Date: Wed, 6 Dec 1995 12:13:16 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Cc: hackers@freebsd.org Subject: Re: How big are queues on a typical router ? Message-ID: <199512061913.MAA01675@phaeton.artisoft.com> In-Reply-To: <199512060718.IAA17205@labinfo.iet.unipi.it> from "Luigi Rizzo" at Dec 6, 95 08:18:54 am
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> I have a (hopefully simple) question: how big is, typically, the > queue (I mean, the place where incoming IP segments can be stored > after being received and before being processed/delivered) in a > router ? > > Is there any relation between the queue size and the line speed ? It depends. > 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. This is an oversimplification based on inbound and outbound processing rates being equal. It turns out that most commercial routers that are reasonably fast at all (ie: Cisco) do outbound filterin rather than inbound, mostly because the filter information can be attaches to the destination routing information. It sounds like your router is simply overleaded by 20%. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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