Automatic route selection of a private telephone network path on the basis of a public telephone network number

摘要

A data structure and program routines for use in a private branch exchange telephone system (PBX) for automatically routing calls via a private telephone network in response to a dialed public telephone network number and for restricting outgoing calls from the PBX to specific public network telephone stations. In a large corporate PBX switching network interconnected by both a public telephone network and a private telephone network, a telephone set connected to one PBX system establishes a switch connection through the private network by dialing the public telephone network's number for a destination telephone set connected to another PBX system. In response to the dialed number, the first PBX system automatically determines that the destination telephone set can be reached via the private telephone network and automatically converts the dialed public telephone network number to a private telephone network number designating the destination telephone set. The data structure allows access by PBX telephone sets to designated groups of telephone stations or specific individual telephone stations connected to the public telephone network to be restricted. In addition, if a PBX telephone set attempts to dial a restricted public telephone network station, the system first verifies that the dialed station is restricted to that particular PBX telephone set and then provides a procedure whereby the telephone user can enter a personal authorization code to enable the user to complete the call.