Basic information on configuring an industrial wireless LAN

Basic information on configuring an industrial wireless LAN
Cover
Basics of Setting up an
Industrial Wireless LAN
SCALANCE W
System Manual May 2013
Applications & Tools
Answers for industry.
Siemens Industry Online Support
This entry is taken from the Siemens Industry Online Support. The following link
takes you directly to the download page of this document:
http://support.automation.siemens.com/WW/view/en/22681042
Caution:
The functions and solutions described in this entry are mainly limited to the
realization of the automation task. In addition, please note that suitable security
measures in compliance with the applicable Industrial Security standards must be
taken, if your system is interconnected with other parts of the plant, the company’s
network or the Internet. For more information, please refer to Entry ID 50203404.
http://support.automation.siemens.com/WW/view/en/50203404
For further information on this topic, you may also actively use our Technical
Forum in the Siemens Industry Online Support. Share your questions, suggestions
or problems and discuss them with our strong forum community:
Copyright
Siemens AG 2013 All rights reserved
http://www.siemens.com/forum-applications
2
IWLAN
V3, Entry ID: 22681042
s
SIMATIC NET
Basics of IWLAN
Copyright
Siemens AG 2013 All rights reserved
System Manual
IWLAN
V3, Entry ID: 22681042
Radio Waves as Basis of
a Shared Medium
Network
1
The IEEE 802.11 WLAN
standard
2
Alternative Radio
Technologies to IWLAN
3
Topology, Configuration
and Organization of
IWLANs
4
Data Security and
Encryption
5
Coexistence of IWLANs
with other Radio
Networks
6
Country Approvals
7
SIEMENS NET Products
for Setting up an IWLAN
8
Accessories for Wireless
Networks (WLANs)
9
IWLAN in Use
10
Glossary
11
Internet Links
12
3
Warranty and Liability
Warranty and Liability
Note
The Application Examples are not binding and do not claim to be complete
regarding the circuits shown, equipping and any eventuality. The application
examples do not represent customer-specific solutions. You are responsible for
ensuring that the described products are used correctly. These Application
Examples do not relieve you of your responsibility to use safe practices in
application, installation, operation and maintenance. When using these
Application Examples, you recognize that we cannot be made liable for any
damage/claims beyond the liability clause described. We reserve the right to
make changes to these Application Examples at any time and without prior
notice. If there are any deviations between the recommendations provided in this
Application Example and other Siemens publications – e.g. Catalogs – the
contents of the other documents shall have priority.
We do not accept any liability for the information contained in this document.
Siemens AG 2013 All rights reserved
Any claims against us - based on whatever legal reason - resulting from the use of
the examples, information, programs, engineering and performance data etc.,
described in this application example shall be excluded. Such an exclusion shall
not apply in the case of mandatory liability, e.g. under the German Product Liability
Act (“Produkthaftungsgesetz”), in case of intent, gross negligence, or injury of life,
body or health, guarantee for the quality of a product, fraudulent concealment of a
deficiency or breach of a condition which goes to the root of the contract
(“wesentliche Vertragspflichten”). The damages for a breach of a substantial
contractual obligation are, however, limited to the foreseeable damage, typical for
the type of contract, except in the event of intent or gross negligence or injury to
life, body or health. The above provisions do not imply a change of the burden of
proof to your detriment.
Copyright
Any form of duplication or distribution of these Application Examples or excerpts
hereof is prohibited without the expressed consent of Siemens Industry Sector.
4
IWLAN
V3, Entry ID: 22681042
Preface
Preface
Purpose of the document
This document provides you with an overview of the specific requirements for
setting up an Industrial Wireless LAN and familiarizes you with the properties of the
relevant SIEMENS products.
First, you will be introduced to the topic of wireless local networks (“WLANs”) in the
industrial environment and you will be informed on the essential technical
principles. Subsequently, we will show you different SIEMENS products, examine
their fields of application and provide you with decision guidance, enabling you to
select the optimum solution to your problem.
Core contents of this document
This document deals with the following key issues:
Properties of WLANs in general,
SIEMENS products for setting up wireless networks particularly in industrial
environments.
Copyright
Siemens AG 2013 All rights reserved
Topics not covered by this application
This document does not include a detailed description of the software installation
and the commissioning of the individual components.
Current and detailed information on this topic is available in the manuals and
operating instructions of the corresponding products.
Reference to Automation and Drives Service & Support
This document is an entry from the Internet Application Portal of Siemens Industry
Automation and Drive Technologies Service & Support. The following link takes
you directly to the download page of this document.
http://support.automation.siemens.com/WW/view/en/22681042
IWLAN
V3, Entry ID: 22681042
5
Table of Contents
Table of Contents
Warranty and Liability .............................................................................................. 4
Preface ...................................................................................................................... 5
1
Radio Waves as Basis of a Shared Medium Network ................................... 9
Siemens AG 2013 All rights reserved
1.1
1.2
1.2.1
1.2.2
1.2.3
1.3
1.4
1.4.1
1.4.2
1.4.3
1.4.4
1.5
1.5.1
1.5.2
1.5.3
1.6
1.7
2
The IEEE 802.11 WLAN standard ................................................................. 22
Copyright
2.1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.3
2.3.1
2.3.2
2.4
2.4.1
2.4.2
2.4.3
The network standards of the IEEE 802 series ................................. 22
Communication standard of the IEEE 802.11 ................................... 23
IEEE 802.11a .................................................................................. 24
IEEE 802.11b .................................................................................. 25
IEEE 802.11g .................................................................................. 26
IEEE 802.11n .................................................................................. 27
IEEE 802.11ac ................................................................................ 29
IEEE 802.11ad ................................................................................ 29
Transmission range and special antennas ....................................... 30
Other IEEE 802.1x standards .......................................................... 30
IEEE 802.11e and WMM: “Quality of Service” .................................. 30
IEEE 802.11h and the 5 GHz band .................................................. 31
Channal distribution in the IEEE 802.11 standard............................. 31
The 2.4 GHz band ........................................................................... 31
The 5 GHz band .............................................................................. 32
Comparison of the properties of the 2.4 GHz and 5 GHz band ......... 33
3
Alternative Radio Technologies to IWLAN .................................................. 34
4
Topology, Configuration and Organization of IWLANs .............................. 36
4.1
4.1.1
4.1.2
4.2
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.4
6
Overview of radio standards .............................................................. 9
Introduction to radio networks ............................................................ 9
Comparison between radio waves and cables.................................... 9
Complexity of the radio field ............................................................... 9
Access rules in a “Shared Medium” network .................................... 10
Preferred fields of application........................................................... 10
The physics of radio waves .............................................................. 11
Propagation ..................................................................................... 11
Interferences ................................................................................... 12
Transmission range and data rate .................................................... 12
Frequencies, frequency spacings and channels ............................... 13
Antennae ......................................................................................... 14
Characteristics of an antenna .......................................................... 15
Omnidirectional and directional antennae......................................... 16
Fresnel zone.................................................................................... 20
Modulation and multiplex method..................................................... 21
Requirements for radio communication in the industrial
environment..................................................................................... 21
The structure of a WLAN ................................................................. 36
Structuring by cell distribution .......................................................... 36
Connection of individual radio cells: “Access points” and
“clients” ........................................................................................... 37
The “roaming” method ..................................................................... 39
Infrastructure networks .................................................................... 40
Standalone networks ....................................................................... 40
Mixed networks................................................................................ 41
Multi-channel configuration .............................................................. 42
Wireless Distribution System (“WDS”) .............................................. 43
Redundant radio connection ............................................................ 44
Coordinating the data transfer.......................................................... 46
IWLAN
V3, Entry ID: 22681042
Table of Contents
4.4.1
4.4.2
4.4.3
4.5
4.5.1
4.5.2
4.5.3
4.5.4
4.6
4.6.1
4.6.2
4.6.3
4.6.4
4.6.5
Copyright
Siemens AG 2013 All rights reserved
5
DCF (“Distributed Coordination Function”) ....................................... 46
“Hidden Station and RTS/CTS” method for collision avoidance ........ 47
PCF (“Point Coordination Function”) ................................................ 47
Functions for the network management ........................................... 48
VLANs (“Virtual LANs”) .................................................................... 48
STP (“Spanning Tree Protocol”) ....................................................... 49
RSTP (“Rapid Spanning Tree Protocol”) .......................................... 50
MSTP (“Multiple Spanning Tree Protocol”) ....................................... 50
Proprietary expansions of the IEEE 802.11 standard: iFeatures ....... 51
iPCF (“Industrial Point Coordination Function”) ................................ 51
iPCF-MC (“iPCF – Management Channel”) ...................................... 53
Dual client technology...................................................................... 54
Usalbe IWLAN devices .................................................................... 57
iFeatures and PROFINET I/O .......................................................... 58
Data Security and Encryption ...................................................................... 59
5.1
5.1.1
5.1.2
5.1.3
5.2
5.2.1
5.2.2
5.3
5.3.1
5.3.2
5.4
Attack scenarios and security mechanisms ...................................... 59
Basics of WLAN security.................................................................. 59
Attack scenarios .............................................................................. 59
IEEE 802.11 security mechanisms................................................... 61
Measures for increasing the WLAN security ..................................... 62
The IEEE 802.11i expansion............................................................ 62
Wi-Fi Protected Access security standard ........................................ 63
Authentication and key management ............................................... 64
IEEE 802.1X authentication ............................................................. 64
Pre-Shared Key (PSK)..................................................................... 65
Security functions and data rate ....................................................... 65
6
Coexistence of IWLANs with other Radio Networks ................................... 66
7
Country Approvals ....................................................................................... 68
7.1
7.2
8
SIEMENS NET Products for Setting up an IWLAN ...................................... 70
8.1
8.1.1
8.1.2
8.2
8.3
8.3.1
8.3.2
8.4
8.4.1
8.4.2
8.5
8.5.1
8.5.2
8.6
8.7
8.7.1
8.7.2
8.7.3
9
General ........................................................................................... 68
Country approvals in the SCALANCE W devices ............................. 69
General Information ......................................................................... 70
Overview of the product range ......................................................... 70
Division of the SCALANCE W products............................................ 71
SCALANCE WLC711 IWLAN controller ........................................... 72
SCALANCE W Standalone Access Points ...................................... 74
Access Points IEEE 802.11n ........................................................... 74
IEEE 802.11a/b/g access points ...................................................... 79
Controller-based SCALANCE W access points ................................ 83
Access Points IEEE 802.11n ........................................................... 83
IEEE 802.11a/b/g access point ........................................................ 84
SCALANCE W clients ...................................................................... 85
IEEE 802.11n client modules ........................................................... 85
IEEE 802.11a/b/g client modules ..................................................... 87
Configuring the SCALANCE W devices ........................................... 90
Further SIMATIC WLAN clients........................................................ 91
SIMATIC Mobile Panels 277(F) IWLAN V2 ...................................... 91
SIMATIC ET 200pro IWLAN interface module IM 154-6 PN HF ........ 92
IWLAN/PB Link PN IO ..................................................................... 93
Accessories for Wireless Networks (WLANs) ............................................. 94
9.1
9.1.1
9.1.2
9.2
IWLAN
V3, Entry ID: 22681042
Optional storage media.................................................................... 94
KEY-PLUG ...................................................................................... 94
C-PLUG........................................................................................... 94
RCoax leaky wave cable.................................................................. 95
7
Table of Contents
9.3
9.3.1
9.3.2
9.3.3
9.3.4
9.4
9.5
9.6
9.6.1
9.6.2
Antennae ......................................................................................... 97
Overview of the WLAN antennae ..................................................... 97
Antennae with omnidirectional characteristic .................................... 99
Antennae with beamforming .......................................................... 101
Antennae for RCoax ...................................................................... 102
Connections and cabling................................................................ 103
Additional accessories ................................................................... 104
Selection and ordering aids............................................................ 110
TIA Selection Tool ......................................................................... 110
SIMATIC NET Selection Tool (SNST) ............................................ 112
IWLAN in Use.............................................................................................. 114
11
Glossary...................................................................................................... 119
12
Internet Links.............................................................................................. 127
13
History ........................................................................................................ 127
Copyright
Siemens AG 2013 All rights reserved
10
8
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
1
Radio Waves as Basis of a Shared Medium
Network
1.1
Overview of radio standards
At present, there are a number of different technologies available for setting up
radio networks, such as, Bluetooth GPRS und UMTSfor cellular telephone
networks, RFID tags for identification and goods tracking, etc. (see also chapter 3)
Within the framework of this document, we focus on WLANs in the strict sense, i.e.
radio networks which follow the IEEE 802.11 standard (see chapter 2). "IWLANs"
("Industrial WLANs") refers to WLANs, which are "hardened" by special measures,
i.e. made ready for requirements and utilization in industrial environments.
1.2
Introduction to radio networks
1.2.1
Comparison between radio waves and cables
Siemens AG 2013 All rights reserved
The use of cables and lines for communication has certain advantages since an
exclusive medium is available: The transmission characteristics of this medium are
well defined and constant (provided that cables, routers or similar components are
not replaced) and it is distinctly recognizable at any time which nodes are
connected to a local area network (abbrev. LAN) and which ones are not.
However, in return, the complexity of the cabling (and the possibility of cable
breaks and other hardware faults) increases with the number of nodes. Eventually,
the use of wire-bound methods for the communication with freely moving nodes is
only feasible in exceptional cases. Radio links additionally enable bridging zones of
sections, for which cabling would otherwise be difficult (streets, waters).
Copyright
In these fields of application, radio-based networks can show their advantages
(which, in summary, consist in the fact that they are less tied to a specific location).
In these cases, the possibly higher investment costs are compensated by
increased customer benefits.
1.2.2
Complexity of the radio field
Radio waves propagate through space, are diffracted, reflected at obstacles or
attenuated when passing through and thus generate a complex radio field which
even changes when the obstacles move. It is obvious that the range illuminated by
one or several transmitter(s) is not sharply defined. Thus, there is no clear
delimitation of the radio field which causes a fluctuation of the transmission
characteristics for the individual nodes of the radio network, depending on their
position. In addition, it is practically impossible to discover a “silent listener” in a
radio network.
These properties have considerable consequences on questions regarding
connection reliability and eavesdropping security or interference immunity of a
network. Assuming responsible administration, careful planning and the use of
trained employees who are sensitized to the specific concerns of a radio network,
radio networks are as reliable, secure and robust as wire-bound networks.
IWLAN
V3, Entry ID: 22681042
9
1 Radio Waves as Basis of a Shared Medium Network
1.2.3
Access rules in a “Shared Medium” network
Radio networks are so called “shared medium” networks, i.e. all stations share the
network. To prevent multiple accesses to the network, there has to be a rule, which
node is allowed to transmit when.
This is what the CSMA (Carrier Sense Multiple Access) is for. This procedure
requires a check from each station whether the medium is free before transmitting.
Only then can the data be sent.
However, if this check occurs from two stations at the same time, it may happen
that both detect the medium as free and send data at the same time. A collision
occurs and the data becomes unusable. A wireless transmitting station cannot
determine a signal collision itself. The dedicated signal covers the signals of other
stations and collisions cannot be distinguished from interferences.
1.3
Preferred fields of application
Due to their special properties, radio networks are the preferred, if not the only
possible medium in numerous environments.
The fields of application for which radio networks are predestined include:
connection of freely movable nodes to one another and to stationary nodes,
connection of mobile nodes with cable-based networks (Ethernet, etc.),
contact to rotating nodes (cranes, carousels, ...),
Copyright
Siemens AG 2013 All rights reserved
In order to avoid these non-recognizable collisions as best as possible, the CA
(Collision Avoidance) system is additionally used. If the occupied medium is now
free, a station ready to transmit, will not start straight away with the data
transmission but it will wait for a randomly determined time. After the lapse of this
wait time, the station will again check the status of the medium. Because of this
random wait time, it is very unlikely that both will start to transmit at the same time.
connection of nodes with limited mobility (monorail conveyors, high-bay racking
systems, …), for the replacement of sliding contacts or trailing cables,
setup of wireless bridges between physically separated (different buildings,
streets, waters) cable-based subnets,
communication with nodes in areas which are difficult to access.
10
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
1.4
The physics of radio waves
1.4.1
Propagation
Unlike signals in a line, radio signals propagate three-dimensionally in space as
electromagnetic waves.
Obstacles and objects influence the propagation of radio waves, effects such as
reflexion, diffusion, absorption, interference and diffraction occur.
Reflexion and absorption
When the waves hit an object, they are reflected virtually completely if the object is
electroconductive. If the object is non-conducting, a part of the waves is reflected,
another part is absorbed in the object and a rest is finally let through the object.
When hitting edges, radio waves are scattered into practically all directions.
Figure 1-1
Copyright
Siemens AG 2013 All rights reserved
Reflexion
Absorption
Diffusion
Fading and diffraction
Two additional properties are important for the propagation of the radio waves:
On the one hand, radio waves (unlike incoherent light) can amplify or even
extinguish one another (so called “fading or interference”). If a receiver is
located in both, the direct beam and the reflection of a transmitter, it does not
necessarily detect the double signal strength, but it will possibly not detect any
signal at all.
On the other hand, the propagation properties of the waves depend on their
wavelength, i.e. high-frequency radio waves behave differently than lowfrequency radio waves. In particular, radio waves of long wavelength (i.e. lowfrequency) can be “diffracted” around objects. Similar to sound or water waves,
it is then possible to receive signals even in the “shadow” of a radio source.
Interference and diffraction phenomena are basically in magnitudes that
correspond to the wavelength of the used radiation. For WLANs following the IEEE
802.11 standard it is between 12 cm and 6 cm, which means that shifts by one
module width may already cause a changed transmission and reception behavior.
IWLAN
V3, Entry ID: 22681042
11
1 Radio Waves as Basis of a Shared Medium Network
Frequency sensitivity of the properties of radio waves
As a rule of thumb, it can be said that the higher the frequency and the shorter the
wavelength of the oscillations, the closer the properties of radio waves come to the
properties of light: high-frequency transmitters propagate in a straight line and no
longer reach receivers behind objects. On surfaces, they are almost completely
absorbed or reflected.
Signals of longer wavelength, however, also go “around objects” and penetrate
deeper into non-conducting objects or can pass through them.
1.4.2
Interferences
Each object that is spatially located within a radio network can disturb this network
if it sends signals on the frequency used by the transmitters. In contrast to lines,
which can be shielded relatively easily and reliably, radio networks are susceptible
to interferences by any device in their proximity which, intermittently or
continuously, can radiate on strictly limited channels or emit broadband radiation.
These devices include devices designed as transmitters such as cordless phones
and Bluetooth devices, microwave ovens, welding devices, etc.
1.4.3
Transmission range and data rate
The transmission range and the achievable data rate of a radio transmitter depend,
among other things, on the frequency used.
Range
Basically, the transmission range of transmitters of short wavelength (higherfrequency) is shorter than the range of transmitters of long wavelength: the shortwave signals behave similarly to light, can only propagate in a straight line and are
completely absorbed or reflected by objects. This results in a considerable
decrease of the signal quality if the free line of sight between transmitter and
receiver is impaired. However, the transmission range can be significantly
increased by using directional antennas.
Copyright
Siemens AG 2013 All rights reserved
However, such interferences can already be counteracted before they occur by
carefully planning the radio network.
With the SIMATIC NET Selection Tool (see chapter 9.6) the range can be
determined in dependence of several parameters, such as frequency and
transmission power.
Data rate
The maximum data rate that can be transmitted on a carrier wave is proportional to
the band width that is available, i.e. the larger the band width, the larger the
1
attainable data rate.
Transmitters on a frequency of 2.4 GHz (as used by the IEEE 802.11 method) can
typically achieve ranges between approx. 30 m or 100 m (indoors or outdoors) with
omnidirectional antennas (see also Table 2-2). The data rates which can be
transmitted on this band amount to up to 450 Mbps.
1
The theoretically attainable gross data rate (in bit/s) is proportional to the band width. This
dependency is described by the Shannon–Hartley theorem.
12
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
Relevance of the data rate
Which data rate is actually necessary or sufficient for a specific application
depends – even if the connections are optimal – not only on the quantity of the
user data. Depending on the protocol, a more or less large overhead results for the
handling of the radio communication and interconnected devices such as access
points, routers, etc. also cause delays which develop when the signals are relayed.
The achievable net data rate is thus influenced in multiple ways by the design and
the parameterization of the actually existing radio network.
1.4.4
Frequencies, frequency spacings and channels
Only one node can transmit on each radio frequency at any time. If several stations
send simultaneously on the same frequency, none of the two can be received; this
case is referred to as a “collision”.
One of the most important tasks of a WLAN protocol – i.e., the rules according to
which the nodes of the network communicate – is to avoid the occurrence of
collisions since collisions always require a time-consuming repetition of the
individual messages.
Frequencies and required spectrum
Siemens AG 2013 All rights reserved
Strictly speaking, the statement that a transmitter emits on exactly one frequency is
not correct: this would only be the case for a pure sinusoidal signal. The transmitter
also assumes a range of frequencies above and below the carrier frequency. This
is the reason why the transmitters have to maintain a frequency spacing to each
other that is proportional to the data rate used: This is referred to as the “band
width” of the transmitter.f2
Copyright
Figure 1-2
I0
97
98
99
100
f/MHz
The example shown in the above figure illustrates the behavior of a VHF
transmitter. Aside from the actual carrier frequency (approx. 98.4 MHz), a
frequency band is used on both sides (blue). In this case, the band width is
exaggerated; in reality 40 kHz are sufficient for an FM signal.
2
The transmission capacity is generally colloquially referred to as “bandwidth”.
IWLAN
V3, Entry ID: 22681042
13
1 Radio Waves as Basis of a Shared Medium Network
Bands and channels
To keep the clarity, the radio spectrum, i.e. the entire frequency range of the radio
communication, is divided into individual “bands”. The different bands differ in the
radio characteristics (transmission range, susceptibility to interferences, possible
data rate, etc.) and consequently also in their applications.
The frequency bands are divided into “channels” which are distributed on the
respective band at a specific distance.
The 2.4 GHz range of the ISM band3 e.g. is divided into 13 channels with center
frequency between 2.412 GHz and 2.472 GHz, the distance between the
neighboring channels is 5 MHz each. Theoretically, thirteen transmitters can use
the band simultaneously.4
1.5
Antennae
Task
Electromagnetic waves
Electromagnetic waves consist of an electric field vector Ex and a magnetic field
vector Hy which are always at a right angle to each other. The current is the cause
of the magnetic field vector and the voltage causes the electric field vector (see
graphic).
Figure 1-3
Copyright
Siemens AG 2013 All rights reserved
An antennae transforms electrical currents into electro-magnetic waves and vice
versa. They send out electro-magnetic waves and receive them in the same way.
Each antenna has a certain frequency range within which the coupling between the
antenna current and the surrounding wave is at its maximum.
3
"Industrial, Scientific and Medical"; also see glossary.
However, since the frequency ranges of transmitters of neighboring channels overlap, there
are only three channels that are mutually interference-free (see also chapter 2.4).
4
14
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
1.5.1
Characteristics of an antenna
Impedance
Impedance refers to a frequency-dependent resistor. For the IWLAN components
(antenna, cable) this resistor has 50 Ohm. It is important here that the impedances
of an antenna, (i.e. input/output at the antenna and at the antenna cable) are
matched.
Polarization
The polarization specifies the direction of the vector of the electric field intensity in
the radiated electromagnetic wave. It is differentiated between linear and circular
polarization. For linear polarization the electric field lines run in one plane. If they
are directed vertical to the ground surface this is referred to as vertical polarization;
if they run horizontal to ground level this is a horizontal polarization.
If the direction of the electric field component is not fixed but runs continuously in
form of a circle, this is referred to as circular polarization. Depending on the
direction, this is also referred to as clockwise and anticlockwise polarization.
Table 1-1
Copyright
Siemens AG 2013 All rights reserved
Polarization
Electric field direction
Magnetic field direction
Linear vertical
Vertical
Horizontal
Linear horizontal
Horizontal
Vertical
Circular
Constantly circulating around the axis of propagation
(clockwise/anticlockwise)
For optimum reception it is important that for corresponding antennae, the
polarization of both is identical. If the polarization levels differ by, e.g. 90°, an
attenuation of 20 dB is not rare.
This is why it is especially important to pay attention to the alignment of the
polarization levels for antennae with several beams in one housing (dual / MIMO).
IWLAN
V3, Entry ID: 22681042
15
1 Radio Waves as Basis of a Shared Medium Network
1.5.2
Omnidirectional and directional antennae
The radiation of antennas can be either omnidirectional or directional. In general,
directional antennas achieve higher transmission ranges; however, this is not the
effect of a higher transmission power but the result of the shape of the radio field.
Antenna gain
The antenna gain is a parameter which describes how strong an antenna transmits
and receives compared with a reference emitter.
An isotropic radiator, i.e. an idealized point source which continuously sends to and
receives from all directions of space. The gain of the isotropic point source is set to
zero.
The unit of the antenna gain is normally “dBi” (i = isotropic point source). A gain of
3 dBi corresponds approximately to a doubled send/receive line.f5
Antenna diagrams
A horizontal antenna diagram is a front view of the electromagnetic field of an
antenna with the antenna at the center. The gain is plotted as distance from the
center of the coordinate system above the send/receive angle.
A vertical antenna diagram is a side view of the electromagnetic field of the
antenna. The antenna gain is plotted above the angle to the symmetry plane of the
antenna.
The following graphic shows a horizontal (left) and a vertical (right) antenna pattern
of a directional antenna.
Figure 1-4
Copyright
Siemens AG 2013 All rights reserved
An antenna describes the directional characteristic of an antenna in which the
direction-independent antenna gain is measured. Normally, the representation of
the directional diagram occurs in polar coordinates.
5
Since the antenna gain is measured in logarithms, 6 dBi correspond to 4 times the power,
9 dBi 8 times the power etc..
16
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
Aperture angle
The aperture angle refers to the angular distance at which the field intensity of the
antenna has dropped to approximately half 3 dBi of the maximum. On the
example of an antenna pattern, the following graphic shows how the aperture
angle can be determined. The -3 dBi circle is represented green, which marks half
of the signal maximum (= 0 dBi). The intersections of the blue antenna gain pattern
with the green circle define the aperture angle of the antenna. (Here: approx. 30°)
Figure 1-5
The horizontal and vertical aperture angles of an antenna usually differ depending
on the geometry.
Copyright
Siemens AG 2013 All rights reserved
-3 dBi
IWLAN
V3, Entry ID: 22681042
17
1 Radio Waves as Basis of a Shared Medium Network
Omnidirectional antennae
Omnidirectional antennae always have the form of a rod or a straight wire. The
term is misleading in so far as the radiation intensity is not isotropic, i.e. not equal
in all directions. The radio field of the antenna reaches the maximum intensity on a
plane, at a right angle to the antenna axis (compare Figure 1-6). The field intensity
quickly decreases above and below the “vertical aperture angle” of this plane and
most of the time, no noteworthy signal can be expected vertically above and below
the antenna.
The radio field is radial symmetrical; this means that the field intensity is identical in
all directions when viewed from the top along the antenna axis. In this case, the
“horizontal aperture angle” is 360°.
Copyright
Siemens AG 2013 All rights reserved
Figure 1-6
18
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
Directional antennae
Directional antennas, which typically have the form of a flat box, generate a radio
field in the shape of a cone or similar at a right angle to the box.
The cone is defined by a horizontal and a vertical aperture angle; outside this angle
the field intensity decreases quickly.
Copyright
Siemens AG 2013 All rights reserved
Figure 1-7
In the maximum field intensity direction the transmission range of a directional
antenna is typically ten times as large as the range of an omnidirectional antenna.
Antennae for SCALANCE W devices
Chapter 9.3 provides an overview of antennas suitable for operation with the
SCALANCE W devices.
Leaky wave cable
Leaky wave cables for which the developing radio field is limited to the direct
proximity of the conductor, are alternatives to conventional antennas.
The fields of application of such leaky wave cables are moving nodes which move
along defined paths (e.g. monorail conveyors, automated guided vehicle systems),
tunnels and similar areas that are difficult to cover using cabling.
An example of a leaky wave cable is the RCoax cable from chapter 9.1
IWLAN
V3, Entry ID: 22681042
19
1 Radio Waves as Basis of a Shared Medium Network
1.5.3
Fresnel zone
As described in the previous chapter, obstacles and objects have an influence on
the propagation of radio waves and therefore on the attainable range.
In order to be able to specify the possible range, the Fresnel zone was defined.
The Fresnel zone describes certain spatial areas between transmitter and receiver
antenna and therefore characterizes the signal propagation. For the calculation of
the free space loss, the following is required
1. direct line-of-sight connection between the transmission path of transmitter and
receiver and
2. that there is another area around this line-of-sight contact that must also be
free of obstacles.
6
It is subdivided in several orders. The first order is the most significant one, since
this is where the main part of the signal energy is transmitted.
The Fresnel zone is in the shape of an ovoid and is irrespective of the frequency of
the radio waves and the distance between transmitter and receiver. The diameter
of these zones becomes smaller with increasing frequency, and it becomes larger
with increasing distance between transmitter and receiver station.
Figure 1-8
Antenna
ANT793-8DJ
Copyright
Siemens AG 2013 All rights reserved
The above mentioned conditions for the application of the free space loss are
fulfilled, if the first Fresnel zone is free of obstacles.
Access Point
SCALANCE
W788-2
Antenna
ANT793-8DJ
Node 2
Access Point
SCALANCE
W788-2
Node 1
6
The first Fresnel zone is the place where the sum of the distance of the two antennae is /2
larger than the line-of sight connection d ( corresponds to the wave length of the frequency).
20
IWLAN
V3, Entry ID: 22681042
1 Radio Waves as Basis of a Shared Medium Network
1.6
Modulation and multiplex method
To transmit a signal by means of an oscillation, the signal has to be “modulated”
onto a carrier wave. The “sum” made up of carrier wave and signal is transmitted to
the receiver which “subtracts” the carrier wave from the received oscillation and
thus receives the pure signal.
If radio transmission is analog, e.g. the amplitude of the carrier wave or its
frequency can change depending on the signal. Medium wave stations use the
former method, VHF uses the latter; this is the reason why these bands are
referred to as “AM” (“amplitude modulation”) or “FM” (“frequency modulation”) in
the Anglo-American language area.
For the transmission of digital data more complex methods such as the modulation
methods “Orthogonal Frequency Division Multiplexing” (OFDM) and “Direct
Sequence Spread Spectrum” (DSSS) are used (see chapter 2.2).
Copyright
Siemens AG 2013 All rights reserved
1.7
Requirements for radio communication in the
industrial environment
Requirements for industrial networks differ in some points from the networks of the
office or home environment.
Data volumes
In the office environment files of several megabytes are typically moved, for the
industrial application the data packets are often much smaller.
Transmission speed and latency
A temporal delay in the communication between office devices, for example, when
sending a print job and performing it, generally does not cause any problems.
However, in the industrial environment measured values and control commands
(such as an emergency off) must often be exchanged within milliseconds.
Fail-safety and reliability
Data loss or data corruption during transmission in the office environment is
normally uncritical, since the transmission can always be repeated. However, for
industrial plants the delays through failed transmissions and their repetition are
often unacceptable.
Additional interferences in the industrial area
Office and home environments are usually characterized by a low degree of
interference from objects which are not part of the radio network. However,
naturally, the industrial environment exhibits some very intensive interference
which is unfavorable for the propagation of electromagnetic waves. Metal parts or
other signal sources, such as RFID can be found almost everywhere, which can
disturb or interrupt the transmission.
The metal areas, e.g. reflecting radio waves can course loss of packages or even
obliterate the radio signal.
IWLAN
V3, Entry ID: 22681042
21
2 The IEEE 802.11 WLAN standard
2
The IEEE 802.11 WLAN standard
2.1
The network standards of the IEEE 802 series
The Institute of Electrical and Electronics Engineers IEEE7 is dedicated to
developing, publishing and promoting electronic and electrotechnical standards.
Under the project number “802”, a number of task groups have been formed to
develop standards for the installation and operation of networks. For instance,
group “802.3” is concerned with the standards for Ethernet connections.
Task group “802.11” has now developed specifications for wireless LANs.
Nowadays, these specifications are the de facto standard for radio networks, the
most important variants being “802.11a/b/g/h/n”.
The IEEE continuously develops the standards to adapt them to new requirements
and technical conditions.
The following table gives an overview of the topics of some IEEE 802 standards
regarding IWLANs.
Table 2-1
Copyright
Siemens AG 2013 All rights reserved
Standard
7
Definition area
802.11a
Communication
802.11ac
Communication
802.11ad
Communication
802.11b
Communication
802.11e
Quality of Service (see chapter 2.3.1)
802.11g
Communication
802.11h
Communication (reduce interference)
802.11i
Data security (see chapter 5.2)
802.11n
Communication
802.1Q
Virtual LANs (see chapter 4.5.1)
802.1X
Data security (see chapter 5.2)
See also http://www.ieee.org/portal/site,
22
IWLAN
V3, Entry ID: 22681042
2 The IEEE 802.11 WLAN standard
2.2
Communication standard of the IEEE 802.11
8
The original 802.11 standard (today often referred to as “802.11 legacy” for
reasons of clarity) defines the connection of the network nodes via radio in the
frequency band at 2.4 GHz.
The gross data rate was up to 2 Mbps, however, the actually achieved net data
throughput was considerably less.
The standard was improved by the extensions “b”, “a”, “g”, “h” and “n”, which were
put on the market in this order.
Concerning the frequency bands used (2.4 GHz and 5 GHz), the different
standards vary regarding the simultaneously usable channels and the maximum
data rate.
The transmission capacities were increased by more complex and more efficient
modulation methods.
Over time, other standards were also defined each relating to certain aspects of
operating wireless radio networks.
The following table lists the technical properties of the currently common 801.11
standards.
Siemens AG 2013 All rights reserved
Table 2-2
Frequency band
Max. gross data rate
Modulation /
multiplex method*)
802.11a/h
802.11b
802.11g
802.11n
802.11 ac
802.11 ad
5 GHz
2.4 GHz
2.4 GHz
2.4 GHz and
5 GHz
5 GHz
60 GHz
54 Mbps
11 Mbps
54 Mbps
600 Mbps
7 Mbps
7 Mbps
OFDM
DSSS
OFDM
MIMO and
OFDM
MIMO and
OFDM
*) on the individual modulation methods, see chapter 1.6
Copyright
If the connection quality is not good enough to maintain the maximum data rate,
the transmission rate is successively reduced until a stable connection is achieved.
As a matter of principle, an 802.11a device cannot communicate with an 802.11b/g
device, since they are transmitting on different frequency bands. However, the “b”,
“n” and “g” versions of the standards are compatible to one another.
8
See also http://grouper.ieee.org/groups/802/11/,
http://standards.ieee.org/wireless/overview.html#802.11
IWLAN
V3, Entry ID: 22681042
23
2 The IEEE 802.11 WLAN standard
2.2.1
IEEE 802.11a
Description
The IEEE 802.11a standard was approved in 1999. It uses the 5 GHz frequency
band and the Orthogonal Frequency Division Multiplexing (OFDM) modulation
method and the SISO technology. A maximum gross data rate of 54 Mbps can be
attained.
This frequency band is mainly used by the military for radar in air and marine
traffic. WLAN tends to be used as second rate user.
In order to prevent interferences between WLAN and the radar, the Transmit
Power Control and Dynamic Frequency Selection (see chapter 2.3.2) also has to
be implemented in some countries. For this purpose, the IEEE 802.11h standard
was developed as an extension to IEEE 802.11a.
Orthogonal Frequency Division Multiplexing (OFDM) modulation method
OFDM does not use one frequency to transmit its signal but it transmits on several
hundred to several thousand channels very close to each other; however, only a
narrow frequency band is available to each individual channel.
Siemens AG 2013 All rights reserved
The massive parallel data transmission drastically reduces the data rate over each
individual channel, i.e. there is much more time available for transmitting the
individual bits. Consequently, OFDM connections are significantly less susceptible
to short-term noise or occurring echoes. Even in case of considerable path
differences there is a high probability that a received echo is still associated to the
same bit as the one currently transmitted via the “direct path”.f9 The reduced
transmission rate additionally ensures that the duration of short-term noise peaks is
mostly shorter than the transmission of a bit.
Copyright
The following figure shows the schematic principle of operation of OFDM (bottom)
in contrast to conventional transmission (top): The use of several parallel channels
(only 4 channels are shown for reasons of clarity; this number is significantly higher
in practical operation) considerably increases the time interval Ät available for the
transmission of one individual character so that short-term noise or echoes by path
differences are clearly of less importance.
Figure 2-1
t
f
H
e
l
l
o
,
_
W
o
r
l
d
…
t
t
f
H
o
o
…
e
,
r
…
l
_
l
…
l
W
d
…
t
The top of the figure shows the “conventional” way of transmitting, the bottom
shows the transmission with OFDM. The representation clearly shows how the
transmission time Ät for an individual character is increased without compromising
the overall data rate of the transmission.
9
In other words: the runtime difference remains lower than the duration of the transmission of
one bit.
24
IWLAN
V3, Entry ID: 22681042
2 The IEEE 802.11 WLAN standard
OFDM is used in a large number of transmission methods, e.g. for ADSL, DAB
(Digital Audio Broadcasting) or DRM (Digital Radio Mondiale).
2.2.2
IEEE 802.11b
Description
Also in 1999, the IEEE 802.11b standard was developed and it operates at 2.4
GHz frequency band. Here, the Direct Sequence Spreading Spectrum (DSSS) is
used together with the Single Input Single Output (SISO) technology as modulation
method. This makes a maximum data rate of 11 Mbps possible.
Direct Sequence Spread Spectrum” (DSSS) modulation method
DSSS, which at first glance takes the opposite way, is an alternative to OFDM: The
data stream that is to be transmitted, is multiplied with a series of pseudo random
numbers (so called “chips”) which have a larger data rate than the data stream.
The receiver, which must know the “chips” (they can either have been generated
by a cryptographic algorithm or previously transmitted separately), simply
subtracts them from the received stream and obtains the unmodified signal.10
This has several effects:
Siemens AG 2013 All rights reserved
Although only one carrier wave is used, the spectrum of the transmitted signal
broadens superproportionally. Consequently, the effects of interferences that
are limited to a very narrow range of the spectrum are less serious.
Due to the use of pseudo random numbers, the transmitted signal, at first
glance, appears as noise. In other words, it is not apparent to a listener that
any transmission takes place at all.
Even if a listener knows that a transmission is active, he can only listen in if he
knows which sequence of chips was used by the transmitter.
Copyright
Except for WLANs, DSSS is also used in GPS, UMTS and WirelessUSB.
10
This is of course a simplified representation and strictly speaking it is not an addition or
subtraction but XOR operations of data with its keys.
IWLAN
V3, Entry ID: 22681042
25
2 The IEEE 802.11 WLAN standard
Figure 2-2
A)
B)
C)
t
The above figure illustrates the function of DSSS.
A) The user data signal,
C) The encrypted signal is identical to the chips as long as the user data signal is
“1” (black sections); otherwise, it is created by inverting the chips (green).
In practical operation, the chips would be more complicated and a bit length which
is a multiple of the chip length would not be used for the user data.
2.2.3
IEEE 802.11g
Description
This standard is the extension of IEEE 802.11b and also operates in the 2.4 GHz
frequency band. IEEE 802.11g works with the OFDM modulation method and the
SISO technology and can therefore reach a maximum data rate of 54 Mbps. This
standard is downward compatible to IEEE 802.11b. If both standards are used in a
network, the DSSS modulation method with the respectively lower data
transmission rate is used.
Copyright
Siemens AG 2013 All rights reserved
B) The “chips” used for encryption. This is only a short sequence (red) that is
continuously repeated. The bit string of the “chips” changes much faster than in the
user data.
OFDM modulation method
See chapter 2.2.1
26
IWLAN
V3, Entry ID: 22681042
2 The IEEE 802.11 WLAN standard
2.2.4
IEEE 802.11n
Description
The IEEE 802.11n is the latest standard and can use the 2.4 GHz as well as the 5
GHz band. In addition to the OFDM modulation method, the Multiple Input Multiple
Output (MIMO) technology is used. This considerably increases the transmission
speed compared to the previously mentioned standards and can be up to
600 Mbps.
WLANs in accordance with 802.11n are compatible to 802.11a, 802.11b, 802.11g
and 802.11h networks.
OFDM modulation method
See chapter 2.2.1
Copyright
Siemens AG 2013 All rights reserved
Diversity systems
Diversity is a technology to increase the transmission security in a radio system.
The principle is to transmit and receive the information in one radio channel several
times (redundantly). The basis of all diversity systems is to transmit the signals via
several parallel paths that are independent from each other. The separation can be
in terms of time, via the frequency or in terms of space.
Special separation is mainly used in today’s radio systems.
The special diversity is distinguished by the fact that it can be implemented without
additional resources such as transmission time and bandwidth. The special
differences in the channel are utilized here. For this purpose, several antennae are
either used on the transmitter (MISO; Multiple Input Single Output) or on the
receiver (SIMO; Single Input Multiple Output).
What information is to be evaluated by what antenna, is decided by test
measurements that are carried out during the establishment of the connection. The
antenna that receives the data with the best signal-to-noise ratio will be used for
further data transmission. The signal of the other antenna is ignored. Concretely
used are therefore only the data of one transmission path.
Multiple Input / Multiple Output systems
In order to increase the receiving field intensity and therefore the reception quality
and the data rate to be transmitted, the MIMO technology is used. This technology
is used in the IEEE 802.11n extension.
A MIMO system differs from diversity systems by not only using one channel for
redundant signal transmission, but several parallel subchannels. These additional
data channels make it possible to transfer different data with the same antennae
irrespective from each other on the same frequency band and at the same time, so
called multiplexing (“spatial multiplexing”).
The technology requires the transmitter as well as the receiver to be equipped with
a minimum of two and a maximum of four antennae.
Beamforming enables the transmitter and the receiver to block out interferences in
the channel and therefore establish a secure and high-quality connection.
The principle is to combine the signals of the individual antennae elements via
adjustable phase shifters and enhancement factors. This results in “beamforming”,
which can be electronically adjusted via so called intelligent antenna (smart
antennae).
This MIMO method makes it possible to significantly increase the data throughput.
A max. gross of 150 Mbps is transferred per data stream at IEEE 802.11n. When
IWLAN
V3, Entry ID: 22681042
27
2 The IEEE 802.11 WLAN standard
utilizing the maximum of the four possible data channels 600 Mbps can be
achieved.
The following graphic illustrates the MIMO technology when three antennae and
three data streams are used:
Figure 2-3
Access Point
SCALANCE
W788-1
Client
SCALANCE
W748-1
Data stream 1
Data stream 2
Data stream 3
The guard interval prevents that different transmissions are mixed. After the lapse
of the transmission time there is an intermission (guard interval) between the two
transferred OFDM symbols before the next transmission starts.
The guard interval of IEEE 802.11a/b/g is 800 ns. IEEE 802.11n can use the
shortened guard interval of 400 ns.
Channel bonding
Channel bonding is the summary of several channels, in order to achieve a higher
data throughput.
For IEEE 802.11n data can be transmitted via two directly neighboring channels.
The two 20 MHz channels are combined to one channel with 40 MHz. This makes
it possible to double the channel band width and increase the data throughput. In
order to use channel bonding, the receiver has to support 40 MHz transmissions. If
this is not the case, it is automatically reduced to 20 MHz. This guarantees the
compatibility between IEEE 802.11n and IEEE 802.11a/b/g devices.
Copyright
Siemens AG 2013 All rights reserved
Shortened guard interval
Figure 2-4
Communication according to IEEE 802.11n standard
1 x 40 MHz channel
Maximum data rate: 450 Mbit/s
28
IWLAN
V3, Entry ID: 22681042
2 The IEEE 802.11 WLAN standard
Frame aggregation
For IEEE 802.11n it is possible to combine individual data packets to one larger
data packet (frame aggregation).
This method minimizes the packet overhead, the wait times between the data
packets are shortened and the data throughput is thus increased.
There are two types of frame aggregation:
Aggregated MAC Protocol Data Unit (A-MPDU) and
Aggregated MAC Service Data Unit (A-MSDU).
Frame aggregation can only be used if the individual data packets are intended for
the same receiver station (client).
MCS (“Modulation and Coding Schemes”)
The Web Based Management page of the SCALANCE W devices (IEEE 802.11n)
displays the available data transmission speeds for the WLAN 802.11n mode. They
can be combined and selected as desired. Only the selected data transmission
speeds are then used by the access point for the communication with the clients.
2.2.5
IEEE 802.11ac
Description
IEEE 802.11ac is a standard that is still in the design stage for a WLAN with data
rates in the gigabit range. By improving the transmission protocol and the WLAN
technology as well as using the OFDM modulation method, data rates of up to 7
Gbps are possible. Data transmission is only in the 5 GHz band.
Copyright
Siemens AG 2013 All rights reserved
The IEEE 802.11n standard supports different data rates.
The data rates are based on the number of transmitter and receiver streams
(spatial streams), the modulation method and the channel coding. The different
combinations are described in “Modulation and Coding Schemes”.
WLANs in accordance with 802.11ac are compatible to 802.11a, 802.11h and
802.11n networks.
OFDM modulation method
See chapter 2.2.1
2.2.6
IEEE 802.11ad
IEEE 802.11ad is also still in the development stage. With IEEE 802.11ad a
specification for a wireless connection between digital video systems in the gigabit
range is being developed. High data rates are achieved by the change of the
frequency range to the 60 GHz band and the optimization of the access protocol.
Due to the change in frequency, WLANs in accordance to 802.11ad loose their
downward compatibility to the other IEEE 802.11 standards.
IWLAN
V3, Entry ID: 22681042
29
2 The IEEE 802.11 WLAN standard
2.2.7
Transmission range and special antennas
Within buildings the antennas used achieve ranges of typically 30m. Since
reflections and shadowing have less effect outdoors, ranges of up to 100m and
more can be achieved. A connection with line-of-sight is particularly advantageous
since the radio waves can then propagate without being disturbed.
By using directional antennas this value can be increased to a multiple of 100m.
Depending on the country of use, line-of-sight and the Fresnel zone (see chapter
1.5.3), even ranges of several kilometers can be covered.
2.3
Other IEEE 802.1x standards
In the course of time a number of further standards were defined for the IEEE
802.11 standard, mostly relating to individual aspects of radio communication:
802.11e: Introduction of “Quality of Service” features for increased
transmission quality.
802.11h: Adaptation to 802.11a, to prevent interference with other devices in
the 5 GHz band.
802.1Q: Virtual LANs for separating a network
802.1X: Security functions for WLANs and VLANs
2.3.1
IEEE 802.11e and WMM: “Quality of Service”
IEEE 802.11e
In the winter of 2005/2006, the IEEE adopted the 802.11e standard. This standard
adds “Quality of Service” criteria to the existing network standards, i.e. a specific
connection quality is guaranteed if this standard is complied with.
Copyright
Siemens AG 2013 All rights reserved
802.11i: Security functions for data encryption and authentication.
Furthermore, IEEE 802.1 standards exist that are important for operating WLANs:
The quality is not only measured at the mean achievable data rate but lower limits
for connection reliability, the duration of possible connection interruptions, etc. are
also defined. A convenient telephone connection e.g. not only requires to transmit
an appropriate quality of sound but also to ensure that dropouts and voice delays
are within narrow limits.
While earlier 802.11 standards placed more emphasis on gross data rates than on
“Quality of Service”, a standard explicitly including the concerns of QoS was
created with the “e” variant.
WMM
“WMM” (“Wireless Multimedia Extensions”) are a subset of the 802.11e standard,
which was defined by the WiFi Alliance to explicitly integrate multimedia services
into the networks.
30
IWLAN
V3, Entry ID: 22681042
2 The IEEE 802.11 WLAN standard
2.3.2
IEEE 802.11h and the 5 GHz band
IEEE 802.11h
The 5 GHz band is only used for few applications other than WLAN. One of these
applications, however, is radar, whose operators are naturally quite sensitive
towards possible interferences.
For this reason the IEEE 802.11h standard introduced modifications which can be
used to minimize interferences between WLAN operated below 5 GHz and radar.
The newly introduced technologies include “DFS” and “TPC”.
DFS (Dynamic Frequency Selection)
DFS describes the automatic switching to another channel if interferences,
originating from a radar device, are detected on the current WLAN channel.
TPC (Transmit Power Control)
2.4
Channel distribution in the IEEE 802.11 standard
The 802.11 standard uses the ISM bands 2.4 GHz and 5 GHz as frequency
channels.
2.4.1
The 2.4 GHz band
The frequency band at 2.4 GHz is a frequency range that can be used without a
license in almost all nations.11 Since it is relatively inexpensive to manufacture
transmitters and receivers, the 2.4 GHz technology is very popular and not only
used for WLANs but also for numerous other applications.
Copyright
Siemens AG 2013 All rights reserved
TPC reduces the transmission power of the nodes until the minimum for a reliable
transmission with the configured data rate has been reached. TPC represents a
compromise between secure communication and preventing overshoot.
The 2.4 GHz band, as used in the 802.11 b/g standard, is normally divided into 13
channels, 12 which have a distance of 5.5 MHz to one another and a band width of
approx. 20 MHz (see chapter 1.4.4). However, this does not at all mean that 13
non-overlapping channels are available for each WLAN.
To exclude that the transmitters in the WLAN disturb each other, it is required that
they keep at least this distance from each other. This reduces the number of
frequencies that can be used independently of one another in practical operation to
three: Usually only the channels 1, 7 and 13 (the so called “non-overlapping
channels”) are simultaneously used for 802.11 networks.
With the 802.11n standard an extension of the band width to 40 MHz per channel
is possible (channel bonding; see chapter 2.2.4). This achieves higher data rates.
11
Updated lists with country approvals for the individual SCALANCE W products are available
at this PDF.
12
Details of the permitted channels are different in every country. The topic is discussed in
detail in chapter 7.
IWLAN
V3, Entry ID: 22681042
31
2 The IEEE 802.11 WLAN standard
Figure 2-5
Communication according to IEEE 802.11a/b/g/h standard
2 x 20 MHz channels
Maximum data rate: 54 Mbit/s
Copyright
Siemens AG 2013 All rights reserved
Communication according to IEEE 802.11n standard
1 x 40 MHz channel
Maximum data rate: 450 Mbit/s
When many access points are used in a network, it is required that many channels
that are independent of one another, i.e. non-overlapping channels, are used. In
this case, it may be advisable to switch to the 5 GHz band of the 802.11a/h/n
standard, which offers a larger number of non-overlapping channels.
2.4.2
The 5 GHz band
For the 5 GHz band, different numbers of non-overlapping channels are approved
in the various regions of the world.13
Generally 5 GHz waves are “harder”, i.e. the propagation behavior is similar to that
of light beams: There is less diffraction around objects, the absorption is higher and
the penetration depth lower than for 2.4 GHz waves. Generally, the practically
achievable transmission range is a little less than in the 2.4 GHz band.
Compared with the 2.4 GHz band the 5 GHz band is clearly less “busy”, and there
are only few interference sources in this range. Military radar and satellite tracking
systems are exceptions, their operators naturally react rather sensitively towards
system interferences from a WLAN.
To harmonize the operation of 5 GHz WLANs with these systems, the
IEEE standard 802.11h (see chapter 2.3.2) was created.
13
Compare with the remarks on country approval of the components, see chapter 7.
Current approval lists can be found on the internet at this PDF.
32
IWLAN
V3, Entry ID: 22681042
2 The IEEE 802.11 WLAN standard
2.4.3
Comparison of the properties of the 2.4 GHz and 5 GHz band
Connection security and interference by other devices:
The great popularity of the 2.4 GHz band also results in the fact that a large
number of devices which actually have nothing to do with WLANs, also transmit in
this range – these devices include microwave ovens as well as Bluetooth devices
and cordless DECT telephones.
This may cause interferences and problems when setting up a WLAN. Depending
on the interference source type, it may be advisable to switch to the 5 GHz band.
In any case the optimal configuration of illumination, frequency band and antennae
must be clarified by a radio field analysis prior to setting up the system.
Size
Due to the shorter wave length used, 5 GHz components of smaller size than
2.4 GHz modules can be produced. (This naturally does not apply for devices
designed for operation in both bands (“dual-use”).)
2.4 GHz as well as 5 GHz networks can be operated without license in most states.
In chapter 7 the issue country approvals is described in more detail.
Copyright
Siemens AG 2013 All rights reserved
Licensing
IWLAN
V3, Entry ID: 22681042
33
3 Alternative Radio Technologies to IWLAN
3
Alternative Radio Technologies to IWLAN
Apart from the IEEE 802.11 standard for WLANs there is also a number of different
technologies which communicate using the radio network and which are used in
the industrial environment.
Bluetooth
“Bluetooth” is the name for the IEEE 802.15.1 standard which describes the
networking of small devices via short distances. Its main area of application is the
application of cable connections between office devices such as PDAs, cellular
phones, computers, printers and other peripheral equipment.
Bluetooth works in the frequency range between 2.402 GHz and 2.480 GHz in the
ISM band, hence it collides with the 2.4 GHz band used by 802.11.
The maximum transmission power is 100 mW with a range of at most approx.
100 m. (However, most portable devices transmit with a lower power in order to
save their batteries; this is why typical ranges are below 10 m.). The data is
transmitted with a speed of up to 24 Mbit/s.
Note
To obtain further information on this topic, please use the following URL:
http://german.bluetooth.com/bluetooth/
Wireless HART
HART (“Highway Addressable Remote Transducer”) is a fieldbus communication
standard which as “WirelessHART” also defines the wireless communication
(based on IEEE standard 802.15.4).
Copyright
Siemens AG 2013 All rights reserved
The standard is checked and further developed by the “Bluetooth Special Interest
Group”14.
WirelessHART also uses the ISM frequency band (2.4 GHz with maximal
250 kBit/s) and automatically builds meshed networks whose extend can be
considerably larger than the nominal radio range of an individual node (approx.
200 m). The network organizes itself by evaluating all connection information from
the WirelessHART Gateway (IE/WSN-PA Link), in order to automatically provide
redundant paths with this information. This can achieve a very high availability of
the communication connection, since bad connections or the failure of individual
nodes can be bridged. Furthermore, the availability of the entire network via the
operation of two redundant gateways can be significantly increased.
The focus during the development of WirelessHART was furthermore the simple
commissioning and maintenance of the self-organizing network, so that the
configuration requires only minimal workload. This comes at the price of real-time
capability; i.e. no response times are guaranteed with WirelessHART.
The main application area of WirelessHART here is the regular transmission of
lower, non-time critical data volumes in large distances (typically between approx.
15 seconds and several hours) over relatively large distances (such as, for
example, in process industry. Due to the lower energy consumption of
WirelessHART devices, long battery runtimes of up to five to ten years can be
achieved, e.g. WirelessHART field devices prove to be extremely low maintenance
during the operating phase.
14
https://www.bluetooth.org
34
IWLAN
V3, Entry ID: 22681042
3 Alternative Radio Technologies to IWLAN
The protocol is very robust and at sufficient illumination of the meshed network, it
automatically “mends” the failure of intermediate stations.
15
WirelessHART is managed by the “HART Communication Foundation” (HCF).
To obtain further information on this topic, please use the following URLs:
Note
http://www.siemens.com/wirelesshart
http://www.hartcomm2.org/hart_protocol/wireless_hart/wireless_hart_
main.html
http://www.hartcomm2.org/hart_protocol/wireless_hart/wireless_hart_
main.html
Zigbee
Copyright
Siemens AG 2013 All rights reserved
Like WirelessHART, Zigbee is also based on IEEE standard 802.15.4 and also
uses the ISM band at 2.4 GHz. However, in comparison to HART the focus here is
not the industrial environment but the area of building automation and building
services. The aim is to install devices in areas that are difficult to access and that
can stay in operation for years without requiring any maintenance (electricity or
heating meters, light switches, etc.).
The Zigbee protocol is less “robust” than that of WirelessHART, and if a central
controller fails, the communication of the entire network may be compromised. In
return, Zigbee offers slower response times and is therefore also suitable for realtime applications.
The Zigbee standard is under the control of the Zigbee alliance 16, which also
provides further information on this topic.
WiMAX
WiMAX (Worldwide Interoperability for Microwave Access) was defined in the IEEE
standard of the 802.16 family and developed in parallel to IEEE 802.1117. This
technology makes a wireless broad band technology for a Metropolitan Area
Network (MAN) possible, without extensive cable-based infrastructure. Due to the
use of a very broad frequency spectrum, in the gigahertz range, WiMAX can be
used worldwide.
Different than the WLAN standards, WiMAX can also bridge bigger distances so
that remote and rural regions can also be supplied with broadband. Due to this
property WiMAX is seen as an alternative to the landline DSL.
The theoretical range is 50 km with a transmission speed of up to 75 Mbit/s.
However, in reality this value is well below.
15
http://www.hartcomm.org/
http://www.zigbee.org/
17
http://www.wimax.com/
16
IWLAN
V3, Entry ID: 22681042
35
4 Topology, Configuration and Organization of IWLANs
4
Topology, Configuration and Organization
of IWLANs
4.1
The structure of a WLAN
4.1.1
Structuring by cell distribution
Unstructured radio networks and their disadvantages
As we have seen in section 1.4.3, the range of radio transmitters is limited in
practical operation. Generally, the area you want to cover by a LAN will be too
large to be reliably “illuminated” by one single transmitter.
Even if it would be technically possible to set the transmission power high enough
for all nodes, in many cases this would not be desired or permitted. If the LAN
nodes were, for example, arranged along a straight line, an unnecessarily large
area on the left and on the right of the line would be illuminated, and it would be
easy for third parties to install additional receivers and to listen in on the radio
communication without being noticed.
Structuring radio networks by radio cells
Siemens AG 2013 All rights reserved
Furthermore, it is more economic to divide the WLAN18 into individual cells since
only one station can send on each channel at any time. If several cells are
available, an active transmitter can be located in each cell and the actual data
throughput increases. Additionally, due to the short distances, only comparably
small transmission power is necessary. The following figure shows the division of
the WLAN into several cells.
Copyright
Figure 4-1
Cell 2
Cell n
Cell 1
18
WLAN
See also http://www.siemens.com/iwlan
36
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.1.2
Connection of individual radio cells: “Access points” and “clients”
The use of “access points” is required to control the communication in a cell or to
connect several radio cells with each other. Their position within the WLAN is
comparable to the position of switches for cable-based networks.
Administrative function of access points
If there is only one radio cell or if the communication occurs only within one cell,
the access point can be used to coordinate the communication within this cell.
When using encryption methods, it can either grant or deny clients access to the
network (see chapter 5). The access point can meet real-time requirements for the
communication by controlling and coordinating the data communication in the
network and by assigning periodic “time slots” to the individual clients within which
they can transmit their data without being disturbed (compare section 4.4).
Access points as a “backbone” of the communication
Siemens AG 2013 All rights reserved
For a WLAN consisting of several radio cells, each access point communicates
with all regular nodes of its cell, the so called “clients” – regardless of whether they
are stationary or mobile. At the same time, the access points of a WLAN maintain
the connection to each other. This is either via cable or via a second, independent
radio network.19 This makes communication beyond the limits of the radio cells
possible.
Copyright
The term “backbone” indicates in this case the combination of the different radio
cells or networks.
19
An access point with two or more radio interfaces is required for this purpose.
IWLAN
V3, Entry ID: 22681042
37
4 Topology, Configuration and Organization of IWLANs
Figure 4-2
Cell n
Cell 1
Siemens AG 2013 All rights reserved
WLAN
Access Point
Cell 2
Client
Copyright
The figure shows the division of a WLAN into three radio cells (yellow, red, green)
with a number of clients and one respective access point. The red arrows follow the
communication path between a client of the yellow cell and a client of the red cell.
38
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.2
The “roaming” method
Motion of clients between the radio cells: Roaming
If a WLAN spans a larger area, the radio field of one access point (radio cell) is
usually not enough. Several radio cells are required to illuminate the area in terms
of radio technology. If the radio areas of the access points overlap only a very little
bit, the clients should be permitted to freely move, without an interruption of the
network connection. Not only within their own radio cells but also transboundary
into other radio cells.
The transfer of the nodes from one access point to the next is called roaming.
However, the term hand-over is also common in the same context as roaming.
For the roaming process it is necessary that the individual radio cells overlap each
other and that the bordering radio cells communicate on different channels with
each other. If all radio cells would use the same channel, a client located in the
overlapping area would permanently have faulty reception. (See section 1.4.4)
Challenges of the roaming process
detect the leaving of the old radio cell by a client and
establish its connection to a new radio cell.
If this time is tolerated by all communication nodes, communication continues
undisturbed.
If very fast update times are required, e.g. for PROFINET I/O communication,
access points and client modules have to be used that support the iPCF proprietary
process (see section 4.6.1) for fast roaming and deterministic data traffic.
Copyright
Siemens AG 2013 All rights reserved
Due to roaming in accordance with the standard from IEEE 802.11, a delay time of
several 100 ms occurs. This time is necessary to
IWLAN
V3, Entry ID: 22681042
39
4 Topology, Configuration and Organization of IWLANs
4.3
Infrastructure networks
The operation of WLANs with the aid of coordinating access points is referred to as
“infrastructure mode”.
The following sections show several examples of infrastructure network topologies.
4.3.1
Standalone networks
Description
Standalone networks consist of a number of clients which are all located in the
radio cell of one single access point. The function of the access point is limited to
the coordination of the client communication to each other.
Illustration
Siemens AG 2013 All rights reserved
Figure 4-3
Client
Client
Copyright
Client
Access Point
Radio cell/ WLAN
The above figure shows such a standalone network. It includes an access point
which coordinates the data communication of the other bus nodes and via which
the entire traffic is directed. The access point determines the “SSID” (“Service Set
Identifier”) of the network, in other words, its “name”.
It is not necessary that all network nodes of a standalone network have direct
contact to each other.
The maximum expansion of such a network is limited by the condition that all
clients have to be located within the range of the access point (red circle).
40
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.3.2
Mixed networks
Description
In mixed networks, the access points are not only used for the communication of
the clients amongst each other but they additionally provide the connection to a
cable-based network. (This cable-based network is normally Industrial Ethernet.)
Several access points can be connected to the cable-based network. This means
that the access points generate several radio cells. If these cells cover a specific
area completely, the clients located in this area can move from radio cell to radio
cell (so called “roaming”, see chapter 4.2).
Illustration
Figure 4-4
Channel A
Client
Client
Client
Client
Copyright
Siemens AG 2013 All rights reserved
Channel A
Access Point
Access Point
Industrial Ethernet
A number of access points are connected by a wire-bound Ethernet line. (Any other
stationary nodes can also be connected to the Ethernet segment.) Several nodes
connected via WLAN (clients) are located within the radio field covered by the
access points (red circles above).
Mixed networks allow roaming, i.e. the change of a mobile node from one radio cell
to a neighboring cell (see above, dotted arrow).
WLANs set up as described above, can theoretically reach any size. Interferences
with reception may occur within the overlapping range of the radio cells since the
access points operate on the same frequency.
IWLAN
V3, Entry ID: 22681042
41
4 Topology, Configuration and Organization of IWLANs
4.3.3
Multi-channel configuration
Description
The multi-channel configuration corresponds to the mixed network (see chapter
4.4.3); however, the individual access points operate on different, non-overlapping
radio channels (see chapter 2.4). This ensures that interferences no longer occur
where radio cells overlap.
At the same time, roaming, thus the change of one client from one cell to another is
facilitated, which results in a considerable increase in performance.
Illustration
Figure 4-5
Channel A
Channel B
Client
Client
Siemens AG 2013 All rights reserved
Client
Client
Copyright
Access Point
Access Point
Industrial Ethernet
In this configuration, the individual access points form a backbone, and are
connected to one another via a cable-based Ethernet cable. (Other stationary
nodes do not have to be connected to the Ethernet segment.) Several nodes
connected via WLAN (clients) are located within the radio field covered by the
access points. The different frequencies on which the access points transmit are
indicated by circles in different colors.
In practical operation, this configuration is most frequently used for WLAN and is
normally chosen.
42
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.3.4
Wireless Distribution System (“WDS”)
Description
In normal operation, the access point is used as interface to a cable-bound network
and communicates with the clients. However, there is also the application case
where several access points have to communicate with each other, for example, in
order to enlarge the range or to establish a wireless backbone (see following
chapter). This mode is possible with WDS (Wireless Distributed System).
WDS corresponds to the multi-channel configuration (see chapter 4.3.3), except for
one important difference: The access points do not maintain the connection to one
another via a second medium (Industrial Ethernet cable in the case of the multichannel configuration) but via the radio network.
If communication between the access points is now permitted and the access of
clients is blocked, it is referred to as a pure WDS.
The WDS is characterized by three properties:
If several WDS connections are used on the same frequency or if the
client-access-point communication is additionally permitted, the effective data
rate of the access point is reduced, since the bandwidth has to be shared.
All access points that are to communicate with each other, have to use the
same channel.
Illustration
Figure 4-6
Channel A
Channel A
Copyright
Siemens AG 2013 All rights reserved
The distance between the access points must be small enough to each other
to ensure that every access point is located within the range of its
communication partner.
Client
Client
Client
WDS
Client
Access Point
Access Point
The above figure illustrates the principle of operation, compare also Figure 4-4.
Several nodes connected via WLAN (clients) are located within the radio field
covered by the access points (red circles above). Additionally, the access points
maintain a further radio connection between each other.
IWLAN
V3, Entry ID: 22681042
43
4 Topology, Configuration and Organization of IWLANs
4.3.5
Redundant radio connection
Description
To establish a redundant backbone it is necessary to use access points which
feature two radio interfaces and which can thus simultaneously transmit on several
frequencies.
With this condition it is possible to establish:
a redundant mixed network or
a redundant wireless distribution system (see chapter 4.3.4), which, based on
its location cannot be established as a wired network.
This ensures high connection reliability in combination with high data rates: Even if
a frequency range is temporarily interrupted by interfering nodes or shadowing or
interferences, it is highly probable that a connection is still possible via the other
channel.
Redundant mixed network
Figure 4-7
Channel B
(redundant radio cell)
(redundant radio cell)
Copyright
Siemens AG 2013 All rights reserved
Channel B
Client
Client
Access Point
Client
Channel A
Client
Access Point
Channel A
The access points establish an independent radio cell per radio interface, where
primarily only one radio cell is used.
If data transfer is no longer possible via the radio cell of the first radio interface, the
clients can automatically switch to the radio cell of the second radio interface. The
communication between the access points is cable-based via industrial Ethernet.
44
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
Redundant WDS
Figure 4-8
Chanel A
Chanel A
Client
Client
Client
Channel B
Client
Access Point
The access points do not communicate with each other on the primary frequency
but on the second frequency with a second set of antennae.
Copyright
Siemens AG 2013 All rights reserved
Access Point
IWLAN
V3, Entry ID: 22681042
45
4 Topology, Configuration and Organization of IWLANs
4.4
Coordinating the data transfer
For a WLAN according to the IEEE 802.11 standard two approaches are
differentiated to coordinate the communication in a shared medium:
the basic access method with distributed coordination function (DCF)
The point coordination function (PCF)
4.4.1
DCF (“Distributed Coordination Function”)
For a WLAN in accordance with the IEEE 802.11 standard, all nodes are principally
“responsible for themselves” and access the radio channel in an uncoordinated
way. The access of nodes with critical data cannot be forecasted.
Figure 4-9
Time
IEEE 802.11
Client 1
Client 3
Client 4
Client 5
Client 6
Access of nodes with critical data
cannot be predicted.
Copyright
Siemens AG 2013 All rights reserved
Client 2
All nodes access to the radio channel
without prioritization.
The data transmission according to the CSMA/CA method is binding for all
participants.
In order to reduce the collision probability, a station ready to transmit, listens to the
medium for a wait time that is made up of a constant wait time (DIFS; Distributed
Coordination Function InterFrame Space) and a random wait time. If the medium is
occupied it is waited until the end of the data transmission. Afterwards a fixed wait
time starts again that is extended with the reduced random wait time. If the medium
is still free, the data transmission will start.
The addressee that has received a message intended for it, will in turn send back
an acknowledgement telegram. Here, a constant wait time (SIFS; Short
Coordination Function InterFrame Space) also has to be maintained first, in order
to avoid collision.
DCF does not guarantee that a specific data volume is transmitted within a
maximum time interval. For this reason, it is primarily suitable for asynchronous
data transmission (such as email or web browser).
The data throughput of some DCF network configurations can be increased by
using the RTS/CTS method.
46
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.4.2
“Hidden Station and RTS/CTS” method for collision avoidance
A station cannot always detect whether the medium is free. This is especially the
case if two nodes of a radio cell cannot “see” each other (i.e., they are not located
within each others reach). This WLAN problem is defined by the expression
“hidden station”.
If, however, both try to communicate with a third node which is located between
them (and which simultaneously has contact with both transmitters), conflicts
occur.
The solution of the “hidden station” problem lies in the RTS / CTS method.
The medium is blocked for other stations – in order to avoid interferences - for a
period of time, by the station ready to transmit and the receiving station by a
request to send (RTS) and clear to send (CTS) dialog. It is sufficient here when all
stations in the catchment area of the transmitting station listen to one of the two
RTS / CTS signal, in order to put them to wait mode.
Copyright
Siemens AG 2013 All rights reserved
With the aid of this method, the number of necessary transmission repetitions is
considerably reduced since the collision is already detected before sending longer
data packets. However, the overhead produced by the RTS/CTS frames can
reduce the achievable data throughput.
4.4.3
PCF (“Point Coordination Function”)
The abbreviation PCF describes an access method defined in the 802.11 standard;
however, the implementation of this method is not mandatory. The method is
suitable to avoid some of the disadvantages of the DCF method.
In PCF, not all network nodes have equal rights but one or several access points
act as central administrators in the network. An access point then assigns time
slots to the other nodes, the clients: within these slots, the frequency is reserved for
these clients and they can transmit without being disturbed.
Figure 4-10
IEEE 802.11
Time
Client 1
Client 2
Client 3
Client 4
Client 5
Client 6
Access for all nodes cannot be
predicted.
All nodes can predictably access the radio
channel.
PCF enables to assign regular network access to the clients and to ensure the
transmission of data within a specific period. For this reason, PCF is preferably
suitable for applications requiring continuous data flows. (Synchronous data
transmission, e.g. video or audio streams and of course also process values.) The
achieved transmission periods, however, are in the range of several hundred
milliseconds and also the speed of the change from one radio cell to the next does
not meet real-time requirements.
IWLAN
V3, Entry ID: 22681042
47
4 Topology, Configuration and Organization of IWLANs
But it is possible to have networks change between DCF and PCF at intervals if
this is required by the communication.
In practical operation, PCF is rarely supported by manufacturers. With iPCF
(“Industrial Point Coordination Function”) SIEMENS provides a proprietary
alternative to PCF (see chapter 4.6.1).
4.5
Functions for the network management
4.5.1
VLANs (“Virtual LANs”)
The segmentation of a physical network into several logic “virtual” networks can be
performed for cable-based as well as radio networks. Today VLANs normally follow
the IEEE 802.1Q standard.20
For this type of network usage, the individual ports of a switch (or access point) are
assigned a so called VLAN ID via the configuration. Communication will then only
be possible within a VLAN (ports with the same VLAN ID).
For this purpose, the Ethernet data packets (“frames”) are extended by one data
block (a “tag”) which contains a VLAN ID. The switches (or access points) forward
the message only to those members of the VLAN, to which the message is
addressed.
Advantages
Using VLANs achieves a number of advantages:
Configuration errors remain restricted to the VLAN, in which they were made,
and can no longer bring down the entire LAN.
Broadcasts, i.e. transmissions to a general circle of receivers, are no longer
performed via the entire LAN but only via the respective VLAN; this reduces
the network load.
Copyright
Siemens AG 2013 All rights reserved
Segmentation of the data traffic
The individual VLANs can have various priorities assigned to them for
preferred transportation of messages from high-priority stations.
In contrast to using IP subnets, the stations of different VLANs can have the
same IP addresses. This makes better use of the restricted IP address space
and production cells of identical structure can be configured with identical IP
addresses, which reduces configuration and administration expenses.
The VLAN configuration is transparent for the end node, i.e. the end nodes do
not know to which VLANs they belong and cannot listen in on their data traffic.
This achieves a certain security of the network.
Note
You can find an animated demonstration system on this issue in the Siemens
Industry Online Support (entry ID 31770396):
http://support.automation.siemens.com/WW/view/en/31770396
20
Older protocols such as ISL (“Inter Switch Link”) and VLT (“Virtual LAN Trunk”) have become
insignificant today.
48
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.5.2
STP (“Spanning Tree Protocol”)
Description
Redundant networks are networks in which messages are forwarded between the
end nodes via switches, where the connection between each pair of end nodes is
made via more than one path. Such a network can be cable-based or wireless; in
the latter case the access points act as switches.
Forwarding the messages via each possible connection would cause unnecessary
network load and clog the network. It makes more sense if the switches or access
points determine the optimal paths between the end nodes and forward the
messages only along this route. They only use an alternative backup path if the
optimal route has been disrupted by interferences or device failures.
For this purpose the “Spanning Tree Protocol” STP was developed as IEEE
standard 802.1d.
This measure reduces the active connection paths of any intermeshed network
structure and passes it into a tree topology (spanning tree).
Copyright
Siemens AG 2013 All rights reserved
Functional sequence
In addition to regular data traffic the switches interexchange particular BPDUs
(“Bridge Protocol Data Units”). The BPDUs list the MAC addresses of the sender
and the forwarding switches. By evaluating this information the self-learning
switches can develop a “map” of the network and learn which data paths are
available.
Which path is optimal is determined by means of two criteria:
Principally the path which contains the lowest “path costs” is preferred. The
path costs are here inversely proportional with the data rate of a connection.
If the path costs of two connections are equal, the route with higher priority is
selected. This priority of the individual ports is configured at the switches
themselves.
In regular operation all messages run via the optimal path.
IWLAN
V3, Entry ID: 22681042
49
4 Topology, Configuration and Organization of IWLANs
4.5.3
RSTP (“Rapid Spanning Tree Protocol”)
One disadvantage of the STP is that the network must reconfigure itself in the
event of a disruption or a device failure: the switches only start negotiating new
paths at the moment of the disruption. This process takes up to 30 seconds; such a
period is not acceptable for many automation processes.
For these reasons, STP was expanded to the “Rapid Spanning Tree Protocol”
(RSTP, IEEE 802.1w). This mainly differs from STP by the switches, which already
collect information on alternative routes at the time of undisturbed operation.
This enables reducing the reconfiguration time for an RSTP-controlled network to a
few seconds.
Note
4.5.4
Further information on the topic of “RSTP in wireless LANs” is available in the
Siemens Industry Online Support (entry ID 30805917):
http://support.automation.siemens.com/WW/view/en/30805917
MSTP (“Multiple Spanning Tree Protocol”)
Siemens AG 2013 All rights reserved
STP as well as RSTP works with a global tree topology (spanning tree) for the
entire network. Certain paths are not used to guarantee loop freedom. The existing
path resources are therefore not efficiently used. An individual spanning tree has
the disadvantage that the reconfiguration takes relatively long for large networks.
The Multiple Spanning Tree Protocol (MSTP) is a further development of RSTP
and can often be found together with VLANs.
Copyright
MSTP does not only work with a tree topology but also operates an individual
spanning tree in each VLAN. Long reconfiguration times can be avoided by shorter
STP instances and which are made available by the paths blocked by RSTP within
individual VLANs.
50
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.6
Proprietary expansions of the IEEE 802.11 standard:
iFeatures
4.6.1
iPCF (“Industrial Point Coordination Function”)
iPCF (“Industrial Point Coordination Function”) provides a proprietary alternative to
PCF developed by SIEMENS, which solves several problems related to PCF (see
chapter 4.4.3). Furthermore iPCF enables the clients a very fast exchange of the
radio cell, where the log-off and new logon of the client ("handover") happens so
quickly that the real time requirements to the communication are still met.
Principle of operation
In iPCF, the access points poll the clients in their radio cell at regular, very short
intervals. They can register their requirement to send longer data frames, however,
they only start sending after having received the permission by the access point.
Copyright
Siemens AG 2013 All rights reserved
These properties result in the following effects:
The access point can be parameterized to perform the pollings in a very fast
sequence. This results in very short guaranteed response times (deterministic
transmission): The response times can be reduced to about 2 ms per network
node, i.e. a response time of less than 10 ms is guaranteed for 4 clients.
The transmission of larger, non-time critical messages is delayed until free
cycle time is available.
Polling a node can be seen by all other nodes in the radio cell. This is how a
client can detect the quality of the radio connection to the access point even if
it does not itself communicate with the access point.
Due to the shorter polling cycle times a client will very quickly know whether
the connection to its access point still exists or not. If the contact has got lost,
the client can react very quickly and establish a connection to an alternative
access point.
In the iPCF mode, the search for a new access point as well as the logon to
this access point is optimized in its time behavior. Handover times of clearly
below 50 ms are achieved.
iPCF particularly provides industrial applications with medium real-time
requirements in the two-digit millisecond range with WLAN-capability. This field
also includes the wireless connection of PROFINET I/O devices.
An optimal performance with iPCF is achieved if the clients follow fixed paths (e.g.
when using RCoax cables). For movable nodes in communication with stationary
access points the application of iPCF-MC is recommended (see 4.6.2)
IWLAN
V3, Entry ID: 22681042
51
4 Topology, Configuration and Organization of IWLANs
Restrictions by iPCF
iPCF can only be operated alone. A combination with other industrial functionalities
(iFeatures such as, for example, iPCF-MC, Dual Client) is not possible.
The iPCF method is an internal development of Siemens AG and works only with
nodes where iPCF has been implemented. For one access point with two WLAN
interfaces, however, it is possible to simultaneously set iPCF as well as standard
WLAN.
If the iPCF mode is enabled, only the “open system” security settings with the
encryption methods WEP or AES with 128 bit key length are supported.
Compatibility with other WLAN standards
Copyright
Siemens AG 2013 All rights reserved
“Mixed networks”, in which part of the devices is connected via DCF/iPCF, are not
possible with iPCF.
52
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.6.2
iPCF-MC (“iPCF – Management Channel”)
iPCF and iPCF-MC
iPCF-MC was developed in order to make the advantages achieved by iPCF also
possible for freely movable nodes (see chapter 4.6.1) that communicate
irrespective of an RCoax cable or directional antennae. For iPCF-MC, the client still
searches for potentially suitable access points if it receives iPCF requests of the
access point and the existing connection to an access point works interference
free. If required, this enables a very fast change to a different access point. As
compared to iPCF, the handover times of the iPCF-MC depend on the number of
the radio channels used.
Principle of operation
iPCF-MC uses both radio interfaces of the access points differently: One interface
works as management channel and transmits short telegrams (“beacon”) with
administrative information (e.g. channel setting of the data channel and SSID). The
other interface (data channel) only transmits the user data.
Figure 4-11
SCALANCE
W788-2
SCALANCE
W788-2
Copyright
Siemens AG 2013 All rights reserved
SIMATIC S7-300F
Mobile Panel
277F IWLAN
Radio cell 1
Radio cell 2
Interface 1: Management Channel
Interface 2: Data Channel
Restrictions by iPCF-MC
iPCF-MC can only be operated alone. A combination with standard WLAN and/or
other industrial functionalities (iFeatures such as, for example, iPCF, Dual Client) is
not possible. Thus a separate WLAN infrastructure is required for iPCF-MC.
The iPCF-MC method is an internal development of Siemens AG and works only
with nodes where iPCF-MC has been implemented.
IWLAN
V3, Entry ID: 22681042
53
4 Topology, Configuration and Organization of IWLANs
Requirements
For the use of this function, the following requirements are necessary:
Management cannel and data channel must be operated in the same
frequency band and have to match regarding their radio coverage. iPCF-MC
will not function if both radio interfaces are equipped with directional antennae
which cover different areas.
The management channel of all access points between which a client should
change must use the same channel. A client only scans this one channel to
find an accessible access point.
For the management channel the transmission method according to IEEE
802.11h cannot be used. However, 802.11h is possible for the data channel.
4.6.3
Dual client technology
The use of the dual client method is particularly recommended if a high data
throughput is demanded at the same time as very short handover times and
security mechanisms according to IEEE 802.11i (compare chapter 5.2.1) are to be
implemented.
Siemens AG 2013 All rights reserved
Principle of operation
Copyright
With the dual client procedure the devices are not connected to a radio network via
one WLAN client, as usually, but via two client devices simultaneously. Both clients
take on different functions. The so-called “active client” handles the regular data
traffic with the access point as this would be the case even without the connected
second client. The second client, the so-called “standby client”, meanwhile
permanently scans the radio field for alternative access points and always
establishes a connection with the access point that provides the best transmission
quality, however, without performing a data transfer. Furthermore, the stand-by
client regularly receives information on the quality of the connection between active
client and access point.
As soon as the connection quality of the stand-by client with the connected access
point is better than the quality of the connection between active client and access
point, the roles are exchanged within few milliseconds, and the previous stand-by
client takes on the data transfer. The previously active client now takes on the role
of the stand-by client and scans the radio field for access points.
For each dual client connection two client devices must exist which are
interconnected via Ethernet. Both clients need not necessarily be of the same type.
54
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
Figure 4-12:
Copyright
Siemens AG 2013 All rights reserved
Client
Access
Point
Client
Access
Point
The clients are employed in dual client mode. Between the right client and the right
access point there is an active connection, via which the data exchange occurs.
Between the client and the access point on the left side there is a connection,
however, this is without data exchange (stand-by connection).
Restrictions by dual client
Dual client can only be operated alone. A combination with other industrial
functionalities (iFeatures such as, for example, iPCF, iPCF-MC) is not possible.
The dual client method is an internal development of Siemens AG and works only
with nodes where the function has been implemented.
Requirements
The following prerequisites must be fulfilled in order to use the dual client
technology:
Dual client can only be used with devices activated for layer 2 tunneling.
A separate WLAN infrastructure is not mandatory for the dual client
functionality. The IWLAN access point has to support the dual client
functionality; however, standard WLAN clients can also additionally connect
themselves with the IWLAN access point.
IWLAN
V3, Entry ID: 22681042
55
4 Topology, Configuration and Organization of IWLANs
Boundary conditions
If an IWLAN access points fails or if a communication is interrupted, the
roaming times are between 500 ms and 1000 ms, provided the standby IWLAN
client has a connection to a working IWLAN access point.
If one of the two dual client nodes fails due to a defect, the communication to
the access points is instantly interrupted.
The larger the number of nodes per access point, the longer the reestablishment of the communication after roaming.
–
have communication to the same IWLAN access point (in this case, the
same channel is used for the two IWLAN clients). The clients exchange
information with each other, which at the time of establishing the
communication, is currently the active and which the standby client.
–
have communication to an access point on different channels in the same
frequency band (e.g. 2.4 GHz). In this case, the clients are logged on far
enough from each other at different access points and exchange
information with each other, which one, at the time of establishing the
communication, is currently active and which one is the standby client.
Conditions for the application of RSTP
Within the context of the Rapid Spanning Tree Protocol (RSTP, compare chapter
4.5.3) please note the following:
The subnet with the clients in dual client mode must not contain any network
components with enabled (R)STP functionality.
All bridge ports of a SCALANCE W700 access point, which represents a node
in dual client mode, are automatically defined as edge ports when using
(R)STP. The generation of redundant network paths is prevented by the
internal functioning of the dual client function.
Copyright
Siemens AG 2013 All rights reserved
In order to make optimal use of the functionality, both clients should at any time
either:
Note
Further documents on the topic of “Current IWLAN technologies” is available on
the SIEMENS automation portal under URL:
http://www.automation.siemens.com/net/html_00/support/whitepaper.htm
56
IWLAN
V3, Entry ID: 22681042
4 Topology, Configuration and Organization of IWLANs
4.6.4
Usable IWLAN devices
The following table gives an overview which iFeatures are compatible with which
IWLAN devices:21
Table 4-1
IWLAN device
IEEE standard
iPCF
AP
Copyright
Siemens AG 2013 All rights reserved
IE/PB Link PN IO
802.11a/b/g
iPCF-MC
Client
AP
Client
Dual Client
AP
Client
x
x
x
Mobile Panel 277 IWLAN
x
x
x
ET200pro IWLAN
x
x
x
x
x
x
SCALANCE W788-1 RR
x
x
SCALANCE W788-2 RR
x
x
x
x
x
x
SCALANCE W786-2 RR
x
x
x
x
x
x
SCALANCE W784-1 RR
x
x
x
x
x
SCALANCE W747-1 RR
x
x
x
SCALANCE W747-1
x
x
x
SCALANCE W788-1
RJ45 / M12 (EEC)
KEY
KEY
SCALANCE W788-2
RJ45 / M12 (EEC)
KEY
KEY
SCALANCE W786-1
RJ45
KEY
KEY
SCALANCE W786-2
RJ45 / SFP
KEY
KEY
SCALANCE W748-1
RJ45 / M12
802.11n
KEY
21
x:
The function is available
KEY: The function requires enabling via KEY-PLUG W780/ W740 iFeatures
(see chapter 9.1.1).
IWLAN
V3, Entry ID: 22681042
57
4 Topology, Configuration and Organization of IWLANs
4.6.5
iFeatures and PROFINET I/O
PROFINET is an open, cross-vendor product standard based on Industrial Ethernet
which facilitates the vertical integration of the automation, i.e. the networking of all
levels of the production process. PROFINET I/O is designed for the data exchange
in real time.
The WLAN is a shared medium in its origin. All nodes are principally “responsible
for themselves” and access to the radio channel in an uncoordinated way. The
access of nodes with critical data cannot be forecasted. Under these conditions
PROFINET I/O can only be used at very limited or certain boundary conditions in a
standard WLAN.
Real time communication is also made possible for a radio network through the
proprietary SIEMENS iFeatures
iPCF
iPCF-MC
Copyright
Siemens AG 2013 All rights reserved
.
58
IWLAN
V3, Entry ID: 22681042
5 Data Security and Encryption
5
Data Security and Encryption
5.1
Attack scenarios and security mechanisms
5.1.1
Basics of WLAN security
WLANs can easily create a feeling of insecurity with the user, as it is not necessary
for an intruder, for example, to access a factory site and to physically connect with
the network in order to listen to data: in principle, anybody located within the radio
range can listen to the data traffic of a network. However, this assumption is
misleading as there are hardly any cable-based isolated LANs left today: in reality,
most LANs are connected with the internet and so they are potentially subject to
attacks from outside. Security must be intentionally configured for radio networks
as well as for cable-based networks.
Due to advances in security standards and the performance of the components,
the radio networks today can be considered as secure as cable-based networks.
Copyright
Siemens AG 2013 All rights reserved
One of the simplest measures of securing a radio network consists, for example, in
configuring the access points and their transmission performance so they actually
only cover the required space and no overshoot occurs. This restricts the radio
network to the company site and prevents listening from outside.
A reduction of the radio power can of course only provide limited protection and
cannot be realized at any scale. More advanced, effective and secure methods are
the selection of a suitable infrastructure as well as the use of powerful encryption
and authentication protocols, as described in the following chapter.
5.1.2
Attack scenarios
Compromising the safety concept
The security concept of a WLAN can unintentionally be compromised in several
ways:
Access Points configured with errors: Access points which were connected
with the cable-based network by an internal user but contain a configuration
error. If, for example, no security settings were made, the respective access
point provides free network access for all.
Ad hoc wireless network: Operating systems such as Windows enable
configuring networks consisting of several wireless clients without the access
point in between. If one of the computers is configured so that it forms part of
an ad hoc network as well as establishing connections with the company
WLAN, it may provide unintentional access for hackers.
Faulty client connections: If companies are located directly within physical
vicinity, the company WLANs most probably use the same network
information. In this case a wireless client connects with the first accessible
access point. However, if it is part of a neighboring WLAN, this may cause a
security risk.
IWLAN
V3, Entry ID: 22681042
59
5 Data Security and Encryption
Attack methods
Malicious users can often benefit from the above described security gaps.
However, the following examples also describe scenarios in which you can create
your own WLAN accesses:
Rogue Access Points: An illegal access point connects with the cable-based
network and creates free LAN access for malicious or unauthorized users.
Honeypot Access Points: Some hackers are capable of determining the
configuration settings of WLANs and use an access point with the same
settings within network reach. Through this intentional faulty connection the
clients create a connection with these "honeypots" assuming that they are
contacting an official access point. Experienced hackers can make use of this
by connecting network resources with the AP, which act as bait so that the
users log on as usual and so give the hacker the opportunity to take
unauthorized possession of passwords or confidential documents.
Access Point MAC Spoofing: Wireless client computer can be configured as
access points. This way a hacker can abuse a normal PC as honeypot.
Manipulation options
Siemens AG 2013 All rights reserved
If a hacker has found its way into the network – either through an existing gap or by
creating a gap – there are various options of manipulating the company network:
Unauthorized client accesses: Hackers permanent search access options in
wireless networks. If a network has a weak, or non-existent user
authentication, access to the company network is made very easy and the
hackers can retrieve information or attack resources, leading to failures.
Copyright
Denial of Service (“DoS”) Networked devices must react to all client requests.
Hackers use this property by flooding a network resource with more requests
than they can handle. Distributed DoS attacks increase the problem by
preparing a number of “ignorant” computers using a hidden code, which then
simultaneously perform DoS attacks of a possibly enormous proportions.
“Man in the Middle”: If data is unprotected, hackers can intercept messages
and manipulate contents by disguising themselves as nodes on the travel path
of a communication connection.
IP Spoofing: By manipulating the source IP address in the package header, a
hacker can access traffic of a correctly authenticated user and pretend that the
user uses the computer of the hacker. Subsequently, all data and messages of
the server go back to the hacker.
Hijacking: Using software, secretly installed on the PC of a company user, a
hacker can take control over the affected computer and gain access to the
resources which the user can access, or damage servers or other computers.
60
IWLAN
V3, Entry ID: 22681042
5 Data Security and Encryption
5.1.3
IEEE 802.11 security mechanisms
To protect from unauthorized accesses and attacks to the company network it is
essential to enable suitable security mechanisms in the WLAN components.
WEP
WEP (“Wired Equivalent Privacy”) is the oldest and, at the same time, the least
secure encryption method with which WLAN transmissions are protected against
unauthorized intruders according to the 802.11 standard.
This method uses a user password that is used as a key, to generate a sequence
of pseudo-random numbers. Each character of the message to be transmitted is
then encrypted with the next number from this sequence and decrypted by the
receiver.
On the other hand, statistical methods can be used to determine characteristics
from the transmitted message traffic, which again enable to draw conclusions
about the used key as long as there is an adequate number of messages for the
analysis.22
Using appropriate tools the data traffic in WEP encrypted networks can be
decrypted within a few minutes. For these reasons, WEP is generally no longer
considered to be adequately secure.
ACL access control
In the network management, filter tables (“Access Control List”) with IP addresses
can be created which allow or refuse access to specific addresses. This way,
simple, albeit comparatively insecure access protection can be implemented for the
network.
Copyright
Siemens AG 2013 All rights reserved
The method is relatively simple and can be compromised comparatively easily for
two reasons: on the one hand, the key must be exchanged between sender and
receiver when establishing the connection; this exchange is, of course,
unencrypted.
It actually cannot be excluded that IP addresses are manipulated (so called
“spoofing”) so that ACL will only offer adequate protection for a network in
connection with other measures.
SSID
The SSID (“Service Set Identifier”) is a freely selectable name for the WLAN and
identifies it.
A WLAN access point sends this SSID if a client searches for wireless networks.
For this reason – from a security point of view - SSID should not give any clues to
the company, purpose of the network or location, otherwise the curiosity of hackers
or other unauthorized people could be aroused.
However, the transmission of the network name can also be suppressed. Since the
clients can no longer “see” the radio network, the SSID has to be entered correctly
in the client configuration so that it can connect with the desired WLAN.
22
Frequent manual change of the key by the user would increase security, however, in practice
this is rarely pursued conscientiously.
IWLAN
V3, Entry ID: 22681042
61
5 Data Security and Encryption
Note
Since no encryption is used for the SSID transmission, this function can only
basically protect from unauthorized accesses. The use of an authentication
method (e.g. WPA2 (RADIUS), if not possible WPA2-PSK) offers greater
security. Furthermore, it has to be expected that certain terminal devices may
have problems with access to a hidden SSID.
5.2
Measures for increasing the WLAN security
5.2.1
The IEEE 802.11i expansion
The WEP method has some weaknesses, so that this type of encryption can no
longer be considered reliable.
IEEE has detected these security risks and responded accordingly. A new task
group for the expansion of the 802.11i standards was founded that deals with the
security of the data transmission via WLANs, especially with the definition of
encryption algorithms and integrity checks23 for wireless transmission.
The aim of the IEEE 802.11i extension is the development of standardized security
measures for wireless data transmission that satisfy today’s security requirements.
Copyright
Siemens AG 2013 All rights reserved
Three methods were the result:
TKIP (“Temporary Key Integrity Protocol”) as temporary solution for older
WLAN devices.
AES-CCMP (“Advanced Encryption Standard”, “CTR / CBC-MAC Protocol”) as
final encryption method which today is recommended by the NIST (“National
Institute of Standards and Technology”).
AKM (“Authentication and Key Management”) to secure a unique
authentication in a WLAN.
TKIP
With TKIP an optional encryption method was developed by the task group which
is based on the WEP method but largely fills its security gaps. This interim solution
was necessary to guarantee the operation of older WLAN devices in a network.
To encode a message, the “Temporal Key Integrity Protocol” uses a key as well as
an additional initialization vector. Various combinations of initial key and
initialization vector makes the encoding work as if the key was continuously
changed which makes cracking the code more difficult.
The integrity check (MIC; “Message Integrity Check”) is performed via a special
HASH algorithm, called “Michael”.
23
An integrity check can prevent data manipulation during the data transmission.
62
IWLAN
V3, Entry ID: 22681042
5 Data Security and Encryption
AES-CCMP
AES-CCMP is the final method for encrypting the data in a WLAN.
This method requires new WLAN chip sets and can therefore no longer be used on
older WLAN products.
AES-CCMP, like WEP, exercises the “adding up” of a key to the message. One
block of the raw data is processed with the corresponding identical key, but several
processing sequences with respectively varying block boundaries take place.
Calculating the integrity check (MIC; “Message Integrity Check”) is performed via
temporary keys. The MAC address (i.e. the unique hardware ID) of the transmitter
is incorporated into the keys, making it even more difficult to falsify the address of
the sender of a message.
AKM
Apart from the definitions for secure data transmission and checking the frame
integrity, the IEEE 802.11i extension also intends further authentication measures
and algorithms for automatic key management. As authentication method the
standards of IEEE 802.11X or PSK (“Pre-Shared Key) are used (see chapter 5.3).
Copyright
Siemens AG 2013 All rights reserved
5.2.2
Wi-Fi Protected Access security standard
The development of an encryption algorithm that was supposed to replace WEP by
the IEEE task group 802.11i was delayed so that the “Wi-Fi Alliance”
recommended the application of WPA (“Wi-Fi Protected Access”) with TKIP as a
subset of the 802.11i standard as an interim solution.
WPA provides two options as authentication:
WPA (RADIUS): The authentication by a server (RADIUS server) is mandatory
for WPA (RADIUS) (see chapter 5.3.1). Further security is built in through
dynamic key exchange at each data frame.
WPA-PSK: For this method, the authentication is by password and not by
server (see chapter 5.3.2). This password is configured manually on the client
and on the server.
However, following the adoption of the 802.11i standard this is superfluous and the
Wi-Fi alliance has established WPA2 (“Wi-Fi Protected Access 2”) as the new
security standard. The encryption of WPA2 orientates itself on the full
implementation of the IEEE 802.11i extension and uses AES-CCMP.
As for WPA, the authentication can be performed via an authentication server or
PSK.
IWLAN
V3, Entry ID: 22681042
63
5 Data Security and Encryption
5.3
Authentication and key management
5.3.1
IEEE 802.1X authentication
Standard IEEE802.1X does not define the encryption of the data traffic between
access point and client, but the login procedure as well as the assignment of
access rights for clients. For this purpose, the RADIUS protocol is used on the
basis of “EAP” (“Extensible Authentication Protocol”) for larger networks and PSK
in office networks.
RADIUS protocol
The RADIUS protocol (“Remote Authentication Dial In User Service”) for the
authentication at the network was originally developed for cable-based systems,
however, it has also proven itself successful especially in the radio sector.
For RADIUS there is a central so-called RADIUS server, which contains a list with
the access authorizations of all nodes. If a client wishes to connect to the network,
the access point forwards the request to the RADIUS server. It reacts by
generating a “challenge”, i.e. a request for which the client can only send the
appropriate “response” if it has the password saved on the RADIUS server.
The password is never sent via the network in plain text, it can therefore not be
intercepted by somebody without authorization.
Since the access authorizations are saved on a central server, the method is
particularly suitable when using roaming clients. Not all access points need to
store the access data of the clients, but they can request them any time at the
RADIUS computer.
EAP
EAP is a widely used framework for different authentication methods for network
access. In other words, the actual EAP is not an authentication method but
describes the mechanism according to which client and server can agree on a
method.
Copyright
Siemens AG 2013 All rights reserved
This method has two advantages:
One of the methods which can be used under EAP is “EAP-TLS” (“EAP Transport
Layer Security”), in which the network nodes have to be “certified” before they are
authorized for the network communication, i.e. they must be authenticated at a
central server. This method is comparable to SSL, familiar from the internet.
Aside from this method, a large number of other, partly manufacturer-specific,
protocols exist that can be used with EAP.
64
IWLAN
V3, Entry ID: 22681042
5 Data Security and Encryption
5.3.2
Pre-Shared Key (PSK)
The pre-shared key is an alternative to the RADIUS authentication and, amongst
others, is made up of a clearly defined key that has to be known by the nodes
before communicating.
Further parameters for generating the PSK are the SSID and the SSID length.
5.4
Security functions and data rate
Please note that the increasing complexity of the encryption methods generates an
increasing transmission overhead and consumes more computing time of the
nodes which may reduce the effective data rate.
If a WLAN has to be operated with a very high performance (data throughput and
response times, e.g. PROFINET I/O), it may become necessary to use an
encryption method that is less secure also but resource-saving.
Further information regarding SCALANCE W devices is available in chapter 8.1.2
Observe the following notes to protect your network from attacks:
Use as secure connection with HTTPS. In contrast to HTTP, HTTPS enables
you secure access to the configuration of WLAN clients and access points via
the web based management.
Use WPA2/WPA2-PSK with AES in order to prevent password abuse. WPA2/
WPA2-PSK with AES offers greater security.
Protect your network from man-in-the-middle attacks by a network setup that
makes it more difficult for the attacker to get into the communication path
between two terminal devices:
WLAN device, for example, can be protected by the agent IP, only being
accessible via an individual management VLAN.
Copyright
Siemens AG 2013 All rights reserved
Note
Another possibility is to install an independent HTTPS certificate on the
WLAN client / access point. The HTTPS certificate checks the identity of
the device and regulates the encrypted data exchange. You can install
the HTTPS certificate, for example, via HTTP.
Use SNMPv3. SNMPv3 offers you the greatest possible security when
accessing WLAN devices via SNMP.
IWLAN
V3, Entry ID: 22681042
65
6 Coexistence of IWLANs with other Radio Networks
6
Coexistence of IWLANs with other Radio
Networks
Possible sources interfering with the operation
In the industrial environment there are basically three sources of interference which
can affect the function of an IWLAN:
An environment with obstacles and objects that have an influence on the
propagation of radio waves (e.g. metal etc.),
other radio transmitters using the same frequency band (other WLAN nodes,
but also Bluetooth, etc.),
devices sending unspecific interference pulses (welding devices, switching
devices)
Since the 2.4 GHz band is also used by more radio systems than the 5 GHz band,
larger operational difficulties must be expected in the 2.4 GHz band.
“Radio” as such is no limited resource. Due to its nature as a “shared medium” it is
not possible to increase the capacity by simply installing more cables, for example.
Due to a proactive coexistence management it is possible to use this resource
optimal, which in most cases meets the requirements of industrial application.
An expert should always be consulted for the coexistence management.
Radio analysis
The first step should always be a radio analysis of the environment. It evaluates the
individual transmitters according to the various criteria:
On which frequency does the transmitter work?
Copyright
Siemens AG 2013 All rights reserved
Coexistence management
Is its application time or security critical?
How large is the data volume to be transferred?
Does the transmission occur cyclically, sporadically or continuously?
Where are the nodes stationed?
The principle of decoupling
The individual radio fields can work independent of one another if they are
"decoupled" in at least on of the four domains, i.e. they are separated from each
other:
space
frequency
time
code
Spatial decoupling is achieved by keeping the overlap between the various radio
systems as low as possible. This is achieved by reducing the transmission power
to the required minimum (no overshoot), by selecting suitable antennae (directional
antennae or omnidirectional, compare chapter 9.3), as well as optimizing the setup
location of access points and clients, as far as possible within the framework of the
function of the system.
66
IWLAN
V3, Entry ID: 22681042
6 Coexistence of IWLANs with other Radio Networks
For the frequency decoupling it is decisive that the frequency ranges of the
individual radio systems overlap as little as possible. In the easiest case this is
done by selecting the respective radio channels, in a more advanced case this is
achieved by modulation and multiplex method (see chapter 1.6), such as, for
example, MIMO.
For the temporal decoupling the configuration of the individual nodes is decisive.
These must be selected in a way so that the probability of a time-critical
transmission such as PROFINET I/O which overlaps with another transmission,
becomes as low as possible. (It is possible, for example, to reserve a channel
exclusively for time-critical transmissions, as long this is practically feasible)
For code decoupling it is mainly the separation and distinction of different and
parallel transmitted data streams via a jointly used frequency band that has priority.
For reasons of distinction, the data streams of the nodes are each coded with
independent and individual spreading codes (orthogonal codes). This is how it can
be clearly detected on the receiver, which signal belongs to which user.
Figure 6-1
Copyright
Siemens AG 2013 All rights reserved
The following graphic shows an example for decoupling in the frequency range:
The MP277 Mobile Panel can communicate with the robot, even though it is at the
same time within in the transmission range of the cellular phone, since both
communicate on different frequencies (orange: 5 GHz, purple: 2.4 GHz).
Even though the fields overlap in space and time, they are decoupled in the
frequency domain.
IWLAN
V3, Entry ID: 22681042
67
7 Country Approvals
Note
More information on this issue can be found on the web in the following brochure
which was edited by “ZVEI – Zentralverband Elektrotechnik- und Elektronikindustrie e.V”24:
ZVEI_Koexistenz_von_Funksystemen_in_der_Automatisierungstechnik
The individual steps of the coexistence management are summarized in the
VDI/VDE guideline 2185 (payable download)
"Funkgestützte Kommunikation in der Automatisierungstechnik"
7
Country Approvals
7.1
General
Not all radio modes are approved in all countries. Among other things, nationally
different restrictions for approved configurations can refer to
permitted frequency bands and channels,
indoor/outdoor mode,
802.11 standards (“a”, “b”, “g”, “h”, “n”, “Turbo”),
specific methods for improving the transmission quality such as DFS and TCP
(compare chapter 2.3.1)
If you require a specific configuration when configuring your network, please
consult your Siemens customer adviser.
Respective components
A radio network is considered as an “entity” in which the respective approvals must
exist for all participating systems. These are primarily all active components that
have direct influence on the network, such as:
Copyright
Siemens AG 2013 All rights reserved
maximum transmission power,
access points
clients (including interface modules (compare chapter 8.7.2, 8.7.3))
mobile operator panels (see chapter 8.7).
antennae
Note
Passive components (e.g. network sniffer software, power supplies) do not have
their own approvals but are approved in the system together with the access
points and clients. More information can be found in the list of countries at this
PDF. (Link see chapter 12).
Responsibility
Principally, the responsibility for proper operation of a radio system lies with the
operator, and not the manufacturer. Technically, it is now possible at any time to
configure a device approved in a country in such a way that in actual operation it
violates the standards of this country.
24
www.zvei.org
68
IWLAN
V3, Entry ID: 22681042
7 Country Approvals
7.2
Country approvals in the SCALANCE W devices
The national standards that were current at the time the firmware was published
are stored in the firmware of each SCALANCE W device (compare chapter 8.1.2).
These standards can be read out via the web interface of the access point or the
client.
Note
Current descriptions can be found in the manual of the respective device. They
can be found in the Siemens Industry Online Support:
http://support.automation.siemens.com/WW/view/en/39961954/133300
Please note that this list is for your information only; it is not related to a functional
restriction of the respective device: operating an access point or client in a radio
mode that is not approved in the respective country does not require additional
measures. Operating SCALANCE W devices is not permitted in countries that are
not listed in the country list.
Copyright
Siemens AG 2013 All rights reserved
The following screenshot shows a possible country approval list from an access
point. The excerpt below shows the entries of the radio modes permitted in Italy.
Figure 7-1
Note
Updated lists with country approvals for the individual SCALANCE W products
are available at this PDF (Link see chapter 12).
IWLAN
V3, Entry ID: 22681042
69
8 SIEMENS NET Products for Setting up an IWLAN
8
SIEMENS NET Products for Setting up an
IWLAN
8.1
General Information
8.1.1
Overview of the product range
For the setup of a secure and reliable WLAN, SIEMENS offers a wide product
range. The next chapters introduce you to these properties and show you the
application and the practical use.
The following figure shows you an overview of SIMATIC wireless products. Top
row from left to right Access Points W788 (IEEE 802.11n), W786 (IEEE 802.11n
and IEEE 802-11abg), W784 and W788 (both IEEE 802.11abg); bottom row:
IWLAN interface IM 154-6 PN HF, Mobile Panel 277F, IWLAN/PB Link PN IO, in
between various antennae and RCoax cables (figure not to scale)
Copyright
Siemens AG 2013 All rights reserved
Figure 8-1
Note
70
Further, continuously updated information on SCALANCE W products are
available at: http://www.siemens.com/iwlan
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
8.1.2
Division of the SCALANCE W products
The SCALANCE W product series (“wireless”) consists of components for
connecting Industrial Ethernet and WLAN in industrial environments.
The product portfolio is made up of two different product families:
The first product palette of SCALANCE W products with the
IEEE 802.11a/b/g standard.
The latest product range with the IEEE 802.11a/g/n standard.
Note
For devices with the IEEE 802.11a/g/n standard, the IEEE 802.11b standard is
supported in the compatibility mode; however, it cannot be selected as
transmission mode.
The SCALANCE W device family comprises the products:
IWLAN controller,
Access Points and
Client module.
Copyright
Siemens AG 2013 All rights reserved
The IWLAN controller
The SCALANCE WLC711 IWLAN controller is a network device for the central
management of a wireless LAN in the industrial environment. It supports
commissioning, diagnostic, access control and security settings of the wireless
network as well as firmware updates of the access points.
Note
More and detailed information on SCALANCE WLC711 can be found in the
Siemens Industry Online Support:
http://support.automation.siemens.com/WW/view/en/58674679/133300
The access points
In this series, the W78x modules are access points which are used as network
switches of the individual radio cells and as transitions between Industrial Ethernet
and WLAN segments. Two different variants of access points belong to W78x:
Standalone Access Points
Controller-based access points
Note
Manuals on SCALANCE access points can be found in the Siemens Industry
Online Support:
http://support.automation.siemens.com/WW/view/en/58686893/133300
The client modules
The client modules have the designation “W74x”. They are connected to mobile
end nodes via Ethernet and communicate via the access points.
IWLAN
V3, Entry ID: 22681042
71
8 SIEMENS NET Products for Setting up an IWLAN
Note
8.2
Manuals on SCALANCE clients can be found in the Siemens Industry Online
Support:
http://support.automation.siemens.com/WW/view/en/58686771/133300
SCALANCE WLC711 IWLAN controller
SCALANCE WLC711 is a network instance for the central management of a
wireless LAN in the industrial environment. It supports commissioning, diagnostic,
access control and security settings of the wireless network as well as firmware
updates of the access points.
Only controller-based access points can be operated on the SCALANCE WLC711.
General
Siemens AG 2013 All rights reserved
The requirements to WLAN in the industrial area as well as the variety of the
possible applications and uses have continuously increased over the last years.
Aspects such as higher performance and data rate as well as low management
effort of the network, present new challenges today. As a reply, a further
architecture has established itself in WLAN networks in the office area for years:
the controller-based architecture.
With this architecture, access points are no longer as operated as standalone but
are controlled by an IWLAN controller. Via the controller, management data and
user data can be transmitted to and from the individual access points.
With the SCALANCE WLC711 the SIMATIC NET portfolio offers the option of
controller-based IWLANs.
Copyright
Figure 8-2
Basic hardware
The basic hardware is a fan-less industrial PC with two separate gigabit Ethernet
interfaces:
Management port: The controller is configured via this port.
Data port: This is where the data is transmitted.
72
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
Properties
The SCALANCE WLC711 is characterized by the following characteristics:
Central configuration and firmware upgrade of the access points via a user
interface in the controller.
Monitoring of larger WLAN networks: The IWLAN controller offers the option to
monitor the network in real time via the “Wireless Assistant Home Screen”.
Assigning of properties to groups of users, devices and services.
Roll-based security functions (authentication, intrusion detection, rogue AP
detection, firewalls, etc.).
Fast layer2 and layer3 roaming (e.g. for logistic scanner and VoIP).
Expanded QoS functions guarantee end-to-end IP prioritization for voice, video
& data.
RF management (automatic setting of channels and transmission power).
Internal and external captive portal (guest portal): The guest is automatically
forwarded to a login web site where s/he has to enter his/her login data.
Note
More and detailed information on SCALANCE WLC711 can be found in the
Siemens Industry Online Support:
http://support.automation.siemens.com/WW/view/en/58674679/133300
Copyright
Siemens AG 2013 All rights reserved
Reliable meshed WLAN through redundant paths: In the event of a failure of a
connection or an access point, the network and the packet route is
automatically reconfigured.
IWLAN
V3, Entry ID: 22681042
73
8 SIEMENS NET Products for Setting up an IWLAN
8.3
SCALANCE W Standalone Access Points
Standalone means that the access points are configured individually and that there
is no higher instance that can control the network.
The SCALANCE W access points are divided as follows:
Access points in accordance to IEEE 802.11a/g/n standard
Access points in accordance to IEEE 802.11a/b/g standard
8.3.1
Access Points IEEE 802.11n
The IEEE 802.11n standard is an expansion of the IEEE 802.11 and can work in
the 2.4 GHz band as well as in the 5 GHz band (see chapter 2.2.4).
Using special mechanisms and new technologies, a data throughput of up to
450 Mbps (gross) and an improved radio coverage is possible.
Copyright
Siemens AG 2013 All rights reserved
Per radio module up to three antennae can be connected. This divides the data
stream between up to three transmitting antennae (spatial multiplexing).
74
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W788-x RJ45 Access Points
The SCALANCE W788-x RJ45 modules are built according to protection class
IP30 and are, amongst other applications, very suitable for the control cabinet in
industrial environments.
The Ethernet interface has been designed electrically (RJ45). For the connection of
the external antennae, R-SMA sockets are provided.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-3
The SCALANCE W788-x RJ45 can be ordered in the following variants:
W788-1 RJ45 with one radio interface
–
Order number: 6GK5788-1FC00-0AA0 or
–
Order number: 6GK5788-1FC00-0AB0 (US variant)
W788-2 RJ45 with two radio interfaces that are independent from each other
–
Order number: 6GK5788-2FC00-0AA0 or
–
Order number: 6GK5788-2FC00-0AB0 (US variant)
IWLAN
V3, Entry ID: 22681042
75
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W788-x M12 (EEC) Access Points
The SCALANCE W788-x M12 is available in two versions:
The standard W788-x M12 variant
The EEC variant W788-x M12 EEC (Enhanced Environment Conditions)
Both access points have protection class IP65 and are suitable for internal
installation within industrial environments with particularly demanding
environmental conditions.
Additionally, the EEC variant can be used in high-performance plant networks and
applications with high temperature or EMV requirements.
The Ethernet interface has been designed electrically (M12). For the connection of
the external antennae, robust N connect sockets are provided.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-4
The SCALANCE W788-x M12 can be ordered in the following variants:
W788-1 M12 with one radio interface
–
Order number: 6GK5788-1GD00-0AA0 or
–
Order number: 6GK5788-1GD00-0AB0 (US variant)
W788-2 M12 with two radio interfaces that are independent from each other
–
Order number: 6GK5788-2GD00-0AA0 or
–
Order number: 6GK5788-2GD00-0AB0 (US variant)
W788-2 M12 EEC with two radio interfaces that are independent from each
other
76
–
Order number: 6GK5788-2GD00-0TA0 or
–
Order number: 6GK5788-2GD00-0TB0 (US variant)
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W786-x RJ45/SFP access points
The SCALANCE W786-x RJ45/SFP access points have been designed for
protection class IP65 for the use within industrial environments with particularly
demanding environmental conditions in public spaces or outside of buildings. The
most important properties include insensitivity to extreme effects of the weather
such as salt water spray, but also the rugged design in an impact-resistant and
shock-proof plastic housing without destructible parts facing outwards.
The Ethernet interface is either designed as RJ45 or SFP.
SFP interface modules (Small Form Factor Pluggable) are small compact and
pluggable transceiver modules and form the physical interface between the
transmission medium and gigabit Ethernet. SPF modules are offered for various
fiber optic cables.
Note
Further information on SFP can be found in the operating instruction for the
SCALANCE W786 in the Siemens Industry Online Support (entry ID 62521860):
http://support.automation.siemens.com/WW/view/en/62521860
For the connection of the external antennae, R-SMA sockets are provided.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-5
IWLAN
V3, Entry ID: 22681042
77
8 SIEMENS NET Products for Setting up an IWLAN
The SCALANCE W788-x RJ45/SFP can be ordered in the following variants:
W786-1 RJ45 with one radio interface and external antennae
–
Order number: 6GK5786-1FC00-0AA0 or
–
Order number: 6GK5786-1FC00-0AB0 (US variant)
W786-2 RJ45 with two radio interfaces that are independent from one another
and external antennae
–
Order number: 6GK5786-2FC00-0AA0 or
–
Order number: 6GK5786-2FC00-0AB0 (US variant)
W786-2IA RJ45 with two radio interfaces that are independent from each other
and internal antennae
–
Order number: 6GK5786-2HC00-0AA0 or
–
Order number: 6GK5786-2HC00-0AB0 (US variant)
W786-2 SFP with two radio interfaces that are independent from one another
and external antennae
Order number: 6GK5786-2FE00-0AA0
–
Order number: 6GK5786-2FE00-0AB0 (US variant)
Copyright
Siemens AG 2013 All rights reserved
–
78
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
8.3.2
IEEE 802.11a/b/g access points
The access point in accordance with IEEE 802.11a/b/g standard can work in the
2.4 GHz band (IEEE 802.11b/g) as well as in the 5 GHz band (IEEE 802.11a)´, see
chapter 2.2).
Depending on the standard, gross data rates of 11 Mbps (IEEE 802.11b) or
54 Mbps (IEEE 802.11a/g) are possible.
Two antennae can be connected per radio module.
SCALANCE W784-1xx access points
The W784-1xx access points are cost-effective models intended for application in
less demanding environment conditions, such as, for example in switching cabinets
(protection class IP30). Their compact form factor makes them particularly suitable
for installation in areas with difficult access as for the integration into a device or
machine.
The reduction of the hardware installed on the access point to necessary
components ensures an optimum price/performance ratio.
The Ethernet interface has been designed electrically (RJ45). For the connection of
the external antennae, R-SMA sockets are provided.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-6
The SCALANCE W784-1xx can be ordered in the following variants:
W784-1 with one radio interface:
–
Order number: 6GK5784-1AA30-2AA0 or
–
Order number: 6GK5784-1AA30-2AB0 (US variant)
W784-1RR with one radio interface and iFeatures:
–
Order number: 6GK5784-1AA30-6AA0 or
–
Order number: 6GK5784-1AA30-6AB0 (US variant)
IWLAN
V3, Entry ID: 22681042
79
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W788-xPRO/RR access points
These access points have the IP65 protection class and are suitable for installation
indoors in industrial environments.
The Ethernet interface has been designed electrically (RJ45). For the connection of
the external antennae, R-SMA sockets are provided.
Siemens AG 2013 All rights reserved
Figure 8-7
The SCALANCE W788-x can be ordered in the following variants:
Copyright
W788-1 PRO with one radio interface:
–
Order number: 6GK5788-1AA60-2AA0 or
–
Order number: 6GK5788-1AA60-2AB0 (US variant)
W788-2 PRO with two radio interfaces that are independent from each other:
–
Order number: 6GK5788-2AA60-2AA0 or
–
Order number: 6GK5788-2AA60-2AB0 (US variant)
W784-1 RR with one radio interface and iFeatures:
–
Order number: 6GK5788-1AA60-6AA0 or
–
Order number: 6GK5788-1AA60-6AB0 (US variant)
W788-2 RR with two radio interfaces that are independent from each other and
iFeatures:
Note
–
Order number: 6GK5788-2AA60-6AA0 or
–
Order number: 6GK5788-2AA60-6AB0 (US variant)
Application examples can be found in the Siemens Industry Online Support:
For mobile monitoring and operating (entry ID 21524054):
http://support.automation.siemens.com/WW/view/en/21524054
For mobile maintenance (entry ID 21523940):
http://support.automation.siemens.com/WW/view/en/21523940
80
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W786-xPRO/RR access points
The SCALANCE W786-xPRO/RR access points are designed for the use in
particularly demanding ambient conditions, in public areas or outside of buildings
because of the protection type IP65. The most important properties include
insensitivity to extreme effects of the weather such as salt water spray, but also the
rugged design in an impact-resistant and shock-proof plastic housing without
destructible parts facing outwards.
The Ethernet interface is either electrical (RJ45) or optical (BFOC).
For the connection of the external antennae, R-SMA sockets are provided.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-8
With a RJ45 Ethernet interface the SCALANCE W786-x can be ordered in the
following variants:
W786-1 PRO with one radio interface and internal antennae:
–
Order number: 6GK5786-1BB60-2AA0 or
–
Order number: 6GK5786-1BA60-2AB0 (US variant)
W786-1 PRO with one radio interface and external antennae:
–
Order number: 6GK5786-1AA60-2AA0 or
–
Order number: 6GK5786-1AA60-2AB0 (US variant)
W786-2 PRO with two radio interfaces that are independent from one another
and internal antennae:
–
Order number: 6GK5786-2BA60-2AA0 or
–
Order number: 6GK5786-2BA60-2AB0 (US variant)
W786-2 PRO with two radio interfaces that are independent from one another
and external antennae:
–
Order number: 6GK5786-2AA60-2AA0 or
–
Order number: 6GK5786-2AA60-2AB0 (US variant)
IWLAN
V3, Entry ID: 22681042
81
8 SIEMENS NET Products for Setting up an IWLAN
W786-3 PRO with three radio interfaces that are independent from one another
and internal antennae:
–
Order number: 6GK5786-3AA60-2AA0 or
–
Order number: 6GK5786-3AA60-2AB0 (US variant)
W786-2 RR with two radio interfaces that are independent from each other,
internal antennae and iFeatures:
–
Order number: 6GK5786-2BA60-6AA0 or
–
Order number: 6GK5786-2BA60-6AB0 (US variant)
W786-2 RR with two radio interfaces that are independent from each other,
external antennae and iFeatures:
–
Order number: 6GK5786-2AA60-6AA0 or
–
Order number: 6GK5786-2AA60-6AB0 (US variant)
With a BFOC Ethernet interface the SCALANCE W786-x can be ordered in the
following variants:
Siemens AG 2013 All rights reserved
W786-1 PRO with one radio interface and internal antennae:
–
Order number: 6GK5786-1BB60-2AA0 or
–
Order number: 6GK5786-1BB60-2AB0 (US variant)
W786-1 PRO with one radio interface and external antennae:
–
Order number: 6GK5786-1AB60-2AA0 or
–
Order number: 6GK5786-1AB60-2AB0 (US variant)
Copyright
W786-2 PRO with two radio interfaces that are independent from one another
and internal antennae:
–
Order number: 6GK5786-2BB60-2AA0 or
–
Order number: 6GK5786-2BB60-2AB0 (US variant)
W786-2 PRO with two radio interfaces that are independent from one another
and external antennae:
–
Order number: 6GK5786-2AB60-2AA0 or
–
Order number: 6GK5786-2AB60-2AB0 (US variant)
W786-3 PRO with three radio interfaces that are independent from one another
and internal antennae:
82
–
Order number: 6GK5786-3AB60-2AA0 or
–
Order number: 6GK5786-3AB60-2AB0 (US variant)
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
8.4
Controller-based SCALANCE W access points
Controller-based access points can only be used in a network with an IWLAN
controller, because they need its central management functions.
The controller-based access points are divided as follows:
Access points in accordance to IEEE 802.11a/g/n standard
Access points in accordance to IEEE 802.11a/b/g standard
8.4.1
Access Points IEEE 802.11n
The controller-based access points in accordance with the IEEE 802.11n standard
work in the 2.4 GHz band as well as in the 5 GHz band.
Regarding design and functionality they are identical to the standalone access
points for IEEE 802.11n (see chapter 8.3.1). In contrast to those, the controllerbased access points can only be used together with a controller.
The following controller-based access points can be ordered from the product
portfolio:
Copyright
Siemens AG 2013 All rights reserved
SCALANCE W788C-2 RJ45 with two radio interfaces that are independent
from each other:
–
MLFB 6GK5788-2FC00-1AA0
SCALANCE W788C-2 M12 with two radio interfaces that are independent from
each other:
–
MLFB 6GK5788-2GD00-1AA0
SCALANCE W788C-2 M12 EEC with two radio interfaces that are independent
from each other:
–
MLFB 6GK5788-2GD00-1TA0
SCALANCE W786C-2x RJ45 in the following variants:
–
W786C-2 RJ45 with two radio interfaces that are independent from one
another and external antennae:
MLFB 6GK5786-2FC00-1AA0.
–
W786C-2IA RJ45 with two radio interfaces that are independent from each
other and internal antennae
MLFB 6GK5786-2HC00-1AA0
W786C-2 SFP with two radio interfaces that are independent from one another
and external antennae
–
IWLAN
V3, Entry ID: 22681042
Order number: 6GK5786-2FE00-1AA0
83
8 SIEMENS NET Products for Setting up an IWLAN
8.4.2
IEEE 802.11a/b/g access point
The SCALANCE W786-2 HPW access point can work in the 2.4 GHz band (IEEE
802.11b/g) as well as in the 5 GHz band (IEEE 802.11a).
It is identical to the standalone access points for SCALANCE W786-xPRO
regarding design and functionality (see chapter 8.3.2). In contrast to it, the
SCALANCE W786-2 HPW can only be used together with a controller.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-9
With a RJ45 Ethernet interface the SCALANCE W786-2 HPW can be ordered in
the following variants:
W786-2 HPW with two radio interfaces that are independent from one another
and internal antennae:
–
MLFB 6GK5786-2BA60-1CA0.
W786-2 HPW with two radio interfaces that are independent from one another
and external antennae
–
MLFB 6GK5786-2AA60-1CA0
With a BFOC Ethernet interface the SCALANCE W786-2 HPW can be ordered in
the following variants:
W786-2 HPW with two radio interfaces that are independent from one another
and internal antennae:
–
MLFB 6GK5786-2BB60-1CA0
W786-2 HPW with two radio interfaces that are independent from one another
and external antennae
–
84
MLFB 6GK5786-2AB60-1CA0
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
8.5
SCALANCE W clients
The SCALANCE W clients can be operated as standalone access points, as well
as controller-based access points.
The modules are identical in construction to the corresponding access points
W78x-1 (see chapter 8.3).
However, the software differs in the functionalities, so that these devices are not
intended for the network management as the access points, but for a
communication amongst each other and with other network devices.
The clients furthermore form the interface between Ethernet-connected devices
and WLAN. However, they do not transmit the complete network traffic, but only
the messages of a limited number of Ethernet nodes.
The SCALANCE W clients are divided as follows:
Clients in accordance to IEEE 802.11a/g/n standard
Clients in accordance to IEEE 802.11a/b/g standard
IEEE 802.11n client modules
The IEEE 802.11n standard is an expansion of the IEEE 802.11 and can work in
the 2.4 GHz band as well as in the 5 GHz band.
Using special mechanisms and new technologies, a data throughput of up to
450 Mbps (gross) and an improved radio coverage is possible.
The clients have a radio module. Up to three antennae can be connected here.
Thus, the data stream can be divided between up to three transmitting antennae
(spatial multiplexing).
The SCALANCE W748-1 modules supply up to eight Ethernet nodes.
Copyright
Siemens AG 2013 All rights reserved
8.5.1
IWLAN
V3, Entry ID: 22681042
85
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W748-1 RJ45 clients
The SCALANCE W748-1 modules are built according to protection class IP30 and
are, amongst other applications, very suitable for the control cabinet in industrial
environments.
The Ethernet interface has been designed electrically (RJ45). For the connection of
the external antennae, R-SMA sockets are provided.
Siemens AG 2013 All rights reserved
Figure 8-10
Copyright
The SCALANCE W748-1 RJ45 can be ordered in the following variants:
Order number: 6GK5748-1FC00-0AA0 or
Order number: 6GK5748-1FC00-0AB0 (US variant)
86
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W748-1 M12 clients
These clients have the IP65 protection class and are suitable for installation
indoors in industrial environments.
The Ethernet interface has been designed electrically (M12). For the connection of
the external antennae, robust N connect sockets are provided.
Siemens AG 2013 All rights reserved
Figure 8-11
The SCALANCE W748-1 M12 can be ordered in the following variants:
Copyright
Order number: 6GK5748-1GD00-0AA0 or
Order number: 6GK5748-1GD00-0AB0 (US variant)
8.5.2
IEEE 802.11a/b/g client modules
The clients in accordance with IEEE 802.11a/b/g standard can work in the 2.4 GHz
band (IEEE 802.11b/g) as well as in the 5 GHz band (IEEE 802.11a).
Depending on the standard, gross data rates of 11 Mbps (IEEE 802.11b) or
54 Mbps (IEEE 802.11a/g) are possible.
All clients have a radio module. Here, up to two antennae can be connected.
The individual variants differ in the number of Ethernet nodes they can manage, in
the support of the iFeatures, as well as the protection class which determines the
environment conditions for which they are suitable.
IWLAN
V3, Entry ID: 22681042
87
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W74x-1 clients
The W74x-1 clients are cost-effective models intended for application in less
demanding environment conditions, such as, for example in control cabinets
(protection class IP30). Their compact form factor makes them particularly suitable
for installation in areas with difficult access as for the integration into a device or
machine.
The Ethernet interface has been designed electrically (RJ45). For the connection of
the external antennae, R-SMA sockets are provided.
The W744-1 can only connect one single node to the Ethernet, the models W746-1
and W747-1 supply up to 8 nodes.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-12
The SCALANCE W74x-1 can be ordered in the following variants:
SCALANCE W744-1
–
Order number: 6GK5744-1AA30-2AA0 or
–
Order number: 6GK5744-1AA30-2AB0 (US variant)
SCALANCE W746-1
–
Order number: 6GK5746-1AA30-4AA0 or
–
Order number: 6GK5746-1AA30-4AB0 (US variant)
SCALANCE W747-1 with iFeatures
88
–
Order number: 6GK5747-1AA30-6AA0 or
–
Order number: 6GK5747-1AA30-6AB0 (US variant)
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
SCALANCE W74x-1 xx clients
These clients have the IP65 protection class and are suitable for installation
indoors in industrial environments.
The Ethernet interface has been designed electrically (RJ45). For the connection of
the external antennae, R-SMA sockets are provided.
W744-1PRO can only connect one single node, the models W746-1PRO and
W747-1RR supply up to 8 nodes.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-13
The SCALANCE W74x-1xx can be ordered in the following variants:
SCALANCE W744-1 PRO
–
Order number: 6GK5744-1AA60-2AA0 or
–
Order number: 6GK5744-1AA60-2AB0 (US variant)
SCALANCE W746-1 PRO
–
Order number: 6GK5746-1AA60-4AA0 or
–
Order number: 6GK5746-1AA60-4AB0 (US variant)
SCALANCE W747-1 RR with iFeatures
–
Order number: 6GK5747-1AA60-6AA0 or
–
Order number: 6GK5747-1AA60-6AB0 (US variant)
IWLAN
V3, Entry ID: 22681042
89
8 SIEMENS NET Products for Setting up an IWLAN
8.6
Configuring the SCALANCE W devices
The SCALANCE W700 access points, client modules and controllers can be
configured via “Web Based Management” (WBM) or Telnet via the command line
(“Command Line Interface”, CLI).
For WBM the SCALANCE W configuration data is accessed via the Ethernet
interface or an existing WLAN connection. A web browser on the PC of the
configurator communicates with an HTTP server that runs on the SCALANCE W.
With the aid of the HTTP server, the configuration data can be read and changed
with forms as known from conventional websites.
A number of wizards are available in web-based management for user-friendly
installation and configuration of both, access points and client modules. Using
these wizards, the modules can be optimally adapted to the communication task.
Both network mode and the required WLAN security level can easily be set.
Note
A number of configuration manuals are available in the Siemens Industry Online
Support.
Configuration of the SCALANCE W700 (802.11n) via WBM (entry ID
62516763):
http://support.automation.siemens.com/WW/view/en/62516763
Siemens AG 2013 All rights reserved
Configuration of the SCALANCE W700 (802.11n) via CLI (entry ID
62521099):
http://support.automation.siemens.com/WW/view/en/62521099
Configuration of the SCALANCE W700 (802.11a/b/g) (entry ID 60532964):
http://support.automation.siemens.com/WW/view/en/60532964
Copyright
Getting Started for the IWLAN controller WLC711 (entry ID 62523066):
http://support.autIWLANControlleromation.siemens.com/WW/view/en/62523066
90
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
8.7
Further SIMATIC WLAN clients
8.7.1
SIMATIC Mobile Panels 277(F) IWLAN V2
SIEMENS offers a wide range of HMI devices (“panels”) for automation, which can
be used to monitor, surveil and operate complete plants or individual devices within
the series. This also includes “mobile panels” with integrated radio interfaces which
can be used in the course of an IWLAN. These panels are no longer stationary, but
can be moved throughout the plant and used at the required location.
They combine capabilities of an IWLAN client with the function scope of an HMI
panel such as
archive (storage of measured values and entries within temporal context),
recipes (sets of associated process data that are managed “as an entity”)
a highly-developed messaging, protocol and alarm system.
Operation is via touch screen, the configurable function buttons or via hand wheel,
key switches and illuminated push-button. The SIMATIC mobile panels 277(F)
IWLAN V2 have been constructed according to protection type IP 65 and
communicate via the WLAN standard IEEE 802.11a/b/g/h via PROFINET.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-14
Note
Further information on this product is available in the SIEMENS Industry Mall at:
http://www.automation.siemens.com/panels
Note
An application example incl. Safety (entry ID 25702331) can be found in the
Siemens Industry Online Support at:
http://support.automation.siemens.com/WW/view/en/21523940
IWLAN
V3, Entry ID: 22681042
91
8 SIEMENS NET Products for Setting up an IWLAN
8.7.2
SIMATIC ET 200pro IWLAN interface module IM 154-6 PN HF
SIMATIC ET 200pro is a modular I/O system with high protection type IP65/66/67
for machine-based application without cabinet. ET 200pro is distinguished by its
small size and modular concept. IM 154-6 PN HF is an interface module for
communication handling between ET 200pro and a higher-level PROFINET I/O
controller via Industrial Wireless LAN. This makes ET 200pro IWLAN-capable.
The interface module communicates according to the IEEE 802.11a/b/g/h
standards on 2.4 GHz and 5 GHz and provides the security features according to
IEEE 802 e/i to protect from unauthorized access, espionage, bugging and
falsification (e.g. WPA2 with AES).
Note
Further information on these products can be found in the Siemens Industry
Online Support in a Document collection Interface modules IM 154-6 PN IWLAN.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-15
92
IWLAN
V3, Entry ID: 22681042
8 SIEMENS NET Products for Setting up an IWLAN
8.7.3
IWLAN/PB Link PN IO
The IWLAN/PB link module provides a high-performance and flexible interface
between Industrial Wireless LANs on the one hand and PROFIBUS networks on
the other, which saves using a decided client here.
Copyright
Siemens AG 2013 All rights reserved
Figure 8-16
IWLAN/PB Link PN IO is a network transition which connects the two network
types Industrial Wireless LAN (control level) and PROFIBUS (cell level/field level).
In addition, far-reaching options are opened up for mobile applications by using
Industrial Wireless LAN (IWLAN) with RCoax and WLAN antennas for wireless or
seamless data transmission. Fields of application include monorail conveyors or
stacker crane systems.
Note
Further information on this product can be found in the Siemens Industry Online
Support in the IWLAN/PB Link Manual (Entry ID: 21379908).
IWLAN
V3, Entry ID: 22681042
93
9 Accessories for Wireless Networks (WLANs)
9
Accessories for Wireless Networks
(WLANs)
9.1
Optional storage media
A KEY-PLUG or C-PLUG (“Configuration Plug“) is a removable storage medium
that is plugged into the respective hardware slot.
C and KEY-PLUG have a similar design but differ in function and color.
9.1.1
KEY-PLUG
With the help of various KEY-PLUGs, additional functions are made available in
several industrial network components of Siemens AG.
In connection with the SCALANCE W7xx for IEEE 802.11a/g/n the iFeatures are
enabled with the KEY-PLUG W780 or W740 (see chapter 4.6):
the KEY-PLUG W780 iFeatures enables the iFeatures in the access point
mode and in the client mode,
the KEY-PLUG W740 iFeatures only enables the iFeatures in client mode.
Copyright
Siemens AG 2013 All rights reserved
Figure 9-1
Thus, every SCALANCE W 11n standard device can be upgraded to a device with
iPCF function and future iFeatures without having to exchange the hardware.
In addition, the KEY-PLUG has the same functions as the C-PLUG.
9.1.2
C-PLUG
The SCALANCE W700 devices in accordance with the IEEE 802.11a/b/g/n
standard and the IWLAN/PB Link PN IO have an internal flash storage as well a CPLUG slot for storing the configuration data.
If a C-PLUG has been plugged, the configuration data and their changes are
always stored on it. This makes easy replacement possible. A simple exchange of
C-PLUG enables adopting all data to a substitute device without a programming
device.
94
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
Further information on the use of C-PLUG with SCALANCE W devices can be
found in the Siemens Industry Online Support (entry ID 29823212):
Note
http://support.automation.siemens.com/WW/view/en/29823212
Part 2 of the “Network transition IWLAN/PB Link PN IO” manual contains
information on configuring and using C-PLUG:
http://support.automation.siemens.com/WW/view/en/21379908
9.2
RCoax leaky wave cable
Description
The RCoax cables are leaky wave cables that act as special antennae for
environments that are demanding from the point of view of radio technology, for
SCALANCE W access points.
Figure 9-2
Cable sheath
Dielectric
Wave propagation
Copyright
Siemens AG 2013 All rights reserved
Leaky wave cables are coaxial transmission lines whose external shield is
interrupted in a defined way. This constructive structure has the effect that a
defined, cone-shaped radio field is formed along the RCoax line.
Inner
conductor
Mains lead with
opening
The RCoax cable
The RCoax cables replace the standard radio antennas at selected access points
by an antenna segment with a selectable length. They transmit and receive in the
2.4 GHZ or 5 GHZ band. They are preferably used in environments in which the
nodes move in limited areas or exclusively on defined paths (monorail conveyors,
high-bay racking systems) and where many shadings or reflections are to be
expected.
The RCoax cable can be bent during installation of the plant and hence be
adjusted to the local conditions: it can, for example, directly follow the course of a
monorail overhead conveyor. In difficult environments, this offers the option to
reliably illuminate sections of the radio cell that are difficult to access. Highmaintenance sliding contacts or trailing cables can thus be saved.
IWLAN
V3, Entry ID: 22681042
95
9 Accessories for Wireless Networks (WLANs)
iPCF and PROFINET I/O
The IEEE 802.11 protocol of the access point is not influenced by the use of the
RCoax cables, particularly the data rates and the protocols for data backup are not
changed. iPCF and the communication via PROFINET I/O are possible as before –
provided the respective access points and clients are available.
Note
An application example for using RCoax cables in a PROFINET I/O environment
is available in the Siemens Industry Online Support (entry ID 23488061):
http://support.automation.siemens.com/WW/view/en/23488061
Data rate and segment length
Each SCALANCE W access point can be equipped with an RCoax cable.
In order to generate longer, uninterrupted radio ranges, several leaky wave
segments (with an assigned access point) can be arranged one after another.
Attenuation of the RCoax cable increases along the leaky wave cable and the
signal strength is reduced. With increasing cable length and increasing distance
from the cable the achievable data rate is also reduced.
Further information on this topic and performance data is available in the “RCoax
System Manual” in Siemens Industry Online Support (entry ID 21286952):
http://support.automation.siemens.com/WW/view/en/21286952
Connecting of mobile nodes
In a RCoax network the RCoax cable is fed by an access point. The RCoax cable
acts as antenna to mobile partner stations (e.g. SCALANCE W clients), that move
along the RCoax cable and which receive the information via their antenna from
this cable or which couple into it.
Copyright
Siemens AG 2013 All rights reserved
Note
The connection to the wireless RCoax network is performed via antennae that are
to be installed by means of the flexible connection cable in the immediate vicinity of
the RCoax cable.
Note
96
Updated product information on RCoax cables is available on the web at:
http://www.automation.siemens.com/mcms/industrialcommunication/en/industrial-wireless-communication/network_components/iwlanrcoax/Pages/rcoax.aspx
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
9.3
Antennae
9.3.1
Overview of the WLAN antennae
For optimum radio field architecture, antennae are top priority, next to the selection
of the devices. Decisive are particularly these points:
Characteristic of the antenna (radio coverage)
Place of application (indoors or outdoors)
Required data rates (IEEE 802.11 a/b/g with up to 54 Mbps, IEEE 802.11n with
up to 450 Mbps).
The SIMATIC portfolio has a number of omnidirectional antennae and directional
antennae available (basic information on antennae, see also chapter 1.5). They
can be either installed directly or separate from the device, e. g. at a mast or a wall,
in order to achieve an optimum illumination of the space to be covered.
Antennae with two (dual slant) or three connections (MIMO) increase the data
throughput and the reliability by targeted use of the multipath propagation.
An overview of the WLAN antennae is displayed by the following figure:
Copyright
Siemens AG 2013 All rights reserved
Figure 9-3
IWLAN
V3, Entry ID: 22681042
97
9 Accessories for Wireless Networks (WLANs)
The properties of the most important antenna types are listed in the following table:
Table 9-1
Type
Installation
Property
Antenna gain
IEEE 802
Frequency
2.4 GHz
ANT795-4MC
2.4 GHz: 3.0 dB
5.0 GHz: 5.0 dB
ANT795-4MD
ANT795-4MA
ANT795-4MR
Directly on the
device
Omnidir.
ANT792-6MN
2,4 GHz: 4.0 dB
5.2 GHz: 5.0 dB
5.8 GHz: 4.5 dB
11a/b/g
2.4 GHz: 6.0 dB
Wall or mast
ANT793-6MN
5.0 GHz: 5.0 dB
ANT795-6MN
2,4 GHz: 6,0 dB
5,0 GHz: 8,0 dB
Ceiling
Siemens AG 2013 All rights reserved
11n
2.4 GHz: 4.0 dB
5.0 GHz: 5.0 dB
ANT795-4MS
Copyright
5 GHz
11n +
11a/b/g
ANT795-6MT
2.4 GHz: 4.0 dB
5.0 GHz: 6.0 dB
ANT795-6DC
5.0 GHz: 9.0 dB
ANT793-6DG
5.0 GHz: 9.0 dB
ANT793-6DT
5.0 GHz: 8.0 dB
ANT795-6DN
2.4 GHz: 9.0 dB
5.0 GHz: 9.0 dB
11a/b/g
ANT792-8DN
2.4 GHz: 14.0 dB
11n +
11a/b/g
ANT793-8DN
5.0 GHz: 18.0 dB
11a/b/g
ANT793-8DJ
5.0 GHz: 18.0 dB
ANT793-8DK
5.0 GHz: 23.0 dB
Wall or mast
Directional
11n
11n
11n
ANT793-4MN
Omnidir.
5.0 GHz: 6.0 dB
Directional
2.4 GHz: 4.0 dB
RCoax
ANT792-4DN
11n +
11a/b/g
Note on name convention for IWLAN antennae
The most important functional characteristics are stored in a code in the name of
the antennae types:
ANT79w-xyz
w = 2 / 3 / 5:
frequency range 2.4 GHz / 5 GHz / dual band (2.4 and 5 GHz)
x = 4 / 6 / 8:
Measure for passive amplification
y = M / D:
Omni (omnidirectional) / directional
Example: ANT792-8DN (2 GHz, high amplification, directional, N-Connect)
98
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
9.3.2
Antennae with omnidirectional characteristic
SIMATIC NET offers a well-balanced range of antennae with omnidirectional
characteristics for various application cases for indoors as well as outdoors. The
antennae differ in view of their place of installation, the connections, the protection
class and the frequency range.
ANT795-4Mx antenna
The antennae of type ANT795-4Mx are suitable for installation directly on the
access point or client.
Copyright
Siemens AG 2013 All rights reserved
Figure 9-4
The following table shows the variants:
Table 9-2
Antenna
Connection
Class of
protection
Remark
ANT795-4MC
1 x N-Connect male
IP65
even
ANT795-4MD
1 x N-Connect male
IP65
Window 90° angle
ANT795-4MA
1 x R-SMA male
IP30
With additional joint; pivotable at
an angle of between 0° and 90°.
ANT795-4MR
1 x R-SMA male
IP65
Window 90° angle; displayed in
the figure above.
ANT795-4MS
1 x R-SMA male
IP30
With additional joint; pivotable at
an angle of between 0° and 90°.
IWLAN
V3, Entry ID: 22681042
99
9 Accessories for Wireless Networks (WLANs)
Antenna ANT792-6MN / ANT793-6MN
The antennae of type ANT79x-4MN can be installed on a wall as well as on a mast.
Figure 9-5
Copyright
Siemens AG 2013 All rights reserved
The following table shows the variants:
Table 9-3
Antenna
Connection
Class of
protection
ANT792-6MN
1 x N-Connect female
IP65
ANT793-6MN
1 x N-Connect female
IP65
Remark
Displayed in the figure above.
ANT795-6Mx antenna
The installation of antennae of type ANT795-6Mx can be directly on a wall, ceiling
or roof.
Figure 9-6
The following table shows the variants:
Table 9-4
Antenna
100
Connection
Class of
protection
ANT795-6MN
1 x N-Connect female
IP65
ANT795-6MT
3 x QMA female
IP65
Remark
MIMO antenna; displayed in the
figure above.
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
9.3.3
Antennae with beamforming
The product range of SIMATIC NET also offers a large selection of directional
antennae. The antennae differ with regard to place of installation, protection class
and frequency range.
The antennae of type ANT79x-xDx have been designed for wall or mast
installation.
Copyright
Siemens AG 2013 All rights reserved
Figure 9-7
The following table shows the variants:
Table 9-5
Antenna
Connection
Class of
protection
Remark
ANT795-6DC
1 x N-Connect female
IP67
Displayed in the figure above.
ANT793-6DG
2 x N-Connect female
IP67
Dual Slant
ANT793-6DT
3 x QMA female
IP67
MIMO antenna
ANT795-6DN
1 x N-Connect female
IP55
ANT792-8DN
1 x N-Connect female
IP23
ANT793-8DN
1 x N-Connect female
IP65
ANT793-8DJ
2 x N-Connect female
IP67
Dual Slant
ANT793-8DK
2 x N-Connect female
IP67
Dual Slant
IWLAN
V3, Entry ID: 22681042
101
9 Accessories for Wireless Networks (WLANs)
9.3.4
Antennae for RCoax
When using an RCoax system, the portfolio offers two antennae that only differ
regarding their frequency range.
Figure 9-8
The following table shows the variants:
Table 9-6
Note
Connection
Class of
protection
ANT793-4MN
1 x N-Connect female
IP66
ANT792-4DN
1 x N-Connect female
IP65
Remark
Displayed in the figure above.
Further product information regarding antennae can be found at the URL:
http://www.automation.siemens.com/mcms/industrialcommunication/en/industrial-wireless-communication/network_components/iwlanrcoax/Pages/rcoax.aspx
Copyright
Siemens AG 2013 All rights reserved
Antenna
Information on RCoax antennae is available in the “RCoax System Manual” in the
Siemens Industry Online Support (entry ID 21286952):
http://support.automation.siemens.com/WW/view/en/21286952
102
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
9.4
Connections and cabling
In the industry, different antenna plugs are used, depending on the field of
application. They vary in size, mechanical properties and area of use.
The SCALANCE W access points and clients have N-connect or R-SMA
connection, depending on the model. The antennae additionally have QMA
connections. These applications are marked by high-class transmission, reliable
connections and the application of cap nuts and a low form factor.
N-Connect connection
The N plug has been designed for all coaxial cable types. Due to a mechanical
fixture it has a high robustness and is very well suited for outdoor use due to its
additional sealing ring.
SMA connection
The SMA connection is a miniature coaxial plug or socket and is made up of a
thread and inner contact. It is offered in two designs:
SMA variant
Copyright
Siemens AG 2013 All rights reserved
Reverse (R-)SMA variant.
The differences are shown in the following table:
Table 9-7
Plug/socket variant
Characteristic
SMA plug
Internal thread and pin as inner contact
SMA socket
External thread and cup as inner contact
R-SMA plug
Internal thread and cup as inner contact
R-SMA socket
External thread and pin as inner contact
For SCALANCE W with connections of this size, the R-SMA variant is used.
QMA connection
QMA connections have the same electric power as the SMA series with simpler
and faster installation. QMA connections are mainly used for the new generation of
SCALANCE W antennae (IEEE 802.11n) where several connections are placed in
a very small space.
IWLAN
V3, Entry ID: 22681042
103
9 Accessories for Wireless Networks (WLANs)
9.5
Additional accessories
For a flexible combination and installation of the individual IWLAN components,
indoors as well as outdoors, an extensive and well-balanced range of coaxial
accessories is offered. It comprises antennae connection cables as well as diverse
plug connectors, lightning protection elements, a power splitter and an attenuator.
Note
The FAQs in the Siemens Industry Online Support (entry ID:22167025) show
what connection cables and additional devices can be used for the connection of
an external antenna to the SCALANCE W:
http://support.automation.siemens.com/WW/view/en/22167025
Lightning protection element
The LP798-2N lightning protection element expands the applications of
SCALANCE W700 products with remote antennas particularly for outdoors.
Copyright
Siemens AG 2013 All rights reserved
Figure 9-9
A lightening protection element secures the active device against destructive
overvoltage (e.g. lighting) via the antennae connections. If an overvoltage event
occurs, the respective currents are grounded.
The lighting protection element should be installed and grounded as near as
possible to the active device (e.g. the control cabinet wall). It is connected to the
antenna and the active device via antennae connection cables.
Different variants of lightening protection elements are available.
Terminating resistor
The TI795-1R terminating resistor (see figure) or TI795-1N has to be used for each
antenna connection that is not used for SCALANCE W700 products, in order to
terminate them in terms of high-frequency.
104
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
Copyright
Siemens AG 2013 All rights reserved
Figure 9-10
IWLAN
V3, Entry ID: 22681042
105
9 Accessories for Wireless Networks (WLANs)
Flexible connection cables
The flexible IWLAN RCoax/antenna connection cables are required for the
connection of RCoax segments or antennae with active devices. They can
furthermore be used as adapter cables if the antenna and the WLAN modules have
different connections. They are available in different lengths (0.3 m to 10 m) and
connection combinations
(N-Connect, R-SMA, SMA, QMA).
The following figure shows a QMA/N-Connect male/female connection cable:
Figure 9-11
Siemens AG 2013 All rights reserved
The next figure shows a connection cable that is used between a
SCALANCE W78x RJ45 and e.g. a remote antenna or a different component with
N-Connect connection:
Copyright
Figure 9-12
Note
Further information as well as application examples can be found in the FAQ
“What connection cable and IWLAN device can you use, in order to connect an
external antenna to the SCALANCE W?” (Entry ID 43895062)
http://support.automation.siemens.com/WW/view/en/43895062
The cables provide low attenuation so that the quality of the radio signal is only
minimally affected. All antenna cables are flame-retardant, chemically resistant and
silicone free.
106
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
Power Splitter
Figure 9-13
SITOP PS307 power supply
The SITOP PowerSupply is a high-quality DC voltage supply for the use in the
industrial environment with protection type IP20. Special additional modules protect
the power supply from disturbances on the side of the network as well as on the
DC side and provide the required supply security.
Figure 9-14
Copyright
Siemens AG 2013 All rights reserved
With the help of the power splitter, the transmission power of an access point is
divided between two RCoax or antenna segments. This enables radio coverage in
two different areas, with only one access point.
Note
When using the SITOP PS307 for the SCALANCE W788 M12 devices the power
supply has to be installed in a control box.
IWLAN
V3, Entry ID: 22681042
107
9 Accessories for Wireless Networks (WLANs)
Alternating voltage power supply with IP65
The SCALANCE W modules (IEEE 802.11 a/b/g) in protection type IP65 can be
directly supplied with voltage supplied from the socket via the PS791-1PRO power
supply. Due to the broad input voltage range (input voltages of AC 90 to 265 V), it
can be used worldwide.
Figure 9-15
Attenuator
The attenuator is always used when the transmitted power has to be reduced in
sending and receiving direction. Typical fields of application are short RCoax
segments or radio path where the extent is to be limited. The insertion loss of the
attenuator is 10 dB.
Figure 9-16
Copyright
Siemens AG 2013 All rights reserved
The power supply unit itself has a robust metal housing with protection from water
and dust in protection class IP65. Short-circuit strength, open-circuit safety and the
bridging of short power network disturbances guarantee high operational safety.
108
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
Control cabinet feed-throughs
The control cabinet feed-throughs together with the connection cables enable a
simple connection of remotely installed antennae with the active components
located in the control cabinet/box. The control cabinet feed-through is available in
the following connection combinations:
SMA-female / N-female for wall thickness up to max. 4.5 mm
N-Connect female / N-Connect female for wall thickness of up to max. 4.5 mm
Note
Further product information on passive network components can found in the
“SIMATIC NET Industrial Wireless LAN Passive network components IWLAN
System Manual” in the Siemens Industry Online Support (entry ID 67701823):
http://support.automation.siemens.com/WW/view/en/67701823
Copyright
Siemens AG 2013 All rights reserved
Figure 9-17
IWLAN
V3, Entry ID: 22681042
109
9 Accessories for Wireless Networks (WLANs)
9.6
Selection and ordering aids
General
The TIA Selection Tool and SIMATIC Selection Tool selection and ordering aids,
assist you in selecting Industrial Ethernet switches and components for industrial
wireless communication.
The tools are primarily there to simplify the ordering process and to assist the
customer in selecting the products.
Description
The two tools have a java-based, graphic interface. The individual selection options
and products are displayed as tabs. It is possible to directly select the tab or to be
guided step-by-step with the help of the tool.
9.6.1
TIA Selection Tool
Copyright
Siemens AG 2013 All rights reserved
Description
The TIA selection tool is the successor of the SIMATIC selection tool and unites
already known configurators for automation technology in one tool with clearly
more products than the predecessor.
It offers several wizards to select the desired devices and networks. There are
furthermore configurators for selecting modules and accessories as well as
checking the correct functioning.
A complete order list can be generated from the product selection or the product
configuration. You can export it directly into the shopping cart of the Industry Mall
or to the CA 01.
HMI screen
The user interface of the TIA selection tool is similar to the engineering software of
the TIA portal.
Figure 9-18
110
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
Supported components
The following products can be selected and configured with the TIA selection tool:
SIMATIC S7,
SIMATIC ET 200,
SIMATIC HMI Panels,
SIMATIC IPC, SIMATIC
HMI Software
Industrial communication components
Furthermore PROFIBUS and PROFINET networks can be generated, their
topology can be configured and the appropriate cables and plugs can be selected.
Installation
The TIA selection tool can be started directly in Siemens Industry Mall or
downloaded as file.
Further information can be found under URL: http://www.siemens.com/tiaselection-tool
Copyright
Siemens AG 2013 All rights reserved
Note
IWLAN
V3, Entry ID: 22681042
111
9 Accessories for Wireless Networks (WLANs)
9.6.2
SIMATIC NET Selection Tool (SNST)
Description
The SIMATIC NET Selection Tool assists you in selecting the right products.
Various strategies are offered:
Direct selection from the portfolio overview
According to technical requirements
Depending on the type of application
The result of the selection or configuration is an order list that can be exported:
as .csv (Excel)
as .pdf
to clipboard.
HMI screen
The following screenshot shows the start screen of the SIMATIC NET Selection
Tool:
Copyright
Siemens AG 2013 All rights reserved
Figure 9-19
Supported components
The following products can be selected and configured with the SIMATIC NET
selection tool:
Industrial Ethernet
Cables
Plug connectors
Industrial wireless components.
112
IWLAN
V3, Entry ID: 22681042
9 Accessories for Wireless Networks (WLANs)
Installation
The SNST can be used in online mode as well as in offline mode.
Online version: http://www.siemens.com/snst
Offline version: http://www.siemens.com/snst-download
An overview of all currently available configurators of Industry MALL, including
their description and start options can be found under URL:
https://eb.automation.siemens.com/mall/en/de/Catalog/Configurators
Copyright
Siemens AG 2013 All rights reserved
Note
IWLAN
V3, Entry ID: 22681042
113
10 IWLAN in Use
10
IWLAN in Use
By using wireless data networks, processes can be designed significantly more
efficiently. The advantage of wireless solutions is mainly the simple and flexible
reachability of mobile or difficult to reach participants.
Due to wireless communication to automation devices and industrial terminal
devices, a higher flexibility is attained, maintenance work is simplified, service and
downtimes are reduced and staff can be used most effectively.
Even demanding applications with real time and redundancy requirements in the
industry can be realized with Industrial Wireless LAN (IWLAN).
Copyright
Siemens AG 2013 All rights reserved
Based on selected places of application and application examples, the use of
IWLAN is briefly demonstrated below.
114
IWLAN
V3, Entry ID: 22681042
10 IWLAN in Use
Driverless transport system: Roaming of moving devices
The figure below shows an example from intralogistic, where individual W788-1
access points span several neighboring radio cells. Interconnected via a cablebased Ethernet string they mediate the communication between the driverless
transport system on which a W748-1 client module and a mobile S7-300 CPU are
located, and a stationary S7-400 CPU on one hand and an HMI panel on the other
hand.
This configuration enables the driverless transport system to change from radio cell
to radio cell (“roaming”) without losing contact.
Figure 10-1
S7-400
Radio cell 1
Radio cell 2
Access Point
SCALANCE
W788-1
Access Point
SCALANCE
W788-1
Field PG
Client
SCALANCE
W748-1
Copyright
Siemens AG 2013 All rights reserved
SIMATIC HMI
Client
SCALANCE
W748-1
Client
SCALANCE
W748-1
Driverless transport system
IWLAN
V3, Entry ID: 22681042
115
10 IWLAN in Use
Overhead conveyor system: Using RCoax
In the example below from the automotive industry, the IWLAN RCoax leaky wave
cable is used for setting up a wireless data transmission along the coding rail. It
creates a defined and reliable radio field. The W788-1 access points are used as
supplying station for the RCoax cable.
The mobile screwing stations – each equipped with one client module
W748-1, a SIMATIC S7-1200, two screwdrivers and a panel – move along the path
of the overhead conveyor system and can communicate with the cable-based
network via their client module and the access point.
Figure 10-2
Screwing data
server
Server for Shop Floor
SIMATIC
S7-400
Information System
SCALANCE X400
Field PG
Access Point
SCALANCE W788-1
Siemens AG 2013 All rights reserved
Access Point
SCALANCE W788-1
RCoax cable
Copyright
SIMATIC
S7-1200
Screwdriver station
Hanger
116
Client
SCALANCE
W748-1
Client
SCALANCE
W748-1
Client
SCALANCE
W748-1
Screwdriver Panel
RCoax cable
SIMATIC
S7-1200
Screwdriver Screwdriver Panel
Screwdriver station
Hanger
SIMATIC
S7-1200
Screwdriver Scewdriver Panel
Screwdriver
Scewdriver station
Hanger
IWLAN
V3, Entry ID: 22681042
10 IWLAN in Use
Controller-based WLAN: Using SCALANCE WLC711
The use of controller-based WLANs is shown exemplary on a container loading
and unloading plant. For an efficient transfer of the container, driverless transport
systems are used which can freely move on the large area of the terminal.
Since driverless transport systems are moving outdoors, it is important that a
robust connection that is suitable for outdoors is established so that the position
data and drive commands can be safely and reliably transmitted.
A suitable solution can be established with different products of the
SCALANCE W portfolio. The driverless transport systems are equipped with W7481 RJ45 client modules. The communication between the driverless transport
system is then controlled by the controller-based SCALANCE W786-2C access
points.
By using the SCALANCE WLC 711 the W786-2C access points can be centrally
configured and operated. The controller furthermore supplies additional features in
order to yet again increase the quality of the solution. This is how, for example, an
even distribution of the clients on the individual access points can be achieved via
load balancing.
Figure 10-3
Copyright
Siemens AG 2013 All rights reserved
Container Terminal
Automation center
Access Points SCALANCE W786-2C
FTS
ANT7956MT
IWLAN Controller
WLC711
FTS
Client
SCALANCE
W748-1
FTS
FTS
Access Points SCALANCE W786-2C
Container ship
IWLAN
V3, Entry ID: 22681042
117
10 IWLAN in Use
Safety over Wireless: PROFIsafe with SCALANCE W
PROFIsafe is a protocol extension of PROFIBUS / PROFINET for safety-related
communication.
In the example below, the safety-related operation of a robot is demonstrated.
Since PROFIsafe is a protocol extension, mixed traffic of “secure” and standard
messages can take place on the same network.
Figure 10-4
Control cabinet
CPU315F-2PN/DP
Secure data communication
Siemens AG 2013 All rights reserved
TD 17
Access Point
SCALANCE
W788-1
Portal robot
ET 200S F
Copyright
MicroBox
Client
SCALANCE
W748-1
SIMOTION
118
IWLAN
V3, Entry ID: 22681042
11 Glossary
11
Glossary
802.11
A number of standards for wireless network protocols developed by
IEEE.
Access Point
“Access point”, a node of a
WLAN which simultaneously performs administrative
functions in the network and which e.g. provides the connection to wire-bound
networks to
clients, other clients in the same radio cell or in other radio cells.
See chapter 4.1.2
Acknowledgement button
During handling in hazardous environments, the staff can use handheld
acknowledgment buttons which have three button positions. Operation of the
device controlled by the enabling button is only possible in the central position by
means of a moderately firm grip. If the acknowledgement button is released or held
very firmly (“panic switch”) the emergency stop of the device is triggered.
An unstructured
WLAN without
access points. The
clients communicate
“at their own responsibility” without higher-level coordination. The opposite is a
network in
infrastructure mode.
AES
“Advanced Encryption Standard”, an encryption method, see chapter 5.2.2.
Antenna pattern
A graphic display of the antenna's radiation pattern, to be able to estimate its
performance. The values for the antenna pattern are measured and recorded or
generated through simulation programs.
Copyright
Siemens AG 2013 All rights reserved
Ad hoc network
Antenna Diversity
The simultaneous availability of two radio interfaces on one device. Enables to
dynamically change to the interface with the frequency that currently provides the
best reception conditions in difficult radio environments.
Antenna gain
The concentration of the radio field of an antenna in a limited spatial direction is
achieved through suitable design. This achieves a (passive!) amplification in this
direction in space in comparison to an isotropic radiator. Other directions are
weakened in turn. The form of the radio field is specified in more detail in the
antenna pattern
Bandwidth
Can be described as “maximum available data rate”. The term derives from the fact
that a proportionally wide section of the radio spectrum is used by the transmission
at a specific data rate. See also chapter 1.4.4.
Bluetooth
A short-range radio standard for communication between office devices and
cellular phones, see chapter 3.
IWLAN
V3, Entry ID: 22681042
119
11 Glossary
CCMP
Counter Mode with Cipher Block Chaining Message Authentication Code Protocol,
an encryption algorithm used in within the framework of
WPA2, see chapter
5.2.2.
Client
Here: a node of a WLAN which has no internal infrastructure capabilities but
which accesses a radio network via an
access point.
CSMA/CA
“Carrier Sense Multiple Access with Collision Avoidance”, a method for the
detection of “collisions”, i.e. the attempt of several transmitters to simultaneously
start their transmission on one frequency. If this happens, both transmitters abort
their transmission and wait until a more or less random period expires. They only
start their repetition if the other transmitter has not again started transmitting during
this period. A second collision occurs only if the two randomly selected delays are
identical.
“Distributed Coordination Function”, an organization model for radio networks (see
chapter 4.4.1)
DFS
“Dynamic Frequency Selection”, similar to an extension of the
802.11h standard.
If, during operation, another (non-network) user is detected on a channel, the
access point changes the used channel. Influencing by other systems using the
5 GHz band (radar, satellite radio and satellite navigation) is to be avoided.
DoS
Copyright
Siemens AG 2013 All rights reserved
DCF
“Denial of Service”, an attack method against a network.
DSSS
“Direct Sequence Spread Spectrum“, a spread spectrum communication method
for IEEE 802.11b.
EAP
Extensible Authentication Protocol”, a method within the framework of the
RADIUS protocol with which server and client can agree on one method of
authentication before the actual authentication.
GFSK
“Gaussian Phase Shift Keying“, a modulation method for IEEE 802.11.
GPRS
“General Packet Radio Service”, a data transmission service used for cellular
phone communication.
Handover
The transition of a mobile client from one access point and its radio cell to the next
roaming); particularly the re-integration into the network.
120
IWLAN
V3, Entry ID: 22681042
11 Glossary
Hidden node problem
Same as
Hidden station problem
Hidden station problem
A connection problem which occurs if one receiver is simultaneously addressed by
two senders, which cannot hear each other, which results in collision at the
receiver.
HMI
“Human/Machine Interface”, display and operating devices for plant control, such
as, for example, SIMATIC mobile panels
IEEE
“Institute of Electrical and Electronics Engineers” (read I-Triple-E), a US
association which among other things develops guidelines and technical
recommendations; in the broader sense comparable to DIN (German Standards
Institution).
.
Copyright
Siemens AG 2013 All rights reserved
Infrastructure mode
A radio network organized in such a way that one or several
access points form
cells, giving the network a “structure”. The opposite is an
ad hoc network.
IP 30
A protection class indicating that a component categorized accordingly is protected
against ingress of solid foreign bodies (with a diameter of 2.5 mm and more) but
not against ingress of water. This corresponds to a conventional electrical
household appliance.
IP 65
A protection class indicating that a component categorized accordingly is
completely protected against dust and jet-water. This corresponds to an almost airtight enclosure.
iPCF
“Industrial Point Coordination Function”, a proprietary network protocol supported
by SIEMENS which enables short
handover times (in the range of 30 ms) during
roaming of the mobile nodes. iPCF is not compatible with
iQoS.
iQoS
“Industrial Quality of Service”, a method in which a specific
bandwidth is
reserved for individual
clients. The result is a response time that is complied
with, with a high probability but not with certainty. iQoS thus meets less strict realtime requirements than
iPCF; it is not compatible with
iPCF.
ISM
“Industrial, Scientific and Medical”, a band of the radio spectrum which, among
other things, also includes the 2.4 GHz frequency range used by the
802.11
protocol.
IWLAN
V3, Entry ID: 22681042
121
11 Glossary
LAN
“Local Area Network”, locally defined network, in contrast to, for example, the
internet
Leaky wave cable
A coaxial cable whose outer shield is interrupted at defined points. As a
consequence, the cable generates a spatially limited radio field that can be
“formed” since it follows the cable bend.
Link Check
An access point functionality for monitoring the connection to the clients. Different
events (logging on, logging off of the clients, etc.) can cause automated reactions
of the access point (sending mails/traps, turning on Fault LED, etc.). All
SCALANCE W access points support link check.
MAC
“Media Access Control”, a protocol used to control the access to a transmission
medium (cable, radio) which cannot be used simultaneously by all nodes.
An identification number for each hardware component of importance in a network
that is unique worldwide.
MAC
Middleware
Software performing a mediating function between operating systems and drivers
on the one hand and user applications on the other hand.
MIMO
"Multiple Inputs, Multiple Outputs", a method where each radio node sends and
receives simultaneously with several antennae. MIMO is part of the
IEEE
802.11n standard.
Copyright
Siemens AG 2013 All rights reserved
MAC address
MPI
“Multi-Point Interface”, a Siemens-proprietary RS485-based bus for serial
PROFIBUS communication with a larger number of nodes.
N-Connect
A connection system for IWLAN antennae.
OFDM
“Orthogonal Frequency Division Multiplex”, a modulation method for IEEE 802.11a
and g.
PCF
“Point Coordination Function”, an organization model for radio networks.
PoE
“Power over Ethernet”, power supply of bus nodes via the Industrial Ethernet cable.
122
IWLAN
V3, Entry ID: 22681042
11 Glossary
Polling
Regular polling of status data or variables from a data source (“server”) by a client.
(This client is not necessarily the client of a WLAN.) The alternative to this is eventcontrolled transmission. Here, the server independently transmits data to the client
as soon as there are any changes in the data.
PROFIBUS
A field bus system for serial data transmission in automation technology based on
MPI hardware specifications.
PROFINET
An extension of the Ethernet communication standards to meet the “Industrial
Ethernet” requirements, i.e. the use in an industrial environment. New properties
are the measures to increase the transmission security and fault tolerance and the
use of sturdy components, etc. The SCALANCE product generation is designed for
use with PROFINET.
PROFIsafe
Copyright
Siemens AG 2013 All rights reserved
A protocol extension for
PROFIBUS and
PROFINET with which the
transmission security is considerably increased.
PSK
“Pre-Shared Key”, a method for authentification within the framework of the
WPA/WPA2 protocols.
Quality of Service
Transmission quality guaranteed in the framework of a network.
RADIUS
“Remote Authentication Dial In User Service”, an access control method in which
the authentication between client and access point is handled via a third, separate
server on which the access data is stored.
Rapid spanning tree
A method for optimizing the data paths in networks, similar to
Spanning Tree.
Rapid Spanning Tree, however, was configured to keep the reconfiguration time as
short as possible in the event of an access point failure.
RC4
An encryption algorithm used within the framework of the
standards.
WEP and
WPA
RCoax
A
leaky wave cable used for setting up realtime-capable radio networks with
limited range, particularly suitable for
clients with fixed motion paths (e.g.
automated guided vehicle systems) or in heavily shaded environments (e.g.
tunnels).
IWLAN
V3, Entry ID: 22681042
123
11 Glossary
RFID
“Radio Frequency IDentification”, a method where objects (e.g. books in a library)
are fitted with passive radio transponders. The transponder responds to the
request of a sender (e.g. read device at the borrowing section of the library) with an
ID to track them. The transponders are small, cheap and are fed by the energy of
the reading device. Range and data capacity, however, are low.
Roaming
The motion of a
WLAN node from one radio cell to the next.
R/SMA
“Reverse (Polarity) SubMiniature (version) A (Connector)”, a connection system for
WLAN antennae.
RSTP
RTS/CTS
“Read-to-Send/Clear-to-Send”, a method for the avoidance of network collisions
and for avoiding the
Hidden Station problem.
Spanning Tree
A method for optimizing the data paths in (radio) networks. The spanning tree
method determines physically redundant network structures and prevents the
generation of loops by disabling redundant paths. The data communication then
takes place exclusively on the remaining connection paths. If the preferred data
path fails, the spanning tree algorithm searches for the most efficient way possible
with the remaining network nodes. See also
Rapid Spanning Tree
Copyright
Siemens AG 2013 All rights reserved
“Rapid Spanning Tree Protocol”, an algorithm used by switches in a network to
automatically determine the optimal travel to the data transmission between two
end nodes, and also to determine alternatives in the event of a failed transmission
point. See chapter 4.5.3.
Spoofing
Same as “Parody, swindle”, a general term for attacks to networks where the
attacker disguises its own IP or MAC address (“IP spoofing”, “MAC spoofing”),
faking the “identity” of a (authorized) network node.
SSID
“Service Set Identifier”, in the framework of a
“Wi-Fi” WLAN, the name of a
network which, must be known to all of its network nodes at the same time and
which is part of each transmitted message. SSIDs alone only provide extremely
weak access protection against third parties and should in any case be completed
by other encryption methods.
SSL
“Secure Sockets Layer”, a protocol for encrypted data transmission on the internet
which receives its security by using “public key” algorithms.
124
IWLAN
V3, Entry ID: 22681042
11 Glossary
TKIP
“Temporary Key Integrity Protocol”, a method for the dynamic change of the keys in
a
WLAN.
TPC
“Transmit Power Control”, an extension of the
802.11h standard in which only
the transmission power that is required for interference-free reception of the known
clients is radiated. This prevents the generation of overreaches.
UMTS
“Universal mobile telecommunication system”, a mobile radio standard for data
transmission with high capacity.
VLAN
“Virtual LAN”, a protocol extension for cable-based and wireless networks used for
dividing a physical network into several logic subnets.
VPN
“Virtual Network Services”, the organization of logical networks within one or
several physical networks.
VoIP
“Voice over IP”, the transmission of telephone conversations over the internet or
other IP-based networks.
VPN
“Virtual Private Network”, a protocol expansion that is closely related to
VLANs,
where the data traffic of a (virtual) subnet within a larger network is “tunneled”, e.g.
invisible for the other nodes. This property makes VPNs suitable for increasing the
security of a network.
Copyright
Siemens AG 2013 All rights reserved
VNS
WAN
“Wide Area Network”, a limited network with a larger expansion than a
LAN.
WBM
“Web Based Management”, configuration of an access point or client via a web
interface.
WDS
“Wireless Distribution System”, an
infrastructure mode for
access points set up a redundant network.
WLANs, where the
WEP
“Wire Equivalent Protocol”, an encryption method in wireless data communication.
IWLAN
V3, Entry ID: 22681042
125
11 Glossary
Wi-Fi
Designation introduced by the “WiFi Alliance” group of manufacturers for
WLAN
products which are compatible with a specific subset of the
802.11 standard;
occasionally also (incorrectly) used as a synonym for WLAN in general.
Wireless HART
(“Highway Addressable Remote Transducer”), the wireless variant of a field bus
standard.
WLAN
“Wireless Local Area Network”, a “local radio network”, thus a radio-based
LAN.
WMM
“Wireless Multimedia Extensions”, a subset of the
IEEE
802.11e standard.
WPA, WPA2
“WiFi Protected Access”, two encryption methods in wireless data communication.
Siemens AG 2013 All rights reserved
Zigbee
Copyright
A radio standard similar to
WirelessHART, however, it is used for operation in
home or facility automation.
126
IWLAN
V3, Entry ID: 22681042
12 Internet Links
12
Internet Links
Note
Websites with relevant material have, where reasonable, already been linked
directly in the text.
Table 12-1
Topic
/1/
Reference to this entry
http://support.automation.siemens.com/WW/view/e
n/22681042
/2/
Siemens Industry Online Support
http://support.automation.siemens.com
/3/
Updated lists with country approvals
for the individual SCALANCE W
products
http://www.automation.siemens.com/mcms/industrialcommunication/en/support/ikinfo/Documents/lz_laenderliste_wlan_en.pdf
13
History
Table 13-1
Version
Date
Modifications
V1.0
01.04.2006
First version
V2.0
01.01.2010
Various updates
V2.1
08.02.2011
Various updates
V3.0
04/2013
Complete revision of the structure and extension with new
functions / devices for IEEE 802.11n
Copyright
Siemens AG 2013 All rights reserved
Title
IWLAN
V3, Entry ID: 22681042
127
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