The conferencing mechanisms being developed in SIPPING/XCOM explicitly include end system mixing. There is a central FOCUS, but not a central mixer. This means that one element (which could be one of the endpoints) has dialogs with all participants, and sends out the SDP with all the streams.
For three way calls, a UA with an existing dialog could REFER it's existing partner to the conference URI and INVITE the 3rd party to the URI (assuming it doesn't need to REFER itself). The dialogs would have either multiple unicast, a single multicast, or multiple multicast descriptions in it. Each UA would get two streams, either two streams in one multicast, or two streams in unicast or multicast and mix them. Brian -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Vadim Lebedev Sent: Monday, August 09, 2004 11:25 AM To: [EMAIL PROTECTED] Subject: [Sip-implementors] 3 way conf calls Hello, I need advice on SIP RFC's or drafts relevant to implementation of 3 way conf calls using distributed mixing. The idea is �that each partcipant send his media stream to all other participants using multicast or multi-unicast. �And each participant does audio mixing locally. All SIP RFCs and drafts seems to suggest centralised mixing by conference focus which redistribute the mixed stream to other participants... I can imagine how the distributed mixing can be done using multicast (for example using re-Invites to parties with multicast address in the SDP), �but how to do it in case of multi-unicast? Suppose that endpoint A is in session with B and now B want to bring C into conference. So B send an INVITE to C and establish a 2 way call... Now B has to direct C to establish a call to A and inform somehow A and C that the newly established call is actually a part of a conference, so that A and C will be a) able to mix incoming streams and b) send data from local source to two different destinations. Any pointers or advices? Thanks Vadim _______________________________________________ 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
