Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request
From: tcora@pica.army.mil (Tom Coradeschi)
Newsgroups: comp.dcom.telecom
Subject: Re: Crosstalk on Two lines on One Four-Wire Cable
Message-ID: <11864@accuvax.nwu.edu>
Date: 7 Sep 90 13:58:13 GMT
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Organization: Electric Armaments Div, US Army Armaments RDE Center
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With all the discussion of crosstalk between data and voice lines run
in the same physical cable, I thought I might relate our experiences
here.

Our building was recently (like one year ago) rewired for phones. Each
phone has an individual drop, with three pair feeding it. Aside from
upper level mucky-mucks, no phone uses more than one pair (the Army
doesn't allow us lowly engineers the "luxury" of a two-line phone).

At about the same time, we replaced the LocalTalk cabling we bought
from Apple with PhoneNet. PhoneNet uses twisted pair phone lines to
network Macs, IBMs, and the like at 230kbps using AppleTalk protocols.
Not ethernet speed, but faster than walking around the office with
diskette in hand. And AppleTalk is built into every Mac ever sold.

We set up a six node star, with each node being an office. We then ran
a backbone around the perimeter of each office, with RJ-11's about
every ten feet.  To get into each office, we used one of the existing
three pair phone lines.

The phone on my desk and the PhoneNet drop into my office use two pair
from the same line. I've honestly never noticed ANY noise in the phone
line - and I spend a LOT of time on the phone - and never noticed any
AppleTalk problems due to the phone being in use. This goes for both
voice transmissions, as well as data, i.e. modem (remember, I don't get
two lines:-{).

So, I guess what I'm wondering is - what's the problem? Is it possible
that the problems others experience, or think they experience, are due
to other factors? Poorly terminated lines, bad grounds, etc?


tom coradeschi  <+>   tcora@pica.army.mil   <+>   tcora@dacth01.bitnet