Skype for Business Integration - Encryption reqirement

[majeed002]

Current setup is - CUCM where TP endpoints are registered.  SIP trunk without encryption is configured between CUCM & Expressway-C (Lync gateway).  Trunk shows up in both the sides.  B2B integration with FE server of Skype for business is done with TLS (5061) as Skype for business is configured with "Require Encryption" mode.  Both Expressway and B2B are shown as "Alive" in the Expressway-C.

But the calls are failing with error "Call rejected at the Microsoft end as there are no DNS SRV records" (not the exact message but a similar message).  Am I missing some thing. 

Is it supported to have non-TLS trunk between CUCM & Expressway-C and TLS trunk between Expressway-C & Skype for Business.  

Thanks in advance.

[Jonathan Schulenberg]

Do you have SIP debugs from Expressway? Who sends the 487 Cancel or Bye? If it's Lync/S4B then you need to look at the logs there.

At face value based solely on that error: does the calling Cisco SIP URI resolve to the Expressway using DNS SRV?