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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199512061932.UAA18137@labinfo.iet.unipi.it>
Subject: Re: How big are queues on a typical router ?
To: terry@lambert.org (Terry Lambert)
Date: Wed, 6 Dec 1995 20:32:28 +0100 (MET)
Cc: hackers@freebsd.org
In-Reply-To: <199512061913.MAA01675@phaeton.artisoft.com> from "Terry Lambert" at Dec 6, 95 12:12:57 pm
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> > Is there any relation between the queue size and the line speed ?
> 
> It depends.

I know. but a colleague here said that Ciscos (at least some models)
come with a default "pool size" of 40 slots (whatever is a slot) and he
usually brings it up to 330.

> > I am asking because during some tests (on a connection which
> > apparently goes through a ~256Kbit/s line) I experienced large
> > packet losses, yet an upper bound on the RTT of about 1.2s compared
> > to a lower bound of ~.3s . This makes me think that the queue on
> > the routers is about 1s-worth of data (approx 32KB). Is this correct ?
> 
> The RTT value you have is the minimum pool retention time for a
> successful transit of the router.
> 
> This time dictates the number of packets, maximum, you can see in a
> given interval, and thus how much memory (what pool size) would be
> required.

sorry I don't get this.

...
> It sounds like your router is simply overleaded by 20%.

nor i can understand where the 20% comes from, how it relates to the
loss rate measured by a (20-minutes long) sequence of pings, and if
it is reasonable that this is a steady-state situation.

	Luigi
====================================================================
Luigi Rizzo                     Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it       Universita' di Pisa
tel: +39-50-568533              via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522              http://www.iet.unipi.it/~luigi/
====================================================================