Gateway path selection list

This word of the parameter list points to the list of gateway paths available for this LU-LU session. Table 1 shows the format of this list.

The list has entries for all the gateway paths defined to VTAM® (by the GWPATH definition statements) for each gateway NCP for which the gateway SSCP is performing gateway path selection. The gateway path entries are passed to the session management exit routine in the order they are defined to VTAM. However, the gateway NCP used for an SSCP-SSCP session is always placed first in the list if this SSCP is in session with the gateway NCP. If the SSCP is not in session with the gateway NCP being used for the SSCP-SSCP session, the first entry in the selection list is the entry that matches the subarea address and the adjacent network that is being used for the SSCP-SSCP session (the adjacent network as specified on the ADJNET operand on the GWPATH statement).

Note that the gateway path selection function might be processed in one SSCP to select a gateway for an adjacent SSCP.

Table 1. Format of gateway path selection list
	Dec (Hex) Offset	Size (Bytes)	Description
	0 (0)	2	Total length of the gateway NCP path list (excluding this field). Do not use this field to determine the last gateway path entry.
	2 (2)	8	Network ID of the adjacent SSCP
	10 (A)	2	Number of gateway path selection entries (n). Use this number to determine the last gateway path entry.
This header is followed by a variable number (n) of gateway path selection entries:
	0 (0)	1	Length of the following gateway path information (excluding this field). Use this field to determine the end of this path specification and the beginning of the next one.
	1 (1)	8	Name of the gateway NCP connecting this network to the adjacent network (obtained from the GWN operand on the GWPATH definition statement or determined from the SUBAREA operand on the GWPATH statement). This field is set to zeros if the GWN operand was not coded on GWPATH and this SSCP is not in session with the gateway NCP.
	9 (9)	4	Subarea address of the gateway NCP in this network (obtained from the SUBAREA operand on the GWPATH definition statement or determined from the GWN operand on the GWPATH statement). This field is set to zeros if this SSCP is not in session with the gateway node and the SUBAREA operand was not coded on GWPATH. Note: If both the GWN and SUBAREA operands are coded on the GWPATH definition statement, you cannot determine whether this SSCP is in session with the gateway NCP.
	13 (D)	8	Network ID of the adjacent network accessed by this gateway NCP (from the ADJNET operand on the GWPATH statement).

You can modify the gateway path selection list in the following ways:

You can reduce the number of gateway path entries in the list by decreasing the number of entries specified in the list header. If the exit routine returns fewer alternate gateway nodes than presented to it at entry (in the gateway path selection list), VTAM uses the smaller list of entries. In its attempt to find a gateway node to use for the LU-LU session, VTAM searches that list of entries in the order the exit routine returns the entries to VTAM.
You can change the order of the gateway path entries in the list. The exit routine returns the entries to VTAM in the same order the gateway path entries are used to attempt LU-LU session setup.

For a list to be correct, the following requirements must be met:

Each returned gateway path entry must match one of the entries originally received. You cannot add new entries to the list.
The number of entries returned cannot be greater than the number of entries passed to the exit.
The adjacent NETID field of the adjacent SSCP must remain unchanged.
The returned gateway path list must contain at least one valid entry.

If the list returned by the exit routine is not valid for any of these reasons, the original list that was sent to the exit routine is used.

The address of the gateway path selection list should remain unchanged. The modified gateway path list should use the same storage that VTAM passed to the exit routine.