Novel message formats for use in a distributed transaction environment are disclosed. Each message includes a message type field, a message length field, and a data field, typically in the foregoing order, and each field in the message has a fixed number of bytes. The message type and data length fields may be comprised of a single header. The data field may include novel groups of OSI TP PDUs where each grouping characterizes the content of the data in the PDU. A novel apparatus for use in a distributed transaction environment also is disclosed. The apparatus may include a peer processing machine and a multiplexed TCP/IP connection for exchanging messages with other peer processing machines in the distributed transaction environment.