Session management exits

The session management exit routine can be used to:

Check or restrict the use of a logical unit (session authorization)
Gather accounting information (session accounting)
Select adjacent SSCP for LU-LU session and resource status requests
Process a session takeover by the alternate XRF application program

Code a session management exit routine if you want to use these functions. There is no default session management exit routine. If you do not code a session management exit routine, it is assumed that all session requests are authorized and no accounting data is collected by VTAM®.

VTAM calls the session management exit routine whenever a session between logical units is established, ended, taken over, or recovered. The session management exit routine is invoked by every VTAM in the session setup path. It is also called for session accounting when an LU-LU session ends.

Note: Improper use of the session management exit routine can impact VTAM operation. For example, you should consider the following possibilites:

A program error can affect VTAM, the operating system, and other programs. Although abnormal end recovery is provided for errors within the exit, the exit code can accidentally corrupt VTAM storage.
Lengthy processing time could degrade VTAM performance. While these routines are running, VTAM cannot process any new VTAM operator requests to initiate or end sessions. To reduce the effect on VTAM performance, any analysis of the information collected should be done later by another program.

In a multiple domain environment, the session management exit routine can be invoked in the domains in which each of the session partners resides and can be used to select adjacent SSCPs for LU-LU session and resource status requests.

The adjacent SSCP selection function in the session management exit routine can be used to control the SSCP to which a session request is sent. The exit allows you to shorten or reorder the list of adjacent SSCPs, or to not route at all. You can use this function with the dynamic adjacent SSCP table facility so that you can avoid defining adjacent SSCP tables while maintaining control of session request routing.

VTAM supports session authorization exit routines, which can be used to control session initiation. These routines can accept or reject the session based on various information that is passed to them. VTAM also supports session accounting exit routines that can be used to perform accounting functions for established sessions.

The session authorization and session accounting exit routines provide some of the same functions as the session management exit routine. These exits are invoked before the corresponding session management function. However, these exit routines do not provide all of the functions that are available in the session management exit routine, and they are not recommended.

For further information about the session management, session authorization, and session accounting exit routines, including a detailed description of the vector lists and the information provided to the routines, see z/OS Communications Server: SNA Customization.