If an independent LU has an existing leased or switched LEN connection (and no APPN connection), VTAM® can dynamically select session paths for outbound sessions from the boundary function to the independent LU. VTAM attempts to use leased connections first, and then tries active switched connections. If the first adjacent link station in the adjacent link station list is not available, VTAM tries to use an alternate connection from a default adjacent link station list that VTAM creates. When the first adjacent link station (the primary connection) does become available, VTAM uses that adjacent link station for any new sessions. However, sessions already allocated to the alternate adjacent link station do not change.

To control selection of an alternate session path when an independent LU is connected to VTAM by only LEN links, use the ALS selection function of the session management exit routine. VTAM then establishes the path between the independent LU and the boundary function; this continues to be the path for the remainder of that session. You can select a different adjacent link station for each session.

Using the ALSREQ start option, you can limit the adjacent link stations that an independent LU can use.

You can code the session management exit routine to choose a PU from the default list or another PU by overriding the default PU list. For information about writing a session management exit routine, see z/OS Communications Server: SNA Customization.