Some calls fail before call setup completes...In my case it was mostly landline calls, cell calls worked fine.
A wireshark trace showed that Lync was "getting bored" waiting for a response from my SIP gateway. Then sends a CANCEL to which the gateway sends a SIP 487.
The Lync Mediation Server is sending a CANCEL on call setup, after a very short time (seemed like 8 seconds but must have been 10 seconds all up)
After the Lync 2010 CU4 update from Microsoft, Lync has become impatient and if the remote party has not responded with more that “100 Trying” during 10 sec the Mediation Server sends a CANCEL !
This timer was earlier 30 – 40 seconds, but is now only 10 !!
The remote party can’t respond with more that “100 Trying”, until they have received anything from the Called Party.
<add key=”MinGwWaitingTime” value=”1″/>
The file is found under
C:\Program Files\Microsoft\Lync Server 2010\Server\Core on the Lync 2010 FrontEnd Server.
C:\Program Files\Microsoft\Lync Server 2013\Server\Core on the Lync 2013 FrontEnd Server.
After changing this value, it’s recommended to reboot the server. I tried restarting services but wasn't successful.
Next time you run Lync updates this value may be reset to 10000 - Keep a record!
This one caught me out a second time after an update reset the timer to 10 seconds