To transmit and receive information such as images, voice and data in an optimally set environment fitting the communication speed and use situation of a connected communication line by eliminating setting work fitting the communication line as much as possible.
In a data communication system performing two-way communication through a communication line 7 between terminal devices 1 with each other, at least one among an image, voice and data is selected as information to be transmitted from one terminal device 1 and a connection request is performed to the other, the other terminal device 1 receiving the connection request recognizes and starts a function needed to transmit information at the point of time when the line 7 is connected, and a compression system for the selected information is set between the terminal devices 1 in accordance with the transfer speed of the line 7.
INAGAKI KANJI
OTSU RYUICHI
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