CSU/DSU vs. Modem

Explanation

CSU/DSU is used to convert digital signals from a router to a network circuit such as a T1, while a modem is used to convert digital signals over a regular POTS line.

Both CSU/DSU and modems are networking devices that are used to connect a router to a WAN (Wide Area Network). However, they differ in their functionality and the type of signals they convert.

A CSU/DSU (Channel Service Unit/Data Service Unit) is a device that is used to convert digital signals from a router to a format that can be transmitted over a leased line. A leased line is a dedicated line that is rented from a service provider to provide a direct and secure connection between two locations. The CSU/DSU functions as a digital modem that converts the digital signals from the router to a format that can be transmitted over the leased line. The CSU/DSU also provides line conditioning and diagnostic capabilities to ensure that the line is functioning properly.

On the other hand, a modem (short for modulator-demodulator) is a device that is used to convert digital signals from a computer or router to analog signals that can be transmitted over a phone line. The modem also performs the reverse function of converting analog signals from a phone line to digital signals that can be understood by a computer or router. Modems are commonly used to provide internet connectivity over traditional phone lines.

Therefore, option D is the correct answer: A CSU/DSU converts digital signals from a router to a leased line; a modem converts digital signals from a router to a phone line.