Skip to main content
   

The farside

radio operators on ship, 1930s

Messages and signals : the two basic components

Messages and signals are essential components of telecommunications. But what is the difference?

A message is the product of communication, in other words the information we need to convey. It may be audible (a telephone call or voicemail message for instance) or visual (an e-mail, a telegram or a text on your mobile). These are all examples of messages.

A signal is the electrical activity that sends our message or the product of our communication.

To turn signals into messages you need two more components - a 'transmission protocol' and a code. 

flags of the maritime signal code

Bearer and intelligence : the two basic actions

The process of telecommunications can be separated into two elements: 'the bearer' and 'the intelligence' it carries.

The bearer element is the one that carries the message. This is the system that carries signals from one place to another. You could see it as the electrical equivalent of the postal system, only using wires, optical fibres or radio waves instead of postmen and mail vans.

Intelligence or information is what the system carries, just like the news within a letter or the pictures in a book delivered by mail. Various methods are used to convert these messages into electrical signals and back again into a form understandable to the recipient.

postmen, with handcarts; c1900

Protocols : open the door ...

When the postman arrives with a packet, he's carrying a message. When he knocks on the door, that's the signal telling you there's a message waiting.

The protocol is the understanding that links sender and receiver - you hear the knock or bell so you open the door.

In telecommunications the 'protocol' is the particular set of 'understandings' for exchanging information between two devices in a communications network. Protocols provide a set of rules or procedures that determine the format and timing of information transmission.

Look at it this way: you could put two people at random at either end of a telephone line. But unless they could both speak the same language and agreed not to talk until the other had finished, no meaningful communication would be achieved.

illustration of needle telegraph fascia

Codes : turning signal into language

Being able to send a signal is one thing - but turning that signal into a message is quite another.

Signals are 'dumb' - they only tell you someone is there at the other end of the line or link. Making signals talk requires one more component - a code.

A code defines the pulse, tone, flag, semaphore or light patterns that will be transmitted - so that each pattern can be recognised as a separate component. Then it assigns each pattern to a letter, number, word or phrase that makes sense to us.

Code applies human intelligence to the dumb signal to allow it to communicate a message. So in morse code you would realise that dot dot dot dash dash dash dot dot dot actually means sos, which in turn signifies an urgent distress message.

fun and games

Can you beat our games? Explode equipment to see what's inside, hear the changing sounds of telecommunications, see how telecommunications designs have changed over time or send an e-postacard.

what's on

The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

audio history

Take a trip down memory lane with extracts of the interviews which have been recorded as part of the Connected Earth oral history programme.

featured story

100 years of automatic switching!
In 1912 the GPO installed Britain's first automatic telephone exchange in Epsom.

Discover the early days of the telephone...