Assume that an OperationTimeoutException exception occurs on a PSTN gateway in a Lync Server 2010 environment. This environment has a Mediation server and a PSTN gateway deployed. In this situation, a SIP/2.0 408 Request Timeout error message is logged on the Mediation server. Therefore, the Outbound Routing application on Lync Server 2010 does not try to route the call.
Note A 504 Gateway Timeout error message should be logged on the Mediation server instead.
To resolve this issue, install the following cumulative update:
2502810 Description of the cumulative update for Lync Server 2010, Mediation Server: April 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.