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From: phil@portal.UUcp (Phil Sih)
Newsgroups: net.dcom
Subject: Re: Thin Ethernet really works...
Message-ID: <136@portal.UUcp>
Date: Fri, 25-Apr-86 05:29:27 EDT
Article-I.D.: portal.136
Posted: Fri Apr 25 05:29:27 1986
Date-Received: Sun, 27-Apr-86 05:48:44 EDT
References: <735@hoptoad.uucp>
Organization: Portal Communications, Cupertino, CA
Lines: 28
Summary: why thick ethernet was

> Why did xeroX go with expensive custom cabling originally?  They figured
> that standard TV style thin cables wouldn't permit a big enough network?
> -- 
> John Gilmore  {sun,ptsfa,lll-crg,ihnp4}!hoptoad!gnu   jgilmore@lll-crg.arpa

In part you are right.  The thick Ethernet cable was developed especially
for its characteristics like loss and propagation delay. The delay is important
as it along with the end-to-end span of the network, clock frequency, and
encoding method determine things like the minimum packet size, time to backoff
after collision, jam time, etc.  The bottom line is the higher the wave
velocity in the cable and the lower the loss, the longer you can make the
Ethernet installation limit and the higher you can make the data rate, both
desirable attributes.

If you are really curious, try getting a copy of the version 1.0 Ethernet
"blue book" that I think came out in 1980. (I have no idea where you would
get one now. Maybe an engineering lib.)

Thin Ethernet works because as long as the impedance of the cable is
matched (50ohm) and there are no "bumps" at the connectors or bends to
cause funkie reflections in the wire (just like regular EN) the protocol
can't tell the difference below a certain network size and intertransceiver
(?) minimum distance. I think "Cheapernet" as it has been called is a 
good idea for situations where EN is overkill. Yours sounds like a 
case in point. Ours probably is too since we have a pair of 3/160's in a
closet connected by a big honkin' coil of cable.

- Phil