
Key change administration, 440–441
Ki (unique key), 115
Kyocera Corp., 278
Lamarr, Hedy, 341–342
LANs (see Local area networks)
LAPB (Link Access Procedure—
Balanced), 77
Laser diodes, IR, 165–166
Laser transmission, 195–198
LATAs (local access and transport
areas), 183
LDs (see Laser diodes)
LECs (Local Exchange Carriers), 8
LEDs (see Light-emitting diodes)
LEO satellites (see Low-earth-orbit
Light-emitting diodes (LEDs),
Limited Size Messaging (LSM), 260
Link Access Procedure—Balanced
(LAPB), 77
Link compression, 77–78
Link test diagnostics, 466
Linksys, 4, 29, 308, 309
LLC (Logical Link Control), 28
LMDS (see Local Multipoint
Distribution Service)
LNP (see Local number portability)
Local access and transport areas
(LATAs), 183
Local area networks (LANs):
bridges, 27–30
data compression, 77–78
HomeRF, 154, 156
IR, 164–168, 172
laser transmission, 195
microwave communications, 214, 215
peer-to-peer networks, 243
repeaters, 302—303
routers, 305, 308
telemetry, 359
VSATs, 316
WEP, 389, 391
Wi-Fi, 411, 413
wireless Internetworking, 425–429
wireless security, 437–444
Local Exchange Carriers (LECs), 8
Local Multipoint Distribution Service
(LMDS), 198–205
applications, 199–200
CLECs, 68
development history, 202–204
fixed wireless access, 104
IXCs, 184
Local Multipoint Distribution Service
(LMDS) (Cont.):
microwave, 216
microwave communications, 213,
MMDS, 220
operation, 200–201
potential problems, 204–205
spectrum auctions, 201–202
wireless Internet access, 419
Local number portability (LNP),
Location-reporting technology, 42–43
Lockheed Martin, 321
Logical Link Control (LLC), 28
Long-distance carriers, 183
Lotus Notes, 404
Low-earth-orbit (LEO) satellites,
313, 420
Low-power frequency-modulated
(LPFM) radio services, 205–208
Low-Power Radio Service (LPRS),
LP10 service, 206
LP100 service, 206
LPFM radio services (see Low-power
frequency-modulated radio
LPRS (see Low-Power Radio Service)
LSM (Limited Size Messaging), 260
MAC (see Media Access Control)
Management information base (MIB),
290–296, 298–301
Marconi, Guglielmo, 351–354
Maritime Fixed Service, 212
Maritime mobile-Satellite Service,
Maritime Mobile Service, 211–212
Maritime Radiodetermination
Service, 212
Mass Media Bureau (FCC), 101
Master station radio, microwave, 215
Master-switching centers, 51
MAUs (multiple access units), 165
MCs (see Message centers)
MDLP (Mobile Data Link Layer
Protocol), 261
MDS (see Multipoint Distribution
Media Access Control (MAC):
bridges, 28
IR, 167–168
RMON, 291–292, 296–300
Medical systems, 369
Mentat, Inc., 315
MEO (middle-earth-orbit)
satellites, 312
Mesh topology, 428–429
Message centers (MCs), 240, 259
Metricom, 416–418
MIB (see Management
information base)
MicroProfile, 106–107
Microsoft, 176, 178, 179, 270–271
Microwave communications,
applications, 214
LMDS, 198
MMDS, 220
network configurations, 215–216
regulation, 216–217
wireless cable, 216
Middle-earth-orbit (MEO)
satellites, 312
MIN (see Mobile Identification
Mixed-channel payload data
compression, 78
MMDS (see Multichannel Multipoint
Distribution Service)
Mobile communications:
FDMA, 119–122
GSM, 139–147
IMT, 186–183
PHS, 273–279
Mobile Data Link Layer Protocol
(MDLP), 261
Mobile Identification Number (MIN),
114, 219
Mobile messaging, 231
Mobile Packet Data, 320
Mobile radio, iDEN, 172–174
Mobile satellite communications,
Mobile station sign-on, 62
Mobile stations (MSs), 141–142
Mobile Switching Centers (MSCs):
fraud management system, 112
GSM, 141, 143–144
PCS 1900, 240
telemetry, 358
Mobile telephone service, 6–8
Mobile Telephone Switching Office
(MTSO), 6–7, 31, 217–219
Mobile Terminals, 260
Mobile transport serving office
(MTSO), 50
Modems, PDA, 272
Morse, Samuel Finley Breese,
Morse Code, 349–352
Motorola, 138, 172–174, 178, 236,
323, 329, 470, 471
Moving Pictures Experts Group
(MPEG), 75
MP3, 171
MPEG (Moving Pictures Experts
Group), 75
MSCs (see Mobile Switching
MSs (see Mobile stations)
MTSO (see Mobile Telephone
Switching Office)
MTSO (mobile transport serving
office), 50
MTSO/MSC-based network, 458–459
Multichannel Multipoint Distribution
Service (MMDS), 220–222
channel derivation, 221–222
fixed wireless access, 104
IXCs, 184
microwave, 216
microwave communications, 213, 216
operation, 220–221
wireless Internet access, 419
Multichannel Video Distribution and
Data Service (MVDDS), 223–224
Multichannel video program distribution (MVPD), 93
Multimode/multiband systems,
Multipath, 343
Multiple access units (MAUs), 165
Multipoint Distribution Service
(MDS), 190, 220
MVDDS (see Multichannel Video
Distribution and Data Service)
MVPD (multichannel video program
distribution), 93
N-AMPS (see Narrowband AMPS)
NAM (numeric assignment
module), 38
Narrowband AMPS (N-AMPS),
121, 329
Narrowband fixed wireless access,
103–104, 418–419
Narrowband PCS, 263–264
National Aeronautics and Space
Administration (NASA), 311
National Coordination Committee
(NCC), 483
National Telecommunications and
Information Administration
(NTIA), 216–217, 338–340
UWB, 368, 371
Natural Voices, 378
Navi Roller, 45
Navstar satellites, 131
NCC (National Coordination
Committee), 483
Network interface card (NIC), 243,
245, 248, 249
Network interface units (NIUs), 201
Network management system (NMS),
Network optimization, 53–54
cable, 304
HomeRF, 152–158
iDEN, 172
Neural tree networks, 110–111
Nextel, 174
NextWave Telecom, 340
NIC (see Network interface card)
NiCd batteries (see Nickel-cadmium
Nickel—metal hydride (NiMH)
batteries, 40
Nickel-cadmium (NiCd) batteries,
NiMH (NiMH) batteries, 40
911, 392–394
1900-MHz Personal Communication
Service (PCS 1900), 238–243
advanced services and features,
architecture, 239–240
smart cards, 242
NIUs (network interface units), 201
NMS (see Network management
NMT (Nordic Mobile Telephone), 186
Nokia, 44–46, 188, 324, 329
Non-spread-spectrum radio, 343–344
Nordic Mobile Telephone (NMT), 186
Nortel, 460, 463
Notifications Group, 295–296
NTIA (see National
Telecommunications and
Information Administration)
NTT, 273
Numeric assignment module
(NAM), 38
Numeric paging, 232
Nynex, 162
OFDM (Orthogonal Frequency
Division Multiplexing), 412
1000BaseT Gigabit Ethernet, 303
OnStar, 138
Open Shortest Path First (OSPF),
306, 307
Open Systems Interconnection
(OSI) model:
bridges, 28–30
pACT, 260
repeaters, 302
routers, 304
wireless PBX, 479
OpenView, 4, 463
Operation Desert Storm, 133–134
Operations support system (OSS):
CLECs, 69
ILECs, 162
PCS 1900, 240
WLL, 455
Oracle, 433
ORiNOCO, 442, 465–467
Orthogonal Frequency Division
Multiplexing (OFDM), 412
OSI (see Open Systems
Interconnection model)
OSPF (see Open Shortest Path First)
OSS (see Operations support system)
Over-the-air service activation,
Pacific Bell, 407, 408
Pacific Telesis, 162
Packet Capture Group, 295
Packet-filtering firewalls, 442, 443
Packet radio networks, 416–418
cellular data communications,
GPRS, 47
PACS (see Personal Access
Communications Systems)
pACT (see Personal Air
Communications Technology)
pACT data intermediate system
(PDIS), 258
PageWriter, 236
Paging, 229–238
applications, 231
e-mail, 471–472
origins, 229–230
pACT, 254–256
signaling protocols, 237–238
system components, 233–237
types of services, 231–233
WTB, 481–482
Paging Channel (PCH), 145
Palm Computing, 267
Palm III, 135–136
Palm OS, 270
Palm V, 267
PBX (see Private Branch Exchange;
Public Branch Exchange)
PCH (Paging Channel), 145
PCM (see Pulse Code Modulation)
PCMCIA (Personal Computer
Memory Card International
Association), 239
PCN (Personal Communications
Networks), 139
PCS (see Personal Communications
PCS 1900 (see 1900-MHz Personal
Communication Service)
PDAs (see Personal digital assistants)
PDBS (see pACT data base stations)
PDBS (PACT data base stations), 258
PDC (Personal Digital Cellular), 360
PDIS (pACT data intermediate
system), 258
PDN (Public Data Networks), 240
Peer-to-peer networks, 243–250
configuration details, 245–249
Windows networking, 244–245
WLANs, 447–448
Personal Access Communications
Systems (PACS), 251–253, 409
Personal Air Communications
Technology (pACT), 254–261
applications, 255–257
network management system,
system overview, 257–259
voice compression, 383
Personal call management, 241
Personal Communications Networks
(PCN), 139
Personal Communications Services
(PCS), 262–266
broadband and narrowband,
cell sites, 33
fraud management systems,
113, 114
GSM, 139
network, 262–263
PACS, 251, 253
PCS 1900, 238–239
software-defined radio, 326
TDMA, 361
3G migration, 265–266
wireless E911, 392
wireless Internet access, 416
WTB, 482
Personal Computer Memory Card
International Association
(PCMCIA), 239
Personal digital assistants (PDAs),
47, 266–273
applications, 268
components, 268–273
Personal digital assistants (PDAs)
GPRS, 130
i-Mode, 160
IR, 168
Personal Digital Cellular
(PDC), 360
Personal Handyphone System (PHS),
advantages over cellular, 274
applications, 275–276
handsets, 274–275
network architecture, 276–277
PACS, 251, 252
PCS, 262
service features, 277–278
voice compression, 383
Personal identification
numbers (PINs):
fraud management systems,
106–107, 109–111
GSM, 141, 142
PCS 1900, 242
Personal Wireless
Telecommunications (PWT), 479
Phone breaking, 119
PHS (see Personal Handyphone
Piconets, 18, 20, 432
PIN (positive-intrinsic-negative), 166
Ping Pong, 325
PINs (see Personal identification
PLMRS (see Private Land Mobile
Radio Services)
Plumtree, 433
Pocket PC platform, 270–271
PocketNet, 416
POCSAG (see Post Office Code
Standardization Advisory Group)
“Point and play,” 170
Point-of-sale (POS), 170
Point-to-multipoint microwave
systems, 215
Point-to-Point Protocol (PPP), 77
Point-to-point topology, 429, 430
Port Operations Service, 212
POS (point-of-sale), 170
Positive-intrinsic-negative (PIN), 166
Post Office Code Standardization
Advisory Group (POCSAG),
Power control, CDMA, 64–65
PPP (Point-to-Point Protocol), 77
PrimeStar, 91
CDMA, 64
ITV, 180
Private Branch Exchange (PBX):
cellular voice communications, 53
cordless, 72, 73
fraud management systems, 111
LMDS, 201
wireless Centrex, 405, 406
Private Land Mobile Radio Services
(PLMRS), 279–285
applications, 282–283
General Access Pool, 281–282
Industrial/Business Pool, 281
PCS 1900, 240
Public Safety Radio Pool, 280–281
radio trunking, 283–284
Proximity I, 460, 463
PSAP (see Public safety
answering point)
PSTN (see Public Switched Telephone
PSTN-based direct connect, 458
Public Data Networks (PDN), 240
Public safety answering point
(PSAP), 43, 392–394
Public Safety Radio Pool, 280–281
Public Switched Telephone Network
cell sites, 31
DECT, 83–84
fixed wireless access, 103
FRS, 97
GSM, 143
HomeRF, 154, 155
microwave communications, 213
MTSO, 217, 219
paging, 229, 235
PCS, 263
PCS 1900, 240
PHS, 275
Rural Radiotelephone Service, 310
Public Switched Telephone Network
(PSTN) (Cont.):
satellite technology, 314
SMR, 332
WCS, 410
wireless Internet access, 418
WLL, 455
Pulse Code Modulation (PCM):
Bluetooth, 22
TDMA, 363
voice compression, 381–382
PWT (Personal Wireless
Telecommunications), 479
Quadrature amplitude modulation
(QAM), 172
Qualcomm, 403
RACH (Random Access Channel), 145
Radio communication:
GMDSS, 123–125
HomeRF, 152–158
Maritime Mobile Service, 211
WLANs, 446–447
Radio communication interception,
Radio exchanges, 407
Radio frequency interference
(RFI), 195
Radio interface technology, 191–192
Radio resource management
(RRM), 259
Radio services:
Air-Ground Radiotelephone, 8–12
Amateur Radio Service, 12–15
BETRS, 17–18
CB, 55–59
FRS, 97–99
GMRS, 125–128
GPRS, 128–131
LPFM, 205–206
LPRS, 208
PLMRS, 279–285
Rural Radiotelephone
Service, 310
Radio trunking, 283–284
Radio waves (microwave), 213
Radiofrequency fingerprinting,
Radiofrequency (RF), 33, 328
RADIUS (see Remote Authentication
Dial-In User Service)
Rand McNally, 136
Random Access Channel (RACH), 145
RC4 encryption, 390
Real-time usage reporting, 112–113
RECC (Reverse Control Channel), 357
Receiver-decoder unit, 91
Regenerators, 303
Remote Authentication Dial-In User
Service (RADIUS), 440–441, 444
Remote control, 92
Remote Monitoring (RMON), 290–301
applications, 291–292
Ethernet Object Groups, 292–297
RMON II, 299–301
Token Ring Extensions, 297–299
Remote radio transceiver, 216
Repeaters, 126, 301–304
Residential service system
(RSS), 460–461
Reuters, 394
Reverse Control Channel (RECC), 357
RF (see Radiofrequency)
RFI (radio frequency interference), 195
Ricochet service, 416–418
Ring Station Configuration, 299
Ring Station Configuration
Control, 298
Ring Station Control Table, 297–298
Ring Station Order, 299
Ring Station Table, 298
RIP (see Routing Information Protocol)
RJ45 jacks, 243, 245, 249
RMON (see Remote Monitoring)
RMON II, 299–301
Routers, 304–309
protocols, 306–307
routing types, 306
types (routers), 307–309
Routing Information Protocol (RIP),
RRM (radio resource management), 259
RSS (see Residential service system)
Rural Radiotelephone Service,
17–18, 310
Safety of Life at Sea (SOLAS)
Convention, 123, 125
Satellite communications, 311–314
Satellite Home Viewer Improvement
Act of 1999 (SHVIA), 93
Satellite technology, 314–321
communications protocols, 317–319
mobile satellite communications,
network management, 316–317
VSAT, 316
wireless Internet access, 419–420
DBS, 87–94
GPS, 131–133
SBC (see Southwestern Bell
Scanners, 288–289
Scattering, 196
Scatternet, 20
SCF (service control function), 374
SCO (see Synchronous connectionoriented links)
SDCCH (Stand-Alone Dedicated
Control Channel), 145
SDF (see Service data function)
SDF (service data function), 374
SDMA (see Space Division Multiple
SEC (Securities and Exchange
Commission), 485
Secure Sockets Layer (SSL), 159
Securities and Exchange Commission
(SEC), 485
GMS, 145–146
peer-to-peer networks, 247
telemetry, 355–356
UWB, 369
WEP, 389–391
Wi-Fi, 413
wireless IP, 435, 436
wireless LAN, 437–444
Selective Operator-Assisted Voice
Paging, 231–232
September 11, 2001 terrorist
attacks, 483
Serial Infrared (SIR) protocol, 169
Service control function (SCF), 374
Service data function (SDF), 374
Service providers:
DBS, 91
fraud management, 115–117
Service Set Identifier (SSID), 438–439
Shared Wireless Access Protocol
(SWAP), 153–156
HomeRF, 153, 154–156
Shimmer, 196
Ship Movement Service, 212
Short Mail, 325
Short Messaging Service (SMS), 44,
GSM, 140
PCS 1900, 241
SHVIA (Satellite Home Viewer
Improvement Act of 1999), 93
SID (see System Identification Code)
Signal attenuation, 302
SIM (see Subscriber Identification
Simple Network Management
Protocol (SNMP):
AP, 4
pACT, 259, 260
peer-to-peer networks, 249
RMON, 290, 294, 296
wireless management tools,
Single-bit errors, 363
Single-key callback, 231
SIR (Serial Infrared) protocol, 169
Site monitor, 466–467
Skytel, 323, 471
SkyX Gateway, 315
Smart cards, 113–115, 242
SMR (see Specialized Mobile Radio)
SMS (see Short Messaging Service)
SNA (see Systems Network
SNA (Systems Network
Architecture), 375
SNET (Southern New England
Telephone), 161
SNMP (see Simple Network
Management Protocol)
Software-defined radio, 326–332
generations, 326–327
Software-defined radio (Cont.):
multimode/multiband, 328–330
operation, 327–328
regulation, 330–331
SOLAS (see Safety of Life at Sea
Source Routing Statistics, 298
Southern New England Telephone
(SNET), 161
Southwestern Bell
Communications, 406
Southwestern Bell Communications
(SBC), 162–163
Space Division Multiple Access
IMT, 192
SPASUR radar system, 209
Spatial diversity, 65–66
Specialized Mobile Radio (SMR),
332–334, 392
Specialized Mobile Radiowireless
Application Protocol, 394–401
WAP 2.0, 399–400
WAP applications environment,
Spectrum allocations, IMT, 190–191
Spectrum auctions, 201–202, 334–338
Spectrum planning, 338–341
Speech software, 377–278
SpeechWorks, 380
Spread-spectrum radio, 341–348
frequency assignment, 343–344
spreading, 344–348
Sprint, 183, 185, 264, 265,
322–323, 325
Sputnik, 311
SSID (see Service Set Identifier)
SSL (Secure Sockets Layer), 159
Stand-Alone Dedicated Control
Channel (SDCCH), 145
Star topology, 428
Stream cipher, 390
StreetFinder, 136
Subscriber Identification Module (SIM):
fraud management systems,
GSM, 140–142, 144, 145
PCS 1900, 242
Sun Microsystems, 404
Surveillance systems, 369
Swift64, 320
Synchronous connection-oriented
(SCO) links, 21, 22
System Identification Code (SID),
219, 220
Systems Network Architecture
(SNA), 375
T1, 304, 307, 308
T-NETIX, Inc., 110
TACS (see Total Access
Communications System)
TASI (see Time Assigned Speech
TCP (see Transmission Control
TCP/IP (see Transmission Control
Protocol/Internet Protocol)
TDD (see Time Division Duplexing)
TDM (Time Division
Multiplexing), 20
TDMA (see Time Division Multiple
TDMA/TDD (see Time Division
Multiple Access/Time Division
TDOA (Time Difference of Arrival), 43
TeleCommunication Systems, 323
Telecommunications Act of 1996:
cell sites, 33
CLECs, 69
IXCs, 183
wireless LNP, 464
Telecommunications Industry
Association (TIA), 59, 478
Telecommunications management
network (TMN), 374–375
Telecommunications services:
AMPS, 6–8
BETRS, 17–18
CLECs, 67
cordless, 70–73
fixed wireless access, 103–105
iDEN, 172–174
ILECs, 161–162
Teledesic, 420
Telegraphy, 349–354
early attempts, 349–351
Morse code, 351, 352
wireless, 351–354
Telemetry, 354–360
role of cellular carriers, 357–358
security application, 355–356
traffic monitoring, 356–357
Web-enabled, 358–360
Telephone networks, 235
Telephones, cellular, 36–48
Teleservices, 139–140
cable, 93, 263
DirecTV, 87–88
HDTV, 87, 88
ITV, 175–181
MVDDS, 224
“Ten-codes,” 57, 58
Terabeam Magna, 198
Text-to-speech, 378
Third-generation (3G) mobile
communications systems, 46–47
iDEN, 174
IMT, 186–188, 190–193
PCS, 265–266
spectrum planning, 340
UMTS, 371
Through-wall imaging systems, 369
TIA (see Telecommunications
Industry Association)
Time Assigned Speech Interpolation
(TASI), 387–388
Time Difference of Arrival (TDOA), 43
Time Division Duplexing (TDD):
Bluetooth, 22–23
cordless, 72
MMDS, 221–222
Time Division Multiple Access
(TDMA), 154, 360–366
call handoff, 364–365
CDMA, 60
DCCH, 365
DECT, 82
EDGE, 95, 96
FDMA, 120, 122
framing, 361–363
GPRS, 129, 130
Time Division Multiple Access
(TDMA) (Cont.):
GSM, 144, 145, 146
HomeRF, 154, 156
iDEN, 172, 174
IMT, 192
network functions, 363–364
PCS 1900, 239
satellite technology, 318
SMS, 322, 325
software-defined radio, 327
time slots, 361
UMTS, 371
WLL, 455, 457
Time Division Multiple Access/Time
Division Duplexing
(TDMA/TDD), 72, 276
Time Division Multiplexing (TDM), 20
Time overlap patterns, 112
TiVo, 92
TMN (see Telecommunications
management network)
Token Ring Extensions, 297–299
Token Ring MAC Layer History, 297
Token Ring MAC Layer Statistics, 297
Token Ring Promiscuous History, 297
Token Ring Promiscuous
Statistics, 297
Token Rings:
IR, 166–168
microwave communications, 215
routers, 307
Tone paging, 232
Total Access Communications System
FDMA, 120
IMT, 186
Towers, microwave, 215
Traffic Matrix Group, 296–297
Traffic monitoring, 356–357
Transmission channels, 51–52
Transmission Control
Protocol/Internet Protocol
header compression, 76–77
routers, 307
telemetry, 359
Transmission Control Protocol (TCP):
cellular data communications, 35
Transmission Control Protocol (TCP)
satellite technology, 315
WAP, 395
Transmission lines, microwave, 215
Triangulation, 132–134
Trunked radio system, 283–284
Tunnel switching capability, 435
2001: A Space Odyssey (Arthur C.
Clarke), 311
2–Way Text Messaging service, 324
UDP/IP (User Datagram
Protocol/Internet Protocol), 254
UHF (ultra-high-frequency), 125
ULS (see Universal Licensing
Ultra-high-frequency (UHF), 125
Ultra wideband (UWB), 367–371
UMTS (see Universal Mobile
Telecommunications System)
UMTS Terrestrial Radio Access
(UTRA), 371
Unique key (Ki), 115
United Telecommunications,
Universal Licensing System (ULS),
Universal Mobile
Telecommunications System
(UMTS), 371–376
bearer services, 375
description, 372–373
EDGE, 96
functional model, 373–375
GPRS, 129
objectives, 372
Universal Serial Bus (USB),
University of California at
Berkeley, 390
U.S. Appeals Court, 340
U.S. Census Bureau, 32
U.S. Defense Department, 131,
133–134, 138
U.S. Department of Justice (DoJ), 162
U.S. Navy, 209
US West, 162
USB (see Universal Serial Bus)
User Datagram Protocol/Internet
Protocol (UDP/IP), 254
UTRA (UMTS Terrestrial Radio
Access), 371
Vail, Alfred Lewis, 351
Variable-rate ADPCM, 385–386
VEC (volunteer examinercoordinator), 12
Vector Orthogonal Frequency
Division Multiplexing (VOFDM),
221, 222
Vector Sum Excited Linear Predictors
(VSELP), 172
Vehicle tracking, 135
Vehicular radar systems, 370
Velocity patterns, 112
Verizon, 162, 325, 340, 406
Very Fast Infrared (VFIR) Protocol,
26, 169, 170
Very-high frequency (VHF), 208
Very small aperture terminals
(VSATs), 316–319, 427
VFIR Protocol (see Very Fast Infrared
VHF (very-high frequency), 208
Virtual private networks (VPNs),
391, 431
Virtual routing, 435–436
Visitor Location Register (VLR):
GSM, 143, 144
PCS 1900, 240
VOFDM (see Vector Orthogonal
Frequency Division Multiplexing)
Voice activation, 40–41
Voice cloning, 377–380
applications, 378–379
ownership issues, 379–380
Voice communications, cellular, 48–55
Voice compression, 380–388
basics, 382–385
CVSD, 386–387
PCM, 381—382
TASI, 387–388
variable-rate ADPCM, 385–286
Voice detection and encoding, 63–64
Voice mail, 241
Voice over Interactive Protocol
(VoIP), 177
Voice verification, 110–112
VoiceStream, 325, 340
VoIP (Voice over Interactive
Protocol), 177
Volunteer examiner-coordinator
(VEC), 12
VPNs (see Virtual private networks)
VSATs (see Very small aperture
VSELP (Vector Sum Excited Linear
Predictors), 172
W-CDMA (Wideband Code Division
Multiple Access), 129
WACS (Wireless Access
Communications System), 251
WAE (see Wireless Application
Wall-imaging systems, 369
WANs (see Wide area networks)
WAP (see Wireless Application
WAP 2.0, 399–400
WASPs (see Wireless application
service providers)
W3C (World Wide Web
Consortium), 399
WCS (see Wireless Communications
WDCT (Worldwide Digital Cordless
Telephone), 87
Web-enabled telemetry, 358–360
WebTV, 176, 179
WEP (see Wired Equivalent Privacy)
Western Union, 354
WGS-84 (Worldwide Geodetic System
1984), 133
Wi-Fi (see Wireless Fidelity)
Wi-Fi5, 412
Wide area networks (WANs):
bridges, 28, 29
data compression, 76–78
fraud management system, 112
routers, 308
VSATs, 316
wireless Internetworking, 427–430
Wideband Code Division Multiple
Access (W-CDMA), 129
Windows (peer-to-peer networks),
Wired Equivalent Privacy (WEP),
access points, 2
PDAs, 272
Wi-Fi, 413
wireless LAN security, 438–442
WLANs, 452
Wireless Access Communications
System (WACS), 251
Wireless Application Environment
(WAE), 397–399
Wireless Application Protocol (WAP):
i-Mode, 160
Internet-enabled mobile phones,
43, 44, 46
PCS, 265
specialized mobile radio, 394–401
wireless Intranet access, 431
Wireless application service providers
(WASPs), 401–405
Wireless bridges, 425–427
Wireless cable, microwave, 216
Wireless Centrex, 405–409
features, 406–407
service, 407–408
Wireless Communications Services
(WCS), 409–411
Wireless Device Server, 433
Wireless E911, 392–394
Wireless Ethernet Compatibility
Alliance (WECA), 438, 454
Wireless Fidelity (Wi-Fi), 411–414
GPRS, 130
routers, 308
wireless Intranet access, 432
Wireless Internet access, 414–422
methods, 415–420
service caveats, 420–421
Wireless Internet service providers
(WISPs), 422–425
Wireless Internetworking, 425–430
bridges, 425–427
routers, 427–429
Wireless Intranet access, 430–434
Bluetooth, 432
Wireless Intranet access (Cont.):
packaged solutions, 433
virtual private networks, 431
WAP portals, 431
Wi-Fi, 432
Wireless IP, 434–437
Wireless Knowledge, 403
Wireless LAN security, 437–444
authentication via RADIUS, 440
closed systems, 441–442
encryption enhancements, 439–440
firewalls, 442–444
key change administration,
Wireless LANs, 444–454
applications, 444–445
configurations, 447–450
DECT, 86
operation, 446–447
standards, 450–454
technologies, 445–446
Wireless local loops (WLLs), 454–464
architectures, 458–463
base station, 461–462
cordless, 72
DECT, 84–86
MTSO/MSC, 458–459
operations, administration and
maintenance, 462–463
proprietary networks, 460
PSTN-based direct connect, 458
RSS, 460–461
Wireless local number portability,
Wireless management tools, 465–468
Wireless Markup Language (WML), 46
WAP, 395, 397
wireless Intranet access, 431
Wireless Medical Telemetry Service
(WMTS), 468–470
Wireless messaging, 470–473
e-mail over paging nets, 471–472
integrated applications, 472
Wireless’ mMode, 161
Wireless PBX, 473–481
applications, 473–474
call handoff, 478–479
standards, 478–479
system components, 474–478
Wireless routers, 427–429
Wireless Telecommunications Bureau
(WTB), 14–15, 100, 481–483
Wireless telecommunications
investment fraud, 483–486
avoiding fraud, 484–486
warning signs, 484
Wireless Telegraph and Signal
Company, Ltd, 353
WISPs (see Wireless Internet service
WLLs (see Wireless local loops)
WML (see Wireless Markup
WMLScript, 398–399
WMTS (see Wireless Medical
Telemetry Service)
World Radio Conference 2000 (WRC2000), 190, 191
World Wide Web Consortium
(W3C), 399
WorldCom, 183, 185, 233, 234
Worldwide Digital Cordless
Telephone (WDCT), 87
Worldwide Geodetic System 1984
(WGS-84), 133
WTB (see Wireless
Telecommunications Bureau)
XO Communications, 204
Yahoo, 264
ZoneAlarm, 443
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About the Author
Nathan J. Muller is an independent consultant specializing
in telecommunications technology marketing, research, and
education. A resident of Sterling, VA, he serves on the
Editorial Board of the International Journal of Network
Management and the Advisory Panel of Faulkner Information Services. Among the 24 books he has authored are
The Desktop Encyclopedia of Telecommunications and
Network Manager’s Handbook.
Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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