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TCP Connection Closing

Created by: joedub at: 7/17/2008 4:00 PM (10 Replies)

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7/17/2008 4:00 PM	Rate (0)
joedub Posts: 9 Rating: (0)	Hello, I have a S7-416 with two TCP Connections, via CP-443 standard, to a piece of thrid party software. The third party software is the client and initiates the connection. The connections are at ports 2000 and 2001. I have the connections successfully established and am sending and receiving data via the AG_LSEND and AG_LRECV. However, the connection is periodically closing. This happens once a minute or so. We had a network sniffer on the line and it indicated that the connection was being closed by the S7. Does anyone have any ideas on this one? Thank you for the help.
joedub Posts: 9 Rating: (0)
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7/18/2008 11:28 AM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello, I would expect that it might be a problem with the TCP Keep Alive setting in your Ethernet CP. Please check if you set up the TCP Keep Alive to 30 or less seconds, if so and your PC does not support TCP Keep alive the Connection is being shut by the PLC. To prevent this you can set the TCP Keep Alive to 0 and this disables this function at all. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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7/24/2008 5:15 PM	Rate (0)
joedub Posts: 9 Rating: (0)	Thanks for the response. I did try the keep alive as well. We just found the problem yesterday. The third part software that were connected to was sending a QoS bit. The CP card seemed to respond by closing the connection. This is a new one for me.
joedub Posts: 9 Rating: (0)
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7/26/2008 11:53 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hi, a QoS bit??? Well... I have no idea right now... but I will try to find out something about it. Best regards J_Bell
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8/2/2008 8:00 PM	Rate (0)
jim3846 Posts: 5 Rating: (0)	Expert Bell I had this same issue QoS bit set in the packet received from a TCP client connection. Its caused by the switch putting a limit on the amount of data over that port. Once it hits that limit, the QoS or Quality of Service bit is set. Then these packets cause your great Ethernet card 443 advanced to disconnect. But it reconnects a few seconds afterwards. This is a VoIP restriction on the switch. Problem went away when the IT people lifted the restriction on the port the PLC and client was using. But you still need to handle the QoS packet reject better than just closing the connection and resetting the card. I sent wireshark sniffer file to your siemens experts. I believe Siemens fixed this QoS problem with firmware 2.4 for ProfiNet CBA but failed to fix it for TCP.
jim3846 Posts: 5 Rating: (0)
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8/2/2008 8:39 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello, thank you for this information. To tell you the truth... I did not know about that yet. Have you heard anything about this from the SIEMENS Experts yet? I think if this is a known issue you would have heard something... and there might be a solution... but in some cases you have to keep on asking. I will try to hear if someone I know heard about it. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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8/4/2008 4:58 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello, I wonder... is it possible that you mean a TOS bit... instead of a QoS bit? I still have no idea where the QoS bit would be in the Ethernet frame. Best regards J_Bell
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8/4/2008 6:14 PM	Rate (0)
jim3846 Posts: 5 Rating: (0)	http://findarticles.com/p/articles/mi_m0CMN/is_1_41/ai_112448829 LOOK AT THIS LINK FOR INFO
jim3846 Posts: 5 Rating: (0)
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8/4/2008 8:14 PM	Rate (0)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	Hello, QoS stands for quality of service. It covers several techniques allowing several traffics to get a certain quality (priority, jitter, ...). A firts major classification is DiffServ (Differntiated services) and IntServ (Integrated services). For DiffServ: In layer 2, for Ethernet frames, a typical way is to tag frames with a VLAN ID complying with 802.1Q. In this header, there is a field of 3 bits, called CoS (cost of Service), used by IEEE802.1p to set a traffic priority. With 3 bits you can specify 8 priorities. Modern switches evaluate this field to organise some queues anf to forward urgent traffic first (like VoIP, or Profinet IO) Onceyou have routers involved (layer 3), the priority info contained in the VLAN header Ethernet info may be lost from IP segment to another. That's why a mapping can be configured between the CoS in Ethernet with a field available inIP headers, the ToS (Type of Service). A router receiving an Ethernet frame with a give, CoS, will forward it by marking it with a ToS in the IP header. In this way the next router will know that the traffic is urgent or not. If the ToS = 0, you have best effort forwarding by the router. With other values standardised by the DiffServ standards, you get assured forwarding traffic classes and expedited forwarding classes. These classes corresponds to traffic queues with forwarding priorities and also drop levels (if the router gets congestionned on that interface).
	Best regards jklm Suggestion was helpful? Feel free to rate it.
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8/5/2008 10:26 AM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello, well... if we change the VLAN tagging this is very disturbing for the CP, especially if this is done with PROFINET. About the TOS I know that it might lead to disturbance too, because the change of the type of service might require this... even so it is not always needed today... formerly this was different. This is a behavior I would personally switch off in a Network I use with automation at all. Therefore I am notsure if the mix-up of VOIP and automation networks is that muchuseful at all... but this is my personal taste. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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