Re: [AVTCORE] [MMUSIC] BUNDLE: a single stream with multiple MIDs?

Suhas Nandakumar <suhasietf@gmail.com> Fri, 08 July 2016 00:52 UTC

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From: Suhas Nandakumar <suhasietf@gmail.com>
Date: Fri, 08 Jul 2016 06:22:01 +0530
Message-ID: <CAMRcRGRMp-tehSjwaXh4rzwedsHHjXaxhJ=pd0-9XiSCiLG_2Q@mail.gmail.com>
To: Jonathan Lennox <jonathan@vidyo.com>
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Subject: Re: [AVTCORE] [MMUSIC] BUNDLE: a single stream with multiple MIDs?
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Hi Jonathan

  Clarification question :

   if we have 2 m=lines

m = ...
a=mid1
<manager>

m=...
a=mid2
<loudest speaker>

does these 2 correspond to same media source ? It felt so from the
duplicate design you mentioned but wanted to confirm

Thanks
Suhas



On Fri, Jul 8, 2016 at 4:06 AM, Jonathan Lennox <jonathan@vidyo.com> wrote:

> Hi, all —
>
> (This was an issue I raised in AVTCORE in Buenos Aires — I promised to
> send e-mail to the list but hadn’t remembered to get around to it until
> now.)
>
> When finishing up the CLUE RTP mapping draft, I realized that one of
> CLUE’s RTP requirements didn’t actually end up getting satisfied by BUNDLE
> (which is the solution CLUE converged on).  This isn’t a CLUE-specific
> issue, so I’m raising it here.
>
> The issue is whether we want to support a use case, in BUNDLE, where a
> single RTP stream corresponds to more than media description (and thus has
> more than one MID value)?
>
> The use case is where one m-line has a semantic of “always view this
> person” (my boss, say, or my customer); and another m-line has a semantic
> of “the current loudest speaker”. (In CLUE, these would be a single content
> capture in the former case, and a switched capture for the latter.)
> Whenever the boss *is* the current loudest speaker, the same content would
> be sent for both m-lines.
>
> A naive implementation would simply duplicate all the packets for the two
> m-lines, with different MID values, but this has two problems.  First off
> all, it obviously wastes bandwidth.  Potentially more seriously, it
> precludes any RTP middlebox topology which doesn’t rewrite SSRC values,
> since the same content (arriving with a single SSRC value at the middlebox)
> would need to be sent with two different SSRC values down from the
> middlebox.  If PERC goes with its current consensus of no SSRC rewriting,
> this will particularly be a problem for PERC.
>
> I certainly don’t think this is something that should block BUNDLE’s
> completion, but I think it could be a pretty easy extension.
>
> (My initial design proposal was to allow multiple SDES values of the same
> type, and multiple SDES header extensions items of the same type, to be
> sent simultaneously in RTP — protocol-syntactically this is trivial, you’d
> just need to negotiate that you support it.  But I’m not wedded to this
> solution.)
>
> What do people think — is this worth working on?  Is there interest in
> discussing it in Berlin, and if so, in what venue?
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