How does the telephone network operate? A guide to the basic workings of the telephone network
Introduction
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).
The PSTN
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.
PSTN Diagram
The PSTN Network Worldwide Fixed Line Network
Cellular Network
Cellular Network
PBX Network
PBX Network
Fixed Line 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.
Cellular Networks
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.
PBX 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.