TM resources: VTAM terminal nodes

IMS defines nodes to RM to enforce name uniqueness for single-session VTAM® terminals and to recover node status.

Node name uniqueness

IMS enforces name uniqueness of VTAM terminals to ensure only one terminal can be logged on at one time and to ensure data integrity. These terminals include all VTAM terminals except LU 6.1 (ISC) parallel sessions.

IMS does not enforce name uniqueness for LU 6.1 parallel sessions, but data integrity is ensured by user name uniqueness. For LU 6.1 sessions, node name uniqueness can be ignored by using the DFSINTX0 user exit routine. See IMS Version 15.6 Exit Routines for more information on this exit routine.

Note: Some session manager products that assign non-unique ETO node names to terminals logging onto multiple systems in an IMSplex will not work properly with RM. IMS prevents the same non-ISC node name from being active in more than one system at a time.

Node creation and deletion

IMS defines a node to RM when the node becomes active during terminal logon. Logon is rejected if the node is already active on another IMS system, except for ISC parallel sessions. IMS also defines a node to RM when recoverable commands that process significant status are processed. These commands include the commands that set global MFSTEST, STOP, and TRACE.

When a node becomes inactive and there is no significant status data, IMS deletes the node. A node is deleted in three situations:

  • During logoff
  • When a command deleting significant status is processed
  • During resource cleanup after an IMS failure and no significant status exists