(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 It was withdrawn from service in 1977 when it was replaced by a TXE4. An equipment practice was needed quickly, and it was realised that a matrix of reed relays would be about the same size as a crossbar switch. Therefore, the equipment practice of AT&E's crossbar system was adopted for the TXE1 apart from the common control, which had its own equipment practice. The common control consisted of 14 racks and made up a complete suite of the exchange. It was made entirely from discrete components as integrated circuits were not yet in common use. There was much discussion by all contractors as to whether there was a reliable connector available to make units interchangeable. STC decided to have the units that could be withdrawn and AT&E and AEI did not. It turned out that the connectors used were reliable and they had a great advantage in fault finding. It also allowed the STC engineers to place a suspect faulty unit in an outrigger so it could be tested in situ. One of the functions of the common control was to decide which was the best connection to be used through the switching network, and this part was called the route choice. The interrogators would return the available paths and the route choice would make a choice and tell the markers to mark that route.