JES benefits from the use of the common coupling services component

Both JES2 and JES3 use the JES common coupling services component and benefit from:

Access to a common time reference available through the Sysplex Timer
Use of a high-speed messaging service
Monitoring system and address space events and status.

Further, JES2 uses the component's macros and exits for checkpoint reconfiguration processing to simplify what would otherwise require a complex, operator-intensive dialog. (The component provides a communication mechanism that informs each JES2 MAS member of system events such as system status, and checkpoint data set and structure status.) JES3 uses the component to allow communication across the JES3 complex that would otherwise require JES3-managed channel-to-channel (CTC) hardware. Additionally, your installation can use the component's macros and exits to satisfy your processing needs in JES installation exits and modifications. Figure 1 shows a simplistic view of a JES member-to-member link as provided by the XCF and the JES XCF.

Figure 1. JES communication mechanism

There are several ways your installation might chose to use the JES XCF macros and exits. When each JES subsystem is a member of a JES XCF group, you can use the JES XCF macros to send and receive messages among the JES members. Thus, your installation is capable of creating multi-system modifications which increases the quality of your current or future installation modifications.

To ease diagnosis and future migration tasks, IBM recommends that you invoke the JES XCF macros within standard JES exits and JES3 DSPs. JES XCF allows you to:

Add to or modify JES component messages
You can use exits IXZXIT01, IXZXIT02, and IXZXIT03 to modify JES processing by changing the data that JES sends from one JDU to another. You can affect JES functions and thereby modify JES to meet more of your installation's processing requirements through IBM-supplied exits.
Write a JES3 DSP
You cannot write a JES3 DSP to provide function such as tape management unless your installation has the ability to modify or create function at the same level that IBM JES3 code requires. The JES common coupling services provide an interface to allow you to write such code.
Use ESCON architecture
In JES3, you can eliminate the use of JES3-managed 3088 channel-to-channel (CTC) hardware and replace it with MVS XCF-managed enterprise systems connection (ESCON) architecture hardware. Depending upon your specific application, you can use either CTCs or the coupling facility. Using the coupling facility provides increased ease of system management through more simplified system-to-system connectivity. The coupling facility eliminates the exponential growth of CTC connections associated with the addition of each new system to your sysplex. Refer to z/OS Parallel Sysplex Application Migration, SA22-7662. for further information concerning the choices of available hardware and its use in a JES3 complex.