XCF2 is part of the MVS/ESA base control program, providing
high performance communication links between MVS images that are linked in
a sysplex (systems complex) by channel-to-channel links, ESCON® channels, or coupling facility links3. The IRC provides an XCF access method that makes it unnecessary
to use VTAM® to communicate between MVS images within the same MVS sysplex. Using
XCF services, CICS regions join a single XCF group called DFHIR000. Members
of the CICS XCF group that are in different MVS images select the XCF access
method dynamically when they wish to talk to each other, overriding the access
method specified on the connection resource definition. The use of the MVS
cross-system coupling facility enables MRO to function between MVS images in a sysplex environment, supporting all the usual
MRO operations, 4 such as:
- Function shipping
- Asynchronous processing
- Transaction routing
- Distributed program link
- Distributed transaction processing.
CICS regions linked by XCF/MRO can be at different release levels;
see Multiregion operation. Depending on the versions of CICS installed in
the MVS images participating in XCF/MRO, the versions of DFHIRP installed
in the link pack areas of the MVS images can be different. If a single MVS image contains different releases of CICS, all using XCF/MRO
to communicate with regions in other images in the sysplex, the DFHIRP module
in the MVS LPA should be that from the most current CICS release in the image,
or higher. For full details of software and hardware requirements for
XCF/MRO, see Requirements for XCF/MRO.
CICS MRO in an XCF sysplex environment is illustrated in Figure 2.
Figure 2. A sysplex (SYSPLEX1) comprising two MVS images (MVS1 and MVS2). In this illustration,
the members of the CICS group, DFHIR000, are capable of communicating via
XCF/MRO links across the MVS images.
In MVS1, the DFHIRP module
in the LPA should be at the level of the highest CICS TS z/OS release in
the image.
Because it contains only CICS TS OS/390, Version 1 Release 3 regions,
the DFHIRP module in the LPA can be at the CICS TS OS/390, Version 1 Release 3 level, or later.
In Figure 2, the MRO links between CICS1 and CICS2, and between
CICS3 and CICS4, use either the IRC or XM access methods, as defined for the
link. The MRO links between CICS regions on MVS1 and the CICS regions on MVS2
use the XCF method, which is selected by CICS dynamically.
Some of the benefits of cross-system MRO using XCF links are:
- A low communication overhead between MVS images, providing much better
performance than using ISC links to communicate between MVS systems. XCF/MRO
thus improves the efficiency of transaction routing, function shipping, asynchronous
processing, and distributed program link across a sysplex. (You can also use
XCF/MRO for distributed transaction processing, provided that the LUTYPE6.1
protocol is adequate for your purpose.)
- Easier connection resource definition than for ISC links, with no VTAM
tables to update.
- Good availability, by having alternative processors and systems ready
to continue the workload of a failed MVS or a failed CICS.
- Easy transfer of CICS systems between MVS images. The simpler connection
resource definition of MRO, and having no VTAM tables to update, makes it
much easier to move CICS regions from one MVS to another. You no longer need
to change the connection definitions from CICS MRO to CICS ISC (which, in
any event, can be done only if CICS startup on the new MVS is a warm or cold
start).
- Improved price and performance, by coupling low-cost, rack-mounted, air-cooled
processors (in an HPCS environment).
- Growth in small increments.

XCF. The MVS/ESA cross-system coupling facility that
provides MVS™ coupling services. XCF services allow authorized programs in a multisystem
environment to communicate (send and receive data) with programs in the same,
or another, MVS image. Multisystem applications can use the services of XCF,
including MVS components and application subsystems (such as CICS®), to communicate
across a sysplex. See the MVS/ESA Setting Up a Sysplex manual,
GC28-1449, for more information about the use of XCF in a sysplex.
Coupling facility links. High-bandwidth fiber optic links that
provide the high-speed connectivity required for data sharing between a coupling
facility and the central processor complexes attached to it.
XCF/MRO does not support
shared data tables. Shared access to a data table, across two or more CICS
regions, requires the regions to be in the same MVS image. To access a data
table in a different MVS image, you can use function shipping.
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