Subject: [MMUSIC] SDP Capability Negotation: Minutes of 1/23/07 design team conference call

From: Flemming Andreasen <[email-masked]>
Date: Mon, 29 Jan 2007 17:51:51 -0500

Greetings

The SDP Capability Negotiation Design team had a conference call on 
1/23/07. The attendees were:

    Matt Lepinski
    Flemming Andreasen
    Roni Even
    Christian Scmidt
    Thomas Stach
    Bob Gilman
    Colin Perkins

The topics discussed were:
1. Splitting the current solution document in two
2. Specific technical issues in current document
3. Media capabilities
4) Media Stream Dependency draft

1) Splitting the solution document in two
There have been concerns expressed on the list as well in private about 
the scope, perceived complexity and timeliness for coming up with a 
capability negotiation solution. The pressing need here is to address 
capability negotiation for transport protocols and associated attributes 
(e.g. secure RTP).
A lot of the perveived complexity, and the majority of the open issues 
have to do with media capabilities and their associated negotiation 
semantics. In order to address the concerns expressed, the design team 
agreed to split the current solution document in two parts:
a) A core part that contains a general capability negotiation framework 
as well as transport protocol capabilities and attribute capabilities.
b) An extension for providing media capabilities, which can be used to 
address the codec negotiation and latent media stream requirements.

The goal is to progress the two documents in parallel and have a solid 
proposal in place for the Praque meeting, however the core part can (and 
will) proceed independently of the media capabilities extension if 
necessary.

Flemming will split the core solution document accordingly and update 
the requirements document to reflect this as well. Bob Gilman, Roni 
Even, and Flemming will work on producing the media capabilities 
document as well.

2) Specific technical issues.
The team had a discussion around the numbering scope for transport 
protocol capability handles. Currently, the document provides a single 
global numbering scope for the entire session, irrespective of whether 
transport protocol capabilities are provided at the session level or the 
media level.  This provides a simple and easy way to ensure handle 
uniqueness and enable referencing between the session and media-level. 
It does however require that numbering to be coordinated between the 
individual media streams. The team eventually agreed that the scope 
should be global (the entire session description) as is specified 
currently.

A similar discussion took place for the attribute capability and the 
same conclusion was reached.

It did however bring up a related issue, namely what does it mean to 
include a session-level attribute capability in a media-level potential 
configuration ? The updated solution document will propose a solution 
for that.

Another (related) issue is that of ordering of potential configurations 
between the session and media-level - the updated solution document will 
propose a solution for that as well.

3) Media Capabilities
Bob Gilman had sent out a modified proposal for media capabilities (on 
1/16/07) based on the design team discussions that had taken place 
previously. There was general concensus in the design team around the 
proposal (modulo a few nits) and hence it will form the basis for the 
media capabilities document that will be provided separately. One 
potential issue with the proposal was discussed, namely whether the cmed 
attribute should provide the same MIME subtype more than once, or 
whether we should rather have a level of indirection that allows us to 
build composite capabilities above and beyond that provided by proposed 
"cenc" and "cfmt" attributes. Flemming felt that this warranted further 
consideration.

4) Media Stream Dependencies
Christian Schmidt suggested the design team consider 
draft-schmidt-mmusic-media-dependency-00.txt in its further work. The 
team felt that was a bit premature since it has just been submitted as 
an individual draft and there appears to be potential overlap with some 
existing work related to signaling for layered codecs.

Thanks

-- Flemming

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