Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
Christian Groves <Christian.Groves@nteczone.com> Thu, 25 February 2016 00:24 UTC
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From: Christian Groves <Christian.Groves@nteczone.com>
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Date: Thu, 25 Feb 2016 11:24:33 +1100
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Subject: Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
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Hello Juergen and Paul, Please see at end. Regards, Christian On 24/02/2016 8:26 AM, Paul Kyzivat wrote: > ..snip.. >> >> 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. [CNG] I don't see what the example buys? I don't see that the behaviour is any different between using additional attributes in the datachannel vs. the non data channel case. E.g. for c=IN IP4 10.10.10.1 m=message 7394 TCP/MSRP * a=accept-types:message/cpim text/plain text/html a=lang:.... a=framerate:... The ignore behaviour would be the same. In the above example the attributes are scoped by the m= line. In the data channel case the attributes are scoped by the relevant a=dcmap: line. Regards, Christian > > Thanks, > Paul > > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic >
- 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