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:
- Go to your FE server’s core directory, e.g. C:\Program Files\Microsoft Lync Server 2010\Server\Core\
- Open the file OutboundRouting.exe.config for editing.
- Change the value of FailOverTimeout to 20000 or you may also succeed with 15000 too.
- Save the OutboundRouting.exe.config file.
- Restart your FE server.
But be warned, this is not an official solution from Microsoft. I figured it out myself by digging deep into logs and monitoring file access of different processes.
If you find any unwanted side effect, please share with me.
You may also have similar problem with GSM gateways. Certain gateway models may let you set the SIP configuration to reply with “Session Progress” before GSM network responds. In this case you don’t need to change the OutboundRouting.exe.config file.