Which device enables communication over telephone lines by modulating and demodulating signals?

Which device enables communication over telephone lines by modulating and demodulating signals?

• A. Modem
• B. Router
• C. Switch
• D. Hubs

Answer: (A)

To send data over traditional telephone lines, you must convert digital signals from a computer into analog signals that can travel over copper wires, and then convert those analog signals back into digital form at the other end. That conversion is exactly what a modem does, since it stands for modulator-demodulator. The sending side modulates the digital data into an analog signal suitable for the phone line, and the receiving side demodulates the analog signal back into digital data the computer can use. Other devices listed don’t perform this signal conversion over phone lines. A router directs data between different networks, a switch connects devices within a local network at the data-link layer, and a hub simply repeats signals to all ports without modulating or demodulating. Therefore, the device that enables communication over telephone lines by modulating and demodulating signals is the modem.

To send data over traditional telephone lines, you must convert digital signals from a computer into analog signals that can travel over copper wires, and then convert those analog signals back into digital form at the other end. That conversion is exactly what a modem does, since it stands for modulator-demodulator. The sending side modulates the digital data into an analog signal suitable for the phone line, and the receiving side demodulates the analog signal back into digital data the computer can use.

Other devices listed don’t perform this signal conversion over phone lines. A router directs data between different networks, a switch connects devices within a local network at the data-link layer, and a hub simply repeats signals to all ports without modulating or demodulating. Therefore, the device that enables communication over telephone lines by modulating and demodulating signals is the modem.