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From: brian@sdcsvax.UUCP (Brian Kantor)
Newsgroups: net.lan
Subject: Re: Need Thin Ethernet Info
Message-ID: <1380@sdcsvax.UUCP>
Date: Tue, 4-Feb-86 13:15:33 EST
Article-I.D.: sdcsvax.1380
Posted: Tue Feb  4 13:15:33 1986
Date-Received: Fri, 7-Feb-86 08:40:09 EST
References: <1575@emory.UUCP>
Reply-To: brian@sdcsvax.UUCP (Brian Kantor)
Distribution: net
Organization: UCSD wombat breeding society
Lines: 38

Actually, a good scheme is to run thin ethernet cable into each
office, and somewhere in the office cut the cable, install two BNC male
connectors, and a BNC barrel-fitting (double female union) to reconnect
the cable.  Then when you want to install some equipment in that room,
just pop the barrel-fitting out and install one or more BNC
T-connectors.  You can add a loop of cable at the same time if you have
more than one device to install.  And if you want to put in a standard
"Thick-Ethernet" transceiver, you just use a pair of BNC-to-N between
series adaptors.  And you can attach your thin ethernet cable to the end
of a thick ethernet using the same adaptors.

The reasons for not leaving an exposed T-fitting on the cable is that
they 1) radiate interference from the open end, and 2) might short out
if something metallic (staples, etc) happens to fall into the open end.
You can buy non-shorting caps for the T-fittings, but barrel fittings
are cheaper in the first place.

Believe it or not, you can probably get all those kinds of connectors at
Radio Shack.  Here at UCSD, the campus storeroom stocks them because the
physics and video people all use them heavily.

The 3-COM EtherLink book gives the formula for combining the cables
of a thin and thick ethernet:
	(3.28 * T) + E <= 1000
where T is the length in meters of the thin ethernet, E the thick.  They
then go on to note that this is true only if its soley their equipment on
the cable; if you mix other people's transceivers you need to reduce the
total length to a maximum of 500 meters (from 1000).  Apparently their
transceivers are a bit more forgiving than other people's and allow you
to violate some spec by a factor of 2.  Or something.

	Brian Kantor	UCSD Office of Academic Computing
			Academic Network Operations Group  
			UCSD B-028, La Jolla, CA 92093 (619) 452-6865

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