When the user of a dependent SLU initiates a session request with a TPF application program, VTAM® search processing begins. In response to a CDINIT from the SSCP that owns the SLU, the SSCP that owns the DLU (and has the logon manager) drives the USERVAR exit for the USERVAR representing the TPF application program.

The sample USERVAR exit processes only volatile USERVARs. When the sample exit receives a request to translate a static or dynamic USERVAR, the USERVAR exit turns off the translation bit and returns a nonzero return code to indicate that the session establishment request failed.

For a volatile USERVAR, the sample USERVAR exit does not translate the name. The exit instead sets the value of the USERVAR equal to the generic USERVAR name. Although the name is not translated, the exit turns on the translation flag. The translation flag must be turned on to ensure that VTAM drives the logon manager through the logon exit.

The logon manager then drives the CLU search exit for each pair of contending CLUs for the session. The CLU search exit compares each pair of contending CLUs and identifies the better CLU from the pair to service the application program. After the list of contending CLUs is exhausted and all pairs have been compared, the CLU search exit returns the name of the best CLU to the logon manager. The best CLU is the one that meets the criteria described in Contending CLUs for dependent SLU-initiated sessions. The logon manager sends a session initiation request to the best CLU. The logon exit rejects the session so that the SLU will be in session with TPF rather than with the logon manager. The logon manager issues the CLSDST with sense code 0842FFFF so that the LU is not notified of session failure. TPF uses the session initiation request to build a BIND. TPF sends the BIND from the application program LU associated with the best CLU to the network resource that requested the session.