A logical unit (LU) acts as the intermediary between the user and the network. Before two users can communicate, their LUs must be in session with one another. Communication occurs only between LUs of the same LU type. The LU-LU session manages the flow of data between the users.

VTAM® supports LU types 0, 1, 2, 3, and 6.2. These types support the communication requirements of a variety of users. Each type supports a specific set of communication requirements. The number of the LU type is not related to the PU or node type.

LU types 0, 1, 2, and 3 support communication between application programs and peripheral equipment, such as workstations or printers. LU type 6.2 supports communication between two programs located at type 5 subarea nodes, type 2.1 peripheral nodes, or both, and between programs and devices. LU type 6.2 supports multiple concurrent sessions, called parallel sessions.