IMS to CICS using the RETRIEVE EXEC command
The following figure illustrates the general CICS® application program flow in asynchronous mode from IMS to CICS.
Replies resulting from previous asynchronous input transactions
and unsolicited asynchronous output from an IMS front-end to a CICS back-end
are sent to CICS asynchronously
(that is, with the ATTACH and SCHEDULER FM headers). When IMS is the front-end subsystem, asynchronous
mode is the only flow supported. The CICS mirror
transaction obtains the input, analyzes the incoming message, and
schedules (using START) the transaction that is to
be initiated as a result of the incoming DPN or the first four characters
of the data. If this transaction is sending output to a terminal,
the mirror transaction issues the START with the TERMID parameter
(from the PRN parameter of the incoming FMH), so that the asynchronous
transaction that is scheduled owns the terminal to which output is
to be sent.
If a reply to IMS is required,
the CICS application must wrap
the incoming RTERMID and RTRANSID into the TERMID and TRANSID fields
to be used in a subsequent START. These fields indicate,
respectively, the destination LTERM or transaction within IMS and the IMS editor
or MFS MID that is to receive the message. The START command
to send this reply to IMS is
processed.
If no reply to IMS is required, RETURN can
be issued to terminate the session.