IBM SC34-7012-01 manual Communication error processing, Terminal error processing

Chapter 9. Communication error processing

The types of communication error that can occur include terminal error processing and intersystem communication failures.

Terminal error processing

There are two main CICS programs that participate in terminal error processing. These are the node error program, DFHZNEP, and the terminal error program,

DFHTEP.

CICS controls terminals by using VTAM (in conjunction with NCP for remote terminals). These communication access methods detect transmission errors between the central processing complex (CPC) and a remote terminal, and automatically invoke error recovery procedures, if specified. These error recovery procedures generally involve:

vRetransmission of data a defined number of times or until data is transmitted error-free.

vRecording of information about the error on a data set, or internally in control blocks. You can, at times, access data recorded in control blocks using communication system commands.

If the data is not transmitted successfully after the specified number of retries:

vCICS terminal management is notified.

vOne of the following CICS terminal error transactions is initiated:

–Control can pass to a user-written node error program (DFHZNEP).

–Control can pass to a user-written terminal error program (DFHTEP).

For programming information about coding your own node error programs and terminal error programs, see the CICS Customization Guide.

Node error program (DFHZNEP)

You can specify your own processing for VTAM errors in a node error program (NEP). You can use the sample NEP supplied, change the sample, or write your own.

The NEP is entered once for each terminal error; therefore it should be designed to process only one error for each invocation.

In some circumstances, VTAM communication system errors can be passed to an application program. If you issue an EXEC CICS HANDLE command with the TERMERR condition specified, the application program can decide on the action to take in response to the error condition. The TERMERR condition is raised if the DFHZNEP program, if you have one, schedules an ABTASK action (ATNI abend) for a terminal error while the task is attached. It is raised for the current or next terminal control request.

Terminal error program (DFHTEP)

You can specify your own processing for non-VTAM communication errors in a terminal error program (TEP). You can use the sample TEP supplied with CICS (DFHXTEP), change the sample, or write your own.

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