# Multi-CICS Environment

Substation ES interacts with CICS in many ways. The CICS features that Substation ES uses depend on how the CICS is configured.

Other considerations pertain to the applications with which Substation ES interacts and depend on whether they conform to CICSPlex.

Substation ES can operate in a CICSPlex in many scenarios, which do not depend on the features of Substation ES itself, but take advantage of the fact that Substation ES is simply an External Call Interface (EXCI) client that is using MRO capabilities. That way, Substation ES can leverage a CICS system configurations.

Note: For more information about CICSPlex, see TIBCO Substation ES Operations and Administration.

For the transactions that have some form of application AOR affinity, configure Substation ES as a standalone CICS system. For the transactions that can run in a CICSPlex environment, the following are some of the scenarios that exist:

- Externally Initiated Request or Request/Reply
- Externally Initiated “Fire and Forget” (External Transaction Starts)
- Externally Initiated “Fire and Forget” to TD or TS Queue
- CICS to TD Queue (CICS-Initiated “Fire and Forget”)
- CICS Application-Initiated Request Reply

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