Overview of function shipping

CICS® function shipping enables CICS application programs to:

Applications can be written without regard for the location of the requested resources; they simply use file control commands, temporary-storage commands, and other functions in the same way. Entries in the CICS resource definition tables allow the system programmer to specify that the named resource is not on the local (or requesting) system but on a remote (or owning) system.

An illustration of a shipped file control request is given in Figure 4. In this figure, a transaction running in CICA issues a file control READ command against a file called NAMES. From the file control table, CICS discovers that this file is owned by a remote CICS system called CICB. CICS changes the READ request into a suitable transmission format, and then ships it to CICB for execution.

In CICB, the request is passed to a special transaction known as the mirror transaction. The mirror transaction recreates the original request, issues it on CICB, and returns the acquired data to CICA.

The CICS recovery and restart facilities enable resources in remote systems to be updated, and ensure that when the requesting application program reaches a synchronization point, any mirror transactions that are updating protected resources also take a synchronization point, so that changes to protected resources in remote and local systems are consistent. The CICS master terminal operator is notified of any failures in this process, so that suitable corrective action can be taken. This action can be taken manually or by user-written code.

Figure 4. Function shipping
 The picture shows two CICS systems, CICA and CICB, which are connected by an ISC or MRO link. On CICA, the definition of a file called "NAMES" specifies REMOTESYSTEM(CICB). On CICB, "NAMES" is defined as a local file. A program on CICA issues an EXEC CICS READ FILE(NAMES) command. CICA sees that "NAMES" is owned by CICB and ships the request to CICB. In CICB, the mirror transaction is attached. The mirror issues the READ command against "NAMES" and passes the retrieved data back to the program on CICA.

Related concepts
Design considerations
The mirror transaction and transformer program
Function shipping-examples
Related tasks
Introduction to CICS intercommunication
Application programming for CICS function shipping
[[ Contents Previous Page | Next Page Index ]]