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

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

> From: Arjun Roychowdhury [mailto:arjunrc at gmail.com]
>
> However, if C wants to break into a call between A & B when it was not
> in the path to begin with, it _must_ happen with the consent of the
> participants. If not, imagine how simple it would be for me to break
> into someone's private conversation and start a recording process.

In any case, I would expect that it would require C to know the dialog-info
(Call-Id, to-tag, from-tag) for the A-B dialog.  But we have already agreed
that the dialog-info is sensitive and should only be known by UAs that have
the right to intervene in the dialog -- If C knows the the dialog-info, it
can use existing mechanisms to hijack the dialog in various ways.  There are
no *new* security/privacy concerns here.

> Not sure I followed your thought below. If A and B already implement
> the standards required (REFER/INVITE/Replaces/dialog events etc) then
> these are all that are needed to effect this change.

I have yet to see how to implement this operation with existing mechanisms.

> 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.

Dale


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