Path: utzoo!attcan!uunet!know!zaphod.mps.ohio-state.edu!usc!ucsd!rutgers!bellcore-2!bellcore!cellar.bae.bellcore.com!louie
From: louie@cellar.bae.bellcore.com (Paul Louie)
Newsgroups: comp.dcom.lans
Subject: Implementing LAN using RS-232 Serial Ports
Message-ID: <28236@bellcore.bellcore.com>
Date: 26 Oct 90 15:42:13 GMT
Sender: news@bellcore.bellcore.com
Reply-To: louie@cellar.bae.bellcore.com (Paul Louie)
Organization: Bell Communications Research
Lines: 58

In article <1990Oct15.030111.28548@eagle.lerc.nasa.gov> 
tidedu@mars.lerc.nasa.gov (William T. Dedula) writes:

>Hello All;
>I am currently evaluating low cost, easily implemented methods 
>of connecting 6 or 7 IBM PC-XT/AT's in a Local Area Network.
..stuff deleted...
>I have heard that it is possible to utilize RS-232 serial ports
>on each computer to implement the network. If anyone has heard
>of (Or done) this, I'd be interested in knowing the BEST, and 
>MOST EFFICIENT way this can be done.

Yes, I have tried this method once and I abandoned it.  It was a good
thing that my hardware supplier have a 30 days trial policy on all irons
they sales.

There are three major problems with this methods, performance, maintenance,
and cost (eroneous assumption of saving money).

1. - Performance.  All serial lan boxes, aka zero-slot lan, can only support
a maximum throughput of 19,200 kps due to the limitation of the PC's serial
port.  Although they allow you to access files stored at another PC through
a logical drive interface, the speed limitation make it impractical for
you to do that.  Therefore, you must store a copy of each program at each
PC and file transfer the need data files before you can work.  

2. - Maintenance.  Due to reason stated in 1, you therefore can't have 
centralized control of programs and data.  This eventually lead to the 
problem of having different version of programs and multiple version of 
a document.  The DOCUMENT problem is a major one, since you don't have 
file locking no one can know if something is checked out currently.  The 
PROGRAM problem you might be able to get away with if you work hard to keep 
everyone in line.

3. - Cost.  Let's analyze the total cost of having a zero-slot lan vs. 
installing, let's say, Netware ELS II using thin-coax.  We can disregard
wiring cost, since this kind of installation is done by yourself and the
material cost between thin-coax and phone wire are neglegible.  A PLUS - 
if you buy Antheme's NE-1000 you get 20' of coax and a T-connector
with each board.

Zero-Slot:	Box+Software			$1000
		40mb HD ($350x7)		$2450
						-----
						 3450

ELS II:		Netware				$1200
		NE1000 ($145x7)			$1015
		150mb HD w/ ESDI controller	$1200
		Ethernet Terminator		$  20
						-----
						$3435

As you can see for the same cost you'll have a system that's high performance
and easy to manage.  That's why zero-slot lan has never been that popular.


Paul