| 摘要 |
PURPOSE:To perform stable operation to a trunk line incoming call by monitoring the free/engaged state of a nighttime attendant board all the time, and placing trunk lines whose number suits to reception service in an invariably incoming ready state. CONSTITUTION:When a nighttime zone is entered, two trunk lines L1 and L2 of a public telephone network which interface with trunk line trunks COT 41 and COT 42 are ready for incoming and other trunk lines L3- are switched and connected to a telephone guide device TG 80 through SW 50. A central controller 60 monitors the contents of memories Ma 22 and Mb 24 all the time to confirm that nighttime attendant boards NAT 21 and NAT 23 are free, and when it is found that the COT 41 is used by an extension telephone set STA 10, a switch w3 corresponding to the COT 43 is read out of a main storage device MEM 70 and the SWC 90 is switched to a state shown by the solid line sw3 in the figure.
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