POWER SUPPLY INTERRUPTION DETECTION METHOD AND SYSTEM FOR CUSTOMER LINE TERMINAL UNIT IN OFFICE LINE TERMINAL UNIT

PROBLEM TO BE SOLVED: To obtain a power supply state monitor method and a system by which the state of power supply of a customer line terminal unit(DSU) is surely monitored at a high speed. SOLUTION: A customer line terminal unit(DSU) inserts power supply interruption information by n-frames to main data at the time of the occurrence of power supply interruption and transmits the resulting data to an office line terminal unit(OCU), the OCU extracts the power supply interruption information from the main data transmitted from the DSU and discriminates whether or not the power interruption is normal by a majority decision theory as to the n-frames from the extracted power supply interruption information. For example, the OCU discriminates that the power of the DSU is interrupted in the case that the power supply interruption information is detected in the two frames even when the power supply interruption information cannot be detected by the one frame among the three fromes due to deterioration in transmission quality or the like.