| 摘要 |
PURPOSE:To maintain all branch offices by permitting a maser office to sequentially poll respective branch offices so as to transmit maintenance information request signals through the use of a maintenance channel, to receive maintenance information answer signals from respective branch offices and to decide fault based on the presence and absence of the detection of the maintenance information answer signals. CONSTITUTION:A circuit for transmitting maintenance information request signal 12 inputs the maintenance information request signals to transmission means 3 and 3', and the signals are time division multiplexed with the time division signals of an information channel as the time division signals of the maintenance channel. A transmission switching circuit 4 selects the normal side of the output signals from the transmission means 3 and 3' and transmits them to respective branch offices through a transmission path 17, whereby the master office 11 sequentially polls the branch offices 15-1 and 15-2. A fault decision/switching control circuit 14 decides whether the fault is in the master office or in the branch offices based on the detection of the maintenance information answer signals, and if the fault is decided to be in the master office, it outputs the switching control signals to the transmission switching circuit 4 and a reception switching circuit 7, and selects either of a normal system from the transmission means 3/reception means 6 or the transmission means 3' reception means 6 '.
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