Forum Discussion

Copper Contributor

Feb 26, 2020

REASON Q.850;cause 18 text Call Controller timed out while waiting for acknowledgement.

Incoming calls to Microsoft teams get disconnected automatically after 20 seconds. You can make a call from outside, teams phone rings, answer the call, 2 way communication is there but still teams c...

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Eerik Kiskonen

Copper Contributor

Feb 28, 2020

We are seeing the exactly same issue with one customer, an another deployment works just fine. Let us know if you hear anything about the solution.

Devaraj Narayanappa

Copper Contributor

Mar 10, 2020

Eerik Kiskonen Our issue is finally fixed.

The solution was SBC was sending the IP address in ACK messages for 200 OK it received from Teams. Teams expect contact header FQDN from the 200 OK in the ACK message, not the IP.

nicolastanski
Copper Contributor
Apr 19, 2020
Devaraj NarayanappaCould you share with us what is the correct way to send the Contact header in inbound calls?

I am trying like this but occur the same error.
Contact: <sip:CALLERID_NUMBER@SBC_FQDN:5061;transport=tls>

Thanks.
Eerik Kiskonen
Copper Contributor
Mar 16, 2020
Devaraj Narayanappa

Great, have to try if that works. How did you exactly change it in the SBC?
- Eerik Kiskonen
  Copper Contributor
  Apr 19, 2020
  Actually for us this was not the reason, the reason was related to the network architecture and the Always Use Source Address parameter. This particular SBC is in a bit strange network configuration where the Teams-facing interface is on the public network and the internal SIP trunk and the user endpoints can only be reached via an MPLS connection of a 3rd party ISP connected to another interface.
  
  The fix was to disable the Always Use Source Address on the SIP trunk IP Group as the SIP trunk could not be reached by Teams.