Roles of Devices in a WAN

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In a Wide Area Network (WAN), various devices play specific roles to facilitate communication between different networks over a large geographical area. Let's go through each option and explain their roles:

A. A CSU/DSU terminates a digital local loop: A CSU/DSU (Channel Service Unit/Data Service Unit) is a device that connects a digital circuit, such as a T1 or T3 line, to a customer's network equipment. It terminates the digital signal received from the service provider and provides a connection point for the customer's equipment.

B. A modem terminates a digital local loop: A modem (modulator-demodulator) is a device used to transmit digital data over analog communication lines, such as traditional telephone lines. However, it does not terminate a digital local loop. Modems are typically used to establish connections over analog lines, converting digital signals from a computer or network device into analog signals that can be transmitted over the telephone line. Therefore, this option is incorrect.

C. A CSU/DSU terminates an analog local loop: A CSU/DSU does not terminate an analog local loop. As mentioned earlier, a CSU/DSU is used to terminate digital circuits, not analog ones. Therefore, this option is incorrect.

D. A modem terminates an analog local loop: This option is correct. A modem is used to terminate an analog local loop. It connects to the analog telephone line and converts the analog signals received from the service provider into digital signals that can be understood by the customer's equipment.

E. A router is commonly considered a DTE device: This option is incorrect. In WAN terminology, DTE (Data Terminal Equipment) refers to the end-user device that communicates with the WAN network. Routers, on the other hand, are considered DCE (Data Communications Equipment) devices. DCE devices provide clocking and synchronization signals to DTE devices. Therefore, a router is commonly considered a DCE device, not a DTE device.

F. A router is commonly considered a DCE device: This option is correct. As mentioned earlier, routers are commonly considered DCE devices in a WAN. They provide clocking and synchronization signals to the connected DTE devices (such as computers or switches) to establish communication over the WAN.

In summary, the correct answers are: A. A CSU/DSU terminates a digital local loop. D. A modem terminates an analog local loop. F. A router is commonly considered a DCE device.