Conference 7.286::fddi

817.0. "Copper FDDI Standard Update" by LEVERS::B_CRONIN () Mon Dec 21 1992 10:18

    This month's TP-PMD update is relatively short, as the committee is
    now fleshing out the details of the standard, rather than debating the
    religious aspects of FDDI on copper cable. 
    
    Progress was made at this meeting on the details of the MLT-3 encoder
    and decoder, as well as some more detail in the channel budget. The
    current channel budget will allow a 10 dB (at 16 MHz) insertion loss 
    for category 5 UTP. 
    
    There is some contention around the required transmit level to meet
    both Class B emissions, and a 3 V/m susceptibility test. It is possible
    that a system that only meets Class A emissions will be the result, but
    it is premature to predict that this will be the outcome. More work is
    being done to try to make Class B.
    
    The 8 pin RJ45 looks like it will be the connector for the UTP system.
    There is a battle underway as to where the crossover gets located. One
    camp wants the crossover to be in the cable, and the connectors to be
    identical for all products. The other camp wants the crossover to be 
    in the connectors, specifically in the M port of a concentrator (A,B,S 
    ports have one pinout, M has the complementary pinout.) This works fine 
    for connections to M ports, but makes A to B, S to S or S to A or B 
    connections require a different jumper cable than an M to S connection. 
    Do any of you reading this have any opinions on this point? 
    
    That's it for now, next update will be after the February FDDI meeting. 

I'd say crossover should NOT depend on port type.  The FDDI topology rules
are already random enough without any additional committee-created confusion
thrown in.

	paul

We don't need more cable types than we already have.

    Give customers (& the Field) a break: Don't invent port-specific cable
    types.

    The argument for the cable-centric people is that we are inventing a
    new cable to replace the straight through patch cord that the office
    inhabitants now use for 10BASE-T. I personally think the confusion
    is minimized with an FDDI specific crossover cable that always works.
    Some will claim that we are inventing FDDI specific cables where
    generic cables already exist - does anyone agree with their opinions? 
    
    Thanks for the comments so far, 
    
    Bill

I would think that if the cables are not common between 10baseT and TP-PMD
then there is less chance of screwing up network if you mistakenly plug in
a TP-PMD cable into a 10baseT plug or vis versa.

To my mind, having separate cables is goodness.  As long as they are planly
marked as TP-PMD cables, that is.