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From: dgc@ucla-cs.UUCP
Newsgroups: net.med
Subject: Re: ethernet in a hospital
Message-ID: <8192@ucla-cs.ARPA>
Date: Sat, 28-Dec-85 15:32:09 EST
Article-I.D.: ucla-cs.8192
Posted: Sat Dec 28 15:32:09 1985
Date-Received: Sun, 29-Dec-85 20:12:24 EST
References: <188@bigtuna.UUCP> <1895@saber.UUCP> <623@osiris.UUCP> <783@petrus.UUCP>
Reply-To: dgc@ucla-cs.UUCP (David G. Cantor)
Distribution: net
Organization: UCLA Computer Science Department
Lines: 41
Keywords: ethernet, reliability
CC:             bellcore!petrus!mwg@topaz.arpa

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I think the various notes about ethernets miss the real question:

    Just how reliable are ethernets?  How do they compare in reliability
    with more classical "star" nets such as that used by telephones? 
    Are they inherently unreliable?

To explain the last question further:  Ethernets and other
non-redundant, non-star nets have the feature that ANYone on the net,
ANYwhere can at ANYtime take down the entire system, and with very
little effort.  This has happened at ethernet installations.

What, for example, if the technician who installs "vampires" makes a
mistake and, while installing one, shorts the cable just while the
ethernet is being used to monitor some critical life support function?

Please don't misunderstand me.  I believe that ethernets (and similar
nets) have their places, primarily in controlled environments where
the cost of catastrophic failure (that is entire system failure is not
too great).  It's worth noting that AT&T, which is noted for reliable,
conservative design, stated when it first announced them, that its
electronic switches had an expectation of no more than 30 minutes
system down-time (and no more than twice) in a 20 year interval.  Time
has proved that they were optimistic.  We don't have as much
experience with ethernets and the small evidence that has accumulated
indicates that they will be much less reliable than classical networks.


David G. Cantor

ARPA:	dgc@LOCUS.UCLA.EDU	(current)
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-- 


David G. Cantor

ARPA:	dgc@LOCUS.UCLA.EDU	(current)
ARPA:	dgc@UCLA-LOCUS.ARPA	(former)
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