Newsgroups: comp.dcom.lans
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Ethernet and IEEE 802.3
Message-ID: <1991Apr26.190639.7754@zoo.toronto.edu>
Date: Fri, 26 Apr 1991 19:06:39 GMT
References: <NG.91Apr25224522@neutron.mpr.ca>
Organization: U of Toronto Zoology

In article <NG.91Apr25224522@neutron.mpr.ca> ng@neutron.mpr.ca (Steve Ng) writes:
>I know that both Ethernet and IEEE 802.3 specify CSMA/CD as the MAC
>layer, but a guy in here said that Ethernet will not interwork with an
>implementation of 802.3. In other word, Ethernet is not conforming to
>the 802.3 standards. I suspicious that he is wrong, but can the Ethernet
>and 802.3 experts out there educate me on this subject?  Thanks.

He's wrong.  Ethernet rev 1, Ethernet rev 2, and 802.3 are all completely
compatible on the coax, with the possible exception of cases where you
are pushing the specs to the limit on things like cable length and repeater
count.  They are *not* compatible at the AUI level, though, so you need
to be sure that transceiver, transceiver cable, and host interface agree
on which flavor is in use between transceiver and host.

He may be confusing the software issue -- whether the first two bytes of
the data in a packet are a protocol code or a length count -- with the
hardware.  Ethernet revs 1+2 say it's a protocol code, 802.3 says it's a
length, and almost everybody does it right and makes it a protocol code.
This was simply a botch by 802.3, which most people have sensibly ignored.
The two can coexist, but machines that want to communicate with each
other naturally have to agree on protocol issues like this.
-- 
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  henry@zoo.toronto.edu  utzoo!henry
