# Example of ESB Request – Reply and Trigger

This example illustrates how a TIBCO messaging client application initiates a request message to invoke an IMS Message Processing Program (MPP) by using the IMS message queue through Substation ES.

The IMS MPP replies by putting information into the IO-AREA and inserting it to the IMS message queue. In addition, the MPP uses `ALT-PCB` to insert the output data to the destined Substation ES trigger TPipe. Substation ES picks up that data and delivers the reply and trigger messages to the IVP Sender Listener. In both directions, the Substation ES Transformer processes the data conversion according to the selected conversion rules in the recipe and trigger.

For more information about the process flow, see the TIBCO Substation ES Concepts manual.

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