Connections between subsystems

This section presents a brief overview of the ways in which subsystems can be connected for intersystem communication. There are three basic forms to be considered:

A possible configuration is shown in Figure 3.

Figure 3. A possible configuration for intercommunicating systems
 The picture shows two IBM 3725s. The first supports two operating systems--z/OS and OS/390. On z/OS, there are two CICS TS z/OS regions, CICSA and CICSB, and a VTAM domain, VTAM1. On OS/390, there is one CICS TS for OS/390 region, CICSC, an IMS region, IMSA, and a VTAM domain, VTAM2. The first 3725 is configured with a multichannel adaptor that connects the two VTAM domains. The second 3725 supports one operating system--VSE. On VSE, there are two CICS/VSE regions, CICSD and CICSE, and a VTAM domain, VTAM3. The two 3725s are connected.

Single operating system

ISC within a single operating system (intrahost ISC) is possible through the application-to-application facilities of ACF/VTAM. In Figure 3, these facilities can be used to communicate between CICSA and CICSB, between CICSC and IMSA, and between CICSD and CICSE.

In an MVS™ system, you can use intrahost ISC for communication between two or more CICS® systems (although MRO is a more efficient alternative) or between, for example, a CICS system and an IMS™ system.

From the CICS point of view, intrahost ISC is the same as ISC between systems in different VTAM® domains.

Physically adjacent operating systems

An IBM® 3725 can be configured with a multichannel adapter that permits you to connect two VTAM domains (for example, VTAM1 and VTAM2 in Figure 3) through a single ACF/NCP/VS. This configuration may be useful for communication between:

Direct channel-to-channel communication is available between systems that have ACF/VTAM installed.

Remote operating systems

This is the most typical configuration for intersystem communication. For example, in Figure 3, CICSD and CICSE can be connected to CICSA, CICSB, and CICSC in this way. Each participating system is appropriately configured for its particular location, using MVS or Virtual Storage Extended (VSE) CICS or IMS, and one of the ACF access methods such as ACF/VTAM.

For a list of the CICS and non-CICS systems that CICS Transaction Server for z/OS® can connect to via ISC, see Intersystem communication. For detailed information about using ISC to connect CICS Transaction Server for z/OS to other CICS products, see the CICS Family: Communicating from CICS on System/390® manual.

Related concepts
Intercommunication concepts and facilities
Intersystem sessions
Multiregion operation
Considerations for IMS
Related tasks
ACF/VTAM definition for CICS
Establishing intersystem sessions
Defining APPC links
Related reference
Modules required for ISC

5.
The operating systems may or may not be located in the same physical box.

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