[MMUSIC] Comments on draft-pthatcher-mmusic-rid-00
Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 05 October 2015 16:25 UTC
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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Mon, 05 Oct 2015 12:22:29 -0400
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Subject: [MMUSIC] Comments on draft-pthatcher-mmusic-rid-00
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Here are some comments on draft-pthatcher-mmusic-rid-00 that I made during my initial reading: * Section 6: All of the parameters mentioned pertain to video. Perhaps it should be mentioned that these must only be used with compatible codecs. This is hinted at in section 7.2.2, but isn't very explicit. It might also be good to mention that parameters meaningful for non-video codecs may be defined in the future. In addition to the parameters listed here, there is another ('depend') that is mentioned in a few places. The closest thing to a real definition of the semantics of if are in section 10.3. I think there ought to be an explicit definition of it here - or at least a mention with a cross reference to the section where it is defined. * Section 7.2.2: Bullet 2 requires that any pt mentioned in a=rid must also be mentioned in an a=rtpmap or a=fmtp attribute. Did you intend to exclude the use of default PTs - that generally work without rtpmap or fmtp? Wouldn't it be better here to simply require that the PT in the rid line also be mentioned in the m-line? (I realize that default PTs are only for audio, and there is currently no need for rid with audio, but that might not always be the case.) * Section 7.3: Each rid line in the offer has a direction of send or recv. Presumably that is from the perspective of the sender of the sdp. I would expect (and the examples show) that in the answer each send would be changed to recv and visa versa. But this isn't mentioned. In the case of errors, the rule is to omit the rid line for the rid in the answer. The effect of this is to process the media stream as if there were no rid constraints. It might be good to mention that if the answerer doesn't want to handle the media stream, or the specific PTs involved, without any rid constraints, then it should reject the m-line, or omit the affected PTs from the m-line in the answer. rid-fmt allows the general 'fmt' syntax from 4566. That allows non-numeric values for non-rtp transports, but requires numeric PT values for RTP. Since rid applies only to RTP, the syntax here could be restricted to numeric PT formats. * Section 9: This doesn't quite conform to the pattern introduced in rfc4566bis. (It is not good to include "a=" in the syntax definition for individual attributes.) I suggest replacing the rid-syntax line with: rid-value = rid-identifier SP rid-dir SP rid-fmt-list SP rid-attr-list (And also see my comment on section 12.2.) The syntax of rid-identifier permits '-----', '-_" and other similar non-human-friendly identifiers. It might be good to limit this (for readability). E.g. rid-identifier = 1*alpha-numeric *(("-" / "_") 1*alpha-numeric) The 'pt=' is entirely redundant. (The rid-fmt-list can be identified positionally.) Why is it there? There seems to be some ambivalence in the text whether you are defining rid *attributes* or rid *parameters. In section 6 they are called parameters. Here there is a rid-attr-list but the elements of the list are called rid-xxx-param. Can you please decide on one term for these that stick to it? * Section 10.*: The a=rid lines in most/all of the examples are inconsistent with the syntax. E.g. The following: a=rid:1 send pt=*; max-width=1280; max-height=720; max-fps=30 ought to be: a=rid:1 send pt=* max-width=1280;max-height=720;max-fps=30 * Section 10.1: This example shows that the proposed mechanism isn't ideal for this case. There are a *lot* of duplicated sdp lines devoted to specifying the identical attributes for multiple rid values. It seems like there ought to be syntax to avoid that redundancy. * Section 12.2: This doesn't quite conform the the pattern introduced in rfc4566bis. I suggest the following: This document defines "rid" as SDP media-level attribute. The "rid" attribute is used to identify characteristics of RTP stream with in a RTP Session. Name: rid Value: rid-value Usage Level: media Charset Dependent: possibly This attribute is generally not charset dependent. However individual rid-level-attributes may be defined to be charset dependent. Syntax: See section 9. Example: a=rid:1 send pt=* max-width=1280;max-height=720;max-fps=30 * Section 12.3: I'm still unclear of the relationship between rid-level attributes and other (session/media) attributes. Those others, regardless of the levels they apply to, belong to a single namespace. Do rid attributes occupy another level within the same namespace, or do they define a new namespace? If they occupy a new namespace, it would be valid to define a rid-level attribute with the same name as (for example) a media-level attribute. That would be very confusing. Thanks, Paul On 10/2/15 6:48 PM, Suhas Nandakumar wrote: > Hello All > > As indicated by Adam in his email , we have submitted the draft > defining "RID". > > The draft can be found here: > https://datatracker.ietf.org/doc/draft-pthatcher-mmusic-rid/?include_text=1 > > Please provide your feedback on the same. > > Thanks > Suhas
- [MMUSIC] Simulcast: Short timelines, draft impend… Adam Roach
- Re: [MMUSIC] Simulcast: Short timelines, draft im… Harald Alvestrand
- Re: [MMUSIC] Simulcast: Short timelines, draft im… Byron Campen
- Re: [MMUSIC] Simulcast: Short timelines, draft im… Suhas Nandakumar
- [MMUSIC] Comments on draft-pthatcher-mmusic-rid-00 Paul Kyzivat
- Re: [MMUSIC] Simulcast: Short timelines, draft im… Flemming Andreasen
- Re: [MMUSIC] Simulcast: Short timelines, draft im… Magnus Westerlund
- Re: [MMUSIC] Simulcast: Short timelines, draft im… Flemming Andreasen
- Re: [MMUSIC] Comments on draft-pthatcher-mmusic-r… Byron Campen
- Re: [MMUSIC] Comments on draft-pthatcher-mmusic-r… Byron Campen
- Re: [MMUSIC] Comments on draft-pthatcher-mmusic-r… Byron Campen