[SR-Users] SDP in fifth 200 OK is not the same as in first four

Roman Romanchenko rromanchenko at sipwise.com
Mon Oct 8 11:59:37 CEST 2018

Hi all,

I have an issue with SDP from Kamailio side in the following scenario: simple call from A to B.
When B answers a call and sends '200 OK' to A, A delays ACK for a while, so '200 OK' re-transmission happens.

After the fourth try to re-send '200 OK' towards A, Kamailio changes SDP (specifically connection information 'c', IP address become address of A instead of proxy IP as it was in the previous attempts). At some point A sends ACK and call is established, but last received '200 OK' has invalid SDP and it prevents successful media establishment.

I wonder if there any re-transmission counter or whatever what can affect this scenario and change SDP?

Roman Romanchenko
VoIP devel
Sipwise GmbH

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