Time-division multiplexing communication system for performing a plurality of communications having different data speeds

A communication system in which a plurality of terminal devices connected respectively through node devices to a loop transmission line perform data transmission/reception in a time-division multiplexing manner by using a communication frame constituted by a plurality of sub-frames circulating on said transmission line, each of said sub-frames being constituted by a plurality of time slots, each of said node devices comprising:

• first means for storing a first parameter for specifying at least one of said plurality of sub-frames allotted to the respective node device;
• second means for storing a second parameter for specifying at least one of said plurality of time slots of said at least one of said plurality of sub-frames allotted to said respective node device;
• third means for receiving said communication frame from said loop transmission line;
• fourth means for identifying said at least one of said time slots specified by said second parameter in said at least one of said sub-frames specified by said first parameter in said communication frame received by said third means;
• fifth means for inserting data received from a corresponding terminal device and an indicator into said time slot identified by said fourth means in said communication frame and for sending said communication frame onto said loop transmission line, said indicator indicating validity of said data inserted in said time slot identified by said fourth means;
• and
• sixth means for extracting data from said time slot identified by said fourth means from said communication frame received by said third means and for transferring the extracted data to said corresponding terminal device when said indicator inserted in said time slot identified by said fourth means indicates said data in said time slot identified by fourth means to be valid.