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Txe

The meaning of «txe»

TXE, (telephone exchange electronic) was a family of telephone exchanges developed by the British General Post Office (GPO), designed to replace the ageing Strowger systems.

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 the 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.

Just before World War II, Tommy Flowers MBE, 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. In the Siemens team was an engineer called Jim Warman. It was his 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 (this 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, although Tommy Flowers did not approve as he advocated going straight to a digital system.

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