Re: [MMUSIC] AD Evaluation of draft-ietf-mmusic-rfc4566bis-32

Colin Perkins <> Tue, 12 March 2019 11:08 UTC

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From: Colin Perkins <>
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Date: Tue, 12 Mar 2019 11:08:39 +0000
Cc: Paul Kyzivat <>,
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To: Ben Campbell <>
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Subject: Re: [MMUSIC] AD Evaluation of draft-ietf-mmusic-rfc4566bis-32
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> On 11 Mar 2019, at 23:22, Ben Campbell <> wrote:
> Sent from my iPhone
>> On Mar 11, 2019, at 5:26 PM, Paul Kyzivat <> wrote:
>> On 3/11/19 1:43 PM, Colin Perkins wrote:
>>>>> §5 has several changes to normative language. Most are okay, but I think the change from “all MUST appear in exactly the order given here” to “all must appear” weakens it too much, and I’d prefer that to remain a MUST.
>>>> The reason for changing that is because the *normative* specification of the ordering is from the ABNF. The text here is explanatory and non-normative. (Note that a couple of paragraphs prior to this is a new statement emphasizing that the ABNF is normative.)
>>> Sorry, but I think this change is problematic. The text needs to use normative language that is consistent with the ABNF.
>> My thinking is that we don't like to have redundant normative specification, just in case they aren't consistent. The ABNF is normative. This section is of necessity an approximation.
>> But I defer to Ben or whoever.
> I agree with both of you. :-) 
> That is, we should avoid duplication normative requirements when possible, because it increases the chance of  spec errors. But we should still try to make sure the sections agree.
>>>>> This is a normative requirement of RTP, however. If we want to avoid normative examples, which I’d agree makes sense, then this needs to be rewritten as just “An RTP-based system in recvonly mode SHOULD…”.
>>>> That is the way it was. The change from "SHOULD" to "should" was to make it non-normative.
>>>> Or were you requesting to remove “e.g."?
>>> Remove the “e.g.”, yes, but also change “should” back to “SHOULD”.
>> I thought the point was that the RTP specs are normative and this is only an example, and so shouldn't be normative.
> I do not have the text in front of me, but I agree that examples should not be stated normatively.

This is documenting a perhaps unexpected interaction between SDP and RTP. That is, when set to recvonly in SDP, an RTP endpoint SHOULD send RTCP. I do think that it’s important that we spell this out clearly here, with normative language. 

Colin Perkins