Re: [MMUSIC] "a=extmap" with BUNDLE

Taylor Brandstetter <deadbeef@google.com> Mon, 27 March 2017 17:44 UTC

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From: Taylor Brandstetter <deadbeef@google.com>
Date: Mon, 27 Mar 2017 10:44:45 -0700
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To: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <ibc@aliax.net>
Cc: Suhas Nandakumar <suhasietf@gmail.com>, mmusic WG <mmusic@ietf.org>
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Subject: Re: [MMUSIC] "a=extmap" with BUNDLE
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If extension IDs aren't unique across bundled m= sections, then on
receiving a packet, an implementation may need to determine which m=
section it's "associated" with before knowing how to interpret the
extension IDs. To do this, it may need to use the MID, which means that at
a minimum, the MID extension must be using a unique ID.

But this increases implementation complexity without much benefit (the
benefit being that by sharing IDs, you could more easily avoid running out
of spare IDs). So I'd be in favor of just requiring them to be unique.

On Sat, Mar 25, 2017 at 6:35 PM, Iñaki Baz Castillo <ibc@aliax.net> wrote:

> 2017-03-24 19:28 GMT+01:00 Taylor Brandstetter <deadbeef@google.com>om>:
> > saw that. Which means that individual documents are responsible for
> defining
> > how their extensions work with BUNDLE.
> >
> > But something still would need to define the general restrictions for
> using
> > "extmap" with BUNDLE, such as the ID restriction. Or is that just
> something
> > that's common sense and doesn't need to be specified?
>
> https://tools.ietf.org/html/rfc5285#section-6 just mandates that the
> IDs must be unique within a m= section, but at the end, all the WebRC
> implementations use unique ID values across the entire SDP.
>
> There are some RTP extensions, such as
> http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01,
> that work at *transport* level (rather than at m= section level), but
> nothing prevents such a spec to work even if its ID is not unique
> within the m= sections.
>
> This is, IMHO we don't need a global behavior/requirement for the ID
> values within bundled m= sections.
>
>
> --
> Iñaki Baz Castillo
> <ibc@aliax.net>
>