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From: julian@bongo.uucp (Julian Macassey)
Newsgroups: comp.dcom.telecom
Subject: Re: RJ45 vs RJ11
Message-ID: <8765@accuvax.nwu.edu>
Date: 7 Jun 90 05:18:56 GMT
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In article <8642@accuvax.nwu.edu>, utstat!tg@uunet.uu.net (Tom Glinos) writes:

> I'm looking for the advantages of RJ45 over RJ11.

> Each cubicle that I'm planning will have two jacks.  The jacks will
> either be phone or data in any combination.

> The present data requirements are RS232 and Twisted Pair Ethernet.  (I
> can't speculate about future requirements)

> I'd prefer RJ45 but (bean counters and other bureaucrates) tell me
> that RJ11 will suffice.

	First of all I assume you mean RJ25C not RJ11C. RJ11 is a
single pair of wires on a six conductor jack. RJ25C is three pairs of
wires on a six conductor jack.

	Under some circumstances you can run RS-232 type sigs on a
RJ25C. In fact DEC do I believe, and I have clients that run serial
printers and serial terminals on RJ25 set ups.

	But the price difference between four pair wire and RJ45s and
three pair wire and RJ25s is not that much. But it does give you more
flexibility. The labor is the same whether you pull three pair cable
or twelve pair. But if you don't pull the right cable the first time,
it costs much more to do it over. Once stuff is built and furniture is
replaced, it takes three times longer to run cable. Do it right the
first time. Yes, you can plug a RJ25 type plug into a RJ45 type jack,
so you could wire the RJ45s for regular POTs phones and plug 'em in
with no problems. Cable is about $40 a kilofoot (1,000 ft), labour is
$40.00 per hour minimum and some interconnects want $80.00 per hour to
come out and fix stuff. Yup, one less hour of labor buys another 1,000
feet of three pair or twenty jacks. Explain that to the suit dweebs.

	One way to handle the bean counter types is show them some
official looking docs on RJ45 use and say "See, it has to be this
way."

	There are some AT&T docs on sending RS-232 on RJ45Cs and there
is a DEC doc on sending RS-232 on RJ25s. I have never seen these docs,
but I am told they exist and I doubt they are an urban legend. I do
have AT&T "Data Services Reference Handbook", Vols I - V and see no
reference there, although there is lotsa stuff on DB-25s. I believe
the AT&T 3B2 docs cover RS-232 on an RJ45c.

	My motto: "Never pull less than six pair". And sometimes I
regret not pulling twenty-five pair.


Julian Macassey, n6are  julian@bongo.info.com  ucla-an!denwa!bongo!julian
N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495