Public Switched Telephone Network (PSTN)

A Public Switched Telephone Network, or PSTN for short, refers to a telecommunications network which allows subscribers at different sites to communicate by voice. The term plain old telephone service (POTS) is also frequently used. The features of a PSTN are:

  • Subscribers can be connected by entering telephone numbers
  • The existing connections are primarily used to transmit speech information
  • After hanging up the connection is closed and the resources used become available to other subscribers

The term public switched telephone network is primarily used for public landlines. With traditional analogue landlines speech is transmitted analogue, a ISDN network transmits speech information digitally.

The traditional structure of the Public Switched Telephone Network

The traditional public switched telephone network has a strictly hierarchic architecture and a star structure. The individual subscriber lines are connected to a local exchange, which in turn communicates with trunk exchanges, main and central exchanges. Lines within a local exchange typically have the same area code. To call a number outside the local exchange the area code must be added. International calls require dialling the country code. These start with a double zero.

Replacing the Public Switched Telephone Network with Voice over IP telephony (VoIP)

Since the introduction of Voice over IP telephony (VoIP), traditional public switched telephone networks are slowly being replaced. Voice over IP uses the internet for speech communication and transmits the voice data as individual data packets. Unlike public switched telephone networks, there is no static connection between the two subscribers, instead data is dynamically routed over the data network using a virtual connection. Since each data packet has a destination address, the packets can even be routed differently over the network. On the other end they are reassembled in the correct order and converted back into analogue speech.

Further information

Voice over Internet Protocol (VoIP)

Voice over Internet Protocol, ook wel IP-telefonie genoemd, is een communicatiemethode om te bellen via een breedbandinternetverbinding als alternatief voor gewone gesprekken via een analoge telefoon…

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Integrated Services Digital Network (ISDN)

In telecommunications technology, the abbreviation ISDN stands for the technical term "Integrated Services Digital Network" and refers to a digital standard for telephone networks. As the name…

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