A local area network is provided for a plurality of autonomous computers (10) which operate at different rates and under different protocols coupled by network bus adapters (12) to a global bus (14). A host computer (HC) divides a message file to be transmitted into blocks, each with a header that includes a data type identifier and a trailer. The associated network bus adapter (NBA) then divides the data into packets, each with a header to which a transport header and trailer is added with frame type code which specifies one of three modes of addressing in the transmission of data, namely a physical address mode for computer to computer transmission using two bytes for source and destination addresses, a logical address mode and a data type mode. In the logical address mode, one of the two addressing bytes contains a logical channel number (LCN) established between the transmitting and one or more receiving computers. In the data type mode, one of the addressing bytes contains a code identifying the type of data. Every NBA initialized to accept specified types of data will automatically accept all data of the types it is conditioned to accept. Protocol handling is carried out by a module in each NBA.