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.
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
In the externally initiated request or request/reply scenario, a Substation ES is in each z/OS LPAR, and each Substation ES instance uses Enterprise Message Service messaging by means of queues; connections to CICS use the IBM EXCI facility. - Externally Initiated “Fire and Forget” (External Transaction Starts)
The externally initiated “fire and forget” scenario shares the same architecture with the externally initiated request or request/reply scenario. CICS transactions are invoked with a CICS START function call. - Externally Initiated “Fire and Forget” to TD or TS Queue
The externally initiated “fire and forget” to TD or TS queue shares the same architecture for the preceding scenarios, except that the inbound data is written to a CICS TS or TD queue. The TD queues can be local to that AOR or shared with another AOR. - CICS to TD Queue (CICS-Initiated “Fire and Forget”)
In the CICS to TD queue scenario, a CICS application writes data to “publish” to a TD queue. The Substation ES queue server is initiated within the CICSPlex in the region to which that Substation ES instance is connected. - CICS Application-Initiated Request Reply
In the CICS application-initiated request reply scenario, a CICS application initiates an external request that expects a response by linking to a supplied CICS program that passes the COMAREA to Substation ES, and then waits for a response for a predefined time.