How does the telephone network

operate?

A guide to the basic workings of the telephone network

The telephone network is actually one great communication system which encompasses many different networks. The main system which forms the world’s telephone network is called the Public Switched Telephone Network (PSTN).

Introduction

The PSTN is the system which allows any phone in the world to connect to any other phone in the world. It encompasses the rest of the world’s circuit-switched telephone networks. This includes each country’s fixed line and cellular networks as well as their private PBX networks.

The PSTN

PSTN Diagram

WorldwideFixed Line Network

Cellular Network

PBX Network

Cellular Network

PBX Network

The PSTN Network

The fixed line network is the backbone of the telephone network. It is a great web of physically connected telephone lines and telephone exchanges which cover the globe. The fixed line network originally carried analogue signals, but is nowadays almost completely digital.

Fixed Line Network

The cellular networks connect mobile phones to the PSTN. They are owned and operated by the major mobile phone companies. The cellular networks comprise of a grid of masts which are connected to the network by fixed lines.

Cellular Networks

PBX networks are private phone networks used by companies and organisations. They connect to the fixed line network through dedicated gateways. Not all PBX networks connect to the PSTN; some are used only internally for security reasons e.g. military networks.

PBX Networks