Data communication apparatus, method and system and programs for data communication process stored in computer readable storage medium

In a data communication apparatus for encoding information data by using a predetermined encoding method, encoded information data is transmitted isochronously with a predetermined communication cycle when the encoding method corresponds to a decoding method at an object node apparatus and non-encoded information data is transmitted asynchronously with the communication cycle when the encoding method does not correspond to the decoding method at the object node apparatus. It is therefore possible to perform an encoding process for the information data to be transmitted, in accordance with a decoding performance at the object node apparatus, to improve a communication efficiency, and to reduce a capacity of a memory used for communications.