Article: 5893 of comp.dcom.lans.ethernet
Newsgroups: comp.dcom.lans.ethernet
From: vjs@calcite.rhyolite.com (Vernon Schryver)
Subject: Re: But errors are bad (was Re: Collisions Are Good)
Message-ID: 
Organization: Rhyolite Software
Date: Mon, 21 Feb 1994 21:16:40 GMT
References: <5a.3016.308.0N1C9C42@ase.com>  <2kack1$g8f@news.iastate.edu>
Lines: 24

In article <2kack1$g8f@news.iastate.edu> john@iastate.edu (John Hascall) writes:
>Vernon Schryver  answers:
>
>  One thing to watch (which I haven't seen mentioned this time around),
>  is packets lost or mangled.  1% lost or corrupt *will* definitely
>  degrade your performance (esp. some protocols).
>
>  Let's take NFS with the default timeo=7 and lets assume normally
>  you can transmit 1MB as 1000 packets of 1KB in 1 second (1MB/s)
>  [round numbers for easy math :) ].  Now imagine dropping 10
>  (1%) of those and waiting the retry interval of 0.7 second each.
>  It now takes 1 + (10 * 0.7) = 8 seconds = 0.125MB/s.
>  Even if you drop all the way down to timeo=2, that's 3 secs = 0.333 MB/s.

That's a good point.

One of the favored ways to lose 1% of your packets and so 90% of your
performance is to have a "late collision" rate of 1%.

Late collisions are catasrophically bad.
Collisions are good.


Vernon Schryver    vjs@rhyolite.com