Path: utzoo!attcan!uunet!jarthur!elroy.jpl.nasa.gov!decwrl!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.dcom.lans
Subject: Re: FDDI vs HPPI [was FDDI over copper]
Message-ID: <52725@sgi.sgi.com>
Date: 5 Mar 90 19:50:06 GMT
References: <1990Feb28.105322.4274@hellgate.utah.edu> <549@sword.bellcore.com> <53312@bu.edu.bu.edu>
Sender: vjs@rhyolite.wpd.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <53312@bu.edu.bu.edu>, kwe@buit13.bu.edu (Kent England) writes:
> 			...  FDDI is
> limited to fiber, which means that you can't substitute cheaper media
> and trade-off distance and stay within the spec. ...


What would be wrong with a pair (or more) of cooperating stations having
copper, string or any other media between them, and fiber to their
neighbors?  There is no way I can see for the token to see what kind
of media it is passing thru.  Of course you would not be using officially
sanctioned MIC connectors between the cooperating stations, and the
Protocol Police might come and take you way.

What if you had a dual-attach "concentrator" with 0 M-ports and 20 MAC's
connected with copper, whether on a back plane or in coax, and what if
this "concentrator" happens to have 20 fast CPU's with disks, operating
system, terminals, and so forth, and further, happens to put many
normal LLC frames on the rings?  What if this "concentrator" happens to be
a physically large machine, spread over an entire building?  It would
be completely within the letter if not the spirit of FDDI spec.,
so you would be safe from the Protocol Police.

This is not a pure academic nit, given the current cost of the optics.
(Yes, as you might guess from my signature, I've heard the "trust me, they
will be real cheap real soon now" pitches from the ODL vendors.  As you
might also guess, I currently have no choice but belief.)


Vernon Schryver
Silicon Graphics
vjs@sgi.com