Hi, >I am surprised that this caused any confusion. RFC 3264 seems >pretty clear to me. > >Citing from section 6.1: > "The answerer MUST send using a media format in the offer > that is also listed in the answer, and SHOULD send using the most > preferred media format in the offer that is also listed in > the answer."
The question is not what the offerer is supposed to send, but what he should be able to receive. >and from section 7: > "The offerer MAY immediately cease listening for media formats that > were listed in the initial offer, but not present in the answer." Yes. The problem with the "MAY" is that the other party doesn't know whether the offerer will listen or not, so therefor I think it's more saft to only use codecs which BOTH entities include in the SDP. >So, why should the offerer be expected to deal with formats >not present in the answer? (Of course, the offerer must be >prepared to receive ALL offered formats BEFORE the answer arrives) In many cases the offerer will not - due to different kind of reasons - accept anything before he receives the answer (yes, yes, I know what RFC3261 says...). Regards, Christer > > -----Original Message----- > > From: Christer Holmberg [mailto:[EMAIL PROTECTED] > > Sent: Thursday, November 22, 2007 11:34 AM > > To: [EMAIL PROTECTED]; [EMAIL PROTECTED]; > [email protected] > > Subject: RE: [Sip] SIPit 21 : Topics that attendees argued about > > > > > > Hi, > > > > I agree with Ravi. > > > > Eventhough you in theory is supposed to be able to receive what you > > offer - no matter what you get in the answer - I think that in real > > life the only codecs that participants will be prepared to > > send/receive are the ones sent both in the offer and the > answer. That > > is also the reason why the answer normally doesn't contain > additional > > codecs - it mostly contains a subset of the codecs in the offer. > > > > Regards, > > > > Christer > > > > > > > > >I was surprised to find > > > > > >>* There were implementations that offered an m-line with > > codecs A, B, > > >>and C, got an answer with C, then got upset when they got > > RTP with A > > >>(which is quite legal). > > > > > >On the list (like others who argued about it I think). > > > > > >I had some offline discussions with some of the members on this. > > >While I agree this seems legal, this seems very > counter-intuitive and > > >may result in wasted resources, would it not? > > > > > >For example, if the offerer is a conference bridge or a > transcoder, > > >and has a limited number of codecs of each type he offers, > why should > > >it hold on to one codec of each type for the duration of > the session, > > >even though the answerer has not supported it? > > > > > >Any particular reason why this should be continued as a legal > > >scenario? > > >Would it not be possible change it to say that the Offerer > needs to > > >expect only those codecs which answerer has explicitly > supported in > > >the answer? > > > > > >Regards, > > >Ravi. > > > > > > -- > > > > > > Ravishankar. G. Shiroor > > > Wipro Technologies, Bangalore. > > > > > > [EMAIL PROTECTED] > > > -- > > > > > > > -----Original Message----- > > > > From: Robert Sparks [mailto:[EMAIL PROTECTED] > > > > Sent: Tuesday, November 20, 2007 2:38 AM > > > > To: sip List > > > > Subject: [Sip] SIPit 21 : Topics that attendees argued about > > > > > > > > Digging through my notes: > > > > > > > > Here are some of the topics where people were arguing. I'm > > > capturing > > > > the smaller topics here. Larger arguments will get their > > > own message. > > > > > > > > * There were arguments about the dynamic payload map from > > > numbers to > > > > codecs (identified in the SDP and sent in the RTP) being > > > the same in > > > > the offer and the answer . The spec says they SHOULD. Some > > > > implementations were insisting they MUST. > > > > * There were arguments around preserving the relative order > > > of codecs > > > > on an m-line between the offer and the answer. The specs > > say SHOULD. > > > > * There were implementations that offered an m-line with > > > codecs A, B, > > > > and C, got an answer with C, then got upset when they got > > > RTP with A > > > > (which is quite legal). > > > > * There were arguments about deleting rejected m-lines on > > > re-invites > > > > (which you cannot do), and on reusing the slot they > occupy in re- > > > > invites (which you can do). > > > > * There were implementations that didn't add the > > refresher tag in a > > > > session-refresh message when they were the refresher and > > there were > > > > arguments about whether that meant the other side could > > > take the role. > > > > * Several implementations handled a=sendonly as a session > > > attribute, > > > > but not a media attribute - it can appear in either place. > > > > > > > > > > > > > > > > _______________________________________________ > > > > Sip mailing list https://www1.ietf.org/mailman/listinfo/sip > > > > This list is for NEW development of the core SIP Protocol Use > > > > [EMAIL PROTECTED] for questions on > current sip Use > > > > [EMAIL PROTECTED] for new developments on the application of sip > > > > > > > > > _______________________________________________ > > > Sip mailing list https://www1.ietf.org/mailman/listinfo/sip > > > This list is for NEW development of the core SIP Protocol Use > > > [EMAIL PROTECTED] for questions on current sip Use > > > [EMAIL PROTECTED] for new developments on the application of sip > > > > > > > > > _______________________________________________ > > Sip mailing list https://www1.ietf.org/mailman/listinfo/sip > > This list is for NEW development of the core SIP Protocol Use > > [EMAIL PROTECTED] for questions on current sip Use > > [EMAIL PROTECTED] for new developments on the application of sip > > > _______________________________________________ Sip mailing list https://www1.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip
