From owner-freebsd-net  Fri Jul 19 20:46: 1 2002
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Date: Fri, 19 Jul 2002 23:45:44 -0400 (EDT)
From: Garrett Wollman <wollman@lcs.mit.edu>
Message-Id: <200207200345.g6K3jise017051@khavrinen.lcs.mit.edu>
To: Rik van Riel <riel@conectiva.com.br>
Cc: freebsd-net@FreeBSD.ORG
Subject: Re: Another go at bandwidth delay product pipeline limiting for TCP
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<<On Sat, 20 Jul 2002 00:12:46 -0300 (BRT), Rik van Riel <riel@conectiva.com.br> said:

> Absolutely. On my DSL things work best when I limit myself
> to 220 kbit/s down (from the maximum 256 kbit/s), or about
> 85% of the bandwidth.

That is hardly surprising.  In fact, that is a well-known result of
Queueing Theory.  It is impossible to achive better than 85-90%
utilization in the presence of appreciable non-scheduled traffic
competing for the same channel.  (That's a big part of why protocols
like ATM were designed to require everything to go through admission
control and shaping: otherwise you can't make tight guarantees of
latency and drop rates while still maximizing channel utilization.)

-GAWollman


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