TXE (Telephone eXchange Electronic) was a family of telephone exchanges developed by the British General Post Office (GPO), designed to replace the ageing Strowger switches. When World War II ended, the UK telephone exchange suppliers supported the GPO's decision to stay with Strowger until a viable electronic system became available. The GPO largely did this to protect their success in the export market, but it actually had the effect of ultimately destroying it. This allowed competitors to develop their own improved switching systems ahead of the GPO. In 1960 the situation rapidly changed when the Australian Postmaster-General's Department rejected a system from a consortium of British manufacturers who offered a register-controlled version of a motor-uniselector system in favour of a crossbar system from LM Ericsson. Suddenly the rules had changed and the race was on to develop an electronic telephone exchange that could operate with the current GPO telephones used in the UK, including shared service.
Introduction Just before World War II Tommy Flowers, employed at the GPO, had been working on VF (voice frequency) signalling, using valves (vacuum tubes), and this had led him to realise that valves could be very reliable if not switched on and off. This gave him the confidence during the war to build the world's first digital computer, called Colossus, at Bletchley Park. After the war, the success of Colossus encouraged him to contemplate the possibility of telephone exchanges each using tens of thousands of valves. He was told that this was impossible and he could not say he had already done it with Colossus because he was bound by the Official Secrets Act. However, a fully electronic prototype Time-Division Multiplex Model Exchange was constructed at the Post Office Research Station at Dollis Hill and then an experimental TDM exchange system was built and tested at Highgate Wood in 1962, but it was found to be beyond the technology of the time: the solid-state switching worked well, but the analogue transmission (which had worked on the short cable runs of a laboratory model at Dollis Hill) was too noisy for public service on the long cable runs of a large exchange. However, the principles would be used later, as transmission became digital, in the development of digital exchanges the world over, including System X. Siemens Brothers (later taken over by Associated Electrical Industries, who renamed each section accordingly, e.g. AEI Telecoms) had set up an electronic switching lab at Blackheath. This lab was headed by John Flood, who had been a founder member of Tommy Flowers' electronic switching team at Dollis Hill. The Siemens team included an engineer called Jim Warman, whose trunking ideas (sectionalisation, serial trunking, line scanning, route choice, repeat attempt etc.), which were to be central to the development of the British TXE exchanges. Following the failure to win major contracts in Australia in 1960 and the subsequent failure of Highgate Wood, it was necessary for the British manufacturers to come up with something different until a fully digital system could be developed (which eventually turned out to be System X and System Y). Ericsson had twenty years of experience of manufacturing the crossbar system and reducing its cost, so there was no point in trying to compete with them (Plessey Telecommunications, a subsidiary of Plessey, took a different view and continued to urge the GPO to adopt crossbar). At this time, in the US, Bell Labs were developing a system based on electronically controlled reed relays, and this looked promising. One of Ericsson's marketing points for crossbar was that it used precious-metal contacts, but reed relays would be even better as their precious metal contacts were hermetically sealed. Also their very short operating and release times (<1 ms) made them ideal for electronic control, and these reed-electronic exchanges were considered the most practical switching system to proceed with at the time, and electronic enough until a truly electronic system could be developed; Tommy Flowers did not approve as he advocated going straight to a digital system. The manager at AEI (W G Patterson) decided that reed-electronic space-division switching was the way to go, and it was then that the term 'TXE' (Telephone eXchange Electronic) was coined, even although the reed relays themselves were not regarded as electronic components. A much bigger team was needed to undertake the detailed development and AEI persuaded AT&E and STC to join them in the work. The initial result of their work was a prototype system called TXE1.
TXE1
The TXE1 was developed by three members of the Joint Electronic Research Committee (JERC) which was formed in 1956 and lasted until 1969. The JERC consisted of the GPO, Siemens Brothers (later AEI), Automatic Telephone & Electric (later Plessey), the Ericsson Telephones (also later Plessey), General Electric Company (GEC), and Standard Telephones and Cables (STC). STC built the common control; AEI the switching and scanners, line scanning, and test console; and AT&E the dialling capturing equipment (registers) and the incoming and outgoing junctions. (A 'junction' in British telephonic terms was not a junction in the everyday sense, but the name given to the pair of wires connecting a call between a satellite exchange and the main exchange.) The development of the TXE1 started around 1963. There were models of the AEI equipment at Blackheath and the ATE equipment at Edge Lane, Liverpool. AEI called TXE1 their REX (reed electronic exchanges). Completion was delayed but the TXE1 went into service in 1968 in Leighton Buzzard. Although designed to handle 10,000 subscribers, it started out with a capacity of 3000, with 152 incoming junctions and 166 outgoing junctions. Later, instead of expansion of the TXE1, capacity was increased with three TXE2 exchanges and a TXE6. The exchange was housed in a prototype K-type single-story building on the site of the former Lake House in Lake Street. The construction included thermal insulation panels, double-glazing, and under-floor electrical heating. Ventilation arrangements were by eight ventilating units, each handling 600 cu. ft. per min, and a series of "hit-and-miss"-type louvers above the windows on each side of the building provided outlets for heated air. It was withdrawn from service in 1977 when it was replaced by a TXE4.
Description of mechanism
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