Re: [clue] comment on conclusion 7 of the interim meeting report

Paul,
I think that the change I proposed is in-line with conclusion 9, where the
media started based on the first offer answer and the advertisement may be
done later.
 This is also the call flow in
http://tools.ietf.org/html/draft-romanow-clue-call-flow-02 .
Roni
-----Original Message-----
From: clue-bounces@ietf.org [mailto:clue-bounces@ietf.org] On Behalf Of Paul
Kyzivat
Sent: 09 October, 2012 5:55 PM
To: clue@ietf.org
Subject: Re: [clue] comment on conclusion 7 of the interim meeting report

Roni,

On 10/9/12 3:03 AM, Roni Even wrote:
> Hi
>
> 7) Empty Advertisement:  Is this allowed and what does it mean?
>
> Conclusion: Yes. It means you have nothing you are willing to send. 
> May also still want media in other direction.
>
> I think that the correct sentence is "It means you have nothing you 
> are willing to advertise". The SDP is still there and you can still 
> send media based on the SDP.

Hmm. I think what you say requires some discussion.

When a clue endpoint connects with another endpoint that doesn't support
clue it is clear that one should decide what to do based on the SDP in a
normal non-clue way.

But when both ends support clue and exchange advertisements it isn't clear
to me what should be done about stuff described in SDP that isn't negotiated
via the advertisements.

ISTM that there are different possible philosophies here, that we haven't
discussed, or even realized need to be discussed. Off the top of my head:

1) we could consider that advertisements and configurations provide the high
level view of the session, while the SDP provides a lower level mechanism to
support that and fill in details. There is a clear mapping from elements in
the configurations to elements in the SDP. The meaning of the SDP for proper
rendering can't be discerned from the SDP alone - the advertisement and
configuration are required to understand it. Any "extra" SDP that isn't
referenced from the advertisements and configurations then probably doesn't
apply to the telepresence session. 
It may be ignored, or else may relate to some other "application" 
sharing the same session.

2) we could consider that the negotiated SDP in the session is the primary
representation of the telepresence session. In principle this could be
sufficient without exchange of any advertisements and configurations.
Advertisements and configurations are exchanged to
*supplement* this - provide extra hints about what to do when the SDP itself
isn't sufficient, and also to provide hints about what SDP would be fruitful
to negotiate. Any SDP that isn't referenced by advertisements and
configurations should be taken at face value and fitted into the
telepresence session using local algorithms.

Frankly I had been thinking that (1) was the intended way. It wasn't until
your message that I realized there might be another view.

It seems to me that this needs careful consideration.

	Thanks,
	Paul

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