Subject: [MMUSIC] Comments on draft-ietf-mmusic-sdp-capability-negotiation-06

From: Paul Kyzivat <[email-masked]>
Date: Sat, 21 Jul 2007 22:42:20 -0400

Flemming,

I have been studiously avoiding all the earlier versions of this draft, 
because it clearly required more bandwidth than I was prepared to 
devote. Now that it is almost done I decided to read it.

This is an impressive piece of work. You have managed to wedge a huge 
increase in functionality into a format that really isn't well suited to 
it. While the result is still ugly, in the context of SDP it is really 
quite elegant.

I was looking for issues in all the corners, but it seems somebody 
generally beat me to it, so almost all of the ones I thought I had found 
were covered by subsequent text.

I think I found one thing that wasn't covered:

> 3.7.3. Offerer Processing of the Answer
...
>         For each media description where the offerer included a potential
>         configuration attribute ("a=pcfg"), the offerer MUST first examine
>         the media description for the presence of an actual configuration
>         attribute ("a=acfg"). If an actual configuration attribute is not
>         present in a media description, then the offerer MUST process the
>         answer SDP for that media stream per the normal offer/answer rules
>         defined in [RFC3264]. ...

Something seems to be missing here.

If there is more than one media description in the answer, and one 
contains a=acfg and the other does not, then the one that does may cause 
a change in session level attributes, and that can affect the way the 
media description without a=acfg is processed.

There is text covering this for the offerer, but it is lacking here in 
the procedures for the answerer.

That is the only thing I could find. Congratulations!

	Thanks,
	Paul

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---

From: Flemming Andreasen <[email-masked]>
Date: Mon, 23 Jul 2007 14:29:27 -0400

Paul Kyzivat wrote:
> Flemming,
>
> I have been studiously avoiding all the earlier versions of this 
> draft, because it clearly required more bandwidth than I was prepared 
> to devote. Now that it is almost done I decided to read it.
>
> increase in functionality into a format that really isn't well suited 
> to it. While the result is still ugly, in the context of SDP it is 
> really quite elegant.
>
Thanks Paul, and thank you for doing a review.
> generally beat me to it, so almost all of the ones I thought I had 
> found were covered by subsequent text.
>
> contains a=acfg and the other does not, then the one that does may 
> cause a change in session level attributes, and that can affect the 
> way the media description without a=acfg is processed.
>
Good point. I will add a note pointing out this potential issue and 
noting that the session-level attribute added will apply to all the 
media descriptions, whether they used the capability negotiation 
framework or not.

> That is the only thing I could find. Congratulations!
Thanks

-- Flemming