PURPOSE: To prevent invasion into a system while unnecessitating passwords by executing line connection for an opposite side station, for which data transmission is requested for establishing data link, with the telephone number of a data transmission requesting station stored in advance after the opposite side station temporarily disconnects a line.
CONSTITUTION: For data transfer between a center device 1 and remote device 61-6a, the line is temporarily disconnected after the line is connected to any one of the remote devices 6, and the device 1 disconnects the line as well. After the disconnection is completed, the device 6 executes the operation of connection with the device 1 by using the previously stored phone number of the device 1. The device 6 confirms whether communication is originally from the device 1 or not. At such a time, the confirmation is executed not by using the conventional password for establishing data link but by reconnection due to the phone number from the side of the device 6 receiving polling or selecting to the device 1. Thus, since no password is provided, invasion into the system caused by being stolen, etc., is prevented. Further, a software on the side of the remote device 6 can simplify processings such as the request or confirmation of the password.
OISHI TATSUYA
UNNO TETSUO
