VTAM® dynamically builds an LU-mode table for an application program when an OPEN ACB macroinstruction is processed. Once the table is built, it contains the names of the LUs that are possible partners and the logon mode names and their session limit characteristics as defined for each LU. The table associates the logon mode names with the partner LUs.

Each LU-LU pair can have unique modes that have unique session limits. As a result, one LU-LU pair might have different capabilities than another LU-LU pair. For more information on logon mode names, refer to z/OS Communications Server: SNA Programming.