Define modem and explain in details the different transmission modes for modems?

A modem (modulator-demodulator) is a device that converts digital signals from a computer into analog signals suitable for transmission over telephone lines and vice versa. The primary transmission modes for modems are half-duplex and full-duplex. In half-duplex mode, data transmission can occur in both directions but not simultaneously, meaning one device must wait while the other transmits. In contrast, full-duplex mode allows for simultaneous two-way communication, enabling both devices to send and receive data at the same time, which enhances overall communication efficiency.