Dependent LUs are supported by VTAM® in both subarea and APPN networks.

A dependent LU requires assistance from a system services control point (SSCP) to activate an LU-LU session; therefore, it requires an SSCP-LU session. Both subarea and APPN VTAM nodes provide SSCP support for dependent LUs in their domains. A VTAM APPN node provides SSCP support for those LUs in its domain even though it has no SSCP-SSCP sessions with other nodes.

Dependent LUs can use APPN and subarea connections to access VTAM application programs in other domains. For example, a dependent LU type 2 terminal session originating in one VTAM can be rerouted to CICS® on a VTAM end node.

To resources in the APPN network, a dependent LU appears to be located on the node that is providing SSCP services to the LU. Through the use of DLUS/DLUR, VTAM can establish SSCP-LU sessions across APPN links. Therefore, a VTAM node can be the owner of a dependent LU that is on an attached non-VTAM APPN node, such as an AS/400®, PS/2, or 3174 controller, regardless of whether the VTAM node has a CP-CP session with the other node.

How dependent LUs are defined

Dependent LUs are owned by a VTAM node and are defined to VTAM. They are considered to be in the domain of the VTAM node. If a type 2.1 node has dependent LUs attached to it, the dependent LU must also be defined to VTAM.

Dependent LUs such as terminals and printers appear as cross-domain resources to other VTAM hosts. If the LUs are registered, and if all nodes in the network are connected by CP-CP sessions, the cross-domain resource definition statements in other hosts might not be required. Some other hosts do support the dynamic creation of CDRSCs, even in a subarea environment. In an APPN environment, other hosts will still build CDRSCs when sessions are established.

How dependent LUs participate in sessions

Dependent LUs can start a session when the primary LU is owned by VTAM. Dependent LUs can be the secondary LU in sessions with partner LUs in the APPN or subarea network.

Sessions initiated by secondary LUs (such as LU type 2 displays) to a primary LU that is in a VTAM node in the APPN network are supported. Also supported are APPN LUs that initiate sessions with application programs in the subarea network.