Abstract: A clock change circuit contains: a clock gate unit for receiving first and second clock signals, and detecting a timing at which both the first and second clock signals are at an inactive level to output an active timing signal indicating the timing; a delay unit for inputting a select control signal and the timing signal, and outputting a delayed select control signal the state of which is changed to the same state of the select control signal after the active timing signal is received from the clock gate unit; and a select unit for inputting the first and second clock signals, and selects one of the first and second clock signals according to the delayed select signal to output the selected clock signal.

Abstract: A first terminating unit terminates a subscriber line at a first end of the line, the first terminating unit being connected to a public telecommunication network. A second terminating unit terminates the subscriber line at a second end of the line, a terminal equipment being connected to the second terminating unit. A monitoring device monitors at least the subscriber line and the second terminating unit and an alarm generating unit generates an alarm input concerning a condition of at least the subscriber line and the second terminating unit. An alarm controlling device examines a result of the monitoring by the monitoring device, the alarm controlling device controlling, according to a result of the examination, how the alarm input generated by the alarm generating unit is handled.