Re: [Diffserv-interest] congestion in diffserv network

Brian E Carpenter <brc@zurich.ibm.com> Wed, 29 October 2003 11:10 UTC

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Date: Wed, 29 Oct 2003 12:07:02 +0100
From: Brian E Carpenter <brc@zurich.ibm.com>
Organization: IBM
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To: John Schnizlein <jschnizl@cisco.com>
CC: Feng Y <feng6@uwindsor.ca>, diffserv-interest@ietf.org
Subject: Re: [Diffserv-interest] congestion in diffserv network
References: <4.3.2.7.2.20031028122043.02283790@wells.cisco.com>
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Another way to look at it is that what diffserv does is split the network
into several separate networks, but each of them retains the statistical
properties of a single Internet.

   Brian

John Schnizlein wrote:
> 
> The simple reason that congestion can occur is that the TCA
> need not limit incoming traffic sufficiently to avoid it.
> The TCA for expedited forwarding is the only one, of many
> traffic classes, that seeks to eliminate potential congestion,
> in order to minimize delay and jitter.
> 
> The parameters of other class definitions, assured forwarding
> for example, are intended to mark traffic at different ingress
> rates for different treatment when congestion occurs. Note
> that this anticipates that congestion will occur.
> 
> Please recall that the high link utilization in an IP network
> is obtained in large measure because traffic loads are high
> enough to produce occasional congestion. Cooperative management
> of this congestion is the responsibility of transport-layer
> protocols.
> 
> John
> 
> At 10:43 AM 10/28/2003, Feng Y wrote:
> >... I wonder why the
> >overloading or even congestion occurs in diffserv network.
> >In diffserv architecture, the “DS ingress node is
> >responsible for ensuring that the traffic entering the DS
> >domain conforms to any traffic conditioning agreement (TCA)
> >between it and the other domain to which the ingress node
> >is connected” [RFC 2475]. Moreover,   “Traffic conditioning
> >performs metering, shaping, policing and/or re-marking to
> >ensure that the traffic entering the DS domain conforms to
> >the rules specified in the TCA, in accordance with the
> >domain's service provisioning policy”. So what causes the
> >overloading or congestion in diffserv? Does anyone explain
> >it for me or give me some references. Thanks in advance.
> 
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> Diffserv-interest@ietf.org
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-- 
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Brian E Carpenter 
Distinguished Engineer, Internet Standards & Technology, IBM 

NEW ADDRESS <brc@zurich.ibm.com>; PLEASE UPDATE ADDRESS BOOK

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