Subject: [MMUSIC] SDP Capability Negotiation to address multiple RTP profiles and other issues

From: Flemming Andreasen <[email-masked]>
Date: Wed, 21 Jun 2006 16:11:37 -0400

Greetings.

Greetings

I have submitted a draft on adding capability negotiation to SDP which 
you can retrieve from (abstract below):

http://www.ietf.org/internet-drafts/draft-andreasen-mmusic-sdp-capability-negotiation-00.txt

The primary motivation for this is to address the proliferation of RTP 
profiles and the associated problem of negotiating which of possibly 
several supported RTP profiles to use for a given media stream. For 
example, an entity may support one or more of "vanilla" RTP (RTP/AVP), 
secure RTP (RTP/SAVP), RTP with RTCP-based feedback (RTP/AVPF) or secure 
RTP with RTCP-based feedback (RTP/SAVPF). This is not the only set of 
problems related to capability negotiation though. To that effect, the 
draft contains the following:

- A set of proposed requirements for SDP capability negotiation (not 
just limited to the alternative profile issue)
- Review of existing work related to SDP capability negotiation and 
evaluation of how suitable each is to address the above requirements.
- A proposal for extending SDP with a capability negotiation mechanism 
that addresses the above requirements.

Feedback is hereby solicited. In particular, it would be very helpful if 
people could take a look at the requirements and see if they agree with 
them (too much, too little, anything wrong/missing, etc.) before we get 
into detailed discussion around the proposed solution. Having said that, 
all comments are welcome.

Thanks

-- Flemming

<Abstract>
        The Session Description Protocol (SDP) was intended for describing
        multimedia sessions for the purposes of session announcement, 
session
        invitation, and other forms of multimedia session initiation. 
SDP was
        not intended to provide capability indication or capability
        negotiation, however over the years, SDP has seen widespread 
adoption
        and as a result it has been gradually extended to provide limited
        support for these. SDP and its current extensions however do not 
have
        the ability to negotiate one or more alternative transport 
protocols
        (e.g. RTP profiles) which makes it particularly difficult to deploy
        new RTP profiles such as secure RTP and RTP with RTCP-based 
feedback.  
        The purpose of this document is to address that by identifying a 
set
        of requirements, evaluate existing work in this area, and provide a
        recommended solution for extending SDP with capability 
negotiation. 
</Abstract>

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