| 摘要 |
PURPOSE:To make a circuit selecting control information transmitting part of a center side backup device unnecessary by measuring the time required for detecting an incoming of a calling signal to a terminal side from a center, converting this time to circuit selecting control information, and switching one circuit of a leased circuit to two circuits of an exchange by this control information. CONSTITUTION:In case a fault is generated in leased circuits 7-9, relays 6a, 6b of an exchange circuit switching part 6 of a center side backup device 1 are switched to the side of telephone sets 3, 4 respectively. Subsequently, a switching control part 15 of a terminal side backup device 12 is called by the telephone set 3. The control part 15 detects an incoming of a calling signal of the center, returns a calling signal incoming confirming tone and starts a time counting. Subsequently, the same operation is executed by the telephone set 4, and the time counting of the control part 15 is stopped. In case of a fault of the circuit 7, a switching part of the leased circuit 7 of a terminal side leased circuit switching part 14 is switched to an exchange side by the control part 15. The center switches a switching part of the leased circuit 7 of a leased circuit switching part 5, to a switching part 6 side, and also switches the switching part 6 to the leased circuit switching part 5 side. |
