How the logon manager operates

How the logon manager receives control depends on whether a dependent or independent LU is accessing the TPF application program. If the logon request is from a dependent SLU, the logon manager receives control when VTAM® drives its logon exit. If the logon request is from an independent PLU, the logon manager receives control when VTAM drives the USERVAR exit, ISTEXCUV. ISTEXCUV is driven because the logon manager creates a USERVAR (with UVEXIT=YES) to represent the generic name of each TPF application program.

After the logon manager receives control, the control point LUs that support the generic application are identified. Each pair of supporting control point LUs is then passed to the CLU search exit, ELMCLUEX, to determine the LU best able to provide the service. The selection criteria of the ELMCLUEX exit can be determined by the user or the default can be used. The default criteria are:

LU is below the session limit
LU has the lowest hop count to the device
LU has the fewest number of active sessions

For dependent LU access, the TPF application program can be defined as either a type 5 or type 2.1 PU.

For independent LU access, the TPF application program must be defined as a type 2.1 PU.