Third party Initiate

A session can be initiated by an LU that is not one of the session partners, or by the SSCP. In VTAM® there are two ways this can happen:

CLSDST OPTCD=PASS. An application program acting as a PLU in a session can "pass" its session partner (the SLU) to another LU which acts as the PLU in a new session with that session partner. This permits the SLU to be passed from application program to application program in a sequence strictly controlled by the application programs involved. The types of session initiation previously discussed do not allow this; instead, for them, sessions are established in the order in which the corresponding Initiate requests are received by the SSCP.
Network Definition or VTAM Operator Command. The VTAM operator can cause a session to be established with a particular application program (called the controlling application program) by issuing a VARY LOGON command for a device-type LU. This means that whenever the device-type LU has no LU-LU session, or for an independent LU that has no LU-LU session with the controlling application program but can have other LU-LU sessions, a session is automatically initiated between the controlling application program and the device-type LU; this automatic session initiation is not done if the last session that the device-type LU had is with the controlling application program and the session ended normally, for example, with CLSDST. A similar session is established by VARY ACT if the device-type LU is defined to have a controlling application program (by the LOGAPPL keyword on the LU definition statement). These techniques allow a session to be initiated without requiring either the application program or the device-type LU to do the session initiation. To each of the LUs, it appears almost as if the other LU had initiated the session. Refer to z/OS Communications Server: SNA Operation for more information on the VARY LOGON and VARY ACT commands.
Application programs that support LU 6.2 protocols can request automatic activation of a specified number of sessions used for LU 6.2 conversations. Refer to z/OS Communications Server: SNA Programmer's LU 6.2 Guide for more information on the definition of LU 6.2 application programs.

Session-termination requests can come from the following sources: