Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!purdue!haven!rutgers!att!mtunh!mkd From: mkd@mtunh.ATT.COM (Mark Darby) Newsgroups: comp.dcom.lans Subject: Re: 10BaseT operation, spec? Message-ID: <653@mtunh.ATT.COM> Date: 25 Apr 89 15:01:00 GMT References: <1627@Portia.Stanford.EDU> Organization: AT&T ISL Middletown NJ USA Lines: 106 In article <1627@Portia.Stanford.EDU>, morgan@jessica.stanford.edu (RL "Bob" Morgan) writes: > > I'm puzzled by various references I've seen recently, in this forum > and elsewhere, to the operation of the proposed 10BaseT Ethernet. Is > the draft spec available from anywhere, either on paper or (better) > on-line? Is there some nice, descriptive article somewhere that talks > about 10BaseT operation and terminology? > > When the battle to define the standard was going on last year, I > thought there was a clear split between the "3Com approach" and the > "Lattisnet approach." The 3Com method involves simply modifying the > standard Ethernet transmission to work acceptably over twisted pair, > more or less like a Balun does for other coax-to-TP purposes. In this > case the TP is really just an Ethernet cable, the transceiver > functions are performed at the station, and the machinery in the > wiring closet is just a multiport repeater with one Balun per port. > The Lattisnet method, on the other hand, uses the TP as an extension > of the transceiver cable, so that most (some? all?) transceiver > functions are performed by the wiring-closet machinery, which is > more-or-less a multiport transceiver. The device at the station is > required to multiplex the signals that are normally carried on the > multiple-conductor transceiver cable so they'll fit on the TP, but > isn't really a transceiver in the normal sense. There is no repeater > in the normal sense (auto-partitioning, retiming, etc) at all. > > Of course, the Lattisnet approach "won" the standards battle. Now, > I've seen people referring to the 10BaseT wiring closet device as a > repeater. Is this just loose terminology or is my understanding of > 10BaseT/Lattisnet wrong? > > Thanks, > > - RL "Bob" Morgan > Networking Systems > Stanford I've been involved with the 10BaseT task force since I began work with AT&T in August '87. I'll try to answer some of your questions here the best that I can. First and foremost, the "Lattisnet" proposal did not win acceptance in the 10BASET task force. It wasn't even one of the three remaining contenders in the proposal race before the final proposal won out. The three final proposals were from Hewlett Packard, 3Com and David Systems. A note that the final offering from 3Com was a joint effort with DEC. The 3Com proposal is as you have mentioned. The proposal was withdrawn because technical feasibility couldn't be shown. Because the signal involved in their proposal (using a BALUN) is DC coupled and with a data content that is much lower in level it is a great source of interference to other services and likewise is much more susceptible to interference from other services. The David Systems proposal is one I admittedly know little of. I do know that it was based on a two-pair system, each link connecting a MAU to a modified multiport repeater. The MAU in question is asymmetric; that is the transmit link was based on Manchester signaling, the receive link was based on modified Manchester signaling. David Systems likewise withdrew their proposal, but I am unaware of the reason (anyone who can expand on this, please do so). The Hewlett Packard was the first proposal to be presented to the 10BASET task force. It was also the proposal which was finally accepted by the 10BASET task force after 3Com and David Systems withdrew their proposals. The HP proposal is based on specifying the MAU only. Each link is 2-pair from MAU to MAU, each MAU having an AUI interface. The central point of a 10BASET network for this proposal is assumed to be a multiport repeater (MPR), an entity which is already standardized in IEEE (see Chapter 9, IEEE 802.3 Supplement Book). Signaling is Manchester in both directions. There are fundamental differences between the HP and SynOptics proposals. The SynOptics proposal has a network architecture based on a MAU to active concentrator link. The active concentrator is not an IEEE repeater in any sense in that there is no retiming, no fragment extension, no auto-partition capabilities at the central connection point which would maintain network reliability. SynOptics LOST on their proposal because of this. While the MPR specification has the Auto-partition algorithm as an optional feature, 10BASET has mandated that the algorithm be mandatory on a per port basis. Just a note that, while the SynOptics proposal didn't win in the standards body, SynOptics has an MPR in their product line available now. The extent of its functionality is not known, however. There are also some operational differences, especially in the areas of transmit voltage levels and equalization techniques. The differences are substantial enough to warrant increased scrutiny when attempting to bundle equipment which is not even close to the proposed 10BASET draft with other services, including equipment which IS close to the 10BASET proposed specifications. The draft is now in letter ballot form. The document is P802.3I/D6, it is currently being voted upon by the 802.3 working group, and the cut off date is May 19, 1989. It's expected that 10BASET will meet in June to resolve any NO votes from the balloting. Try to find a voting member of 802.3 to get a copy, or you can obtain a copy from IEEE. I hope this helps! --------------------------------------------------------------------- Mark K. Darby AT&T Bell Laboratories AT&T: (201)957-2706 200 Laurel Ave. uucp:..!att!mtunh!mkd Middletown, NJ 07748 DISCLAIMER: The above is a statement of my own opinions and does not reflect those of the corporation for which I work.