Implementing VTAM autoinstall

This list explains how to set up autoinstall for your VTAM® terminals.
  1. Are your terminals eligible for autoinstall?
    The terminals that can be autoinstalled are:
    • VTAM locally attached 3270 terminals (non-SNA), both displays and printers
    • VTAM logical unit type 0 terminals
    • VTAM logical unit type 1 terminals, including SCS printers
    • VTAM logical unit type 2 terminals
    • VTAM logical unit type 3 terminals
    • VTAM logical unit type 4 terminals
    • VTAM logical unit type 6.2 single-session terminals
    • TLX or TWX terminals using NTO
    Terminals that cannot be autoinstalled are:
    • Pipeline terminals
    • Automatic teller machines (3614 and 3624)
    • Non-VTAM resources
    • VTAM logical unit type 6.1 ISC and MRO sessions
  2. Should you use autoinstall?
    You are likely to benefit from autoinstall if your system has:
    • A significant number of VTAM terminals
    • Frequent changes to your network
    • Many VTAM terminals logged off much of the time
    • Many VTAM terminals using other applications much of the time
    • Many VTAM terminals that need access to multiple, but unconnected, CICS® systems
    Autoinstall might be less beneficial if you have:
    • A small, static network
    • Many terminals more or less permanently logged on to one CICS system
    • Many terminals logging on and off frequently
    • Many terminals logging on and off at the same time
  3. Decide which devices to autoinstall.

    This decision depends on how you use your VTAM terminals. For example, a terminal that is logged on all the time can be autoinstalled, but you might choose to define it individually.

    An autoinstall logon is slower than a logon to a terminal individually defined to CICS, so if you switch continually between applications and have to log on to CICS frequently, you may require individual definitions for some terminals.

    You should also consider your use of automatic transaction initiation (ATI), terminal list tables (TLTs), and the intercommunication methods in use in your installation. See Deciding which terminals to autoinstall.

  4. Create your TYPETERM and model TERMINAL definitions.

    CICS supplies some TERMINAL and TYPETERM definitions; these are listed in TYPETERM definitions in group DFHTYPE and Model TERMINAL definitions in group DFHTERM. You can use these definitions if they are suitable; if not, create your own using CEDA or DFHCSDUP.

    Define an autoinstall model for each different kind of terminal to be autoinstalled. Try to keep the number of definitions to a minimum, so that the autoinstall control program can be as simple as possible.

    When you create your definitions, consider whether you want to use the QUERY structured field (see TYPETERM definition attributes). It can help the autoinstall control program to choose which model on which to base a definition, and so speed up the autoinstall process.

  5. Redefine DFHZCQ.

    For every region using autoinstall, redefine DFHZCQ to be RESIDENT(YES). (DFHZCQ is in the CICS-supplied group DFHSPI). See the CICS Performance Guide for guidance on why you should consider making programs resident.

  6. Ensure that your VTAM LOGMODE table entries are correct.

    Autoinstall and VTAM explains the relationship between CICS autoinstall and VTAM. For programming information, including a list of VTAM LOGMODE table entries, see the CICS Customization Guide.

  7. Design and write an autoinstall control program.

    The terminal autoinstall control program is invoked by CICS every time there is a valid request for a TCT entry to be autoinstalled, and every time an autoinstalled TCT entry is deleted.

    For programming information about the autoinstall control program, see the CICS Customization Guide. The autoinstall control program for VTAM terminals provides a summary of what the program is about.

    Before beginning your program, look at the CICS-supplied autoinstall control program DFHZATDX in group DFHSPI to see if it is suitable for what you want to do with autoinstall.

  8. Enable terminal autoinstall.

    You can enable autoinstall for terminals either by using the system initialization table (SIT) or by using the EXEC CICS or CEMT INQUIRE∨SET SYSTEM command.

    Five system initialization parameters relate to terminal autoinstall:

    AIEXIT
    specifies the name of the autoinstall program to be used. It defaults to DFHZATDX, the name of the IBM®-supplied autoinstall control program.
    AIQMAX
    specifies the maximum number of terminals that can be queued concurrently for autoinstall. When this limit is reached, CICS requests VTAM to stop passing LOGON and BIND requests to CICS until CICS has processed one more autoinstall request.

    The purpose of the limit is to protect the system from uncontrolled consumption of operating system storage by the autoinstall process, as a result of some other abnormal event. Normally, in the process of autoinstall, the principal consumer of CICS storage is the autoinstall task (CATA) itself. The amount of CICS storage consumed by the autoinstall process during normal operation can therefore be controlled by creating an appropriate TRANCLASS definition to limit the number of autoinstall tasks that can exist concurrently.

    AILDELAY
    specifies the time interval, expressed as hours, minutes, and seconds (hhmmss), which elapses after an autoinstall terminal logs off before its TCTTE is deleted. The default value is 0, indicating that TCTTEs are deleted at logoff time and at warm shutdown as CLSDST is issued for the autoinstall terminals still in session. Specifying an AILDELAY interval permits the TCTTE to be reused should the terminal log back on before the interval has expired.
    AIRDELAY
    specifies the time interval, expressed as hours, minutes, and seconds (hhmmss), which elapses after emergency restart before terminal entries are deleted if they are not in session. The default value is 700, indicating a restart delay of 7 minutes.
    GRPLIST
    specifies the list or lists containing the group or groups of autoinstall models created.

    For information on how to specify these system initialization parameters, see CICS System Definition Guide.

    Three options relate to terminal autoinstall on the INQUIRE∨SET AUTOINSTALL command:

    CUR(value)
    specifies the number of autoinstall logon requests that are currently being processed.
    MAXREQS(value)
    specifies the largest number of autoinstall requests that are allowed to queue at one time, in the range 0-999.

    You can prevent more terminals from logging on through autoinstall by setting this value to 0. This allows autoinstalled entries for terminals currently logged on to be deleted by the autoinstall program when they log off.

    PROGRAM(pgrmid)
    specifies the name of the user program that is controlling the autoinstall process. The default is the CICS-supplied program DFHZATDX.