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Date:      Fri, 5 Sep 2003 11:24:59 -0700
From:      Luigi Rizzo <rizzo@icir.org>
To:        Yuchung Cheng <ycheng@cs.ucsd.edu>
Cc:        ipfw@freebsd.org
Subject:   Re: dummynet and modem pipes
Message-ID:  <20030905112459.A78583@xorpc.icir.org>
In-Reply-To: <20030905095038.D28924@cs.ucsd.edu>; from ycheng@cs.ucsd.edu on Fri, Sep 05, 2003 at 09:50:39AM -0700
References:  <20030905095038.D28924@cs.ucsd.edu>

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On Fri, Sep 05, 2003 at 09:50:39AM -0700, Yuchung Cheng wrote:
> when simulating modem pipes using dummynet, how do we simulate the
> modem compressions? one way is to pick a compress rate, say 2, and setup

basically there is no way to accurately simulate modem compression.
As a rule of thumb, for bulk traffic you can think that the main
effect is the bandwidth changes (the exact ratio depends on the
type of traffic), whereas for interactive apps (e.g. rpc and the
like) more than compression what affects you is the additional
delay that the modem causes to decide that it is time to build&send
a new packet.

also you'd need to take care of ip compression, not just what
happens in the modem itself

	cheers
	luigi


> fake larger bandwidth, but do different traffic (html, jpg, mpg) affect 
> the compression latency or compression rate significantly? tia
> 
> -yuchung
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