The 10-second timer was added to Lync Server 2010 OBR components by the update that is described in Knowledge Base (KB) article 2565378. After update 2565378 is applied, the OBR component routes calls to other PSTN gateways if a PSTN gateway does not send a provisional or final response within 10 seconds. For example, the OBR component reroutes the call if the PSTN gateway does not send a 183 session progress message. However, in certain network environments, the gateway takes longer than 10 seconds to send a response. Therefore, calls are canceled before they can be completed.