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From: scarter@caip.RUTGERS.EDU (Stephen M. Carter)
Newsgroups: net.lan
Subject: Re: Need Ethernet help- H4000 vs. H4005
Message-ID: <1287@caip.RUTGERS.EDU>
Date: Mon, 17-Feb-86 02:10:53 EST
Article-I.D.: caip.1287
Posted: Mon Feb 17 02:10:53 1986
Date-Received: Tue, 18-Feb-86 04:26:39 EST
References: <585@adelie.UUCP>
Reply-To: scarter@caip.UUCP (Stephen M. Carter)
Distribution: net
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 46
Keywords: Ethernet, transceivers/-cable

In article <585@adelie.UUCP> barry@adelie.UUCP (Barry A. Burke) writes:
>
>Q0.	What's the difference between the xcvrs and cables mentioned?
>Q1.	Which xcvr+cables should I use for:
>
>    On to XEROX.  The XEROX xcvr cables are somewhat different (at least
>    in spec) than the DEC cables in that while there seems to be the
>    same number of wires, they are paired and shielded differently.
>
>Q2.	Despite the differences, can I use DEC xcvr cables to connect
>	XEROX equipment to my coax?
>Q4.	Is there really a "standard"?  I'd like to pre-run the xcvr
>	cables without regard to which vendors equipment is gonna get
>	used where- I also thought that was the intent of Ethernet
>	(semi- ;-).
>

Another difference between the "Dec" and the "Xerox" is that "Dec" likes to
use one gauge heavier wire.   As far as most things go, the good ole Xerox
works fine for version 1/2.  We use them for our Dec machines without problems.

Now, on to IEEE.  The major difference between IEEE and Xerox is the ground
shield pin.   In Xerox, they use pin 1 and in IEEE, pin 4.  Also in IEEE the
ground is not shield.  (ie pin 4 is isolated from case/shield/case).  In most
cases, you can mix without problems.  However, one high-level guru told me that
he has seen cases where it has caused problems.   I have seen machines where 
the bulkhead<-->board cable does not even run ground and is had from the
chassis/connector.  This would be one example where the cable type doesn't
matter much.  But to answer your question, you can get a cable to handle
everything.  This is by having a "IEEE/Xerox" cable.  To get these, you can:

		1) Buy pre-assembled.  I know Cabletron offers these
		2) Make your own.  Use IEEE format (ie isolate ground and
shield), then jumper pin 1 to pin 4.  Note the drain wire on this cable
is wrapped with one of the pairs and isolated from outer shield.
		3) Use IEEE cables, either jumper 1 and 4 before you install,
or do it as needed.

and on a final note, be sure to use Teflon if your building code requires it,
and keep maximum lengths < 50 meters..  (and if you will be getting close
to this length, consider the heavier wire....)


-SCarter
uucp:   ...{harvard, seismo, ut-sally, sri-iu, ihnp4!packard}!topaz!scarter
arpa:   SCARTER@RUTGERS or SCARTER@RED.RUTGERS.EDU