A telephone exchange is telecommunications equipment that connects and switches phone lines between callers and receivers. It serves as the heart of the telephone network, analyzing dialed numbers to select optimal routing and establish calls. It is the central component of the PSTN (Public Switched Telephone Network).
The history of telephone exchanges is the history of telephony itself. Telephone networks began with manual switching, in which human operators connected lines by hand using plugs and jacks. In Japan, telephone exchange service began in 1890 in the cities of Tokyo and Yokohama and between them, using magneto manual switchboards. In 1926 the introduction of automatic exchanges began, automating the operator's work so that dialing alone would connect a call. Later evolution from step-by-step switching to crossbar exchanges, and then to electronic and digital exchanges, raised processing speed and line capacity. Manual switchboards stayed in service at small exchanges even after automatic exchanges spread, supporting farming villages and remote islands until Japan reached full nationwide automation of telephone service in 1979.
In telephone networks built on IP, the role of the exchange is filled by softswitches (software-based exchanges). While traditional hardware exchanges physically connected lines using dedicated circuits, softswitches manage call control through software running on general-purpose servers. They use the SIP protocol to manage call setup and teardown, with voice data transmitted as IP packets over trunk lines.
The local switching equipment for landline service (subscriber telephone and INS Net) was moved to IP networks region by region from January 1, 2024. NTT East states that this switchover has been completed (as of August 2026). Calls accordingly moved from circuit-switching (dedicating a line for each call) to packet-switching (dividing data into small packets transmitted over shared lines). For enterprise telephone exchanges (PBX systems) there is also the option of cloud PBX, which is used over the internet instead of installing equipment on company premises. See How Japanese Phone Numbers Work for the overall telephone network and History of Phone Number Digit Lengths for the evolution of the numbering system.
Digitalization of switches also laid the groundwork for supplementary services. Digital exchanges such as NTT's D60 series process voice as digital signals, which improved call quality and made it easier to offer services such as caller ID display and call forwarding.