Existing single-region CICS® systems can generally be converted to multiregion CICS systems with little or no reprogramming.
CICS function shipping allows operators of terminals owned by an existing command-level application to continue accessing existing data resources after either the application or the resource has been transferred to another CICS region. Applications that use function shipping must follow the rules given in Application programming for CICS function shipping. To conform to these rules, it may sometimes be necessary to modify programs written for single-region CICS systems.
CICS transaction routing allows operators of terminals owned by one CICS region to run transactions in a connected CICS region. One use of this facility is to allow applications to continue to use function that has been discontinued in the current release of CICS. Such coexistence considerations are described in the CICS Transaction Server for z/OS® Migration from CICS TS Version 2.3. In addition, the restrictions that apply are given in Application programming for CICS transaction routing.
It is always necessary to define an MRO link between the two regions and to provide local and remote definitions of the shared resources. These operations are described in Defining intercommunication resources.