Hi Herbert,
This is difficult to troubleshoot. Sometimes it is a sip communication problem between the gateway and the mediation server.
To analyze this problem, you should activate tracing on the gateway and also cls logging (alwaysON) on the SfB Mediationserver.
With this traces, you can analyze this problem a littlebit deeper. Maybe it is a timer problem.
The traffic use TCP, so you can also use wireshark for analyzing.
best regards Holger Bunkradt Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.