Cisco Certified Network Associate (CCNA) Practice Exam

What does a CSU/DSU do?

1. Converts analog signals to digital for routers

2. Converts digital signals from a router to a leased line

3. Amplifies signals for long-distance transmission

4. Codifies data for secure transmission

The correct answer is: Converts digital signals from a router to a leased line

A CSU/DSU, which stands for Channel Service Unit/Data Service Unit, serves a crucial function in telecommunications, particularly in the context of connecting a router to a digital circuit, such as a leased line. The primary role of a CSU/DSU is to convert the digital signals generated by a router into a format suitable for transmission over a leased line. This conversion is essential because leased lines often require specific signaling formats that differ from the digital signals used internally within most network devices. Additionally, the CSU/DSU performs several functions that help maintain the integrity and reliability of the data transmitted. It provides line termination, signal conditioning, and may include diagnostics to ensure that the connection is functioning as expected. By handling these responsibilities, the CSU/DSU serves as an essential link between a local area network and the wider telecommunications network, making it indispensable in many enterprise networks. The other options refer to functions that are not pertinent to the primary role of a CSU/DSU. For example, the conversion of analog signals to digital is typically handled by different types of devices, such as modems. Amplifying signals is a function of repeaters or amplifiers, which address limitations in signal strength over distances, and codifying data for secure transmission relates