Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!oliveb!pyramid!voder!blia!ted
From: ted@blia.BLI.COM (Ted Marshall)
Newsgroups: comp.dcom.lans
Subject: Re: Thinwire ethernet: Question about drop cables
Message-ID: <4375@blia.BLI.COM>
Date: 22 Mar 88 19:26:13 GMT
References: <4491@june.cs.washington.edu> <13364@uflorida.cis.ufl.EDU>
Organization: Britton Lee, Los Gatos, CA
Lines: 28
Summary: how the rules were written


The thing to remember is that the general rules were designed as a
simple set of rules that, if followed, you would not exceed the actual
design limits. Thus, you can break these rules SO LONG AS YOU MAKE THE
NECESSARY ADJUSTMENTS ELSEWHERE. This is true of thick and thin wire.
For example, with thickwire, you can place transceivers closer than 2.5m
apart if you limit the total length of the segment (and maybe the number
of transceivers).  The misplaced transceivers will set up standing waves
on the cable, but if you only have 100m of cable and 20 stations, the
signal levels will be high enough to drown out the noise.

So you may be able to add 8' drop cables to your thinwire without
problems IN YOUR CURRENT CONFIGURATION. Later, if you extend the segment
to full length or add a transceiver that is a little weak but within
specifications, it may break. I have seen a number of sites that were
very sloppy installing their network and it worked fine until the
network grew near the limit specified by the rules. Then it fell apart.

So the bottom line is: if you must break a rule, document that fact so
that later, after you've left, the new network manager knows why it
doesn't work even though he's within the specifications. If possible,
get a Ethernet expert (no, I'm not that good) to figure out the
trade-offs.

-- 
Ted Marshall       ...!ucbvax!mtxinu!blia!ted <or> mtxinu!blia!ted@Berkeley.EDU
Britton Lee, Inc., 14600 Winchester Blvd, Los Gatos, Ca 95030     (408)378-7000
The opinions expressed above are those of the poster and not his employer.