Re: [MMUSIC] FW: Issue #27: Allow RTP attributes in non-media m= sections

[Eric Rescorla <[e-mail]>]

Yes, I think we do

On Mon, Feb 27, 2017 at 5:10 AM, Christer Holmberg <
[e-mail]> wrote:

> Hi,
>
> Do people think we need to discuss this face-to-face in Chicago? Note that
> I have currently NOT requested agenda time for BUNDLE.
>
> As far as document changes are concerned, we would AT LEAST need some
> clarification text in BUNDLE and/or draft-mux-attributes.
>
> Regards,
>
> Christer
>
> From: Eric Rescorla <[e-mail]>
> Date: Sunday 19 February 2017 at 00:28
> To: "[e-mail]" <[e-mail]>
> Cc: Christer Holmberg <[e-mail]>, Taylor
> Brandstetter <[e-mail]>, "[e-mail]" <[e-mail]>
>
> Subject: Re: [MMUSIC] FW: Issue #27: Allow RTP attributes in non-media m=
> sections
>
>
>
> On Sat, Feb 18, 2017 at 1:38 PM, Paul Kyzivat <[e-mail]>
> wrote:
>
>> On 2/18/17 1:45 PM, Eric Rescorla wrote:
>>
>>>
>>>
>>> On Sat, Feb 18, 2017 at 8:09 AM, Paul Kyzivat <[e-mail]
>>> <mailto:[e-mail]>> wrote:
>>>
>>>     On 2/18/17 4:35 AM, Christer Holmberg wrote:
>>>
>>>         Hi,
>>>
>>>         I invite anyone who has a suggestion on text that needs to be
>>>         modified/added/removed to provide a pull request (or send text
>>>         to the list) to do so; in draft-bundle, draft-mux-attributes,
>>>         and/or any other specification...
>>>
>>>
>>>     IMO it doesn't make sense to put attributes on one bundled m-line
>>>     that only apply to some other bundled m-line - current or future.
>>>
>>>
>>> Why? The whole principle is that they are supposed to span all the m=
>>> lines.
>>>
>>
>> They are supposed to span all the m-lines in the bundle that it is
>> meaningful for them to be used with.
>>
>
> Yes, and so it doesn't matter which one they are attached to.
>
>
> The closest thing we currently have to this situation is session-level
>> attributes. Some of those are defined as valid at both session and media
>> level, and that the value at session level is a default for media level.
>> These in some sense need to be evaluated in the context of every m-line,
>> even the ones where they aren't defined.
>>
>> But we have no standard rule for these. Every attribute needs to say if
>> it is defined at session level and if that should be treated as a default
>> for a value at media level. And in the process it is specifying (at least
>> implicitly) which m-lines it applies to.
>>
>> In principle this could also be done for all the attributes that are to
>> be identical in bundles. But that means making all the changes to do that,
>> and maintain it in the future.
>
>
> Huh? We already have a document that analyzes every single attribute and
> tells you how it
> is to be handled (https://tools.ietf.org/html/draft-ietf-mmusic-sdp-mux-
> attributes-16) and
> tells you how to hoist stuff from one m= line to all of them. And we're
> already handling
> it that way if the m= line associated with the bundle tag is a media
> section. The only
> difference is how it's handled if it's a data section.
>
> -Ekr
>
>     As an alternative, how about picking the first tag in the bundle
>>>     attribute that identifies an m-line of an appropriate type to carry
>>>     the attribute?
>>>
>>> Seems much more complicated to implement and specify.
>>>
>>> To conserve e-mails, responding to Christer as well here: I don't think
>>> we need to update any of the relevant RFCs (other than potentially
>>> putting them in some
>>> useless Updates: line at the top of the doc). The idea here is that
>>> BUNDLE overrides them for cases where it applies.
>>>
>>
>> Again, maybe it is possible to craft some words that clearly and
>> precisely state how this is to work, in a general way without taking it one
>> attribute at a time. But I want to see them.
>>
>> Then we can discuss whether that is simpler than what I suggested above.
>>
>>         Thanks,
>>         Paul
>>
>> -Ekr
>>>
>>>
>>>             Thanks,
>>>             Paul
>>>
>>>
>>>         Regards,
>>>
>>>         Christer
>>>
>>>         -----Original Message-----
>>>         From: Paul Kyzivat [mailto:[e-mail]
>>>         <mailto:[e-mail]>]
>>>         Sent: 17 February 2017 18:51
>>>         To: Taylor Brandstetter <[e-mail]
>>>         <mailto:[e-mail]>>
>>>         Cc: Christer Holmberg <[e-mail]
>>>         <mailto:[e-mail]>>; IETF MMUSIC WG
>>>         <[e-mail] <mailto:[e-mail]>>
>>>         Subject: Re: [MMUSIC] FW: Issue #27: Allow RTP attributes in
>>>         non-media m= sections
>>>
>>>         On 2/16/17 9:27 PM, Taylor Brandstetter wrote:
>>>
>>>                 So, to make this work I think it will be necessary to
>>>             ammend the
>>>                 definitions of the particular attributes to specify this
>>>             usage. And
>>>                 then future new attributes that pertain to RTP would
>>>             also need to
>>>                 address this.
>>>
>>>
>>>             sdp-mux-attributes already amends the definitions of these
>>>             attributes,
>>>             such that a TRANSPORT attribute in m= section "A" can be
>>>             used for
>>>             media described by m= section "B". So, I don't see why it
>>>             couldn't go
>>>             a step further, and explicitly allow TRANSPORT and IDENTICAL
>>>             category
>>>             attributes to appear in m= sections with proto values not
>>>             normally
>>>             used with those attributes.
>>>
>>>
>>>         I will reserve judgement until I see specific text.
>>>
>>>                 Thanks,
>>>                 Paul
>>>
>>>             On Thu, Feb 16, 2017 at 3:50 PM, Paul Kyzivat
>>>             <[e-mail] <mailto:[e-mail]>
>>>             <mailto:[e-mail]
>>>
>>>             <mailto:[e-mail]>>> wrote:
>>>
>>>                 On 2/16/17 12:10 PM, Christer Holmberg wrote:
>>>
>>>                     Hi Paul,
>>>
>>>                     I assume you have an opinion on this :)
>>>
>>>                     The suggestion is to allow RTP-specific parameters
>>>             (SDP rtcp-mux
>>>                     attributes etc) in non-RTP m= lines (e.g., data
>>>             channel).
>>>
>>>
>>>                 This is a nasty issue.
>>>
>>>                 The problem with allowing this is: what do these
>>>             parameters *mean*
>>>                 when so attached? And where do I look to find out?
>>>
>>>                 I'm not certain if they are currently permitted or not.
>>>             AFAIK there
>>>                 is no *general* mechanism for specifying with which
>>>             proto values a
>>>                 particular attribute may be used. I haven't studied the
>>>             definitions
>>>                 of the "RTP-related" attributes to see if they make a
>>>             specific
>>>                 statement about this. My guess is that they don't, but
>>>             that they
>>>                 only define the meaning in the context of an RTP session.
>>>
>>>                 If that is so, perhaps the rule that unknown attributes
>>>             are to be
>>>                 ignored should apply to those attributes when used with
>>>             a non-RTP
>>>                 media section. But if that rule were to apply, then we
>>>             would expect
>>>                 that with O/A the rules for how these attributes in an
>>>             offer affect
>>>                 what goes in the answer would not apply. I guess that
>>>             won't be
>>>                 sufficient here.
>>>
>>>                 So, to make this work I think it will be necessary to
>>>             ammend the
>>>                 definitions of the particular attributes to specify this
>>>             usage. And
>>>                 then future new attributes that pertain to RTP would
>>>             also need to
>>>                 address this.
>>>
>>>                 IMO this is a can of worms. So my opinion is that these
>>>             should *not*
>>>                 be used with non-RTP m-lines, with or without bundle.
>>>
>>>                 Note that data channel is a special case. While we have
>>>             agreed not
>>>                 to consider it for now, it is possible, in principle, to
>>>             run RTP
>>>                 over a data channel. If that were defined then these
>>>             attributes
>>>                 would also be needed. But then they would not be used as
>>>             media-level
>>>                 attributes. Instead, they would be dcsa attributes.
>>>
>>>                         Thanks,
>>>                         Paul
>>>
>>>                     *From:*mmusic [mailto:[e-mail]
>>>             <mailto:[e-mail]>
>>>                     <mailto:[e-mail]
>>>             <mailto:[e-mail]>>] *On Behalf Of *Christer
>>>                     Holmberg
>>>                     *Sent:* 16 February 2017 19:07
>>>                     *To:* Eric Rescorla <[e-mail]
>>>             <mailto:[e-mail]> <mailto:[e-mail]
>>>             <mailto:[e-mail]>>>; mmusic
>>>                     WG <[e-mail] <mailto:[e-mail]>
>>>             <mailto:[e-mail] <mailto:[e-mail]>>>
>>>
>>>                     *Subject:* Re: [MMUSIC] Issue #27: Allow RTP
>>>             attributes in
>>>                     non-media m=
>>>                     sections
>>>
>>>
>>>
>>>                     Hi,
>>>
>>>                     * *
>>>
>>>                     *>*See:
>>>
>>>
>>>             https://github.com/cdh4u/draft-sdp-bundle/issues/27
>>>             <https://github.com/cdh4u/draft-sdp-bundle/issues/27>
>>>
>>>             <https://github.com/cdh4u/draft-sdp-bundle/issues/27
>>>             <https://github.com/cdh4u/draft-sdp-bundle/issues/27>>
>>>
>>>
>>>                         https://github.com/rtcweb-wg/jsep/issues/528
>>>             <https://github.com/rtcweb-wg/jsep/issues/528>
>>>                         <https://github.com/rtcweb-wg/jsep/issues/528
>>>             <https://github.com/rtcweb-wg/jsep/issues/528>>
>>>
>>>
>>>
>>>
>>>                         The basic issue is that it's possible to have a
>>>             situation
>>>                         where you
>>>
>>>                     have both
>>>
>>>                         media and data m= sections but the BUNDLE tag is
>>>             associated
>>>                         with the data
>>>
>>>
>>>                         m= section and now you need to put the TRANSPORT
>>> and
>>>             IDENTICAL
>>>
>>>
>>>                         attributes somewhere. The JSEP editors discussed
>>>             this and
>>>                         came to the
>>>
>>>
>>>                         conclusion that it should go with the BUNDLE tag
>>>             (i.e., in
>>>                         the data m=
>>>
>>>                     section)
>>>
>>>                         and that BUNDLE should forbid this, but it
>>>             requires a change
>>>                         to BUNDLE.
>>>
>>>
>>>
>>>
>>>                     Did you mean to say that BUNDLE should NOT forbid
>>> this?
>>>
>>>
>>>
>>>                     Based on your GitHub discussion, my understanding is
>>>             that you
>>>                     want to
>>>                     allow to include RTP-specific parameters
>>>             (‘rtcp-mux’, ‘rtcp’,
>>>                     ‘rtcp-mux-only’ attributes etc) in the data m=
>>> section.
>>>
>>>
>>>
>>>                     To repeat what I said on GitHub:
>>>
>>>
>>>
>>>                     This has been discussed in the past, and the outcome
>>>             has been to now
>>>                     allow RTP-specific parameters in non-RTP m= sections.
>>>
>>>
>>>
>>>                     A solution would be to simply change the bundle tag
>>>             when the RTP m=
>>>                     sections are added.
>>>
>>>
>>>
>>>                     …OR, we change the mux category for the RTP-specific
>>>             parameters.
>>>                     But,
>>>                     that of course means they have to be added to every
>>>             RTP m= section.
>>>
>>>
>>>
>>>                     Regards,
>>>
>>>
>>>
>>>                     Christer
>>>
>>>
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>>>
>>>
>>>
>>>
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>>>
>>
>