Subject: [tsvwg] review of draft-ietf-tsvwg-sctp-dtls-encaps-00

From: Magnus Westerlund <[email-masked]>
Date: Wed, 20 Mar 2013 13:56:53 +0100

Hi,

I have reviewed the SCTP in DTLS encapsulation draft and have some
comments.

1. Abstract:
SCTP
   over DTLS is used by the RTCWeb protocol suite for transporting non-
   media data between browsers.

I think if one likes to include something like this in the abstract one
should word it like "An initial usage of ..."

2. Section 5.5:
   The SCTP implementation MUST support the extension defined in
   [RFC3758].

I wonder why this is required in a protocol encapsulation declaration?
This specification is from my perspective a common tool that anyone that
has similar requirements as WebRTC can choose to use. CLUE WG is clearly
one with high probability to have need for UDP/DTLS/SCTP. However, I
don't yet know if CLUE for example has any requirements that requires
partial reliability.

So please explain why mandating the partial reliability is necessary for
a DTLS encapsulation of SCTP. I think it is fine for the RTCWEB data
channel document to mandate the support of the PR-SCTP extension in the
context of WebRTC. But, please try to have the correct specifications in
the appropriate places.

3. Section 5.6:
The same as 2) appears to be true also here. Are there reasons why one
needs this extension when one uses the DTLS encapsulation?

4. Section 5.7:
To my understanding this is a pure performance enchancement. Thus I
wonder over the SHOULD level of an extension that yet not exist. I think
it is fine to indicate the issue. And if you actually have a draft ready
do an informative reference. But I do question the need for a normative
reference here. Isn't it better to let this specification be published
in a timely fashion?

5. Section 5.8:
Yet another case of a potential issue when running in common context
with real-time applications. This encapsulation does not in any way is
solely for real-time applications. Thus I think both using MAY is
unwarranted and I question how necessary this whole discussion are.

I think this document is suffering from an issue of not getting the
correct separation between the documents. This needs to specify the DTLS
encapsualtion of SCTP and what is needed. But I think is the wrong place
to have requirements on SCTP extensions that are specific in the context
of particular applications or class of applications. So please ensure
that you have the basics of the encapsulation in place, then ensure that
the extensions can be negotiated and allow the applications to make the
choices it needs on what features of SCTP it requires.

Cheers

Magnus Westerlund

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From: Michael Tuexen <[email-masked]>
Date: Sat, 23 Mar 2013 20:03:38 +0100

> reference here. Isn't it better to let this specification be published
I think this extension is really needed. In the meantime there is an
ID for it:
http://tools.ietf.org/html/draft-stewart-tsvwg-sctp-ndata-01
The document is not complete yet, but we plan to have it completed
and implemented by the IETF in Berlin...
> choices it needs on what features of SCTP it requires.
You are right. The document contains stuff which deals with
(a) generic SCTP over DTLS encapsulation and
(b) SCTP usage for RTCWeb.

I'm not sure if using SCTP over DTLS makes sense outside the RTCWeb scope.
For general usage, I would suggest to use SCTP over UDP...

So I guess you are you suggesting to move (b) into a different document.
Would make
http://wiki.tools.ietf.org/html/draft-ietf-rtcweb-data-channel-04
more sense for you?

Best regards
Michael

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From: Michael Tuexen <[email-masked]>
Date: Sun, 24 Mar 2013 19:27:30 +0100

> http://wiki.tools.ietf.org/html/draft-ietf-rtcweb-data-channel-04
What I missed... One possibility to make things clearer would be to
move all RTCWeb specific stuff into a separate section within the encaps
document. This would also make things clear. Would that be OK for you?

Best regards
Michael