Subject: [Tsvwg] Comments on: draft-ietf-tsvwg-rsvp-bw-reduction-01.txt

From: Bob Braden <[email-masked]>
Date: Thu, 8 Sep 2005 15:50:43 -0700 (PDT)

Hi.  I would like to comment on:

 	Title		: A Resource Reservation Protocol Extension for 
                          the Reduction of Bandwidth of a Reservation Flow
	Author(s)	: J. Polk, S. Dhesikan
	Filename	: draft-ietf-tsvwg-rsvp-bw-reduction-01.txt

Since it has a TSVWG file name, I assume it is a work item of TSVWG.

I suspect that this proposal is fundamentally flawed, at least in its
description of the problem.  It concerns the "priority" of RSVP
microflows, and cites Shai Herzog's RFC 3181.  However, note that 3181
does NOT talk about RSVP, and that there is no concept of flow
"priority" in RSVP itself.  Deliberately.  The priority of flows is a
higher-level notion that has no place in RSVP itself.  Thus, Herzog's
notion of priority is part of the policy mechanism, not part of TCP.

Layering and modularity in protocols matters.

Bob Braden

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From: Antonio De Simone <[email-masked]>
Date: Thu, 08 Sep 2005 20:37:19 -0400

Bob Braden wrote:

> The priority of flows is a
> higher-level notion that has no place in RSVP itself. 
>
Bob,

I don't know if draft-ietf-tsvwg-rsvp-bw-reduction-01.txt is a bad 
idea,  but I have heard many bad ideas on this topic.  I'd like to hear 
a good idea.  Do you have a notion of how priority of flows, which is, 
exactly as you say, a higher-level notion tied to policy and not to 
characteristics of the traffic, would be supported?

Tony

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From: Fred Baker <[email-masked]>
Date: Fri, 9 Sep 2005 10:12:59 -0700

I agree and I disagree.

As you say, RSVP applies no intrinsic policy to reservations - not  
even "is there enough bandwidth". It is a means by which a policy can  
be parameterized along a path and the policy applied.

What 3181 describes is the policy element that might be carried in  
the POLICY_DATA object (which is described in various sections of RFC  
2205 but left as a placeholder for future definition and was further  
described in RFCs 2750-2753 and further updated by 3181/3182) that  
assigns a reservation and a hold priority for a reservation, and  
which in turn be implemented under a policy that might include  
prioritization and preemption of reservations.

So, no, RSVP does not intrinsically describe policy. However, the  
information elements it carries have the capability of parameterizing  
a policy that a policy manager might then apply. And if the policy  
involves treating some reservations as more equal than others, those  
capabilities exist.