Subject: [Sipping] Inserting a B2BUA into an existing dialog

From: "Dale Worley" <[email-masked]>
Date: Fri, 10 Jun 2005 14:53:51 -0400

We are considering conference bridging applications, and it would be
convenient to be able to insert the conference bridge (a B2BUA) into an
existing dialog.  It turns out that it's simple to *remove* the bridge from
between two UAs, as it can send a REFER for an INVITE with Replaces to one
of the UAs to get it to talk directly to the other UA.  But I've not been
able to figure out how to *insert* the bridge into an existing dialog.  Has
there been any work on this sort of thing?

Thanks,

Dale

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From: Tom Taylor <[email-masked]>
Date: Fri, 10 Jun 2005 15:08:01 -0400

One method is for the conference initiator to use REFERs to get the 
bridge to dial out to all the participants.  In the simplest case, if A 
is talking to B and wants to set up a conference, A sends an INVITE to 
the server C, then sends a REFER/Replaces->B to C to pick up the A-B 
dialogue.

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From: Arjun Roychowdhury <[email-masked]>
Date: Fri, 10 Jun 2005 15:15:56 -0400

Dale,
depending on how you want your conference to begin, one of the several
scenarios listed in draft-ietf-sipping-cc-conferencing-06.txt may
help.
For example, section 4.10 is one mechanism 

regds
arjun

-- 
Arjun Roychowdhury

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 10 Jun 2005 16:09:27 -0400

> there been any work on this sort of thing?

Who is doing the inserting?

If A is talking to B but would like to use a bridge, it just creates a 
focus F, establishes its own dialog and media stream between A and F, 
and then sends a REFER/Replacing to F referring to its dialog with B. Of 
course A must also locally manage the way it manages its media to 
coordinate the handoff from the old media stream with B to the new one 
with F.

	Paul

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From: 李立 <[email-masked]>
Date: Sat, 11 Jun 2005 13:39:39 +0800

I think Dale's problem has been resolved in
draft-ietf-sipping-cc-conferencing-06.But there's a more complex scenario.
if A is talking to B,and they are in a session with an intermediate 3pcc
controller which is referred to in rfc3725.when A want to initiate a
conference with B,then how he work to do that?

Dale Worley wrote:

Thanks,

Dale

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From: "Dale Worley" <[email-masked]>
Date: Fri, 17 Jun 2005 13:35:05 -0400

So it would seem that the minimal feature a UA needs to allow this operation
is:

Define a new "hold" parameter for the Replaces: header.  If it is present,
the UAS that receives it, when accepting the INVITE, should not immediately
terminate the dialog being replaced, but "put it on hold".  If that dialog
is not terminated by the other end after (say) 30 seconds, the UA may
terminate it.

That's satisfyingly simple, at least.

Dale

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 17 Jun 2005 15:09:20 -0400

I don't think you even need that much.
What is needed is a clarification that when receiving an 
INVITE/Replaces, you should not terminate the replaced dialog until you 
have at least completed the offer/answer seqeuence for the replacement 
dialog.

	Paul

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From: "Dale Worley" <[email-masked]>
Date: Fri, 17 Jun 2005 15:32:16 -0400

> From: Paul Kyzivat [mailto:[email-masked]]
>

That would suffice, if the B2BUA could control the timing of its answers
relative to the INVITEs it was sending out.  But that might be hard to do in
a layered architecture, where each INVITE transaction might be proceeding
independently.

Dale