Subject: AW: [Simple] draft-ietf-simple-prescaps-ext-03 <notsupported>

From: "Beck01, Wolfgang" <[email-masked]>
Date: Mon, 21 Mar 2005 11:27:56 +0100

> I believe in most cases you can just leave not supported event
> packages out. It is probably true that use of <notsupported>
> is not that likely as use of <supported> but there are still
> use cases for that.
Could you give an example? If User Agent A wants to check if B 
supports event package xy, it can just look into <supported>.
If it's not there, B does not support xy.

If B's <notsupported> contains xy, the information is redundant
as xy is not in <supported>.

If B's neither <notsupported> nor <supported> do contain xy,
B is unlikely to support xy. Again, <notsupported> is redundant.

I was just checking the changes between -01 and -03 and found
that <notsupported> was introduced after -01 (btw a 'Changes
from draft-..-<version>' section would be nice).

Wolfgang

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From: Paul Kyzivat <[email-masked]>
Date: Mon, 21 Mar 2005 19:47:36 -0500

Wolfgang,

Prescaps is semantically related to callee-caps (relative to 
callerprefs). There is an explicit attempt to keep the two 
representations equivalent. In callerprefs, the matching algorithm for 
preferences vs capabilities is defined so that if a capability is not 
mentioned, then it matches both a preference for the capability and a 
preference against it.

So for instance, if you mention that you have a capability for audio, 
but say nothing about video, then you will match a caller with a desire 
for both audio and video.

The matching algorithm was originally defined for another purpose and 
then referenced from callerprefs. It is by no means a perfect solution, 
but there were competing objectives and that is where we ended up.

In prescaps there is no defined matching algorithm, but we still try to 
keep the meaning of the capabilities the same.

Yes, you can't enumerate all the things not supported, but when you do 
mention them it makes life better.

	Paul