Which of the following describes the roles of devices in a WAN?()
A、A. A CSU/DSU terminates a digital local loop.
B、B. A modem terminates a digital local loop.
C、C. A CSU/DSU terminates an analog local loop.
D、D. A modem terminates an analog local loop.
E、E. A router is commonly considered a DTE device.
F、F. A router is commonly considered a DCE device.