Using the OWNER operand on the PCCU definition statement enables you to easily identify and coordinate ownership of NCPs. You can also specify ownership of resources at the physical unit (PU) level for peripheral nodes attached to an SDLC link. You can share ownership of resources on a line and ownership of the lines. In addition, the use of the OWNER operand has implications in backup and recovery plans involving shared NCPs.

The acquisition and release of resources of a shared NCP allow more selectivity in specifying which resources are affected. The VARY ACQ and VARY REL operator commands, with the OWNER support command, enable you to selectively acquire and release resources. The VTAM® operator can specify VARY ACQ,OWNER=sscp name,ID=ncp name to specify that the VARY ACQ command is to apply only to those resources defined as belonging to the specified owner. Using an equivalent VARY REL operator command, the VTAM operator can selectively release ownership of a resource.

The TYPE=GIVEBACK operand on the VARY REL operator command permits the VTAM operator to release ownership of the resource without disrupting an LU-LU session. However, because this function operates only at the line level, all physical units attached to that line also have the ownership terminated without disrupting LU-LU sessions. If a host wants to relinquish ownership of the logical unit, it releases or deactivates the logical unit and its associated physical unit.

Every resource attached to the NCP is owned by a VTAM host. The values you code for each NCP major node determine which host owns which resources. The value of the OWNER operand on the PCCU definition statement is matched with the OWNER operands on the GROUP, LINE, and PU definition statements in the NCP.

More than one host can share ownership of a line or a PU type 4 link station. You specify this in the NCP by coding the appropriate names as values of the OWNER operand on the GROUP or LINE definition statements. In this situation, the first host to activate the physical unit becomes its owner. Other hosts cannot activate this physical unit unless ownership is relinquished. In addition, ownership of PUs can be specified by the OWNER operand on the PU definition statement.

Use the BACKUP operand on the PCCU definition statement to allow a backup host to take over NCP resources when there is a failure in the host that owns them. Code BACKUP=YES to identify all resources that this host can take over in case of a failure. When a failure occurs, an operator can issue a VARY ACQ operator command to acquire these resources without disrupting sessions.

If more than one VTAM host will activate the NCP, you can code a PCCU definition statement for each host. Each PCCU definition statement describes the functions performed by the host that it is associated with. For example, if you want to assign a second host to back up a communication management configuration (CMC) host, code a PCCU definition statement for the backup host. The definition statement is not used until a failure occurs, at which time the backup host activates the NCP.