Designing CICS applications for ISC

CICS® differs from IMS in that many of the flows that must occur on an ISC session occur under the control of the CICS application program.

The CICS application must do the following:

• Build outbound ATTACH function management headers
• Supply fields for SCHEDULER function management headers (if required)
• Examine inbound ATTACH function management headers and process their contents
• Issue sync points at appropriate intervals during the application program's processing.

The SNA bracket, SEND/RECEIVE, and sync-point protocols associated with CICS-generated messages depend upon the EXEC commands (The EXEC commands are SEND/RECEIVE for synchronous and START/RETRIEVE for asynchronous.) used by the application program, and when the sync points are issued during the application flow.

Information is inserted into the ATTACH and SCHEDULER function management header DPN, RDPN, PRN, and RPRN fields for message editing and routing by IMS system code, and can be overridden only by using the IMS Message Format Service (MFS). For CICS, insertion of information into the ATTACH and SCHEDULER function management headers is performed under the control of the CICS application.