If you use the ALS selection function to choose an ALS that is not in the ALS list, the PU name returned in this vector becomes the ALS for this session. Depending on the flag settings in this vector, the PU name might be added to the ALS list for this independent LU. If you want the PU name to be added to the list, and the list already exists, the PU name is added to the end of the list. If there is no list, one is allocated and the PU name becomes the first entry in the list.

The purpose of this vector is to provide multiple potential concurrent session paths for an independent LU. If one of the LU's potential ALSs becomes unusable, VTAM® tries another ALS for subsequent activations. There is no attempt to reroute existing or pending sessions that are using the ALS that has failed.

You can code your exit to specify that an alternate ALS is not to be selected; see Function specifies no alternate ALS for more information.

The PU whose name is returned in this vector must be one of the following:

• An active ALS
• A leased ALS that is in the process of activation and considered usable
• A switched ALS that is pending dial
• A connectable switched ALS

Also, the PU must be either an APPN node or a LEN node. If no PU meets these requirements, you can use a return code from the ALS selection function to specify that VTAM can either choose an ALS from the list, or route the session cross-domain, and session setup can continue. You can also use a return code to specify that VTAM will deny the session activation attempt when the PU does not meet the requirements.