How descriptors are created and used

All descriptors are created during IMS initialization, prior to IMS startup. You must specify that you want the ETO feature support and ensure that the ETO initialization exit routine (DFSINTX0) does not disable ETO.

During IMS initialization, IMS reads and validates all ETO descriptors. IMS initialization then continues, and the descriptors remain in storage for the duration of IMS execution. Any changes you make to descriptors become effective after the next initialization of IMS.

IMS uses descriptors to create both terminal and user structures. IMS rebuilds structures during an IMS restart, if appropriate. For example, if messages are queued for a structure and IMS goes down, the structures are rebuilt when IMS restarts. IMS rebuilds these structures to be the same as they were before the IMS restart. IMS does not use the descriptors or exit routines to rebuild these structures. Therefore, any changes you make to descriptors are only reflected in new structures that are built after IMS restart, and the changes are not reflected in structures that are rebuilt during IMS restart.

Example: USERA signs on using descriptor DESCA which specifies ASOT=20. USERA starts an IMS conversation, and then IMS abnormally terminates. The system programmer changes DESCA to ASOT=10. After the IMS restart, USERB signs on using DESCA. USERA was rebuilt during the IMS restart. USERA still has ASOT=20, and USERB has ASOT=10.