Re: [Sipping] [RAI] draft-ietf-sipping-media-policy-dataset: The implied boolean logic of policy operations

["Worley, Dale R (Dale)" <[e-mail]>]

Gonzalo Camarillo [[e-mail]] writes:
> >    o  The different <stream> elements in a session-policy are
> >       effectively ORed together, in that the policy intends to permit
> >       any stream that conforms to *any one* of the <stream> elements.
> >       This is necessary because e.g. a session-policy can contain one
> >       <stream> that specifies audio media and restricts the codecs
> >       permitted for audio, and another <stream> that specifies video
> >       media and restricts the codecs permitted for video.
> 
> When policies apply to different aspects (e.g., video codecs and audio
> codecs), this is true. However, if different policies apply to the same
> aspect, they need to be merged. And when merging the policies, the
> resulting stream needs to be compliant to all policies (i.e., an AND
> operation). For example, if one policy allows codecs 0 and 8 and another
> only allows 8, the resulting policy is to only use codec 8. If a policy
> allows only codec 0 and another policy only allows codec 8, the result
> is a null session. I am not sure if this is what you are saying above
> (and below in the rest of the section), though.

I'm not sure I'm understanding you completely here.  And it's possible
that we aren't talking about exactly the same thing.

Let me recap my opinion:

- When there are two <stream> elements in *one* session-policy, then
the intention is to OR the specified restrictions:  a stream that
conforms to any one of the <stream> elements is premitted.

- When we "merge" *two* session-policy's, that is an AND, in that the
stream is subject to the restrictions of each session-policy
seperately.

So within one session-policy, one could have a <stream> element that
specifies the allowed audio codecs, and another <stream> element that
specifies the allowed video codecs, because an SDP stream that
conforms to *either* <stream> element would be allowed.  Thus, if one
<stream> allows codec G.729 and another <stream> allows codec G.711,
then either codec could be used in a stream.

But if one is "merging" two session-policy's, an audio stream would
only be acceptable to the resulting merged session-policy if its
codecs conformed to the limitations in both original ession-policy's.
Thus, if one session-policy allows codec G.729 and the other
session-policy allows codec G.711, then no codec could be used in an
audio stream.

Dale