The Telephone Exchange - How calls get from A to B

When was it in use? As you browse these pages, look here for key dates

In the beginning telephone exchanges (the equipment which routes and connects calls) did not exist. Early phones were wired directly to each other often with some sort of call button to ring the bell at the distant end.

This is fine for just two phones, but as the number of phones you want to call increases the number of wires becomes impractical. Furthermore you need some method of identifying each phone and connecting to just that one. For a small number of phones (up to about 10) this might be done with buttons or switches, you simply press the button for the person you wish to talk to, a bit like an intercom on the front door of a block of flats. Beyond just a handful of phones however this method of addressing gets impractical too and a much better method is to give each phone a number and to have some central machine connect you to the number you want

This is the purpose of the telephone exchange or telephone switch as it is often referred. The process of connecting the call is often called switching because it switches the connection from your phone to any number of other phones.

The process of switching calls has evolved over the years from manual switchboards where a person in the exchange made the connection for you, through automatic switching systems of several sorts to todays exchanges which are digital solid state switches controlled by computers. Some phone calls are now also carried by packet-switching systems along with computer data. Here we look at how the technology has evolved from the 1870's to the present day. Packet switching itself is desribed in more detail in the Packet Switching & Internet section of our website