Modems: Full-duplex data transmission on the telephone network: Full-duplex communication is easily achieved at slow speeds. With high-speed modems, sophisticated equipment is needed to keep signals separated

Have you ever tried to talk over a telephone line without using a phone? Probably not, but if you have, it is certain that you failed. A telephone is needed to convert voice and other sounds into analog signals, which can travel over the telephone system's lines. A similar kind of conversion is needed when computers send data over telephone lines, and the device that does it is called a modem. A modem takes its name from what it does: MODulation and DEModulation. When a unit of data terminal equipment (DTE) produces digital data to be sent over a communication channel to a distant DTE, the modem converts that data to analog signals, a process called modulation. At the other end of the line a second modem demodulates the signal, converting it back into the digital data the receiving DTE can accent.