At a customer site there was a Lync Server 2010 that had been running for about a year. This solution was now going to be expanded with a collocated mediation server over a dedicated PSTN network card. The mediation server deployed fine and I added routes and tested connection with the SIP trunk provider over telnet, TCP 5060 and it seemed fine.

The Problem

When I tested the solution with an Enteprise Voice enabled user as an external user it failed with the following diagnostics header: Call failed to establish due to a media connectivity failure when one endpoint is internal and the other is remote. This is a typical routing issue for Edge. The only problem was that everyting else worked perfectly.

• Checking the SIP logs on the Lync server I saw that all ports and IP’s where correct
• Checking the web for similar problems I came over this TechNet forum post
  • http://social.technet.microsoft.com/Forums/en-US/ocsvoice/thread/a54f2371-3a9e-4a2d-973d-6be13fd437fc/
• Two things are stated in the forum post
  • SIP trunk on a collocated mediation server does not work, well that should work so no reason quitting
  • If you have natted AV Edge externally you need to add the AV edge A record and public IP in the internal DNS server
• In my case the AV Edge was not natted
• One interesting point was made
  • The mediation server needs to have an AV Edge server specified when deployed
  • When deploying a standalone mediation server you can specify this in topology builder
  • When deploying a collocated mediation server you can not specify this for the mediation server, it is specified on the Front End pool.
• Using the cmdlet Get-CsService –MediationServer I saw that the mediation server had no Edge server defined
• That was the issue

The Solution

• The solution was simple
• Add the Edge server internal FQDN to the mediation pool using the following cmdlet
  • Set-CsMediationServer -EdgeServer <Edge internal FQDN> -Identity MediationServer:<Front End pool FQDN>
• Gave it two minutes for CMS replication and voila, I could now receive and make calls with users outside the Edge server

Conclusion

I think that when you add a collocated mediation role to an existing Front End server, in my case it was a Standard Edition server, the Edge server FQDN may not be defined in the mediation pool. Since it is already defined for the Front End pool and you are not asked when enabling the role, it may not get set correctly. This is not an issue for Lync servers that are deployed with the collocated mediation role from the start. Since I have seen this once, I am not absolutely sure, it’s just a hypothesis I got. Please comment if you have similar experiences.