Conference netcad::hub_mgnt

    No.  150 ohm is not 10BaseT.  Our repeaters work with 100 ohm STP/UTP.

    Just curious - what would prevent them from working?  i.e. MAY they
    work up to X feet etc...?  What rules are being broken?
    
    Thanks,j
    

    There's an impedance mismatch between the cable and the
    drivers/receivers.  This will cause reflections on the line, ruining
    the shape of the signals.

     Do we know of any other vendors who can do this with 150ohm cable? 
    (Ifso, we may be dead, if not....bob Battersby's suggestion of
    adapters at each end places EVERYBODY at equal disadvantage and we may win.
    ..!)
    
        Regards,j
      

    As I stated, 150 ohm cable is not compatible with 10Base-T.  If you open
    up our products (repeaters, bridges, etc.) and compare them to the way
    other vendors make 10Base-T products, they are the same in this regard. 
    So yes, EVERYBODY is at an equal disadvantage. 

    A customer has pushed back about the 150 ohm specification. Here is the
    points the customer made about it.
    
    I pushed back saying that in order to meet industry specs for 10BaseT
    that the  product must support 100ohm.  Also, wasn't he concerned about
    using a  competitor's 10BaseT product at 150ohm when this was outside
    the standard and  the possible supportabiltiy problems that may arise
    if there were problems. The customer shared the following with me:

    1) 10BaseT Spec suggests 100ohms this is not a requirement, it does not
    disallow  other than 100ohm to be within spec.

    2)  The equivalent 3COM repeater product is documented spec is 96 to
    166 ohm.

    3)  The specfication in 802.3J or 802.3I is for 10BaseT 120 ohm
    distribution.   This spec is geared toward upcoming Cable to Curb
    market , where cable companies  will be providing 10BaseT support to
    the home.

    4)  EIA/TIA Specification 568B describes rules for 100 ohm to 150ohm
    conversion.  If vendors products meet this spec they will work in PSU's
    environment.

    5)  If the selected vendor's product does not work as stated then PSU
    is  prepared to take whatever steps required to make the vendor have
    the product  perform as specified.

    There is a very simple solution, and answer to your customers
    concerns. 
    
    First, there appears to be some misguided or mis-informed information
    your customer has on the requirements for using 100 ohm medium to 
    connect 10baseT products. It's very specific in the IEEE 10baseT spec 
    in several places of the "requirement" and "shall be" statements of using 
    a medium with a differential characteristic impedance between 85 and 111 
    ohms for all frequencies between 5.0 and 10 MHz. The 10baseT IEEE standard 
    is very specific of the model for the driver and receiver characteristics 
    also being matched for 100 characteristic impedance. There *is* no place 
    that I can recall reading within the IEEE 10baseT standard that suggests 
    that this is not a requirement. There *is* a lot of suggestion that in
    order for things to work in a predictable manner that all components
    that make up the 10baseT media attachment points (cable, drivers,
    and receivers), should be required to comply within a impedance
    range between 85-111 ohms.
    
    Now, having said that, there is a solution that should work just
    fine for your customers needs. On page 4-32 of the Open DECconnect
    Structured Wiring System Applications Guide, there is a cable with
    a built-in balun to accomodate 150 ohm to 100 ohm conversions.
    It consists of an 8 pin MJ to IBM connector with built-in Balun.
    The cable part number is a BN26T. This cable is shielded and is
    designed to be used between the IBM cabling system and a 100 ohm
    twisted pair MAU or repeater. If you have any doubts on the use
    of this cable for this type of application, I'd suggest contacting
    Jack Learson here at LKG for additional information on the use of this 
    adapter cable.
    
    Bob

    
    Bob,
    
    	Thanks for the reply. The customer is obviously being lulled into a
    false sense of security with the statements from the other vendors that
    they could do this with their current products. 
    
    	If we had built products such as these other vendors are purporting
    to have, we'd be raked over the coals by these same customers because
    we were exceeding the standards.
    
    	So, we may be asking these questions again and again only because
    our competition is saying they can do it. It therefore makes their
    products non-standard, but allows the customers to cheat in re-using
    old cable plants. 
    
    	So, bear with us as we try and come to grips with these anamolies.

    
    Bob (or anyone else),
    
    	Do you have a pointer to the IEEE 10BaseT spec? Everyone has
    provided specific answers, but we need to cross-reference these answers
    by quoting specific parts of the standard to the customers. We don't
    want to waste your time with this, but I'm not sure where to find the
    actual spec so I can do this work...

    This is from the Ethernet FAQ. I imagine it doesn't help you much but 
    maybe there is a copy in the lending library?
    
    -Mike
    
07.03Q: Where can I get IEEE802.x docs online?
     A: Nowhere.  IEEE documents must be ordered  from the IEEE themselves.
        You can contact them at:

          Institute of Electrical and Electronic Engineers
          445 Hoes Lane
          P.O. Box 1331
          Piscataway, NJ 08855-1331
          U.S.A.
          (800) 678-IEEE

        You can also get order information via e-mail to [email protected].
    

    Thanks Mike, I just got back from vacation and saw the question 
    on where to get the IEEE specs. They are not on-line as Mike said.
    The IEEE does however have a web page with information on how to
    order specs and other related information. 
    The URL is http://stdsbbs.ieee.org
    
    Bob