Re: [Diffserv-interest] congestion in diffserv network

John Schnizlein <jschnizl@cisco.com> Tue, 28 October 2003 17:32 UTC

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Date: Tue, 28 Oct 2003 12:30:55 -0500
To: "Feng Y" <feng6@uwindsor.ca>
From: John Schnizlein <jschnizl@cisco.com>
Subject: Re: [Diffserv-interest] congestion in diffserv network
Cc: diffserv-interest@ietf.org
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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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