Date: Wed, 6 Dec 1995 20:32:28 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: terry@lambert.org (Terry Lambert) Cc: hackers@freebsd.org Subject: Re: How big are queues on a typical router ? Message-ID: <199512061932.UAA18137@labinfo.iet.unipi.it> 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/ ====================================================================
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