Telecommunications | Wikipedia audio article
Telecommunication. Is the transmission, of signs signals. Messages. Words writings, images, and sounds, or information, of any nature by wire radio, optical. Or electromagnetic, systems. Telecommunication. Occurs when the exchange of information between, communication. Participants. Includes, the use of technology. It. Is transmitted, either electrically. Over physical media, such, as cables, or via electromagnetic. Radiation. Such. Transmission. Paths are often divided into communication. Channels, which afford the advantages, of multiplexing. Since. The Latin term communication. Is considered, the social, process, of information exchange, the term, telecommunications. Is often used in its plural form because it involves, many different technologies. Early, means of communicating, over a distance included. Visual signals, such, as beacons smoke, signals semaphore, Telegraph's, signal, flags and optical, heliographs. Other. Examples. Of pre-modern long distance, communication included. Audio messages, such as coded, drumbeats lung blown horns, and loud whistles. 20th. And 21st, century, technologies. For long-distance communication. Usually, involve electrical, and electromagnetic. Technologies. Such, as telegraph. Telephone and, teleprinter. Networks, radio, microwave. Transmission. Fiber optics, and communication. Satellites, a. Revolution. In wireless, communication. Began in the first decade, of the 20th, century with the pioneering, developments. In radio communications. By gilma Marconi, who won the Nobel Prize in Physics in 1909. And, other notable pioneering, inventors, and developers, in the field of electrical and electronic, telecommunications. These. Included, Charles Wheatstone and Samuel Morse inventors. Of the Telegraph, Alexander. Graham Bell inventor, of the telephone Edwin. Armstrong, and leader forest inventors, of radio as well as vladimir, k's where i can John Logie, Baird and Philo Farnsworth. Some of the inventors, of television. Topic. Etymology. The. Word, telecommunication. Is a compound, of the greek prefix, telly telly meaning, distant, far-off or afar and the Latin communicate meaning, to share its. Modern, use is adapted, from the French because it's written use was recorded, in 1904. By the French engineer, and novelist, Eduardo, nee.
Communication. Was first used as an English word in the late 14th, century, it. Comes from old french communication. 14c. Modern, french communication. From latin communication. M nominative, communication. Noun of action from past participle. Stem of communique, to share, divided out communicate. Impart inform join, unite. Participate. In. Literally. To, make common, from. Communis. Topic. History. Topic. Bacon's, and pigeons. Homing. Pigeons, have occasionally, been used throughout, history by, different, cultures pigeon. Post had Persian roots and was later used by the Romans, to aid their military. Front. And has said that 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. 18-49. Paul, Julius, Reuter started, a pigeon service to fly stock prices, between arkin and Brussels a service, that operated, for a year until the gap in the telegraph, link was closed 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 in 1792. Clawd chap a French engineer built the first fixed, visual telegraphy, system, or semaphore, line between Lille and Paris. However. Semaphore, suffered, from the need for skilled operators. And expensive, towers, at intervals, of 10 to 30 kilometers, 6 to 19 miles as a. Result, of competition from the electrical, Telegraph the, last commercial, line was abandoned, in 1880. Topic. Telegraph. And telephone. On the, 25th, of July 1837. The first commercial, electrical, Telegraph was, demonstrated. By English, inventor Sir William, Fothergill cook and English, scientist, Sir Charles, Weston, both. Inventors, viewed their devices an improvement. To the existing. Electromagnetic. Telegraph. Not. As a new device Samuel, Morse independently. Developed, a version of the electrical, Telegraph that, he unsuccessfully, demonstrated. On the 2nd of September, 1837. His. Code was an important, advance over Western signalling, method the, first transatlantic, Telegraph. Cable was, successfully, completed on, the 27th. Of July, 1866. Allowing, transatlantic. Telecommunication. For the first time the conventional, telephone, was invented independently. By Alexander. Bell and Elisha gray in 1876. Antonio. Meucci invented the, first device that allowed, the electrical, transmission of, voice over a line in 18-49. However. Mu Chi's device was of little practical value because. It relied upon the electronic. Effect and thus required, users, to place the receiver in their mouth to hear. What. Was being said, the first commercial, telephone, services, were set up in 1878. And 1879. On both sides of the Atlantic, in the cities of New Haven and London. Topic. Radio. And television. Starting. In 1894. Italian. Inventor Guillermo, Marconi, began developing. A wireless communication using. That their newly discovered phenomenon, of radio waves showing, by 1901. That they could be transmitted, across the Atlantic, Ocean, this. Was the start of wireless telegraphy by radio, voice. And music were demonstrated. In 1900. And 1906. But had little early success. World. War 1 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 two again accelerated. Development of radio for the wartime, purposes of aircraft, and land communication. Radio, navigation, and radar.
Development. Of stereo FM broadcasting. Of radio took place from the 1930s. Onwards in the United, States and displaced a.m. as the dominant, commercial standard. By the 1960s. And by the 1970s. In the United, Kingdom on the 25th, of March 1925. John, Logie, Baird was able to demonstrate the, transmission, of moving pictures at the London department, store Selfridges. Beds. Device, relied, upon the NIP car disk and thus became known as the mechanical, television, it. Formed, the basis of experimental, broadcasts done. By the British Broadcasting, Corporation beginning. The 30th, of September, 1929. However. For, most of the 20th, century, televisions. Depended, upon the cathode ray tube invented, by Carl Brown the. First version, of such a television, to show promise was produced by Philo, Farnsworth, and demonstrated. To his family, on the 7th of September, 1927. After. World war ii the experiments. In television, that had been interrupted were resumed, and it also became, an important, home entertainment, broadcast. Medium. Topic. Computers. Than the Internet. On the 11th, of September, 1940. George debates, 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 with remote dumb terminals, remained popular well, into the 1970s. However. Already. In the 1960s. Research, has 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 the 5th of December 1969. Constituting. The beginnings, of the ARPANET, 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 requests for comment documents, other networking, advancement. Occurred in industrial, laboratories such, as the local area network LAN developments. Of Ethernet, 1983. And the token ring protocol. 1984. Topic. K concepts. Modern. Telecommunication. Is founded, on a series, of key concepts, that experience progressive, development, and refinement in a period of well over a century. Topic. Basic. Elements. Telecommunication. Technologies. May primarily, be divided, into wide and wireless methods, overall. Though a basic, telecommunication. System, consists, of three main parts that are always present in some form or another a. Transmitter. That takes information and, converts it to a signal, a. Transmission. Medium also called, the physical channel that carries the signal an, example. Of this is the free. Space channel a. Receiver. That takes the signal from the channel and converts it back into, usable, information, for the recipient, for example, in a radio broadcasting. Station, the station's, large power amplifier, is the transmitter, and the broadcasting. Antenna is the interface, between the power amplifier and, the free. Space channel, the. Free space channel is the transmission, medium and the receivers, antenna is the interface, between the free space channel and the receiver. Next. The radio receiver is the destination, of the radio signal, and this is where it is converted, from electricity, to sound for people to listen to her. Sometimes. Telecommunication. Systems, are duplex. Two-way. Systems, with a single, box of electronics, working as both the transmitter and a receiver or, a transceiver. For. Example, a cellular, telephone is. A transceiver, the. Transmission. Electronics, and the receiver electronics.
Within A transceiver, are actually, quite independent. Of each other, this. Can be readily explained, by the fact that radio, transmitters. Contain, power amplifiers. That operate, with electrical, power is measured in watts or kilowatts, but radio receivers, deal with radio powers, that are measured in the micro, watts or nano Ed's hence. Transceivers. Have to be carefully, designed and built to isolate, their high-power circuitry, in their low-power, circuitry. From each other as to not cause interference. Telecommunication. Over fixed lines is called point-to-point, communication. Because it is between one transmitter, and one receiver. Telecommunication. Through radio broadcasts. Is called broadcast, communication. Because it is between one powerful, transmitter, and numerous low-power, but sensitive, radio receivers. Tele communications, in which multiple, transmitters, and multiple, receivers have been designed to cooperate, and to share the same physical, channel are called multiplex, systems, the. Sharing, of physical, channels using multiplexing. Often gives very large reductions, in costs. Multiplexed. Systems, are laid out in, telecommunication. Networks, and the multiplex, signals, are switched at nodes through to the correct destination terminal. Receiver. Topic. Analog. Versus, digital, communications. Communication. Signals, can be sent either by analog, signals, or digital, signals, there. Are analog, communication. Systems, and digital communication. Systems, for. An analog signal the signal is varied, continuously with, respect, to the information. In. A digital signal, the information. Is encoded as a set of discrete values for, example a set of ones and zeros. During. The propagation, and reception, the information. Contained in analog signals, will inevitably be, degraded, by undesirable. Physical, noise the output, of a transmitter, is noise free for all practical purposes, commonly. The noise in a communication. System can, be expressed, as adding or subtracting from. The desirable, signal, in a completely, random way. This. Form of noise is called additive, noise with, the understanding. That the noise can be negative, or positive at, different, instants of time, noise. That is not additive noise is, a much more difficult situation, to describe, or analyze and, these other kinds of noise will be emitted here, on. The other hand unless, the additive noise disturbance. Exceeds a certain threshold the, information, contained in digital, signals, will remain intact, their. Resistance, to noise represents. A clear advantage of, digital signals, over analog, signals. Topic. Telecommunication. Networks. 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 rooters 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 Network repeaters. May be necessary to, amplify, or recreate the signal when it is being transmitted, over long distances. This. Is to combat attenuation.
That Can render the signal, indistinguishable. From the noise. Another. Advantage, of digital systems, over analog is that their output is easier to store in memory ie to voltage, States high and low are easier to store than a continuous, range of states. Topic. 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, for sound communications. Glass optical, fibers for some kinds of optical, communications. Coaxial. Cables, for communications. By way of the voltages, and electric, currents in them and free, space for communications. Using visible light infrared, waves, ultraviolet. Light and radio, waves. Coaxial. Cable, 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 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 ninety four point five megahertz megahertz. While another radio, station can. Simultaneously, broadcast. Radio waves at frequencies, in the neighborhood, of 96 point one megahertz, each. Radio, station, would transmit, radio waves over a frequency. Band width of about 180. Kilohertz, 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, kilohertz and the difference, between 200. Kilohertz and 180. Kilohertz, 20 kilohertz is an engineering, allowance, for the affections, 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, timeslot. For example. 20 milliseconds. Out of each second, and to allow each sender to send messages, only within its own time slot this. Method, of dividing the medium, into communication. Channels, is called time. Division multiplexing. TDM. And is used in optical fiber, communication. Some. Radio communication. Systems, use TDM, within an allocated, FDM, channel, hence. These systems, use a hybrid, of TDM, and FDM. Topic. 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. Clean 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, 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. Analog signals, at higher frequencies. This. Is helpful because low frequency, analog, signals, cannot be effectively, transmitted. Over free space, hence. The information. From a low frequency analog. Signal, must be impressed into a higher frequency signal, known as the carrier. Wave before. Transmission. There, are several different, modulation, schemes, available to achieve this two of the most basic being, amplitude, modulation, a.m. and frequency. Modulation, fm an. Example. Of this process, is a disk jockeys voice being impressed, into a 96, mega Hertz 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. Topic. Society. Telecommunication. Has a significant. Social cultural. And economic impact. On modern society. In. 2008. Estimates, placed the telecommunication. Industry's, revenue at four point seven trillion dollars, or just under 3% of the gross world product official, exchange rate. Several. Following, sections, discuss, the impact of telecommunication. On society. Topic. Economic. Impact. Topic. Microeconomics. On the micro economic. 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. Leonard even the conventional, retail, at Walmart has benefited, from better, telecommunication. Infrastructure, compared, to its competitors. In. Cities, throughout the world, home owners use their telephones, to order in a range of 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. Gnashing, died district, isolated. Villages use cellular, phones to speak directly to wholesalers, and arrange, a better price for their goods in Cote. D'Ivoire coffee, growers, share mobile, phones to follow our leave variations. In coffee prices, and sell at the best price. Topic. Macroeconomics. On the macroeconomic. Scale Lars Hendrik, Rolla and Leonard way vermin 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 telecommunications, 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 landline, 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. Topic. 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 since, then the role that telecommunications. Has played in social, relations, has become increasingly, important, in. Recent, years the popularity, of social networking, sites, has increased, dramatically. These. Sites allow users, to communicate, with each other as well as post photographs events. And profiles, for others to see the. Profiles, can list a person's, age interests, sexual, preference, and relationship. Status, in. This way these sites can play important, role in everything from organizing, social engagements. To courtship 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 if sauce 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. Topic. Are there impacts. 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 received their news a, 2006. Survey right, table, of slightly more than 3,000, Americans, by the nonprofit Pew Internet and American Life, Project in, the United, States the majority specified. Television. Or radio /, 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. Topic. Government. 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 IT use, 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, discusses. Some debates in relation, to balancing, conventional. Communications. Such as printing and telecommunications. 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 count a similar broadcast, 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 SMS, 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 alles, hora, which, while banned by the Iraqi, government still. Broadcasts. From, Iraqi. Kurdistan. Even, as coalition. Pressure has forced, it to switch satellite, host several times. On. The 10th of November 2014. President, Obama recommended. The Federal, Communications. Commission, reclassify. Broadband, internet, service as, a telecommunications, service, to preserve net neutrality. Topic. Modern, media. Topic. Worldwide. Equipment. Sales. According. To data collected, by Gartner, and ARS technica sales of main consumers. Telecommunication. Equipment worldwide. In millions of units worse. Topic. Telephone. In, a telephone, network, the caller is connected, to the person they want to talk to by switches, at various, telephone, exchanges. The. Switches, form an electrical, connection between the two users, and the setting of these switches is determined, electronically. When the caller dials the number, once. The connection, is made the caller's voice is transformed. To an electrical, signal using, a small microphone, in the caller's handset, this. Electrical, signal is then sent through the network to the user at the other end where it is transformed. Back into sound by a small, speaker in that person's, handset, as, of. 2015, the, landline, telephones, in most residential, homes, are analog, that is, the speaker's, voice directly. Determines, the signals 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, have number fixed-line subscriptions. In many markets, sales. Of mobile, phones in 2005. Total, eight hundred and sixteen, point six million with that figure being almost equally, shared amongst the markets of asia-pacific. Two hundred and four meters Western, Europe one hundred and sixty four meters C EMEA Central. Europe the Middle East and Africa one hundred and fifty three point five meters, North America. 148. Meters and Latin America, one hundred and two meters, in. Terms of new subscriptions. Over the five years from 1999. Africa, has outpaced other markets, with fifty eight point two percent growth. Increasingly. These phones are being serviced, by systems, where the voice content, is transmitted, digitally such, as GSM, or WCDMA.
With Many markets, choosing to deprecate analog. Systems, such as amps, there have also been dramatic. Changes, Intel phone communication. Behind the scenes. Starting. With the operation, of tat 8 in 1988. The 1990s. Saw the widespread, adoption of systems, based on optical fibers. The. Benefit, of communicating. With optic fibers, is that they offer a drastic, increase in data capacity. Tat. 8 itself, was able to carry ten times as many telephone, calls is the last copper cable, laid at that time and today's optic, fiber 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. Optic, fibers, 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. Lastly. Improvements. In multiplexing. Have led to an exponential. Growth in the data capacity, of a single fiber Assisting, communication. Across many modern, optic fiber 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, bitrate something. That will ensure a callers, voice is not delayed in parts or cut off completely. There. Are competitors, to ATM, such, as multi-protocol. Label switching, MPLS. That perform a similar task and are expected, to supply an ATM, in the future. Topic. Radio. And television. In. A broadcast system, the central high powered broadcast, tower transmits. A high-frequency electromagnetic. Wave. To numerous low powered, receivers, the. High frequency. Wave sent by the tower is modulated, with a signal, containing, visual or audio information. The. Receiver, is then tuned so as to pick up the high frequency, wave and a demodulator is, used to retrieve the signal, containing, the visual or audio information. The. Broadcast, signal can be either analog, signal, is varied, continuously with, respect, to the information or digital, information is encoded, as a set of discrete values the, broadcast, media, industry, is at a critical turning point in its development, with many countries moving, from analog to digital broadcasts. This. Move is made possible by the production, of cheaper faster and more capable, integrated, circuits, the. Chief advantage, of digital broadcasts. Is that they prevent a number of complaints common, to traditional, analog, broadcasts. For. Television, this includes, the elimination of, problems, such as snowy pictures, ghosting, and other distortion, these. Occur because of the nature of analog, transmission which, means that perturbations. Due to noise will be evident, in the final output. Digital. Transmission. Overcomes, this problem, because digital signals, are reduced to discrete, values, upon reception, and hence small perturbations. Do not affect the final output, in. A simplified, example if, a binary message 1011. Was transmitted, with signal amplitudes, 1.0. 0.0. 1.0. 1.0. And received, with signal amplitudes, 0.9. 0.2. 1.1. 0.9. It would still decode to the binary message 1011. A perfect. Reproduction, of what was sent, from. This example a problem, with digital, transmissions. Can also be seen in that if the noise is great enough it can significantly alter, the decoded, message, using. Forward, error correction a, receiver can correct a handful, of bit errors in the resulting, message but too much noise will lead to incomprehensible, output. And hence a breakdown, of the, transmission, 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 caption map all. Three, standards, use mpeg-2, for video compression. ATSC. Uses, Dolby Digital ac3. 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, 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. A.m. 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 the 12th of June 2009. After twice delaying, the switchover deadline. Kenya. Also, entered analog television, transmission. In December, 2014, after, multiple, delays, for. Analog television. There were three standards, in use for broadcasting. Color TV, see a map on adoption, here these. Are known as PAL German, designed, NTSC. American, design and cecum, 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 and amplitude, modulated subcarrier. Is used for stereo FM and, quadrature, amplitude modulation, is, used for stereo AM or SECAM. Topic. Internet. The. Internet, is a worldwide. Of computers, and computer, networks, that communicate with, each other using the Internet, Protocol, IP, 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, is estimated. That 51, percent of the information, flowing through two-way, telecommunications. Networks, in the year 2000. Were flowing through the internet most of the rest 42, percent through the landline, telephone. By. The year, 2007. The internet clearly, dominated, and captured, 97, percent of all the information, in telecommunication. Networks, most of the rest two percent through mobile phones as, of. 2008. An estimated. Twenty one point nine percent of the world population has, access to the Internet with the highest access, rates measured, as a percentage of the population in, North America, seventy, three point six percent Oceania. Australia. Fifty, nine point five percent and Europe, forty eight point one percent, in. Terms of broadband, access iceland. 26.7%. South, Korea twenty, five point four percent and the Netherlands. 25.3%. Led, the world the internet, works in part because of protocols. That govern how the computers, and Reuters 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 1980. Three is 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 addressing. For. The world wide web these IP, addresses. Are. Derived, from the human readable form using, the domain name system eg. 72. Dot 1400. 7.99. Is derived from. Www.google.com/mapmaker. Communication. Adopts, either the transmission. Control protocol, TCP, or the user Datagram, protocol, UDP. TCP. Is. Used when it is essential, every message sent is received, by the other computer, whereas UDP, is used when it is merely desirable. With. TCP. Packets, are retransmitted. If they are lost and placed in order before they are presented to higher layers, with. UDP, packets, are not ordered or retransmitted. If lost, both. TCP and, UDP packets. Carry port numbers with them to specify, what application. Or process the packet should be handled, by, 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 a, 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. Web browsing, pop3. Email, FTP, File. Transfer, RC. 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 ie file, transfer, or email, or buffered, in advance, ie 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. Ie 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. Topic. Local. Area networks, and wide area, networks. Despite. The growth of the Internet the characteristics. Of local area networks, blends computer. Networks that do not extend beyond the few kilometers, remain. Distinct, this. Is because networks, on this scale do not require all the features associated with, larger, networks, and are often more cost effective, and efficient, without them when. They are not connected, with the Internet they also have the advantages, of privacy, and security. However.
Purposefully. Lacking a direct connection to the Internet, 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 land. Wide. Area networks, ones are private, computer networks, that may extend for thousands, of kilometers, once. Again some of their advantages include, privacy, and security prime. Users of private, lands and ones 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, 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 whereas asynchronous, transfer mode ATM. Or multi-protocol. Label switching, MPLS. A typical, data link protocols, for la networks, such as once Ethernet, and token ring a typical, data link protocols, for lands, these. Protocols, differ from the former protocols, in that they are simpler, eg, they emit features, such as quality, of service, guarantees, and offer collision, prevention. Both. Of these differences, allow, for more economical, systems, despite, the modest popularity. Of IBM, token, ring in the 1980s. And 1990s. Virtually, all lands, now use either wired or wireless, Ethernet facilities, at. The physical layer most, wired Ethernet, implementations. Use copper twisted pair, cables, including, the common one obas, ET 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, fir but that suffers, from less usable bandwidth, and worse attenuation. Implying. Poor a long distance performance. Topic. Transmission. Capacity. The. Effective, capacity, to exchange information, worldwide. Through, two-way telecommunication. Networks. Grew from, 281. Petabytes, of optimally, compressed, information in, 1986. To, 471. Petabytes, in 1993. To 2.2. Optimally, compressed, exabytes, in, 2002. 65, optimally, compressed, exabytes, 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 in the global, telecommunications, industry. Was about a four point seven trillion dollars sector in 2012. The. Service, revenue, of the global telecommunications. Industry. Was estimated, to be 1.5, trillion dollars, in 2010, corresponding. To 2.4. Percent of the world's gross domestic product. GDP. Equals. Equals see also.
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