Arthur Lallet wrote:
> Hello,
>
> I'm currently looking at SIP for multipoint conferences.
> I have some problem to understand how the call set-up and control would be done with
>SIP when more than 2 users are in
> a conference call. Can 3 SIP user agents contact each other directly without a
>network server or MCU? Is a proxy or
> redirect server always needed?
>
> Thanks for your help.
> Arthur
This question was answered on the mailing list just last week. Here was
my answer:
> That is one model, but not the only one SIP provides. SIP has four ways
> to do multiparty conferencing:
>
> 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.
> 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 R.
--
Jonathan D. Rosenberg 72 Eagle Rock Ave.
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