Re: [clue] Subject matter for Monday's call

[Mary Barnes <[e-mail]>]

Hi all,

Per the meeting notes that were just posted, this proposal and
concepts will be incorporated into the WG framework document.   So, we
will revisit this topic in the context of the framework document
updates which will hopefully be out within the next couple weeks.

Regards,
Mary
CLUE WG co-chair

On Sat, Dec 1, 2012 at 10:56 AM, Stephan Wenger <[e-mail]> wrote:
> Hi all,
>
> Mark, Andy, and myself had a bit of brainstorming how to most productively
> use our time during the Monday morning call.  Due to travel and vacation
> schedule, our coordination was finalized call only late Friday.  Which may
> serve as an explanation, if not as an excuse, for the late timing of this
> email.
>
> In our opinion, the most pressing issue we have with the framework document
> is it being agnostic to the protocol elements used to convey the various
> messages that are part of the framework.  Clearly, the framework was written
> from a perspective where a CLUE protocol channel would be established, and
> (all?) further signaling would be dealt with over that channel.  So is, more
> or less, the call flow doc.  We believe that there was sufficient pushback
> against that idea to make rapid progress based on this assumption unlikely.
> Accordingly, we believe that we probably best spend most of our time by
> discussing a strawman for a split-up between SDP-represented, SIP-ish,
> Offer-Answer, …, that type of traditional messages, and (XML-coded) messages
> sent over the CLUE.  The focus of our Monday call would be on the initial
> exchange, rather than any updates that may happen during a call.
>
> With reference to the call flow 02 doc
> (https://datatracker.ietf.org/doc/draft-romanow-clue-call-flow/?include_text=1)
> that exchange could look as follows:
>
> Invite from Alice, just like A.1 in call-flow-02
> 200 OK from Bob, A.2
> CLUE Advertisement Alice A.3, covering geometry stuff, encoding groups, etc.
> CLUE Advertisement Bob A.4; note that 3 and 4 would in practice overlap in
> time
> CLUE Response from Alice A.5, with the difference that these reposes DO NOT
> have the side effect of initiating any media channel related activity; they
> are pure signaling
> CLUE Response from Bob, A.6, same remark.. 5 and 6 could overlap in time.
> Re-invite from Alice and Bob, respectively, with media channels as
> CLUE-"negotiated"
> 200 OK from Bob, Alice.  As the endpoints have already established their
> operation points through CLUE, this step will not fail except if an entity
> not involved in the CLUE negotiation intervenes—i.e. a middle box doesn't
> like that call.
>
> The reason for the existence of step 7, rather than setting up media
> channels as side effect of steps 3 through 6 (as assumed in call flow and in
> the current framework doc) is twofold: easier integration into the source
> base of media codecs that currently use SDP for the selection of their
> parameters, and making middlebox people happy.
>
> The reason for the existence of steps 3 through 6 is our agreement that not
> all useful protocol elements envisioned in the framework can be reasonably
> and meaningfully implemented in SDP extensions.  This is certainly true for
> the geometry stuff.
>
> The reason for keeping an encoding group concept in CLUE is that a
> representation of the information that can be conveyed through individual
> encoding descriptions, encoding groups, and the association of media
> captures with encoding groups (section 7 and 8 of the framework) purely
> through grouped m-lines would lead to bloated (if not exploded :-) SDP,
> quite possibly well beyond a reasonable size (i.e. MTU size); the high level
> of abstraction offered by concepts such as encoding groups, simultaneous
> transmission sets, and so on, makes for a very compact representation
> compared to listing all possible permutations of alternative choices in
> grouped m-lines.
>
> Does such a mechanism make at least initial sense?  Should it be fleshed out
> and put into the framework?
>
> Stephan
>
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