Starting an IMS network

To make IMS ready to receive VTAM® logon (session initialization) requests, use the IMS /START command with the DC keyword.

Before a session with IMS can be established, VTAM and NCP must be active.

The /START DC command tells VTAM to pass to IMS any queued VTAM logon requests to IMS, as well as logon requests for any logical unit that is defined to VTAM as belonging to IMS.

The /START DC command activates the following processes:
  • Initiates IMS data communication processing
  • Opens the VTAM access method control block
  • Enables the IMS VTAM Logon exit routine

Any logon requests VTAM receives before the IMS /START DC command but after the IMS VTAM access method control block (ACB) has been opened are queued in VTAM until the /START DC command is completed. If VTAM is active when IMS is initialized, the IMS VTAM ACB is opened. If VACBOPN=DELAY has been specified, then the VTAM ACB open is delayed until the /START DC command is entered.

Use the /START APPC command to start APPC/IMS.