# Trigger Message Flows in CICS

When SXCOTRED receives control, it does a series of steps.

1. Gets parameters from either CommArea or Container.
2. Analyses parameters for validity.
3. Checks for active RED interface in CICS.
4. Gets access to the user data based on input passed.
5. Two methods of SSES selection are available; Primary/Alternative and Round-Robin.
6. Sends the RED message to Substation ES using Send, Send with Confirm, or Send with Reply indicating the RED Service to use.
   - All Substation ES (could be one or many on same or different LPARs) monitoring SXCOTRED requests validate Service availability.
   - SXCOTRED transfers the message to Substation ES.
   - SXCOTRED waits for response (if required) with a timeout.
   - Substation ES handles the message and forward it to its destination, and then gets reply and returns it to the waiting SXCOTRED program.
7. SXCOTRED returns the results of the call in the parameter control block and response message as indicated.

The following figure shows the trigger message transfer in CICS:

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