EVENT 25039, LS Mediation for Server Skype for Business 2015

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While I was playing around in Skype, I inadvertently caused an issue with incoming calls.  After making changes in the Topology Builder for the PSTN gateway, the error below started showing up in the logs for Skype.  And calls are no longer working.

Event 25039, LS Mediation Server

SDP negotiation failed with the Trunk.

Trunk FQDN xxxxxxx; trunk=xxxxxxxx, Reason SRTP is not enabled for Mediation Server.

Cause: The Trunk is either not configured correctly, incompatible with Mediation Server, or not certified.


History and Resolution:

Our PSTN gateway (AudioCodes 500) has 2 NICS, one facing the Shoretel or WAN side of the network and the other facing Skype.  In Skype PSTN gateways configuration for the AudioCodes gateway, I tried changing the IPv4 Address to ‘use all configured IP Addresses‘ which caused the issue.  To fix this, I set ‘Limit service usage to selected IP address‘ and I entered the IP of the AudioCodes NIC facing Skype.


I hope this post helps anyone out there having trouble configuring their skype gateways.  Please feel free to leave a comment or question.


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