Subject: [Megaco] Media negotiation model

From: "Tom-PT Taylor" <[email-masked]>
Date: Sat, 25 Feb 2006 21:19:08 -0500

I'm currently writing a description of H.248 for students, which has 
caused me to reflect on the value of some of the capabilities we built 
into the protocol.

When we were putting together the procedures and syntax for specifying 
media descriptions, at least some of us had multimedia applications 
firmly in mind. I myself was all too aware of the potential complexity 
of video session descriptions in particular, because they have so many 
parameters associated with them. This is why we put in the possibility 
of specifying multiple session descriptions within a Local or Remote 
descriptor. Of course, this capability for resource tradeoffs might have 
been simpler for the MG to apply had we not split the complete session 
description amongst different streams.

What I am wondering now is whether multiple session descriptions are 
used in real implementations. And even if they are used in the MGC-to-MG 
direction, I would be quite surprised to learn that anyone used 
ReserveGroup=true, given the difficulty of matching the result to a SIP 
offer or answer.

Does anyone care to comment on whether my view of applicability of this 
mechanism is overly pessimistic?

Tom Taylor

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