Conditions for reallocation

A session is reallocated as a result of one of the following conditions:

If a secondary logical unit goes through a state change from disabled or inhibited to enabled, the owning VTAM® attempts to set up a session with the controlling application program for the secondary logical unit. The session state is determined by the device and is indicated to VTAM by an ACTLU response from the logical unit or a NOTIFY request from the device.
If a session is terminated, VTAM checks to see whether an automatic logon relationship exists and, if so, reallocates that session if the session being ended is not with the controlling application program.
When an active session between a secondary logical unit and its controlling application program terminates, the VTAM that owns the secondary logical unit decides whether to reallocate the controlling session based on the type of termination request or UNBIND that is received. The controlling session is not reallocated if the termination request or UNBIND type indicates normal termination. If the session was terminated using the VARY TERM command with either TYPE=UNCOND or TYPE=FORCE, the controlling session is reallocated if a session path exists at that time between the two logical units. To avoid redriving the session, issue VARY TERM TYPE=COND instead. For further information, see z/OS Communications Server: SNA Operation.