In the 21st century, virtually all (UK) telephone and data traffic is processed by digital switches, with increasing use of Gigabit routers and TCP/IP techniques.

Here we look back to a time when Strowger, Crossbar and Electronic switching carried the bulk of the calls...

We also find out about the development of Subscriber Trunk Dialling (STD) which greatly simplified the call set-up process.


Photo: Circuits terminating at a TRS Trunk Repeater Station © LSA July 2000.

Very early exchanges used a variety of signalling systems produced by different manufacturers as the most suitable form of switchboard and exchange design evolved over the years. The Central Battery (CB) exchange was the preferred method of providing service in large towns.


Image: Telecom Technology Postcard - Boy operators working the Sunderland exchange in 1883.

Once, all switching equipment used electro-mechanical switches to connect telephone calls. The Strowger system used a step-by-step process to route calls through the exchange. The Crossbar system used cross-point switches with marker control and lots of relays. Even the replacement electronic systems used reed-relays, until the solid-state System X and System Y switches were introduced in the late 1970s.

Photo: Light Straw and Battleship Grey racks at a Ford plant © LSA July 1997.

Prior to December 1958, only local calls (within a few miles of a town) could be directly dialled; all long distance or trunk calls had to be connected via an operator. All medium sized towns had their own operator or Auto-Manual Centre (AMC) at which the calls were received, connected and charged for; a very labour intensive process, which typically employed hundreds of staff at each location.

Subscriber Trunk Dialling (STD) was progressively introduced, but it was not until 1979, that it covered the whole of the UK. So it was that the period from 1960 to 1980 saw the transition from part manual to fully automatic switching of inland calls. 

Photo: Payphones at Steyning IBTE Museum © LSA 2000.

The Recorded Information Services began on 24th July 1936 with the introduction of the Speaking Clock, in the London Director Area. The Test Match, Weather, Dial - A - Disc and many others were to follow...




Photo: TIM - The Speaking Clock, circa 1977 © John Lamble.

Here we take a listen to some of the sounds of a telephone exchange, which you may have heard, during the Strowger Era.






Photo: An exchange tannoy (Reliance) speaker © LSA May 2012.

This section will take a look at the automation of the Telegraph Services from the late 1930s onwards and their evolution into Telex and Datel which were the forerunners of today's dial-up and high speed data links.




Photo: Tape reader and Telex signalling unit - Exhibits at 'Connected-Earth' Amberley Museum © LSA April 2008.

Over the years, a variety of mobile exchanges were built to provide extra exchange capacity where it was most needed and to give emergency cover in the event of a disaster. Typical equipments fitted ranged from special UAX variants, Non-Director to TXE2 as well as containerised Digital and customer switch replacement modules.


Photo: A 'green caravan' at Amberley Museum © LSA April 2008.