What Is a PSTN Phone?
A PSTN phone is a phone operating on the internationally connected Public Switched Telephone Network. This network specializes in circuit-switched voice communication using copper wires. PSTN formerly described phones carrying analog voice data, but now the network is almost entirely digital.
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Switching Centers and Signaling Protocol
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PSTN phones are connected by switching centers. They typically use the Signaling System Number Seven (SS7) signaling protocol.
Bandwidth
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Each connection takes up to 64 kbs of bandwidth, the majority of which is used when a phone is connected through a dial-up modem. PSTN service is increasingly digital and as a result, PSTN phones are now mobile cells as well as fixed landlines.
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Internet Connectivity Technology
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The PSTN network extends beyond phone use. Although its ties to early communications earned it the nickname of plain old telephone service (POTS,) in practice the PSTN is now used as part of VoIP and other Internet connectivity technology.
Hierarchy
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Originally, the PSTN operated on a hierarchy of telephone exchanges (the electronic components that connect calls) to distinguish between local and long-distance calls. Local calls would be handled by the local call center unless they needed to be passed to a higher center for onward routing. As transmission and equipment costs decreased, this hierarchy simplified to a few levels, and calls are now handled on more of a "first come, first serve" basis.
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