Re: [MMUSIC] Why do we need rtcp-mux-exclusive?

Roman Shpount <roman@telurix.com> Mon, 21 March 2016 08:54 UTC

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Date: Mon, 21 Mar 2016 04:54:38 -0400
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From: Roman Shpount <roman@telurix.com>
To: Christer Holmberg <christer.holmberg@ericsson.com>
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Cc: "mmusic@ietf.org" <mmusic@ietf.org>, Paul Kyzivat <pkyzivat@alum.mit.edu>
Subject: Re: [MMUSIC] Why do we need rtcp-mux-exclusive?
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On Fri, Mar 18, 2016 at 7:40 AM, Christer Holmberg <
christer.holmberg@ericsson.com> wrote:

> In my opinion, a=rtcp-mux PLUS a=rtcp with RTP port would be an easy was
> to indicate mux-exclusive, and it would work both with ICE and non-ICE. I
> don’t think we should define multiple mechanisms for doing the same thing.
>
>
I would argue that a=rtcp is completely redundant potentially ignored
information. It does not indicate (at least not yet) that trickle will not
generate RTCP candidates. If ICE is used, the absence of RTCP candidates is
enough to indicate that RTCP should not be sent yet. If ICE is not used,
there is no grantee that a=rtcp is not ignored, so it does not help. So, we
can just include rtcp-mux and do not include any RTCP candidates, and we
will get the result we need without any new specifications.

As far as trickle is concerned, it can detect that remote party supports or
does not support rtcp-mux before it allocates any RTCP candidates. If it
will not include any RTPC candidates, no RTCP will be sent to it.

I think this firmly puts the problem with mux-exclusive outside of anything
ICE enabled. If we are dealing with anything non-ICE, I do not think the
backwards compatible solution can be based on a=rtcp since it is not
guaranteed if remote party will honor it. If you want a solution for
legacy, it should be something that replaces the address in c= line and/or
port in m= line to stop remote from sending any RTCP unless it understands
this extension.
_____________
Roman Shpount