Telecommunication
Telecommunication is the transmission of signs, signals, messages,
words, writings, images and sounds or information of any nature by
wire, radio, optical or other electromagnetic systems.[1][2]
Telecommunication
Telecommunication occurs when the exchange of information between
communication participants includes the use of technology. It is
transmitted either electrically over physiical media, such as cables,
or via electromagnetic radiation.[3][4][5][6][7][8] Such transmission
paths are often divided into communication channels which afford the
advantages of multiplexing. Since the
Latin
Latin term communicatio is
considered the social process of information exchange, the term
telecommunications is often used in its plural form because it
involves many different technologies.[9]
Early means of communicating over a distance included visual signals,
such as beacons, smoke signals, semaphore telegraphs, signal flags,
and optical heliographs.[10] Other examples of pre-modern
long-distance communication included audio messages such as coded
drumbeats, lung-blown horns, and loud whistles. 20th and 21st century
technologies for long-distance communication usually involve
electrical and electromagnetic technologies, such as telegraph,
telephone, and teleprinter, networks, radio, microwave transmission,
fiber optics, and communications satellites.
A revolution in wireless communication began in the first decade of
the 20th century with the pioneering developments in radio
communications by Guglielmo Marconi, who won the Nobel Prize in
Physics in 1909 and
JC Bose
JC Bose and Other notable pioneering inventors and
developers in the field of electrical and electronic
telecommunications include
Charles Wheatstone
Charles Wheatstone and Samuel Morse
(inventors of the telegraph),
Alexander Graham Bell
Alexander Graham Bell (inventor of the
telephone),
Edwin Armstrong
Edwin Armstrong and
Lee de Forest
Lee de Forest (inventors of radio), as
well as Vladimir K. Zworykin,
John Logie Baird
John Logie Baird and Philo Farnsworth
(some of the inventors of television).
Contents
1 Etymology
2 History
2.1 Beacons and pigeons
2.2
Telegraph
Telegraph and telephone
2.3
Radio
Radio and television
2.4 Computers and the Internet
3 Key concepts
3.1 Basic elements
3.2 Analog versus digital communications
3.3
Telecommunication
Telecommunication networks
3.4
Communication
Communication channels
3.5 Modulation
4 Society
4.1 Economic impact
4.1.1 Microeconomics
4.1.2 Macroeconomics
4.2 Social impact
4.3 Other impacts
5 Government
6 Modern media
6.1 Worldwide equipment sales
6.2 Telephone
6.3
Radio
Radio and television
6.4 Internet
6.5 Local area networks and wide area networks
7 Transmission capacity
8 See also
9 References
9.1 Citations
9.2 Bibliography
10 External links
Etymology[edit]
The word telecommunication is a compound of the Greek prefix tele
(τηλε), meaning distant, far off, or afar,[11] and the Latin
communicare, meaning to share. Its modern use is adapted from the
French,[7] because its written use was recorded in 1904 by the French
engineer and novelist Édouard Estaunié.[12][13]
Communication
Communication was
first used as an English word in the late 14th century. It comes from
Old French comunicacion (14c., Modern French communication), from
Latin
Latin communicationem (nominative communicatio), noun of action from
past participle stem of communicare "to share, divide out;
communicate, impart, inform; join, unite, participate in," literally
"to make common," from communis".[14]
History[edit]
Further information: History of telecommunication
Beacons and pigeons[edit]
A replica of one of Chappe's semaphore towers
Homing pigeons have occasionally been used throughout history by
different cultures.
Pigeon post
.png/560px-Pigeon_Messengers_(Harper's_Engraving).png)
Pigeon post had Persian roots, and was later used
by the Romans to aid their military.
Frontinus
Frontinus said that Julius Caesar
used pigeons as messengers in his conquest of Gaul.[15] The Greeks
also conveyed the names of the victors at the Olympic Games to various
cities using homing pigeons.[16] In the early 19th century, the Dutch
government used the system in Java and Sumatra. And in 1849, Paul
Julius Reuter started a pigeon service to fly stock prices between
Aachen
Aachen and Brussels, a service that operated for a year until the gap
in the telegraph link was closed.[17]
In the Middle Ages, chains of beacons were commonly used on hilltops
as a means of relaying a signal.
Beacon
Beacon chains suffered the drawback
that they could only pass a single bit of information, so the meaning
of the message such as "the enemy has been sighted" had to be agreed
upon in advance. One notable instance of their use was during the
Spanish Armada, when a beacon chain relayed a signal from
Plymouth
Plymouth to
London.[18]
In 1792, Claude Chappe, a French engineer, built the first fixed
visual telegraphy system (or semaphore line) between
Lille
Lille and
Paris.[19] However semaphore suffered from the need for skilled
operators and expensive towers at intervals of ten to thirty
kilometres (six to nineteen miles). As a result of competition from
the electrical telegraph, the last commercial line was abandoned in
1880.[20]
Telegraph
Telegraph and telephone[edit]
On July 25, 1837 the first commercial electrical telegraph was
demonstrated by English inventor
Sir
Sir William Fothergill Cooke, and
English scientist
Sir
Sir Charles Wheatstone.[21][22] Both inventors
viewed their device as "an improvement to the [existing]
electromagnetic telegraph" not as a new device.[23]
Samuel Morse
Samuel Morse independently developed a version of the electrical
telegraph that he unsuccessfully demonstrated on 2 September 1837. His
code was an important advance over Wheatstone's signaling method. The
first transatlantic telegraph cable was successfully completed on 27
July 1866, allowing transatlantic telecommunication for the first
time.[24]
The conventional telephone was invented independently by Alexander
Bell and
Elisha Gray
Elisha Gray in 1876.[25]
Antonio Meucci
Antonio Meucci invented the first
device that allowed the electrical transmission of voice over a line
in 1849. However Meucci's device was of little practical value because
it relied upon the electrophonic effect and thus required users to
place the receiver in their mouth to "hear" what was being said.[26]
The first commercial telephone services were set-up in 1878 and 1879
on both sides of the Atlantic in the cities of
New Haven
New Haven and
London.[27][28]
Radio
Radio and television[edit]
Starting in 1894, Italian inventor
Guglielmo Marconi
Guglielmo Marconi began developing
a wireless communication using the then newly discovered phenomenon of
radio waves, showing by 1901 that they could be transmitted across the
Atlantic Ocean.[29] This was the start of wireless telegraphy by
radio. Voice and music were demonstrated in 1900 and 1906, but had
little early success[citation needed].
World War I
World War I accelerated the
development of radio for military communications. After the war,
commercial radio
AM broadcasting
AM broadcasting began in the 1920s and became an
important mass medium for entertainment and news.
World War II
World War II again
accelerated development of radio for the wartime purposes of aircraft
and land communication, radio navigation and radar.[30] Development of
stereo
FM broadcasting
FM broadcasting of radio took place from the 1930s on-wards in
the United States and displaced AM as the dominant commercial standard
by the 1960s, and by the 1970s in the United Kingdom.[31]
On 25 March 1925,
John Logie Baird
John Logie Baird was able to demonstrate the
transmission of moving pictures at the London department store
Selfridges. Baird's device relied upon the
Nipkow disk
Nipkow disk and thus became
known as the mechanical television. It formed the basis of
experimental broadcasts done by the British
Broadcasting
Broadcasting Corporation
beginning 30 September 1929.[32] However, for most of the twentieth
century televisions depended upon the cathode ray tube invented by
Karl Braun. The first version of such a television to show promise was
produced by
Philo Farnsworth
Philo Farnsworth and demonstrated to his family on 7
September 1927.[33] After World War II, the experiments in television
that had been interrupted were resumed, and it also became an
important home entertainment broadcast medium.
Computers and the Internet[edit]
On 11 September 1940,
George Stibitz
George Stibitz transmitted problems for his
Complex Number Calculator in New York using a teletype, and received
the computed results back at
Dartmouth College
Dartmouth College in New Hampshire.[34]
This configuration of a centralized computer (mainframe) with remote
dumb terminals remained popular well into the 1970s. However, already
in the 1960s, researchers started to investigate packet switching, a
technology that sends a message in portions to its destination
asynchronously without passing it through a centralized mainframe. A
four-node network emerged on 5 December 1969, constituting the
beginnings of the ARPANET, which by 1981 had grown to 213 nodes.[35]
ARPANET
ARPANET eventually merged with other networks to form the Internet.
While
Internet
Internet development was a focus of the
Internet
Internet Engineering
Task Force (IETF) who published a series of Request for Comment
documents, other networking advancement occurred in industrial
laboratories, such as the local area network (LAN) developments of
Ethernet
Ethernet (1983) and the token ring protocol (1984)[citation needed].
Key concepts[edit]
Modern telecommunication is founded on a series of key concepts that
experienced progressive development and refinement in a period of well
over a century.
Basic elements[edit]
Telecommunication
Telecommunication technologies may primarily be divided into wired and
wireless methods. Overall though, a basic telecommunication system
consists of three main parts that are always present in some form or
another:
A transmitter that takes information and converts it to a signal.
A transmission medium, also called the physical channel that carries
the signal. An example of this is the "free space channel".
A receiver that takes the signal from the channel and converts it back
into usable information for the recipient.
For example, in a radio broadcasting station the station's large power
amplifier is the transmitter; and the broadcasting antenna is the
interface between the power amplifier and the "free space channel".
The free space channel is the transmission medium; and the receiver's
antenna is the interface between the free space channel and the
receiver. Next, the radio receiver is the destination of the radio
signal, and this is where it is converted from electricity to sound
for people to listen to.
Sometimes, telecommunication systems are "duplex" (two-way systems)
with a single box of electronics working as both the transmitter and a
receiver, or a transceiver. For example, a cellular telephone is a
transceiver.[36] The transmission electronics and the receiver
electronics within a transceiver are actually quite independent of
each other. This can be readily explained by the fact that radio
transmitters contain power amplifiers that operate with electrical
powers measured in watts or kilowatts, but radio receivers deal with
radio powers that are measured in the microwatts or nanowatts. Hence,
transceivers have to be carefully designed and built to isolate their
high-power circuitry and their low-power circuitry from each other, as
to not cause interference.
Telecommunication
Telecommunication over fixed lines is called point-to-point
communication because it is between one transmitter and one receiver.
Telecommunication
Telecommunication through radio broadcasts is called broadcast
communication because it is between one powerful transmitter and
numerous low-power but sensitive radio receivers.[36]
Telecommunications
Telecommunications in which multiple transmitters and multiple
receivers have been designed to cooperate and to share the same
physical channel are called multiplex systems. The sharing of physical
channels using multiplexing often gives very large reductions in
costs. Multiplexed systems are laid out in telecommunication networks,
and the multiplexed signals are switched at nodes through to the
correct destination terminal receiver.
Analog versus digital communications[edit]
Communications signals can be sent either by analog signals or digital
signals. There are analog communication systems and digital
communication systems. For an analog signal, the signal is varied
continuously with respect to the information. In a digital signal, the
information is encoded as a set of discrete values (for example, a set
of ones and zeros). During the propagation and reception, the
information contained in analog signals will inevitably be degraded by
undesirable physical noise. (The output of a transmitter is noise-free
for all practical purposes.) Commonly, the noise in a communication
system can be expressed as adding or subtracting from the desirable
signal in a completely random way. This form of noise is called
additive noise, with the understanding that the noise can be negative
or positive at different instants of time. Noise that is not additive
noise is a much more difficult situation to describe or analyze, and
these other kinds of noise will be omitted here.
On the other hand, unless the additive noise disturbance exceeds a
certain threshold, the information contained in digital signals will
remain intact. Their resistance to noise represents a key advantage of
digital signals over analog signals.[37]
Telecommunication
Telecommunication networks[edit]
A telecommunications network is a collection of transmitters,
receivers, and communications channels that send messages to one
another. Some digital communications networks contain one or more
routers that work together to transmit information to the correct
user. An analog communications network consists of one or more
switches that establish a connection between two or more users. For
both types of network, repeaters may be necessary to amplify or
recreate the signal when it is being transmitted over long distances.
This is to combat attenuation that can render the signal
indistinguishable from the noise.[38] Another advantage of digital
systems over analog is that their output is easier to store in memory,
i.e. two voltage states (high and low) are easier to store than a
continuous range of states.
Communication
Communication channels[edit]
The term "channel" has two different meanings. In one meaning, a
channel is the physical medium that carries a signal between the
transmitter and the receiver. Examples of this include the atmosphere
for sound communications, glass optical fibers for some kinds of
optical communications, coaxial cables for communications by way of
the voltages and electric currents in them, and free space for
communications using visible light, infrared waves, ultraviolet light,
and radio waves.
Coaxial cable
Coaxial cable types are classified by RG type or
"radio guide", terminology derived from World War II. The various RG
designations are used to classify the specific signal transmission
applications.[39] This last channel is called the "free space
channel". The sending of radio waves from one place to another has
nothing to do with the presence or absence of an atmosphere between
the two.
Radio
Radio waves travel through a perfect vacuum just as easily as
they travel through air, fog, clouds, or any other kind of gas.
The other meaning of the term "channel" in telecommunications is seen
in the phrase communications channel, which is a subdivision of a
transmission medium so that it can be used to send multiple streams of
information simultaneously. For example, one radio station can
broadcast radio waves into free space at frequencies in the
neighborhood of 94.5
MHz
MHz (megahertz) while another radio station
can simultaneously broadcast radio waves at frequencies in the
neighborhood of 96.1 MHz. Each radio station would transmit radio
waves over a frequency bandwidth of about 180 kHz (kilohertz),
centered at frequencies such as the above, which are called the
"carrier frequencies". Each station in this example is separated from
its adjacent stations by 200 kHz, and the difference between
200 kHz and 180 kHz (20 kHz) is an engineering
allowance for the imperfections in the communication system.
In the example above, the "free space channel" has been divided into
communications channels according to frequencies, and each channel is
assigned a separate frequency bandwidth in which to broadcast radio
waves. This system of dividing the medium into channels according to
frequency is called "frequency-division multiplexing". Another term
for the same concept is "wavelength-division multiplexing", which is
more commonly used in optical communications when multiple
transmitters share the same physical medium.
Another way of dividing a communications medium into channels is to
allocate each sender a recurring segment of time (a "time slot", for
example, 20 milliseconds out of each second), and to allow each sender
to send messages only within its own time slot. This method of
dividing the medium into communication channels is called
"time-division multiplexing" (TDM), and is used in optical fiber
communication. Some radio communication systems use TDM within an
allocated FDM channel. Hence, these systems use a hybrid of TDM and
FDM.
Modulation[edit]
The shaping of a signal to convey information is known as modulation.
Modulation
Modulation can be used to represent a digital message as an analog
waveform. This is commonly called "keying" – a term derived from the
older use of Morse Code in telecommunications – and several keying
techniques exist (these include phase-shift keying, frequency-shift
keying, and amplitude-shift keying). The "Bluetooth" system, for
example, uses phase-shift keying to exchange information between
various devices.[40][41] In addition, there are combinations of
phase-shift keying and amplitude-shift keying which is called (in the
jargon of the field) "quadrature amplitude modulation" (QAM) that are
used in high-capacity digital radio communication systems.
Modulation
Modulation can also be used to transmit the information of
low-frequency analog signals at higher frequencies. This is helpful
because low-frequency analog signals cannot be effectively transmitted
over free space. Hence the information from a low-frequency analog
signal must be impressed into a higher-frequency signal (known as the
"carrier wave") before transmission. There are several different
modulation schemes available to achieve this [two of the most basic
being amplitude modulation (AM) and frequency modulation (FM)]. An
example of this process is a disc jockey's voice being impressed into
a 96
MHz
MHz carrier wave using frequency modulation (the voice would
then be received on a radio as the channel "96 FM").[42] In
addition, modulation has the advantage that it may use frequency
division multiplexing (FDM).
Society[edit]
Telecommunication
Telecommunication has a significant social, cultural and economic
impact on modern society. In 2008, estimates placed the
telecommunication industry's revenue at $4.7 trillion or just under 3
percent of the gross world product (official exchange rate).[43]
Several following sections discuss the impact of telecommunication on
society.
Economic impact[edit]
Microeconomics[edit]
On the microeconomic scale, companies have used telecommunications to
help build global business empires. This is self-evident in the case
of online retailer
Amazon.com
Amazon.com but, according to academic Edward
Lenert, even the conventional retailer
Walmart
Walmart has benefited from
better telecommunication infrastructure compared to its
competitors.[44] In cities throughout the world, home owners use their
telephones to order and arrange a variety of home services ranging
from pizza deliveries to electricians. Even relatively poor
communities have been noted to use telecommunication to their
advantage. In Bangladesh's Narshingdi district, isolated villagers use
cellular phones to speak directly to wholesalers and arrange a better
price for their goods. In Côte d'Ivoire, coffee growers share mobile
phones to follow hourly variations in coffee prices and sell at the
best price.[45]
Macroeconomics[edit]
On the macroeconomic scale, Lars-Hendrik Röller and Leonard Waverman
suggested a causal link between good telecommunication infrastructure
and economic growth.[46][47] Few dispute the existence of a
correlation although some argue it is wrong to view the relationship
as causal.[48]
Because of the economic benefits of good telecommunication
infrastructure, there is increasing worry about the inequitable access
to telecommunication services amongst various countries of the
world—this is known as the digital divide. A 2003 survey by the
International Telecommunication Union
International Telecommunication Union (ITU) revealed that roughly a
third of countries have fewer than one mobile subscription for every
20 people and one-third of countries have fewer than one land-line
telephone subscription for every 20 people. In terms of Internet
access, roughly half of all countries have fewer than one out of 20
people with
Internet
Internet access. From this information, as well as
educational data, the ITU was able to compile an index that measures
the overall ability of citizens to access and use information and
communication technologies.[49] Using this measure, Sweden, Denmark
and
Iceland
Iceland received the highest ranking while the African countries
Nigeria, Burkina Faso and Mali received the lowest.[50]
Social impact[edit]
Telecommunication
Telecommunication has played a significant role in social
relationships. Nevertheless, devices like the telephone system were
originally advertised with an emphasis on the practical dimensions of
the device (such as the ability to conduct business or order home
services) as opposed to the social dimensions. It was not until the
late 1920s and 1930s that the social dimensions of the device became a
prominent theme in telephone advertisements. New promotions started
appealing to consumers' emotions, stressing the importance of social
conversations and staying connected to family and friends.[51]
Since then the role that telecommunications has played in social
relations has become increasingly important. In recent years, the
popularity of social networking sites has increased dramatically.
These sites allow users to communicate with each other as well as post
photographs, events and profiles for others to see. The profiles can
list a person's age, interests, sexual preference and relationship
status. In this way, these sites can play important role in everything
from organising social engagements to courtship.[52]
Prior to social networking sites, technologies like short message
service (SMS) and the telephone also had a significant impact on
social interactions. In 2000, market research group Ipsos MORI
reported that 81% of 15- to 24-year-old SMS users in the United
Kingdom had used the service to coordinate social arrangements and 42%
to flirt.[53]
Other impacts[edit]
News source preference
of Americans in 2006.[54]
Local TV
59%
National TV
47%
Radio
44%
Local paper
38%
Internet
23%
National paper
12%
Survey permitted multiple answers
In cultural terms, telecommunication has increased the public's
ability to access music and film. With television, people can watch
films they have not seen before in their own home without having to
travel to the video store or cinema. With radio and the Internet,
people can listen to music they have not heard before without having
to travel to the music store.
Telecommunication
Telecommunication has also transformed the way people receive their
news. A 2006 survey (right table) of slightly more than 3,000
Americans by the non-profit Pew
Internet
Internet and American Life Project in
the United States the majority specified television or radio over
newspapers.
Telecommunication
Telecommunication has had an equally significant impact on
advertising.
TNS Media Intelligence
TNS Media Intelligence reported that in 2007, 58% of
advertising expenditure in the United States was spent on media that
depend upon telecommunication.[55]
Advertising expenditures in US in 2007
Medium
Spending
Internet
7.6%
$11.31 billion
Radio
7.2%
$10.69 billion
Cable TV
12.1%
$18.02 billion
Syndicated TV
2.8%
$4.17 billion
Spot TV
11.3%
$16.82 billion
Network TV
17.1%
$25.42 billion
Newspaper
18.9%
$28.22 billion
Magazine
20.4%
$30.33 billion
Outdoor
2.7%
$4.02 billion
Total
100%
$149 billion
Government[edit]
Many countries have enacted legislation which conforms to the
International
Telecommunication
Telecommunication Regulations established by the
International Telecommunication Union
International Telecommunication Union (ITU), which is the "leading UN
agency for information and communication technology issues."[56] In
1947, at the Atlantic City Conference, the ITU decided to "afford
international protection to all frequencies registered in a new
international frequency list and used in conformity with the Radio
Regulation." According to the ITU's
Radio
Radio Regulations adopted in
Atlantic City, all frequencies referenced in the International
Frequency
Frequency Registration Board, examined by the board and registered on
the International
Frequency
Frequency List "shall have the right to
international protection from harmful interference."[57]
From a global perspective, there have been political debates and
legislation regarding the management of telecommunication and
broadcasting. The history of broadcasting discusses some debates in
relation to balancing conventional communication such as printing and
telecommunication such as radio broadcasting.[58] The onset of World
War II brought on the first explosion of international broadcasting
propaganda.[58] Countries, their governments, insurgents, terrorists,
and militiamen have all used telecommunication and broadcasting
techniques to promote propaganda.[58][59] Patriotic propaganda for
political movements and colonization started the mid-1930s. In 1936,
the BBC broadcast propaganda to the Arab World to partly counter
similar broadcasts from Italy, which also had colonial interests in
North Africa.[58]
Modern insurgents, such as those in the latest Iraq war, often use
intimidating telephone calls, SMSs and the distribution of
sophisticated videos of an attack on coalition troops within hours of
the operation. "The Sunni insurgents even have their own television
station, Al-Zawraa, which while banned by the Iraqi government, still
broadcasts from Erbil, Iraqi Kurdistan, even as coalition pressure has
forced it to switch satellite hosts several times."[59]
On 10 November 2014, President Obama recommended the Federal
Communications Commission reclassify broadband
Internet
Internet service as a
telecommunications service to preserve net neutrality.[60][61]
Modern media[edit]
Worldwide equipment sales[edit]
According to data collected by Gartner[62][63] and Ars Technica[64]
sales of main consumer's telecommunication equipment worldwide in
millions of units was:
Equipment / year
1975
1980
1985
1990
1994
1996
1998
2000
2002
2004
2006
2008
Computers
0
1
8
20
40
75
100
135
130
175
230
280
Cell phones
N/A
N/A
N/A
N/A
N/A
N/A
180
400
420
660
830
1000
Telephone[edit]
Optical fiber
Optical fiber provides cheaper bandwidth for long distance
communication.
In a telephone network, the caller is connected to the person they
want to talk to by switches at various telephone exchanges. The
switches form an electrical connection between the two users and the
setting of these switches is determined electronically when the caller
dials the number. Once the connection is made, the caller's voice is
transformed to an electrical signal using a small microphone in the
caller's handset. This electrical signal is then sent through the
network to the user at the other end where it is transformed back into
sound by a small speaker in that person's handset.
The landline telephones in most residential homes are analog—that
is, the speaker's voice directly determines the signal's
voltage.[citation needed] Although short-distance calls may be handled
from end-to-end as analog signals, increasingly telephone service
providers are transparently converting the signals to digital signals
for transmission. The advantage of this is that digitized voice data
can travel side-by-side with data from the
Internet
Internet and can be
perfectly reproduced in long distance communication (as opposed to
analog signals that are inevitably impacted by noise).
Mobile phones
Mobile phones have had a significant impact on telephone networks.
Mobile phone subscriptions now outnumber fixed-line subscriptions in
many markets. Sales of mobile phones in 2005 totalled 816.6 million
with that figure being almost equally shared amongst the markets of
Asia/Pacific (204 m), Western Europe (164 m), CEMEA (Central Europe,
the Middle East and Africa) (153.5 m), North America (148 m) and Latin
America (102 m).[65] In terms of new subscriptions over the five years
from 1999, Africa has outpaced other markets with 58.2% growth.[66]
Increasingly these phones are being serviced by systems where the
voice content is transmitted digitally such as
GSM
GSM or
W-CDMA
W-CDMA with many
markets choosing to deprecate analog systems such as AMPS.[67]
There have also been dramatic changes in telephone communication
behind the scenes. Starting with the operation of
TAT-8 in 1988, the
1990s saw the widespread adoption of systems based on optical fibers.
The benefit of communicating with optic fibers is that they offer a
drastic increase in data capacity.
TAT-8 itself was able to carry 10
times as many telephone calls as the last copper cable laid at that
time and today's optic fibre cables are able to carry 25 times as many
telephone calls as TAT-8.[68] This increase in data capacity is due to
several factors: First, optic fibres are physically much smaller than
competing technologies. Second, they do not suffer from crosstalk
which means several hundred of them can be easily bundled together in
a single cable.[69] Lastly, improvements in multiplexing have led to
an exponential growth in the data capacity of a single fibre.[70][71]
Assisting communication across many modern optic fibre networks is a
protocol known as
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM). The ATM protocol
allows for the side-by-side data transmission mentioned in the second
paragraph. It is suitable for public telephone networks because it
establishes a pathway for data through the network and associates a
traffic contract with that pathway. The traffic contract is
essentially an agreement between the client and the network about how
the network is to handle the data; if the network cannot meet the
conditions of the traffic contract it does not accept the connection.
This is important because telephone calls can negotiate a contract so
as to guarantee themselves a constant bit rate, something that will
ensure a caller's voice is not delayed in parts or cut off
completely.[72] There are competitors to ATM, such as Multiprotocol
Label Switching (MPLS), that perform a similar task and are expected
to supplant ATM in the future.[73][74]
Radio
Radio and television[edit]
Main articles: Radio, Television, and Broadcasting
Digital television
Digital television standards and their adoption worldwide
In a broadcast system, the central high-powered broadcast tower
transmits a high-frequency electromagnetic wave to numerous
low-powered receivers. The high-frequency wave sent by the tower is
modulated with a signal containing visual or audio information. The
receiver is then tuned so as to pick up the high-frequency wave and a
demodulator is used to retrieve the signal containing the visual or
audio information. The broadcast signal can be either analog (signal
is varied continuously with respect to the information) or digital
(information is encoded as a set of discrete values).[36][75]
The broadcast media industry is at a critical turning point in its
development, with many countries moving from analog to digital
broadcasts. This move is made possible by the production of cheaper,
faster and more capable integrated circuits. The chief advantage of
digital broadcasts is that they prevent a number of complaints common
to traditional analog broadcasts. For television, this includes the
elimination of problems such as snowy pictures, ghosting and other
distortion. These occur because of the nature of analog transmission,
which means that perturbations due to noise will be evident in the
final output. Digital transmission overcomes this problem because
digital signals are reduced to discrete values upon reception and
hence small perturbations do not affect the final output. In a
simplified example, if a binary message 1011 was transmitted with
signal amplitudes [1.0 0.0 1.0 1.0] and received with signal
amplitudes [0.9 0.2 1.1 0.9] it would still decode to the binary
message 1011 — a perfect reproduction of what was sent. From this
example, a problem with digital transmissions can also be seen in that
if the noise is great enough it can significantly alter the decoded
message. Using forward error correction a receiver can correct a
handful of bit errors in the resulting message but too much noise will
lead to incomprehensible output and hence a breakdown of the
transmission.[76][77]
In digital television broadcasting, there are three competing
standards that are likely to be adopted worldwide. These are the ATSC,
DVB and
ISDB
ISDB standards; the adoption of these standards thus far is
presented in the captioned map. All three standards use
MPEG-2
MPEG-2 for
video compression. ATSC uses
Dolby Digital
Dolby Digital AC-3 for audio compression,
ISDB
ISDB uses
Advanced Audio Coding (
MPEG-2
MPEG-2 Part 7) and DVB has no
standard for audio compression but typically uses
MPEG-1
MPEG-1 Part 3 Layer
2.[78][79] The choice of modulation also varies between the schemes.
In digital audio broadcasting, standards are much more unified with
practically all countries choosing to adopt the Digital Audio
Broadcasting
Broadcasting standard (also known as the
Eureka 147
Eureka 147 standard). The
exception is the United States which has chosen to adopt HD Radio. HD
Radio, unlike Eureka 147, is based upon a transmission method known as
in-band on-channel transmission that allows digital information to
"piggyback" on normal AM or FM analog transmissions.[80]
However, despite the pending switch to digital, analog television
remains being transmitted in most countries. An exception is the
United States that ended analog television transmission (by all but
the very low-power TV stations) on 12 June 2009[81] after twice
delaying the switchover deadline. Kenya also ended analog television
transmission in December 2014 after multiple delays. For analog
television, there were three standards in use for broadcasting color
TV (see a map on adoption here). These are known as
PAL
PAL (German
designed),
NTSC
NTSC (American designed), and
SECAM
SECAM (French designed). For
analog radio, the switch to digital radio is made more difficult by
the higher cost of digital receivers.[82] The choice of modulation for
analog radio is typically between amplitude (AM) or frequency
modulation (FM). To achieve stereo playback, an amplitude modulated
subcarrier is used for stereo FM, and quadrature amplitude modulation
is used for stereo AM or C-QUAM.
Internet[edit]
The OSI reference model
The
Internet
Internet is a worldwide network of computers and computer networks
that communicate with each other using the
Internet
Internet Protocol (IP).[83]
Any computer on the
Internet
Internet has a unique
IP address
IP address that can be used
by other computers to route information to it. Hence, any computer on
the
Internet
Internet can send a message to any other computer using its IP
address. These messages carry with them the originating computer's IP
address allowing for two-way communication. The
Internet
Internet is thus an
exchange of messages between computers.[84]
It is estimated that 51% of the information flowing through two-way
telecommunications networks in the year 2000 were flowing through the
Internet
Internet (most of the rest (42%) through the landline telephone). By
the year 2007 the
Internet
Internet clearly dominated and captured 97% of all
the information in telecommunication networks (most of the rest (2%)
through mobile phones).[85] As of 2008[update], an estimated 21.9% of
the world population has access to the
Internet
Internet with the highest
access rates (measured as a percentage of the population) in North
America (73.6%), Oceania/Australia (59.5%) and Europe (48.1%).[86] In
terms of broadband access,
Iceland
Iceland (26.7%), South Korea (25.4%) and
the Netherlands (25.3%) led the world.[87]
The
Internet
Internet works in part because of protocols that govern how the
computers and routers communicate with each other. The nature of
computer network communication lends itself to a layered approach
where individual protocols in the protocol stack run more-or-less
independently of other protocols. This allows lower-level protocols to
be customized for the network situation while not changing the way
higher-level protocols operate. A practical example of why this is
important is because it allows an
Internet
Internet browser to run the same
code regardless of whether the computer it is running on is connected
to the
Internet
Internet through an
Ethernet
Ethernet or
Wi-Fi
Wi-Fi connection. Protocols are
often talked about in terms of their place in the OSI reference model
(pictured on the right), which emerged in 1983 as the first step in an
unsuccessful attempt to build a universally adopted networking
protocol suite.[88]
For the Internet, the physical medium and data link protocol can vary
several times as packets traverse the globe. This is because the
Internet
Internet places no constraints on what physical medium or data link
protocol is used. This leads to the adoption of media and protocols
that best suit the local network situation. In practice, most
intercontinental communication will use the Asynchronous Transfer Mode
(ATM) protocol (or a modern equivalent) on top of optic fiber. This is
because for most intercontinental communication the
Internet
Internet shares
the same infrastructure as the public switched telephone network.
At the network layer, things become standardized with the Internet
Protocol (IP) being adopted for logical addressing. For the World Wide
Web, these "IP addresses" are derived from the human readable form
using the
Domain Name System
Domain Name System (e.g. 72.14.207.99 is derived from
www.google.com). At the moment, the most widely used version of the
Internet
Internet Protocol is version four but a move to version six is
imminent.[89]
At the transport layer, most communication adopts either the
Transmission Control Protocol (TCP) or the User Datagram Protocol
(UDP). TCP is used when it is essential every message sent is received
by the other computer whereas UDP is used when it is merely desirable.
With TCP, packets are retransmitted if they are lost and placed in
order before they are presented to higher layers. With UDP, packets
are not ordered or retransmitted if lost. Both TCP and UDP packets
carry port numbers with them to specify what application or process
the packet should be handled by.[90] Because certain application-level
protocols use certain ports, network administrators can manipulate
traffic to suit particular requirements. Examples are to restrict
Internet
Internet access by blocking the traffic destined for a particular port
or to affect the performance of certain applications by assigning
priority.
Above the transport layer, there are certain protocols that are
sometimes used and loosely fit in the session and presentation layers,
most notably the
Secure Sockets Layer (SSL) and Transport Layer
Security (TLS) protocols. These protocols ensure that data transferred
between two parties remains completely confidential.[91] Finally, at
the application layer, are many of the protocols
Internet
Internet users would
be familiar with such as
HTTP
HTTP (web browsing),
POP3 (e-mail), FTP (file
transfer),
IRC
IRC (
Internet
Internet chat), BitTorrent (file sharing) and XMPP
(instant messaging).
Voice over
Internet
Internet Protocol (VoIP) allows data packets to be used for
synchronous voice communications. The data packets are marked as voice
type packets and can be prioritized by the network administrators so
that the real-time, synchronous conversation is less subject to
contention with other types of data traffic which can be delayed (i.e.
file transfer or email) or buffered in advance (i.e. audio and video)
without detriment. That prioritization is fine when the network has
sufficient capacity for all the
VoIP
VoIP calls taking place at the same
time and the network is enabled for prioritization i.e. a private
corporate style network, but the
Internet
Internet is not generally managed in
this way and so there can be a big difference in the quality of VoIP
calls over a private network and over the public Internet.[92]
Local area networks and wide area networks[edit]
Despite the growth of the Internet, the characteristics of local area
networks (LANs)--computer networks that do not extend beyond a few
kilometers—remain distinct. This is because networks on this scale
do not require all the features associated with larger networks and
are often more cost-effective and efficient without them. When they
are not connected with the Internet, they also have the advantages of
privacy and security. However, purposefully lacking a direct
connection to the
Internet
Internet does not provide assured protection from
hackers, military forces, or economic powers. These threats exist if
there are any methods for connecting remotely to the LAN.
Wide area networks (WANs) are private computer networks that may
extend for thousands of kilometers. Once again, some of their
advantages include privacy and security. Prime users of private LANs
and WANs include armed forces and intelligence agencies that must keep
their information secure and secret.
In the mid-1980s, several sets of communication protocols emerged to
fill the gaps between the data-link layer and the application layer of
the OSI reference model. These included Appletalk, IPX, and NetBIOS
with the dominant protocol set during the early 1990s being
IPX due to
its popularity with
MS-DOS
MS-DOS users.
TCP/IP
TCP/IP existed at this point, but it
was typically only used by large government and research
facilities.[93]
As the
Internet
Internet grew in popularity and its traffic was required to be
routed into private networks, the
TCP/IP
TCP/IP protocols replaced existing
local area network technologies. Additional technologies, such as
DHCP, allowed TCP/IP-based computers to self-configure in the network.
Such functions also existed in the AppleTalk/ IPX/
NetBIOS protocol
sets.[94]
Whereas
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM) or Multiprotocol Label
Switching (MPLS) are typical data-link protocols for larger networks
such as WANs;
Ethernet
Ethernet and Token Ring are typical data-link protocols
for LANs. These protocols differ from the former protocols in that
they are simpler, e.g., they omit features such as quality of service
guarantees, and offer collision prevention. Both of these differences
allow for more economical systems.[95]
Despite the modest popularity of IBM Token Ring in the 1980s and
1990s, virtually all LANs now use either wired or wireless Ethernet
facilities. At the physical layer, most wired
Ethernet
Ethernet implementations
use copper twisted-pair cables (including the common 10BASE-T
networks). However, some early implementations used heavier coaxial
cables and some recent implementations (especially high-speed ones)
use optical fibers.[96] When optic fibers are used, the distinction
must be made between multimode fibers and single-mode fibers.
Multimode fibers can be thought of as thicker optical fibers that are
cheaper to manufacture devices for, but that suffers from less usable
bandwidth and worse attenuation – implying poorer long-distance
performance.[97]
Transmission capacity[edit]
The effective capacity to exchange information worldwide through
two-way telecommunication networks grew from 281 petabytes of
(optimally compressed) information in 1986, to 471 petabytes in 1993,
to 2.2 (optimally compressed) exabytes in 2000, and to 65 (optimally
compressed) exabytes in 2007.[85] This is the informational equivalent
of two newspaper pages per person per day in 1986, and six entire
newspapers per person per day by 2007.[98] Given this growth,
telecommunications play an increasingly important role in the world
economy and the global telecommunications industry was about a $4.7
trillion sector in 2012.[43][99] The service revenue of the global
telecommunications industry was estimated to be $1.5 trillion in 2010,
corresponding to 2.4% of the world’s gross domestic product
(GDP).[43]
See also[edit]
Telecommunications
Telecommunications portal
Active networks
Busy override
Digital Revolution
Dual-tone multi-frequency signaling
Information
Information Age
International Teletraffic Congress
List of telecommunications encryption terms
Nanonetwork
New media
Outline of telecommunication
Push-button telephone
Telecommunications
Telecommunications Industry Association
Telecoms resilience
Wavelength-division multiplexing
Wired communication
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External links[edit]
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Telecommunications
Telecommunications at the Wayback Machine
(archived 13 April 2004) (Ericsson removed the book from their site in
September 2005)
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