Subject: [Sipping] Comment on draft-hilt-sipping-session-spec-policy

From: "Medhavi Bhatia" <[email-masked]>
Date: Thu, 10 Mar 2005 11:30:52 -0500

I don't think we discussed this draft today in the meeting.

Here is a quick question: How does the SIP Proxy (P A) know that the client
(UA A) has applied the session specific policy (which may be different from
one session to another originated by UA A).

-Medhavi.

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From: David R Oran <[email-masked]>
Date: Thu, 10 Mar 2005 12:25:07 -0500

On Mar 10, 2005, at 11:30 AM, Medhavi Bhatia wrote:

> I don’t think we discussed this draft today in the meeting.
>
>  
>
> Here is a quick question: How does the SIP Proxy (P A) know that the 
> client  (UA A) has applied the session specific policy (which may be 
> different from one session to another originated by UA A).
>
It doesn't and it doesn't need to. All the proxy needs to do is to 
enforce whatever policy it has been configured to enforce. If there's a 
mismatch with what the UA did because either the UA did not support 
policy, ignored policy, or the policy server was mis-configured is not 
the proxy's problem.

Policy is the way to let the UA know what's likely to work so it can 
avoid trying things that will fail and winding up having to guess its 
way through a complicated parameter space.

Dave.

> -Medhavi.
David R. Oran
Cisco Fellow
Cisco Systems
7 Ladyslipper Lane
Acton, MA 01720 USA
Tel: +1 978 264 2048
Email: [email-masked]

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From: "Medhavi Bhatia" <[email-masked]>
Date: Thu, 10 Mar 2005 14:24:43 -0500

> way through a complicated parameter space.
Ok. That makes sense. I think I got confused when I saw COPS listed as one
of the options for the protocol selection. The slides Volker had listed the
UA as a PEP in the COPS situation, and that is really not the case here. The
enforcement is done outside. Maybe COPS should not be evaluated as an option
because of this reason itself. 

Some of the discussion in the mtg also revolved around CAC, which is really
an enforcement thing. I understand that session policy is quite limited and
you can avoid the enforcement only when some implicit trust can be assumed
between the client and the proxy/policy server.

-Medhavi.

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From: Volker Hilt <[email-masked]>
Date: Thu, 10 Mar 2005 13:45:03 -0600

> because of this reason itself. 
The slides listed the options that were proposed in emails and 
discussions. I agree with you that COPS is probably not a great match 
and nobody in the meeting has argued for using it (so I think its off 
the table).

> between the client and the proxy/policy server.
If your network gets close to loaded, you could e.g. use session 
policies to tell the UAs to switch to low bandwidth codec or stop using 
this high-bandwidth video stream.

However, as Oran had already mentioned, session policies are not for 
enforcing policies. The goal is to tell the UA what's going on in the 
network or what it needs to do to be able to communicate. This enables 
the UA to make an informed decision and successfully set up a session.

Thanks,

Volker