public switched telephone network

Also known as: PSTN

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Last updated

July 13, 2026

Quick Summary

The Public Switched Telephone Network (PSTN) is a global network of interconnected telephone systems. When a call is made, the telephone signals the local central office, which responds with a dial tone. The caller then dials a number, and the central office routes the call either within the same office (intraoffice) or to another office via a long-distance network (interoffice).

Key components include switching, signaling, and transmission. Switching centers are organized hierarchically. Modern PSTN has evolved with digital and packet-switching technologies like Voice over IP (VoIP), allowing voice traffic over data networks. Transmission methods have advanced from single-wire to two-wire circuits, utilizing copper wire and later microwave links for long-distance communication.1234

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mobile telephone
Development of cellular systems
…transmitters and receivers with the public switched telephone network (PSTN) began in 1946, with the introduction of mobile telephone service (MTS) by the American Telephone & Telegraph Company (AT&T). In the U.S. MTS system, a user who wished to place a call from a mobile phone had to search manually…
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…transmitters and receivers with the public switched telephone network (PSTN) began in 1946, with the introduction of mobile telephone service (MTS) by the American Telephone & Telegraph Company (AT&T). In the U.S. MTS system, a user who wished to place a call from a mobile phone had to search manually…
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telephone
…what is known as the public switched telephone network (PSTN). For discussion of broader technologies, see the articles telecommunications system and telecommunications media. For technologies related to the telephone, see the articles mobile telephone, videophone, fax and modem.
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…what is known as the public switched telephone network (PSTN). For discussion of broader technologies, see the articles telecommunications system and telecommunications media. For technologies related to the telephone, see the articles mobile telephone, videophone, fax and modem.
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videophone
Digital videophone systems
…could operate directly over the public switched telephone network (PSTN). The still-frame videophone employs a video camera and a frame-capture system to capture a single video frame for transmission. Since still-frames exhibit no time dependency, they do not have to be transmitted in real time over the PSTN, permitting the…
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…could operate directly over the public switched telephone network (PSTN). The still-frame videophone employs a video camera and a frame-capture system to capture a single video frame for transmission. Since still-frames exhibit no time dependency, they do not have to be transmitted in real time over the PSTN, permitting the…
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