Subject: Re: question: DiffServ versus RSVP

From: jie yang ee stnt <[email-masked]>
Date: Thu, 14 Sep 2000 21:18:21 -0400 (EDT)

David, 
your comments do make sense. 
But, do you mean,the
only point in common for different diffserv providers is that they merge 
flows into different classes? how they merge flows, what kind of QoS they can
provide on each class may be quite different from provider to provider. 
Right? 
I am doubting whether diffserv could offer QoS that meets various end-to-end 
requirements. I was thinking the possibility that at edge router we apply
Interserv mechanisms which is based on flow and at core router we 
use diffserv which is based on class. I doubt, since diffserv is a kind
of coarse grain flow management, it is not easy to guarantee per-flow QoS as
many applications require, if not impossible. 
Jie

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From: David Charlap <[email-masked]>
Date: Fri, 15 Sep 2000 08:31:52 -0400

jie yang ee stnt wrote:
> 
> But, do you mean,the only point in common for different diffserv
> providers is that they merge flows into different classes? how they
> merge flows, what kind of QoS they can provide on each class may be
> quite different from provider to provider.
> Right?

Correct.

If two providers choose to use different QoS levels for different
DiffServ classes, then (hopefully), they should change the DiffServ
values as packets cross from one administrative domain to another.

If they don't, then the QoS values for the classes will change over the
path of the packet.

> I am doubting whether diffserv could offer QoS that meets various
> end-to-end requirements.

It doesn't.  And it isn't meant to.

> I was thinking the possibility that at edge router we apply Interserv
> mechanisms which is based on flow and at core router we use diffserv
> which is based on class. I doubt, since diffserv is a kind of coarse
> grain flow management, it is not easy to guarantee per-flow QoS as

If you need end-to-end per-flow reservations, then you need something
bigger than DiffServ.

MPLS is one possibility.  Another is IP over ATM or Frame Relay. 
Another is to use hop-by-hop routers that can make reservations.

Setting up the QoS levels for such a network can be done through
configuration, management, or signalling.

-- David

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From: Lloyd Wood <[email-masked]>
Date: Fri, 15 Sep 2000 13:38:22 +0100 (BST)

> If they don't, then the QoS values for the classes will change over the

If they do, the QoS values can still be altered as the mappings
between different sets of classes defining different classes are
imperfect, and downstream degradation results.

> If you need end-to-end per-flow reservations, then you need something

you mean edge-to-edge there, surely?

L.

> configuration, management, or signalling.

<[email-masked]>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>