Single node persistent sessions

When a persistence-enabled application program fails, VTAM® retains the sessions, saves the allocated resources and control blocks, and shields the network from knowledge of the application program failure. VTAM stores the incoming data so that the network views the session as active but not currently responding. When the failed application program restarts or another application program takes over, VTAM reconnects the sessions. The backup of a persistence-enabled application program is shown in the following figures:

Figure 1. Application program backup using persistent LU-LU sessions - part 1

This figure shows a sequence of 3 images. In the first image, APPL1 resides on VTAM and is in session with terminal T.

Figure 2. Application program backup using persistent LU-LU sessions - part 2

In the second image, APPL1 fails and the session between APPL1 and terminal T is pending recovery.

Figure 3. Application program backup using persistent LU-LU sessions - part 3

In the final image, a backup application, APPL1', is started and then it restores the session to terminal T.

For more information about enabling an application program to support persistent LU-LU sessions, see the z/OS Communications Server: SNA Programmer's LU 6.2 Guide and z/OS Communications Server: SNA Programming.

The HALT and VARY INACT,TYPE=FORCE commands override single node persistent sessions.