ETO concepts

The main purpose of ETO is to dynamically define terminals to IMS. This topic describes such things as ETO terminal and user structures, descriptors and exit routines for dynamic terminals.

When structures are created and deleted

Structures are created in the following situations:
  • Log on
  • Sign on
  • Output is queued to your LTERM
  • /ASSIGN command is used to assign an LTERM to a non-existent user
  • /ASSIGN command is used to assign a non-existent LTERM to a user
  • /CHANGE USER username AUTOLOGON command is directed to a non-existent user
In all cases, IMS searches for an existing structure (terminal or user) before creating a new one.

IMS creates and deletes user structures in the following sequence (This sequence applies only to terminal logon and logoff and to user signon and signoff. When asynchronous output is queued to a user, IMS creates the user structure, as needed.):

  1. When you establish a session between IMS and an undefined terminal, IMS selects a logon descriptor.
  2. Using the information in the logon descriptor, the customization defaults, and VTAM® information, IMS builds a VTAM terminal control block that describes the new terminal.
  3. When you sign on, if a user structure does not exist, IMS builds one, using information from a user descriptor that it selects, and then connects this user structure to the terminal structure.
  4. IMS deletes terminal or user structures when they are no longer needed to maintain sessions. User structures are typically deleted when you sign off, if no special status needs to be maintained and if no messages remain queued. IMS deletes terminal structures when no terminal status exists (such as trace mode), no user is signed on, and the terminal is idle.

    If you are using Resource Manager and a resource structure, IMS normally maintains status in the resource structure instead of the local control blocks. Therefore, IMS deletes the structures.

    Exceptions: The following terminal structures and user structures are not deleted:
    • SLU P and Finance terminal and user structures are normally only deleted during an IMS cold start if SRM=LOCAL. They can also be deleted, however, if the /CHANGE NODE COLDSESS command is used, in which case they are deleted at the first checkpoint following the command.
    • ISC terminal and user structures are only deleted following a cold session termination if SRM=LOCAL.