Handling IMS response mode or conversational output errors

This topic describes how IMS handles response and conversational mode errors during an ISC session and how to keep the half sessions in sync.

IMS messages cannot be canceled by session termination or protocols after they have been received and enqueued (made available for scheduling). However, errors can be detected by either half session after the input message has been enqueued. If the error is detected by IMS while processing the transaction, but before the reply message is committed (for example, a DFS555 transaction abend occurs), both half sessions are able to back out, because IMS holds the input sync-point response until the reply message is available for output. An exception response and appropriate error recovery process (ERP) message are returned. Errors occurring after the reply message is made available for output result in backout to the last application sync point (the one that made the reply message available). These errors are not communicated to the other half session.

After an exception response to a DFC command, you might need to purge before further sends or receives.

Related reading: For information on the DFC protocols, see z/OS® Communications Server: SNA Programming.