| 摘要 |
PURPOSE:To eliminate the necessity for the nonservice interruption with a battery for the whole device, by securing a self-support for the call given before the service interruption when a service interruption arises and connecting the telephone under an on-hook state to a prescribed trunk line. CONSTITUTION:When a service interruption arises, a control circuit 8 delivers a changeover signal to a service interruption switching circuit 20 in case e.g. a telephone 1-1 is under an on-hook state by the starting of the service interruption detection output given from a service interruption detecting circuit 14. Thus the circuit 20 forms a connection route between the telephone 1-1 and a trunk line 11-1. In case a telephone 1-2 is hooked off, no changeover signal is delivered to the circuit 20 to continue a call through a crosspoint switch 10. When the service interruption is recovered to supply the electric power again, the circuit 8 checks the working state of the circuit 20. Thus the call that is given through the switch 10 before the service interruption is kept as it is. While the call given during the service interruption and through the circuit 20 is switched to a route passing through the switch 10 with the drive of a crosspoint driving circuit 9. |
