> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:sip- > [EMAIL PROTECTED] On Behalf Of Andreas Byström > Sent: Thursday, September 13, 2007 9:48 AM > To: [email protected] > Subject: [Sip-implementors] Early media and forking calls > > Hi everyone, > > I'm working with a case that involves a call from A that a proxy forks to > B > and C. I see a potential problem when the following happens: > * A sends SDP offer > <proxy forks the call to B and C> > * B answers with a 183 including a sdp answer
Please refer to RFC 3264 as it describes the offer/answer scenarios. Also this issue has been discussed in the Sip-implementors list a number of times, and you will learn a lot by reading through them. So, 183 from B will create a dialog. > * C sends 180 with no spd This 180 response is another dialog and A should be prepared to handle this dialog. At this point, the final response (200 OK) could be coming from B or C. > * C answers the call first, which means C sends a sdp response in the 200 > OK. > In this scenario, the call is established between A and C. Typically the proxy will CANCEL the forked call to B. > I have tried to find info on this but have failed to do so. So I was > thinking that someone on this forum have already been facing a scenario > like > this, or maybe know where I can find info on how to solve it in a way that > dont violate specs (and also works of course) > Please refer to the mailing list archives. > How should A handle this (it already got a sdp answer on the offer)? Does > A > or proxy have to start a renegotiation with C? I think your question is how should A handle the answer it received already from B? The proxy CANCELs the call to B. When the C comes back with 200 OK with SDP, that is going to be used. > Should A see in the tag that this is a respone from another UA then from > where it did get the first spd answer (the on in 183 sent from B) and > therefore accept it? That could be bad implementation choice. > Proxy needs to send a cancel to B when it sees that C is replying wiht 200 > OK. Does the proxy also need to say something to A to terminate the media > session already set up between A and B? Proxy doesnt tell anything about media/SDP. It is between endpoints. > Thanks in advance > // Andreas Thanks, Neel. > _______________________________ > > Andreas Byström > Software Engineer > > Teligent AB > Konsul Jonssons väg 17 > P.O. Box 213 > SE 14923 Nynäshamn > > mail: [EMAIL PROTECTED] > web: www.teligent.se <http://www.teligent.se/> > phone: +46 (0)8 4101 7221 > mobile: +46 (0)733 1172 21 > fax: +46 (0)8 520 193 36 > _______________________________ > > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
