ETO descriptors

A descriptor provides information to IMS when IMS builds a dynamic resource for a logon or a signon. The four types of ETO descriptors are: logon descriptors, user descriptors, MSC descriptors, and MFS device descriptors.

IMS stores descriptors in the following IMS.PROCLIB members:

DFSDSCMx: Contains the descriptors that are automatically generated during IMS system definition. The suffix of DFSDSCMx matches the suffix that your installation specifies on the SUFFIX= parameter of the IMSGEN system definition macro.
DFSDSCTy: Contains customized device descriptors that your installation creates. Descriptors in DFSDSCTy override duplicate descriptors in DFSDSCMx, and the last descriptor that is defined is used.

Logon descriptors

A logon descriptor is a skeleton that IMS uses to build an ETO dynamic terminal. It provides information about the physical characteristics of a terminal. IMS uses logon descriptors in conjunction with exit routines to create terminal structures.

The three types of logon descriptors are: generic, group, and specific:

Generic logon descriptor: Provides characteristics for all terminals of a particular type. For example, all SCS printers might share a single generic descriptor. Similarly, all 3270 terminals might share a generic descriptor.

Group logon descriptor: Provides characteristics for a collection of terminals, each of which has compatible hardware characteristics and is defined to IMS in the same manner. The actual characteristics for these terminals are usually identical, but they can differ. IMS uses the group descriptor to derive their characteristics.
Example: You might create separate logon descriptors for different groups of terminals that differ only in the setting for the autologoff (ALOT) time value.
Specific logon descriptor: Provides characteristics for a single terminal, and these characteristics apply only to that terminal. In this case, the descriptor name matches the name of the terminal that it describes.

Note: Although you might need to use specific logon descriptors during the actual migration to ETO, use generic or group logon descriptors after you have migrated to ETO; these kinds of descriptors ease network administration.

User descriptors

A user descriptor is a skeleton from which a user structure is built. A user descriptor can provide user options and queue names.

MSC descriptors

An MSC descriptor is used to create a remote LTERM, which is an LTERM that does not exist on the local IMS. The physical terminal definition (either static or dynamic) for the remote LTERM is in the remote IMS.

Each MSC descriptor for a remote LTERM is loaded during IMS initialization and tells IMS which MSC link to use for output that is destined for that remote LTERM.

MFS device descriptors

MFS device descriptors enable you to add new device characteristics for MFS formatting without requiring an IMS system definition. The MFSDCT utility (DFSUTB00) uses MFS device descriptors to update default formats in the MFS library.

IMS also uses MFS device descriptors to update the MFS device characteristics table. IMS loads this table only during initialization; therefore, updates are not effective until the next IMS initialization.