I have recently been assisting a colleague on a customer site with a Lync 2010 to Lync 2013 Migration and run into some strange behaviour issues after migration of the Mediation Servers from 2010 to 2013.
A large amount of alerts was being generated into SCOM with the event ID 46046
Event 46046, LS Outbound Routing
Call Number: +44xxxxxxxxx
Phone Usage: Long Distance
Cause: All gateways available for this call are marked as down.
Verify that these gateways are up and can respond to calls.
This alert is generated by an unsuccessful call from the Lync Client to the destination number. The behaviour of the outbound call was noticeable different but going back through the logs we could see this issue has been happening for a while with the 2010 Mediation Server but with EnableFastFailoverTimer enabled on the Lync 2013 Mediation Trunk. A lot more calls was getting dropped.
As a temporary solution we have reverted back to the 2010 Mediation Servers and looking at a different SIP Trunk with a 2013 qualified SBA.