PSTN

PSTN stands for Public Switched Telephone Network, or the traditional circuit-switched telephone network. The system has been in general use since the late 1800s with  underground copper wires that carry analogue voice data. The legacy platform has provided businesses and households alike with means to communicate with anyone around the world for generations. The phones themselves are known by several names, PSTN, landlines, Plain old phone services, or fixed-line telephones. PSTN phones are also widely used and still accepted as a standard communication form.

The global system was developed over several decades. From the early research of Alexander Graham Bell, telecommunication companies evolved the architecture that provided yesterday’s telephony services.

  • PSTN stands for Public Switched Telephone Network
  • Uses copper wires to carry analogue voice data
  • Been actively used since the late 1800s
  • PSTN phones are still accepted as a standard form of communication
  • Alexander Graham Bell patented the first voice transmission over wire
  • Laid the foundation of Voice Over Internet Protocol (VoIP)

History

The history of PSTN begins in 1875 when American Alexander Bell formed the American Bell Telephone Company. A year later, he patented the first improvement in telegraphy which was also the first voice transmission over wire.

The first transmission used a ring-down circuit, meaning that you couldn’t dial numbers. Instead, two physical wires were connected between two devices. Remember how kids used to play with two tin cans that were connected with wire to talk to each other and play secret missions. A ring-down circuit isn’t far from it, it’s just over a greater distance.  Initially, telephone users had to whistle into the phone to attract the attention of another user. Soon after Alexander also introduced a calling bell to make signaling easier.

Over time, this simple yet ground-breaking design evolved from a one-way transmission, into a bi-directorial voice mission. This basically means that both users could speak. But this made it all the trickier. The requirement of a physical cable between each location that the user wanted to call, wasn’t scalable. And placing a physical cable between each household that required a telephone was neither effective nor feasible. Bell came to develop another method that could map any phone to another without direct connection, this was called a switch.

With the switch telephone, users only needed connection to a centralized office, which would coordinate connected calls to the final destination. Now image how many copper wires this would constitute with at least one from every household. This meant that the switchboards at the operator offices were huge. The switchboards had a 2-pin connection socket – called a jack socket – for every pair of wires entering the exchange.

So how it worked was that you called the operator and gave them the name and number of the person you wanted to call. The operator would then connect a patch cord between two phones and then they could communicate.

The first operators were teenage boys but tended to be messy, so telephone companies instead began hiring young women to present a more civilized image to customers. Women came to dominate the switchboard profession and were well trained in the technique and deportment.

PSTN today

What started as home to home connections, evolved into home to central switch connection. This in turn evolved into analog switches and then into electronic switches. And a lot has changed since then to say the least. Analog voice signals carried by wire with amplifiers evolved into digital signals that carried across the globe with repeaters. This means that binary data is repeated to the receiver. The digital evolution resulted in better sound quality and vaster distances. It also meant that PSTN could release new features such as call waiting, call forwarding and conference calling.

With the launch of Internet, a new transport format was invented called packets. This came to result in the separate data networks we know today. Instead of transmission over circuit switched network, it was packaged into IP packets over the network. This later became the foundation of Voice Over IP (VoIP).

Summary

PSTN stands for Public Switched Telephone Network, or the traditional circuit-switched telephone network. The system has been in general use since the late 1800s with  underground copper wires that carry analogue voice data. The history of PSTN begins in 1875 when American Alexander Bell formed the American Bell Telephone Company. A year later, he patented the first improvement in telegraphy which was also the first voice transmission over wire. With the launch of Internet, a new transport format was invented called packets. This came to result in the separate data networks we know today. Instead of transmission over circuit switched network, it was packaged into IP packets over the network. This later became the foundation of Voice Over IP (VoIP).

 

Glossary