Re: [MMUSIC] New Version Notification for draft-ietf-mmusic-data-channel-sdpneg-05.txt

Christian Groves <Christian.Groves@nteczone.com> Wed, 21 October 2015 15:02 UTC

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From: Christian Groves <Christian.Groves@nteczone.com>
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Date: Wed, 21 Oct 2015 17:01:51 +0200
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Subject: Re: [MMUSIC] New Version Notification for draft-ietf-mmusic-data-channel-sdpneg-05.txt
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Hello Juergen,

Sorry for the slow reply. Its OK with me.

Regards, Christian

On 9/10/2015 2:54 PM, Juergen Stoetzer-Bradler wrote:
> Hello Paul, Christian,
>
> Thank you for your feedback.
>
> I was indeed much focused on the WebRTC data channel protocol stacks 
> (SCTP over DTLS) when writing the mux category sections for dcmap and 
> dcsa.
> My reading of draft-ietf-rtcweb-data-channel-13 (e.g. sec 6.1) is that 
> DTLS transport of SCTP must actually be used.
> However, in order not to explicitly restrict potential future usage of 
> the dcmap and dcsa attributes to x/DTLS/SCTP m-lines I'd propose to 
> modify the text in section
> 5.1.1.2 as follows. (And correspondingly to also modify the dcsa 
> related text in 5.1.2.2.)
>
> Would you agree to following wording?
>
> 5.1.1.2. dcmap Multiplexing Category
>    Multiplexing characteristics of SDP attributes are described in
>    [I-D.ietf-mmusic-sdp-mux-attributes].  Various SDP attribute
>    multiplexing categories are introduced there.
>
>    The multiplexing category of the "a=dcmap:" attribute is SPECIAL.
>
>    As the usage of multiple SCTP associations on top of a single DTLS
>    connection is outside the scope of [I-D.ietf-mmusic-sctp-sdp], no
>    "a=dcmap:" attribute multiplexing rules are specified for the 
> UDP/DTLS/SCTP
>    and TCP/DTLS/SCTP proto values.
>    This document also does not specify multiplexing rules for this 
> attribute
>    for SCTP or SCTP/DTLS proto values.
>    If future extensions of [I-D.ietf-mmusic-sctp-sdp] define how to 
> negotiate
>    multiplexing of multiple SCTP associations of top of a single DTLS 
> connection
>    or how to multiplex multiple SCTP associations within one BUNDLE group,
>    then multiplexing rules for the "a=dcmap:" attribute need to be 
> defined as
>    well, for instance in an extension of this SDP based data channel
>    negotiation specification.
>
>
> Thanks,
> Juergen
>
> On 09.10.2015 05:17, Christian Groves wrote:
>> Hello Juergen and Paul,
>>
>> You're updates look OK to me. I think this is ready for WGLC.
>>
>> Please see below.
>>
>>>>>
>>>>> Also, saying this is *only applicable* unnecessarily blocks future
>>>>> changes. I think it would be better to say *only defined*, or 
>>>>> *outside
>>>>> the scope*.
>>>> [Juergen] Agree. How about the following?
>>>> "This document defines usage of this attribute only when associated 
>>>> with
>>>> UDP/DTLS/SCTP or TCP/DTLS/SCTP proto SDP "m" lines".
>>>
>>> Ahh! I think we disagree on what the scope of this draft should be.
>>>
>>> draft-ietf-mmusic-sctp-sdp defines several transport configurations 
>>> for sctp: SCTP, SCTP/DTLS, UDP/DTLS/SCTP, TCP/DTLS/SCTP.
>>>
>>> draft-ietf-rtcweb-data-channel defines data channels over sctp, but 
>>> doesn't anything about allowed transport configurations of sctp.
>>>
>>> Elsewhere webrtc specifies that only UDP/DTLS/SCTP and TCP/DTLS/SCTP 
>>> are to be used for webrtc data channels.
>>>
>>> I guess this draft is trying to restrict its applicability to only 
>>> UDP/DTLS/SCTP and TCP/DTLS/SCTP. I see no reason to do that. This 
>>> draft defines the dcmap and dcsa attributes. AFAIK there is 
>>> *nothing* that prevents using data channels and these attributes 
>>> over SCTP or SCTP/DTLS. That ought to be allowed and covered by this 
>>> document.
>>>
>>> Multiplexing in bundles is a different matter. As you point out, use 
>>> in bundles is not defined for SCTP and SCTP/DTLS, while 
>>> UDP/DTLS/SCTP and TCP/DTLS/SCTP can appear at most once in a bundle. 
>>> So multiplexing of these attributes in bundles is currently 
>>> undefined. This needs to be noted (and left for future work), but 
>>> without excluding *unbundled* use with the other transports.
>>
>> Do we really need to extend the scope to SCTP or SCTP/DTLS? The 
>> mechanism is clearly related to the use of WebRTC data channel. Is 
>> SCTP and SCTP/DTLS going to be used for data channel in the future? 
>> There is "something" preventing data channels being used on SCTP or 
>> SCTP/DTLS its draft-ietf-rtcweb-data-channel which clearly shows the 
>> stack as UDP/DTLS/SCTP and TCP/DTLS/SCTP.
>>
>> Regards, Christian
>>
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>
>
>
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