Using node user descriptors

Node user descriptors help in migrating from static terminal definitions to ETO dynamic terminal definitions.

During IMS system definition, node user descriptors are created as an option. Node user descriptors can be useful when exit routines that perform descriptor selection are not yet complete.

Node user descriptors must have the same name as their associated terminals. Therefore, IMS creates unique node user descriptors that retain user options and user structure names that exist in the system definition. When IMS system definition creates ETO descriptors, a node user descriptor is created for each terminal that has a VTAM® TERMINAL macro or VTAMPOOL SUBPOOL macro. Node user descriptors are created even when they match the DFSUSER options (No descriptor is created for an ISC terminal that is defined for parallel session support).

If the LTERM parameter of the node user descriptor contains the same name as a statically defined LTERM, the node user descriptor is ignored. IMS issues message DFS3673W. Consequently, all node user descriptors that are created during system definition are generated as comment statements. To use the node user descriptors, remove the asterisks.

In most cases, node user descriptors are not needed. You only require node user descriptors when the default user descriptor (DFSUSER) or the Signon exit routine (DFSSGNX0) cannot supply the user options you desire. Using a TSO or a z/OS® utility, you can discard most of the node user descriptors that are created during system definition.

Be aware that when you use node user descriptors, you cannot use ETO's ability to eliminate the need for predefining terminals that connect to IMS. Using node user descriptors lose output security for each user as well.

Recommendations:
  • If continuous availability of IMS is critical, eliminate node user descriptors as soon as possible. Because adding new terminals by using node user descriptors requires an IMS restart, use exit routines instead of node user descriptors.
  • To avoid using node user descriptors, use the Signon exit routine (DFSSGNX0) to have IMS build a user structure using the node name as the user name. Although this is similar to using node user descriptors, it avoids predefining large numbers of these descriptors at IMS initialization.
  • You can use node user descriptors to start a session when output is available, using /OPNDST, LOGON, or autologon. To use autologon, specify the SHARE option on the TERMINAL macro.
  • If you select a default user descriptor using the Signon exit routine (DFSSGNX0), you can set a bit to indicate that IMS should create the user structure using the node name for the user structure name. This is the same as selecting a node user descriptor. By creating node-name structures by using the Signon exit routine, rather than by defining a node user descriptor for each terminal, large network installations benefit from decreased complexity.