| 摘要 |
PROBLEM TO BE SOLVED: To monitor a telephone line effectively and/or without disturbing it by providing a monitor circuit high in impedance for monitoring the call state of a telephone by using the telephone line and a display for indicating the direction of the call of the telephone. SOLUTION: A call information detection/reception circuit 12 receives call relating information from a central telephone station 13 through the telephone line 14 and a telephone line interface(TLI) 48. A processor 18 discriminates the three kinds of the states (a voice signal, a DTMF signal and a dial tones, that is silence), of the call by reading a signal level and a modulation state on the telephone line 14. While the DTMF signal is transmitted, a DTMF decoder 18 detects the presence of the number of a telephone set dialed through the telephone line 14. The call relating information is recorded inside a call relating information data base 140 by the processor 18. The display 16 displays the call relating information.
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