| 摘要 |
PROBLEM TO BE SOLVED: To easily decide the difference between a connected terminal device or an arbitrary terminal device and a terminal device currently connected and to enable exactly the same operation of a terminal device with a certain terminal device by monitoring a signal line state, comparing information which is thus detected with previously stored information, and outputting their comparison result. SOLUTION: The modem 1 is connected between a terminal 2 and a public network 3 to enable a data communication between terminals 2 and 4 through an opposite modem 1' connected to the opposite side terminal 4. The modems 1 and 1' and terminals 2 and 4 are interconnected by ITU-T recommendation V.24 and V.28 and they are connected by modem cables 101 and 101'. The modems 1 and 1' are NCU buit-in modems which are widely used for data communication through the public network 3. A monitor part 12 of the modem 1 refers to monitor information in a storage part 13 and monitors plural interface signals between the terminal 2 and control part 11.
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