Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
Paul Kyzivat <pkyzivat@alum.mit.edu> Thu, 25 February 2016 23:44 UTC
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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Thu, 25 Feb 2016 18:44:22 -0500
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Subject: Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
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On 2/25/16 6:09 PM, Christian Groves wrote: > Hello Paul, > > How about an update to draft-ietf-mmusic-rfc4566bis clause 5.14 (or > 8.2.2)? This is the document that defines the PROTO field in the first > place. That would be good, and possible since the bis is still in progress. The hard part is figuring out what it should say! For instance, consider UDP/DTLS/SCTP: what is the sub-protocol? Is it SCTP, or DTLS/SCTP? Or both? Is DTLS a sub-protocol? And note that this is somewhat confusing, since in typical protocol stack diagrams the sub-protocol is at the *top* and is considered to run at a higher level in the "stack". Of course this is all just a matter of definition. But I expect there might be a lot of opinions on it. Thanks, Paul > Regards, Christian > > On 26/02/2016 8:38 AM, Paul Kyzivat wrote: >> On 2/24/16 7:24 PM, Christian Groves wrote: >>> 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. >> >> My concern is that SDP has no notion of subprotocol, even though in >> practice it shows up lots of places. It only has a notion of the >> protocol field in the m-line. Beyond that a *convention* has developed >> to denote a layering within the protocol through use of "/". AFAIK >> this isn't formally written down anywhere. >> >> So, in principle we could define an RTP sub-protocol for use over a >> data channel. And then we could talk about using the attributes that >> apply to RTP in dcsa for a channel using RTP. But note there is no >> formal definition of the *protocol*s where RTP attributes are relevant. >> >> A lot of the very old stuff was just sloppy. To be fair, it was >> probably good enough for the cases in front of them at the time, and >> they weren't yet in a position to foresee how things would evolve. It >> is just another example of how old stuff rots and has to be refreshed >> from time to time. >> >> But I don't think *this* draft is the place to fix it. So, in lieu of >> doing that I'm just looking for some way to clarify things. >> >> Thanks, >> Paul >> >> _______________________________________________ >> mmusic mailing list >> mmusic@ietf.org >> https://www.ietf.org/mailman/listinfo/mmusic >> > > _______________________________________________ > 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