Siemens_Wireless Ethernet Infrastructure Applications Whitep

Industrial Wireless LAN
I-Features, Applications, Examples
SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Aims:
This White Paper explains the technology of Industrial Wireless LAN and its special
features compared with Wireless LAN according to IEEE 802.11. It also outlines
applications and provides examples of use in industry. The White Paper is completed
by a description of the products available today and the products and technologies of
the future.
Note:
Wireless LAN based on the IEEE 802.11 standard and
further wireless technologies
will be dealt with in a separate White Paper
The information in this White Paper is as of Autumn 2004
This symbol highlights references to SIMATIC NET products or special SIMATIC
NET solutions
Published by
Siemens AG
Automation and Drives Group
SIMATIC NET Industrial Communication Subdivision
P.O. Box 4848
90327 Nuernberg, Germany
Further Support:
If you have additional questions, please contact your local Siemens representative.
You will also find SIMATIC NET on the Internet at
http://www.siemens.com/simatic-net
Copyright © Siemens AG 2004
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Aims: .......................................................................................................................................... 1
Aims: .......................................................................................................................................... 2
Introduction ............................................................................................................................... 4
Reliable............................................................................................................................................... 4
Robust Construction ......................................................................................................................... 5
Data Security ..................................................................................................................................... 5
Industrial Wireless LAN ........................................................................................................... 7
I-Features (Industry Features) ........................................................................................................ 7
Robust Construction and Connectors ........................................................................................... 19
Influence of Other Wireless Technologies ................................................................................... 22
Safety-related Signals in Industrial Wireless LAN ...................................................................... 24
Applications of an Industrial Wireless LAN in Automation Engineering............................ 28
Applications ..................................................................................................................................... 28
Examples.......................................................................................................................................... 31
SIMATIC NET Products for Industrial Wireless LAN ......................................................... 36
Access Point SCALANCE W788-1PRO ....................................................................................... 36
Dual Access Point SCALANCE W788-2PRO .............................................................................. 37
Ethernet Client Module SCALANCE W744-1PRO .................................................................... 37
PC Card CP 7515 ............................................................................................................................ 38
PCMCIA Card CP 1515 ................................................................................................................. 39
Power Supply PS791-1PRO ........................................................................................................... 39
FC Modular Outlet Power Insert .................................................................................................. 40
Accessories ....................................................................................................................................... 41
Future Products from SIMATIC NET ................................................................................... 42
Industrial Wireless LAN RR.......................................................................................................... 43
Applications for Industrial Wireless LAN RR ............................................................................. 44
SCALANCE W788-1RR................................................................................................................. 45
SCALANCE W788-2RR................................................................................................................. 46
Ethernet Client Module SCALANCE W747-1RR ....................................................................... 47
IWLAN/PB Link PN IO ................................................................................................................. 48
IWLAN RCoax Cable..................................................................................................................... 49
Antennas .......................................................................................................................................... 49
Glossary ................................................................................................................................... 50
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Introduction
Wireless networks are becoming more and more popular. They
allow a high degree of flexibility reducing costs during
installation and operation of a plant. They are therefore used in
many areas such as
• Manufacturing and process automation
• Foodstuffs and beverages
• Storage/logistics
• Transport (railway/road)
• Crane erection
Without with a wireless link to the communication network,
many applications with moving equipment are impossible or can
only be implemented much less efficiently. Drag chains and slip
rings that are liable to wear and tear are no longer necessary.
Moving vehicles involved in data communication are no longer
restricted to fixed tracks that require considerable effort to
modify.
In a wireless network, production and service data is available
practically everywhere within the company. It can be acquired
and modified simultaneously. During commissioning, engineers
can observe actions affecting the entire plant directly on-site.
Reliable
In industrial applications, operating reliability is of particular
importance. It demands the use of extremely reliable products
providing mechanisms for real-time support (guaranteed
transmission times) and deterministic characteristics
(predictable data traffic). This means that devices such as
programmable controllers (PLCs) can transfer their data reliably
even in critical situations. The wireless standards from the IEEE
working group 802.11 (to which the Wi-Fi seal relates) provide
only limited options. The methods of the IEEE 802.11 standard
can be taken as a good basis that can then be optimized for
industrial application. This is achieved with the I-features of
Industrial Wireless LAN in the products of SIMATIC NET. These
features represent an expansion of IEEE 802.11 and are fully
compatible; in other words, devices complying with IEEE
802.11 (and having, for example, the Wi-Fi seal) can be used in
an Industrial Wireless LAN radio cell.
Apart from the use of reliable products, operating reliability is
also achieved by optimum planning and installation of the
wireless link. With a measurement report of the field strength
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
values of the intended wireless network, the customer is
confident even in the face of dynamic disturbances. There must
be an adequate budget reserve even when a moving fork lift
truck carrying large metal containers causes reflections and
shadows that change the wireless link.
Robust Construction
Apart from being "reliable", a robust construction is an important
requirement of the industrial customer. This is reflected in
housings, that are dust- and waterproof. As a result, devices
can be set up centrally without a switching cabinet and
therefore allow maximum flexibility. This installation flexibility,
however, has a further important aspect. Often, the simplest
location for installation (for example in a switching cabinet) is
not the ideal location from a wireless transmission perspective.
As a simple illustration of this, a switching cabinet functions like
a Faraday cage and traps radio waves. It would be possible to
install a distant antenna on the roof of the switching cabinet but
it must be remembered that the coaxial cable connecting the
antenna and device attenuates valuable output power. This is
not the case when this coaxial cable is not required for
additional antennas because the ideal location in terms of
wireless transmission can be selected and the antennas
supplied with the product can be used.
Data Security
The question as to the degree of security often depends on the
security policy of the company that prescribes clear rules.
In this case, encryption of the data transmitted is important
since the data traffic on a wireless link can be tracked using
directional antennas. However, it is not enough simply to
encrypt the data. Even before any data traffic takes place, it is
necessary to establish that the correct partners are taking part
in the communication. The question "Who are you?" is handled
in suitable authentication protocols. At the same time when this
question is clarified, the question "What am I allowed to do?"
(authorization) can also be decided.
Whatever shape the security solution takes, it is important that
the products used are standardized and do not include
proprietary procedures. The more publicity given to a security
solution, the faster hackers will find possible loopholes. An open
standard provides protection for investment (interoperability
between different providers) and a high degree of data security.
In contrast to other providers (for example Cisco's LEAP
protocol), Industrial Wireless LAN uses only mechanisms that
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
are precisely defined in the standard of the IEEE and the
specifications of the WECA (for example, PA). For this reason,
this White Paper does include information on this topic and the
reader is referred to the separate White Paper on the IEEE
802.11 standard.
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Industrial Wireless LAN
Industrial Wireless LAN from SIMATIC NET provides not only
data communication according to the IEEE 802.11 standard but
also numerous expansions (I-features) that are extremely useful
for industrial customers.
I-Features (Industry Features)
If wireless communication is used in industry in production and
manufacture, the reliability of the wireless channel becomes an
important issue. In contrast to a consumer environment,
machine downtimes involve high costs. To increase operating
reliability, Industrial Wireless LAN from SIMATIC NET provides
additional functions.
Antenna Diversity – Operation with 2 Antennas
If radio is used in the productive sector of a plant, diversity
antennas should be used. With this technique, it is possible to
achieve a significantly more reliable wireless link in a "difficult"
environment in which reflections and multipath reception
interfere with wave propagation. The use of antenna diversity is
easy to recognize because two antennas are available for one
wireless card. The recipient can then evaluate the information
from two different antennas and select the better antenna
dynamically during reception. When transmitting, the diversity
function automatically selects the other antenna after a set
number of failed attempts.
Monitoring the Wireless Channel
In the IEEE 802.11 standard, monitoring of the quality of the
wireless link is required. This factor, however, has a
considerable effect on reliability. If a mobile device is used for
diagnostics or monitoring of a machine (in a comparatively slow
process), is important that the management level knows
whether or not the device is still capable of performing the task.
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Figure 1: Monitoring the wireless channel between an
Internet Pad moving from location A to location B that
leaves the area covered by the access point
If, for example, as shown in Figure 1, the Internet Pad MOBIC
loses radio contact, it is important that the controller at the
management level is informed of this and can take over control
of the process. This situation can occur when the wireless
channel is badly degraded or when the client simply moves out
of the cell (in Figure 1, this is location B) and no longer has
radio contact. The access point must then, for example, send
an SNMP trap to the network management system or an Email. As an option, a software block can also be used in the
controller to query the status of the client cyclically.
In Industrial Wireless LAN, two methods are available with
which monitoring of the wireless channel can be implemented.
Link Check
When the link check is used, if there is no communication
taking place, frames are sent to the node at selectable cyclic
intervals to check its presence in the wireless network. This
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
method somewhat reduces performance but provides a high
degree of operating reliability.
IP-Alive
IP-alive monitors the cyclic communication connections that are
extremely common in automation engineering environments.
On selected IP connections, the monitoring function checks
whether packets are actually exchanged at the times prescribed
by the cycle time. If packets are missing, errors can be reported
in various ways just as with the link check mechanism (error
LED, log file, E-mail, SNMP trap). The user can configure the
method of reporting to suit the situation.
Deterministic, Real-Time
Wireless LAN implemented according to IEEE 802.11 provides
a powerful wireless connection that can be used as it stands for
many applications in the office and home environment.
Unfortunately, the standard does not support applications with
real-time and deterministic requirements. Wireless LAN
according to the IEEE 802.11 standard is a "shared medium" in
which all stations must share access to the common medium.
While this access is controlled, it is not fully predictable.
Reservation of the Data Rate
With this method, Industrial Wireless LAN provides the option of
guaranteeing both a minimum data rate and a "worst-case"
transmission time for selected clients (Quality of Service, QoS).
These parameters are negotiated prior to communication.
Example 1: Cyclic data traffic
If the configuration engineer of an automation application wants
to be sure that a node is capable of sending a 64-byte long
packet every 50 ms over the Industrial Wireless LAN link to the
central controller, the following parameters must be configured:
1. Transmission time (response time)
Less than 50 ms, so that data does not "pile up" at the node.
After 50 ms, the last bit of the previous packet must have been
transmitted so that the next 64-byte packet can be transmitted.
2. Data rate (bandwidth)
If 64 bytes are to be transmitted in 50 ms, a data rate of at least
(64 bytes x 8 bits) / 50 ms = 10.24 Kbps must be set.
These two settings guarantee that the wireless channel is not a
bottleneck in the system and that the cyclic data traffic of the
node can be forwarded smoothly to the central controller.
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Example 2: Transfer of files
If the node has a file with a size of 1 Mbyte for transmission, a
predictable transmission duration can be achieved with the
following settings:
1. Transmission time (response time)
Since a time in the seconds range can be expected, the latency
of the wireless channel is not a major factor. A time of 500 ms
can be selected here.
2. Data rate (bandwidth)
If a data rate of 500 Kbps is set, the entire file will be
transmitted in (1 Mbyte x 8 bits) / 500 Kbps = 16 s.
That individual packets could theoretically have a latency of up
to 500 ms does not play a major role.
The following constraints should be taken into account when
reserving the data rate:
1. The data rate setting is based on the net data rate of the
Ethernet connection. The protocol overhead due to wireless
transmission does not need to be taken into account.
2. When a wireless station is handed over to a different cell, a
station only takes the transmission time and data rate
attributes with it when it is also configured as "critical client"
on the new AP. However, at the precise moment of the
handover from one cell to the next, delays occur because
the station is extremely busy logging on at the next access
point. This phase can take up to several hundreds of
milliseconds. During this time, there is no productive data
traffic. In a future further development of Industrial Wireless
LAN, this property will be improved making handover times
less than 20 ms possible.
3. If a critical wireless station is assigned a transmission time
and data rate, this does not mean that its performance will
not be better in a cell that is not being fully utilized.
Example: A single station in a 2.4 GHz, 54 Mbps cell has the
attributes 100 ms and 500 Kbps. This station naturally has
the entire bandwidth of the wireless channel available when
there are no other stations in the cell.
4. Cyclic data exchange is possible in both communication
directions: Both from the station to the access point
(upstream) and from the access point to the station
(downstream).
5. Comparable methods of other manufacturers simply provide
prioritization of data streams of one category. This means,
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
for example, that the entire voice traffic has priority. Priority
assigned on a device basis is then not possible. In many
cases, these methods also provide prioritization of
downstream data.
Figure 2: By reserving time slots for stations with timecritical data, productive communication presents no
problem
To illustrate the mechanism described above, let us assume an
access point at which 6 stations are logged on (Figure 2, client
1 through 6). If an application requires that clients 1, 2, and 3
(for example mobile controllers) interface with the factory
network over the Industrial Wireless LAN, it must be guaranteed
that these controllers can send a status message at fixed, cyclic
points in time. This is possible only if an additional mechanism
is available to assign the right to transmit. By reserving the data
rate in SIMATIC NET, in the example above, clients 1 and 3
have the opportunity to access the access point in the first
phase although clients 4 and 5 obviously have large files to
transmit. This is followed by a period in which all other stations
have their turn according to the normal rules. In Figure 2, this is
first client 5 and then client 6. This is once again followed by the
phase in which the stations with a reserved data rate can
access the access point. In the schematic in Figure 2, it is also
clear that client 4 is a "victim" of the IEEE 802.11 access
method. Since it is not a client with previously configured
assured performance (QoS), it must wait until clients 5 and 6
have transmitted their data.
Figure 2 also makes it clear that within an Industrial Wireless
LAN, there is both standard-compliant Wireless LAN traffic as
well as prioritized wireless traffic. It must be emphasized that
any IEEE 802.11-compliant device can be included in the
prioritized wireless traffic and that it is not necessary to use only
client products of SIMATIC NET. If there is both IEEE 802.11
traffic as well as prioritized traffic in the cell of an access point,
remember that the performance of the standard traffic
deteriorates disproportionately since the prioritized data traffic
also requires bandwidth for its administration. This response
was tested in an analysis performed by ComConsult.
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
(http://intra1.nbgm.siemens.de/extern/spiegeln/net/html_00/ftp/p
rodukte/2004_07_ComConsult_Siemens_IWLAN.pdf)
Forced Roaming
The IEEE 802.11 standard in no way specifies that an access
point must be connected to the wired network over Ethernet.
Moreover, it is not even specified that a wired network must be
available at all. This means that a station in the cell does not
immediately recognize whether or not the wired interface is
impaired or interrupted. Such a fault has far-reaching
consequences if the station is a mobile controller that sends
important process data to the control room.
Figure 3: Forced roaming of a station if the wired interface
to the logged-on access point is interrupted
If the wired interface to access point 1 is interrupted in Figure 3,
the access point detects the fault and automatically turns off its
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
cell (prerequisite: the user has selected this option in the Web
interface of access point 1). If the cell is designed redundantly
(overlapping cells), the station roams to the next available
access point (AP 2). Without this mechanism, there is no way
that the mobile controller can keep up the connection to the
controlling computer.
Note: This mechanism must not be confused with the
redundancy mode. Difference in this case:
• Point-to-point link
• Dual access point
• Switchover from one wireless card to another within a
dual access point
Storm Threshold
In communication networks, a not insignificant amount of traffic
is generated by multicasts and broadcasts. If such messages
get the upper hand, there is a danger that productive data traffic
will be restricted. This problem in a communication network is
not countered by the Industrial Wireless LAN cell, but must be
handled in the devices themselves. To achieve this, the
SCALANCE W products provide the "storm threshold“ to
prevent overload and to restrict multicast/broadcast traffic to a
maximum value.
Events
A significant cost factor in industrial plants is the effort required
for service and maintenance. Here, there is a considerable
potential for saving when device malfunctions and their causes
can be recognized in good time. Apart from errors, it is also
helpful if important steps during configuration are logged and
are available for later scrutiny.
•
•
•
•
•
•
•
Restart/hot restart
Connection to Ethernet
Error in authentication (Who am I? - Who is logging on?)
Power supply
Monitoring of the wireless link
Reservation of the data rate possible/not possible
Redundancy mode
Figure 4: List of error states and the events detected by
SCALANCE W products
From our perspective, it is not adequate to simply detect the
error and status; suitable reactions must also be triggered. To
allow this, SCALANCE W products provide mechanisms such
as
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
• Error display (LED) on the device
• Sending of E-mails
• SNMP traps
• Logging in a buffer that can be read out later
All the methods of indicating problems can be activated or
deactivated apart from a few serious errors that are always
logged and signaled by the fault/error LEDs.
Wizards
A system can only be as reliable as allowed by the
configuration created by the commissioning personnel. The
best mechanisms will not help if the parameter assignment and
configuration is complicated and can only be undertaken by
experts. This applies, in particular, to settings relating to data
security. Unfortunately, standardization has moved very quickly
in this respect so that the current mechanisms are not
adequately known by everyone.
In such situations, it is important that the customer be
supported with online help and wizards. If users make the
proposed settings of the basic wizard and security wizards with
SCALANCE W products in the specified in order, they can be
sure that the Industrial Wireless LAN cell has a suitable quality
and that no necessary parameters have been forgotten.
Wireless Distribution System, WDS
If an Industrial Wireless LAN needs to be upgraded in a plant, it
is sometimes not possible to connect the access points over
Ethernet to make communication beyond cells possible.
Possible reasons:
• Temporary equipment required for commissioning
• Cable channels cannot be expanded or do not exist
• Installation difficult (for example in a sandpit)
In such situations, the access points can be used in the
Wireless Distribution System mode without being wired.
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Figure 5: Although the access points are not wired, it is
possible for the two stations (laptop and controller) to
communicate with each other
In WDS mode, it is important that an access point can "see" its
neighbors (otherwise the chain would be interrupted!). This can
make it necessary to use special, distant antennas instead of
the supplied antennas.
As shown in Figure 5, stations are perfectly capable of taking
part in wireless operations in this mode. One important property
emerges from its; namely, that stations and access points must
share the entire data rate available. This situation can be made
more critical because in WDS mode, ALL access points and
stations work on the same wireless channel (for example
802.11g and channel 1, 2,4 GHz at 54 Mbps). This restriction
does, of course, have consequences for applications.
Applications in which a high data rate is necessary for large
numbers of stations (for example a hot spot on a trade fair site)
should be avoided. In applications, on the other hand, in which
controllers (several 100 Kbps) or HMI (several Mbps) access
the wireless network, and seldom download large files for
configuration, a bottleneck is not normally to be expected.
The performance of the wireless infrastructure in Figure 5 can
be improved if dual access points (SCALANCE W788-2PRO)
are used (see Figure 6). One wireless card can then be used to
set up the wireless infrastructure (backbone) and the other
wireless card provides the stations with a cell at the location of
the dual access point with which they can access this wireless
infrastructure. Once again, it is possible that special distant
antennas may be required.
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Figure 6: Wireless distribution system with dual access
points to improve the performance of the cell
Another useful application of WDS is when several outlying
plant sections need to be interconnected. This could, for
example, be several docks on the premises of a shipyard that
need to be connected over wireless since cables are unwanted.
Figure 7: WDS in the wireless networking of four plant
sections
A central access point and one wireless card in each of the four
dual access points implement a WDS. The central access point
is used at the same time as an interface to the wired network.
As shown in Figure 6, the dual access points implement a
"local" wireless network at the location where they are installed,
and this is used as a wireless interface by the stations. WDS
therefore once again provides the backbone of the wireless
infrastructure.
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Bridge Operation, Redundancy Mode
In industrial environments, it is often the case that an outlying
part of the plant is connected to the communication network
over a point-to-point link. For this situation, the products of
SCALANCE W provide the option of a bridge mode - a special
wireless distribution system application. Here, directional
antennas are often used so that the wave propagation is
optimized for the point-to-point link. To interface the outlying
part of the plant, the full bandwidth of the Wireless LAN is
available if only the directional wireless link is used.
Figure 8: Bridge operation between two plant sections. To
increase reliability, the redundancy mode is used
In Figure 8, the two communication networks must be
connected (Note: In this situation, communication network
means a large network with lots of stations. To keep the
situation clear, only one controller is shown in the network).
Two SCALANCE W access points are used. For a directional
wireless link, no further stations can be included in their cells.
Redundancy Mode
The wireless link in Figure 8 connects two important parts of a
plant. This means that vital data is transported over this
backbone. Interference of the wireless link would have serious
consequences for the entire plant. The I-feature of SCALANCE
W used here ensures that the data communication is handled
not over one wireless card but also over a second card that
handles the same data stream. In this mode, a dual access
point must, of course, be used (SCALANCE W788-2PRO). The
reliability of the data transmission becomes clear when one
card operates in the 2.4 GHz band and the other in the 5 GHz
band (taking into account transmit power permitted in specific
countries). However, it is not even necessary to change to a
different frequency band. Even using channel 1 and channel 11
at 2.4 GHz, means that the data streams are so far from each
other that there is hardly a disturbance that would cause
problems in both channels. It must be stressed that this
technique is fully transparent for the application and that the
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
access points negotiate which card is currently active and which
is in "hot standby“ mode. If a problem occurs, switchover times
from 20 ms to 25 ms can be achieved. This response was
tested in an analysis performed by ComConsult.
(http://intra1.nbgm.siemens.de/extern/spiegeln/net/html_00/ftp/p
rodukte/2004_07_ComConsult_Siemens_IWLAN.pdf)
Redundant Wireless Infrastructure, Spanning Tree (ST)
To provide protection against the failure of a wireless
infrastructure, and to improve the reliability of a wireless
network even further, it is also possible to use a ring topology
instead of the normal star topology. Such a structure can also
be used to back up a wired network with a wireless network in
risky areas.
Figure 9: Setting up a ring structure with WDS to increase
protection against failure of the wireless network using the
Spanning Tree algorithm
Figure 9 represents a further development of the structure from
Figure 6. The difference is that in Figure 9, the ring is closed at
the last dual access point. To avoid loops in such a wireless
infrastructure, the Spanning Tree algorithm is used.
As a result, in Figure 9, it is possible to select the path for the
data from the wired network in cell 2 over the dual access point
in cell 1. If, however, there is a serious disturbance on the WDS
link between the dual access points of cell 1 and cell 2, the ST
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
mechanism ensures that the wireless network automatically
looks for a new path. In the figure above, this is the path over
the dual access points of cell 3 and cell 4 – a redundant
wireless network is implemented. A precise analysis of the time
response of such a system can be found in an analysis by
ComConsult.
(http://intra1.nbgm.siemens.de/extern/spiegeln/net/html_00/ftp/p
rodukte/2004_07_ComConsult_Siemens_IWLAN.pdf)
Robust Construction and Connectors
The major characteristics of wireless devices for use in industry
are not only high-quality and reliability of the wireless channel
but also their rugged construction and the choice of connectors.
Metal Housing
For wireless products, the robustness provided by a metal
housing and a high degree of protection (for example IP65) are
particularly important. Generally, the simplest location for
installation is not the optimum location for wireless
transmission. A switching cabinet is a Faraday cage that "traps"
radio waves. The only remedy here is to use a distant antenna
installed, for example, on the roof of the switching cabinet.
Unfortunately, the coaxial cable connecting the antenna and the
device attenuates the sensitive radio signals and valuable
output power is lost along with a certain degree of reliability. It is
better if the cable to the distant antenna is unnecessary
because the device itself is installed at an ideal location for
radio transmission and the antenna supplied with the device
can be used. This also saves money.
The robust construction is required not only to allow an
optimum location for the wireless channel, but also keeps the
device functionally in a hard everyday industrial environment.
This is reflected in housings that are dust and waterproof up to
degree of protection IP65. As a result, devices can be set up
centrally without a switching cabinet and therefore allow
maximum flexibility.
Expanded Temperature Range
If additional thermal resistance is added to this defined
protection against dust and water and the permitted
temperature range extended, the products can also be used
outdoors. An expanded temperature range is not only
significant for outdoor use; installation under the roof of the
factory or in unheated logistics areas can lead to considerable
thermal stress.
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Industrial Wireless LAN – I-Features, Applications, Examples
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Condensation
Protection against dampness is particularly important when
devices are operated in sub-zero temperatures (Celsius). If the
device provides protection "only" against sub-zero
temperatures, this by no means guarantees protection against
condensation. If the temperature falls below zero in the building,
for example, when the gates to the workshop are opened, the
humidity in the workshop condenses immediately on and in the
device. If the device, however, is encapsulated so that humidity
cannot enter, this risk is avoided.
Summing up, we can say that in such situations, only products
can be used that are fully operable in negative temperatures
and that also have a high degree of protection (for example
IP65).
Vibration and Shock
Apart from the construction, resistance to vibration and shock is
necessary and must be proven in tests. This is particularly
important because wireless is often used with moving devices.
This cannot, of course, cope with every mechanical load, but
such tests mean far greater operating reliability than is available
with office and home products where the price often plays a
significant role. SCALANCE W products are subjected to
special SIMATIC environmental tests.
The mechanical load caused by turning or moving machine
parts not only affects the device itself. It is also important that
the cable connectors used are secured by screws or clamps to
avoid the high costs that can result from a loose connector. In
the SCALANCE W products, special measures have been
taken in this respect.
Figure 10: Locking mechanism of the hybrid connector
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Industrial Approvals
The Industrial Wireless LAN product line from SIMATIC NET is
characterized not only by its robust construction. Naturally,
industrial approvals such as EMC (electromagnetic
compatibility), FM (Factory Mutual), UL (Underwriters
Laboratories) and ATEX approvals for use in the
petrochemicals industry and in hazardous areas are a matter of
course. When used in paint shops, devices must be free of
silicone. To avoid toxic vapors in the event of fire, there must be
no halogens either in the device or cable.
If the products already have these properties and approvals,
this is an important factor for the customer and helps to avoid
additional costs.
Power over Ethernet
Apart from the power supply, Ethernet data cables must also be
laid to an access point. To be able to use only one cable and to
reduce effort during installation, the IEEE 802.3af working
group has defined the Power-over-Ethernet standard. 802.3af
allows two options:
•
•
Power is modulated onto the data cable. In this case, 4
wires are adequate (phantom power)
In one cable, four wires carry data and four wires carry
power. In this case an 8-wire cable is required.
Unfortunately, the IEEE 802.3af standard (that originated in the
office environment) does not include voltages under 30 V DC.
This is a disadvantage for the automation user because here, a
power network of 24 V DC is common along with devices
requiring 24 V DC power supplies.
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Figure 11: Power and data over one cable for the simplified
installation of an access point, even at 24 V DC
SIMATIC NET provides a complete solution (incl. cables) so
that customers with a 24 V DC supply voltage can also benefit
from simple installation over one cable. In this case, we take
advantage of the 802.3af option allowing power and data over 8
wires. This is made possible by the FC modular outlet power
insert that brings power and data together on one cable.
Apart from this mode, SCALANCE W, of course, supports the
IEEE 802.3af standard with both options.
Influence of Other Wireless Technologies
When looking at the influence of other wireless technologies,
we will pay particular attention to the three most successful
technologies on the market (according to sales): GSM, Wireless
LAN, and Bluetooth.
GSM does not pose problems since the licensed frequency
band cannot be expected to cause regular problems (GSM900:
880..915 MHz and 925..960 MHz, GSM1800: 1710..1785 MHz
and 1805..1880 MHz). Moreover, in the frequency bands being
used, no other services apart from GSM are permitted. (Note:
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Wireless LAN uses the 2.4 GHz and 5 GHz frequency bands).
The situation with wireless LAN and Bluetooth is different since
both use the license-free ISM band at 2.4 GHz.
The first point to make is that both the frequency hopping
mechanism (FHSS) of Bluetooth and the Direct Sequence
Spread Spectrum (DSSS) modulation technique are both
resilient when it comes to interference. Frequency hopping
involves a very fast change in transmission frequency and
therefore "escapes“ possible interference on a specific
frequency. In DSSS, there is powerful redundancy due to the
spreading of the frequency spectrum and it is hoped that this
spread will compensate narrow-band interference. (Note: Broad
band interference affecting an entire frequency range is seldom
with microwaves). During frequency hopping in Bluetooth, it is
perfectly possible that one of the frequencies used is in the
range of the wireless LAN band. Interference occurs, however,
only when the power of the Bluetooth device is great enough
and the redundancy mechanisms of wireless LAN can no longer
correct the error. The decisive factor here is the physical
distance between the Bluetooth transmitter and the WLAN
receiver. It should be noted that the normal Bluetooth class 2/3
transmitter with a power of 1 mW only causes real performance
problems in the immediate vicinity of the wireless LAN station.
As explained below, a plant in which a Bluetooth network and a
Wireless LAN are both used tends to be the exception. Users
have hardly any benefits from the double investment since
many applications of one technology can also be solved by the
other. The solution may not be quite as good but adequate to
make the high costs of a second wireless network unnecessary.
This reduces the question of interference to unwanted radiation,
for example caused by mobile telephones with an active
Bluetooth interface. Here, system operators themselves must
take measures to avoid problems occurring. Just as today in
factories, there must be clear rules for the layout of the
manufacturing area and the routing of cables or IP address
assignment, it will also be necessary in future to control the
active wireless systems used so that certain combinations of
systems are not installed alongside each other.
The responsibility for peaceful coexistence of the two
technologies is, however, not simply pushed onto the user.
There are, for example, positive approaches in the new
specifications of Bluetooth. Here, methods are implemented
that avoid frequencies already in use thus preventing
interference of Wireless LAN. Bluetooth does not lose anything
in performance because the frequency hopping mechanism
simply omits these frequencies and concentrates on those not
being used.
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In Wireless LAN, similar mechanisms are implemented in the
IEEE 802.11h standard. This specifies that a wireless network
must first scan the entire frequency band for existing
transmitters before starting to transmit (Dynamic Frequency
Selection, DFS). A transmitter must also control its power
output (Transmit Power Control, TPC) to avoid a "quiet" station
being "shouted down" by the strong signal.
The simplest way for Wireless LAN to avoid a collision with
Bluetooth is to use the 5 GHz band. Here, there are no
Bluetooth devices.
Safety-related Signals in Industrial Wireless LAN
The transmission of safety-related signals in Industrial Wireless
LAN deals with products such as emergency stop buttons
whose integration in a wireless network involves special
requirements of the wireless channel. Products of this quality
must also be certified by national safety organizations.
Separation or integration
If safety-related signals are transmitted over a wireless network,
the basic question is whether or not these signals need to use a
reserved network or whether they can be transmitted along with
the operational data traffic.
The implementation of a separate infrastructure is one
traditional approach and has the following advantages:
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Reduced bus load
System of less complexity
Simplified troubleshooting
Availability of the system
Simplified certification
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Figure 12: Separation of safety-related data (broken line)
and operational communication (continuous line)
Although the advantages of a separate network are its reduced
complexity, these signals can also be implemented in an
integrated concept. If a wireless network is designed so that it
can transmit safety-related signals alongside operational data,
this opens a new dimension in customer benefits:
• Reduction of planning and configuration effort
• Reduction of the installation and commissioning costs
• Uniform operation
• Reduced effort for infrastructure
• Higher flexibility
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Figure 13: Safety-oriented data (broken line) and
operational communication (continuous line) in one
network
An integrated wireless network is, of course, a great challenge
in terms of technical implementation and also requires
modification of Industrial Ethernet (Safety on Industrial
Ethernet). The major benefits are in the uniform handling of
communication. This significantly reduces life-cycle costs.
Safety Standards
The risk potential of a system is analyzed in the EN 1050 and
EN 292 standards. Taking into account the specified risk, EN
954-1 then describes the general guidelines for implementing
safety-related parts of control systems and divides these into
various categories. This division ranges from the lowest
category B to the highest category 4.
DIN V 19250, on the other hand, considers the fundamental
safety aspects of measurement and control equipment. Once
again taking into account the specified risk, these are divided
into different classes from AK1 through AK8. On the other hand,
DIN 19251 provides requirements and measures for
safeguarded functions according to class. DIN V VDE 0801 and
modification A1 must also be taken into consideration. They
define fundamental aspects for computers in systems with
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safety functions. Since the term computer is to be understood
generally, this standard also applies to micro controller
systems.
IEC 61508
IEC 61508 is a relatively new standard. It deals with the
functional safety of electrical, electronic, and programmable
electronic safety systems and classifies them in safety integrity
levels from SIL 1 through SIL 4. The still valid standards DIN V
19251 and DIN V VDE 0801 are included in this standard.
Naturally, the generally valid standards for electrical safety such
as EN 60204-1 or DIN VDE 0110 and the European directive on
machines (98/37/EEC) as well as the EMC standards must not
be forgotten.
Safe Wireless with Industrial Wireless LAN
The development of wireless transmission mechanisms for
safety-related signals provides additional benefits for
customers, for example in hand-held programming devices for
CNC machines or robots. If safety-related communication is
changed by a protocol at the application level of both
transmitter and receiver, the actual wireless transmission
medium and its interfacing to the transmitter and receiver are of
secondary importance in the engineering of safety-related
functions. (This is known as a "gray channel“). Such a protocol
will be available for PROFINET in 2005. If it is used, it is "only"
necessary to make sure that the communication channel has
the required degree of reliability. From a safety perspective, it is
acceptable that a fail-safe application regularly switches to the
safe state simply because the wireless channel is erratic. From
a customer perspective, however, such a system is unusable.
The I-features of Industrial Wireless LAN provide a wide range
of mechanisms that allow reliable wireless systems to be set
up. Along with a safety protocol for PROFINET, it will then also
be possible to implement fail-safe wireless links.
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Applications of an Industrial Wireless LAN in Automation
Engineering
Applications
Applications can be found wherever mobility and flexibility are
at a premium. This is the case in all processes in which
movement is involved. This mobility makes it possible to
reshape work processes and develop innovative solutions.
Simply substituting hard-wired cables does not normally mean
enough benefit except for temporary installations or new
installations that would involve considerable effort setting up
cable ducts and racks. Typical applications requiring mobility
and flexibility:
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Driverless transport systems
Monorail systems
Moving tables
Moving and rotating machines: Substitute for drag
chains, slip contacts and slip rings
Cranes
Conveyor systems
Mobile service/diagnostics with handheld and laptop
Mobile operation and monitoring
Fast networking of individual manufacturing areas /
isolated groups of machines during commissioning
Mobile data acquisition in stores and logistics.
There are also many applications in the field of automation in
which wireless communication between individual stations is an
additional advantage for the user.
•
Communication with mobile stations, mobile data
acquisition
The user can acquire data from all manufacturing and storage
areas with mobile, industrial Internet pads such as the MOBIC
(Mobile Industrial Communicator) from SIMATIC NET and pass
it on for central data processing. The mobile handhelds used
are not assigned to a specific machine or process but to a user.
The requirements in terms of numbers of devices are reduced
considerably.
Time-consuming transfer of data from paper to the central
database and the potential errors involved are eliminated. With
a fully integrated concept for data acquisition, significant costs
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can be saved particularly at interfaces at which data must be
transferred from one process step to the next.
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Mobile service and diagnostics
If a fault occurs, service personnel can analyze the problem on
site and can obtain information for the fast elimination of the
problem over the MOBIC wireless Internet pad. The availability
of spare parts in the warehouse can be immediately checked
and parts ordered online if necessary.
Diagnostics does not, however, only relate to fault situations.
Operational data such as levels or the load on machines can
also be assessed quickly and reliably by personnel.
Figure 14: Industrial Wireless LAN in Automation
Engineering
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Communication with Mobile Stations and Mobile
Commissioning
Using mobile communication can greatly simplify and speed up
the commissioning phase and lead to considerable cost
savings. Maintenance engineers can monitor machine settings
directly via their wireless service units and intervene
immediately when problems occur. Personnel can use devices
with which they are familiar such as the field PG because they
can be included in the wireless network thanks to standardized
interfaces (PCMCIA wireless adapter).
•
Flexible manufacture in temporary configurations and
communication with outlying units
In today's world, assembly lines can no longer be rigid,
inflexible units requiring considerable time and money before
they can be modified for other uses. Particularly in automobile
manufacturing plants, the factory layout is liable to fast
modification. Flexible production means meeting customer
requirements quickly and without long conversion times. By
using wireless data networking, production units can be
integrated in the data network quickly and with little effort. Test
configurations can also be implemented quickly.
An industrial wireless LAN also allows cost-effective integration
of machines and controllers installed in otherwise inaccessible
locations. Expensive and time-consuming cabling is avoided.
Note: Wireless is preferable to cable only where
an existing cable duct cannot be used (for example data
and power cables must not laid together)
a new cable duct must be installed
data must be transmitted across public thoroughfares or
over water
• Communication with moving stations
The interfacing of moving devices to the data network involves
considerable effort. A wireless connection saves the entire data
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October 2004
busbar installation for monorail systems and avoids systems
with slip contacts for driverless transport systems that easily
become polluted and require considerable maintenance effort.
In both these applications, routes can also be changed simply,
achieving considerable flexibility.
The integration of rotating devices in a data network avoids
wear and tear on the slip rings. The same advantage also
applies to the substitution of drag chains.
Examples
Local Service and Diagnostics on the Company Premises
Application
Works sites are often extensive areas (tens of meters up to
several hundreds of meters) predominantly with indoor areas
but also outdoor units. The environmental conditions often
mean an increased degree of protection for equipment unless it
is installed in switching cabinets. The machines to be monitored
are part of an extensive manufacturing or process plant and are
interdependent so that the output of one machine strongly
influences the operation of another. A communication network
(for example Ethernet) is installed for data exchange between
the control level and field level and ensures reliable data
exchange.
For local servicing (on-site troubleshooting, program uploads,
data downloads, firmware updates, commissioning,
configuring), access to the process must be monitored locally.
This is achieved with a mobile device that has an effective
range of a few meters from the machine. For diagnostics
(process visualization, monitoring of operating data), it is not
absolutely necessary that the process is observed locally so
that the effective range of a mobile device can be between
several meters up to several hundreds of meters.
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Figure 15: Mobic used for service in manufacturing
automation
Solution
To be of benefit to the customer, it is necessary that the
wireless network allows not only for service work in the local
(several meters) vicinity of the machine but that diagnostic
functions are also possible over a much wider area. For
diagnostic purposes or for visualization of process data, an
adequate data rate is important since complex data is also
visualized. For diagnostics, a device with a large display can
therefore be assumed (laptop, Internet Pad). The data must be
transferred with extremely reliable communication devices. This
relates not only to the construction but to the communication
technology. Since laptops or Internet Pads are mobile devices,
there must be mechanisms that inform the process when they
exit the cell so that the process can continue in automatic
mode.
For these reasons (transmission range, data rate, reliability),
the use of an Industrial Wireless LAN must be recommended
for this application. In addition, the roaming function supported
in wireless LAN allows continuous use over large areas since it
is possible to move from one access point to another without
any interruption.
The costs for the installation of a wireless network and for the
purchase of mobile stations are spread over the numerous
machines in the data network that can be included in
diagnostics.
Data Exchange between an Outlying Controller and a Data
Network on the Works Site
Application
Information is exchanged between an outlying controller or
machine and the wired data network (for example Ethernet) on
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the works site over a maximum distance of several hundreds of
meters. The attachment to the data network is not over cable
either because no cable conduits are available or because the
data cable must not be laid in the existing conduit. Regularly
changing factory layouts or setup of test equipment increase
the benefits of setting up a wireless network. Not only
operational data but also alarm messages for maintenance
requests are transmitted over the wireless network. Both the
outlying unit and the wired data network require a wireless
interface.
Solution
In this application, reliable data transfer over a distance that is
normally significantly greater than 10 m but does not exceed
several hundreds of meters on the works site. The wireless
network must be resilient to disturbances and reflections in the
industrial surroundings. The net data rate for shorter data
packets as normally found in automation engineering must not
be too low. Since the controller sends information about critical
states in the equipment in the form of alarm messages, it must
be able to access the communication infrastructure at any time.
To achieve this, suitable technologies must be used.
For these reasons (transmission range, data rate, guaranteed
access to the wireless network), the use of an Industrial
Wireless LAN is practical for this application. The comparatively
high data rate means that mobile handhelds can also be used
in this wireless network. This would reduce the share of
infrastructure costs for the outlying controller. By reserving the
data rate, the controller can send an alarm message at any time
even when other mobile handhelds are communicating in the
same wireless network.
The infrastructure costs for a wireless network play a major role,
in particular, when only one outlying controller needs to be
connected. In this case, the solution should be compared with a
wired solution to determine customer benefits.
Conveyor Systems
Application
In logistics and materials management, vehicles without a driver
are often used today. Travel is either along an induction loop in
the floor or along a guide rail above the goods to be
transported. The data is transferred either inductively, optically
or with a slip contact and connects a mobile controller with a
fixed central unit. Power is supplied either by batteries, over slip
contacts, or inductively. The effective range of such a system is
often over several hundreds of meters.
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Figure 16: Driverless Transport System
Solution
Since a central unit exists that implements the data exchange
with the controllers on the mobile vehicles, a local wireless
network is necessary to allow point-to-multipoint links. An
adequate transmission range must be available. Since there are
numerous stations in the wireless network, a suitable data rate
is also necessary. The controllers on the moving vehicles often
have an Ethernet interface. The provider of wireless products
must therefore offer suitable products.
An Industrial Wireless LAN provides not only the required
transmission range and data rate but also the option of
establishing point-to-multipoint. In such a network that allows
seamless and uninterrupted operation over large areas, stations
are passed on from one access point to the next (roaming). The
conveyor system application is a typical application for wireless
LAN.
Substituting slip contacts that are liable to contamination
problems and optical connections is of great benefit to the user
and the comparatively low costs for a wireless infrastructure
fade into insignificance.
Linking Data Networks (Ethernet) of Remote Plants (many
hundreds of meters up to several kilometers)
Application
Linking the data networks of two plants can be extremely
difficult when, for example, public land, streets, rail tracks or
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water have to be crossed. The customer even benefits from a
wireless link when the link is only temporary or set up for test
purposes.
Solution
In this application, the advantages of Industrial Wireless LAN in
terms of transmission range and data rate come to the fore. To
cover large distances, directional antennas are installed
outdoors on masts or roofs. To avoid the need for unnecessarily
long antenna cables, it makes sense to use devices that are
resistant to the effects of weather (temperature, water). For
such an application, Industrial Wireless LAN provides the
redundancy mode with which data can be transmitted between
the two plant sections with a particularly high degree of
reliability. This is important since the wireless network is the
only link between the two areas.
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SIMATIC NET Products for Industrial Wireless LAN
SIMATIC NET offers the following products for setting up an
industrial wireless network:
Access Point SCALANCE W788-1PRO
An access point suitable for use in industry for setting up a
wireless network (infrastructure) and for attaching to the wired
data network (Ethernet)
Figure 17: Access Point SCALANCE W788-1PRO
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Copyright © Siemens AG 2004
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Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
Wireless LAN 802.11b/g and 802.11a with up to 54 Mbps
at 2.4 GHz and 5 GHz
Forced roaming if wire break on the Ethernet cable
(option)
Wireless Distribution System (WDS) for point-to-point
links
Degree of protection IP65, robust metal housing
Operating temperature –20 °C ... +60 °C resistant to
condensation
Redundant power supply 19 - 57 V DC and power-overEthernet, even at 24 V DC
10/100 Mbps Ethernet port for connection to the wired
network
Advanced data security with WPA and encryption with
AES
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C-PLUG (configuration plug) exchangeable memory
medium for fast device replacement without
programming device
Integration in STEP 7/NCM PC
Dual Access Point SCALANCE W788-2PRO
Dual access point suitable for industrial use with two separate
wireless adapters to establish a high-quality wireless network
(infrastructure) and to connect to the wired data network
(Ethernet)
Figure 18: Dual Access Point SCALANCE W788-2PRO
Identical to the SCALANCE W788-1PRO, plus:
• Second wireless adapter for wireless LAN 802.11b/g and
802.11a
• 2x R-SMA connectors for distant antennas
• Redundancy mode for extremely reliable point-to-point
link between two separate wireless adapters
Ethernet Client Module SCALANCE W744-1PRO
Ethernet adapter suitable for industrial use to connect a node
(with Ethernet attachment) to an Industrial Wireless LAN
network
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Figure 19: Ethernet Client Module SCALANCE W744-1PRO
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Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
Wireless LAN 802. 11b/g and 802.11a with up to
54 Mbps at 2.4 GHz and 5 GHz
Degree of protection IP65, robust metal housing
Operating temperature –20 °C ... +60 °C resistant to
condensation
Redundant power supply 19 - 57 V DC and power-overEthernet, even at 24 V DC
10/100 Mbps Ethernet port for connection to terminals
with an Ethernet port
Advanced data security with WPA and encryption with
AES
C-PLUG (configuration plug) exchangeable memory
medium for fast device replacement without
programming device
Integration in STEP 7/NCM PC
PC Card CP 7515
PC card (32-bit cardbus) with integrated antennas to link a node
(for example field PG) to an Industrial Wireless LAN network
Figure 20: PC Card CP 7515
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Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
Wireless LAN 802. 11b/g and 802.11a with up to
54 Mbps at 2.4 GHz and 5 GHz
PC Card with 32-bit Cardbus interface
Degree of protection IP20
Operating temperature 0 °C ... +55 °C
Advanced data security with WPA and encryption with
AES
Installation and maintenance with management tool for
Windows 2000, XP
Integration in STEP 7/NCM PC
PCMCIA Card CP 1515
PCMCIA card (16-bit) with integrated antennas to link MOBIC
T8 to Industrial Wireless LAN
Figure 21: PCMCIA Card CP 1515
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Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
Wireless LAN 802. 11b with up to 11 Mbps at 2.4 GHz
PCMCIA card for installation in MOBIC T8
Degree of protection IP20
Operating temperature 0 °C ... +55 °C
Data security with WEP
Integration in STEP 7/NCM PC
Power Supply PS791-1PRO
90…265 V AC power supply unit with degree of protection IP65
for free mounting or direct mounting on SCALANCE W-700
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Figure 22: Power Supply PS791-1PRO
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10 W AC/DC power supply unit (90 – 265 V AC / 24 V
DC (±7%))
Perfectly adapted to SCALANCE W-700
Degree of protection IP65, robust metal housing
Operating temperature –20°C ... +60°C with protection
from condensation
Connector that can be assembled on-site with a high
degree of protection against shock and vibration
Power M12 Plug pro for 24 V DC (output)
AC Power 3+PE cable connector (input)
FC Modular Outlet Power Insert
Power insert for combining power (24 V DC) and Ethernet on
an 8-wire cable
Figure 23: FC Modular Outlet Power Insert
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Power and data over one cable
Input: 18 - 57 V DC and 10/100 Mbps Ethernet port RJ45
Output : Power and Ethernet over 8-wire cable
Perfectly adapted to SCALANCE W-700
Insulation displacement technique for 8-wire IE hybrid
cable 2x2 + 0.34
Robust metal housing with dust protection
Wall or standard rail mounting inside or outside the
switching cabinet (IP40).
Ideal EMI protection due to metal housing
Accessories
Figure 24: Accessories (antennas, lightning protection,
cables, connectors)
• Omni-Directional Antenna
ANT 795-4MR: 2.4 GHz and 5 GHz, 4 dBi, R-SMA, mounted
directly on housing
ANT 795-6MR: 2.4 GHz and 5 GHz, 3 dBi, R-SMA,
5 m antenna cable, mounted on mast or wall
• Directed Antenna
ANT 793-8DR: 5.7 GHz, R-SMA, 15 dBi, 20°, 5 m antenna
cable, mounted on mast or wall, USA and Canada only
• Antenna extension cable FRNC, 5 m
• Lightning conductor element LP798-1PRO
• IP67 Hybrid cable connector
• Power M12 cable connector pro (IP65)
Copyright © Siemens AG 2004
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Industrial Wireless LAN – I-Features, Applications, Examples
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Antenna terminator TI795-1R,
if only one antenna is connected
(supplied with 795-6MR and 793-8DR)
Future Products from SIMATIC NET
Note on this section:
All product and technology descriptions represent the
current (provisional) range of functions and are subject to
change. In particular, the names of products and
technologies must be taken as provisional working names.
The Industrial Wireless LAN products from SIMATIC NET
provide the discerning industrial customer with the advantages
of the wireless world for applications in which mobility and
flexibility are demanded. At the same time, Industrial Wireless
LAN is based on the standard mechanisms of IEEE 82.11.
This is particularly clear if we look at the Link Check I-feature.
The access point uses 802.11-compliant data packets to check
whether or not the station is still within the cell.
Another example is the reservation of data rate I-feature. Every
802.11-compliant station can be included in this mechanism.
Devices that are not included in the mechanism are handled as
usual in an 802.11-compliant cell.
Figure 25: Positioning wireless LAN, Industrial Wireless
LAN and IWLAN RR
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
When wireless LAN is used in industry, there are requirements
that cannot be implemented if 100% compatibility (such as
Industrial Wireless LAN) with IEEE 802.11 is demanded. These
requirements include, for example, extremely fast handover
times when a station roams from one cell to another. This
requirement is found particularly often in applications in which
stations move at higher speeds.
If a vehicle in a driverless transport system moves at 10 m/s
and is involved with the handover to the next cell for 500 ms, it
travels 5 m without access to the wireless communication.
Another example, is PROFINET IO communication that
acknowledges with an error message if a station cannot reply
three times in succession because it is busy with the handover
to the next cell.
If such exacting requirements are to be met, the technology
must be expanded but will no longer conform with the standard.
Such a strategy has two important advantages:
1. Such closed systems provide a high degree of data
security since standard stations no longer have access
to the wireless channel without firmware exansion
2. By using standard wireless LAN chipsets, the customer
has the benefit of standardized hardware that is also
available from other vendors.
Industrial Wireless LAN RR
This technology is an expansion of Industrial Wireless LAN and
provides customers with real-time wireless communication even
when stations roam from cell to cell and when transmission
times in the range 10 ms to 100 ms are required. As normal in
Industrial Wireless LAN, even in this cell, communication is
predictable (deterministic). It is important to be aware that no
802.11-compliant stations can be operated in an Industrial
Wireless LAN cell with the RR attribute.
If such stations are required in wireless communication, this can
be achieved with a "shadow cell" in which the SCALANCE
W788-2PRO dual access point is extremely useful when one
wireless card implements the Industrial Wireless LAN cell and
the other works in RR mode.
Copyright © Siemens AG 2004
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Figure 26: Structure of a "shadow cell“ for operating
wireless LAN stations in an Industrial Wireless LAN RR cell
Applications for Industrial Wireless LAN RR
With monorail systems, PROFINET IO1 is being used more and
more because the cyclic data traffic is well suited to support
control of the suspended rail. To avoid the problems of wear
and tear with slip contacts, these applications increasingly use
contactless technology. To be able to transmit data cyclically
with fixed response times, the wireless network must support
this performance. In such situations, the performance of
Industrial Wireless LAN RR can be put to optimum use.
1
Support of the PROFINET real-time property RT
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SIMATIC NET White Paper E.0.1.
Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Figure 27: Monorail system, today still using slip contacts
to transfer the carriage control to the suspension rail, in
future contactless with Industrial Wireless LAN RR
Industrial Wireless LAN RR will basically be used wherever fast
moving stations require close contact with the wireless network
and fast handover times from cell to cell.
SCALANCE W788-1RR
An access point suitable for use in industry for setting up a
wireless network (infrastructure) and for attaching to the wired
data network (Ethernet). Optional support of rapid roaming.
Figure 28: Access Point SCALANCE W788-1RR
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Copyright © Siemens AG 2004
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Very short handover times to support moving
stations when roaming (IWLAN RR)
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IEEE 802.11h for operation with higher power output
in Europe at 5 GHz
Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
Wireless LAN 802. 11b/g and 802.11a with up to
54 Mbps at 2.4 GHz and 5 GHz
Forced roaming if wire break on the Ethernet cable
(option)
Wireless Distribution System (WDS) for point-to-point
links
Degree of protection IP65, robust metal housing
Operating temperature –20 °C ... +60 °C resistant to
condensation
Redundant power supply 19 - 57 V DC and power-overEthernet, even at 24 V DC
10/100 Mbps Ethernet port for connection to the wired
network
Advanced data security with WPA and encryption with
AES
C-PLUG (configuration plug) exchangeable memory
medium for fast device replacement without
programming device
Integration in STEP 7/NCM PC
SCALANCE W788-2RR
Dual access point suitable for industrial use with two separate
wireless adapters to establish a high-quality wireless network
(infrastructure) and to connect to the wired data network
(Ethernet).Optional support of rapid roaming separately for
each individual wireless card.
Figure 29: Dual Access Point SCALANCE
W788-2RR
Identical to the SCALANCE W788-1RR, plus:
• Second wireless adapter for wireless LAN 802.11b/g and
802.11a
Copyright © Siemens AG 2004
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2x R-SMA connectors for distant antennas
Redundancy mode for extremely reliable point-to-point
link between two separate wireless adapters
Ethernet Client Module SCALANCE W747-1RR
Ethernet adapter suitable for industrial use to connect a station
(with Ethernet attachment) to an Industrial Wireless LAN RR
network Optional support of rapid roaming.
Figure 30: Ethernet Client Module SCALANCE
W747-1RR
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Very short handover times to support moving
stations when roaming (IWLAN RR)
Logical support of up to 8 IP addresses
IEEE 802.11h for operation with higher power output
in Europe at 5 GHz
Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
Wireless LAN 802. 11b/g and 802.11a with up to
54 Mbps at 2.4 GHz and 5 GHz
Degree of protection IP65, robust metal housing
Operating temperature –20 °C ... +60 °C resistant to
condensation
Redundant power supply 19 - 57 V DC and power-overEthernet, even at 24 V DC
10/100 Mbps Ethernet port for connection to terminals
with an Ethernet port
Advanced data security with WPA and encryption with
AES
C-PLUG (configuration plug) exchangeable memory
medium for fast device replacement without
programming device
Integration in STEP 7/NCM PC
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
IWLAN/PB Link PN IO
Link between Industrial Wireless LAN and PROFIBUS with
PROFINET IO functionality. Optional support of rapid roaming.
Figure 31: IWLAN/PB Link PN IO
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Very short handover times to support moving stations
when roaming (IWLAN RR)
Extremely reliable due to reservation of data rate and
cyclic monitoring of the link (IWLAN)
PB master interface for flexible integration of field
devices in an IWLAN wireless infrastructure
Attachment of an IWLAN antenna or alternatively an
antenna for operation with RCoax cable
C-PLUG (configuration plug) exchangeable memory
medium for project engineering data for fast device
replacement without programming device
PROFINET communication (IO proxy)
Wireless LAN 802. 11b/g and 802.11a with up to
54 Mbps at 2.4 GHz and 5 GHz
IEEE 802. 11h for operation with higher power output in
Europe at 5 GHz
Degree of protection IP20 for installation on a standard
rail in the switching cabinet
Advanced data security with WPA and encryption with
AES
Note: The device is not suitable for linking to PROFIBUS
networks, but for linking traditional PROFIBUS DP slaves at the
Ethernet control level.
Customer benefits in the monorail system application:
Copyright © Siemens AG 2004
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Integration of PROFIBUS field devices in an Industrial
Wireless LAN (investment protection)
Construction: optimum for installation in a monorail
system along with
vehicle control ET 200 S
Extremely flexible application duty connection of IWLAN
antennas or alternatively antennas for RCoax cable
IWLAN RCoax Cable
Coaxial cable with defined slots for controlled
radiation/reception of an Industrial Wireless LAN cell in the
close vicinity with contactless technology
Figure 32: IWLAN RCoax Cable
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Reliable wireless link
Controlled cell
Highly flexible application
Simple installation
Optimum attachment to SCALANCE W-700
Customer benefits in the monorail system application:
• Wireless and therefore no wear and tear in data
transmission to mobile communication partners
• Contactless technology as substitute for slip contacts
Antennas
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Copyright © Siemens AG 2004
All Rights reserved
Directional antenna (60°) for 2.4 GHz to extend and
optimize the wireless link
Planar antenna (180°) for 2.4 GHz and 5 GHz to extend
and optimize the wireless link
Vehicle antenna (omnidirectional) for 2.4 GHz and 5 GHz
to extend and optimize the wireless link especially in
unmanned transport systems
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Glossary
2G
Digital mobile wireless networks of the second generation, for
example GSM
3G
Digital mobile wireless networks of the third generation, for
example UMTS
Occasionally the term 2.5G is used. In this case, the
expansions of GSM are meant (EDGE, GPRS)
IEC 61508
Standard relating to functional safety (new)
EN 954-1
Standard relating to functional safety (old)
Access point
WLANs are set up using access points. They also connect the
wired data network.
ACK
Acknowledge
Signal in handshake protocol for avoiding the hidden node
problem
ACL
Access Control List
List of MAC addresses with the right to access the wireless
network
Ad hoc network
Wireless network between individual devices (point-to-point)
AES
Advanced Encryption Standard
New standard for encryption of data in WLANs
Antenna diversity
Technique with which a radio receiver is equipped with two
antennas so that it can select the better of two signals
Antenna gain
Improvement of the antenna compared with an isotropic
radiator achieved by suitable construction (passive!)
ATM
Asynchronous Transfer Mode
Wired network used particularly in the backbone for large
distances at high data rates
Authentication
Access control in communication networks (Who am I?) to
increase data security
Authorization
Distribution of authorizations in communication networks
(What can I do?) to increase data security
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October 2004
BPSK
Binary phase shift keying
Modulation technique in WLANs
BQTF
Bluetooth Qualification Test Facility
Facility for monitoring the interoperability of products of
various vendors
BSS
Basic Service Set
WLAN network with access to the infrastructure over a single
access point
CCK
Complementary code keying
modulation mechanism in WLAN
CDMA
Code Division Multiplex
Code-controlled medium access control
CF
Compact flash
CFP
Contention free period
Period during which access is managed by the access point
(to support time-critical services)
CP
Contention period
Period in which access is controlled according to CSMA/CA
(to support time-critical services)
CP
Communications processor
CSMA/CA
Carrier Sense Multiple Access with Collision Avoidance,
medium access control on a wireless IEEE 802.11 network
CSMA/CD
Carrier Sense Multiple Access with Collision Detection,
medium access control for wired Ethernet network
CTS
Clear to send
Signal in handshake protocol for avoiding the hidden node
problem
DDE
Dynamic Data Exchange
DCF
Discrete coordinated function
Normal medium access control in 802.11 in contrast to PCF
DECT
Digital Enhanced Cordless Telecommunications, European
standard for language and data communication
DFS
Dynamic Frequency Selection in the 5 GHz band
Diversity
Wireless receiver with two antennas allowing selection of the
best signal
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October 2004
Downstream
Communication from access point to client
DSSS
Direct Sequence Spread Spectrum (IEEE 802.11b)
EDGE
Enhanced Data Rates for Global Systems for Mobile
Communications Evolution
Further development of GSM with data rates up to 384 Kbps
for video and wireless applications
EIRP
Equivalent isotropic radiated power
The power output that would have to be applied to an
isotropic radiator so that it would radiate the same effective
power as another antenna in a specific direction. An isotropic
radiator is a theoretical antenna that radiates in all directions
with equal intensity (isotropic) and is assumed to be
infinitesimally small.
ESM
Electrical Switch Module
ESS
Extended Service Set
Wireless network consisting of several overlapping basic
service sets (BSS)
ETSI
European Telecommunication Standard Institute
Fall back
Gradual reduction of the data rate when receiving conditions
are bad to allow the connection to be maintained
FDMA
Frequency Division Multiplex Access
FEC
Forward Error Correction
Inclusion of redundant bits in the useful data to make the
signal less sensitive to interference
FHSS
Frequency Hopping Spread Spectrum
A method used in 802.11b and Bluetooth.
FTEG
Law regarding wireless equipment and telecommunications
installations in Germany
GFSK
Gaussian Phase Shift Keying
Modulation technique in 802.11
GPRS
General Packet Radio Service
Expansion of GSM for packet-oriented data communication at
up to a maximum 170 Kbps.
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October 2004
GSM
Global System for Mobile Communications
Digital telephone services at frequencies in the 900 MHz,
1800 MHz and 1900 MHz ranges
GSM-R
GSM for railroad traffic at high speeds
Handover
Mechanism for transferring a station from one radio cell to the
next. The term is often used in conjunction with roaming.
Handshake
Acknowledgment process to establish a connection between
stations ready to communicate.
Hidden node problem Two nodes are arranged in a radio cell so that they are
outside their own transmission range. If they both access the
medium of the same time, collisions result.
HIPERLAN
High-performance Radio LAN in the 5 GHz band
Home RF
Standard for wireless communication between PCs and
home-oriented consumer devices.
HSCSD
High Speed Circuit Switched Data
GSM wireless network for higher data rates
IAPP
Inter Access Point Protocol
Protocol for communication between the APs
IBSS
Independent Basic Service Set
Ad-hoc network for spontaneous and simple establishment of
wireless connections without a wireless infrastructure
IE
Industrial Ethernet
IEEE
Institute of Electrical and Electronics Engineers
IEEE 802.11
Standard for wireless networks in the 2.4 GHz range with
transmission rates of up to 2 Mbps.
IEEE 802.11a
Standard for wireless networks in the 5 GHz range with
transmission rates of up to 54 Mbps.
IEEE 802.11b
Standard for wireless networks in the 2.4 GHz range with
transmission rates of up to 11 Mbps.
IEEE 802.11g
Standard for wireless networks in the 2.4 GHz range with
transmission rates of up to 54 Mbps.
IEEE 802.11h
Standard for wireless networks in the 5 GHz band with
transmission rates up to 54 Mbps. Standard for continental
Europe; condition DFS/TPC
IEEE 802.11i
Security standard that replaces the obsolete WEP standard; It
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includes, among other things, the AES encryption technique
IEEE 802.3af
Standard defining power-over-Ethernet (PoE)
IP
Internet Protocol
Collection of program routines that the TCP protocol
accesses
IP20
Device degree of protection
IP 65
Device degree of protection
IPSec
Internet Protocol Security
Open standard for increasing data security in IP networks
IrDA
Infrared Data Association
Standard for data communication with infrared over short
distances
IS
Intrinsically Safe (protected against explosion)
ISM band
Industrial, Scientific and Medical Band
Frequency band for use without license
ISO
International Organization for Standardization
Kerberos
Security system for the encryption of sensitive data
FOC
Fiber-optic cable
Transmission medium for optical networks.
Multipath propagation Reflections of an electromagnetic wave from different objects.
As a result, the electromagnetic wave arrives at the receiver
with different intensities and after different propagation times
MIC
Message Integrity Protocol
Technique for increasing the integrity of data in WLANs
Mini PCI
Special design of WLAN adapters for direct integration in
products
MSS
Mobile Satellite Service within UMTS
OFDM
Orthogonal Frequency Division Multiplex Method of
modulation in 802.11a
OFDM/CCK
Orthogonal Frequency Division Multiplex/complimentary code
keying
Method of modulation in 802.11a
PAN
Personal Area Network
Network for devices at relatively short distances from each
other.
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PC Card
Construction and use, see PCMCIA. In contrast to PCMCIA,
instead of a 16-bit interface, a 32-bit interface is used allowing
high data rates of up to 54 Mbps in the case of WLAN.
PCF
Point coordinated function
Medium access control technique to support time-critical
services in WLANs
PCMCIA
Standard for PC cards (credit card size). PCMCIA cards
(Personal Computer Memory Card International Association)
are used for input/output (for example modem) or memory
expansions as well as to implement the interface for WLANs
particularly in laptops
PDA
Personal Digital Assistant
Mobile end device
Pico network
Network structure in Bluetooth in which up to eight stations
are organized
QAM
Quadrature amplitude modulation
QPSK
Quadrature phase shift keying
QoS
Quality of Service
R&TTE
Radio and Telecommunications Terminal Equipment Directive
EU directive for telecommunications terminal equipment
RADIUS
Remote Authentication Dial - In User Service
for secure communication networks
RCM
Radio Client Module (Ethernet adapter, Ethernet client)
RegTP
Regulatory body for telecommunication in Germany
RLM
Radio Link Module (access point)
Roaming
Free movement of wireless LAN nodes even beyond the
boundaries of an access point's cell. The station can change
from one radio cell to the next without any noticeable
interruption (see also handover)
RT
Real Time
RTS
Request To Send
Signal in handshake protocol for avoiding the hidden node
problem
Scatter network
Network structure in Bluetooth in which several Pico networks
are organized
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October 2004
SIG
Special Interest Group
The user organization for Bluetooth
SNMP
Simple Network Management Protocol
Standardized protocol for transporting network management
information.
SSID
Service Set Identifier Address
Name of the WLAN
TDMA
Time Division Multiplex Access
TKIP
Temporal Key Integrity Protocol
Scheme for cyclic changing of the keys in WLANs
TPC
Transmission Power Control
Automatic control of transmitter power in the 5 GHz band
UMTS
Universal Mobile Telecommunications System
Mobile wireless transmission for voice, audio, image, video,
and data communications
UNII
Unlicensed National Information Infrastructure
Name of the 5 GHz band in American literature
Upstream
Communication from client to access point
URAN
UMTS Radio Access Network
UTRAN
UMTS Terrestrial Radio Access Network
WCDMA
Wideband CDMA
Method of modulation for high data rates
WDS
Wireless Distribution System
Radio links for connecting the access points for an extended
service set (ESS)
Web pad
Portable device in DIN-A4 size with a touchscreen for Internet
use
WECA
Wireless Ethernet Compatibility Alliance
An alliance of various wireless LAN product manufacturers
who ensure product compatibility through product testing.
WEP
Wired Equivalent Privacy
Encryption scheme for WLANs (obsolete)
Wi-Fi seal
Wireless Fidelity
Seal of approval of the WECA alliance for compatible and
tested components.
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Industrial Wireless LAN – I-Features, Applications, Examples
October 2004
Wired LAN
Network operated on guided media
Wireless LAN
Network operated using unguided media
WLAN
Wireless LAN (here: IEEE 802.11)
WLANA
The Wireless LAN Association
Consortium of wireless LAN providers promoting wireless
LAN technology
WPA
Wireless Protected Access
A provisional security mechanism from WECA that closes
existing security gaps in WEP. The AES encryption scheme is
used. This will be replaced by IEEE 802.11i.
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