The last segment in a message (either sent by the client, or received from the server) is indicated by an end-of-message (EOM) segment. (See End-of-message segment (EOM)).

• Implicit-mode messages sent by the client are received by the Listener and inserted onto the IMS™ message queue. The end-of-message segment indicates to the Listener that there are no more segments to be inserted for this message.
  Note: The server program will not receive the EOM segment; it will receive a QD status code, indicating that there are no more segments for this message.
• Implicit-mode messages to be sent by the server are actually written by the Assist module on behalf of the server program. When the server program sends application data to the client (using the ISRT call), the Assist module intercepts the output data and accumulates it in an output buffer. When the server program issues a subsequent GU to the I/O PCB, the Assist module interprets the GU as an indication that the server has inserted the last segment for that message. The Assist module then adds an end-of-message segment to the output data and issues WRITE commands, which transmit the data to the client.
  Note: The server program should not attempt to insert an EOM segment to the I/O PCB.