PSTN — Public Switched Telephone Network
What is PSTN?
The PSTN (Public Switched Telephone Network) is the traditional, globally interconnected circuit-switched telephone network — the original copper-and-fiber infrastructure that connects landlines and, through carrier interop, mobile and VoIP calls to one another worldwide. Modern VoIP and SIP trunking systems don't replace the PSTN so much as connect to it: a call placed from a cloud phone system typically travels as SIP over the internet until it reaches a carrier gateway that hands it off to (or receives it from) the PSTN.
More detail
Circuit-switching, the PSTN's original design, dedicates a fixed connection path for the duration of a call, unlike the packet-switched, on-demand routing VoIP and the internet use.
Nearly every phone call today touches the PSTN at some point in its path, even when both endpoints are VoIP, because most calls still ultimately terminate to or originate from a traditional phone number.
Frequently asked
- Is the PSTN being replaced by VoIP entirely?
- Not exactly — VoIP has replaced much of the internal transport and switching technology, but the PSTN as a globally interconnected numbering and interop system still exists, with VoIP calls routing through carrier gateways to reach traditional numbers and vice versa.
- What's the difference between the PSTN and a SIP trunk?
- The PSTN is the broader global telephone network itself; a SIP trunk is the specific connection a business phone system uses to reach that network (via a carrier) using SIP signaling instead of physical phone lines.
See also
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