The Development of Telecommunication

1. On March 10^th, 1876, in Boston USA, Alexander Graham Bell spoke the first recognizable words over what was certainly his most famous invention, the telephone. "Mr. Watson, come here. I want you," he called out to an astonished assistant.

It quickly became necessary to link up people using the new invention. This was done through the telephone exchange. In the first simple exchanges, all calls were handled manually by the operator. Using the switchboard in front of her, she plugged the line of the subscriber calling her into the line of the subscriber being asked for.

2. The idea of an automatic exchange was soon suggested. In 1892, three years after patenting his ideas, Almon B. Strowger saw his system installed at La Porte, Indiana. Strowger, an undertaker from Kansas City, found his business was becoming less and less profitable because the operator always connected calls intended for him to other undertakers.

3. Strowger’s automatic exchange underwent several modifications over the next fifty years, but the principle has remained the same ever since. It is known as the 'step-by-step' system and there are still thousands of Strowger exchanges in service throughout the world today.

The next generation of exchanges was first developed in Sweden. Crossbar exchanges, as they are called, consist of a series of vertically and horizontally crossed bars. For the first time a common control system was used. This made crossbar exchanges cheaper than Strowger, for each selector could now carry up to ten calls. They were not as noisy as Strowger, either. These exchanges are electro-mechanically operated, using electromagnets.

4. In 1948, the invention of the transistor at Bell Telephone Laboratories led to a revolution in electronics and to the creation of semielectronic telephone exchanges.

The old mechanical and electromechanical exchanges have now begun to disappear, and since the 1970s they have started to be replaced by exchanges built around electronic components. The latest digital switching centers have several advantages over other types of exchange, for they provide: a substantial reduction in equipment cost; a large reduction in equipment size; shorter procurement times; shorter installation and commissioning times; greater reliability and reduced running costs; new services for the customer; and new facilities for the administration.

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