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From: brian@sdcsvax.UCSD.EDU (Brian Kantor)
Newsgroups: comp.periphs,comp.terminals,comp.dcom.lans
Subject: Re: Telco-style push down blocks and stranded cable
Message-ID: <2440@sdcsvax.UCSD.EDU>
Date: Sat, 10-Jan-87 10:20:19 EST
Article-I.D.: sdcsvax.2440
Posted: Sat Jan 10 10:20:19 1987
Date-Received: Sat, 10-Jan-87 22:45:41 EST
References: <2551@phri.UUCP> <2856@osu-eddie.UUCP> <1634@hoptoad.uucp> <1635@hoptoad.uucp>
Reply-To: brian@sdcsvax.UCSD.EDU (Brian Kantor)
Distribution: world
Organization: UCSD wombat breeding society
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Here at UCSD we have been using punchblocks (66-type) for some time.

The system we devised for using them is that each computer port is
connected to modular plugs (we use the ones from MOD-TAP), and a
"hydra" which takes the individual modular plugs and brings them to
telco-style 50-pin plug inside the computer system (Unibus cabinet,
etc).  A 25-pair cable with appropriate connectors takes this to a
dual-connectorized 66 block on the wall.  For ports which connect to
our LAN or which run to rooms with clusters of terminals, a similar
cable leaves the other half of the 66-block and runs either to a hydra
and modular plugs into the LAN box, or to another punchblock (single
connectorized is ok here) and punched-down inside wire to terminals, or
to a "harmonica" (the other sex of a hydra: modular jacks on a 50-pin
connector).  This way my cross-connect wiring for the majority of our
connections (in the computer room, at least) consists of bridging clips
and is very fast to connect.

Essentially, all RS-232 connections entering the computer room
terminate on a punchblock.  In laboratories and terminal rooms where
I'm likely to have a cluster of connections (i.e., more than 2), I
place a 66-block with 50-pin connector and run a 25-pair cable with
connectors back to the computer room, where it terminates in another
66-block.  Cross-connect is done by bridging clips or 3-pair inside
wire.  For less-dense terminals, either a punchblock is nearby serving
several rooms, or I string longer runs of 3-pair.  I've got 200 and
300 foot runs running at 19,200 and 9600 bps with no problems.

I've also bought a couple of items for troubleshooting - I have a nifty
little connector that you can slip onto the punchblock terminals and
plug a modular connector into - that connects to a breakout box or
datacomm analyzer and you can tap into any line in or out of the
computer without unplugging anything.  If you need to isolate a
connection, you can pop the bridging clips, or simply unplug the
modular plug at the terminal or computer.  Fast fast FAST to
troubleshoot!

Standardization:  We chose a 6-conductor scheme (which gives 8 ports 
on a punchblock, cable, hydra, or harmonica) so that we could wire
modems, printers, and terminals the same way.  (Our LAN boxes look like 
modems and need DTR and CD in addition to the normal TD, RD, and SG, so
we have one spare wire left over.  On modems, that spare wire is RI.)

We use only two kinds of connectors (called a 260 and a 523 by Mod-Tap)
and stock them in both sexes.  A cable with a 260 connector on both
ends is a straight-through cable suitable for connecting to a modem or
LAN box on one end, and a computer or terminal on the other (assuming
the computer is DTE, which most are these days).  A directly-wired
terminal (or other DTE device, such as a printer) will still have a 260
connector on it, but the port on the computer will have a 523 connector
for that line, which gives a null modem to connect the DTE to the
computer DTE port.

Our modem telephone lines are wired similarly, but we use 4-conductor
cable there to match the 2-pair inside wiring that the phone company
uses.  (By the way, ThePhoneCo is happy to terminate incoming lines on
one of our connectorized 66 blocks.  We just tell them to "terminate on
customer-provided RJ21X" and they do it just right.)  With 4-conductor
modular stuff, you get 12 per cable/block/hydra/harmonica.

All this stuff is available from MOD-TAP.  We buy a lot of it from
other people too. What with the installation of our LAN and rewiring
most of the campus, we've probably installed more than 2000 RS-232
connections using variations of this system, and found it to work quite
well.

DEC and others have similar systems with slightly different standards.

	Brian Kantor	UCSD Office of Academic Computing
			Academic Network Operations Group  
			UCSD B-028, La Jolla, CA 92093 USA

Disclaimer: just because I said it doesn't mean its right.  Think for
yourself.