Subject: Re: [Diffserv] Questions regarding PDBs

From: "Mohamed El Gendy" <[email-masked]>
Date: Tue, 15 May 2001 00:31:53 +0300

Brian,

Thank you for your answer, but:

>If you run an MF classifier at the ingress to the second domain, then
>it can classify f1 and f2 differently. Of course, by definition a BA
>classifier cannot distinguish f1 from f2.
>

If I am going to use MF classifier to separate these two flows it means that 
I am doing a "per-flow" processing in a point, Ingress of a DS domain, where 
I should use only BA classification. I think this the heart of DiffServ, not 
to deal with "per-flow" except at the very edges of the network not between 
DS domains which might be in the center of the network. I don't mean "core"!

>Firstly please refer to RFC 3086 which is the final document. > > >Secondly 
>the
>text does not say "should", it says "the transit performance of >traffic 
>aggregates of
>these PDBs will, of necessity, be the same." This is a mathematical >fact - 
>if two
>PDBs are handled by the same PHB, by definition they share the >properties 
>of
>that PHB and they will (statistically) see the same performance. The >fact 
>that
>the two PDBs happen to be created by different classifiers doesn't >affect 
>that;
>it's as if you have a blue PDB and a yellow PDB that are identical in 
> >every
>way but the color. Viewed that way, whether they share ingresses or 
> >egresses
>makes no difference.
>

Then I can use routing information to select between PDBs too like what's 
happening in MPLS-LSPs?

>It's another question whether more than one PDB per PHB is useful; >that's
>an operational choice.

In this case I think that those PDBs must have different nodes, otherwise 
they will be exactly the same!!

Thank you and best regards.

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From: Brian E Carpenter <[email-masked]>
Date: Mon, 14 May 2001 16:49:27 -0500

No, the ingress router is the one place where we expect to see MF classifiers.
We expect to see BA classifiers in the core.

   Brian

-- 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Brian E Carpenter 
Distinguished Engineer, Internet Standards & Technology, IBM 
On assignment for IBM at http://www.iCAIR.org 
Board Chairman, Internet Society http://www.isoc.org

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From: demir <[email-masked]>
Date: Mon, 14 May 2001 15:39:49 -0700 (PDT)

Mohammed,

> DS domains which might be in the center of the network. I don't mean "core"!

There is no restriction on where you use MF or BA classifiers in Diffserv
architecture. Your above interpretation is a general interpretation, but
not a correct one for Diffserv architecture. You can refer to related RFCs
to find out more info. Bilateral agreements and mechanisms
(between/among Diffserv domains) will determine your initial question and
Diffserv has nothing to do with it; at least currently.

> In this case I think that those PDBs must have different nodes

Having different nodes won't change per domain behavior (PDB). What makes
a PDB is its definition (per domain behavior, not a per hob behavior) and
you can refer to related RFC to find out about it. 

> orherwise, they will be exactly the same!!

That is Brian's point.

Alper K. Demir