Subject: [MMUSIC] SDPCapNeg Issue #4: Does 3PCC imply a need to always include "creq" attribute with base option-tag ?

From: Flemming Andreasen <[email-masked]>
Date: Mon, 25 Jun 2007 13:14:22 -0400

The SDP Capability Negotiation currently defines the "creq" attribute as 
follows:

<quote>
   The Required Capability Negotiation Extensions attribute ("a=creq")
   contains a comma-separated list of option tags (see Section 3.3.1. )
   identifying the SDP Capability negotiation extensions that MUST be
   supported by the entity receiving the SDP in order for that entity to
   properly process the SDP Capability Negotiation attributes and
   associated procedures. Support for the basic negotiation framework is
   implied by the presence of an "a=pcfg" attribute (see Section 3.5.1.
   ) and hence there is no need to include the "a=creq" attribute with
   the base option-tag ("cap-v0"). Still, it is allowed to do so. 
</quote>

Jonathan Rosenberg raised the question whether 3PCC can wreak havoc with 
the above scheme of inferring support for the basic SDP Capability 
Negotiation framework by looking for "pcfg" attributes, as opposed to 
explicitly including the "creq" attribute with the base option-tag.

The design team discussed this issue in Prague and didn't see how 
inclusion of the "creq" attribute-tag with a base option-tag would be 
any better than just looking for "pcfg" attributes. In the absence of 
Jonathan pointing out any specific problems with the above scheme, it 
will stay as-is.

If you disagree with this, please let me know.

Thanks

-- Flemming

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