Links between CICS systems

In addition to defining individual CICS® resources, you can use CICSPlex® SM to define and manage the communication links between CICS systems. Rather than identifying each CICS system in a communication network to each of its partners (as RDO requires), you can specify general connectivity information to be used by all the CICS systems in a CICSplex.

For example, to define a communication link between two CICS systems using RDO, you specify:

CICS System A
CICS System B
CONNECTION(SYSB)...
CONNECTION(SYSA)...
SESSION(S0AB)...
SESSION(S0BA)...

In other words, for each pair of CICS systems that are to communicate you need four definitions - two connections and two sessions. And each connection and session definition is unique to a given pair of CICS systems. They cannot be reused for different communication links.

With Business Application Services, on the other hand, you create one system link (SYSLINK) for each pair of CICS systems. The system link definition refers to one connection definition and one session definition that describe the nature of the link. And those connection and session definitions can be used by any number of system links that share the same characteristics.

Figure 11 illustrates the resource definitions that are required for CICSPlex SM to interconnect three CICS systems. In this example, the total number of definitions is five, rather than the 12 definitions that would be required by RDO.

Figure 11. An example of defining communication links
 The diagram shows three CICS systems, EYUMAS1A, EYUMAS2A and EYUMAS3A which are linked in a triangular formation by three system links, SYSLNK12, SYSLNK23 and SYSLNK31. All three system links have access to the same connection definition, C002 and session definition, S0002.

To define links between the CICS systems in a CICSplex, you would:

  1. Define the CICS systems to CICSPlex SM.

    Use the CICSSYS view to identify all of the CICS systems you want to connect. Of course, if you are already using CICSPlex SM, you have already identified your CICS systems. CICSPlex SM uses the CICS system ID (SYSIDNT) you specify to identify the system link.

  2. Define the connections and sessions.

    Use the CONNDEF view to create connection definitions for each type of system link you want to create (such as APPC or EXCI). Similarly, use the SESSDEF view to create an appropriate session definition for each connection. Both connection and session definitions are required for each type of system link in your network.

    Note:
    When defining MRO links it is advisable to set the SESSDEF receive and send prefixes to (< and >). If you define your own receive and send prefixes, you must create a SESSDEF for each SYSLINK to avoid duplicate session names being created.
  3. Define the system links.

    With the names and system IDs of your CICS systems and the appropriate connection and session definitions in place, CICSPlex SM is ready to generate the connections required to link those systems. To define system links, you can:

    Use the Model System field on CICSSYS
    The Model System field allows you to use the existing system links of one CICS system as the model for another system's links. New system links are defined with the same relationships that exist for the model system. This might be useful for a CICS system with a large number of links (such as a TOR in a TOR-to-AOR network).
    Use the CICSSYS CON action command
    The CON action command allows you to use the system links of an existing CICS system as the model for another CICS system. Using the CON action command has the same effect as specifying a Model System when the CICS system is created or updated.
    Use the CICSSYS GEN action command
    The GEN action command is useful when you want to migrate the RDO system link definitions found in a set of active CICS systems to the CICSPlex SM data repository. You are prompted to identify the connection and session definitions for each type of system link found in the network.
    Use the SYSLINK CREate action command
    The CREate action command can be used to define an individual system link to CICSPlex SM. You have to identify the connection and session definitions to be used for the link.

Figure 12 provides an overview of the end-user interface views used to define links between CICS systems.

Figure 12. Views for defining links between CICS systems
 The diagram shows the views which are used to define links between CICS systems. CICSSYS is used to create system definitions and system links. SYSLINK is used to create and install system links. CONNDEF is used to describe connection attributes. SESSDEF is used to describe session attributes.

Related concepts
Using the end user interface to define CICS resources
Common EUI resource definition actions
Common EUI definition fields
Multiple versions of a resource definition
Availability for CICS releases
Creation of resource definitions
Maintenance of resource definitions
Resource definition validation
Management of CICS resources using CICSPlex SM
Installation of CICS resources
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