Subject: [MMUSIC] SDPCapNeg Issue #7: Media-level attributes at the session-level

From: Flemming Andreasen <[email-masked]>
Date: Mon, 25 Jun 2007 13:15:14 -0400

Currently, the SDP Capability Negotiation framework says that you MUST 
NOT provide a media-level attribute capability at the session-level. The 
reason for this is that use of an attribute capability in a potential 
configuration simply adds that attribute to the SDP at the level where 
the attribute was provided. Thus an attribute capability provided at the 
session-level would be added at the session-level, which would be 
incorrect for media-level attributes.

Bob Gilman noted that while this is fine for the basic SDP Capability 
Negotiation framework, it is too restrictive for the media capabilities 
extensions, which needs to list latent media capabilities at the session 
level.

The design team did not discuss this issue in Prague, however below is a 
suggested resolution for it:

Instead of disallowing media-level attribute capabilities at the 
session-level we instead say that the base SDP Capability Negotiation 
framework allows use of media-level attribute capabilities at the media 
level only in a potential configuration, however extensions may modify 
this behavior, as long as it is fully backwards compatible with the base 
specification. Thus, media-level attribute capabilities can be provided 
at the session-level, however they cannot be used by a potential 
configuration that follows the base specification only. Session-level 
attribute capabilities can still only be provided at the session-level.

Please let me know if you disagree with this or otherwise have any 
comments on this.

Thanks

-- Flemming

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