2.1 The Invention Of The Telephone

The telephone was invented by Alexander Graham Bell in 1876. It was a result of his conducting tests to send multiple telegraph signals over a single conductor. The prototype was impractical for commercial use. Refinements lead to the opening of the first exchange in New Haven in 1878.

2.2 The Development Of The Telecommunications Network

The first exchanges were manual systems employing operators to physically connect the caller to the called party’s line using plugs. The line status was indicated by a rotating ball indicator similar the moving eyes used in dolls which lead tothe exchange controls being referred to as ‘Dolly Boards’. These exchanges were very labour intensive and limited in their application to relatively small volumes of call traffic. Each call required human intervention.

The American Telephone and Telegraph Company (AT&T) was formed in the 1880s as the American network carrier. It had a monopoly until the middle of the 1940s when the US Government was forced to review its position as a result of political pressures. Since then its operation and function has been modified on several occasions as the industry developed but AT&T is still a major presence in the world telecommunications marketplace.

1889 saw the invention of the first automatic telephone switch by Almon Brown Strowger. The 'story' behind its invention tells of Strowger , an undertaker, who was in competition with a rival, who’s wife was the operator in the local exchange. Believing that business was being unfairly routed to his rival he developed the automatic switch. The Strowger switch consisted of circular sets of contacts with a central moving arm with the second side of contacts which was stepped along and round using the dial pulses from subscriber telephones. As the number was dialled the switch responded until with the final digit contact was made to the called party’s line.

From this invention the first public automatic exchange was developed and opened in La Porte, Indiana in 1892.

This type of electromechanical switching was used in various forms in telephone exchanges until the 1950s.

By the 1960s the increase in the volume of traffic carried by the networks and developments in electronics technology changed the telecommunications systems dramatically.

In the 1950s reed switches were introduced allowing space savings and smaller exchange equipment. The early 1960s saw the introduction of electronic controllers and the latter part of the 1960s the development of semiconductor technology. Semiconductors allowed more reliable , lower power and still smaller equipment to be produced.

In line with the developments of exchange technology the medium used to transport the signals on the network was changing from analogue to digital systems. These systems allowed greater multiplexing of traffic over a single medium and increased flow, reducing network congestion. Digital equipment was introduced into the network from the early 1970s. Today virtually all the telecommunications network infrastructure is based upon digital technology.

Since the 1950s there has been a growing demand for data transmission across the telephone networks. This can be achieved on analogue lines using a modem, but since the lines have been developed with speech as the primary traffic the bandwidth is limited and data transmission speeds have to be reduced to maintain correct transmission. The theoretical maximum uncompressed speed of an analogue line is 30Kbps (30,000 bits per second) , though for practical purposes the maximum is 28.8Kbps above which transmission becomes unreliable. Data compression techniques allow this to be increased to the quivalent of 33.6Kbps both ways, and 56Kbps from the dialled service with a slower return from the user, for Internet and similar service access where the data flow is mostly to the user. Digital network technology has increased the bandwidths available and increased data rates dramatically speed up data communications. Today providers are selling or testing high-speed digital services for the individual or small office user based on ISDN2, ADSL or proprietary cable modems.