Conference netcad::hub_mgnt

    
    Jason,
    
    	The Thinwire between DEChub 90s doesn't look right too me. Perhaps
        I'm missing something.
    
        Also, the links from the 90FSs which cross over to the opposite
        DEChub 90 doesn't look right. Are these setup as redundant pairs?
        If so, shouldn't they run in parallel to the same DEChub 90? 
    
    Bob

    
    DO NOT USE DECBRIDGE 90 FOR THIS.
    
    This usage is not a supported configuration for them (see the owners
    manual).  Even if it were, a bridge cannot provide nearly the switching
    times you require without setting the bridge timers so low that you
    will cause other problems.
    
    The fiber repeater solution may work - I will ask one of the repeater
    folks to take a look at it.
    
    I cannot overemphasize the first line above - if you do this, don't
    take a plane anywhere in that system.
    

    Ok Guys thanks for your help and understood.
    
    Here is another idea.
    
    
     ________
    |        | Decstation
    |        |
     --------
        |
       ___
      |   |  Cabletron xceiver
       ---
       | |
       | |   Dual homed Shielded UTP
       | |
       |  --------------------------------
     __|_________                   ______|______
    | Dechub 90  |                 | Dechub 90   |
    | 90T        |                 | 90T         |  Spanning Tree disabled
    | 90FS       |                 | DEWGF x 2   |  on bridges. Used as
     ------------                   -------------   non-responder ports
       #         #                #         #
       #            #           #           #
       # P           S #     # S          P #
       #                  #                 #
       #               #     #              #
       #            #           #           #
     __#_________                   ________#____
    | Dechub 90  |                 | Dechub 90   |
    | 90T        |================ | 90T         |
    | 90FS       |   thinwire      | 90FS        |
     ------------                   -------------   
    
    
    
    Rationale :
    
    If each 90FS can be configured to have a primary and backup fibre link,
    then it is possible that the config can use the paths as specified.
    bridges are used in the top right hub to prevent the repeater counts
    blowing out. The thinwire between the two bottom hubs is used to form a
    logical 16 slot hub and avoid interepeater links.         
    
    Ideally, the 90FS units will provide the switching capability and
    prevent networking loops, whilst the bridges serve as non-responder
    ports purely for segmentation purposes.
    
    Please advise.
    
    By the way, I know the configuration is obscure to say the least and we
    have tried to get the customer onto FDDI or a token based or switched
    network but they have chosen Ethernet, hence all the problems.
    
    Many thanks for your replies, once again.
    

    I would quickly convince this customer to purchase FDDI connections for
    this scenario.  The redundancy and failover speeds of FDDI are
    incredible.
    
    I have several DEChub900's with FDDI connections between them, and I
    love to show the customer how fail-over works.  I just have him pull
    out any ANSI MIC connector while his users are logged in, and we watch
    the LED's on the FDDI modules just patch around it.  It happens in
    shorter than a second, and the end users and Hosts CPU's never lose a
    beat.
    
    This is the type of scenario that FDDI's inherent fault tolerance was
    designed for.  You are trying to build a fault-tolerant network using
    Ethernet techology that has redundancy "bolted on as an after-thought", 
    and is not part of the architecture.
    
    The Spanning Tree (which you are trying to disable) is a wonderful
    thing for Ethernet, but as you discovered, it REQUIRES at least 45
    seconds to determine that a link has dropped and patch around it.  I
    don't beleive that you will like the results if you disable the
    spanning tree on two bridges in the same hub, connected to each other
    using repeaters.  I understand that the secondary paths of these
    repeaters are both connected to the bridges, and therefore should never
    see any traffic, but the bridges themselves will be shutting down the
    port that they can't use.  Your Bridges will go into LEARNING mode when 
    the repeater enables itself, and LEARNING mode will take about 15 seconds,
    and PREFORWARDING will take another ten seconds, so you will not have
    the system operating as you wish in this configuration.
    
    If this is an air traffic controller, than it is a MISSION CRITICAL
    application, and should be designed using a mission critical redundancy
    architecture like FDDI.   It's not cheap.  You can't do what you want
    using Ethernet repeaters and bridges.   I would not fly out of this 
    airport either, if the planners were looking for "cheap" networks....
    
    Just my opinion.   I hope you find something that works for you and
    your customer.  I would use DECbridge900MX's and FDDI Concentrators. 
    You have the fiber already.  I would install Digital FDDI controllers
    in the DECstations, (much faster throughput) and you are now state of
    the art. (this gets rid of the cabletron xceiver too).  All you need 
    now is money...    
    
    Good Luck
    
    JR
    
    

    Thanks John.
    
    I know all of that. And yes, we've tried getting the customer to go
    FDDI with the 900 series stuff and even with the older gear. No
    success. See the problem is that the customer is building down to a
    price and not up to a solution.
    
    The initial specification (provided by the customer) called for a
    thickwire backbone with point to point AUI cabling to each device. Hows
    that for a mission critical network?!
    
    Anyway, if you ever come over to Australia..fly into Melbourne Airport
    instead.
    
    In the meantime, I will probably be forced to move the NIU unit
    connections directly to the first floor. This will consolidate the OPS
    display terminals and NIUs onto a common dual hub backplane. The ground
    floor connections will be used for non-critical technical display
    terminals but not the flight control process itself.
    
    Thanking you,
    
    Jason.