Re: FW: Issue #27: Allow RTP attributes in non-media m= sections
Eric Rescorla <[email protected]>
| Newsgroups | gmane.ietf.mmusic |
|---|---|
| Message-ID | <CABcZeBMWexaQ37-TOC-6efSCFmXjDOaf2t6Lhzep+X1+gcy5UQ@mail.gmail.com> |
On Sat, Feb 18, 2017 at 1:38 PM, Paul Kyzivat <[email protected]> wrote: > On 2/18/17 1:45 PM, Eric Rescorla wrote: > >> >> >> On Sat, Feb 18, 2017 at 8:09 AM, Paul Kyzivat <[email protected] >> <mailto:[email protected]>> 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:[email protected] >> <mailto:[email protected]>] >> Sent: 17 February 2017 18:51 >> To: Taylor Brandstetter <[email protected] >> <mailto:[email protected]>> >> Cc: Christer Holmberg <[email protected] >> <mailto:[email protected]>>; IETF MMUSIC WG >> <[email protected] <mailto:[email protected]>> >> 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 >> <[email protected] <mailto:[email protected]> >> <mailto:[email protected] >> >> <mailto:[email protected]>>> 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:[email protected] >> <mailto:[email protected]> >> <mailto:[email protected] >> <mailto:[email protected]>>] *On Behalf Of *Christer >> Holmberg >> *Sent:* 16 February 2017 19:07 >> *To:* Eric Rescorla <[email protected] >> <mailto:[email protected]> <mailto:[email protected] >> <mailto:[email protected]>>>; mmusic >> WG <[email protected] <mailto:[email protected]> >> <mailto:[email protected] <mailto:[email protected]>>> >> >> *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 >> >> >> _______________________________________________ >> mmusic mailing list >> [email protected] <mailto:[email protected]> >> <mailto:[email protected] <mailto:[email protected]>> >> https://www.ietf.org/mailman/listinfo/mmusic >> <https://www.ietf.org/mailman/listinfo/mmusic> >> <https://www.ietf.org/mailman/listinfo/mmusic >> <https://www.ietf.org/mailman/listinfo/mmusic>> >> >> >> >> >> _______________________________________________ >> mmusic mailing list >> [email protected] <mailto:[email protected]> >> https://www.ietf.org/mailman/listinfo/mmusic >> <https://www.ietf.org/mailman/listinfo/mmusic> >> >> >> > _______________________________________________ mmusic mailing list [email protected] https://www.ietf.org/mailman/listinfo/mmusic