Cisco Certified Network Associate (CCNA) Practice Exam

Which device is used primarily for connecting a router to a digital leased line?

1. Hub

2. Switch

3. CSU/DSU

4. Bridge

The correct answer is: CSU/DSU

The correct choice—CSU/DSU—is essential for connecting a router to a digital leased line, such as those provided by telecommunications companies for dedicated Internet access. The Channel Service Unit/Data Service Unit (CSU/DSU) acts as a bridge between the router and the digital circuit, converting the digital signals from the router into a format suitable for transmission over the leased line and vice versa. This device manages the electrical and timing characteristics of a dedicated line and provides protocol conversion. It also ensures that the router can effectively communicate with the service provider's network by addressing the specific requirements of the leased line. Other devices, such as hubs, switches, and bridges, serve different purposes within a network. Hubs and switches are primarily used for connecting multiple devices in a local area network (LAN), facilitating communication among connected devices. Bridges aid in segmenting networks but do not cater specifically to the connections required for leased line communications. Hence, they do not fulfill the role that a CSU/DSU plays in interfacing a router with a digital leased line.