1. Dialup conference bridge: call the bridge just like you call a person. Conference is identified by request URI. Works with rfc2543 - no extensions needed.

2. Distributed multiparty conferencing - no server. Fully distributed. This is what is described in the now-expired draft , and is work in progress (see http://www.softarmor.com/sipwg/teams/callcontrol/index.html for some recent drafts).

3. Multicast conferences - you can run your conference on multicast. Simply INVITE the person to join the multicast session. Works with baseline SIP. In fact, this was the initial purpose of SIP. In this case, there is not a full mesh of SIP signaling.

4. 3-way with local MC/MP function: A and B are talking. A wishes to add C to the call. A can simply call C, but also act as a mixer, so that the media it sends to B contains the A+C media, and the media to C is the A+B media. RTCP CSRC indicate who is in the conference. This also works with baseline SIP. It imposes additional burden on the UA, but otherwise provides this standard feature in a simple way.

There is no preferred way. It depends on the particular application. (Jonathan Rosenberg)
2000-Jul-06 9:16pm islepchin@dynamicsoft.com