IMG unexpectedly releases H.323 call

Symptom:
Established H.323 calls on a Dialogc® IMG 1010 Integrated Media Gateway (IMG 1010) or Dialogic IMG 2020 Integrated Media Gateway (IMG 2020) may be unexpectedly released by the IMG.  Both incoming and outgoing legs are released with cause value 31, Normal, Unspecified.  The following lines are also printed in the IMG call trace:
 

09:28:40.766 CALL(225) (00:53734:00) SERV Socket Closed, connId 49746

09:28:40.766 CALL(225) (00:53734:00) Internal Reason (0xffff) --> Q.931 Cause (31)

 
Reason for the issue:
The IMG uses a socket on TCP port 1720 for each H.323 call.  This socket normally remains open throughout the call until the H.323 leg is released.  If the far-end H.323 stack abnormally closes the TCP socket for a call, with a TCP FIN, the IMG will detect that the socket has been closed, print the above error for the related call leg, and release both legs.  A signaling trace will indicate that the IMG is the source of call failure, because it is the endpoint sending a release.  But an Ethernet trace will show that the release was initiated due to a socket error originating from the far-end.  The above error message also indicates the source as the far-end.
 
Analysis:
Obtain an Ethernet trace of the H.323 signaling between the IMG and endpoint that is terminating the TCP socket for established calls.   Then, select the TCP stream related to a call that ended with the error.  You will find the H.225 connect message, highlighted in green in this example, and the connect ack.  The next packet in the stream will contain the FIN.   The source IP address of the FIN, highlighted in yellow, identifies the source of the call failure:
 
Click the following image to display it full size

Open

Workaround:  
Use a different H.323 endpoint for calls, if possible.

Product List
Dialogc® IMG 1010 Integrated Media Gateway
Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNet™ 2020 Session Border Controller