Re: [MMUSIC] [rtcweb] Translating Plan A into No Plan (Was: No Plan)

Emil Ivov <emcho@jitsi.org> Mon, 03 June 2013 21:35 UTC

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Date: Tue, 04 Jun 2013 00:29:38 +0300
From: Emil Ivov <emcho@jitsi.org>
Organization: Jitsi
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To: Eric Rescorla <ekr@rtfm.com>
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Cc: "Cullen Jennings \(fluffy\)" <fluffy@cisco.com>, MMUSIC IETF WG <mmusic@ietf.org>
Subject: Re: [MMUSIC] [rtcweb] Translating Plan A into No Plan (Was: No Plan)
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Hey Eric,

On 04.06.13, 00:07, Eric Rescorla wrote:
>
> On Mon, Jun 3, 2013 at 2:01 PM, Emil Ivov <emcho@jitsi.org
> <mailto:emcho@jitsi.org>> wrote:
>
>     (moving from rtcweb)
>
>     Hey Eric,
>
>
>     On 03.06.13, 21:33, Eric Rescorla wrote:
>
>
>         On Mon, Jun 3, 2013 at 10:28 AM, Emil Ivov <emcho@jitsi.org
>         <mailto:emcho@jitsi.org>
>         <mailto:emcho@jitsi.org <mailto:emcho@jitsi.org>>> wrote:
>         [...]
>
>              III. Talking to other WebRTC applications
>
>              This is the fun case and the one we should be most
>         concerned with.
>              Let's imagine that the answerer needs to add a fourth video
>         stream.
>              To make this work endpoints would need to do the following:
>
>              a) with Plan A and draft-roach-rtcweb-glareless-____add:
>
>                  - send application specific signalling to the offerer
>                  - have a new O/A exchange
>
>              b) with Plan A:
>                  - have a new O/A exchange
>                  - potentially risk glare with some impact on user
>         experience
>
>              c) with No Plan:
>                  ... nothing
>
>
>         I'm really not following how this works in "No Plan". Ignoring
>         Plan A
>         and Plan B, can you just
>         walk through a complete example of what happens in your plan?
>         I.e., how
>         does browser
>         B learn learn that Browser A wants to send 3 streams instead of one?
>
>
>     It just gets three streams instead of one. It sees three new SSRCs
>     and it generates three new MediaStreams.
>
>
> So, just for clarity: you mean that A advertises one m-lin, B accepts,
> and then A sends some arbitrary number of media flows,

Yes.

> identified
> by SSRC?

What does "identified" mean?

> If so, I've got some questions:
>
> - If B can only display one video stream, how does it say so?

This is something that one app needs to tell another app. They can do so 
however they wish. As far as browsers are concerned: the transmitter 
just sends whatever the application instructs. The receiver just handles 
whatever it can.

> - How does B tell A not to send various streams?

What does "various" streams mean? If what you have in mind is: How does 
B tell A: "don't send me SSRCs 1, 2, 3 and 5" but keep 4 going, then B 
would send the list of SSRCs in app-specific signalling and A would stop 
sending them.

> - How does B tell A to send one stream big and another stream small?

Same as above.

Emil


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