Telephone networks

The telephone network, or the Public Switched Telephone Network (PSTN) is the name for the collection of telephone wires, exchanges, satellites and mobile phone towers that together allow us to make phone calls from any phone to any other phone.

Sometimes this network is also called the Plain Old Telephone Service (POTS).

How your fixed-line phone is connected to the network

Every fixed-line telephone is connected to a phone line, a physical cable. This is usually made of a pair of copper wires and runs from your home to a digital concentrator box near the side of the road.

The electrical signals from your phone are compressed by the digital concentrator into a digitised system of codes. It can then feed them into a cable carrying codes from many other phones in your neighbourhood. This cable (usually a coaxial cable or a fibre-optic cable) carries these phone conversations to the local telephone exchange.

If your call is local, the local telephone exchange will digitally connect your phone call to the line of the person you dialled. While this used to be a manual process, today it is fully automated.

If your phone call is to someone outside your local area, your call is forwarded from the local exchange to a main exchange.

The main exchange will either direct your call to another local exchange to be connected, to another main exchange, or to an international exchange for international calls.

In the past all of these ‘hops’ between exchanges were via physical wires and cables. However, today it is common for some of them to be made via satellite or even microwave transmissions.

Regardless of how many exchanges and how the call travels, it will eventually end up at the local exchange for the person you are calling and your call will be connected to their line.