> From: Dmitry Akindinov [[email protected]] > > On 2011-04-08 12:20, kapila karunarathna wrote: > > > > in which scenario that a server use different tag in TO header in a response > > message. any way rfc3261 says it should be same in all response messages. > > but i have found a session that use different to tag > > and still trying to find why the peer side use it. > > Responses with different To-tags may indicate that the server relays > responses from different entities to which the request has been forked.
More importantly, response messages that have the same to-tag are part of the same dialog, and response messages that have different to-tags are part of different dialogs. An element on the callee side can *pretend* that it is proxying responses from different elements downstream by sending responses with different to-tags. In particular, it can be convenient to provide an early-dialog announcement via a 180 or 183 using one to-tag and to have the actual destination ring using a 180 using a different to-tag. The reason is that since the 1xx messages are parts of different dialogs, their SDP is mostly independent of each other, and they can use different codecs. Dale _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
