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Path: utzoo!linus!vaxine!wjh12!genrad!decvax!cca!ima!haddock!johnl
From: johnl@haddock.UUCP
Newsgroups: net.lan
Subject: Re: Looking for comments on 3COM - (nf)
Message-ID: <145@haddock.UUCP>
Date: Mon, 2-Apr-84 23:38:27 EST
Article-I.D.: haddock.145
Posted: Mon Apr  2 23:38:27 1984
Date-Received: Wed, 4-Apr-84 07:57:18 EST
Lines: 33

#R:utcsrgv:-365500:haddock:19000001:000:1720
haddock!johnl    Apr  2 15:07:00 1984

We currently have an Ethernet on which there's a Vax 780 with an Interlan
interface and six IBM PCs with 3COM cards.  We use a locally hacked up
protocol to do file transfer, mail, remote printing, etc.  (It gateways
transparently to uucp, by the way, so that usenet sites albacore, anemone,
chub, alewife, eel, and wahoo are actually these PCs on Ethernet.  But I
digress.)

I'm reasonably happy with the 3COM cards.  They do work, and cramming the
entire interface and the transceiver onto one card was no mean feat.  We
use their thin Ethernet cable to hook up all of the PCs, spliced to a
fairly short piece of regular fat cable for the Vax hookup.  This all
works fine except when somebody steps on the thin cable, since it's not
very rugged.  We should have it all off the floor and into the walls and
ceiling, at which time that problem should go away.  The documentation is
pretty good and we were able to write our own drivers without undue
trouble.  We haven't tried 3COM's software, since we use PC/IX rather
than PC-DOS.

The biggest complaint I have to make about the 3COM cards is that the
throughput is limited by the single buffer on the card.  To receive a
packet, you enable the receiver, and when the packet arrives it's stored
in the on-card buffer.  The card interrupts the host, which commands the
card to DMA the data into the host memory.  After that the host resets
the interface card, and it's prepared to receive again.  Should a packet
arrive during the fairly long interval between the end of the previous
packet and the card's reenabling, it's jammed and lost.  I realize that
the single buffer is due to real estate limitations on the board, but
it's still a pain.

John Levine, ima!johnl