Electronic Automatic Telephone Central Office

a telephone central office in which the switching of lines and channels as well as the control of the switching operations is performed with equipment that uses such electronic components as semiconductor devices, integrated circuits, and ferrites.

The design of the switching equipment installed at an electronic automatic telephone central office is determined primarily by the method of channel separation to be used—space-, frequency-, or time-division switching. The frequency-and time-division methods are similar to the methods used in line multiplexing (seeLINE MULTIPLEXING). Electronic automatic central offices with space-or time-division switching of lines and channels or a combination of the two have been widely used since 1978 (seeELECTRICAL COMMUNICATIONS).

Electronic automatic telephone central offices with space-division switching include those whose operations are based on space-division semiconductor switching systems. Space-division switching is used primarily by low-and intermediate-capacity central offices.

In electronic automatic telephone central offices with time-division systems, electronic switching centers make a communications line or a group communications circuit available at given moments for the transmission of signal pulses from each channel. Pulse modulation of oscillations is used for message separation: pulse amplitude modulation and pulse-width modulation are used in low-and intermediate-capacity local offices, and pulse-code modulation is used in high-and intermediate-capacity tandem offices. Pulse-code modulation is the most promising of the systems, since its use makes possible the integration of transmission and switching processes and the subsequent creation of integrated digital communications systems.

In English-language scientific and technical literature, electronic automatic telephone central offices with space-division switching include quasi-electronic automatic central offices as well as electromechanical automatic central offices that use miniature crossbar switches.