Bit order description - compilation of Email discussion Initial comment on P802/D21 (Overview and Architecture) Source: Pat Thaler 6.1.2 pg 18 line 19: For the original 802.3 and 802.5 encodings, each bit is represented by a separate symbol on the media and bits can be said to travel in an order. I don't recall if that holds true for all 802.4 encodings. In any case, in the 802.3u and 802.12 encodings block codes covering 4, 5, and 8 bits per block are used. In some cases, the physical layer also sends bits on separate lines at the same time. The concept of bits being transmitted in a specific order does not apply to these block codes. Also, multilevel codes where multiple bits are represented by a single symbol are under consideration. Please modify the text to cover this situation. From: Geoff_Thompson@BayNetworks.COM (Geoff Thompson) To: pat@hprnd.rose.hp.com Cc: p8021@nic.hep.net Subject: Re: O&A Ballot Date: 03 Nov 1995 17:36:11 GMT Pat- I believe that this is also true for (at least) 802.9a From: Pat Thaler Subject: Re: O&A Ballot To: Geoff_Thompson@BayNetworks.COM Date: Fri, 03 Nov 1995 11:56:46 PST Cc: p8021@nic.hep.net I believe you are correct. They use the same FDDI 4B/5B block code that 100BASE-TX uses, though I think the two assign the LSB of the 4B nibble to opposite ends when they do the encoding. So Geoff, do you have any suggestions on how to handle this? It isn't correct to unilaterally talk about bits on the wire, but I have found bits on the wire a very useful concept in explaining address ordering to people. Therefore, I hesitate to totally abandon it without a replacement. One possibility is to explicitly state that discussions of bits on the medium apply to those medium where there is a serial encoding with a single data bit producing a single code symbol or code bit and that some physical layers use more complex? advanced? efficient? encodings where the concept does not apply. Pat From: Geoff_Thompson@BayNetworks.COM (Geoff Thompson) To: pat@hprnd.rose.hp.com Cc: p8021@nic.hep.net, k.dittmann@ieee.org, v.zelenty@ieee.org Subject: Re: Re: O&A Ballot Date: 03 Nov 1995 22:20:12 GMT Pat- I don't consider it to be a conceptual problem for 802.3 as we still have a serial MAC. As such, the definition point can be at the MAC/PHYSICAL LAYER interface for 802.3 Geoff From: Pat Thaler Subject: Re: Re: O&A Ballot To: Geoff_Thompson@BayNetworks.COM Date: Fri, 03 Nov 1995 18:09:31 PST Cc: p8021@nic.hep.net, k.dittmann@ieee.org, v.zelenty@ieee.org Geoff, Yes, but the subject is how 802 O&A should explain bit order, not how 802.3 should explain it. The 802 text should be general to the range of 802. However, it may be possible to generalize. 802.12 does define the serial order of bits in the MAC frame. Any LAN that uses the CRC check on the MAC frame must at some point explain the serial order of bits that the CRC algorithm operates on. If this is not done, there is a danger that different implementations would run incompatible CRC checks and we wouldn't have interoperability. I think pretty much all of the 802 LANs run a CRC check. Some part of 802.6 may not as I have a vague recollection of discussions of them running an alternate form of error detection, but I don't remember the final conclusion. I don't even remember if the discussion was pre- or post-DQDB. So, most and perhaps all of the 802 MACs describe the serial bit order. Pat