| 摘要 |
PURPOSE:To perfectly maintain a secrecy without being connected to an optional terminal by responding to the record of a callee and connecting between the terminal registered beforehand and a central processing unit. CONSTITUTION:When a maintenance center 20 accesses the central processing unit 80, it makes a phone call to the central processing unit 80, and after it transmits a maintenance center number and prescribed time elapses, it switches off the telephone once. An access right checking device 60 responds to the storage of the being called, and an automatic loop-back telephone circuit 61 sends the telephone number of the maintenance center 20 to a network controller 40 through a number information signal group line 40, based on a correspondence table between the plural maintenance center numbers registered beforehand and the telephone numbers and it calls again the maintenance center 20. In the case of a terminal equipment 10 which is the terminal to be called makes a phone call to the central processing unit 80, since the number has not been registered, the automatic loop-back circuit 61 never calls again.
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