Path: utzoo!attcan!uunet!decwrl!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: How can you tell when too many ethernet collisions are occuring?
Message-ID: <73460@sgi.sgi.com>
Date: 27 Oct 90 20:02:47 GMT
References: <69374@lll-winken.LLNL.GOV> <9010271814.AA17575@ucbvax.Berkeley.EDU>
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Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <9010271814.AA17575@ucbvax.Berkeley.EDU>, cmaeda@EXXON-VALDEZ.FT.CS.CMU.EDU (Christopher Maeda) writes:
> Roy Maxion did a paper on this in the last Fault Tolerant Computing
> Conference (FTCS-20).  Basically, he keeps a vector of expected values
> for collisions (also load, packet counts, etc) ...


This work is interesting for detecting anomalies like suddenly broken
hardware, but how do you know if your net is "normally" overloaded?  If you
have 90% collisions every day between 10 am and 4 pm, the envelope/standard
deviation calculation will tell you that everything is just peachy.

We've been using a rule of thumb that says if more than 30% of an active
station's packets collide, it is time to split the network.  That is, does
it make sense to say things are bad if the quotient of the "Opkts" and
"Coll" columns of netstat are >= .3, provided Opkts>100,000?  Ethernets
that met this criterion here have been painfully slow.

(Yes, rather BSD-network-UNIX oriented.  Sorry.)


Vernon Schryver,    vjs@sgi.com