Subject: [Diffserv-interest] congestion in diffserv network

From: "Feng Y" <[email-masked]>
Date: Tue, 28 Oct 2003 10:43:27 -0500

Hi,

Recently, I have read a paper about admission control in
Diffserv network. In the paper the author mentioned the
well-know diffserv “traffic overloading and internal
network state changing” problem. 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.

Yang

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From: John Schnizlein <[email-masked]>
Date: Tue, 28 Oct 2003 12:30:55 -0500

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

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From: Brian E Carpenter <[email-masked]>
Date: Wed, 29 Oct 2003 12:07:02 +0100

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

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Brian E Carpenter 
Distinguished Engineer, Internet Standards & Technology, IBM 

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