Using the LOGAPPL operand, you can define a cross-network controlling primary logical unit on any peripheral node (local or remote, switched or nonswitched). The effect is essentially the same as if a CDRSC within the same network were the controlling primary logical unit, except that the resulting session is cross-network rather than within the same network. The network-qualified name of the controlling primary logical unit can be specified with the LOGAPPL operand.

In a single-network environment, when the SSCP-SSCP session necessary for the establishment of a controlling primary logical unit session is not immediately available, VTAM® stores information necessary for session setup. When the necessary SSCP-SSCP session becomes active, VTAM establishes the LU-LU session.

However, this process does not occur for cross-network sessions. You can establish cross-network controlling primary logical unit sessions through any number of intermediate SSCPs only if all of the required SSCP-SSCP sessions are active when the LU-LU session setup is attempted. In the case where the session setup path consists of more than one SSCP-SSCP session, the session setup proceeds as far as establishing the session control blocks at each active SSCP along the setup path. At some point along the path, an SSCP can determine that the session request cannot be routed any further because it has no active sessions with any SSCPs in its adjacent SSCP list for the specific destination logical unit. If this occurs, the request is rejected, the session control blocks are freed, and the operator is notified of the failure. After the necessary SSCP-SSCP sessions are active, the operator must try to reestablish the session. If all required SSCP-SSCP sessions exist, but the controlling application program is unavailable, VTAM fails the initiation request until the application program is available. When the application program becomes available, VTAM automatically attempts to reestablish the session.