Telecommunications - Wikipedia

Telecommunications - Wikipedia
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(Redirected from
Telecommunication
Transmission of information electromagnetically
"Telecommunication" redirects here. For the A Flock of Seagulls song, see
Telecommunication (song)
Earth station
at the satellite communication facility
Raisting Earth Station
in
Raisting
Bavaria
Germany
Telecommunication
, often used in its plural form or abbreviated as
telecom
, is the transmission of
information
over a distance using
electrical
or
electronic
means, typically through cables,
radio waves
, or other communication technologies. These means of transmission may be divided into
communication channels
for
multiplexing
, allowing for a single medium to transmit several concurrent
communication sessions
. Long-distance technologies invented during the 19th, 20th and 21st centuries generally use electric power, and include the
electrical telegraph
telephone
television
, and
radio
Early
telecommunication networks
used metal wires as the medium for transmitting signals. These networks were used for
telegraphy
and telephony for many decades. In the first decade of the 20th century, a revolution in
wireless communication
began with breakthroughs including those made in
radio communications
by
Guglielmo Marconi
, who won the 1909
Nobel Prize in Physics
. Other early pioneers in electrical and electronic telecommunications include co-inventors of the telegraph
Charles Wheatstone
and
Samuel Morse
, numerous
inventors and developers of the telephone
including
Antonio Meucci
Philipp Reis
Elisha Gray
and
Alexander Graham Bell
, inventors of radio
Edwin Armstrong
and
Lee de Forest
, as well as inventors of television like
Vladimir K. Zworykin
John Logie Baird
and
Philo Farnsworth
Since the 1960s, the proliferation of digital technologies has meant that
voice
communications have gradually been supplemented by data. The physical limitations of metallic media prompted the development of optical fibre.
The
Internet
, a technology independent of any given medium, has provided global access to services for individual users and further reduced location and time limitations on communications.
Definition
edit
At the 1932
Plenipotentiary Telegraph Conference
and the International Radiotelegraph Conference in Madrid, the two organizations merged to form the
International Telecommunication Union
(ITU).
They defined
telecommunication
as "any telegraphic or telephonic communication of signs, signals, writing, facsimiles and sounds of any kind, by wire, wireless or other systems or processes of electric signaling or visual signaling (semaphores)."
The definition was later reconfirmed, according to Article 1.3 of the
ITU Radio Regulations
, which defined it as "Any transmission, emission or reception of signs, signals, writings, images and sounds or intelligence of any nature by
wire
, radio, optical, or other electromagnetic systems".
As such, slow communications technologies like
postal mail
and
pneumatic tubes
are excluded from the telecommunication's definition.
The term
telecommunication
was coined in 1904 by the French engineer and novelist
Édouard Estaunié
, who defined it as "remote transmission of thought through electricity".
Telecommunication is a compound noun formed from the Greek prefix
tele-
(τῆλε), meaning
distant
far off
, or
afar
and the Latin verb
communicare
, meaning
to share
10
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 communicationem (nominative communication), 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.
11
History
edit
Further information:
History of telecommunication
Many
transmission media
have been used for long-distance communication throughout history, from
smoke signals
beacons
semaphore telegraphs
signal flags
, and optical
heliographs
to
wires
and empty space made to carry
electromagnetic signals
Before the electrical and electronic era
edit
A replica of one of
Chappe's
semaphore towers
Long-distance communication was used long before the discovery of electricity and electromagnetism enabled the invention of telecommunications. A few of the many ingenious methods for communicating over distances prior to that are described here.
Homing pigeons
have been used throughout history by different cultures.
Pigeon post
had
Persian
roots and was later used by the Romans to aid their military.
Frontinus
claimed
Julius Caesar
used pigeons as messengers in his conquest of
Gaul
12
The
Greeks
also conveyed the names of the victors at the
Olympic Games
to various cities using homing pigeons.
13
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
and
Brussels
, a service that operated for a year until the gap in the telegraph link was closed.
14
In the Middle Ages, chains of
beacons
were commonly used on hilltops as a means of relaying a signal. 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
to
London
15
In 1792,
Claude Chappe
, a French engineer, built the first fixed visual
telegraphy
system (or
semaphore line
) between
Lille
and Paris.
16
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.
17
Telegraph and telephone
edit
Main articles:
Telegraphy
and
Telephony
On July 25, 1837, the first commercial
electrical telegraph
was demonstrated by English inventor Sir
William Fothergill Cooke
and English scientist Sir
Charles Wheatstone
18
19
Both inventors viewed their device as "an improvement to the [existing] electromagnetic telegraph" and not as a new device.
20
Samuel Morse
independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on September 2, 1837.
His code
was an important advance over Wheatstone's signaling method. The first
transatlantic telegraph cable
was successfully completed on July 27, 1866, allowing transatlantic telecommunication for the first time.
21
After early attempts to develop a
talking telegraph
by
Antonio Meucci
and a
telefon
by
Johann Philipp Reis
, a patent for the conventional telephone was filed by
Alexander Bell
in February 1876 (just a few hours before
Elisha Gray
filed a
patent caveat
for a similar device).
22
23
The first commercial telephone services were set up by the Bell Telephone Company in 1878 and 1879 on both sides of the Atlantic in the cities of
New Haven
and London.
24
25
Radio and television
edit
Main articles:
Radio
and
Television
In 1894, Italian inventor
Guglielmo Marconi
began developing wireless communication using the then-newly discovered phenomenon of
radio waves
, demonstrating, by 1901, that they could be transmitted across the Atlantic Ocean.
26
This was the start of
wireless telegraphy
by radio. On 17 December 1902, a transmission from the
Marconi station in Glace Bay, Nova Scotia, Canada
, became the world's first radio message to cross the Atlantic from North America. In 1904, a commercial service was established to transmit nightly news summaries to subscribing ships, which incorporated them into their onboard newspapers.
27
World War I
accelerated the development of radio for
military communications
. After the war, commercial radio
AM broadcasting
began in the 1920s and became an important mass medium for entertainment and news.
World War II
again accelerated the development of radio for the wartime purposes of aircraft and land communication, radio navigation, and radar.
28
Development of stereo
FM broadcasting
of radio began in the 1930s in the United States and the 1940s in the United Kingdom,
29
displacing AM as the dominant commercial standard in the 1970s.
30
On March 25, 1925,
John Logie Baird
demonstrated the transmission of moving pictures at the London department store
Selfridges
. Baird's device relied upon the
Nipkow disk
by
Paul Nipkow
and thus became known as the
mechanical television
. It formed the basis of experimental broadcasts done by the
British Broadcasting Corporation
beginning on 30 September 1929.
31
Vacuum tubes
edit
Main article:
Vacuum tube
Vacuum tubes use
thermionic emission
of electrons from a
heated cathode
for a number of fundamental electronic functions such as signal
amplification
and current
rectification
The simplest vacuum tube, the
diode
invented in 1904 by
John Ambrose Fleming
, contains only a heated electron-emitting cathode and an anode. Electrons can only flow in one direction through the device—from the cathode to the anode. Adding one or more
control grids
within the tube enables the current between the cathode and anode to be controlled by the voltage on the grid or grids.
32
These devices became a key component of electronic circuits for the first half of the 20th century and were crucial to the development of radio, television, radar,
sound recording and reproduction
, long-distance telephone networks, and analogue and early digital
computers
. While some applications had used earlier technologies such as the
spark gap transmitter
for radio or
mechanical computers
for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, leading to the creation of
electronics
33
For most of the 20th century, televisions depended on a kind of vacuum tube — the
cathode ray tube
— invented by
Karl Ferdinand Braun
. The first version of such a television to show promise was produced by
Philo Farnsworth
and demonstrated to his family on 7 September 1927.
34
After World War II, interrupted experiments resumed and television became an important home entertainment broadcast medium.
Also in the 1940s, the invention of
semiconductor devices
made it possible to produce
solid-state
devices, which are smaller, cheaper, and more efficient, reliable, and durable than vacuum tubes. Starting in the mid-1960s, vacuum tubes were replaced with the
transistor
. Vacuum tubes still have some applications for certain high-frequency amplifiers.
Computer networks and the Internet
edit
Main articles:
Computer network
and
Internet
On 11 September 1940,
George Stibitz
transmitted problems for his Complex Number Calculator in New York using a
teletype
and received the computed results back at
Dartmouth College
in
New Hampshire
35
This configuration of a centralized computer (
mainframe
) with remote
dumb terminals
remained popular well into the 1970s. In the 1960s,
Paul Baran
and, independently,
Donald Davies
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
36
ARPANET eventually merged with other networks to form the Internet. While Internet development was a focus of the
Internet Engineering Task Force
(IETF) who published a series of
Request for Comments
documents, other networking advancements occurred in
industrial laboratories
, such as the
local area network
(LAN) developments of
Ethernet
(1983),
Token Ring
(1984)
citation needed
and
Star network
topology.
Growth of transmission capacity
edit
The effective capacity to exchange information worldwide through two-way telecommunication networks grew from 281
petabytes
(PB) of optimally compressed information in 1986 to 471 PB in 1993 to 2.2
exabytes
(EB) in 2000 to 65 EB in 2007.
37
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.
38
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.
39
40
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).
39
Technical 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 technologies may primarily be divided into
wired
and wireless methods. Overall, a basic telecommunication system consists of three main parts that are always present in some form or another:
transmitter
that takes information and converts it to a
signal
transmission medium
, also called the
physical channel,
that carries the signal (e.g., the
"free space channel"
receiver
that takes the signal from the channel and converts it back into usable information for the recipient
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, where it is converted from electricity to sound.
Telecommunication systems are occasionally
"duplex"
(two-way systems) with a single box of electronics working as both the transmitter and a receiver, or a
transceiver
(e.g., a
mobile phone
).
41
The transmission electronics and the receiver electronics within a transceiver are quite independent of one another. This can be 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 measured in 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 to avoid interference.
Telecommunication over fixed lines is called
point-to-point communication
because it occurs between a transmitter and a receiver. Telecommunication through radio broadcasts is called
broadcast communication
because it occurs between a powerful transmitter and numerous low-power but sensitive radio receivers.
41
Telecommunications in which multiple transmitters and multiple receivers have been designed to cooperate and share the same physical channel are called
multiplex systems
. The sharing of physical channels using multiplexing often results in significant cost reduction. Multiplexed systems are laid out in telecommunication networks and multiplexed signals are switched at nodes to reach the correct destination terminal receiver.
Analogue versus digital communications
edit
Communications can be encoded as
analogue
or
digital signals
, which may in turn be carried by
analogue
or
digital communication
systems. Analogue signals vary continuously with respect to the information, while digital signals encode information as a set of discrete values (e.g., a set of ones and zeroes).
42
During propagation and reception, information contained in analogue signals is degraded by undesirable
noise
. Commonly, the noise in a communication system can be expressed as adding or subtracting from the desirable signal via a
random process
. This form of noise is called
additive noise
, with the understanding that the noise can be negative or positive at different instances.
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 analogue signals. However, digital systems
fail catastrophically
when noise exceeds the system's ability to autocorrect. On the other hand, analogue systems fail gracefully: as noise increases, the signal becomes progressively more degraded but still usable. Also, digital transmission of
continuous data
unavoidably adds
quantization noise
to the output. This can be reduced, but not eliminated, only at the expense of increasing the channel bandwidth requirement.
Communication channels
edit
Main article:
Communication channel
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 fibres
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 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.
43
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 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 neighbourhood of 94.5
MHz
(megahertz) while another radio station can simultaneously broadcast radio waves at frequencies in the neighbourhood of 96.1 MHz. Each radio station would transmit radio waves over a frequency
bandwidth
of about 180
kHz
(kilohertz), centred 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 fibre communication. Some radio communication systems use TDM within an allocated FDM channel. Hence, these systems use a hybrid of TDM and FDM.
Modulation
edit
Main article:
Modulation
The shaping of a signal to convey information is known as
modulation
. Modulation can be used to represent a digital message as an analogue 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.
44
45
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 can also be used to transmit the information of low-frequency analogue signals at higher frequencies. This is helpful because low-frequency analogue signals cannot be effectively transmitted over free space. Hence, the information from a low-frequency analogue 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 carrier wave using frequency modulation (the voice would then be received on a radio as the channel 96 FM).
46
In addition, modulation has the advantage that it may use frequency division multiplexing (FDM).
Telecommunication networks
edit
Main article:
Telecommunications network
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 analogue communications network consists of one or more
switches
that establish a connection between two or more users. For both types of networks,
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.
47
Another advantage of digital systems over analogue 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.
Societal impact
edit
Telecommunication has a significant social, cultural and economic impact on modern society. In 2008, estimates placed the
telecommunication industry
's revenue at US$4.7 trillion or just under three per cent of the
gross world product
(official exchange rate).
39
Several of the following sections discuss the impact of telecommunication on society.
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
but, according to academic Edward Lenert, even the conventional retailer
Walmart
has benefited from better telecommunication infrastructure compared to its competitors.
48
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
Narsingdi 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.
49
Macroeconomics
edit
On the
macroeconomic
scale, Lars-Hendrik Röller and
Leonard Waverman
suggested a causal link between good telecommunication infrastructure and economic growth.
50
51
Few dispute the existence of a correlation although some argue it is wrong to view the relationship as causal.
52
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
(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 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.
53
Using this measure, Sweden, Denmark and
Iceland
received the highest ranking while the African countries
Niger
Burkina Faso
and
Mali
received the lowest.
54
Social impact
edit
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.
55
Since then the role that telecommunications has played in social relations has become increasingly important. In recent years,
when?
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 an important role in everything from organising social engagements to
courtship
56
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.
57
Entertainment, news, and advertising
edit
News source preference of Americans in 2006.
58
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 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 and American Life Project in the United States the majority specified television or radio over newspapers.
Telecommunication has had an equally significant impact on advertising.
TNS Media Intelligence
reported that in 2007, 58% of advertising expenditure in the United States was spent on media that depend upon telecommunication.
59
Advertising expenditures in US in 2007
citation needed
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
Regulation
edit
See also:
List of telecommunications regulatory bodies
Many countries have enacted legislation which conforms to the International Telecommunication Regulations established by the International Telecommunication Union (ITU), which is the "leading UN agency for information and communication technology issues".
60
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 Regulations
adopted in Atlantic City, all frequencies referenced in the
International Frequency Registration Board
, examined by the board and registered on the
International Frequency List
"shall have the right to international protection from harmful interference".
61
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.
62
The onset of
World War II
brought on the first explosion of international broadcasting propaganda.
62
Countries, their governments, insurgents, terrorists, and militiamen have all used telecommunication and broadcasting techniques to promote propaganda.
62
63
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.
62
Modern political debates in telecommunication include the reclassification of
broadband Internet service
as a telecommunications service (also called
net neutrality
),
64
65
regulation of
phone spam
66
67
and expanding affordable broadband access.
68
Modern media
edit
Worldwide equipment sales
edit
According to data collected by Gartner
69
70
and Ars Technica
71
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
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 fibre
provides cheaper bandwidth for long-distance communication.
In a telephone network, the caller is connected to the person to whom they wish to talk 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.
As of 2015
[update]
, the
landline
telephones in most residential homes are analogue—that is, the speaker's voice directly determines the signal's voltage.
72
Although short-distance calls may be handled from end-to-end as analogue 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 and can be perfectly reproduced in long-distance communication (as opposed to analogue signals that are inevitably impacted by noise).
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).
73
In terms of new subscriptions over the five years from 1999, Africa has outpaced other markets with 58.2% growth.
74
Increasingly these phones are being serviced by systems where the voice content is transmitted digitally such as
GSM
or
W-CDMA
with many markets choosing to deprecate analog systems such as
AMPS
75
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 fibres. The benefit of communicating with optical fibres 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 optical fibre cables are able to carry 25 times as many telephone calls as TAT-8.
76
This increase in data capacity is due to several factors: First, optical 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.
77
Lastly, improvements in multiplexing have led to an exponential growth in the data capacity of a single fibre.
78
79
Assisting communication across many modern optical fibre networks is a protocol known as
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.
80
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.
81
82
Radio and television
edit
Main articles:
Radio
Television
, and
Broadcasting
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 analogue (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete values).
41
83
The
broadcast media industry
is at a critical turning point in its development, with many countries moving from analogue 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 analogue broadcasts. For television, this includes the elimination of problems such as
snowy pictures
ghosting
and other distortions. These occur because of the nature of analogue 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.
84
85
In digital television broadcasting, there are three competing standards that are likely to be adopted worldwide. These are the
ATSC
DVB
and
ISDB
standards; the adoption of these standards thus far is presented in the captioned map. All three standards use
MPEG-2
for video compression. ATSC uses
Dolby Digital
AC-3 for audio compression, ISDB uses
Advanced Audio Coding
(MPEG-2 Part 7) and DVB has no standard for audio compression but typically uses
MPEG-1
Part 3 Layer 2.
86
87
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
standard (also known as the
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.
88
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
89
after twice delaying the switchover deadline. Kenya also ended analog television transmission in December 2014 after multiple delays. For analogue television, there were three standards in use for broadcasting colour TV (see a map on adoption
here
). These are known as
PAL
(German designed),
NTSC
(American designed), and
SECAM
(French designed). For analogue radio, the switch to digital radio is made more difficult by the higher cost of digital receivers.
90
The choice of modulation for analogue 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 is a worldwide network of computers and computer networks that communicate with each other using the
Internet Protocol
(IP).
91
Any computer on the Internet has a unique
IP address
that can be used by other computers to route information to it. Hence, any computer on the 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 is thus an exchange of messages between computers.
92
It is estimated that 51% of the information flowing through two-way telecommunications networks in the year 2000 was flowing through the Internet (most of the rest (42%) through the
landline telephone
). By 2007 the Internet clearly dominated and captured 97% of all the information in telecommunication networks (most of the rest (2%) through
mobile phones
).
37
As of 2008
[update]
, an estimated 21.9% of the world population has access to the 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%).
93
In terms of
broadband access
, Iceland (26.7%), South Korea (25.4%) and the Netherlands (25.3%) led the world.
94
The 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 that it allows a
web browser
to run the same code regardless of whether the computer it is running on is connected to the Internet through an Ethernet or
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.
95
For the Internet, the physical medium and data link protocol can vary several times as packets traverse the globe. This is because the 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 optical fibre. This is because for most intercontinental communication, the 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
(e.g., 72.14.207.99 is derived from
Google
). At the moment, the most widely used version of the Internet Protocol is version four but a move to version six is imminent.
96
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 that 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 nor 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.
97
Because certain application-level protocols use
certain ports
, network administrators can manipulate traffic to suit particular requirements. Examples are to restrict 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.
98
Finally, at the application layer, are many of the protocols Internet users would be familiar with such as
HTTP
(web browsing),
POP3
(e-mail),
FTP
(file transfer),
IRC
(Internet chat),
BitTorrent
(file sharing) and
XMPP
(instant messaging).
Voice over 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 calls taking place at the same time and the network is enabled for prioritization, i.e., a private corporate-style network, but the 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.
99
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 kilometres—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 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 kilometres. 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
users.
TCP/IP
existed at this point, but it was typically only used by large government and research facilities.
100
As the Internet grew in popularity and its traffic was required to be routed into private networks, the 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.
101
Whereas Asynchronous Transfer Mode (ATM) or Multiprotocol Label Switching (MPLS) are typical data-link protocols for larger networks such as WANs; 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
medium access control
. Both of these differences allow for more economical systems.
102
Despite the modest popularity of 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 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 fibres.
103
When optic fibres are used, the distinction must be made between multimode fibres and single-mode fibres.
Multimode fibres
can be thought of as thicker optical fibres that are cheaper to manufacture devices for, but that suffer from less usable bandwidth and worse attenuation—implying poorer long-distance performance.
104
See also
edit
Telephones portal
Telecommunications portal
Amateur radio portal
Active networking
Cell site
Control communications
Digital Revolution
Information Age
Institute of Telecommunications Professionals
International Teletraffic Congress
List of telecommunications encryption terms
Military communication
Nanonetwork
New media
Outline of telecommunication
Telecommunications engineering
Telecommunications Industry Association
Telecoms resilience
Telemetry
Underwater acoustic communication
Wavelength-division multiplexing
Wired communication
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Martin, Michael (2000). "Understanding the Network".
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(PDF)
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Bibliography
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Goggin, Gerard
Global Mobile Media
(New York: Routledge, 2011), p. 176.
ISBN
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ISBN
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Wheen, Andrew.
Dot-Dash to Dot.Com: How Modern Telecommunications Evolved from the Telegraph to the Internet
(Springer, 2011).
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