gtps2m2oACF/SNA Data Communications Reference

Remote Initiated LU-LU Sessions

All session initiation requests from remote LUs that want to go into session with TPF LUs will be received by the TPF processor in the loosely coupled complex that has the CP-CP sessions. The select a host user exit, UAPN, allows you to load balance sessions across all TPF processors in the complex.

APPN session initiation requests are called LOCATEs. When the TPF system receives a LOCATE request, UAPN is called to determine which TPF processor will be assigned this new LU-LU session. The LOCATE request is passed to the selected TPF host for processing. UAPN is also valuable in a uniprocessor TPF environment because it allows you to select the path (which ALS to use) for the session.

For LU-LU sessions started by a remote primary LU (PLU), the network rather than the TPF system will do the load balancing in most cases. The BIND request from the remote PLU can be received by the TPF system without any previous LOCATE request being received. Unlike LOCATEs, the BIND does not always flow to the TPF processor with the CP-CP sessions.

For LU-LU sessions started by a remote secondary LU (SLU), the network might do load balancing by providing a suggested route for the LU-LU session on the LOCATE request. If a suggested route is present, the name of the suggested ALS and the CPU ID of the TPF processor connected to that ALS are passed as input to the UAPN user exit. You have the option to use the suggested route, select your own route (TPF host, ALS, or both), or inform the TPF system to select a TPF processor for this LU-LU session.

See TPF System Installation Support Reference for more information about the UAPN user exit.