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.
The first exchanges were manual systems employing operators
to physically connect the caller to the called partys
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
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, whos 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 partys
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
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