Telecommunications Glossary
Telecommunications Glossary
ATM--1. Acronym for Asynchronous Transfer Mode. A network technology capable of
transmitting data, voice, audio, video, and frame relay traffic in real time. Data, including
frame relay data, is broken into packets containing 53 bytes each, which are switched
between any two nodes in the system at rates ranging from 1.5 Mbps to 622 Mbps (over
fiber optic cable). The basic unit of ATM transmission is known as a cell, a packet
consisting of 5 bytes routing information and a 48-byte payload (data). These cells are
transmitted to their destination, where they are reassembled into the original traffic.
During transmission, cells from different users may be intermixed asynchronously to
maximize utilization of network resources. ATM is defined in the broadband ISDN
protocol at the levels corresponding to levels 1 and 2 of the ISO/OSI reference model. It
is currently used in LANs (local area networks) involving workstations and personal
computers, but it is expected to be adopted by the telephone companies, which will be
able to charge customers for the data they transmit rather than for their connect time.
BRI--Acronym for Basic Rate Interface. An ISDN subscriber service that uses two B (64
Kbps) channels and one D (16 Kbps) channel to transmit voice, video, and data signals.
See also ISDN.
cable modem--A modem that sends and receives data through a coaxial cable television
network instead of telephone lines, as with a conventional modem. Cable modems, which
have speeds of 500 kilobits per second (Kbps), can generally transmit data faster than
current conventional modems. However, cable modems do not operate at the same rate
upstream (when sending information) and downstream (when receiving information).
Upstream rates vary from about 2 Mbps to 10 Mbps, downstream rates from about 10
Mbps to 36 Mbps. See also coaxial cable, modem.
coaxial cable--A round, flexible, two-conductor cable consisting of—from the center
outwards—a copper wire, a layer of protective insulation, a braided metal mesh sleeve,
and an outer shield, or jacket of PVC or fire-resistant material. The shield prevents
signals transmitted on the center wire from affecting nearby components and prevents
external interference from affecting the signal carried on the center wire. Coaxial cable is
widely used in networks. It is the same type of wiring as that used for cable television.
See the illustration. Compare fiberoptic cable, twisted-pair wiring.
dense wavelength division multiplexing--A data transmission technique in which
multiple optical signals, each assigned to a separate color (wavelength frequency), are
multiplexed onto a single strand of optical fiber. Because each signal travels separately in
its own color band on the fiber, dense wavelength division multiplexing allows for the
simultaneous transmission of different types of signals, such as SONET and ATM, each
traveling at its own rate of speed. Dense wavelength division multiplexing can greatly
increase the carrying capacity of a single optical fiber. Depending on the number, type,
and rate of the signals involved, bandwidth can range from more than 40 Gbps to
projected highs of 200 Gbps or more. Acronym: DWDM. Also called: wave division
multiplexing, WDM. Compare time division multiple access.
dial-up--Of, pertaining to, or being a connection that uses the public switched telephone
network rather than a dedicated circuit or some other type of private network.
digital modem--1. A communications device that acts as the intermediary between a
digital device such as a computer or terminal and a digital communications channel, such
as a high-speed network line, an ISDN circuit, or a cable TV system. Although a digital
mode
ms
uppor
t
ss
t
a
nda
r
d(
a
na
l
og
)mode
m pr
ot
oc
ol
s
,i
ti
snota“
t
y
pi
c
a
l
”mode
mi
nt
he
sense of being a device whose primary function is to modulate (convert digital to analog)
before transmission and demodulate (convert analog to digital) after transmission. It uses
advanced digital modulation techniques for changing data frames into a format suitable
for transmission over a digital line. See also terminal adapter. Compare modem. 2. A 56
Kbps modem. Such a modem is not purely digital but does eliminate the traditional
digital-to-analog conversion for downstream transmissions—that is, transmissions
moving from the Internet to the end user. A 56 Kbps modem is also digital in that it
r
e
qui
r
e
sadi
g
i
t
a
lc
onne
c
t
i
on,s
uc
ha
sT1,be
t
we
e
nt
het
e
l
e
phonec
ompa
nya
ndt
heus
e
r
’
s
Internet Service Provider (ISP) in order to achieve its highest speed. See also 56-Kbps
modem. 3. A term used to distinguish all-digital communications devices, such as ISDN
a
ndc
a
bl
e“
mode
ms
”f
r
omt
hemor
et
r
a
di
t
i
ona
la
na
l
og
-to-digital, phone-based modems.
DOCSIS--Acronym for Data Over Cable Service Interface Specification. The
International Telecommunications Union standard (ITU Recommendation J.112) that
specifies functions and internal and external interfaces for high-speed, bidirectional
transfer of digital data between cable television networks and subscribers. DOCSIScompliant equipment ensures interoperability between cable modems and the cable
television infrastructure, regardless of manufacturer or provider. Initially developed by a
group of cable television providers, including Time Warner and TCI, DOCSIS was
designed to support data, video, and rapid Internet access. Data rates are 27 Mbps to 36
Mbps downstream (from the cable network) and 320 Kbps to 10 Mbps upstream (to the
cable network). See also cable modem. Compare IEEE 802.14.
DS--Acronym for Digital Services or Digital Signal, a category used in referencing the
speed, number of channels, and transmission characteristics of T1, T2, T3, and T4
communications lines. The basic DS unit, or level, is known as DS-0, which corresponds
to the 64 Kbps speed of a single T1 channel. Higher levels are made up of multiple DS-0
levels. DS-1 represents a single T1 line that transmits at 1.544 Mbps. For higher rates, T1
lines are multiplexed to create DS-2 (a T2 line consisting of four T1 channels that
transmits at 6.312 Mbps), DS-3 (a T3 line consisting of 28 T1 channels that transmits at
44.736 Mbps), and DS-4 (a T4 line consisting of 168 T1 channels that transmits at
274.176 Mbps).
DSL--Acronym for Digital Subscriber Line, a recently developed (late 1990s) digital
communications technology that can provide high-speed transmissions over standard
copper telephone wiring. DSL is often referred to as xDSL, where the x stands for one or
two characters that define variations of the basic DSL technology. Currently, ADSL
(Asymmetric DSL) is the form most likely to be provided, but even it is, as yet, available
only to limited groups of subscribers. The technology exploits unused frequencies on
copper telephone lines to transmit traffic typically at multi-megabit speeds. DSL can
allow voice and high-speed data to be sent simultaneously over the same line. Because
the service is 'always available,' end-users don't need to dial in or wait for call set-up.
With DSL you are wired for speed. DSL comes in two flavors, asymmetric and
symmetric.
Asymmetric flavors
Asymmetrical variations include: ADSL, G.lite ADSL (or simply G.lite), ADSL2,
ADSL2plus, RADSL and VDSL. The standard forms of ADSL (ITU G.992.1, G.992.2,
and ANSI T1.413-Issue 2) are all built upon the same technical foundation, Discrete
Multi Tone (DMT). The suite of ADSL standards facilitates interoperability between all
standard forms of ADSL.
 ADSL: (Full Rate asymmetrical DSL) ADSL offers differing upload and
download speeds and can be configured to deliver up to six megabits of data per
second from the network to the customer that is up to 120 times faster than dialup
service and 100 times faster than ISDN. ADSL enables voice and high-speed data
to be sent simultaneously over the existing telephone line. This type of DSL is the
most predominant in commercial use for business and residential customers
around the world. Good for general Internet access and for applications where
downstream speed is most important, such as video-on-demand. ITU-T
Recommendation G.992.1 and ANSI Standard T1.413-1998 specify full rate
ADSL.
 G.lite ADSL (or simply G.lite): The G.lite standard was specifically developed to
meet the plug-and-play requirements of the consumer market segment. G.lite is a
medium bandwidth version of ADSL that allows Internet access at up to 30 times
the speed of the fastest 56K analog modems ~ up to 1.5 megabits downstream and
up to 500 kilobits upstream. G.lite is an International Telecommunications Union
(ITU) standard, globally standardized interoperable ADSL system per ITU
G.992.2.
 ADSL2—ITU G.992.3 and G.992.4 adds new features and functionality targeted
at improving performance and interoperability, and adds support for new
applications, services and deployment scenarios. Among the changes are
improvements in data rate and reach performance, rate adaptation, diagnostics and
stand-by mode, to name a few. ADSL2 has been specifically designed to improve
the rate and reach of ADSL largely by achieving better performance on long lines
in the presence of narrowband interference. ADSL2 achieves downstream and
upstream data rates of about 12 Mbps and 1 Mbps respectively, depending on
loop length and other factors. ADSL2 accomplishes this by improving modulation
efficiency, reducing framing overhead, achieving higher coding gain, improving
the initialization state machine, and providing enhanced signal processing
algorithms.
 ADSL2plus (ITU G.992.5) doubles the bandwidth used for downstream data
transmission, effectively doubling the maximum downstream data rates, and
achieving rates of 20 Mbps on phone lines as long at 5,000 feet. ADSL2plus
solutions will most commonly be multimodal, interoperating with ADSL and
ADSL2, as well as with ADSL2plus chipsets.
 RADSL: (rate adaptive DSL) A non-standard version of ADSL. Note that
standard ADSL also permits the ADSL modem to adapt speeds of data transfer.
 VDSL (very high bit rate DSL) Up to 26 Mb/s, over distances up to 50 Meters on
short loops such as from fiber to the curb. In most cases, VDSL lines will be
served from neighborhood cabinets that link to a Central Office via optical fiber.
It is particularly useful for 'campus' environments - universities and business
parks, for example. VDSL is currently being introduced in market trials to deliver
video services over existing phone lines. VDSL can also be configured in
symmetric mode.
Symmetric flavors
Symmetrical variations include: SDSL, SHDSL, HDSL, HDSL-2 and IDSL. The equal
speeds make Symmetrical DSLs useful for LAN (local area network) access, videoconferencing, and for locations hosting their own Web sites.
 SDSL: (symmetric DSL) SDSL is a vendor-proprietary version of symmetric
DSL that may include bit-rates to and from the customer ranging of 128 kbps to
2.32 Mbps. SDSL is an umbrella term for a number of supplier-specific
implementations over a single copper pair providing variable rates of symmetric
service. SDSL uses 2B1Q HDSL run on a single pair with an Ethernet interface to
the customer. The industry is expected to quickly move towards the higher
performing and standardized G.shdsl technology developed by the ITU with
support from T1E1.4 (USA) and ETSI (European Telecommunications Standards
Institute).
 SHDSL is state-of-the-art, industry standard symmetric DSL SHDSL equipment
conforms to the ITU Recommendation G.991.2, also known as G.shdsl, approved
by the ITU-T February 2001. SHDSL achieves 20% better loop-reach than older
versions of symmetric DSL, it causes much less crosstalk into other transmission
systems in the same cable, and multi-vendor interoperability is facilitated by the
standardization of this technology. SHDSL systems may operate at many bitrates, from 192 kbps to 2.3 Mbps, thereby maximizing the bit-rate for each
customer. G.shdsl specifies operation via one pair of wires, or for operation on
longer loops, two pairs of wire may be used. For example, with two pairs of wire,
1.2 Mbps can be sent over 20,000 feet of 26 AWG wire. SHDSL is best suited to
data-only applications that need high upstream bit-rates. Though SHDSL does not
carry voice like ADSL, new voice-over-DSL techniques may be used to convey
digitized voice and data via SHDSL. SHDSL is being deployed primarily for
business customers.
 HDSL: (high data rate DSL) This variety created in the late 1980s delivers
symmetric service at speeds up to 2.3 Mbps in both directions. Available at 1.5 or
2.3 Mbps, this symmetric fixed rate application does not provide standard
telephone service over the same line and is already standardized through ETSI
and ITU (International Telecommunications Union). Seen as an economical
replacement for T1 or E1, it uses one, two or three twisted copper pairs.
 HDSL2: (2nd generation HDSL) This variant delivers 1.5 Mbps service each
way, supporting voice, data, and video using either ATM (asynchronous transfer
mode), private-line service or frame relay over a single copper pair. This ANSI
(American National Standards Institute) standard for this symmetric service gives
a fixed 1.5 Mbps rate both up and downstream. HDSL2 does not provide standard
voice telephone service on the same wire pair. HSDL2 differs from HDSL in that
HDSL2 uses one pair of wires to convey 1.5 Mbps whereas ANSI HDSL uses two
wire pairs.
 IDSL: (integrated services digital network DSL) This is a form of DSL that
supports symmetric data rates of up to 144 Kbps using existing phone lines. It is
unique in that it has the ability to deliver services through a DLC (Digital Loop
Carrier: a remote device often placed in newer neighborhoods to simplify the
distribution of cable and wiring from the phone company). While DLCs provide a
means of simplifying the delivery of traditional voice services to newer
neighborhoods, they also provide a unique challenge in delivering DSL into those
same neighborhoods. IDSL addresses this market along with ADSL and G.lite as
they are implemented directly into those DLCs. IDSL differs from its relative
ISDN (integrated services digital network) in that it is an "always-available"
service, but capable of using the same terminal adapter, or modem, used for
ISDN.
DSLAM--Acronym for Digital Subscriber Line Access Multiplexer. A device in a
telephone company central office that splits DSL subscriber lines and connects them to
Internet network hosts and to the public telephone network. The use of a DSLAM makes
it possible to provide both voice and data service through a single pair of copper wires.
DSL Lite--Short for Digital Subscriber Line Lite. A variation of ADSL currently under
development that simplifies installation but transmits more slowly, at 1.544 Mbps. See
also ADSL, DSL.
IDSL--Acronym for Internet digital subscriber line. A high-speed digital communications
service that provides Internet access as fast as 1.1 Mbps (megabits per second) over
standard telephone lines. IDSL uses a hybrid of ISDN and digital subscriber line
technology. See also digital subscriber line, ISDN.
ISDN--Acronym for Integrated Services Digital Network. A high-speed digital
communications network evolving from existing telephone services. The goal in
developing ISDN was to replace the current telephone network, which requires digital-toanalog conversions, with facilities totally devoted to digital switching and transmission,
yet advanced enough to replace traditionally analog forms of data, ranging from voice to
computer transmissions, music, and video. ISDN is available in two forms, known as BRI
(Basic Rate Interface) and PRI (Primary Rate Interface). BRI consists of two B (bearer)
channels that carry data at 64 Kbps and one D (data) channel that carries control and
signal information at 16 Kbps. In North America and Japan, PRI consists of 23 B
channels and 1 D channel, all operating at 64 Kbps; elsewhere in the world, PRI consists
of 30 B channels and 1 D channel. Computers and other devices connect to ISDN lines
through simple, standardized interfaces. See also BRI, channel (definition 2), PRI.
fiberoptic cable or fiber-optic cable--A form of cable used in networks that transmits
signals optically, rather than electrically as do coaxial and twisted-pair cable. The lightconducting heart of a fiberoptic cable is a fine glass or plastic fiber called the core. This
core is surrounded by a refractive layer called the cladding that effectively traps the light
and keeps it bouncing along the central fiber. Outside both the core and the cladding is a
final layer of plastic or plastic-like material called the coat, or jacket. Fiberoptic cable can
transmit clean signals at speeds as high as 2 Gbps. Because it transmits light, not
electricity, it is also immune to eavesdropping.
fiber optics--A technology for the transmission of light beams along optical fibers. A
light beam, such as that produced in a laser, can be modulated to carry information.
Because light has a higher frequency on the electromagnetic spectrum than other types of
radiation, such as radio waves, a single fiber-optic channel can carry significantly more
information than most other means of information transmission. Optical fibers are thin
strands of glass or other transparent material, with dozens or hundreds of strands housed
in a single cable. Optical fibers are essentially immune to electromagnetic interference.
See also optical fiber.
frame relay--A packet-switching protocol for use on WANs (wide area networks).
Frame relay transmits variable-length packets at up to 2 Mbps over predetermined, set
paths known as PVCs (permanent virtual circuits). It is a variant of X.25 but dispenses
wi
t
hs
omeofX.
25’
se
r
r
orde
t
e
c
t
i
o
nf
ort
hes
a
keofs
pe
e
d.See also ATM (definition 1),
X.25. Speed and cost is usually based upon a specified committed information rate (CIR)
and a peak information rate (PIR).
FTTB or FTTH or FTTP--Acronyms for fiber to the business, home, or premise. The
installation and use of fiber-opt
i
cc
a
bl
ef
r
om t
hec
e
nt
r
a
lof
f
i
c
e(
CO)di
r
e
c
t
l
yi
nt
oaus
e
r
’
s
premies. It is a replacement for Plain Old Telephone Service (POTS) that enables the
distribution of telephony, cable TV, Internet access, multimedia, and other
communications over one line.
FTTC--Acronym for fiber to the curb. The installation and use of fiber-optic cable from
the central office (CO) towi
t
hi
nat
hous
a
ndf
e
e
tofaus
e
r
’
shomeorof
f
i
c
e
.Wi
t
hFTTC,
coaxial cable or another medium carries the signals from the curb into the home or office.
FTTC is a replacement for Plain Old Telephone Service (POTS) that enables the
distribution of telephony, cable TV, Internet access, multimedia, and other
communications over one line. Compare FTTH, POTS.
HDSL--Acronym for High-bit-rate Digital Subscriber Line. A form of DSL, HDSL is a
protocol for digital transmission of data over standard copper telecommunications lines
(as opposed to fiber-optic lines) at rates of 1.544 Mbps in both directions. Also called:
High-data-rate Digital Subscriber Line. See also DSL.
last mile--The connection (which may in fact be more or less than one mile) between an
end us
e
r
’
ss
y
s
t
e
ma
ndt
ha
tofas
e
r
vi
c
epr
ovi
de
r
,s
uc
ha
sat
e
l
e
phonec
ompa
ny
.The“
l
a
s
t
mi
l
e
”c
o
nne
c
t
i
onhi
s
t
or
i
c
a
l
l
yha
sr
e
f
e
r
r
e
dt
ot
het
wi
s
t
e
d-pair copper wires used between a
homea
n
dt
het
e
l
e
phonec
ompa
ny
.Whi
l
et
hi
sde
f
i
ni
t
i
onr
e
ma
i
nsa
c
c
ur
a
t
e
,“
l
a
s
tmi
l
e
”i
s
nowof
t
e
nus
e
dmor
ebr
oa
dl
yt
or
e
f
e
rt
ot
hel
i
nkbe
t
we
e
na
ne
ndus
e
r
’
ss
y
s
t
e
ma
ndt
he
high-speed Internet access technology of a service provider, such as an ISP (Internet
service provider). Thus, for modem users accessing the Internet through voice-grade
l
i
ne
s
,t
hel
a
s
tmi
l
ei
ss
t
i
l
le
qui
va
l
e
n
tt
ot
hephonec
ompa
ny
’
st
wi
s
t
e
d-pair copper wiring.
However, because standard modem transmission over voice-grade lines is sometimes
frustratingly slow, other last mile solutions have been designed to provide greater speed
and bandwidth. These include coaxial cable (used in cable TV), fiber optics, or a radio
link (such as a cellular telephone or a point-to-point link). DSL and ISDN are methods
for providing high-speed last-mile data service through twisted-pair copper wires. See
also DSL, ISDN, twisted-pair wiring. Compare local loop.
Modem--1. Short for modulator/demodulator. A communications device that converts
between digital data from a computer or terminal and analog audio signals that can pass
through a standard telephone line. Because the telephone system was designed to handle
voice and other audio signals and a computer processes signals as discrete units of digital
information, a modem is necessary at both ends of the telephone line to exchange data
between computers. At the transmit end, the modem converts from digital to analog
audio; at the receiving end, a second modem converts the analog audio back to its
original digital form. In order to move a high volume of data, high-speed modems rely on
sophi
s
t
i
c
a
t
e
dme
t
hodsf
or“
l
oa
di
ng
”i
nf
or
ma
t
i
onont
ot
hea
udi
oc
a
r
r
i
e
r
—for example,
they may combine frequency shift keying, phase modulation, and amplitude modulation
t
oe
na
b
l
eas
i
ng
l
ec
ha
ng
ei
nt
hec
a
r
r
i
e
r
’
ss
t
a
t
et
or
e
pr
e
s
e
ntmul
t
i
pl
ebi
t
sofda
t
a
.I
n
addition to the basic modulation and demodulation functions, most modems also include
firmware that allows them to originate and answer telephone calls. International standards
for modems are specified by the International Telecommunications Union, or ITU.
Despite their capabilities, modems do require communications software in order to
function. See also amplitude modulation, frequency modulation, quadrature amplitude
modulation. Compare digital modem. 2. Any communications device that acts as an
interface between a computer or terminal and a communications channel. Although such
a device may not actually modulate or demodulate analog signals, it may be described as
a modem because a modem is perceived by many users to be a black box that connects a
computer to a communications line (such as a high-speed network or a cable TV system).
See also digital modem.
OC3--Short for optical carrier 3. One of several optical signal circuits used in the
SONET high-speed fiberoptic data transmission system. OC3 carries a signal of 155.52
Mbps, the minimum transmission speed for which SONET and the European standard,
SDH, are fully interoperable. See also SONET.
POTS--Acronym for Plain Old Telephone Service. Basic dialup telephone connections to
the public switched network without any added features or functions. A POTS line is
nothing but a phone line connected to a simple, single-line telephone instrument.
Satellite--A satellite stationed in geosynchronous orbit that acts as a microwave relay
station, receiving signals sent from a ground-based station (earth station), amplifying
them, and retransmitting them on a different frequency to another ground-based station.
Initially used for telephone and television signals, communications satellites can also be
used for high-speed transmission of computer data. Two factors affecting the use of
satellites with computers, however, are propagation delay (the time lag caused by the
distance traveled by the signal) and security concerns.
PRI--Acronym for Primary Rate Interface. One of two ISDN transmission rate services
(the other is the basic rate interface, BRI). PRI has two variations. The first, which
operates at 1.536 Mbps, transmits data over 23 B channels and sends signaling
information at 64 Kbps over one D channel in the United States, Canada, and Japan. The
second, which operates at 1.984 Mbps, transmits data over 30 B channels and sends
signaling information at 64 Kbps over one D channel in Europe and Australia. See also
BRI, ISDN.
SMDS--Acronym for Switched Multimegabit Data Services. A very high-speed,
connectionless, packet-switched data transport service that connects LANs (local area
networks) and WANs (wide area networks).
SONET--Acronym for Synchronous Optical Network. A high-speed network that
provides a standard interface for communications carriers to connect networks based on
fiberoptic cable. SONET is designed to handle multiple data types (voice, video, and so
on). It transmits at a base rate of 51.84 Mbps, but multiples of this base rate go higher.
T1 or T-1--A high-speed communications line that can handle digital communications
and Internet access at the rate 1.544 Mbps (megabits per second). Although originally
designed by AT&T to carry multiple voice calls over standard twisted-pair telephone
wiring, this high-bandwidth telephone line can also transmit text and images. T1 speed is
attained through multiplexing 24 separate 64 Kbps channels into a single data stream. T1
lines are commonly used by larger organizations for Internet connectivity. Also called: T1 carrier. Compare fractional T1, T2, T3, T4.
T-carrier--A long-distance, digital communications line provided by a common carrier.
Multiplexers at either end merge several voice channels and digital data streams for
transmission and separate them when received. T-carrier service, introduced by AT&T in
1993, is defined at several capacity levels: T1, T2, T3, and T4. In addition to voice
communication, T-carriers are used for Internet connectivity.
twisted-pair wiring--Wiring consisting of two insulated strands of copper twisted around
one another to form a cable. Twisted-pair wiring comes in two forms, unshielded twisted
pair (UTP) and shielded twisted pair (STP), the latter named for an extra protective
sheath wrapped around each insulated pair of wires. Twisted-pair wiring can consist of a
single pair of wires or, in thicker cables, two, four, or more pairs of wires. Twisted-pair
wiring is typical of telephone cabling. Compare coaxial cable, fiberoptic cable.
VDSL--Short for very-high-speed digital subscriber line. The high-speed version of the
xDSL (digital subscriber line) communication technologies, all of which operate over
existing phone lines. VDSL can deliver up to 52 Mbps downstream, but it is effective
only within about 4500 to 5000 feet of the central exchange. The data delivery rate is, in
fact, related to the distance the signal must travel. To attain a rate of 52 Mbps, for
example, the subscriber must be within 1000 feet of the exchange office. At a distance of
3000 feet, the data rate drops to about 26 Mbps; and at 5000 feet, the data rate drops to
about 13 Mbps. See also central office, xDSL.
virtual circuit--A connection between communicating computers that provides the
computers with what appears to be a direct link but can actually involve routing data over
a defined but longer path.
wireless LAN--A LAN (local area network) that sends and receives data via radio,
infrared optical signaling, or some other technology that does not require a physical
connection between individual nodes and the hub. Wireless LANs are often used in office
or factory settings where a user must carry a portable computer from place to place. Also
called: WLAN.
X.25--A recommendation published by the ITU-T (formerly CCITT) international
communications standards organization that defines the connection between a terminal
and a packet-switching network. X.25 incorporates three definitions: the electrical
connection between the terminal and the network, the transmission or link-access
protocol, and the implementation of virtual circuits between network users. Taken
together, these definitions specify a synchronous, full-duplex terminal-to-network
connection. Packet format, error control, and other features are equivalent to portions of
the HDLC (High-level Data Link Control) protocol defined by the International
Organization for Standardization (ISO). See also CCITT X series, HDLC, packet
switching, virtual circuit.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement