Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!kwe
From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England))
Newsgroups: comp.dcom.lans
Subject: Re: Simple thin ethernet question
Message-ID: <35265@bu-cs.BU.EDU>
Date: 25 Jul 89 18:13:43 GMT
References: <2946@ukecc.engr.uky.edu>
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Distribution: usa
Organization: Boston U. Information Technology
Lines: 51

In article <2946@ukecc.engr.uky.edu>
 agollum@ukecc.UUCP (Kenneth Herron) writes:
>
>My question is quite simple:  all the docs we have on installing the
>cables show both halves of the cable running right up to the back of the
>computer, and the T connector attaching directly to the network card
>in the PC.  Does it HAVE to be this way?  Can we keep the main cable 
>and the T in the wall and run a short piece of cable to the network card?
>How long can this stub piece be?  Assuming we can't do this,
>any suggestions for doing this wiring aesthetically?
>
	Thin Ethernet is almost a literal replacement for the thick
cable.  Since transceivers are installed *on* thick cable, it follows
that thin-net transceivers are installed *on* the thin cable.  Since
the transceiver is usually onboard the interface card, the cable has
to come all the way.  Now if you want to use thin exactly like thick,
get outboard transceivers and you can run regular xcvr cable to the
wall or up in the ceiling.

	DEC is the arch-conservative authority on all things Ethernet.
Their DECconnect plan uses thin net only in star configured wiring.
There is only one cable to each outlet.  You run a patch cord from the
single wall outlet to the back of the node, put a T on the node, plug
the patch cord in one side and a terminator on the other side of the
T.  This means one DEMPR port per active outlet.  This negates the
moniker "cheapernet".  So people daisychain, trying to save bucks.

	For those who simply *must* daisychain thin-net and get
"cheapernet", I recommend the AMP Thin TAP solution.  They have a
special wallplate with shorting bar and a dual coax patch cable with
integral T.  This allows you to daisychain aesthetically thru the
walls with nice looking faceplates.  You can also plug and unplug
without taking down the rest of the leg.  The hardware looks robust,
but we have not yet given this stuff a good trial.  Beware.

	MY PERSONAL WARNING:  Don't take the daisychaining too far or
you, as net manager and troubleshooter, will live to regret it.  No
matter how good the AMP stuff might be, you will come to grief if you
have to debug 15 connections on each leg.  Stretch your DEMPR ports to
maybe four outlets or so.  That should be enough upfront savings.
Remember, you can daisychain to your heart's content inside a lab or
terminal room and not suffer diagnostic nightmares.  Remember, too,
that you can run extra wire and not use it.  It's relatively cheap.
But not too much daisychaining- it is just too difficult to debug
media problems.

	Since we have not yet had time to evaluate the AMP stuff,
consider my recommendation as preliminary.  There may be other sources
for the same thing, look around.

	--Kent England, Boston U