What type of modem cables are you talking about? DB-9's, 25's, etc? Or regular old single pair?

Matt Wray
CCNA

The RS-232 'standard' has enough variations so no one knows what pins may be in use, the only reason to hope for USB analog modems is to kill RS-232.  (on PCs, there is also the speed of the UART, but the real hope for USB is to kill RS-232)

I tried to remain child-like, all I acheived was childish.

Basic configurations:  All these are RS232-c standards

DB25-DB25
DB25-DB9
 DB9-DB25

Pin outs - ie: what's what.
DB25         DB9           Signal Name       Direction
 1                           protective gnd

 2            3              TX Data           DTE->DCE

 3            2              Rx Data           DCE->DTE

 4            7              RTS               DTE->DCE

 5            8              CTS               DCE->DTE

 6            6              DSR               DCE->DTE

 7            5              Signal Ground (common)

 8            1              DCD               DCE->DTE

 20           4              DTR               DTE->DCE

 22           9              RI                DCE->DTE

 23                          DSRD              DCE->DTE

Bottom LINE.

All that is absolutely required is TX, RX, and Sig Gnd(common).  Everything else is gravy.  All wires are straight through connections, WITH ONE EXCEPTION.  TX AND RX MUST BE CROSSED. That is TX/RX pins 2/3 on DTE are RX/TX on DCE pins 3/2.

What's DTE and DCE mean.  DTE is data terminal equipment (a pc or printer)  DCE is data communication equipment (modem).

Hope this answers it all.