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Definition: PSTN


(Public Switched Telephone Network) The worldwide voice telephone network. Also called the "plain old telephone system" (POTS) and originally analog only, the backbones of telephone networks today are all digital. However, the lines from the home and office to the digital loop carrier (DLC) junction box in the neighborhood often remain analog. At that point, analog signals are converted to digital.

IP Backbones
The digital infrastructure of the PSTN has increasingly migrated from the traditional TDM-based circuit-switched architecture to IP-based packet switching (see IP telephony). In addition, countless homes and businesses employ Internet-only voice over IP (VoIP) service using IP desk and cordless phones that interact with the PSTN at the service provider's switching centers. See VoIP, digital loop carrier and AIN.




Switched, But Not Too Public
In 1886, this 50-line magneto switchboard, made by Bell Telephone of Canada, was used to switch voice calls in small localities. These instruments were the beginning of the worldwide PSTN. (Image courtesy of Nortel Networks.)