Subject: RE: [Sip] B2BUA

From: "Rosen, Brian" <[email-masked]>
Date: Tue, 3 Dec 2002 11:29:15 -0500

> So the B2BUA is a concatenation of two User Agents, each of 
> which acts both as UAC and UAS. A conference server will 
> probably look like a UA, definitely not a B2BUA, IMHO.
>    
This thread is, hopefully reaching an end (with an agreement to
do some examples with call flows).  However, the above statement
is yet one more example of the confusion people have with B2BUA.

The key thing about a B2BUA is that it looks like a UA to whatever
it is connected to (on both sides).  So, a conference server
looks like a UA to each of it's ports, and it has at least two of
them, and there is some "magic" between them.  If you look at the
concept of the "focus" from the conferencing work, it is a
thing that has a bunch of two ended SIP calls, one with each
participant.  Each participant thinks it is talking to a UA.
While some messages sent from a participant to a UA might be
consumed by the UA (state changes), often, a message will trigger
messages from the focus to other participants.

This seems, to me, to meet the definition of B2BUA in 3261,
and more strongly meets proposed changes in the definition.
Of course, it really doesn't matter if you consider the focus to
be a B2BUA or not.

Brian 
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