Installing MRO support

This topic describes how to install support for multiregion operation (MRO) in your CICS® regions.

CICS multiregion operation (MRO) enables CICS regions that are running in the same MVS™ image, or in the same MVS sysplex, to communicate with each other. MRO does not support communication between a CICS system and a non-CICS system such as IMS™.5

MRO does not require ACF/VTAM or SNA networking facilities. The support within CICS that enables region-to-region communication is called interregion communication (IRC). IRC is implemented in three ways:

  1. Through support in CICS terminal control management modules and by use of a CICS-supplied interregion program, DFHIRP, loaded in the MVS link pack area. DFHIRP is invoked by a type 3 supervisory call (SVC).
  2. By MVS cross-memory services, which you can select as an alternative to the CICS type 3 SVC mechanism. Here, DFHIRP only opens and closes the interregion links.
  3. By the cross-system coupling facility (XCF) of MVS. XCF/MRO is required for links between CICS regions in different MVS images of an MVS sysplex. CICS selects XCF/MRO dynamically for such links, if available.

For information about the design and implementation of interregion communication, and about the benefits of cross-system MRO, see the CICS Intercommunication Guide.

To install support for MRO, complete the following steps (outlined in more detail in this section):

  1. Define CICS as an MVS subsystem.
  2. Install the current versions of the DFHIRP and DFHCSVC modules in the LPA.
  3. If you give the SVC a new number, and you have CICS Version 1 or Version 2 regions that use MRO, regenerate the CICS modules DFHCRC and DFHDRPA for those CICS versions, specifying the SVC number.
  4. Specify appropriate system initialization parameters to enable MRO for each CICS region startup.
  5. If you intend using cross-system MRO (XCF/MRO) you must also:

  6. Install the required sysplex hardware and software.
  7. Define the MVS images as systems in an XCF sysplex.
  8. To use the MRO support, you must also:

  9. Define and install the MRO connections appropriate to your CICS environment.

Start of changeProvided you complete the above steps, you can use MRO to communicate with all levels of CICS from CICS/ESA Version 4.1 onwards.End of change

Start of changeShould MRO be used to communicate between different releases of CICS, the function provided on any connection is that of the lower-level release.End of change

Defining CICS as an MVS subsystem

Multiregion operation with CICS requires MVS Subsystem Interface (SSI) support, and to obtain this you must define CICS as an operating system subsystem, as described in Defining CICS as an MVS subsystem.

Installing the modules DFHIRP and DFHCSVC in the LPA

To enable your regions to communicate by MRO, you must:

  1. Install the current versions of the DFHIRP and DFHCSVC modules into the LPA, as described in Installing CICS modules in the MVS link pack area.
    Note:
    If you are running CICS with MRO at different release levels, all communicating CICS regions must use the latest DFHIRP module and the latest SVC module, DFHCSVC, on the same MVS image. Start of changeDo not use the dynamic LPA function to replace DFHIRP for migration between releases, as this can cause incompatibility between control blocks, resulting in abend situations.End of change
  2. Define the SVC module, DFHCSVC, to MVS, as described in Installing the CICS Type 3 SVC.

Installing required hardware and software for XCF/MRO

To be able to use the cross-systems MRO to communicate between CICS regions on different MVS images, those MVS images must be running with appropriate hardware and software. The hardware and software that are required for MVS systems in a sysplex are in the CICS Transaction Server for z/OS® Program Directory.

Defining MVS images as systems in an XCF sysplex

To use XCF/MRO, all participating MVS images must be defined as part of the same sysplex, as in MVS cross-system MRO definitions.

Note:
Within a parallel sysplex, where MRO communication between MVS images is by XCF/MRO, the DFHIRP programs installed in the different MVS images can be at different release levels. However, DFHIRP must be installed from the highest release of CICS running in an MVS image. For example, a CICS Version 4 DFHIRP can communicate with a DFHIRP across XCF/MRO, but the CICS regions running in the MVS with the Version 4 DFHIRP cannot be later than CICS/ESA Version 4.

Defining MRO connections

Before you can use MRO, you must define and install connections with attributes appropriate to your CICS environment. For information about defining connections, see the CICS Intercommunication Guide .

Enabling MRO for CICS startup

For each CICS region that is to use MRO, you must specify ISC=YES to include the intersystem communication program DFHISP.

If you want a CICS region to establish MRO communication during startup, you should also specify YES on the IRCSTART system initialization parameter.

Alternatively, once your CICS region is running, you can establish MRO communication by using the CEMT SET IRC OPEN command or the EXEC CICS SET IRC OPENSTATUS(cvda) command.

Either method establishes MRO communication with every CICS region that is:

  1. Currently active.
  2. Defined to your region by CONNECTION and SESSIONS definitions that are installed from the CSD. (To establish MRO communication between two CICS regions, the installed CONNECTION definition must specify INSERVICE(YES) in both regions.)

5.
The external CICS interface (EXCI) uses a specialized form of MRO link to support DCE remote procedure calls to CICS programs, and communication between MVS batch programs and CICS .

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