When an application program requests a session, VTAM® selects a dial-out line, unless the application program specifies the dial-out line. Depending on the capabilities of the switched line, the dial-out call can be handled automatically (done entirely by VTAM or by VTAM and the NCP) or manually (done partly by the VTAM operator).

Dial-out requests can be placed on one of a number of switched paths to a physical unit as defined within a switched major node. The dial-out path assignment for switched physical units can be controlled by making switched paths usable or not usable with the VARY PATH command. This command can be used for individual switched paths by specifying the path identifier (PID), or for a group of switched paths by specifying the group identifier (GID). For example, all switched paths that use Wide Area Telephone Service (WATS) lines for dial-out connections can be associated with a GID in the switched major node definition, and can be made usable or not usable as a unit.

For a manual dial-out call, VTAM displays a message with the line and telephone number to use. The VTAM operator manually calls the physical unit. VTAM is notified when the switched connection is complete and then verifies the identity of the physical unit. From this point, the process continues as for a dial-in connection.

If the VTAM operator is unable to complete a manual dial-out call, the VARY INOP command can be used to specify whether VTAM is to select an alternate line or terminate the dial-out operation.