IMS control block storage on ISC parallel sessions

The storage required for the IMS control block structure representing potential sessions is greater than the storage required for control blocks representing input and output message queues.

Installations needing only a few logical units type 6.1, each having a relatively small number of associated parallel sessions, but each requiring that a large number of ISC users (subpools or LTERM sets) be dynamically allocated to them, can have lower storage requirements. For static ISC terminals, these users (subpools) are still statically defined. The IMS control block structure for ISC single session (statically defined and allocated LTERMs) is the same as for other static VTAM® terminal types within IMS.

You do not need to define a maximum number of ETO-ISC sessions. You can continue to add sessions until you run out of storage and processor capacity. Therefore, the SESSION= keyword is not one of the supported keywords on the ETO descriptor. To define the maximum number of sessions for static ISC sessions, use the SESSION keyword on the TERMINAL macro.