What device is necessary for sending and receiving data over analog lines such as phone or cable lines?

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

Answer: (A)

Sending and receiving data over analog lines requires changing digital data into analog signals (and back again). That job is done by a modem (modulator-demodulator). The computer or device on one end speaks in digital bits, but a phone line or similar analog medium can only carry analog signals. The modem encodes the digital stream into tones or RF signals suitable for the line, and at the other end it converts the analog signal back into digital data for the device to use.

Routers, switches, and hubs, on the other hand, operate within networks to forward or route digital data. They don’t convert between digital and analog signals, so they aren’t the device that directly enables communication over an analog line.