Re: [MMUSIC] IDENTICAL-PER-PT in draft-ietf-mmusic-sdp-mux-attributes

Hi Bo,

Thanks – I was updating draft-ietf-avtcore-cc-feedback-message and checking the definition of IDENTICAL-PER-PT in draft-ietf-sdp-mux-attributes, and I noticed that it didn’t explicitly call out the wildcard case. It seems that you and I both interpreted it the same way, so maybe there’s nothing to clarify, but figured it was worth calling out in case. 

Colin

> On 26 Jul 2019, at 10:11, Bo Burman <bo.burman@ericsson.com> wrote:
> 
> Hi,
> 
> It seems very clear to me that it must be identical for all PT values in all
> bundled media descriptions when at least one media description in the bundle
> includes a wildcard. A PT wildcard requires same handling for all PT in the
> media description where it is included, and IDENTICAL-PER-PT requires same
> PT handling across all bundled media descriptions.
> 
> I guess that could be clarified, but I also see no other reasonable
> interpretation and therefore don't think the text is broken in any way.
> 
> I don't know what triggered the question, but I would assume that it has
> something to do with a=rtcp-fb:*?
> Is there e.g. a risk that IDENTICAL-PER-PT is incorrectly interpreted as
> IDENTICAL-PER-PT-PER-MEDIA-TYPE?
> 
> I can imagine a case where a=rtcp-fb:* was used in a non-BUNDLE SDP for the
> video media description but not for the audio media description, which I
> think is a very common case. When updating that SDP to use BUNDLE, the
> a=rtcp-fb:* is (mistakenly) kept, causing it to apply also to all of the PT
> in the audio media description, which might not be what the one updating the
> SDP to be BUNDLE'd intended or expected. 
> 
> Do you think there is significant risk of implementation mistakes if that
> clarification is not made?
> If so, is this one particularly error-prone or are there also other
> potential clarifications that should be made to avoid mistakes when bundling
> media descriptions without enough understanding of the BUNDLE implications?
> 
> Cheers,
> Bo (as individual)
> 
>> -----Original Message-----
>> From: mmusic <mmusic-bounces@ietf.org> On Behalf Of Colin Perkins
>> Sent: den 9 juli 2019 00:04
>> To: IETF MMUSIC WG <mmusic@ietf.org>
>> Subject: [MMUSIC] IDENTICAL-PER-PT in draft-ietf-mmusic-sdp-mux-
>> attributes
>> 
>> Hi,
>> 
>> draft-ietf-mmusic-sdp-mux-attributes-17 lists the a=rtcp-fb: attribute from
>> RFC 4585 as IDENTICAL-PER-PT. This makes sense, except that a=rtcp-fb:
>> allows a wildcard PT. Should Section 4.7 of sdp-mux-attributes state that
>> IDENTICAL-PER-PT means identical for *all* PT values when used with a
>> wildcard PT?
>> 
>> Colin
>> 
>> 
>> --
>> Colin Perkins
>> https://protect2.fireeye.com/url?k=70455e75-2ccf72ed-70451eee-
>> 0cc47ad93eae-
>> 23c263c7e25ea2e2&q=1&u=https%3A%2F%2Fcsperkins.org%2F
>> 
>> 
>> 
>> 
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