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Socket connection being lost


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I have a project that has reliability issues that seem to stem from the PLC losing connection to its router on socket 20256.


On a PLC where the connection is lost:

  • If I ask the router to do a standard ping against the router, it succeeds. 
  • If I ask the router to do a TCP socket ping with 20256, it fails.  (on a PLC I am successfully getting data from, this succeeds)


The kludgy way I am temporarily getting round this, is the router is set to do a hard reset every 4 hours which reinitialises everything


Bit of background:  Remote server using unicomdriv.dll is communicating via VPN over a GSM modem to the PLC over Ethernet (sounds dodgier than it actually is!).  I have a screenshot of the bits of code that manage the connection on the PLC code, what I am thinking is I need something to detect a situation of the PLC losing connection or no successful data transfer over socket 1, and initiate a sequence to regain the connection.


Any suggestions?  Any suggestions of parameter settings for timeout and keepalive ect... on the PLC itself?




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