Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
Christian Groves <Christian.Groves@nteczone.com> Thu, 25 February 2016 23:09 UTC
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From: Christian Groves <Christian.Groves@nteczone.com>
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Subject: Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
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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. 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 >
- 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