Overview of how shipped terminals are deleted

In a transaction routing environment, terminal definitions can be "shipped" from a terminal-owning region (TOR) to an application-owning region (AOR) when they are first needed, rather than being statically defined in the AOR.

Note:
The "terminal" could be an APPC device or system. In this case, the shipped definition would be of an APPC connection.

Shipped definitions can become redundant if:

At some stage redundant definitions must be deleted from the AOR (and from any intermediate systems between the TOR and AOR17). This is particularly necessary in the last case above, to prevent a possible mismatch between termids in the TOR and the back-end systems.

CICS® method of deleting redundant shipped definitions consists of two parts:

Selective deletion

Each time a terminal definition is installed, CICS creates a unique "instance token" and stores it within the definition. Thus, if the definition is shipped to another region, the value of the token is shipped too. All transaction routing attach requests pass the token within the function management header (FMH). If, during attach processing, an existing shipped definition is found in the remote region, it is used only if the token in the shipped definition matches that passed by the TOR. Otherwise, it is deleted and an up-to-date definition shipped.

The timeout delete mechanism

You can use the timeout delete mechanism in your back-end systems, to delete shipped definitions that have not been used for transaction routing for a defined period Its purpose is to ensure that shipped definitions remain installed only while they are in use.

Note:
Shipped definitions are not deleted if there is an automatic initiate descriptor (AID) associated with the terminal.

Timeout delete gives you flexible control over shipped definitions. CICS allows you to:

The parameters that control the mechanism allow you to arrange for a "tidy-up" operation to take place when the system is least busy. Your operators can use the CEMT transaction to modify the parameters online, or to invoke the mechanism immediately, should fine-tuning become necessary.

Related tasks
Implementing timeout delete
Tuning the performance of timeout delete

17.
For brevity, we shall refer to AORs and intermediate systems collectively as "back-end systems".

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