Private telephone systems are independent telephone systems that are owned or leased by a company or individual. Private telephone networks include key telephone systems (KTS), private branch exchange (PBX), computer telephony (CT), wireless PBX, LAN telephony, and multimedia communication (e.g. videoconferencing).

Private telephone systems are composed primarily of telephones (called stations or terminals ), local wiring, and switching systems. Telephone stations are the interface between the user and the telephone network. Wiring connects telephone stations to switching systems or distribution points. Local wiring in private systems varies from shared lines (key systems) to individual lines (digital stations). Switching systems interconnect stations to each other or to outside telephone lines or interoffice trunks.

Private telephone systems are often equipped with key assemblies and systems including voice mail, call accounting, a local maintenance terminal, and data interfaces. The voice mail system is controlled by the PBX only receiving calls when the PBX or computer telephony software determines a message can be left or retrieved. The call accounting system receives system message details on all call activities that occur within the PBX. The local terminal provides onsite access to the PBX for maintenance activities. The dial-in capability also provides access to the PBX for maintenance activities.

Figure 9.5 shows some of the basic types of private telephone systems; key telephone systems (KTS), private branch exchange (PBX), and computer telephony integration (CTI) systems. The most simplistic private telephone network is a single telephone attached to a business line. Key systems allow each...