Using FEPI with VTAM persistent sessions

When creating FEPI applications, you need to be aware of the possible effects of the use of VTAM® persistent sessions in the front- or back-end systems. For information about CICS® support for VTAM persistent sessions, see the CICS Recovery and Restart Guide.

Restart of front-end system using persistent sessions

Using persistent sessions in the front-end does not give FEPI any additional recoverability benefits. FEPI is always cold started; thus, to FEPI, the effect of restarting a front-end system for which persistent sessions support is enabled is indistinguishable from a cold start of CICS.

Restart of back-end system using persistent sessions

In the back-end system, there are terminal definitions that are used when the FEPI simulated terminals establish sessions with the target. These definitions may be hard-coded, or may be autoinstall model definitions. If the terminal definitions have been set up to use persistent session support, and the back-end system is restarted within the persistent session delay interval, the terminal sessions are recovered.

Effect on FEPI application programs

It is likely that FEPI application programmers have little say in the way that persistent session support is used in the back-end system. They therefore need to be aware of the different ways in which terminal sessions can be recovered, so that their applications cater for all possibilities. If the back-end (target) is a CICS Transaction Server for z/OS®, Version 3 Release 1 system, the way in which a session is recovered depends on the setting of the RECOVOPTION and RECOVNOTIFY options of the TYPETERM definition.

RECOVOPTION(SYSDEFAULT)
On restart within the persistent session delay interval, CICS selects the optimum procedure to recover a session.

For LU2, if the session is busy and CICS is in send mode, CICS sends an end bracket. If the session is busy and CICS is not in send mode, CICS sends an SNA CLEAR request to reset the conversation state.

If a FEPI conversation is in progress when the target system terminates, your application could see one of the following:

You must also consider the value specified for RECOVNOTIFY:

RECOVNOTIFY(MESSAGE)
A message (defined in the BMS maps DFHXRC3 and DFHXRC4) is sent to the "terminal". Your FEPI application must contain logic to deal with this data flow.

If there is no active conversation at the time of restart, the flow is received as unsolicited data at the FEPI front-end.

RECOVNOTIFY(TRANSACTION)
A transaction is initiated in the target. The default is the Good Morning transaction. Your application must contain logic to deal with this data flow.

If there is no active conversation at the time of restart, the flow is received as unsolicited data at the FEPI front-end.

RECOVNOTIFY(NONE)
The "terminal" is not notified that a restart has occurred. Your application need take no special action.
RECOVOPTION(CLEARCONV)
On restart within the persistent session delay interval, CICS sends an SNA CLEAR request to reset the conversation states. The CLEAR is sent only if the session was busy at the time of system restart. If a FEPI conversation is in progress when the target system terminates, your application could see one of the following:

You must also consider the value specified for RECOVNOTIFY. The possible values are as described above, for RECOVOPTION(SYSDEFAULT).

RECOVOPTION(RELEASESESS)
On restart within the persistent session delay interval, CICS sends an UNBIND request to release an active session. The request is sent only if the session was busy at the time of system restart.

If a FEPI conversation is in progress when the target system terminates, your application could see one of the following:

RECOVOPTION(UNCONDREL)
On restart within the persistent session delay interval, CICS sends an UNBIND request to release an active session. The request is sent whether or not the session was busy at the time of system restart.

If a FEPI conversation is in progress when the target system terminates, your application could see either of the symptoms described for RECOVOPTION(RELEASESESS).

RECOVOPTION(NONE)
Even if the system is restarted within the persistent session delay interval, the session is not recovered--it has no persistent session support.

Deal with this in the normal way for a session loss.

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