Direct distance dialingDirect distance dialing (DDD) is a telecommunication service feature in North America by which a caller may, without operator assistance, call any other user outside the local calling area. Direct dialing by subscribers typically requires extra digits to be dialed as prefixes to the directory telephone number of the destination. International Direct Distance Dialing (IDDD) extends the system beyond the geographic boundaries of the North American Numbering Plan (NANP).
Crossbar switchIn electronics and telecommunications, a crossbar switch (cross-point switch, matrix switch) is a collection of switches arranged in a matrix configuration. A crossbar switch has multiple input and output lines that form a crossed pattern of interconnecting lines between which a connection may be established by closing a switch located at each intersection, the elements of the matrix. Originally, a crossbar switch consisted literally of crossing metal bars that provided the input and output paths.
Telephone switchboardA telephone switchboard was a device used to connect circuits of telephones to establish telephone calls between users or other switchboards, throughout the 20th century. The switchboard was an essential component of a manual telephone exchange, and was operated by switchboard operators who used electrical cords or switches to establish the connections. The electromechanical automatic telephone exchange, invented by Almon Strowger in 1888, gradually replaced manual switchboards in central telephone exchanges around the world.
Rotary dialA rotary dial is a component of a telephone or a telephone switchboard that implements a signaling technology in telecommunications known as pulse dialing. It is used when initiating a telephone call to transmit the destination telephone number to a telephone exchange. On the rotary dial, the digits are arranged in a circular layout, with one finger hole in the finger wheel for each digit. For dialing a digit, the wheel is rotated against spring tension with one finger positioned in the corresponding hole, pulling the wheel with the finger to a stop position given by a mechanical barrier, the finger stop.
Telephone exchangeA telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers. In historical perspective, telecommunication terms have been used with different semantics over time. The term telephone exchange is often used synonymously with central office, a Bell System term.
