APPLs reside in one or more members of the SYS1.VTAMLST system library. Each APPL must also connect to a logon mode table (MODETAB) and class of service table (COSTAB).

When APPC/MVS is initializing, it tries to connect each of its LUs to the network by issuing a VTAM® OPEN macro. The OPEN macro tells VTAM to open an ACB corresponding to the LU name. If VTAM is not yet started, or if the OPEN fails, APPC/MVS will periodically issue the OPEN until it succeeds or until an APPCPMxx parmlib member containing an LUDEL statement for that LU is added to the configuration by a SET APPC operator command.

Figure 1 shows the relationship between the various pieces of VTAM configuration data.

Figure 1. Application Definition to VTAM