On Apr 22, 15:18, ajp166 wrote: 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