Including IMS ETO in the IMS system

IMS Extended Terminal Option (IMS ETO) enables VTAM® terminals to log on to IMS TM, regardless of whether they were defined during the system definition process.

IMS TM dynamically builds the required control blocks and queues based on VTAM information and IMS skeleton definitions called descriptors. Without IMS ETO, adding, deleting, or changing terminals that are defined to IMS TM requires that your online system is terminated to incorporate the changes. Additionally, the stage 1 system definition input can become large if you are defining many terminals. IMS ETO is an optional feature; its installation is verified during IMS TM initialization.

Definitions: Terminals that are defined using system definition are static terminals. Terminals not defined through a system definition are dynamic terminals.

The IMS ETO feature applies to all VTAM terminals except for MSC VTAM, MTO terminals, and XRF surveillance links. These terminals, and terminals that are supported by non-VTAM access methods, still require an IMS system definition process to introduce changes. The number of terminals that you define dynamically is limited only by your resource constraints.

With IMS ETO, you can:

• Improve system availability by reducing the scheduled down time that is associated with adding or deleting VTAM terminals
• Improve IMS security by relating output message queues (LTERMs) to users rather than to terminals
• Reduce the number of macro statements that are required for static, system-defined VTAM terminals
• Reduce the amount of virtual storage used for IMS ETO terminals and users by allocating storage only when it is required
• Add new terminals and users without terminating and cold starting IMS TM

System definition can build IMS ETO descriptors that support terminals that are currently generated statically, allowing an easy transition to the IMS ETO environment.

Dynamic allocation of VTAM terminals does not require the use of VTAM TYPE, TERMINAL, NAME, VTAMPOOL, or SUBPOOL macros, or the use of MSC remote NAME macros, for the system definition stage 1 input. Instead, you include IMS ETO with the ETOFEAT keyword on the IMSCTRL macro, which causes IMS TM to generate descriptors. IMS TM uses descriptors to build the required control blocks and queues that are associated with terminal definition. With IMS ETO terminals, configuration information from VTAM control blocks is dynamically merged with information from IMS ETO descriptors when a user signs on to IMS TM. Terminal control blocks are not built for IMS ETO terminals until an ACF/VTAM session is established between the terminal and IMS TM, or until a user structure is built. User control blocks are not built until a user signs on to a terminal.

Requirement: Static terminal definition is still required for:

• MTO and secondary master terminals
• MSC physical/logical links
• XRF ISC Surveillance link
• Non-VTAM devices

IMS ETO descriptors are described in Enabling IMS ETO for ACF/VTAM terminals.