[OpenSIPS-Users] To-tag value in ACK

John Quick john.quick at smartvox.co.uk
Tue Feb 2 14:01:56 EST 2021

I am seeing a problem in calls made to MS Teams via OpenSIPS configured as
an SBC.
The usual INVITE, 180, 183, 200 OK sequence looks okay, but the ACK request
is not accepted by MS Teams.
When I say "not accepted", I mean an ACK is sent to the Teams Proxy, but
Teams responds after 30 seconds with BYE, reason is:
"Call Controller timed out while waiting for acknowledgement"

I am able to compare the sip trace for the failing call with a very similar
call scenario on another Teams system that works.
The only explanation I can suggest is that the UAC did not use the same
value for the To-tag as it received in the 200 OK.
Could this explain why Teams is failing to match it against the previous

John Quick
Smartvox Limited
Web: www.smartvox.co.uk

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