Loop transmission system with improved bypass routing arrangement

A loop transmission system comprising:

• first and second loop-shaped transmission routes enabled to transmit a message in first and second directions, respectively;
• a plurality of terminal units for communications through said first and second transmission routes;
• a plurality of first transmission control units connected between said first transmission route and corresponding terminal units, respectively, for controlling the transmissions of the message on said first transmission route;
• a plurality of second transmission control units connected between said second transmission route and corresponding terminal units, wherein each of said second transmission control units is coupled to mate with a corresponding one of said first transmission control units and is connected with the same corresponding terminal unit to which said corresponding first transmission control unit is connected, said second transmission control units controlling the transmission of the message on said second transmission route;
• and
• a plurality of bypass routes enabled to transmit the message in two ways and respectively connecting said first and second transmission control units mating with each other,
• said message containing, in addition to data to be transferred, a sending address, which is equal to the address of the transmission control unit having transmitted said message, and a bypass code capable of taking a first or second value,
• each of said first and second transmission control units including:
• means for sending the message to said bypass routes;
• means for receiving the message from said bypass routes;
• and means for storing and determining whether a minor loop is operating abnormally, said minor loop being comprised of said transmission control unit itself, a corresponding transmission control unit mated to said transmission control unit itself and located on a different transmission route, a bypass route for connecting said transmission control unit itself and the corresponding transmission control unit on a different path, a transmission control unit adjacent to said transmission control unit itself along the same transmission path, a transmission control unit corresponding to said adjacent transmission control unit and lying in the different transmission route, and a bypass route for connecting adjacent transmission unit and its corresponding transmission control unit;
• and
• means for controlling the sending process of the message received at each of said first and second transmission control units so that, when said storing means indicates that said minor loop is abnormal in a case where said message is received from the corresponding loop-shaped transmission route to which said transmission control unit itself is coupled, said message having its bypass code corrected is fed out of said control unit such that said message having its bypass code corrected to the first value is fed out to the corresponding loop-shaped transmission route if the sending address of the message received is equal to the address of its mating transmission control unit and if said bypass code takes said second value, and such that said message is fed out to the corresponding bypass route if the sending address of the message received is equal to the address of its mating transmission control unit and if said bypass code takes said first value.