> From: Aaron Clauson [[email protected]]
> 
> I've had a request from a user wanting to be able to initiate a 3 way call
> from my B2BUA. I don't do any media handling on my B2BUA so employing a
> server side audio mixer or such is not an option.

Your description is sort of confusing because you don't have a
consistent terminology for the various SIP dialogs (legs).

But as a general observation, it's difficult to alter the actual
remote end of the media without starting a new SIP dialog, due to the
strict rules regarding what updates can be made to the SDP of an
existing dialog.

E.g., if one wanted to implement "3 way calling" in a B2BUA
(presumably driven by DTMF from the phone), every time the phone
orders a switch from one remote to the other, the B2BUA whould have to
do an INVITE-with-Replaces back to the phone in order to start a new
SDP offer/answer sequence, or perhaps an INVITE-with-Replaces to the
remote phone -- there is no way to "resynchronize" the SDP
offer/answer sequences of both the local phone and the new remote
phone.

Dale

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