Re: [rtcweb] No Plan

Paul Kyzivat <> Thu, 30 May 2013 15:08 UTC

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Date: Thu, 30 May 2013 11:07:46 -0400
From: Paul Kyzivat <>
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Subject: Re: [rtcweb] No Plan
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On 5/30/13 4:24 AM, Stefan Håkansson LK wrote:
> Hi Emil,
> a couple of comments:
> "1.  Expose the SSRCs of all local MediaStreamTrack-s that the
>         application may want to attach to a PeerConnection."
> I don't think that would be possible, or desirable. SSRC _only_ come
> into play when a MediaStreamTrack is to be transported over the network
> - it is useless in local cases. And, the same local MediaStreamTrack
> could be sent to several peers (using different PeerConnections) and
> could have different SSRC's (and even different number of SSRC's) for
> the different peers.
> I think SSRCs would only be available for MediaStreamTracks that are
> attached to a PeerConnection.

If that is true, then I think it calls for exposing to the API an object 
that binds MediaStreamTrack to the PeerConnection, so that there is a 
place to hang the SSRC attribute.


> One thing I like about Plan A and B is that the naive application
> developer does not have to deal with things below MediaStream and
> MediaStreamTrack level. The application would simply add a MediaStream
> (containing MediaStreamTracks) to the PeerConnection, do the
> createOffer/setLocal and exchange signaling blobs that it need not look
> into, and the MediaStream with MediaStreamTrack's would be reflected at
> the remote end. The application would not have to deal with PT's, SSRC's
> etc.
> I think that the "No Plan" proposal could be made similar if the info
> about how MediaStreamTrack's relate to SSRC's (including those for FEC
> and RTX) is exchanged using some blobs that the (naive) app can just
> exchange and need not look into.
> If done that way, "No Plan" seems to me to be quite similar to Plan B,
> with the difference being that the info about how SSRC's relate to
> MediaStreamTrack's is exchanged not in the core SDP but in separate
> messages. This could be seen as an improvement I think.
> Stefan
> On 2013-05-29 20:59, Emil Ivov wrote:
>> Hey all,
>> Based on many of the discussions that we've had here, as well as many
>> others that we've had offlist, it seemed like a good idea to investigate
>> a negotiation alternative that relies on SDP and Offer/Answer just a
>> little bit less.
>> The following "no plan" draft attempts to present one such approach:
>> The draft relies on conventional use of SDP O/A but leaves the
>> intricacies of multi-source scenarios to application-specific
>> signalling, with potentially a little help from RTP.
>> Hopefully, proponents of Plans A and B would find that the
>> interoperability requirements that concerned them can still be met with
>> "no plan". Of course they would have to be addressed by
>> application-specific signalling and/or signalling gateways.
>> Comments are welcome!
>> Cheers,
>> Emil
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