On Apr 22, 15:18, ajp166 wrote:
> From: Tony Duell <ard_at_p850ug1.demon.co.uk>
> >AFAIK it is not backwards-compatible, at least in the sense that no
> >10Mbps ethernet controller supports the 3Mbps data rate (at least, I've
> >never seen one that does).
>
> Neither have I. Also Eithernet AKA 802.x was never that slow. The
> 3 mb/s stuff I'd always called ARCNET.
ARCnet is different, it's a proprietary system, not at all the same as the
original 3Mb/s Ethernet, which is sometimes referred to as "Experimental
Ethernet". BTW, ARCnet is 2.5Mb/s, not 3Mb/s. Instead of CSMA/CD access
control, it uses a token-passing system, rather like Token Ring or FDDI,
although it's a bus (like thick Ethernet) not a ring. Which is why its
other name is Token Bus :-)
The original Experimental Ethernet is very similar to 802.3 in many
respects, including the topology, CSMA/CD, and several other things, but
not in details like addressing, packet framing, packet length. I think it
uses 75-ohm devices rather than 50-ohm, but I've never seen a live 3Mb/s
system, so I can't be sure. It led directly to the DIX (DEC-Intel-Xerox)
consortium's Ethernet specification, which in turn led to the 802.3
standard. If you want to read the original spec, the relevant paper is at
http://www.acm.org/classics/apr96/
--
Pete Peter Turnbull
Network Manager
Dept. of Computer Science
University of York
Received on Sun Apr 22 2001 - 19:11:56 BST