| 摘要 |
PROBLEM TO BE SOLVED: To suppress erroneous recognition caused by signals equal with 1st and 2nd tone signals to a minimum by recognizing service start based on the sequential detection of the 1st and 2nd tone signals and the interval of that detection. SOLUTION: When the 2nd tone signal cannot be detected within a prescribed time after the detection of the 1st tone signal, a control part 8 makes invalid 1st tone signal detection and returns processing to the first step. When the 2nd tone signal is detected within this prescribed time, the control part 8 controls a mute circuit 3 and mutes transmission/reception to a hand set 2. Continuously, after a response signal composed of prescribed DTMF is returned through a line connection part 1 to a station exchange while controlling a DTMF sending part 7, the transmission of FSK data from the station exchange is waited. When these data are received, the control part 8 controls the mute circuit 3, cancels muting to the hand set 2 and returns processing to the first step.
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