The ideal way to solve this is with simcap. Thats why it was done: http://www.ietf.org/internet-drafts/draft-andreasen-mmusic-sdp-simcap-04.txt
You had also asked previously: > I have a problem, > > INVITE: M=audio 3456 RTP/AVP 2 9 15 > 200: m=audio 5004 RTP/AVP 2 9 > > Every side give the coders that it can receive (reverseChannels) > But how would the UAC will know what was picked by the UAS for transmission > (forwardChannel). > > In other words: lets say I have a machine that can do payload types 2 9 15 > But it must know what algorithm to load before its start receiving. > This is the same problem, more or less. Note that the uas SHOULD send with codec 2 in this case, but can use the others in cases like silence suppression and rfc2833 dtmf encoding, which require on-the-fly changes. -Jonathan R. Shen, Eran wrote: > Another query: > > What is the SIP recommended behavior for UA that can accept only one payload > format at a time (can not change on the fly w/o re-INVITE)? > I can think of some ideas: > > 1. Try always to be the second party that sends SDP, and choose 1st payload > format. > 2. If you are the 1st side that sends SDP open your receiving media on the > 1st codec the remote side sent in his own SDP. > 3. If the remote side SDP includes a=receiveonly or a=transmitonly (must be > a subset of yours), your media will open the 1st from receiveonly for you to > transmit and 1st from transmitonly for your receive. > 4. re-INVITE with your one coder. > 5. re-INVITE when you are getting bad payload format (a one you did not > expected). > > Any comments? > > Thanks, > > Eran. > > Eran Shen > > Intel Corporation > Telecommunications and Embedded Group > P.O Box 58, Migdal Tefen, Israel > Tel: +972-4-9105020 > <mailto:[EMAIL PROTECTED]> > > > > > -----Original Message----- > From: Vikram Varma [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, November 27, 2001 3:55 PM > To: 'Shen, Eran '; 'Sip-Implementors (E-mail) ' > Subject: RE: [Sip-implementors] Problem with media channels in SIP. > > > I believe you have interpreted the standard correctly. If you advertise you > can receive codec x, y, and z, I dont believe there is a particular order in > which the sender is bound to send his data. I believe the bottom line is > that if you advertise a list of codecs, then you have to analyze the RTP > headers to figure out which is being sent - further, I believe that the > sender can also switch on the fly. > If you want to narrow down the codec, I think you have a few options: > Narrow down the list to a single codec by including a new SDP in the ACK > (I'm not sure if this is OK) > Renegotiate using a reInvite from the list you obtained. > Vikram > > > -----Original Message----- > From: Shen, Eran > To: Sip-Implementors (E-mail) > Sent: 11/27/2001 5:34 AM > Subject: [Sip-implementors] Problem with media channels in SIP. > > I have a problem, > > INVITE: M=audio 3456 RTP/AVP 2 9 15 > 200: m=audio 5004 RTP/AVP 2 9 > > Every side give the coders that it can receive (reverseChannels) > But how would the UAC will know what was picked by the UAS for > transmission > (forwardChannel). > > In other words: lets say I have a machine that can do payload types 2 9 > 15 > But it must know what algorithm to load before its start receiving. > > In one hand I want to advertise I can do all of the above, to increase > compatibility to other vendors. > > On the other hand I would like to know what the remote is going to send > me > without looking at the payload type field in the RTP packet header. > > How can I signal that in SIP/SDP? > > In H.323 you have TCS and than OLC & OLCA > Or in fastStart: > OLC & OLCA for forwardChannel > OLCA and then OLC for reverseChannel > > But in SIP the remote side does not pick from your list and tells you > what > will be transmitted, it just start transmitting. > > So if you compare it to H.323 its: > TCS from one side > TCS from the other side > > And start transition without saying what will I transmit. > This can cause many interop problems. > Do you know a solution for that problem? > Do I interpret the standard correctly? > > Thanks, > > Eran. > > Eran Shen > > Intel Corporation > Telecommunications and Embedded Group > P.O Box 58, Migdal Tefen, Israel > Tel: +972-4-9105020 > <mailto:[EMAIL PROTECTED]> > > > > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > -- 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
