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From: hedrick@topaz.rutgers.edu (Charles Hedrick)
Newsgroups: comp.dcom.lans
Subject: Re: Need help with a Novell network question
Message-ID: <12878@topaz.rutgers.edu>
Date: Wed, 24-Jun-87 04:18:46 EDT
Article-I.D.: topaz.12878
Posted: Wed Jun 24 04:18:46 1987
Date-Received: Thu, 25-Jun-87 06:41:55 EDT
References: <239@irs1.UUCP> <764@nu3b2.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 36

I certainly have no objections against twisted pair, if you can get
the necessary speed on it.  But I am mystified about your advice to
stay away from coax because of space.  Your comments seem to imply a
separate piece of coax to each office.  Some technologies may do that,
but Ethernet and similar LAN's certainly don't.  With traditional
Ethernet (i.e. not the new thin Ethernet), you run one piece of coax
down the hall, and install a tap outside each office, or install a
group of taps for small clusters of offices.  Of course the actual
topology depends upon the size of your building and your data rates.
But it would be unusual to have more than 2 or 3 pieces of coax
running between floors, even in an installation with lots of high-data
rate workstations.  We certainly have problems with RS232 cables
filling up our conduits, but we breath a sigh of relief when we move
to Ethernet-based terminal servers, precisely because the coax between
floors takes up almost no space compared to older wiring.  

The comments you repeat about data rate on Ethernet are probably based
on slightly imprecise wording by your informant.  It is quite true
that it is unusual to see more than 1Mbit/sec in a single conversation
on an Ethernet.  However it is possible to have several 1Mbit/sec
conversations at a time.  The other 9Mbit/sec is not taken up by
collisions and retransmissions.  It is unused.  The reason a single
conversation doesn't use the full bandwidth is that no LAN software
that I know of is designed to put packets onto the network at that
high a rate.

My understanding is that the market pressure for twisted pair is
because of buildings that have lots of twisted pair installed for
phones, and find it impossible for political reasons to install any
kind of new cable whatsoever.  The impression I have gotten from the
trade press is that with the advent of lower-cost Ethernet interfaces,
Ethernet is now overtaking the proprietary networks.  Of course if you
are just going to have a few PC's, it doesn't much matter.  But as
soon as you decide you want to connect to a minicomputer, or you get a
Unix-based workstation, or anything else changes, you'll wish you had
gotten a network that every vendor under the sun supports.