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

["Dale Worley" <dworley at pingtel.com>]

> From: Paul Kyzivat [mailto:pkyzivat at cisco.com]
>
> Then can you be more explicit about
> - the starting state of all participants
> - the desired end state
> - what set of restrictions you want to operate under

What I was hoping for was that this topic had been well-discussed and a good
solution was already known...

What I'd like to see runs along these lines:

Usage scenario:

1) Dialog between UAs A and B.  Ideally, A and B need no features other than
those already defined in SIP.

2) UA C decides to insert istelf "between" A and B.  (In general, C could be
the same as A or B, but in that case, it's clear how to implement it.)

3) C sends appropriate messages to A and B.  After they are executed: at UA
A, the dialog A-C has replaced dialog A-B, and at UA B, dialog B-C has
replaced dialog A-B.  C provides a media path between dialog A-C and B-C.

Trivially, we could assume that UA A knows how to implement the appopriate
messages to B, etc., and that this facility in A can be triggered by a
message from C.  But that is really ugly.  I'd like to assume that A and B
provide no more facilities than are already defined in SIP (e.g., REFER,
INVITE/Replaces, dialog events, etc.), and that C can use these operations
to effect this transformation.

(Oddly, if one is already in situation (3), it is straightforward for C to
transform it to (1).)

I hope that makes it clearer.

Dale


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