Jonathan, But the offer-answer I-D says only that the recipient _SHOULD_ use the preferred codec, not that it _MUST_. Therefore, I suppose it depends on what you mean by "mistake," but isn't the scenario that Lorenzo describes compliant behavior?
Paul Long ipDialog, Inc. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Jonathan Rosenberg Sent: Monday, December 31, 2001 11:16 AM To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: Re: [Sip-implementors] Two media type in SDP answer. comments inline. [EMAIL PROTECTED] wrote: > Take a look to this scenario! > > A UAC sends an INVITE containing SDP like the following: > > v=0 > o=- 0 0 IN IP4 149.35.48.216 > s=SIP Call > c=IN IP4 149.35.48.216 > t=0 0 > m=audio 5008 RTP/AVP 0 8 4 18 > a=rtpmap:0 PCMU/8000 > a=rtpmap:8 PCMA/8000 > a=rtpmap:4 G723/8000 > a=rtpmap:18 G729/8000 > > The UAS respond with an OK containing the following SDP: > > v=0 > o=MxSIP 0 0 IN IP4 149.35.48.175 > s=SIP Call > c=IN IP4 149.35.48.175 > t=0 0 > m=audio 5006 RTP/AVP 0 8 > a=rtpmap:0 PCMU/8000 > a=rtpmap:8 PCMA/8000 > > The UAC start to send RTP packet using PCMU codec. > The UAS start to send RTP packet using PCMA codec. > > Who are making a mistake? The UAS. The offer-answer spec is fairly clear on this point: In all cases, the codecs in the m line are listed in order of preference, with the first codec listed being preferred. In this case, preferred means that the recipient of the answer SHOULD use the codec with the highest preference that is acceptable to it. The UAS has violated the SHOULD by not using the codec with the highest preference (codec 0). -Jonathan R. -- Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Avenue Chief Scientist First Floor dynamicsoft East Hanover, NJ 07936 [EMAIL PROTECTED] FAX: (973) 952-5050 http://www.jdrosen.net PH: (973) 952-5000 http://www.dynamicsoft.com _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
