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

[Paul Kyzivat <pkyzivat at cisco.com>]

Dale Worley wrote:
> > From: Paul Kyzivat [mailto:pkyzivat at cisco.com]
> >
> > The obvious question is: How would C know to do that? Either C is
> > already in cooperation with A or B, or else C is operated by
> > the user of
> > A or B.
> >
> > The other obvious reaction is that you are trying to institutionalize
> > wire tapping. That won't make you popular. (Well, maybe with the FBI,
> > but not with people here.)
>
>
> One possibility is that C is the attendant console in an office PBX, and
> e.g. the attendant is setting up a conference call.

possible

> Another possibility is that A's UA does not have a conference bridge
> capability, but by hitting some keys, a second call can be placed from the
> UA to a conference bridge device to activate it.  The conference bridge
> device then needs to direct (dumb) UAs A and B to finish the conference
> set-up.

Might work in some cases. But is also likely that other things will go 
amiss in this case. A-B call is on hold while calling the bridge device. 
 Depending on how it does hold, bridge may not be able to figure out 
the dialog. Or, since this requires multiple calls from A, maybe there 
is more than one call on hold and the bridge is confused about which one 
to  conference.

Nevertheless, will just assume there are plausible cases.

> > How about:
> >
> > - C subscribes to dialog event package for both A and B
> >   (probably already did to know it wants to do this)
> > - C sends an INVITE/Replaces to A with no offer.
> > - A responds to the invite with offer SDP1
>
> A sends BYE to B.

It would be very unwise of B to send the BYE at this time, since the 
invite/replaces hasn't yet succeeded and could still fail. In most 
transfer scenarios the BYE is done quite late.

> > - C then sends INVITE/Replaces to B with SDP1
>
>
> B responds "No such dialog".

If A waited, as it should, before doing the BYE, then this won't happen.

	Paul

> Dale
>
>
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