My two cents of thought. I think when the answerer will include additional media format, the media has to be again re-negotiated between offerer-answerer and that should be done by offerer if he thinks that additional media format is best way to exchange media ( The only question would be if the offerer did support this new additional media format, then why did it not include it in the original offer. May be due to some limit like offer max 'x' code even though he may support more than 'x' )
Absent any media re-negotiation for the additional media from answerer, the answerer MUST send using a media format in the "offer" that is also listed in the "answer". Regards, Indresh >>-----Original Message----- >>From: sip-implementors-boun...@lists.cs.columbia.edu >>[mailto:sip-implementors-boun...@lists.cs.columbia.edu] On >>Behalf Of ext Rockson Li (zhengyli) >>Sent: Friday, August 14, 2009 2:42 AM >>To: sip-implementors@lists.cs.columbia.edu >>Subject: [Sip-implementors] Can EP send media only peer supports >> >>Hi folks, >> >>Going through RFC3264, I find some inconsistency between offerer and >>answerer. >> >>Suppose offer/answer below >> >>Offer: >> m=audio 49170 RTP/AVP 0 4 >> a=rtpmap:0 PCMU/8000 >> a=rtpmap:4 G723/8000 >> >>Answer: >> m=audio 49172 RTP/AVP 0 18 >> a=rtpmap:0 PCMU/8000 >> a=rtpmap:18 G729/8000 >> >>I think answerer can add additional codec G729 here per sec 6.1 of >>rfc3264 >> >><snip> >> The stream MAY indicate additional media formats, not listed in the >> corresponding stream in the offer, that the answerer is willing to >> send or receive >></snip> >> >>However, here comes the inconsistency. >> >>When answerer send media, it cannot send G723 packets to >>offerer per sec >>6.1 of RFC3264 >> >><snip> >>The answerer MUST send using a media format in the offer >> that is also listed in the answer, >></snip> >> >>Whereas RFC3264 does not forbid offerer to send G729 packets >>to answerer >>per sec 7 >> >><snip> >>It MUST send using a media format listed in the answer, >>and it ***SHOULD*** use the first media format listed in the >>answer when >>it >> does send. >></snip> >> >>NOTE: there's some explanation that tells us why this is only >>a SHOULD, >>not must, >> which clearly indicates offerer can send G729 to >>answerer on >>the fly >> >>Any thoughts on this issue? >> >>Thanks >>Regards, >>-Rockson >> >>_______________________________________________ >>Sip-implementors mailing list >>Sip-implementors@lists.cs.columbia.edu >>https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors >> _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
