Selecting a load station

When loading an NCP, VTAM® needs to know the name of the adjacent link station to be used. The load station can be either a channel link station or an SDLC link station within an NCP. VTAM can select a load station, or you can specify a load station. You specify the load station on the LOADSTA operand of the PCCU definition statement for the NCP or on the VARY ACT command, or during NCP error recovery if VTAM asks you whether to reload the NCP. VTAM selects the load station whenever there is no load station name currently in effect.

VTAM maintains a list of link stations over which a remote NCP can be contacted, loaded, or dumped. This list is maintained whether the NCP is active or inactive. This list of link stations is organized in a last-in-first-out (LIFO) order.

When activating the NCP, VTAM updates this list with any new link stations that are found in the NCP definitions or the VARY ACT command. VTAM searches this list for a suitable link to contact or load and then selects a link station by activating any link station that is not already active.

VTAM uses the first active link station it finds in the list. If it does not find an active link station by the time it reaches the end of the list, VTAM selects the last link station in the list and waits for it to complete activation before proceeding with the NCP activation.

If you want to override a load station name specified in an NCP definition, use the LOADSTA operand of the VARY ACT command to specify the name of another link station. You can also use this override capability to specify that VTAM should select the load station, despite the NCP definition. Do this by specifying a null value for the load station (that is, specifying the LOADSTA operand without a value). If you choose not to override the NCP definition value, VTAM uses that definition value to determine the link station to use.

When selecting a load station, the following restrictions apply:

The load station must be specified for automatic activation with the NCP, or must be already active when it is needed (with VTAM thus knowing of its connection to the NCP). The former method is recommended.
The link station must not be connected to a communication controller other than the one you want to load. Otherwise, you might load the wrong communication controller.
The reconnection of cross-subarea links from one communication controller to another might require the changing of load station specifications for those NCPs intended to run in the communication controllers.
Avoid the WARM start option and the WARM operand of the VARY ACT command when activating the affected NCPs if you change the load station specifications.
Improperly specified LOADSTA values for two or more NCPs can result in a deadlock during their activation, with the activation of each NCP load station waiting for the adjacent NCP activation, which in turn can be waiting for the availability of a load station.
You must define any link to be used as a load station link to both the NCP and the communication controller as being capable of initial program load (IPL):
- For the NCP, specify IPL=YES on the LINE definition statement in the NCP definition.
- For the communication controller, indicate the ability of a link to accept an IPL in the configuration file (CDF) residing in the communication controller diskette storage.