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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:
v Retransmission of data a defined number of times or until data is transmitted
error-free.
v Recording 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:
v CICS terminal management is notified.
v One 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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