*Can answerer add new codecs which were not present in offer to answer SDP?*
Yes. *OR * *Should answerer select codecs only in offer and list formats in the same relative order they were present in the offer?* Not necessarily. It will be answerer's discretion to add whatever media formats it wants and list them in whatever order it wants as long as there is atleast one common media format between offer and answer. Here is a quote from section 6.1 of RFC 3264: For streams marked as recvonly in the answer, the "m=" line MUST contain at least one media format the answerer is willing to receive with from amongst those listed in the offer. The stream MAY indicate additional media formats, not listed in the corresponding stream in the offer, that the answerer is willing to receive. For streams marked as sendonly in the answer, the "m=" line MUST contain at least one media format the answerer is willing to send from amongst those listed in the offer. For streams marked as sendrecv in the answer, the "m=" line MUST contain at least one codec the answerer is willing to both send and receive, from amongst those listed in the offer. 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). Rajnish > > On 3/11/07, Sumin Seo <[EMAIL PROTECTED]> wrote: > > > > Hi All, > > > > I have a question regarding on SDP offer and answer. > > One of our engineers interprets rfc 3264 like below. > > "rfc 3264 doesn't say that answer MUST not include more codecs which are > > not in offer. > > rfc 3264 also says that the answerer MAY list the formats in their > desired > > order of preference. > > It is RECOMMENDS that the answerer list formats in the same relative > order > > they were present in the offer. > > So, Session MUST be established as long as there is one common codec in > > answer regardless of order of preference or existence of codecs not in > > answer. " > > > > Based on his interpretation, following negotiations should work. > > Offer Answer Offer Answer > > ----------> ---------------> > > (a, b, c) (a, b ,c) > > <---------- <---------------- > > (d, b, c, e, f) (b, c, d, e, f) > > I did some interop tests with several carriers. As long as first codec > in > > answer is one of codecs in offer, calls are successfully connected. > > > > *Can answerer add more codecs which were present in offer?* > > *OR * > > *Should answerer select codecs only in offer and list formats in the > same > > relative order they were present in the offer?* > > > > > > Thanks in advance. > > -Sumin. > > > > > > > > > > > _______________________________________________ > 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
