Count the number of wires used in a null-modem cable and you will see only 7 wires are needed. Some general purpose telecommunications cable has 9 wires. This wire is probably not paired. 25-wire cable is the oldest RS232 cable since all 25 pins of the DB25 connector can be connected across the cable. Although still used, it is less popular as only 9 of the original 25 signals are widely used today.
Modems are devices which allow digital data signals to be transmitted across an analog link.
Modem stands for MO dulator DEM odulator . At the other end, another modem receives the signal and converts it back to digital. Remember that baud rate is the number of signal changes per second. Therefore the term bps is more accurate and should be used. This modem is distinguished by the way it handles data.