Patent ID: 7680057

Claim:
A data transmission method for placing variable-length transmission data in each frame having a fixed time length to transmit the frame without transmitting rate information of the transmission data, a length of the transmission data being one of two values, a predetermined fixed value X (X≠0) and the value 0, the data transmission method comprising the steps of: at a transmitting side, calculating an error-detecting code of the transmission data in the frame only if the frame contains the transmission data; generating frame data containing the transmission data and the calculated error-detecting code of the transmission data if the frame contains the transmission data, and generating frame data that contains neither the transmission data nor the error-detecting code of the transmission data if the frame does not contain the transmission data; and transmitting the generated frame data, the generated frame data not including a field indicating length; and at a receiving side, receiving the frame data; assuming only one final bit position in the received frame data which is the final bit position where the length of the transmission data is X, assuming the transmission data and the error-detecting code of the transmission data based on the assumed final bit position, and calculating an error-detecting code based on the assumed transmission data; deciding that the received frame data contains the transmission data if the assumed error-detecting code matches the error-detecting code calculated based on the assumed transmission data, and deciding that the received frame data does not contain the transmission data or the received frame data contains an error if the assumed error-detecting code does not match the calculated error-detecting code; and obtaining the transmission data in the received frame data based on the result of the decision.