Which of the following describes the roles of devices in a WAN?

Which of the following describes the roles of devices in a WAN? (Choose three.)

A.
A CSU/DSU terminates a digital local loop.

B.
A modem terminates a digital local loop.

C.
A CSU/DSU terminates an analog local loop.

D.
A modem terminates an analog local loop.

E.
A router is commonly considered a DTE device.

F.
A router is commonly considered a DCE device.

Explanation:
The idea behind a WAN is to be able to connect two DTE networks together through a DCE
network. The network’s DCE device (includes CSU/DSU) provides clocking to the DTEconnected interface (the router’s serial interface).

A modem modulates outgoing digital signals from a computer or other digital device to
analog signals for a conventional copper twisted pair telephone line and demodulates the
incoming analog signal and converts it to a digital signal for the digital device. A CSU/DSU is
used between two digital lines –

For more explanation of answer D, in telephony the local loop (also referred to as a
subscriber line) is the physical link or circuit that connects from the demarcation point of the
customer premises to the edge of the carrier or telecommunications service provider’s
network. Therefore a modem terminates an analog local loop is correct.