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 CABLES TO CONNECT A COMPUTER TO A MODEM

 A normal modem cable runs straight through with pin 1 to pin 1,
 pin 2 to pin 2 etc.  The end that hooks onto the terminal
 presents a female connector to the terminal's male, and the end
 that hooks onto the modem presents a male end to the modem's
 female.

 Sometimes the sex of connectors can get confused and you will
 need non standard sexed ends on your cable.

 Nearly always one end of the connection will support a different
 subset of the pins from the other.  For example, the modem may
 be watching RTS but the terminal doesn't support it.  In that
 case you have to fake it by strapping the RTS pin permanently ON
 by connecting it to the +12V test pin, or by strapping it to
 some other signal such as DTR that the terminal does support.

 The pins you have trouble with most often are 4, 5, 8, and 20
 (on a 25 pin connector).

 You can find out which lines are being supported by perusing
 documentation or by using a $200 breakout box.  A breakout box
 is a set of 25 LEDs.  Fancy versions use Red/Green/Yellow to
 indicate line state.  They also come with a set of switches and
 little jumper wires so that you can build experimental cables
 instantly.  One of these days when I am rich I am going to get
 one.  You can also see if signals are in spec.  Sometimes the
 signals that are nominally +5 volts droop down in the 2.5 volt
 range, which is no-man's land.  Ordinary LED tests will not show
 up the trouble.  Once you find the magic combination you can get
 a permanent cable built for about $30.