Overview of transaction routing

CICS® transaction routing allows terminals connected to one CICS system to run with transactions in another connected CICS system. This means that you can distribute terminals and transactions around your CICS systems and still have the ability to run any transaction with any terminal.

Figure 16 shows a terminal connected to one CICS system running with a user transaction in another CICS system. Communication between the terminal and the user transaction is handled by a CICS-supplied transaction called the relay transaction.

Figure 16. The elements of transaction routing
 The picture shows a TOR connected to an AOR by an MRO or APPC link. A terminal is connected to the TOR, in which the CICS relay transaction is running. In the AOR, the user transaction is running.

The CICS system that owns the terminal is called the terminal-owning region or TOR, and the CICS system that owns the transaction is called the application-owning region or AOR. These terms are not meant to imply that one system owns all the terminals and the other system all the transactions, although this is a possible configuration.

The terminal-owning region and the application-owning region must be connected by MRO or APPC links. Transaction routing over LUTYPE6.1 links is not supported.

In transaction routing, the term terminal is used in a general sense to mean such things as an IBM® 3270, or a single-session APPC device, or an APPC session to another CICS system, and so on. All terminal and session types supported by CICS are eligible for transaction routing, except those given in the following list:

The user transaction can use the terminal control, BMS, or batch data interchange facilities of CICS to communicate with the terminal, as appropriate for the terminal or session type. Mapping and data interchange functions are performed in the application-owning region. BMS paging operations are performed in the terminal-owning region. (More information about BMS operations is given under Basic mapping support (BMS).)

Pseudo-conversational transactions are supported (except when the "terminal" is an APPC session), and the various transactions that make up a pseudo-conversational transaction can be in different systems.

More information about writing transactions used in transaction routing is given in Application programming for CICS transaction routing.

Initiating transaction routing

Transaction routing can be initiated in the following three ways:

  1. A request to start a transaction can arrive from a terminal connected to the TOR. On the basis of an installed resource definition for the transaction, and possibly on decisions made in a user-written dynamic routing program, the request is routed to an appropriate AOR, and the transaction runs as if the terminal were attached to the same region.
  2. A transaction can be started by automatic transaction initiation (ATI) and can acquire a terminal that is owned by another CICS system. The two methods of routing transactions started by ATI are described in:
  3. A transaction can issue an ALLOCATE command to obtain a session to an APPC terminal or connection that is owned by another system.

In addition to these methods, CICS provides a special transaction (CRTE) that can be used for the occasional invocation of transactions in other systems. See Using the routing transaction (CRTE).

Related concepts
Introduction to CICS dynamic routing
Terminal-initiated transaction routing
Traditional routing of transactions started by ATI
Allocation of remote APPC connections
The relay program
Basic mapping support (BMS)
Defining indirect links for transaction routing
Related tasks
Routing transactions invoked by START commands
Using the routing transaction (CRTE)
System programming for transaction routing
Defining remote resources for transaction routing
Application programming for CICS transaction routing
Related reference
Appendix A. Intercommunication rules and restrictions checklist
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