Telecommunications
Telecommunications, devices and systems
that transmit electronic or optical signals across long distances.
Telecommunications enables people around the world to contact one another, to
access information instantly, and to communicate from remote areas. Telecommunications
usually involves a sender of information and one or more recipients linked by a
technology, such as a telephone system, that transmits information from one
place to another. Telecommunications enables people to send and receive
personal messages across town, between countries, and to and from outer space.
It also provides the key medium for delivering news, data, information, and
entertainment.
Telecommunications devices convert
different types of information, such as sound and video, into electronic or
optical signals. Electronic signals typically travel along a medium such as
copper wire or are carried over the air as radio waves. Optical signals
typically travel along a medium such as strands of glass fibers. When a signal
reaches its destination, the device on the receiving end converts the signal
back into an understandable message, such as sound over a telephone, moving
images on a television, or words and pictures on a computer screen.
Telecommunications messages can be
sent in a variety of ways and by a wide range of devices. The messages can be
sent from one sender to a single receiver (point-to-point) or from one sender
to many receivers (point-to-multipoint). Personal communications, such as a
telephone conversation between two people or a facsimile (fax) message (see Facsimile
Transmission), usually involve point-to-point transmission. Point-to-multipoint
telecommunications, often called broadcasts, provide the basis for commercial
radio and television programming.
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HOW TELECOMMUNICATIONS WORKS
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Telecommunications begin with
messages that are converted into electronic or optical signals. Some signals,
such as those that carry voice or music, are created in an analog or wave
format, but may be converted into a digital or mathematical format for faster
and more efficient transmission. The signals are then sent over a medium to a
receiver, where they are decoded back into a form that the person receiving the
message can understand. There are a variety of ways to create and decode
signals, and many different ways to transmit signals.
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Creating and Receiving the Signal
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Telegraph
In 1837 the first electrical telegraph
instruments were invented by Samuel Morse in the United States and by Sir
Charles Wheatstone and Sir William F. Cooke in Britain. Morse sent the first
public telegraph message in 1844. Pictured here is the original Morse receiving
device.
Devices such as the telegraph
and telephone relay messages by creating modulated electrical impulses, or
impulses that change in a systematic way. These impulses are then sent along
wires, through the air as radio waves, or via other media to a receiver that
decodes the modulation. The telegraph, the earliest method of delivering
telecommunications, works by converting the contacts (connections
between two conductors that permit a flow of current) between a telegraph key
and a metal conductor into electrical impulses. These impulses are sent along a
wire to a receiver, which converts the impulses into short and long bursts of
sound or into dots and dashes on a simple printing device. Specific sequences
of dots and dashes represent letters of the alphabet. In the early days of the
telegraph, these sequences were decoded by telegraph operators (see Morse
Code, International). In this way, telegraph operators could transmit and
receive letters that spelled words. Later versions of the telegraph could
decipher letters and numbers automatically. Telegraphs have been largely
replaced by other forms of telecommunications, such as electronic mail
(e-mail), but they are still used in some parts of the world to send messages.
The telephone uses a diaphragm
(small membrane) connected to a magnet and a wire coil to convert sound into an
analog or electrical waveform representation of the sound. When a person speaks
into the telephone’s microphone, sound waves created by the voice vibrate the
diaphragm, which in turn creates electrical impulses that are sent along a
telephone wire. The receiver’s wire is connected to a speaker, which converts
the modulated electrical impulses back into sound.
Broadcast radio and cellular
radio telephones are examples of devices that create signals by modulating
radio waves. A radio wave is one type of electromagnetic radiation, a form of
energy that travels in waves. Microwaves are also electromagnetic waves, but
with shorter wavelengths and higher frequencies. In telecommunications, a
transmitter creates and emits radio waves. The transmitter electronically
modulates or encodes sound or other information onto the radio waves by varying
either the amplitude (height) of the radio waves, or by varying the frequency
(number) of the waves within an established range (see Frequency
Modulation). A receiver (tuner) tuned to a specific frequency or range of
frequencies will pick up the modulation added to the radio waves. A speaker
connected to the tuner converts the modulation back into sound.
Broadcast television works in a
similar fashion. A television camera takes the light reflected from a scene and
converts it into an electronic signal, which is transmitted over high-frequency
radio waves. A television set contains a tuner that receives the signal and
uses that signal to modulate the images seen on the picture tube. The picture
tube contains an electron gun that shoots electrons onto a photo-sensitive
display screen. The electrons illuminate the screen wherever they fall, thus
creating moving pictures.
Telegraphs, telephones, radio, and
television all work by modifying electronic signals, making the signals
imitate, or reproduce, the original message. This form of transmission is known
as analog transmission. Computers and other types of electronic
equipment, however, transmit digital information. Digital technologies convert
a message into an electronic or optical form first by measuring different
qualities of the message, such as the pitch and volume of a voice, many times.
These measurements are then encoded into multiple series of binary numbers, or
1s and 0s. Finally, digital technologies create and send impulses that
correspond to the series of 1s and 0s. Digital information can be transmitted
faster and more clearly than analog signals, because the impulses only need to
correspond to two digits and not to the full range of qualities that compose
the original message, such as the pitch and volume of a human voice. While
digital transmissions can be sent over wires, cables or radio waves, they must
be decoded by a digital receiver. New digital telephones and televisions are
being developed to make telecommunications more efficient.
Personal computers primarily
communicate with each other and with larger networks, such as the Internet, by
using the ordinary telephone network. Increasing numbers of computers rely on
broadband networks provided by telephone and cable television companies to send
text, music, and video over the Internet at high speeds. Since the telephone
network functions by converting sound into electronic signals, the computer
must first convert its digital data into sound. Computers do this with a device
called a modem, which is short for modulator/demodulator. A modem
converts the stream of 1s and 0s from a computer into an analog signal that can
then be transmitted over the telephone network, as a speaker’s voice would. The
modem of the receiving computer demodulates the analog sound signal back into a
digital form that the computer can understand.
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Transmitting the Signal
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Telephone Switching Hub
The telephones in a large office
building must still be manually connected together with wires. In the central
switching hub pictured here, several connections come together.
Telecommunications systems deliver
messages using a number of different transmission media, including copper
wires, fiber-optic cables, communication satellites, and microwave radio. One
way to categorize telecommunications media is to consider whether or not the
media uses wires. Wire-based (or wireline) telecommunications provide the
initial link between most telephones and the telephone network and are a
reliable means for transmitting messages. Telecommunications without wires,
commonly referred to as wireless communications, use technologies such as
cordless telephones, cellular radio telephones, pagers, and satellites.
Wireless communications offer increased mobility and flexibility. In the future
some experts believe that wireless devices will also offer high-speed Internet
access.
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Wires and Cables
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Great Eastern
Launched in 1858, the Great Eastern was
the largest steamship in the world until surpassed by the Oceania in 1899. It
was 211 m (693 ft) long and propelled by paddlewheels, a propeller, and six
auxiliary sails. It is best remembered for laying the first trans-Atlantic
telegraph cable the year it was launched.
Wires and cables were the
original medium for telecommunications and are still the primary means for
telephone connections. Wireline transmission evolved from telegraph to
telephone service and continues to provide the majority of telecommunications
services. Wires connect telephones together within a home or business and also
connect these telephones to the nearest telephone switching facility.
Other wireline services employ
coaxial cable, which is used by cable television to provide hundreds of video
channels to subscribers. Much of the content transmitted by the coaxial cable
of cable television systems is sent by satellite to a central location known as
the headend. Coaxial cables flow from the headend throughout a community and
onward to individual residences and, finally, to individual television sets.
Because signals weaken as distance from the headend increases, the coaxial
cable network includes amplifiers that process and retransmit the television
signals.
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Fiber-Optic Cables
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Fiber-optic cables use specially
treated glass that can transmit signals in the form of pulsed beams of laser
light. Fiber-optic cables carry many times more information than copper wires
can, and they can transmit several television channels or thousands of
telephone conversations at the same time. Fiber-optic technology has replaced
copper wires for most transoceanic routes and in areas where large amounts of
data are sent. This technology uses laser transmitters to send pulses of
light via hair-thin strands of specially prepared glass fibers. New
improvements promise cables that can transmit millions of telephone calls over
a single fiber. Already fiber optic cables provide the high capacity,
'backbone' links necessary to carry the enormous and growing volume of
telecommunications and Internet traffic.
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Radio Waves
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Wireless telecommunications use radio
waves, sent through space from one antenna to another, as the medium for
communication. Radio waves are used for receiving AM and FM radio and for
receiving television. Cordless telephones and wireless radio telephone
services, such as cellular radio telephones and pagers, also use radio waves.
Telephone companies use microwaves to send signals over long distances.
Microwaves use higher frequencies than the radio waves used for AM, FM, or
cellular telephone transmissions, and they can transmit larger amounts of data
more efficiently. Microwaves have characteristics similar to those of visible
light waves and transmit pencil-thin beams that can be received using
dish-shaped antennas. Such narrow beams can be focused to a particular
destination and provide reliable transmissions over short distances on Earth.
Even higher and narrower beams provide the high-capacity links to and from
satellites. The high frequencies easily penetrate the ionosphere (a layer of
Earth’s atmosphere that blocks low-frequency waves) and provide a high-quality
signal.
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Communications Satellites
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Communications satellites provide a
means of transmitting telecommunications all over the globe, without the need
for a network of wires and cables. They orbit Earth at a speed that enables
them to stay above the same place on Earth at all times. This type of orbit is
called geostationary or geosynchronous orbit because the satellite’s orbital
speed operates in synchronicity with Earth’s rotation. The satellites receive
transmissions from Earth and transmit them back to numerous Earth station
receivers scattered within the receiving coverage area of the satellite. This
relay function makes it possible for satellites to operate as “bent pipes”—that
is, wireless transfer stations for point-to-point and point-to-multipoint
transmissions. Communications satellites are used by telephone and television
companies to transmit signals across great distances. Ship, airplane, and land
navigators also receive signals from satellites to determine geographic positions.
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TELECOMMUNICATIONS SYSTEMS
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Individual people, businesses,
and governments use many different types of telecommunications systems. Some
systems, such as the telephone system, use a network of cables, wires, and switching
stations for point-to-point communication. Other systems, such as radio and
television, broadcast radio signals over the air that can be received by anyone
who has a device to receive them. Some systems make use of several types of
media to complete a transmission. For example, a telephone call may travel by
means of copper wire, fiber-optic cable, and radio waves as the call is sent
from sender to receiver. All telecommunications systems are constantly evolving
as telecommunications technology improves. Many recent improvements, for
example, offer high-speed broadband connections that are needed to send
multimedia information over the Internet.
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Telegraph
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Radio Telegraph Operators
Navy radio telegraph operators on shore
type messages to ships at sea in this photo. Radio telegraph transmitters send
typed messages by radio waves to receiving stations located within broadcasting
range of the transmitter. Early radio telegraphs transmitted keystrokes into
electric pulses, which the receiving telegraph would translate into letters.
Telegraph services use both
wireline and wireless media for transmissions. Soon after the introduction of
the telegraph in 1844, telegraph wires spanned the country. Telegraph companies
maintained a system of wires and offices located in numerous cities. A message
sent by telegraph was called a telegram. Telegrams were printed on paper and
delivered to the receiving party by the telegraph company. With the invention
of the radio in the early 1900s, telegraph signals could also be sent by radio
waves. Wireless telegraphy made it practical for oceangoing ships as well as
aircraft to stay in constant contact with land-based stations.
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Telephone
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Telephone Control Center
Long distance telephone circuits are
maintained in telephone control centers. The number of calls on a given circuit
are monitored, and problems are identified and resolved. If there is a problem,
calls can be switched to alternate circuits while workers search for the cause.
The telephone network also uses
both wireline and wireless methods to deliver voice communications between
people, and data communications between computers and people or other
computers. The part of the telephone network that currently serves individual
residences and many businesses operates in an analog mode, uses copper wires,
and relays electronic signals that are continuous, such as the human voice.
Digital transmission via fiber-optic cables is now used in some sections of the
telephone network that send large amounts of calls over long distances.
However, since the rest of the telephone system is still analog, these digital
signals must be converted back to analog before they reach users. The telephone
network is stable and reliable, because it uses its own wire system that is
powered by low-voltage direct current from the telephone company. Telephone
networks modulate voice communications over these wires. A complex system of
network switches maintains the telephone links between callers. Telephone
networks also use microwave relay stations to send calls from place to place on
the ground. Satellites are used by telephone networks to transmit telephone
calls across countries and oceans.
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Teletype, Telex, and Facsimile
Transmission
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Fax Machine
Facsimile (fax) transmission involves
machines designed to transmit graphical information via normal telephone lines.
After a special fax number is dialed and the phone connection established,
documents are fed through the machine, which takes approximately one to six
minutes to scan and convert the information into electrical impulses. The
impulses are carried across phone lines and a receiving machine changes the
impulses back to text, making a copy, or facsimile, of the document in the
sending machine. Particularly in time-sensitive business transactions, fax
communication has become a popular alternative to express mail because it is
faster and generally less expensive.
Teletype, telex, and facsimile
transmission are all methods for transmitting text rather than sounds. These
text delivery systems evolved from the telegraph. Teletype and telex systems
still exist, but they have been largely replaced by facsimile machines, which
are inexpensive and better able to operate over the existing telephone network.
The Internet increasingly provides an even more inexpensive and convenient
option. The teletype, essentially a printing telegraph, is primarily a
point-to-multipoint system for sending text. The teletype converts the same
pulses used by telegraphs into letters and numbers, and then prints out readable
text. It was often used by news media organizations to provide newspaper
stories and stock market data to subscribers. Telex is primarily a
point-to-point system that uses a keyboard to transmit typed text over
telephone lines to similar terminals situated at individual company locations. See
also Office Systems: Communications; Telegraph: Modern Telegraph
Services.
Facsimile transmission now provides a
cheaper and easier way to transmit text and graphics over distances. Fax machines
contain an optical scanner that converts text and graphics into digital, or
machine-readable, codes. This coded information is sent over ordinary analog
telephone lines through the use of a modem included in the fax machine. The
receiving fax machine’s modem demodulates the signal and sends it to a printer
also contained in the fax machine.
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Radio
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Radios transmit and receive
communications at various preset frequencies. Radio waves carry the signals heard
on AM and FM radio, as well as the signals seen on a television set receiving
broadcasts from an antenna. Radio is used mostly as a public medium, sending
commercial broadcasts from a transmitter to anyone with a radio receiver within
its range, so it is known as a point-to-multipoint medium. However, radio can
also be used for private point-to-point transmissions. Two-way radios, cordless
telephones, and cellular radio telephones are common examples of transceivers,
which are devices that can both transmit and receive point-to-point messages.
Personal radio communication is
generally limited to short distances (usually a few kilometers), but powerful
transmitters can send broadcast radio signals hundreds of kilometers. Shortwave
radio, popular with amateur radio enthusiasts, uses a range of radio
frequencies that are able to bounce off the ionosphere. This electrically
charged layer of the atmosphere reflects certain frequencies of radio waves,
such as shortwave frequencies, while allowing higher-frequency waves, such as
microwaves, to pass through it. Amateur radio operators use the ionosphere to
bounce their radio signals to other radio operators thousands of kilometers
away.
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Television
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Television is primarily a public
broadcasting medium, using point-to-multipoint technology that is broadcast to
any user within range of the transmitter. Televisions transmit news and
information, as well as entertainment. Commercial television is broadcast over
very high frequency (VHF) and ultrahigh frequency (UHF) radio waves and can be
received by any television set within range of the transmitter. Televisions
have also been used for point-to-point, two-way telecommunications.
Teleconferencing, in which a television picture links two physically separated
parties, is a convenient way for businesspeople to meet and communicate without
the expense or inconvenience of travel. Video cameras on computers now allow
personal computer users to teleconference over the Internet. Videophones, which
use tiny video cameras and rely on satellite technology, can also send private
or public television images and have been used in news reporting in remote
locations.
Cable television is a
commercial service that links televisions to a source of many different types
of video programming using coaxial cable. The cable provider obtains coded, or
scrambled, programming from a communications satellite, as well as from
terrestrial links, including broadcast television stations. The signal may be
scrambled to prevent unpaid access to the programming. The cable provider
electronically unscrambles the signal and supplies the decoded signals by cable
to subscribers. Television users with personal satellite dishes can access
satellite programming directly without a cable installation. Personal satellite
dishes are also a subscriber service. Fees are paid to the network operator in
return for access to the satellite channels.
Most television sets outside
of the United States that receive programming use different types of standards
for receiving video signals. The European Phase Alternative Line standard
generates a higher-resolution picture than the sets used in the United States,
but these television sets are more expensive. Manufacturers now offer digital
video and audio signal processing, which features even higher picture
resolution and sound quality. The shape of the television screen is changing as
well, reflecting the aspect ratio (ratio of image height to width) used
for movie presentation.
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Global Positioning and Navigation
Systems
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Launching a GPS Satellite
A Navstar global positioning system
(GPS) satellite is launched into orbit by a Delta rocket. GPS satellites
continuously transmit data about the satellite’s position and the current time.
Military and civilian navigators use the information gathered from several
satellites to compute their own position.
The United States Global
Positioning System (GPS) and the Russian Global Orbiting Navigation Satellite
System (GLONASS) are networks of satellites that provide highly accurate
positioning information from anywhere on Earth. Both systems use a group of
satellites that orbit around the north and south poles at an altitude of 17,500
km (10,900 mi). These satellites constantly broadcast the time and their
location above Earth. A GPS receiver picks up broadcasts from these satellites
and determines its position through the process of triangulation. Using the
time information from each satellite, the receiver calculates the time the
signal takes to reach it. Factoring in this time with the speed at which radio
signals travel, the receiver calculates its distance from the satellite.
Finally, using the location of three satellites and its distance from each
satellite, the receiver determines its position.
GPS services, originally
designed for military use, are now available to civilians. Handheld GPS
receivers allow users to pinpoint their location on Earth to within a few
meters. One type of navigational tool used in automobiles integrates a GPS
receiver with an intelligent compact disc player capable of displaying road
maps and other graphical information. Upon receiving the GPS location data, the
CD player can pinpoint the location visually on one of the road maps contained
on disc.
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Personal Computers
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Computer Networking
Networks are connections between groups
of computers and associated devices that allow users to transfer information
electronically. The local area network shown on the left is representative of
the setup used in many offices and companies. Individual computers are called
work stations (W.S.), and communicate to each other via cable or telephone line
linking to servers. Servers are computers exactly like the W.S., except that
they have administrative functions and are devoted entirely to monitoring and
controlling W.S. access to part or all of the network and to any shared
resources (such as printers). The red line represents the larger network
connection between servers, called the backbone; the blue line shows local
connections. A modem (modulator/demodulator) allows computers to transfer
information across standard telephone lines. Modems convert digital signals
into analog signals and back again, making it possible for computers to
communicate, or network, across thousands of miles.
Personal computers use
telecommunications to provide a transmission link for the delivery of audio,
video, text, software, and multimedia services. Many experts believe that the
convergence of these services will generate consumer demand for new generations
of high-speed, broadband networks. Currently, the delivery of most of these
audio, video, and text services occurs over existing telephone connections
using the Internet. Some computers connect directly to the digital portion of
the telephone network using the Integrated Services Digital Network (ISDN) or
Digital Subscriber Lines (DSL), but this requires special equipment at user
locations. Telephone and cable television companies must also make upgrades to
their lines so that they can handle high-speed data transmission. In many
locations companies and individuals with high-speed data requirements now have
the option of securing DSL service from telephone companies and cable modem
service from cable television companies.
Electronic mail, or e-mail,
is a key attraction of the Internet and a common form of computer
telecommunications. E-mail is a text-based message delivery system that allows
information such as typed messages and multimedia to be sent to individual
computer users. Local e-mail messages (within a building or a company)
typically reach addressees by traveling through wire-based internal networks.
E-mail that must travel across town or across a country to reach the final
destination usually travels through the telephone network.
Instant messaging is another
key feature of computer telecommunications and involves sending text, audio, or
video data in real time. Other computer telecommunications technologies that
businesses frequently use include automated banking terminals and devices for
credit card or debit card transactions. These transactions either bill charges
directly to a customer’s credit card account or automatically deduct money from
a customer’s bank account.
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Voice Over Internet Protocol (VOIP)
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Voice Over Internet Protocol
(VOIP) is a method for making telephone calls over the Internet by sending
voice data in separate packets, just as e-mail is sent. Each packet is assigned
a code for its destination, and the packets are then reassembled in the correct
order at the receiving end. Recent technological improvements have made VOIP
almost as seamless and smooth as a regular telephone call.
In February 2004 the Federal
Communications Commission (FCC) ruled that VOIP, like e-mail and instant
messaging, is free of government regulation as long as it involves
communication from one computer to another. The FCC did not rule on whether
VOIP software that sends voice data from a computer directly to a regular
telephone should be regulated. Such services became available in the early part
of the 21st century and are expected to become widely available. They require a
broadband connection to the Internet but can reduce telephone charges
significantly while also offering for free additional services such as call
waiting, caller identification, voice mail, and the ability to call from your
home telephone number wherever you travel.
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HISTORY
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Communicating over long
distances has been a challenge throughout history. In ancient times, runners
were used to carry important messages between rulers or other important people.
Other forms of long-distance communication included smoke signals, chains of
searchlights and flags to send a message from one tower to another, carrier
pigeons, and horses. Modern telecommunications began in the 1800s with the
discovery that electricity can be used to transmit a signal. For the first
time, a signal could be sent faster than any other mode of transportation. The
first practical telecommunications device to make use of this discovery was the
telegraph.
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The Telegraph
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Beginning in the mid-1800s,
the telegraph delivered the first intercity, transcontinental, and transoceanic
messages in the world. The telegraph revolutionized the way people communicated
by providing messages faster than any other means provided at the time.
American art professor Samuel F. B. Morse pursued an interest in
electromagnetism to create a practical electromagnetic telegraph in 1837. Morse
partnered with Alfred Vail and was able to commercialize the technology with
financial support from the U.S. government. In 1843 Morse built a demonstration
telegraph link between Washington, D.C., and Baltimore, Maryland. On May 24,
1844, the network was inaugurated for commercial use with the message, “What
hath God wrought!”
Telegraph use quickly spread;
the first transcontinental link was completed in 1861 between San Francisco,
California, and Washington, D.C.Railroad companies and newspapers were the
first major telegraphy users. Telegraph lines were constructed parallel to
railroad beds. Telegraphy helped the railroads manage traffic and allowed news
organizations to distribute stories quickly to local newspapers. Within a few
years, several telegraph companies were in operation, each with its own network
of telegraph wires. Consolidation occurred in the telegraph industry (as it has
in numerous telecommunications industries), and by the 1870s the Western Union
Telegraph Company emerged as the dominant operator.
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Commercial Growth of the Telephone
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In 1876 American inventor
Alexander Graham Bell ushered in a new era of voice and sound telecommunication
when he uttered to his assistant the words, “Mr. Watson, come here; I want
you,” using a prototype telephone. Bell received the patent for the first
telephone, but he had to fight numerous legal challenges to his patent from
other inventors with similar devices. Bell was able to make his prototype
telephone work, and this enabled him to attract financial backers, and his
company grew. The telephone was a vast improvement over the telegraph system,
which could only transmit coded words and numbers, not the sound of a human voice.
Telegraph messages had to be deciphered by trained operators, written down, and
then delivered by hand to the receiving party, all of which took time. The
telephone transmitted actual sound messages and made telecommunication
immediate. Improved switching technology (used to transfer calls from one local
network to another) meant individual telephones could be connected for personal
conversations.
The first commercial telephone
line was installed in Boston, Massachusetts, in 1877. Early telephones required
direct connections to other telephones, but this problem was solved with
telephone exchange switches, the first of which was installed in New Haven,
Connecticut, in 1878. A telephone exchange linked telephones in a given area
together, so a connection between the telephone and the exchange was all that
was needed. Telephones were much more convenient and personal than telegrams,
and their use quickly spread. By 1913 telephone lines from New York City to San
Francisco had been established, and by 1930 radio signals could transmit
telephone calls between New York and London, England. Eventually, long-distance
telephone service in the United States was consolidated into one company, the
American Telephone and Telegraph Company (now known as AT&T, Inc.), which
was a regulated monopoly.
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The Emergence of Broadcasting
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Telephones and telegraphs are
primarily private means of communications, sending signals from one point to
another, but with the invention of the radio, public communications, or
point-to-multipoint signals, could be sent through a central transmitter to be
received by anyone possessing a receiver. Italian inventor and electrical
engineer Guglielmo Marconi transmitted a Morse-code telegraph signal by radio
in 1895. This began a revolution in wireless telegraphy that would later result
in broadcast radios that could transmit actual voice and music. Radio and
wireless telegraph communication played an important role during World War I
(1914-1918), allowing military personnel to communicate instantly with troops
in remote locations. United States president Woodrow Wilson was impressed with
the ability of radio, but he was fearful of its potential for espionage use. He
banned nonmilitary radio use in the United States as the nation entered World
War I in 1917, and this stifled commercial development of the medium. After the
war, however, commercial radio stations began to broadcast. By the mid-1920s,
millions of radio listeners tuned in to music, news, and entertainment
programming.
Television got its start as
a mass-communication medium shortly after World War II (1939-1945). The expense
of television transmission prevented its use as a two-way medium, but radio
broadcasters quickly saw the potential for television to provide a new way of
bringing news and entertainment programming to people. For more information on
the development of radio and television, see Radio and Television
Broadcasting.
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Government Regulation
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The number of radio broadcasts
grew quickly in the 1920s, but there was no regulation of frequency use or
transmitter strength. The result was a crowded radio band of overlapping
signals. To remedy this, the U.S. government created the Federal Communications
Commission (FCC) in 1934 to regulate the spreading use of the broadcast
spectrum. The FCC licenses broadcasters and regulates the location and
transmitting strength, or range, stations have in an effort to prevent
interference from nearby signals.
The FCC and the U.S. government
have also assumed roles in limiting the types of business practices in which
telecommunications companies can engage. The U.S. Department of Justice filed
an antitrust lawsuit against AT&T Corp., arguing that the company used its
monopoly position to stifle competition, particularly through its control over
local telephone service facilities. The lawsuit was settled in 1982, and
AT&T agreed to disperse its local telephone companies, thereby creating
seven new independent companies.
In 1996 the U.S. government
enacted the Telecommunications Reform Act to further encourage competition in
the telecommunications marketplace. This legislation removed government rules
preventing local and long-distance phone companies, cable television operators,
broadcasters, and wireless services from directly competing with one another.
The act spurred consolidation in the industry, as regional companies joined
forces to create telecommunications giants that provided telephone, wireless,
cable, and Internet services.
Deregulation, however, also led to
overproduction of fiber optic cable and a steep decline in the fortunes of the
telecommunications industry beginning in 2000. The increased competition
provided the backdrop for the bankruptcy of a leading telecommunications
company, WorldCom, Inc., in 2002, when it admitted to the largest accounting
fraud in the history of U.S. business.
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International Telecommunications
Networks
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Satellite Control Room
Communications satellite operations are
monitored from control rooms such as this one, where minor orbit adjustments
can be made and communications functions can be regularly checked. If problems
occur, technicians can attempt repairs or transfer communications to a
different satellite.
In order to provide overseas
telecommunications, people had to develop networks that could link widely
separated nations. The first networks to provide such linkage were telegraph
networks that used undersea cables, but these networks could provide channels
for only a few simultaneous communications. Shortwave radio also made it
possible for wireless transmissions of both telegraphy and voice over very long
distances.
To take advantage of the
wideband capability of satellites to provide telecommunications service,
companies from all over the world pooled resources and shared risks by creating
a cooperative known as the International Telecommunications Satellite
Organization, or Intelsat, in 1964. Transoceanic satellite telecommunications
first became possible in 1965 with the successful launch of Early Bird, also
known as Intelsat 1. Intelsat 1 provided the first international television transmission
and had the capacity to handle one television channel or 240 simultaneous
telephone calls.
Intelsat later expanded and
diversified to meet the global and regional satellite requirements of more than
200 nations and territories. In response to private satellite ventures entering
the market, the managers of Intelsat converted the cooperative into a private
corporation better able to compete with these emerging companies. The
International Mobile Satellite Organization (Inmarsat) primarily provided service
to oceangoing vessels when it first formed as a cooperative in 1979, but it
later expanded operations to include service to airplanes and users in remote
land areas not served by cellular radio or wireline services. Inmarsat became a
privatized, commercial venture in 1999.
F
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Current Developments
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Personal computers have pushed
the limits of the telephone system as more and more complex computer messages
are being sent over telephone lines, and at rapidly increasing speeds. This
need for speed has encouraged the development of digital transmission
technology. The growing use of personal computers for telecommunications has
increased the need for innovations in fiber-optic technology.
Telecommunications and information
technologies are merging and converging. This means that many of the devices
now associated with only one function may evolve into more versatile equipment.
This convergence is already happening in various fields. Some telephones and
pagers are able to store not only phone numbers but also names and personal
information about callers. Wireless phones with keyboards and small screens can
access the Internet and send and receive e-mail messages. Personal computers
can now access information and video entertainment and are in effect becoming a
combined television set and computer terminal. Television sets can access the
Internet through add-on appliances. Future modifications and technology
innovations may blur the distinctions between appliances even more.
Convergence of telecommunications
technologies may also trigger a change in the kind of content available. Both
television and personal computers are likely to incorporate new multimedia,
interactive, and digital features. However, in the near term, before the
actualization of a fully digital telecommunications world, devices such as
modems will still be necessary to provide an essential link between the old
analog world and the upcoming digital one.
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