Deferring the control region identify

The external subsystem can defer the control region identify if it prefers to have the connection established at some later time.

IMS schedules and gives control to application programs whether or not a connection exists to the external subsystem. The external subsystem thus could choose to wait until an application program call has to be serviced (first call for its resources) before connecting to IMS. Of course, to process calls, the control and dependent region connections and the application thread must exist.

When the control region identify is deferred, the identify is done when:
  • The external subsystem, with an exit routine, activates the IMS Subsystem Startup Service.
  • An MPP or IFP dependent region that can access the external subsystem is started.
  • A /START SUBSYS command naming the external subsystem is processed.