JDUs running in any JES environment can use the JES XCF macro IXZXIXSM to send messages to a JDU running in a JES2 or JES3 address space, or to a JES3 JDU running in the functional subsystem (FSS) address space. Messaging is the process of one software component (JES JDU) running on one member sending the data packet (up to 60 kilobytes of data) to the same or other member in the group.

All messages are received in the order in which they are sent, and multi-segment messages are not sent until the entire message (all segments) is available. This message-ordering feature allows you to eliminate any previously written installation code you might have provided for that purpose. (See Message Segments for an explanation of message segments.)

Then:

1. JES XCF places the message in the receiver's mailbox
2. JES XCF passes control to the POST exit routine, which notifies the receiver of a mail delivery
3. The receiver processes the message.

   The receiver must acknowledge the message to JES XCF and optionally can return data or an acknowledgement to the sender.

Delivery, and subsequent processing, is determined by three message characteristics that are specified by the value of the REQTYPE= parameter on the IXZXIXSM macro. Refer to Table 1 for a summary of the REQTYPE values and the message processing characteristics of each.