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

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

> From: Arjun Roychowdhury [mailto:arjunrc at gmail.com]
>
> > > If you want C to indicate to A & B that its a dialog
> replacement, then
> > > C can send invites with the replaces header
> >
> > It could, but consider what happens when A processes the
> INVITE/Replaces --
> > It sends a BYE on the A-B dialog.  If B receives the BYE
> and processes it
> > before its INVITE/Replaces arrives from C, the user at B
> perceives that the
> > call was dropped.
>
> No - If B receives a Replaces header with an INVITE (either from C or
> A), that is an indication to B that the existing dialog is being
> replaced by another - that is not the same as dropping call.

That's true, but only if the dialog that the Replaces refers to exists at
that moment.  But if C sends an INVITE/Replaces to A, A may manage to get a
BYE sent to B before C sends an INVITE/Replaces to B.  Thus, B terminates
the A-B dialog *before* it receives the INVITE/Replaces from C.

> To avoid this, the only thing I can
> think of is the C does not invite both A & B instead it just invites
> one party and the other invites his peer - this is again within the
> parameters of the conferencing extensions for SIP - just that I am not
> sure if in your scenario, you are willing to put the intelligence into
> the UA to be able to send a replaces to its peer if it is switching a
> dialog .

The problem with this idea is that there is no currently defined way to
instruct a UA to do this.

Dale


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