DMG responds to SIP BYE with ICMP message

Symptom

After successfully setting up a SIP call between a Dialogic 1000 Media Gateway or Dialogic 2000 Media Gateway and a SIP endpoint, the call teardown fails when the endpoint sends a BYE to the DMG Gateway, which responds to the BYE with an ICMP "destination unreachable" message.  

Reason for the issue

When the SIP call was initially set up, the SIP endpoint sent traffic to a port different from the standard 5060 for SIP.  When the DMG Gateway responded with a "200 OK", it specified port 5060 (or some other port decided upon) in the SIP contact field.  The endpoint may have then sent its ACK to the original port and the DMG Gateway accepted that, the reason being the DMG keeps the port open for 30 seconds.  However, subsequently when the SIP endpoint sent a BYE to the DMG Gateway at the end of the call, it kept sending to that original port which has since been closed by the DMG Gateway.  Therefore the DMG Gateway responds with the ICMP message "destination unreachable".  

Fix / Solution

That SIP endpoint has to be set up so that it sends SIP traffic to the port specified by the DMG Gateway in the SIP contact field when the DMG Gateway acknowledged that endpoint's "INVITE" with a "200 OK".  Normally the port used is 5060, but it can vary.