| 摘要 |
PURPOSE:To prevent an erroneous outgoing call caused by erroneously recognizing a used telephone line by identifying the kind of a connected telephone line network by detecting a dial tone signal and automatically adding a line switching signal to a destination telephone number at need so as to transmit a selection signal corresponding to it. CONSTITUTION:By analyzing the dial tone signal 14, the dial tone signal 6 identifies the telephone line network connected at present time and outputs a line identification signal 15. A line switching signal generation part 3 decides whether or not the switching of line is needed with the line identification signal 15 and outputs the line switching signal 2 if the telephone line network connected at the present time is an extension exchange network. And if the telephone line network is directly connected to the exchange network of a central office, the line switching signal is not outputted. Composing a destination telephone number signal 10 and a line switching signal 11, a telephone number generation part 4 generates and outputs the telephone number signal 12 which should be actually called,and a selection signal generation part 5 generates and outputs the selection signal 13 corresponding to the telephone number signal 12.
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