In a combined APPN and subarea environment, an independent LU can be accessible over APPN and LEN connections. In this case, VTAM® always gives preference to APPN connections, if the connections are known and available. APPN connections are known when an APPN-capable PU name or ISTAPNPU is included in the ALSLIST for the resource. If no APPN connection is available, an LEN connection is used (if available).

To cause VTAM to sometimes use an LEN connection or sometimes use an APPN connection, use the adjacent link station selection function of the session management exit routine. For information about coding this exit routine, see z/OS Communications Server: SNA Customization.

To force VTAM to use particular LEN connections and not allow a search of the APPN network, include only those LEN adjacent link stations on the ALSLIST operand and also code ALSREQ=YES for the resource. Session setup will continue using an LEN adjacent link station from the list even if a route exists through the APPN network.