Hi all. I think that all media formats in the answer have not to be in the offer.
RFC3264/6.1 Unicast Streams 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 (of course, it will not be able to send them at this time, since it was not listed in the offer). Regards, Shinji "Brett Tate" <[EMAIL PROTECTED]> >I basically agree with Paul's interpretation. One of the reasons for >offerer to be lenient concerning the received answer formats is >mentioned within RFC 3264 section 6: "media formats listed are ignored". > >The following are some snippets from RFC 3264. > >Section 6: "To reject an offered stream, the port number in the >corresponding stream in the answer MUST be set to zero. Any media >formats listed are ignored. At least one MUST be present, as specified >by SDP." > >Section 6.1: "If the answerer has no media formats in common for a >particular offered stream, the answerer MUST reject that media stream by >setting the port to zero." > >Section 8.2: "A stream that is offered with a port of zero MUST be >marked with port zero in the answer. Like the offer, the answer MAY >omit all attributes present previously, and MAY list just a single media >"format from amongst those in the offer." > > >> -----Original Message----- >> From: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] On Behalf Of Paul Kyzivat >> Sent: Thursday, October 16, 2008 9:36 AM >> To: Rohit Aggarwal >> Cc: [email protected] >> Subject: Re: [Sip-implementors] Significance of media format in answer SDP >> when stream is rejected >> >> >> >> Rohit Aggarwal wrote: >> > Hi >> > >> > I have a query regarding the media format list for rejected >> stream in answer SDP. >> > >> > An offered media stream can be rejected by setting media >> port to 0 in the m-line corresponding to the rejected stream. >> In this m-line, is it necessary that the media format list >> needs to be same (or subset) as in the offered m-line? >> >> AFAIK, the rules of o/a in 3264 have the same requirements >> for the media format list regardless of whether the port >> number is zero or not. So when constructing an answer you >> would be well advised to set it up correctly. >> >> BUT I think many implementations don't do this. In some cases >> they may not offer *any* media formats, even though this is a >> syntax violation. >> Or they may replicate one or more format numbers from the >> offer without defining them in the answer, or might just >> supply zer such as you see. >> While these aren't strictly legal, in the interests of >> interoperability you might be well advised not to get upset by this. >> >> Thanks, >> Paul >> >> > For example, consider the following offer-answer: >> > Offer SDP >> > v=0 >> > o=PQR 256 1 IN IP4 61.246.39.21 >> > s=SipSession >> > c=IN IP4 61.246.39.21 >> > t=0 0 >> > m=audio 1024 RTP/AVP 0 >> > m=video 10560 RTP/AVP 104 102 103 >> > a=rtpmap:104 H263-1998/90000 >> > a=fmtp:104 CF=3;QCIF=1 >> > a=rtpmap:103 H263-2000/90000 >> > a=fmtp:103 CF=3;QCIF=1 >> > a=rtpmap:102 H263-2002/90000 >> > a=fmtp:102 CF=3;QCIF=1 >> > >> > Answer SDP >> > v=0 >> > o=XYZ 12345 787 IN IP4 10.10.6.94 >> > s=Session >> > c=IN IP4 10.10.6.94 >> > t=0 0 >> > m=audio 5624 RTP/AVP 0 >> > a=rtpmap:0 PCMU/8000/1 >> > a=ptime:20 >> > m=video 0 RTP/AVP 0 >> > >> > In this example, video stream is rejected but the media >> format contains '0'. Is this valid assuming that the offerer >> shall ignore the media format since the stream has been rejected? >> > >> > >> > Regards >> > Rohit Aggarwal >> > Aricent _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
