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Telephone Exchange/Wire Centre

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Edmonton delayed introducing Crossbar switching in the hope that electronic switching using computer technology would be available before the Step by Step equipment had to be replaced. Electronic equipment was undergoing field trials in 1960 in the eastern United States. However, it was not widely available by the 1970s and Edmonton introduced Crossbar switching in that decade.

Edmonton’s first digital switching units were installed in 1980. Electronic switching was made possible by the invention of the transistor (1947) and this switching technology featured stored program control. Like other early computers, the first models depended on magnetic tapes for data storage. (In stressful moments in the original Star Trek series, Captain Kirk often refers to information on the ‘tapes,’ because that was the leading edge computer technology of the 1960s.)

Today’s electronic switching equipment uses circuit boards like those found in personal computers and calculators. The circuit boards contain different levels of circuitry built onto the platform unit. Different packages are manufactured for different purposes and can be customized for special installation. The electronic circuits are compact, reliable and silent in operation. They can perform diagnostic procedures to identify problems and defective components are replaced by new boards.

Small internal switching operations have been a feature of businesses, hotels and other large organizations such as hospitals and government offices. These systems are generally referred to as a PBX (Private Branch Exchange) or a PABX (Private Automatic Branch Exchange). A PBX operated like a manual switchboard and required an operator to place calls between offices or to connect employees to outside numbers. They were replaced by PABX units which allowed direct dialing of a three digit number for connections inside the organization or direct dialing of outside calls by using ‘9’ before the number. PABX systems used the same switching principles as the equipment in telephone exchanges. Edmonton’s first PABX installations were installed in its petroleum refineries.

Both PBX and PABX systems needed space in the host organization’s office. In order to work effectively, the systems needed their own designated room but companies were often reluctant to allocate the required space. When the switching equipment was in a storage room or closet it would not function properly and customers complained. When digital systems were developed, they required precise temperature control in their surroundings. This made the allocation of suitable space even more important.

In the 1970s, larger, more complex organizational systems began to rely on switching done by the telephone company’s Central Office, as in the Centrex system. In 1974 Edmonton Telephones installed a complex Centrex system for the provincial government. It was the world’s largest Centrex system when it was installed.

Today, new digital Central Office switches and fibreoptic transmission cables have combined to make the PABX obsolete.

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