Consider the following scenario:
You have a Microsoft Lync Server 2010 environment that has more than one Mediation server and a Public Switched Telephone Network (PSTN) gateway deployed. The Mediation servers are configured to use dual Network Adapters.
A Mediation server cannot connect to the PSTN gateway because of a network issue that is specific to the Mediation server.
You call a PSTN number by using Lync 2010.
The call is routed to the Mediation server.
In this scenario, the Outbound Route application in Lync Server 2010 does not route the calls to a different Mediation server. Additionally, the Mediation server returns the following error message:
SIP/2.0 504 Cannot connect to gateway. Socket error: TimedOut
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.