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Telecommunication is the transmission of information by various types of technologies over
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...
, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems (such as
postal mail The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...
) are excluded from the field. The
transmission media A transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. Signals are typically imposed on a wave of some kind suitable for the chosen medium. For example, data can modulate ...
in telecommunication have evolved through numerous stages of technology, from
beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
s and other visual signals (such as smoke signals, semaphore telegraphs, signal flags, and optical heliographs), to electrical cable and electromagnetic radiation, including light. Such transmission paths are often divided into
communication channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...
s, which afford the advantages of
multiplexing In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
multiple concurrent
communication session In computer science and networking in particular, a session is a time-delimited two-way link, a practical (relatively high) layer in the tcp/ip protocol enabling interactive expression and information exchange between two or more communication d ...
s. ''Telecommunication'' is often used in its plural form. Other examples of pre-modern long-distance communication included audio messages, such as coded drumbeats, lung-blown horns, and loud
whistle A whistle is an instrument which produces sound from a stream of gas, most commonly air. It may be mouth-operated, or powered by air pressure, steam, or other means. Whistles vary in size from a small slide whistle or nose flute type to a larg ...
s. 20th- and 21st-century technologies for long-distance communication usually involve electrical and electromagnetic technologies, such as
telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
, telephone, television and
teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Initi ...
, networks, radio,
microwave transmission Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300MHz to 300GHz(1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signals are normally limi ...
,
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means t ...
, and
communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. ...
s. A revolution in
wireless communication Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...
began in the first decade of the 20th century with the pioneering developments in radio communications by
Guglielmo Marconi Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system. This led to Marconi bei ...
, who won the
Nobel Prize in Physics ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
in 1909, and other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included
Charles Wheatstone Sir Charles Wheatstone FRS FRSE DCL LLD (6 February 1802 – 19 October 1875), was an English scientist and inventor of many scientific breakthroughs of the Victorian era, including the English concertina, the stereoscope (a device for dis ...
and Samuel Morse (inventors of the telegraph),
Antonio Meucci Antonio Santi Giuseppe Meucci ( , ; 13 April 1808 – 18 October 1889) was an Italian inventor and an associate of Giuseppe Garibaldi, a major political figure in the history of Italy.
and
Alexander Graham Bell Alexander Graham Bell (, born Alexander Bell; March 3, 1847 – August 2, 1922) was a Scottish-born inventor, scientist and engineer who is credited with patenting the first practical telephone. He also co-founded the American Telephone and T ...
(some of the inventors and developers of the telephone, see
Invention of the telephone The invention of the telephone was the culmination of work done by more than one individual, and led to an array of lawsuits relating to the patent claims of several individuals and numerous companies. Early development The concept of the ...
),
Edwin Armstrong Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American electrical engineer and inventor, who developed FM (frequency modulation) radio and the superheterodyne receiver system. He held 42 patents and received numerous awar ...
and
Lee de Forest Lee de Forest (August 26, 1873 – June 30, 1961) was an American inventor and a fundamentally important early pioneer in electronics. He invented the first electronic device for controlling current flow; the three-element "Audion" triode v ...
(inventors of radio), as well as Vladimir K. Zworykin,
John Logie Baird John Logie Baird FRSE (; 13 August 188814 June 1946) was a Scottish inventor, electrical engineer, and innovator who demonstrated the world's first live working television system on 26 January 1926. He went on to invent the first publicly demo ...
and Philo Farnsworth (some of the inventors of television). According to ''Article 1.3'' of the Radio Regulations (RR), telecommunication is defined as ''« Any
transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission ** ...
, emission or reception of signs, signals, writings, images and sounds or intelligence of any nature by
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...
, radio, optical, or other electromagnetic systems''.» This definition is identical to those contained in the Annex to the
Constitution and Convention of the International Telecommunication Union The International Telecommunication Union (ITU) Constitution and Convention of the International Telecommunication Union (short: ITU Constitution and Convention or ITU CS CV) is an international treaty, signed and ratified by almost all countrie ...
(Geneva, 1992). The early telecommunication networks were created with copper wires as the physical medium for signal transmission. For many years, these networks were used for basic phone services, namely voice and telegrams. Since the mid-1990s, as the internet has grown in popularity, voice has been gradually supplanted by data. This soon demonstrated the limitations of copper in data transmission, prompting the development of optics.


Etymology

The word ''telecommunication'' is a compound of the Greek prefix ''tele-'' (τῆλε), meaning ''distant'', ''far off'', or ''afar'', and the Latin ''communicare'', meaning ''to share''. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist
Édouard Estaunié Édouard Estaunié (4 February 1862 in Dijon – 2 April 1942 in Paris) was a French novelist. Estaunié trained as a scientist and engineer, working at the Post and Telepgraph service and training further in Holland, before turning to the novel i ...
. ''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 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."


History


Beacons and pigeons

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 Sextus Julius Frontinus (c. 40 – 103 AD) was a prominent Roman civil engineer, author, soldier and senator of the late 1st century AD. He was a successful general under Domitian, commanding forces in Roman Britain, and on the Rhine and Danube ...
claimed Julius Caesar used pigeons as messengers in his conquest of Gaul. The Greeks also conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Java and Sumatra. And in 1849,
Paul Julius Reuter Paul Julius Reuter (born Israel Beer Josaphat; 21 July 1816 – 25 February 1899), later ennobled as Freiherr von Reuter (Baron von Reuter), was a German-born British entrepreneur who was a pioneer of telegraphy and news reporting.Aachen Aachen ( ; ; Aachen dialect: ''Oche'' ; French and traditional English: Aix-la-Chapelle; or ''Aquisgranum''; nl, Aken ; Polish: Akwizgran) is, with around 249,000 inhabitants, the 13th-largest city in North Rhine-Westphalia, and the 28th- ...
and
Brussels Brussels (french: Bruxelles or ; nl, Brussel ), officially the Brussels-Capital Region (All text and all but one graphic show the English name as Brussels-Capital Region.) (french: link=no, Région de Bruxelles-Capitale; nl, link=no, Bruss ...
, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of
beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
s 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. In 1792,
Claude Chappe Claude Chappe (; 25 December 1763 – 23 January 1805) was a French inventor who in 1792 demonstrated a practical semaphore system that eventually spanned all of France. His system consisted of a series of towers, each within line of sight o ...
, a French engineer, built the first fixed visual telegraphy system (or semaphore line) between
Lille Lille ( , ; nl, Rijsel ; pcd, Lile; vls, Rysel) is a city in the northern part of France, in French Flanders. On the river Deûle, near France's border with Belgium, it is the capital of the Hauts-de-France region, the prefecture of the No ...
and Paris. 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.


Telegraph and telephone

On July 25, 1837, the first commercial electrical telegraph was demonstrated by English inventor Sir
William Fothergill Cooke Sir William Fothergill Cooke (4 May 1806 – 25 June 1879) was an English inventor. He was, with Charles Wheatstone, the co-inventor of the Cooke-Wheatstone electrical telegraph, which was patented in May 1837. Together with John Ricardo he fo ...
and English scientist Sir
Charles Wheatstone Sir Charles Wheatstone FRS FRSE DCL LLD (6 February 1802 – 19 October 1875), was an English scientist and inventor of many scientific breakthroughs of the Victorian era, including the English concertina, the stereoscope (a device for dis ...
. Both inventors viewed their device as "an improvement to the xistingelectromagnetic telegraph" and not as a new device. 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. The conventional telephone was patented by Alexander Bell in 1876.
Elisha Gray Elisha Gray (August 2, 1835 – January 21, 1901) was an American electrical engineer who co-founded the Western Electric Manufacturing Company. Gray is best known for his development of a telephone prototype in 1876 in Highland Park, Illinois ...
also filed a caveat for it in 1876. Gray abandoned his caveat and because he did not contest Bell's priority, the examiner approved Bell's patent on March 3, 1876. Gray had filed his caveat for the variable resistance telephone, but Bell was the first to document the idea and test it in a telephone. 8
Antonio Meucci Antonio Santi Giuseppe Meucci ( , ; 13 April 1808 – 18 October 1889) was an Italian inventor and an associate of Giuseppe Garibaldi, a major political figure in the history of Italy.
invented a device that allowed the electrical transmission of voice over a line nearly 30 years before in 1849, but his device was of little practical value because it relied on the electrophonic effect requiring users to place the receiver in their mouths to "hear." 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.


Radio and television

In 1894, Italian inventor
Guglielmo Marconi Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system. This led to Marconi bei ...
began developing a wireless communication using the then-newly discovered phenomenon of
radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (shor ...
s, showing by 1901 that they could be transmitted across the Atlantic Ocean. This was the start of wireless telegraphy by radio. On 17 December 1902, a transmission from the Marconi station in
Glace Bay Glace Bay (Scottish Gaelic: ''Glasbaidh'') is a community in the eastern part of the Cape Breton Regional Municipality in Nova Scotia, Canada. It forms part of the general area referred to as Industrial Cape Breton. Formerly an incorporated t ...
, 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. World War I accelerated the development of radio for
military communications Military communications or military signals involve all aspects of communications, or conveyance of information, by armed forces. Military communications span from pre-history to the present. The earliest military communications were delivered b ...
. After the war, commercial radio
AM broadcasting AM broadcasting is radio broadcasting using amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave (also known as "AM band") transmi ...
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. Development of stereo FM broadcasting of radio began in the 1930s in the United States and the 1970s in the United Kingdom, displacing AM as the dominant commercial standard. On March 25, 1925,
John Logie Baird John Logie Baird FRSE (; 13 August 188814 June 1946) was a Scottish inventor, electrical engineer, and innovator who demonstrated the world's first live working television system on 26 January 1926. He went on to invent the first publicly demo ...
demonstrated the transmission of moving pictures at the London department store Selfridges. Baird's device relied upon the Nipkow disk and thus became known as the
mechanical television Mechanical television or mechanical scan television is a television system that relies on a mechanical scanning device, such as a rotating disk with holes in it or a rotating mirror drum, to scan the scene and generate the video signal, and a si ...
. It formed the basis of experimental broadcasts done by the
British Broadcasting Corporation #REDIRECT BBC Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
beginning on 30 September 1929. However, for most of the 20th century, televisions depended on the
cathode ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictu ...
invented by Karl 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. After World War II, interrupted experiments resumed and television became an important home entertainment broadcast medium.


Thermionic valves

The type of device known as a '' thermionic tube'' or ''thermionic valve'' uses 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 Sir John Ambrose Fleming FRS (29 November 1849 – 18 April 1945) was an English electrical engineer and physicist who invented the first thermionic valve or vacuum tube, designed the radio transmitter with which the first transatlantic radi ...
, 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 grid The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode. The control grid usually consist ...
s within the tube enables the current between the cathode and anode to be controlled by the voltage on the grid or grids. 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 A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...
. 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. In the 1940s, the invention of
semiconductor devices A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity l ...
made it possible to produce
solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their ...
devices, which are smaller, cheaper, and more efficient, reliable, and durable than thermionic tubes. Starting in the mid-1960s, thermionic tubes were replaced with the transistor. Thermionic tubes still have some applications for certain high-frequency amplifiers.


Computer networks and the 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. This configuration of a centralized computer (
mainframe A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
) with remote dumb terminals remained popular well into the 1970s. 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 mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
. A four-
node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines, ...
network emerged on 5 December 1969, constituting the beginnings of the
ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical foun ...
, which by 1981 had grown to 213 nodes. 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) and
Token Ring Token Ring network IBM hermaphroditic connector with locking clip. Screen contacts are prominently visible, gold-plated signal contacts less so. Token Ring is a computer networking technology used to build local area networks. It was introduc ...
(1984).


Growth of transmission capacity

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. 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. 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.Introduction to the Telecommunications Industry
, Internet Engineering Task Force, June 2012.
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).


Technical concepts

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

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: * A transmitter that takes information and converts it to a signal * A transmission medium, also called the ''physical channel,'' that carries the signal (e.g. the "free space channel") * A 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 An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspea ...
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 In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. T ...
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). 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. 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 through to the correct destination terminal receiver.


Analog versus digital communications

Communications signals can be sent by
analog signal An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage varies c ...
s or
digital signals A digital signal is a signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog signal, which represents continuous values; at ...
via analog communication systems or digital communication systems. Analog 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). During propagation and reception, information contained in analog signals is degraded by undesirable physical noise. Commonly, the noise in a communication system can be expressed as adding or subtracting from the desirable signal in a random way. 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 analog signals. However, digital systems fail catastrophically when noise exceeds the system's ability to autocorrect. On the other hand, analog systems fail gracefully: as noise increases, the signal becomes progressively more degraded but still usable. Also, digital transmission of
continuous data In mathematics and statistics, a quantitative variable may be continuous or discrete if they are typically obtained by ''measuring'' or ''counting'', respectively. If it can take on two particular real values such that it can also take on all ...
unavoidably adds quantization noise to the output. This can be reduced, but not entirely eliminated, only at the expense of increasing the channel bandwidth requirement.


Communication channels

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 An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
for sound communications, glass
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means t ...
s for some kinds of optical communications,
coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner Electrical conductor, conductor surrounded by a concentric conducting Electromagnetic shielding, shield, with the two separated by a dielectric (Insulato ...
s 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 wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (shor ...
s. 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. 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 A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...
, 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 The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
(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 Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
of about 180 
kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
(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 In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth (signal processing), bandwidth available in a communication channel, communication medium is divided into a series of non-overlapping freque ...
". 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

The shaping of a signal to convey information is known as 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 Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at ...
,
frequency-shift keying Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather ball ...
, and
amplitude-shift keying Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, a symbol, representing one or more bits, is sent by transmitting a fixed-amplitude ca ...
). The "
Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is limit ...
" system, for example, uses phase-shift keying to exchange information between various devices. 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 Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signal ...
" (QAM) that are used in high-capacity digital radio communication systems. 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 In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a m ...
") before transmission. There are several different modulation schemes available to achieve this wo_of_the_most_basic_being_amplitude_modulation_(AM)_and_frequency_modulation.html" ;"title="amplitude_modulation.html" ;"title="wo of the most basic being amplitude modulation">wo of the most basic being amplitude modulation (AM) and frequency modulation">amplitude_modulation.html" ;"title="wo of the most basic being amplitude modulation">wo 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"). In addition, modulation has the advantage that it may use frequency division multiplexing (FDM).


Telecommunication networks

A telecommunications network is a collection of transmitters, receivers, and
communications channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...
s 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 networks, repeaters may be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combat
attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable at ...
that can render the signal indistinguishable from the noise.ATIS Telecom Glossary 2000
, ATIS Committee T1A1 Performance and Signal Processing (approved by the American National Standards Institute), 28 February 2001.
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.


Societal impact

Telecommunication has a significant social, cultural and economic impact on modern society. In 2008, estimates placed the
telecommunication industry The telecommunications industries within the sector of information and communication technology is made up of all telecommunications/ telephone companies and internet service providers and plays a crucial role in the evolution of mobile communicatio ...
's revenue at US$4.7 trillion or just under three percent of the gross world product (official exchange rate). Several following sections discuss the impact of telecommunication on society.


Microeconomics

On the
microeconomic Microeconomics is a branch of mainstream economics that studies the behavior of individuals and firms in making decisions regarding the allocation of scarce resources and the interactions among these individuals and firms. Microeconomics focu ...
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, Inc. ( ) is an American multinational technology company focusing on e-commerce, cloud computing, online advertising, digital streaming, and artificial intelligence. It has been referred to as "one of the most influential economi ...
but, according to academic Edward Lenert, even the conventional retailer Walmart has benefited from better telecommunication infrastructure compared to its competitors. 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 Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...
'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 Ivory Coast, also known as Côte d'Ivoire, officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital is Yamoussoukro, in the centre of the country, while its largest city and economic centre is ...
, coffee growers share mobile phones to follow hourly variations in coffee prices and sell at the best price.


Macroeconomics

On the macroeconomic scale, Lars-Hendrik Röller and Leonard Waverman suggested a causal link between good telecommunication infrastructure and economic growth. Few dispute the existence of a correlation although some argue it is wrong to view the relationship as causal. 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. Using this measure, Sweden, Denmark and Iceland received the highest ranking while the African countries Nigeria, Burkina Faso and Mali received the lowest.


Social impact

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.Fischer, Claude S. Touch Someone': The Telephone Industry Discovers Sociability." Technology and Culture 29.1 (January 1988): 32–61. . . Since then the role that telecommunications has played in social relations has become increasingly important. In recent years, the popularity of
social networking site A social networking service or SNS (sometimes called a social networking site) is an online platform which people use to build social networks or social relationships with other people who share similar personal or career content, interests, ac ...
s 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 Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
. 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.


Entertainment, news, and advertising

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.


Regulation

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". 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". From a global perspective, there have been political debates and legislation regarding the management of telecommunication and broadcasting. The
history of broadcasting It is generally recognized that the first radio transmission was made from a temporary station set up by Guglielmo Marconi in 1895 on the Isle of Wight. This followed on from pioneering work in the field by a number of people including Alessa ...
discusses some debates in relation to balancing conventional communication such as printing and telecommunication such as radio broadcasting. The onset of World War II brought on the first explosion of international broadcasting propaganda. Countries, their governments, insurgents, terrorists, and militiamen have all used telecommunication and broadcasting techniques to promote propaganda. 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. 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 Al-Zawraa Sports Club ( ar, نادي الزوراء الرياضي) is an Iraqi sports club based in Utayfia, Karkh District (near Tigris River), Baghdad. Their football team compete in the Iraqi Premier League, the top-flight of Iraqi footbal ...
, which while banned by the Iraqi government, still broadcasts from
Erbil Erbil, also called Hawler (, ar, أربيل, Arbīl; syr, ܐܲܪܒܹܝܠ, Arbel), is the capital and most populated city in the Kurdistan Region of Iraq. It lies in the Erbil Governorate. It has an estimated population of around 1,600,000. Hu ...
, Iraqi Kurdistan, even as coalition pressure has forced it to switch satellite hosts several times."Garfield, Andrew.
The U.S. Counter-propaganda Failure in Iraq
", Fall 2007, ''The Middle East Quarterly'', Volume XIV: Number 4, Accessed 21 July 2009.
On 10 November 2014,
President Obama Barack Hussein Obama II ( ; born August 4, 1961) is an American politician who served as the 44th president of the United States from 2009 to 2017. A member of the Democratic Party, Obama was the first African-American president of the U ...
recommended the Federal Communications Commission reclassify broadband Internet service as a telecommunications service to preserve net neutrality.


Modern media


Worldwide equipment sales

According to data collected by Gartner and Ars Technica sales of main consumer's telecommunication equipment worldwide in millions of units was:


Telephone

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 Speaker may refer to: Society and politics * Speaker (politics), the presiding officer in a legislative assembly * Public speaker, one who gives a speech or lecture * A person producing speech: the producer of a given utterance, especially: ** In ...
in that person's handset. As of 2015, the landline telephones in most residential homes are analog—that is, the speaker's voice directly determines the signal's voltage. 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 and can be perfectly reproduced in long-distance communication (as opposed to analog 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). In terms of new subscriptions over the five years from 1999, Africa has outpaced other markets with 58.2% growth. Increasingly these phones are being serviced by systems where the voice content is transmitted digitally such as
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
or W-CDMA with many markets choosing to deprecate analog systems such as AMPS. 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 optical 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 optical fibre cables are able to carry 25 times as many telephone calls as TAT-8. 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 In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, ind ...
which means several hundred of them can be easily bundled together in a single cable. Lastly, improvements in multiplexing have led to an exponential growth in the data capacity of a single fibre. Assisting communication across many modern optical fibre networks is a protocol known as
Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of ...
(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 If a network service (or application) wishes to use a broadband network (an ATM network in particular) to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performanc ...
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. 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.


Radio and television

In a broadcast system, the central high-powered
broadcast tower Radio masts and towers are typically tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the tallest human-mad ...
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 Demodulation is extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated ...
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). 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 .0 0.0 1.0 1.0and received with signal amplitudes
.9 0.2 1.1 0.9 '' 0.9'' is the fourth studio album by French rapper Booba. 0.9 may also refer to: *0.9, a fractional number *0. or 0.999..., a repeating decimal {{numberdis ...
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. In digital television broadcasting, there are three competing standards that are likely to be adopted worldwide. These are the
ATSC Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that ...
,
DVB Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...
and
ISDB Integrated Services Digital Broadcasting (ISDB; Japanese: , ''Tōgō dejitaru hōsō sābisu'') is a Japanese broadcasting standard for digital television (DTV) and digital radio. ISDB supersedes both the NTSC-J analog television system and ...
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 Dolby Digital, originally synonymous with Dolby AC-3, is the name for what has now become a family of audio compression technologies developed by Dolby Laboratories. Formerly named Dolby Stereo Digital until 1995, the audio compression is lossy ( ...
AC-3 for audio compression, ISDB uses
Advanced Audio Coding Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. Designed to be the successor of the MP3 format, AAC generally achieves higher sound quality than MP3 encoders at the same bit rate. AAC has been standa ...
(MPEG-2 Part 7) and DVB has no standard for audio compression but typically uses
MPEG-1 MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to about 1.5 Mbit/s (26:1 and 6:1 compression ratios respectively) without excessive quality loss, making ...
Part 3 Layer 2. 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. 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 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 Here is an adverb that means "in, on, or at this place". It may also refer to: Software * Here Technologies, a mapping company * Here WeGo (formerly Here Maps), a mobile app and map website by Here Television * Here TV (formerly "here!"), a ...
). These are known as PAL (German designed), NTSC (American designed), and
SECAM SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
(French-designed). For analog radio, the switch to digital radio is made more difficult by the higher cost of digital receivers. 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 C-QUAM (Compatible QUadrature Amplitude Modulation) is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published ...
.


Internet

The Internet is a worldwide network of computers and computer networks that communicate with each other using the
Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. I ...
(IP). Any computer on the Internet has a unique
IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
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. It is estimated that 51% of the information flowing through two-way telecommunications networks in the year 2000 were 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). , 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%). In terms of
broadband access Internet access is the ability of individuals and organizations to connect to the Internet using computer terminals, computers, and other devices; and to access services such as email and the World Wide Web. Internet access is sold by Interne ...
, Iceland (26.7%), South Korea (25.4%) and the Netherlands (25.3%) led the world. The Internet works in part because of
protocols Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...
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 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. 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 optic fiber. 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 address In computing, a logical address is the address at which an item ( memory cell, storage element, network host) appears to reside from the perspective of an executing application program. A logical address may be different from the physical add ...
ing. 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 www.google.com). At the moment, the most widely used version of the Internet Protocol is version four but a move to version six is imminent. At the transport layer, most communication adopts either the Transmission Control Protocol (TCP) or the
User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...
(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 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. 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. Finally, at the application layer, are many of the protocols Internet users would be familiar with such as
HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, w ...
(web browsing), POP3 (e-mail), FTP (file transfer),
IRC Internet Relay Chat (IRC) is a text-based chat system for instant messaging. IRC is designed for group communication in discussion forums, called '' channels'', but also allows one-on-one communication via private messages as well as chat a ...
(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.


Local area networks and wide area networks

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 AppleTalk is a discontinued proprietary suite of networking protocols developed by Apple Computer for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no prior setup or the ...
, IPX, and NetBIOS with the dominant protocol set during the early 1990s being IPX due to its popularity with
MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few oper ...
users.
TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
existed at this point, but it was typically only used by large government and research facilities. 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 The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...
, allowed TCP/IP-based computers to self-configure in the network. Such functions also existed in the AppleTalk/ IPX/ NetBIOS protocol sets. 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 In IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware responsible for interaction with the wired, optical or wireless transmission medium. The MAC sublay ...
. Both of these differences allow for more economical systems. 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 1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...
networks). However, some early implementations used heavier coaxial cables and some recent implementations (especially high-speed ones) use optical fibers. 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 suffer from less usable bandwidth and worse attenuation—implying poorer long-distance performance.Fiber Optic Cable Tutorial
, Arc Electronics. Retrieved June 2007.


See also


References


Citations


Bibliography

* Goggin, Gerard, ''Global Mobile Media'' (New York: Routledge, 2011), p. 176. . * OECD
''Universal Service and Rate Restructuring in Telecommunications''
Organisation for Economic Co-operation and Development (OECD) Publishing, 1991. . * Wheen, Andrew. ''Dot-Dash to Dot.Com: How Modern Telecommunications Evolved from the Telegraph to the Internet'' (Springer, 2011).


External links


International Teletraffic Congress

International Telecommunication Union (ITU)

ATIS Telecom Glossary

Federal Communications Commission

IEEE Communications Society

International Telecommunication Union
* (Ericsson removed the book from their site in September 2005) {{Authority control Economics of transport and utility industries Mass media technology ja:通信