Re: [AVTCORE] Draft new: draft-holmberg-avtcore-5761-update-00

Paul Kyzivat <pkyzivat@alum.mit.edu> Thu, 23 June 2016 14:01 UTC

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To: Christer Holmberg <christer.holmberg@ericsson.com>, "avt@ietf.org" <avt@ietf.org>
References: <D386CB5E.AC1C%christer.holmberg@ericsson.com> <140601d1cc9d$9a49e1c0$cedda540$@gmail.com> <7594FB04B1934943A5C02806D1A2204B381009F3@ESESSMB209.ericsson.se> <144401d1cccc$2b41eaf0$81c5c0d0$@gmail.com> <e8df15c7-42ae-9521-6e95-250b92516ef7@alum.mit.edu> <D3918A4D.B629%christer.holmberg@ericsson.com>
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Thu, 23 Jun 2016 10:01:24 -0400
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Subject: Re: [AVTCORE] Draft new: draft-holmberg-avtcore-5761-update-00
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On 6/23/16 5:44 AM, Christer Holmberg wrote:
> Hi,
>
>>> */That is tied to my question about can the answerer use a=RTCP to
>>> receive multiplex RTP and RTCP without explicitly using rtcp-mux
>>> attribute?/*
>>
>> I agree that is fuzzy. IMO, attempts to do that ought to be considered
>> an error. But I don't know what sort of recovery action should be taken
>> for this error.
>>
>> Note that for an *answerer* to attempt this leads to nonsense. It means
>> the offerer will be sending both RTP and RTCP to a single port while the
>> answerer (who set this up) must still send them to separate ports. And
>> since it wasn't anticipating that these be multiplexed it will
>> presumably be buffering as if they are going to separate ports. I would
>> think that would make a mess.
>>
>> It would be less problematic if first signaled by the offerer, because
>> then the answerer knows what is going on if it also uses a single for
>> both in the answer. But in this case they ought to be explicitly
>> signaling that they are multiplexing.
>>
>> It would be good to revise the definition of a=rtcp to clarify this, so
>> somebody not aware of a=rtcp-mux doesn't do this by accident.
>
>
> I guess we¹d just need to add an sentence (to section 2.1 of RFC 3605)
> saying that one MUST NOT include the RTP port value in the attribute,
> right?

I *think* that's right, at least in general. I haven't considered 
whether it might make sense in certain contexts in conjunction with 
other options/parameters.

	Thanks,
	Paul