Persistent LU-LU session support can be used by a VTAM® application program to facilitate recovery after a failure, or to manage a planned takeover. There are two types of persistent session support.
Single-Node persistent session support is used to help recover sessions that are disrupted by an application failure. When a VTAM application program fails after it has enabled persistence, VTAM retains the LU-LU sessions. In order for sessions to be retained as single-node persistent sessions, VTAM and the operating system must remain active.
Multinode persistent session support is used to help recover sessions that are disrupted by a node failure, such as a failure in the hardware, operating system or VTAM. Multinode persistent session support is available in a sysplex environment. Information used to reestablish the LU-LU session environment with their associated modes is maintained in the coupling facility.
After the recovery of the application program, these retained sessions and modes must be restored to permit continued use. (Refer to the information about using persistent LU-LU session support in z/OS Communications Server: SNA Programming for more information about how the two types of session persistence can be used to recover from unplanned or planned outages.)