Using the IMS Subsystem Startup Service

When the control region identify is deferred, the external subsystem can activate the IMS Subsystem Startup Service when it wants the control region Identify exit routine to be driven.

To be more specific, if a connection does not exist when the first application call for external subsystem services is processed by a dependent region, IMS does not automatically attempt to identify. The external subsystem must activate the Startup Service to establish the connection (if it wants to process application calls).

The Startup Service is also used to establish dependent region connections. When an external subsystem call from an application is processed before the control region or dependent region has been identified to the external subsystem, the dependent region activates the Subsystem Not Operational exit routine. The external subsystem is expected to call the Subsystem Startup Service from this exit routine to establish the connection.

When activated, the Startup Service establishes the control and dependent region connections, if the control region identify has not been done. If the control region identify has been done, it establishes only the dependent region connection. If IMS is waiting for the external subsystem to send the notify message, which it accepted on a previous Identify exit routine invocation, the Startup Service returns an error return code and does not establish the connection. For details on using the Subsystem Startup Service exit routine, see IMS Version 15.5 Exit Routines.