cire@CISCO.COM (cire|eric) (05/26/89)
I and some of my colleagues have been working with various protocols running across Ethernet/IEEE 802.3 and Token Ring. Because of the different transmission orders we've run into an interesting problem of integrating networks consisting of these two media. I'm wondering if others out there have run into the problem and what if anything has been done. In particular I'm interested in any established conventions set by oh DEC or perhaps Xerox. On Ethernet and IEEE 802.3 media data is transmitted MSByte to LSByte but the first bit transmitted is the least significant. On Token Ring media the bytes are shipped out in the same order but the transmission starts with the most significant bit. In either case the very first bit transmitted is the Individual/Group (multicast) bit and the next bit is the Universal/Local address administration bit. If for example I'm working with DECNet I would have the Ethernet address AA00.0400.06CC assigned to one of my nodes. If this address were used on a Token Ring it would be multicast. One possibility is to swap each byte. Thus the above address becomes 5500.2000.6033. Perhaps that is why AA was chosen. Similar problems present themselves for XNS. Any thoughts will be appreciated. Please mail directly to me and I will summarize to the net. Please do not respond directly to this list. It already deal with a lot of traffic. -c cire|eric Eric B. Decker cisco Systems - engineering Menlo Park, California email: cire@cisco.com uSnail: 1360 Willow Rd., Menlo Park, CA 94025 Phone : (415) 326-1941
tmallory@BBN.COM (06/07/89)
Eric, I've been a little behind in my mail, and have saved your message for a later moment, which is now. Though I don't have a copy in front of me, my memory is that the cover letter which the IEEE sent with a block address assignment, as well as the address itself, explicitly addressed the fact that the bit orders for 802.3 and 802.4-5 are reversed. The assigned address block refers to the bits as they appear on the wire(fiber, etc.). Our address was printed in three forms: binary network order, 802.3 hex, and 802.5 hex. Reversing the bits in each byte is the correct way to go for the different network types. BTW There was a recent tip-ip posting concerning the hardware addresses from some well-known manufacturer's equipment which did not match the assigned address block(perhaps AT&T?), that appeared to be a bit-reversal problem. Hope this is helpful, and that you didn't get too many versions of this message. Tracy Mallory