Scenario: When trying to join a call from a Skype for Business 2016 client through a Cisco VCS, the call is dropped. Earlier Lync 2013/Skype 2013 clients work as expected.

While troubleshooting this issue, I was checking my client logs for my Skype 2016 client and could see in the BYE that ICE negotiation was failing:

Ice Processing Failed

I thought this was odd as both clients were internal, and using Lync 2013 with Skype UI updates joins just fine. I would expect a failed ICE negotiation if we were in different networks separated by a firewall. I could also see in the client logs during call setup where we did agree on an ICE candidate and video codec (m=video 56886 RTP/AVP 122).

Quick Google search pointed me to Cisco Bug CSCuw51599. The bug states that the newer Skype for Business 2016 client introduced a new version of STUN that includes different fields from previous versions. This causes an integrity check to fail and the call is ended. This matches the environment I was working in and will require an update of VCS to 8.7, which is listed as a known fixed release. Another good case of Cisco and Microsoft not playing nicely together!