freeswitch

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Describe the bug Freeswitch/Sofia discards subsequent 18x messages after receiving a provisional response (excluding 100, of course). Unfortunately, this behavior causes issues, as many operators—particularly incumbents—send "Session Progress" messages followed by "Ringing."

The feature "sip_ignore_183nosdp" doesn't resolve the problem, as "Session Progress" messages often precede "180" both with and without SDP, as observed in numerous traces. As a result, the A-party doesn’t receive any ringing notification at all.

It's important to highlight that there is no RFC prohibiting the transmission of 18x messages in descending order. In fact, sending multiple 18x messages is both allowed and practical, as it enables pre-connect-announcements (e.g., tariff information) before ringing. Moreover, this is simply a widespread reality.

To Reproduce Steps to reproduce the behavior:

1. outgoing call to an external operator (e.g. incumbent) who sends back 183 and subsequent 180
2. Freeswitch does not forward the received 180 to the bridged A-leg

Expected behavior be transparent for subsequent Provisional Responses

Package version

• Version 1.10.10