Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site deepthot.UUCP
Path: utzoo!watmath!deepthot!julian
From: julian@deepthot.UUCP (Julian Davies)
Newsgroups: net.lan
Subject: Re: Ethernet <=> Ethernet Link
Message-ID: <340@deepthot.UUCP>
Date: Tue, 31-Jul-84 21:44:56 EDT
Article-I.D.: deepthot.340
Posted: Tue Jul 31 21:44:56 1984
Date-Received: Wed, 1-Aug-84 05:56:14 EDT
References: <435@ittral.UUCP>, <708@CS-Arthur>
Organization: UWO CS, London Canada
Lines: 26

In the original request starting this line of discussion, I seem to
remember that the two ethernets were several miles apart.  In this
case no kind of "repeater" is appropriate, no matter if it uses fibre
optics, microwave or anything else.   Ethernet has a maximum
end-to-end propagation delay, which is assumed predictable for
determining the length of time needed to listen for contention when
trying to grab the ether.  The geographical distance limit is usually
quoted as 1500m (say 5000 feet) on thick ethernet cable, or one third
of this on 'thin' cable.  Fibre-optic links etc still have the same
speed of light propagation speed limit for information pulses, so the
lengths of any such links must be counted towards the 1500m limit.

To go over about a mile, you MUST use a full-fledged gateway or bridge
which buffers each packet being transferred and rebroadcasts it on the
other cable as a separate activity.  It seems that quite a few
organizations are using broadband cable for networks over distances of
a few miles; these can be set up to operate over longer distances than
ethernet, by various means, and some organizations like the
flexibility of combining video with several different carriers of
data.  The trade-offs depend on the particular needs though.  PBXs in
various flavours, and local packet-switched networks (X.25 type) are
also possible solutions (though the latter is fairly unusual in N.
America -- but is getting quite common in the UK and maybe in Europe.)

	Julian Davies
{deepthot|uwo}!julian