You may encounter with the Mediation Server SIP CANCEL problem when your SIP trunk operator doesn’t send the “Session Progress” or “Ringing” status messages quick enough. According to my measures it tends to be 6 seconds available for the operator to send back something useful. If they are too slow, Mediation Server will just CANCEL the call.
To solve this problem you have to fine-tune the OutboundRouting.exe application:
