| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that a conventional telephone line connection method has required for a user to manually set line parameters. SOLUTION: Whether a telephone line is an extension or an external line is discriminated based on a call tone from the telephone line, when the external line is detected, a prescribed DTMF (dual tone multi frequency) tone or a pulse signal is transmitted and the presence/absence of a call tone is detected to discriminate whether the telephone line is a tone line or a pulse line. When it is discriminated that the telephone line is the extension, a number of a plurality of objects of external line call numbers set in advance is transmitted by a DTMF tone signal or a pulse signal, the presence/absence of the call tone is detected to discriminate whether the telephone line is a tone line or a pulse line, when no call tone is detected, a succeeding number of a plurality of the objects of the external line call numbers is transmitted and the presence/absence of the call tone is detected. Then the above processing is repeated until the call tone is detected from the telephone line and when the call tone is detected, the number transmitted by the DTMF tone signal or the pulse signal just before the detection is determined to be an external line transmission number.
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