Re: [MMUSIC] SDP work needed for WebRTC stuff

Eric Rescorla <> Sat, 08 December 2012 23:21 UTC

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From: Eric Rescorla <>
Date: Sat, 08 Dec 2012 15:21:06 -0800
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To: "Cullen Jennings (fluffy)" <>
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Subject: Re: [MMUSIC] SDP work needed for WebRTC stuff
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On Sat, Dec 8, 2012 at 2:41 PM, Cullen Jennings (fluffy)

> I was looking over everything that needs to be completed to finish a fist
> cut of the WebRTC related work. There are a handful of big SDP problems
> that are currently blocking some of the WebRTC work and I'd like to figure
> out how to make some progress on them.
> Let me loosely characterize them as
> 1) If we have several video streams, how do theses map up to 1 or more m
> lines.
> 2) if we are doing port multiplexing, what does the SDP look like (the
> bundle problem)
> 3) How do we map the RTCWeb track and stream label concepts to identifiers
> in SDP
> 3) SDP for application running over SCTP/DTLS

I don't want to speak for all the various chairs but I am under the
> impression that most of chairs of related groups in W3C and IETF believe
> these are issues that need to be resolved primarily in the MMUSIC WG and
> that they impact both WebRTC and CLUE as well as the general long term use
> of SDP in SIP and other protocols.
> I'd like to get some discussion going on how we can make some progress on
> these. I don't think we are going to solve these in 20 minutes of
> discussion at an IETF meeting so I think we probably need some interim
> (virtual or face to face) to sort this out.
> Thoughts?

Wow, I'm totally confused here.

I had assumed that the SDP-related issues were going to be the main
topics at the WebRTC/RTCWEB interim in January. Is that not the case?

IMO the lack of clarity around how to encode various media
configurations into SDP is the major thing blocking progress here. In
particular, Firefox has opted not to implement multiplexing of media
streams over the same transport flow (whether of the bundle or
multiple m-line variety) until the SDP for it is well-defined. The
same thing applies to the question of how to map multiple m-lines to
incoming MediaStreams/Tracks.

We really need to cover these issues in the interim.