Newsgroups: comp.dcom.lans
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Ethernet collisions
Message-ID: <1990Dec11.174941.12301@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <467@pirates.UUCP> <2184@cybaswan.UUCP>
Date: Tue, 11 Dec 90 17:49:41 GMT

In article <2184@cybaswan.UUCP> iiitih@cybaswan.UUCP (Ivan Izikowitz) writes:
>... Just take a look at any of the published
>performance curves for the 802.3 protocol - throughput is severely
>degraded once the offered load exceeds a certain value (I think about
>40% of channel capacity?)

What published performance curves for what protocol?  The throughput of
802.3, aka Ethernet, is monotonic increasing as load increases.  There
is no "severe degradation".  Even under massive overload it continues
to move data, although collisions limit it to something like 70% of the
theoretical channel capacity under those conditions.

(Note, this assumes multiple sources of traffic.  A single source of
traffic can run an Ethernet at circa 100% of theoretical, so 70% is down
somewhat compared to that ideal state.)

Many of the early simulation studies of "Ethernet" were actually studying
different protocols with inferior performance, either because the folks
involved thought they could "improve" Ethernet or because they didn't
understand it very well to begin with (often both).  The numbers and curves
from those studies are completely irrelevant to real Ethernet, although
myths derived from them are persistent among Ethernet's detractors.
-- 
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu   utzoo!henry