Industrial Communications Siemens

Real-time communication for industrial WLAN

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Using a newKey-Plug, the Scalance W product familyfrom the Siemens Industry AutomationDivision can now be equippedfor integrated real-time transmissionover Industrial Wireless LAN(IWLAN)in compliance with the IEEE 802.11nstandard.

The Key-Plug, a swap medium similarto the proven C-Plug, can beused to enable so-called iFeatures –in other words supplementary functionsspecifically for industrial use –which offer the deterministic datacommunication needed for real-timerequirements. The iPCF(industrialPoint Coordination Function) activatedin this way can be realized usingProfinet IO from minimal cycle timesof 16 ms and over. With this function,it is even possible to trigger a Profisafeemergency stop command overIWLAN, meaning that data communicationover WLAN can now be usedin applications such as passengertransport.

The Key-Plug is availablein two different versions: Key-PlugW780 iFeatures for Scalance W AccessPoints and Key-Plug W740iFeatures for Scalance W Client Modules.As well as enabling iFeatures,the Key-Plug also offers facility forsaving configuration data. This allowsa device to be exchanged withoutloss of time in case of failure –without the need for intermediateconnection of a PC or programmingdevice. Additional functions are plannedfor the Key-Plug in 2013 whichwill extend the scope of feature setscapable of being enabled.


Background: the WLAN standardIEEE 802.11n does not define specificmethods either for rapid roamingbetween several access points ordeterministic data communication.The key requirements for real-timetransmission over WLAN can be selectivelyupgraded using iPCF. Underthese conditions, seamless real-timetransmission over Industrial WirelessLAN(IWLAN) offers an alternative towired networks. Areas of applicationinclude uses in which the laying ofcables would be excessively laboriousor expensive, or where cableswould be subject to rapid wear.

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