EXCHANGE FOR HOUSING ISDN SUBSCRIBER

摘要

PURPOSE:To continue a service by switching to the service of a general telephone sat in the power failure of a commercial power source in a customer system by switching an ISDN terminal and the general telephone set corresponding to the state of the commercial power source in an ISDN subscriber residence. CONSTITUTION:When the power failure occurs in the commercial power source in the customer system, a customer network terminating device (NT) 3 automatically connects a subscriber line 6 to a jack 4, and in an exchange, an ISDN layer synchronism supervisory circuit(SUP) 9 detects the step out of a layer 1 for a constant period, and reports it to a CPU 15 via a CPU bus 14. The CPU 15 drives a relay(Rb) 7 by issuing an instruction to a relay drive instruction input/output port (I/O) 12 via the CPU bus 14. A contact rl is set at a state shown in broken line by the operation of the RL 7, and the subscriber line 6 is switched to a general telephone subscriber termination circuit(SLC) 10 side. At this time, the CPU 15 performs a call processing by judging the outgoing/incoming call of the SLC 10 as the one identical to that of an ISDN layer termination circuit(DLC) 8. In such a way, a telephone service can be offered by using the general telephone set (TPH) 5 in the power failure of the subscriber residence.