Re: FW: Issue #27: Allow RTP attributes in non-media m= sections
Christer Holmberg <[email protected]>
| Newsgroups | gmane.ietf.mmusic |
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| Message-ID | <D4EEEFE6.19C62%[email protected]> |
Hi, Nobody has objected to this, so assuming we are moving forward with this I am not sure there is anything to discuss in Chicago? Regards, Christer From: Eric Rescorla <[email protected]<mailto:[email protected]>> Date: Monday 27 February 2017 at 16:32 To: Christer Holmberg <[email protected]<mailto:[email protected]>> Cc: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>>, Taylor Brandstetter <[email protected]<mailto:[email protected]>>, "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Subject: Re: [MMUSIC] FW: Issue #27: Allow RTP attributes in non-media m= sections Yes, I think we do On Mon, Feb 27, 2017 at 5:10 AM, Christer Holmberg <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> Date: Sunday 19 February 2017 at 00:28 To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Cc: Christer Holmberg <[email protected]<mailto:[email protected]>>, Taylor Brandstetter <[email protected]<mailto:[email protected]>>, "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[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]> <mailto:[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]> <mailto:[email protected]<mailto:[email protected]>>] Sent: 17 February 2017 18:51 To: Taylor Brandstetter <[email protected]<mailto:[email protected]> <mailto:[email protected]<mailto:[email protected]>>> Cc: Christer Holmberg <[email protected]<mailto:[email protected]> <mailto:[email protected]<mailto:[email protected]>>>; IETF MMUSIC WG <[email protected]<mailto:[email protected]> <mailto:[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]>> <mailto:[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]>> <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]>> <mailto:[email protected]<mailto:[email protected]> <mailto:[email protected]<mailto:[email protected]>>>>; mmusic WG <[email protected]<mailto:[email protected]> <mailto:[email protected]<mailto:[email protected]>> <mailto:[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]>> <mailto:[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]> <mailto:[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