Setup

Instance A sets UDP as default transport protocol via sip_transp_set_default().
Instance B sets TLS as default.

Start a dialog by INVITE from A to B.
Call termination by BYE from B to A.

Issue

The BYE is sent via TLS to port 5060. Then A is not able to process the TLS/SIP BYE at port 5060.

Questions

• (A) Is a protocol mix during a SIP dialog allowed? The RFC-3261 (SIP) does nothing state about the transport protocol in Section 12.2 "Requests within a Dialog".
• (B) Is it allowed to force the transport protocol of following SIP request to the transport protocol of the first SIP transaction in a SIP dialog?

Background

• We shortly added a default SIP transport protocol setting. This currently is used for each SIP request if no ;transport= parameter is given.
• Without this setting the default is UDP, like it was before this setting was added.

Possible Solution

Currently already e.g. the port number of the dialog route is used as target port number for the BYE. Should we also store the transport protocol in the sip_dialog and use this for following SIP requests during a dialog?