COMMUNICATION SYSTEM

PURPOSE:To make different data transmission systems available in mixture in a same communication line by providing a setting means for protocol update information to a prescribed area of a data and applying data transmission based on the information of the received data. CONSTITUTION:A protocol update information part 11 as a means setting protocol update information to a frame format of a data is provided as shown in figure. In the communication by communication equipments 1, 2, 3..., a frame data is received at first from other equipment, the information part 11 of the received frame is read and whether or not the version number is supported by the firmware of the equipment is discriminated by collating with the version number stored in advance in the equipment. When the received version number is smaller than the stored version number, since the received version is supported by the system, the frame data is fetched and relevant transmission reception is implemented. Moreover, when the received protocol version is not supported by the equipment, the data is not fetched but the reception of the frame data is finished.