Marcus Better wrote: > Hi, > > I'm considering to apply SIP in an application, but using a custom > session description format that is not SDP. The endpoints must be able > to exchange longer sequences of offers before reaching an agreement, not > just two (offer and answer) as in RFC3264. Is it possible to use SIP in > such a scenario?
Yes, its possible. But I suggest you think long and hard before abandoning SDP in favor of a different session description format. That will cut you off from interop with the rest of the world. I know SDP is limited and ugly. But in spite of that it has been stretched to cover a lot of stuff. Some time ago there was a proposal for SDPng which was to be the successor to SDP. It was "modern" with xml encoding and lots of fancy new features, plus being a functional superset of SDP. But it was eventually abandoned because no one could come up with a workable migration plan nor a way to motivate migrating. Why don't you try spelling out what it is you are trying to do that leads you to take this approach. Maybe someone will have a suggestion for another way to accomplish the same thing. > I'm considering to use a sequence of reliable provisional responses and > PRACKs, each carrying a session description, and repeating until the > session parameters are agreed. > > Sample flow: > > UAC UAS > | | > INVITE > - -------------------------> > > 183 Session Progress > <------------------------- > PRACK > - -------------------------> > > 183 Session Progress > <------------------------- > PRACK > - -------------------------> > > 200 OK > <------------------------- > ACK > - -------------------------> > > > Is this a workable solution? You don't spell out in the above which messages have offers and answers, and that matters to whether this is workable. Also, you don't show the 200 responses to the PRACKs. There are limited ways you can insert offers and answers into these. Take a look at: http://www.ietf.org/id/draft-ietf-sipping-sip-offeranswer-13.txt Also, look at RFCs 3312, 4032, and 5027 on preconditions which will give you examples of multiple o/a exchanges. Thanks, Paul _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
