A guide to the basic workings of the telephone network.

1. How does the
telephone network
operate?
A guide to the basic workings of
the telephone network

2. 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).

3. 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.

4. PSTN Diagram
The PSTN
Network
Worldwide
Cellular PBX
Fixed Line
Network Network
Network
Cellular PBX
Network Network

5. 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.

6. 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.

7. 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.