Public Switched Telephone Network

(P-S-T-N)

Basically another name for Plain Old Telephone Service (POTS). PSTN refers to the global network of interconnected telephone companies. While PSTN started out as an operator-operated "Hello Central" system it has evolved into an extensive digital network except for the "last mile" (the connection to each subscriber). The phone signals continue to be largely analog and this is what makes a modem necessary when connecting a computer to the telephone system.

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