Processing conversations with APPC

APPC/IMS supports standard, modified, and CPI Communications driven application programs.

The three types of application programs supported by APPC/IMS

• Standard: No explicit use of CPI Communications facilities.
• Modified: Uses the I/O PCB to communicate with the original input terminal. Uses CPI Communications calls to allocate new conversations and to send and receive data.
• CPI Communications driven: Uses CPI Communications calls to receive the incoming message and to send a reply on the same conversation. Uses the DL/I APSB call to allocate a PSB to access IMS databases and alternate PCBs.

In the modified or CPI Communications driven application programs, if an APPC conversation is allocated with SYNCLVL=SYNCPT, z/OS® manages the sync-point process for the APPC conversation participants: the application program and IMS. Transaction rollback and rescheduling is possible, because IMS issues the SRRCMIT or SRRBACK calls on behalf of the modified IMS APPC application program. If the CPI-C driven program is linked with the IMS stub code (DFSCPIR0) as required in previous releases, IMS also issues the SRRCMIT or SRRBACK calls. If the program is not linked with the stub code, then IMS is driven by the z/OS sync point manager when the application issues these calls. With z/OS as the sync point manager, failures can also be backed out.

You can schedule your standard and modified application programs locally and remotely using MSC or APPC/MVS. The logic flow for local scheduling differs from the logic flow for remote scheduling.

Scheduling programs remotely through MSC is not supported if an APPC/MVS conversation with SYNCLVL=SYNCPT is specified.