Adjacent link station list information vector

This vector contains the list of known potential adjacent link stations (ALS) for this LU-LU session. A different PU represents each ALS in the list. VTAM® selects a PU name from the list. The PU determines the session path that will connect the independent LU with the subarea network. If you want the independent LU to use an ALS that is not in the current ALS list, you can code the ALS selection function to select another ALS and override the list by passing the new ALS in the ALS name information vector.

If the session management exit does not specify (through the ALS name information vector) an ALS to use, or if the specified ALS is unavailable and the return code indicates that processing is to continue, VTAM examines the ALS list and selects the most usable entry to use as the ALS. VTAM examines the ALS entries in the order they appear in the list and searches for an ALS by using the following criteria, listed in order of preference:

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

If you code your exit to support the ALS selection function, VTAM invokes the function for each session. Therefore, you can choose a different ALS for each session involving an independent LU serving as a DLU.

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 format of the ALS list information vector is shown in Table 1.

Table 1. ALS list information vector
	Dec (Hex) Offset	Size (Bytes)	Description
	0 (0)	2	Total length of the ALS list information vector (excluding this field)
	2 (2)	2	Number of PU entries in the list (n). Use this number to determine the last PU entry.
	4 (4)	4	Reserved
This header is followed by a variable number (n) of PU entries:
	0 (0)	2	Length of the following PU entry (excluding this field). Use this field to determine the end of this PU entry and the beginning of the next one.
	2 (2)	1	PU status flags B'1... ....' The PU is non-switched. B'0... ....' The PU is switched. B'.000 ....' The PU is inactive or unknown. B'.001 ....' The PU is connectable (CONCT). B'.010 ....' The PU is pending active and is usable for LU-LU sessions. B'.011 ....' The PU is active. B'.100 ....' The PU is pending active, or pending takeover, and is not usable for LU-LU sessions. B'.... 1...' The PU supports dynamic definitions for independent LUs. B'.... 0...' The PU does not support dynamic definitions for independent LUs. B'.... .1..' The PU was dynamically associated with this LU by an inbound session request. B'.... .0..' The PU was associated with this independent LU by a MODIFY ALSLIST command or a definition statement. The remaining bits are reserved.
	3 (3)	1	Reserved
	4 (4)	8	PU network ID (if known)
	12 (C)	8	PU name
	20 (14)	4	PU subarea address
	24 (18)	2	Count of independent LU (ILU) sessions associated with this PU
	26 (1A)	2	Reserved