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From: coffler@grok.DEC (Jeff Coffler)
Newsgroups: net.dcom
Subject: re: Request for info on local building wiring
Message-ID: <243@decwrl.UUCP>
Date: Thu, 13-Dec-84 09:56:49 EST
Article-I.D.: decwrl.243
Posted: Thu Dec 13 09:56:49 1984
Date-Received: Sat, 15-Dec-84 01:43:24 EST
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
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>My campus is about to embark on project that will replace lots of four
>wire data circuits supplied by the telephone company with connection
>boxes on a broadband cable.  ...

>Is there any standard for the association (by color code or location on
>the RJ11 jack) of the individual leads in the cables and the pins of the
>RS232 connector?

I don't know about any standards here, but with the typical "harmonica",
you really don't need to worry about it.  Plug the harmonica into both
ends, plug the RJ11's into the harmonica, and presto.  You very well may
prefer to use a distribution panel on one end (i.e. the computer end);
if you get the equipment from the same supplier, you should have no troubles.

>In the absence of standards, are there well know pieces of equipment
>from IBM, ATT, or other companies that we should regard as an effective
>standard?

AT&T themselves sell the harmonicas for 4, 6, and 8 wire implementations.
AT&T uses them in all sorts of ways (especially with on-site telephone
equipment, like the Horizon).  As standards go, AT&T has the most out, so
they are probably closest to setting a standard ... (there may indeed be
a standard, but I don't know of any)

>Although four wire circuits have been sufficient for most of our
>terminal connections in the past, in this project we plan to install
>six wire circuits for future flexibility.  We've chosen 6 wires
>primarily since this seems to provide adequate signaling in both
>directions and because such circuits can use RJ11 connectors.  More
>wires require significantly more expensive equipment.  Are we making a
>mistake here?

Yeah, I do believe that's a mistake.  Regardless of 4-wire, 6-wire, or
8-wire, the costs are the same for the connectors.  The only problem is
that, for an 8-wire installation, you need twice the number of cable runs
as you would for a 4-wire installation (you use twice the number of wires).
If your equipment is using XON/XOFF protocol, then 4 wires is really all
that you need ... modems and/or CTS handshaking require more pins.

Your computer equipment (plus future plans for computer equipment) should
probably dictate just how many wires you use.  If you use XON/XOFF type of
handshaking, and intend to continue (a surprising number of terminals can
ONLY do XON/XOFF handshaking), then 4 wire is fine for local terminals
(i.e. terminals that are directly connected, not modem terminals).  We used
the same wiring for modems and for terminals, so in our case, we just ran
8-wire all the way.

	-- Jeff