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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!decwrl!Glacier!Cascade!trewitt
From: trewitt@Cascade.ARPA
Newsgroups: net.lan,net.periphs
Subject: Re: Interlan boards and evil waves
Message-ID: <870@Cascade.ARPA>
Date: Thu, 18-Apr-85 01:34:34 EST
Article-I.D.: Cascade.870
Posted: Thu Apr 18 01:34:34 1985
Date-Received: Sat, 20-Apr-85 03:15:22 EST
References: <1044@cbosgd.UUCP>
Organization: Stanford University Computer Systems Laboratory
Lines: 41
Xref: watmath net.lan:758 net.periphs:735

> We've run up against an interesting property of our Ethernet, and
> would like to report it and see if anybody else has seen the same
> behavior.
	:
	:

Well, we've got a fairly short net that has two VAXen (750+interlan,
780+deuna), 1 SUN running the Stanford V-System, 3 SMI UNIX SUNs (1 server,
2 clients), and several Iris workstations.  We try to use TCL transceivers,
but since many things come with 3Com transceivers we will use them even
though they are a pain to install.  (Both TCL and 3Com transcievers seem to
work fine, though.)

However, we have had the following compatibility problems:

DEC H4000 transceivers won't work with the SUNs (3Com interfaces).  I hear
that there is a jumper on the 3Com board that will fix this, but I don't
know that I beleive.

The transceiver cables that DEC supplies with H4000s/DEUNAs won't work when
placed between a SUN and a 3Com transceiver!  Please believe this simple,
apparently ridiculous statement.  I have seen similar problems with Xerox
experimental 3Mb installations.  It seems to be an impedence mismatch
generating reflections/attenuations.  (Although I thought that the Ethernet
spec gave a figure for this to avoid such problems.)  Chalk one up for DEC!

When we upgraded one of our SUNs (S/N 60) from 3Mb to 10Mb Ethernet, SUN
gave us a little ribbon cable to go from the 3Com board to the back panel.
Believe it or not, this sucker was bad!  Not solidly broken, not even
intermitent -- it exhibited behaviour very similar to that described by Mark
Horton -- slow nd booting, nd not responding, then picking up again, etc.
We had a spare and it fixed the problem.  I don't know what was wrong with
the cable and I don't want to.  By the time I had taken the guts out of the
SUN for the second time to get to this cable I was so mad that I just tied
the thing into a bow tie and nailed it to the door.

Good hunting!
	- Glenn Trewitt

...!sun!decwrl!shasta!trewitt
trewitt@SU-amadeus.ARPA