Information and Communication Technology

4.1.2 Data Communication Using Modems

Computer to computer communication can be made in two ways:

• Using M odems
• Using networks

Modems, allow computers to use telephone lines to send and receive data. Networks connect computers directly, either through special wire or some wireless medium.

A computer-to-computer communication system using modems and telephone lines is illustrated below. Telephone lines are designed to transmit analog signals and therefore we need to convert the digital output signals of the computer into analog signals at the sending end and convert the analog signals back into digital input signals at the receivi ng end. The devices that perform these special tasks of encoding and decoding data are known as modems, a term derived from the words modulation and demodulation. A modem at the sending end modulates digital signals (received from the sending computer) int o analog form for transmission over telephone lines. A modem at the receiving end demodulates the analog signals back into digital form for input to the receiving computer.

A person wishing to transmit data needs to only dial a number to establish the con nection. A modem performs both the functions, modulation and demodulation, depending on whether it receives digital signals from the computer or analog signals from the transmission line.