Subject: [SIP] call-flow; each user has 2 UAs

From: [email-masked]
Date: Tue, 28 Nov 2000 12:50:21 +0200

I'd like to ask a call-flow question. Excuse me if I asked a similar
question before, but perhaps I did not state it clearly earlier.

What happens if two people EACH have two UA's, each on a different media.
This is a reasonable scenario, since people may buy multiple devices or
applications, and system integrators may wish to integrate separate
applications without altering their software.

As a simple example, say that the two medias are audio and video (although
in real life, of course, an app/device with video will also likely have
audio).

Jack                         Jill
Audio  <-------------------------------------------------> Audio
Video  <-------------------------------------------------> Video

The important point is that the Audio and Video devices are NOT integrated
and have separate UA's, yet we want all four apps/devices to be joined in
one "session", with Jack's audio talking to Jill's audio, and Jack's video
talking to Jill's video. Perhaps we can assume that Jack's audio and video
both have the same SIP URL.

We need some sort of four-way session with proper use of SDP to distinguish
media types. To add two UA's on the UAS side, we need forking with
non-exclusive response from two UA's. We also have to decide how to bring
in two UA's on the UAC side.

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---

From: Billy Biggs <[email-masked]>
Date: Tue, 28 Nov 2000 08:44:36 -0600

[email-masked] ([email-masked]):

> As a simple example, say that the two medias are audio and video
> (although in real life, of course, an app/device with video will also
> likely have audio).
> 
> Jack                         Jill
> The important point is that the Audio and Video devices are NOT
> integrated and have separate UA's, yet we want all four apps/devices
> to be joined in one "session", with Jack's audio talking to Jill's
> audio, and Jack's video talking to Jill's video. Perhaps we can assume
> that Jack's audio and video both have the same SIP URL.

  The session you describe is an abstraction layer above a SIP session.

  I see two ways of handling this:

        Remote               The first method is to have a SIP call
	  |  SIP             between the remote side and some
	Master               controller which communicates to the A and
       /      \  ?           V apps and incorporates their addresses
    Video    Audio           into a common SDP.  The master can be a
			     3pcc server if you use SIP to talk to A/V.

                             The second method is simply to have two
         Remote              calls up, and use some other means of
        |      | SIP         association higher up.  This may simply be
      Video   Audio          Jack telling Jill about the other session,
                             or some new header which flags the app
                             telling it to associate the two calls.

> We need some sort of four-way session with proper use of SDP to
> distinguish media types. To add two UA's on the UAS side, we need
> forking with non-exclusive response from two UA's. We also have to
> decide how to bring in two UA's on the UAC side.

  You don't need to get so complicated.

-- 
Billy Biggs, 3Com               Email: [email-masked]
http://www.div8.net/billy/      Phone: [email-masked]