• 2 replies
  • Latest Post - ‏2013-08-20T09:19:08Z by MassimoGreggio
344 Posts

Pinned topic Telnet connections questions

‏2013-07-30T16:43:53Z | idle keep-alive telnet timeout

I'm sure this has been asked before, but since I cannot search the forum I'll ask it again.

I have a connection to the host, in my case TN3270e.  The project is a Web services project, but I doubt that matters to the crux of the question, using chained IOs.

Our client runs FIC and logs in, one or more MIC, then remains idle for a prolonged period of time, say 2-3 hours.  Is there any "keep-alive" talking going on the Telnet connection during the idle period?  I believe not, but I need to make sure.  The host basically has disabled the idle timeout, so it is possible that an idle connection will sit there for days, e.g across a weekend, unless some external action occurs, such as cycling the CICS application.  If the Web services client servlet were to be reset, then no LIC would be sent to release the connection.  Then if the Web services client were to restart all new connections would be established.  

I curious if there might be some activity that the host could do or look for,  at an IP level, that would indicate that the client was gone and automatically clean up.

The above scenario is happening and when it does a couple of things occur:

  1. The host pool of LUs becomes exhausted causing the connections to fail.  
  2. If the pool is sufficiently large the WAS server runs out of available ports/threads and hangs.  Then trying to terminate that application will result in the Telnet sessions being released, but the threads are still hung and attempt to terminate may fail.

Has anyone seen this last scenario before?  This condition only happens under extreme load.  I would expect this condition to have been encountered during performance testing that resulted in the recommendations document.

Any feedback would be appreciated.

  • alaynap
    12 Posts

    Re: Telnet connections questions


    Hi George,

    Our performance tuning document has some information about TCP/IP tuning specific to operating systems.  Please take a look to see if that helps resolve the issue. HATS Tuning Guide:

    Thank you,



  • MassimoGreggio
    1 Post

    Re: Telnet connections questions


    Hi George

    I have no experience on web services exposing, as I'm using HATS in a rich client environment, but some time ago it happened that some time the TN3270 connection was hanging after some idle time. After some inspection we found that there was a firewall cutting the connection because of a too short timeout.

    When the connection were cut, it remained 'hanged' until the user closed and opened the RCP application.

    Maybe you could verify if there's something between your server and the host that, in some way, cuts the connection