the reasons behind the cisco rollover cable pinout

Discussion in 'Cisco' started by Perdition, May 25, 2006.

  1. Perdition

    Perdition Guest

    what is the practical reason why they inversed the order of the pins?

    Thanks for your insight in advance,
    Michael
    Perdition, May 25, 2006
    #1
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  2. Perdition

    Guest

    Perdition wrote:
    > what is the practical reason why they inversed the order of the pins?


    Inversed with respect to what?

    Here is how it works.

    There are two kinds of cable:-
    Rolled and straight.

    There are two kinds of headshell:-
    "Terminal" and "Modem"

    If you use 2 x X pin "Terminal" headshells
    (X = 9 or 25) and:-

    1 - straight through cable you get an X pin D to X pin D
    straight thru cable.

    2 - rolled cable you get a null modem cable.

    Changing 1 headshell to the other type
    is the same as changing the cable to the other type
    except that Modem headshels are male
    and Terminal ones female.

    The newer "blue" cables with the molded on
    9 pin are equivalent to a rolled cable and a 9 pin
    "Terminal" headshell.

    I have never seen a 9 pin "Modem" headshell.
    Modems always have 25 pin female connectors.

    This cabling system was invented when
    router console ports all had D type connectors.

    The RJ45 connectors consoles were conveniently
    fitted into the existing system which of course
    includes the Terminal Servers and the
    Octal cables that they use.

    Of course there is always the Cat 5500 supervisor 3
    (IIRC) debacle where some poor soul used the wrong
    pinout making it the odd one out. That mistake has
    not been made again.
    , May 25, 2006
    #2
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