Which type of device converts digital signals to analog for transmission over phone lines?

A modem is a device specifically designed to convert digital signals generated by a computer or a digital device into analog signals that can be transmitted over traditional phone lines. This process is essential because standard telephone lines are designed for analog communication, which means that any digital data must be translated into a format that can travel through these systems.

When sending data over analog lines, the modem modulates digital signals into a format that can be sent as an analog wave. Upon receiving the signal, the modem demodulates the incoming analog signal back into digital format for the receiving device. This capability makes modems essential for internet connections through DSL and dial-up services, where the underlying infrastructure uses analog technology.

In contrast, other devices mentioned have different primary functions. For instance, a network switch directs data packets between devices on a network without converting signals, a router manages traffic between different networks, and a repeater amplifies signals to extend transmission distances without converting the signal type. These distinctions clarify why a modem is the correct answer for converting digital signals to analog.