End-of-message segment

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. When the client program sends an EOM segment, the Listener interprets the EOM as an indication that no more message segments are to be received and inserts the segments onto the IMS™ message queue.
• Implicit-mode messages received by the client 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. (The client program should test for the EOM segment to determine when the last segment of the message has been sent by the server program.)