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From: bob@islenet.UUCP (Robert P. Cunningham)
Newsgroups: net.dcom
Subject: Re: Request for info on local building wiring
Message-ID: <852@islenet.UUCP>
Date: Tue, 18-Dec-84 16:44:48 EST
Article-I.D.: islenet.852
Posted: Tue Dec 18 16:44:48 1984
Date-Received: Fri, 21-Dec-84 07:42:11 EST
References: <243@decwrl.UUCP> <588@cbosgd.UUCP>
Organization: Hawaii Institute of Geophysics
Lines: 103

I use the same scheme as Darlabs Inc. does with their Mod-Tap (tm)
components.  I suspect AT&T components use similar wiring.  There are
actually several schemes:

	4-wire, based upon the RJ11-series plugs & jacks
	6-wire, also based on the RJ11
	8-wire, based upon the RJ45/RJ13 series

I'm only detailing the 4 & 6-wire arrangements here, but surprisingly,
it all works together.  RJ11 plugs actually fit into the RJ45 jacks,
and even work if the wiring combinations are correct.

If you take an RJ11 plug (regular modular phone plug at the end of a cord),
and look at it from the top -- with the key (plastic nib with the little
lever) on the BOTTOM, the modular wire numbers are as follows:

	1 2 3 4 5 6

If you have an ordinary single-line RJ11, look at it very carefully.
You'll see that there are actually six little grooves for contacts -- but
only the middle four actually have metal in them, which I'll call:

	  2 3 4 5

The Mod-Tap coresponding RS232 pin assignments are as follows:

	  	   system	terminal	modem
	modular    DTE		DTE		DCE
	1	   20				20,4
	2	   2		3		2
	3	   6,8		6,8,20		8
	4	   3		2		3
	5	   7		7		7
	6	   22				22
		(jumper 4&5)	(jumper 4&5)	(don't jumper 4&5)

Thus, you can use a 6-wire RJ11 to connect a computer system distribution
panel to a modem.  Using the exact same modular jack, you can also plug in
a terminal, with a 4-wire RJ11 (there are different TelCo suffixes on the 4
vs. 6 wire RJ11's).

To do this right, you need several things: 1) RS232-plug-to-modular-jack
adapters (actually different ones for the three different columns above,
in whatever RS232 gender applies for your equipment); 2) "harmonicas" which
have either 12 modular jacks (for 4-wire connections) or 8 modular jacks
(for 6-wire connections) -- and a 50-pin Telephone connector (aka
"Champ" connector).

You'll also need 4 and/or 6-wire modular cable (typically comes in 500'
rolls), a bag of 4 and/or 6-wire plastic modular plugs to put on the ends,
and a special tool that crimps the plugs onto the wire to make modular
cords of any length (el cheapo tools with plastic dies available at
Radio Shack for under $20; tools with steel dies run about $150 -- you
get what you pay for).

Then, you can use regular vinyl-covered 25-pair telephone cable for trunk
lines between the harmonicas (presumably one end at the computer, the other
end at a room or close cluster of rooms with terminals).  Note that the
standard phone company 25-pair wire is fairly small gauge (#24, I think),
and suitable for RS232-type signals only over a fairly limited distance
(I use larger-gauge wire for runs 500 feet or more).

[Note that these wiring schemes are not completely compatible with
"group termination" 25-wire cabling on Micom and other PACX's.
Special inter-connect cables (which you can make yourself) are required
to use both together.]

You can also get "harnesses" that have the 50-pin connector at one end, and
a set of pigtails with RJ11 modular jacks on the other.

Modular patch panels are also available, and very handy.  They've 50-pin
connectors on the back, modular jacks on the front, and you can cross-patch
using modular cords.

Then there's the old standby: the "R66" punch-on terminal block that takes
25-pair or 50-pair cables and allows you to punch on individual 4/6 (or
whatever) wire sets for running individual terminal lines.

For a reasonably-good explanation about how all this works, take a look at
Dave Mallery's article "The maze untangled; a solution to the terminal
distribution problem" in the May 1984 issue of The DEC Professional.

Most of the equipment you can probably buy from the supply company
subsidiary of your local phone company.  A whole collection of these (and
other related equipment) is manufactured by Darlabs Inc. (phone
617-456-3500 and ask for their catalog, it's worth looking at even if you
don't buy their brand).  Darlabs prefers to sell through their distributors,
notably Glascal (201-768-8082, and their catalog is also worth having for
the extensive listings of these and other data communications equipment).

At the moment, I'm in the process of wiring up Yet Another Building for
terminals here at the University of Hawaii.  Traditionally, we've been
using multiple runs of 4 or 6-wire TelCo-type "station wire" in conjunction
with R66 blocks -- and solder on the necessary RS232 plugs.  This time, I'm
using the 25-pair cabling system with modular harmonicas, modular patch
panels and RS232-to-modular adapters.  Sure goes in a lot quicker.

Incidentally, we're still using some inter-building leased phone lines for
terminals.  What we order is a "4-wire control circuit" rather than two
single-pair leased phone lines.
-- 
Bob Cunningham   ..{dual,ihnp4,vortex}!islenet!bob
Honolulu, Hawaii