> My question is how must a SDP be constructed if a participant wants to > join a conference. As the participant receives multicast he doesn't need > to provide a unicast contact in his offer. He only needs the answer from > the conference focus to know where to send his unicast stream and the > mulicast announcement. > So, is should really the offer/answer model be used for that scenario? > Or does the participant sends a blank SDP to the focus and the focus > consucts a SDP with the multicast media description and the unicast > media description for reception?
> I couln't find any information in the RFCs and IETF drafts. Hi Michael, It's legal to send an INVITE without any SDP body. In this case the offer is made by the called UA and delivered on the 200 OK message (or in any 1xx response but the 200 has to confirm these "unreliable" offers). At this point, the caller fills out the ACK with his SDP response. Check sections 13.2.2.4 and 13.3.1.4 in RFC3261 for further details. Ettore _______________________________________________ Sip-implementors mailing list [email protected] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
