Dependent and Independent LUs

A dependent LU depends on a system services control point (SSCP) to activate a session. A dependent LU needs an active SSCP-LU session, which the dependent LU uses to start an LU-LU session with an LU in a subarea node. A dependent LU can have only one session at a time with the subarea LU. For communications with a transaction program at a subarea node, each dependent LU can have only one conversation at a time, and each dependent LU can support communications for only one transaction program at a time.

An independent LU does not depend on an SSCP to activate a session. An independent LU supports multiple concurrent sessions with other LUs in a subarea node, so you can have multiple conversations and support multiple transaction programs for communications with subarea transaction programs. LUs between peripheral nodes also use this support.

The distinction between a dependent LU and an independent LU is meaningful only when discussing a session between an LU in a peripheral node and an LU in a subarea node. Otherwise, dependent and independent LUs both support multiple concurrent sessions and conversations when communicating between type 2.1 peripheral nodes (for example, between two workstations). Personal Communications or Communications Server LUs can support a single session with a dependent LU or multiple sessions with an independent LU.