A telephone exchange operated within an organisation, used for switching calls between internal lines and between internal and PSTN lines.

A private automatic telephone exchange that provides for the transmission of calls to and from the public telephone network. See also private branch exchange (PBX).

System providing telephone call switching to an organization or even several locations. Connects extensions to extensions and extensions to and from public networks. Also known as PBX, Switch.

A small switching system installed on a business customer's premises which provides internal telephone switching, as well as outside connections. The system can be either mechanically or electronically controlled.