Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
Paul Kyzivat <pkyzivat@alum.mit.edu> Tue, 23 February 2016 21:26 UTC
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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Tue, 23 Feb 2016 16:26:07 -0500
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Subject: Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
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Hi Juergen, See response at end. On 2/23/16 8:29 AM, Juergen Stoetzer-Bradler wrote: > Hi Paul, > > Thanks for your feedback to the updates in version 08. > Please find my remarks inserted below your comments. > > Thanks, > Juergen > > > On 19.02.2016 17:42, EXT Paul Kyzivat wrote: >> On 2/17/16 8:12 AM, Juergen Stoetzer-Bradler wrote: >>> Hi Paul, Christian, Flemming, Bo, >>> >>> Have just submitted version 08 of draft-ietf-mmusic-data-channel-sdpneg. >>> The changes compared to version 07 are essentially as follows. >>> >>> * Two new paragraphs in section 5.1.2.1 (dcsa Attribute) regarding the >>> relationship of subprotocols and their attributes. >>> * Two new SDP offer/answer considerations in section 5.2.5 (Various >>> SDP Offer/Answer Scenarios and Considerations) regarding unknown >>> subprotocol attributes or known subprotocol attributes, whose data >>> channel transport specific semantic is not known. >>> * A new paragraph in section 8.1 (IANA Considerations / Subprotocol >>> Identifiers) related to cases, where a subprotocol is defined for data >>> channel and Websocket transport. >>> >>> These changes should address the points discussed in this email thread. >> >> This is an improvement. But I think things could still be made clearer. >> >> Consider the following addition to 5.1.2.1: >> >> It is assumed that in general the usages of subprotocol related media >> level attributes are independent from the subprotocol's transport >> protocol. Such transport protocol independent subprotocol related >> attributes are used in the same way as defined in the original >> subprotocol specification, also if the subprotocol is transported >> over a data channel and if the attribute is correspondingly embedded >> in a "a=dcsa" attribute. >> >> There may be cases, where the usage of a subprotocol related media >> level attribute depends on the subprotocol's transport protocol. In >> such cases the subprotocol related usage of the attribute is expected >> to be described for the data channel transport. A data channel >> specific usage of a subprotocol attribute is expected to be specified >> in the same document, which registers the subprotocol's identifier >> for data channel usage as described in Section 8.1. >> >> This text makes sense when there is a clear distinction between >> subprotocol and protocol. Unfortunately, the way SDP has evolved there >> is no such clear distinction in many cases, such as RTP over UDP or >> TCP, etc. Those are combined into a single protocol value. While that >> can usually be parsed apart at slashes, there isn't good terminology >> for it. >> >> My point is that when I read the above, I don't know how it applies >> to, say, RTP attributes. Or does it only apply for attributes that are >> clearly defined for a *sub*protocol? >> >> I think this is primarily that we lack well defined vocabulary for all >> of this. But I think it would be too much to expect this draft to >> *solve* the vocabulary problem. In lieu of doing so, maybe it would be >> sufficient to give some concrete examples, even if they have to be >> hypothetical ones. > > [Juergen] Agree that it would be helpful to have more precise > definitions of the differences of the terms protocol and subprotocol, > especially when those terms are used outside the scope of data channels > (or Websockets). When only focusing on data channels the notion of a > "subprotocol" seems to be clearer - at least > draft-ietf-rtcweb-data-protocol explicitly refers to the "WebSocket > Subprotocol Name Registry" when specifying DCEP's "Protocol" parameter. > (But draft-ietf-rtcweb-data-channel does not define what a data > channel's "subprotocol" is.) So far the sdpneg draft relatively > informally starts using the term "subprotocol" in the introduction and > there refers to Websocket "subprotocols". Perhaps we should add the term > "subprotocol" to the list of used terminology in section 3. > > The sdpneg document, together with the data channel subprotocol specific > document (which defines the value of the a=dcmap attribute's > "subprotocol" parameter), should certainly give clear guidance on how to > interpret SDP offers or answers like e.g.: > > m=application 10001 UDP/DTLS/SCTP webrtc-datachannel > c=IN IP4 10.10.10.1 > a=max-message-size:100000 > a=sctp-port:5000 > ... > a=dcmap:0 subprotocol="MSRP" > a=dcsa:0 accept-types:message/cpim text/plain > a=dcsa:0 framerate:... > a=dcsa:0 lang:... > > An implementation receiving such an offer would need to decide what to > do with the dcsa embedded framerate and lang attributes. Or, someone > implementing MSRP over data channel based services may need to decide > whether or not to use these attributes, and if yes, how. > (I am using these two attributes just as hypothetical examples - don't > want to suggest that those may indeed be used for MSRP over data channel > transport). > > The msrp-usage-data-channel document doesn't mention these two > attributes. When looking at the IANA SDP attribute registry tables, I > would find both attributes specified in RFC 4566. There, "framerate" is > explicitly said to be defined only "for video media". Just to be sure I > could additionally have a look at the MSRP specifying documents, RFC > 4975 and RFC 4976, but there would not find any text at all related to > "framerate". So this case seems pretty clear and I would therefore > conclude that the "framerate" attribute should not be used for MSRP, and > that a receiver of such an offer or answer should ignore it. > > When looking at the definition of the "lang" attribute in RFC 4566 I > would not see any explicit hint of what protocols this attribute might > be used with, especially if "lang" could be used when negotiating an > MSRP session. When then looking at RFC 4975 I would indeed find "lang" - > but not as SDP attribute, rather as XML tag parameter within an example > MSRP message payload. Thus, the case of the "lang" attribute might not > be as unambiguous as the one with the "framerate" attribute, but here > too I think the typical choice would be to ignore that attribute when > receiving such an offer or answer. > It seems to me that the two new "ignore" rules in section 5.2.5 of > sdpneg-08 may also be applied in these cases. > > Admittedly, these examples may seem a bit far-fetched, but would those > go into the direction you had in mind? Yes. Note that using examples is just me grasping at straws, since a real solution looks like to big a problem for this draft to tackle by itself. I am entirely open to other ideas for how to deal with this. Thanks, Paul
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-… Bo Burman
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… DRAGE, Keith (Keith)
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… DRAGE, Keith (Keith)
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Schwarz, Albrecht (Nokia - DE)
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Christian Groves
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Flemming Andreasen
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Juergen Stoetzer-Bradler
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat
- Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-chan… Paul Kyzivat