Subject: [dispatch] Stephen Farrell's Yes on charter-ietf-perc-00-03: (with COMMENT)

From: "Stephen Farrell" <[email-masked]>
Date: Fri, 05 Jun 2015 06:22:06 -0700

Stephen Farrell has entered the following ballot position for
charter-ietf-perc-00-03: Yes

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The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/charter-ietf-perc/

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COMMENT:
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This is a good thing. I have a few non-blocking questions. It's
fine if those are answered now or during external review.

- I think I'm fine with the WG figuring this out but do we have
any current view as to how much metadata has to be visible to 
the media distribution devices?

- does "source authentication" here really mean identifying 
the source (e.g. as a person/user) or simply as a valid 
participant in the conference (e.g. via possession of some
key shared by the UAs and the media distribution device)?

- What does "implementable by" SIP and WebRTC mean? Do you
mean a single call with both kinds of UA present or not?

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From: Magnus Westerlund <[email-masked]>
Date: Mon, 8 Jun 2015 13:59:04 +0200

Hi Stephen,

An attempt to answer your comments and questions.

> https://datatracker.ietf.org/doc/charter-ietf-perc/

There has been some work ongoing also on this. For voice activity based 
switching, at minimal something like the client to mixer audio levels 
(RFC6464) will be needed.

To be able to determine where it is appropriate to perform an actual 
switch for media encodings with long prediction chains, like video, 
there is a draft for an header extension for frame markings:
https://datatracker.ietf.org/doc/draft-berger-avtext-framemarking/

> key shared by the UAs and the media distribution device)?

It means at a minimal to determine that the streams comes from a valid 
participant. As SRTP normally do not provide stronger guarantees, the 
only cipher for SRTP that can do more is TESLA based integrity checks 
defined in RFC 4383. However, my understanding is that it would be 
desirable to know which participant is the actual source of the content 
of an RTP stream. I think it should be a topic for the WG to discuss if 
the trade-offs for the security levels and decide on what is included in 
the solution.

> mean a single call with both kinds of UA present or not?

The solution proposals so far indicates a single solution for how to 
accomplish two tier of RTP payload data protection in SRTP. To that is 
the key-management solution. So far the discussed solutions are two 
components, one is the (likely EKT) method to provide (in-band) the 
actual transmission key used by a particular source for the inner 
security. The other part is how to key the other component with the 
necessary group key.

 From my perspective supporting the SRTP and EKT? parts in both types of 
end-points have no issues, thus enabling conference instances with both 
type of endpoints participating. For the master group key distribution 
there might exist reasons why that may differ between a SIP and WebRTC 
endpoint, but preferably they are common solutions. However, here I 
think the WG must be open and discuss how the integration of user 
authentication mechanism can occur, and the differences in server 
infrastructure for the relevant entities and what protocols are already 
in place.

I hope this helps

Cheers

Magnus Westerlund

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From: Stephen Farrell <[email-masked]>
Date: Mon, 08 Jun 2015 13:24:25 +0100

> An attempt to answer your comments and questions.

Tanks Magnus, those are good (enough:-) answers.

BTW - just to clarify in case it's useful - I interpret
the name of this WG and the charter to be implicitly
saying that the goal is to minimise the amount of data
(whether metadata or not) that is meaningful to the
media distribution device. If that's a bad assumption
then it'd probably be good to bottom out on that during
chartering. If it's a good assumption then maybe it's
something to consider being explicit about in the
charter. (Sorry, I forgot to say that in my initial
ballot.)

Cheers,
S.