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PROFINET-IO through WiFi

Created by: OliStotch at: 8/14/2009 9:40 AM (4 Replies)

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8/14/2009 9:40 AM	Rate (0)
OliStotch Posts: 14 Rating: (0)	Dear All! Is there a possibility to run PROFINET-IO through WiFi channels with relatively big packetdelay (3..4 up to 8..9 ms ping) with possible chanel breaks? The test configuration is two IM 151-3 (old ones, 3AA22, but with newest firmware) and Simatic NET OPC with SOFTNET IE configuration. With WiFi stations one near other - all OK. With placement at projected distance (up to 100m, infrastructure), the ping is as described above - I can't say it's too bad for radio from my experience. Everything else is OK - http, ftp, etc. In OPC - items quality is Bad, and the connection is estabilished at seldom occurences, but running well. It may happen after a half day of waiting, and the system works the rest of the time. Tried to increase the IO cycle of ET-200S stations from 8 ms up to 256 ms and greater - no result. WireShark shows PNIO packets are running all the time, IO controller and stations find eachother through LDAP, start sending a bunch of cyclic PNIO packets, write requests from IE-general are also seen and accepted by stations. Still, cyclic packets are running in packs with some interruption, up to3-4 s, though the rest of packets (TCP/IP, ICMP) are running good during theese pauses. Will the situation be better with a hardware PROFINET-IO controller (CP343-1 V2 or other), or such PROFINET distributed IO usage is impossible? Is there anything I can do more? Thank you for your attention.
OliStotch Posts: 14 Rating: (0)
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8/14/2009 10:09 AM	Rate (0)
INS Gold Member Joined: 4/6/2006 Last visit: 2/5/2024 Posts: 604 Rating: (56)	Hi, Yes Wireless LAN and ProfiNet IO is possible if the settings and environment is suitable. This is one of the benefits of Profinet IO over different Ethernet based bussystems. First of all running Profinet IO with an update time on 8 ms is not a good idea. You can see this already on your ping replies where you have delays from over 8 ms. As soon as a PN IO Telegramm takes more then the PN IO Update you have set you are running in a retry from which (by default) you have 3. This would mean that your system is less stable then you want to. In an ideal situation Siemens advice to use an Upadte Time from at least 16 ms with the default retries. Furthermore it also depends on the environment you have. Which WLAN Protocol (802.11 a/b/g/h) and Channel (1, 2 ... 13; 36...48, 100 ... 165)) did you choose? Is a interfence free channel? This could be checked in the AP or client by checking available/overlapping AP's, with a Laptop working in the same frequency bandsor with a Spectrum Analyser. Could you tell me what kind of Wireless products you use? Is it Scalance W which is specially designed for industrial use? If so could you tell what settings you have made as MAC-Mode? And how is it wired are there 1 or more device behind a WLAN Client or do you use a Wireless Distribution System (WDS) between your WLAN Devices? Since you use a SIMATIC NET OPC Server for PN IO do you use your WLAN interface from the PC? This is not possible OPC Server for PN IO only works with a 'normal' LAN card? Maybe you could make a rough sketch and place it as an attachment so it's easier to see how your components are connected? If you are using Office Equipment is it an AP with or withourt a firewall? As you see there are a lot of questions but they need to be answerred to help you solve your issue.
	Best regards, INS
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8/14/2009 12:15 PM	Rate (0)
OliStotch Posts: 14 Rating: (0)	Thank you very much for reply! Wewere unsure about the result, so investing into Scalance W just for testing would be a little bit risky . We're using easily available at local market Senao/EnGenius EOC-2610. Theconfiguration is in attachment. Two AP in WDS modewith uni-directional10⁰ anthenas are facing each other, one is the main AP, the second one is a repeater.Two clients with the same stations and omni-anthenas are placed between them in line, both with WDS enabled. All the components are connectedto AP's through TP ports, including PC withOPC server. 802.11b/g is set to auto,channel is set to 12. Thechannel is free of interference. There's neither firewall in AP, nor MAC filtering enabled. The IO cycle of stations is set to 256 ms.Everything else (http access to AP, remote desktop to PC,etc.) is working fine. The PROFINET-IO itselfsometimes is working too, but only with one client, and nottoo often unfortunately . The number of retrys are set to 3, and is not changeable. Attachment WiFi_sketch.jpg (851 Downloads)
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8/14/2009 1:13 PM	Rate (0)
INS Gold Member Joined: 4/6/2006 Last visit: 2/5/2024 Posts: 604 Rating: (56)	Hi, This is a very bad solution for a WLAN setup in combination with PN IO. In WDS your AP's function in a Half Duplex way. This means only one of the sends data at the same time. If your left client is connected to the left AP and the Right to the Right AP (Repeater) then it could be that the time the Left AP is inactive the the Left Client isn't able to send his data inside the configured PN IO Update time. Another issue could occur when the client 'block'the signal in between the Right AP (Repeater) and the Left AP and the clients are connected to your Right AP at that time. You could also have a hidden node problem here. One of the clients doesn't reacht the AP or the other way around. To make it short I'm not a fan of this setup and this won't be something I would advice. Also when you need a range of 'only' 100 meter in a free area you could solve this with one AP and a Directional Antena with 60° degrees for example. If you did this to get around obstacles or to get more redundancy I would not use this setup due to interference on your Channel 12 which could happen your whole system will fail. In the atachment I've created 2 possible solution based on Scalance W products. For your information I've basedthe setups on the fact that the moving vehicles run on a fixed track in between the AP's on the floor. And keep in mind that I don't have knowledge about the environment where it should be installed it's just theorethical. I'm more favourite for the 2nd solution with the Multimode Fiber connection. Attachment Possible Setup.jpg (1001 Downloads)
	Best regards, INS
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8/14/2009 4:13 PM	Rate (0)
OliStotch Posts: 14 Rating: (0)	I understood the problem. I'll check the system without WDS (with a single client) first. Thanks for the good advice!
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