[OpenSIPS-Users] To-tag value in ACK
john.quick at smartvox.co.uk
Wed Feb 17 14:57:24 EST 2021
I took a fresh look at this case and found that the To-tag used in the ACK matches the To-tag that was in the first 180 Ringing.
However, Teams has returned different To-tags in the 180 Ringing and in the 183 Session Progress and 200 OK.
This appears to be common behaviour for Teams as I can see the same thing in the SIP trace for a completely different customer.
Teams uses different To-tags when it responds to an INVITE as follows:
SBC <------> Teams
<-- 100 Trying no To-tag
<-- 180 Ringing To-tag A
<-- 180 Ringing To-tag B
<-- 180 Ringing To-tag C
<-- 183 Sess.Prog. To-tag D
<-- 200 OK To-tag D
Is this compliant with the RFC's?
Unfortunately, the UAC used by my customer is responding to the 200 OK with an ACK that has To-tag A instead of To-tag D.
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