From Wikipedia, the free encyclopedia
Telecommunication is communication at a distance by technological means, particularly through electrical signals or electromagnetic waves.[1][2][3][4][5][6] Due to the many different technologies involved, the word is often used in a plural form, astelecommunications.
Early telecommunication technologies included visual signals, such as beacons,smoke signals, semaphore telegraphs, signal flags, and optical heliographs.[7] Other examples of pre-modern telecommunications include audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Electrical and electromagnetic telecommunication technologies include telegraph, telephone, andteleprinter, networks, radio, microwave transmission, fiber optics, communications satellites and the Internet.
A revolution in wireless telecommunications began in the 1900s with pioneering developments in radio communications by Guglielmo Marconi. Marconi won theNobel Prize in Physics in 1909 for his efforts. Other highly notable pioneering inventors and developers in the field of electrical and electronic telecommunications include Charles Wheatstone and Samuel Morse (telegraph), Alexander Graham Bell(telephone), Edwin Armstrong, and Lee de Forest (radio ), as well as John Logie Baird and Philo Farnsworth (television).
The world's effective capacity to exchange information through two-way telecommunication networks grew from 281 petabytes of (optimally compressed) information in 1986, to 471 petabytes in 1993, to 2.2 (optimally compressed)exabytes in 2000, and to 65 (optimally compressed) exabytes in 2007.[8] 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.[9] 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.[10][11] 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).[10]
Etymology[edit]
The word telecommunication was adapted from French.[5] It is a compound of the Greek prefix tele- (τηλε-), meaning "distant", and the Latin communicare, meaning "to share".[12] The French word télécommunication was first invented in the French Grande Ecole "Telecom ParisTech" formerly known as "Ecole nationale supérieure des télécommunications" in 1904 by the French engineer and novelist Édouard Estaunié.[13]
History[edit]
For more details on this topic, see History of telecommunication.
Ancient systems[edit]
Greek hydraulic semaphore systems were used as early as the 4th century BC. The hydraulic semaphores, which worked with water filled vessels and visual signals, functioned as optical telegraphs. However, they could only utilize a very limited range of pre-determined messages, and as with all such optical telegraphs could only be deployed during good visibility conditions.[14]
During 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 that signaled the arrival of the Spanish warships.[15]
Further information: Optical communication
Systems since the Middle Ages[edit]
Main article: Semaphore line
In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system (or semaphore line) between Lille and Paris.[16] However semaphore systems suffered from the need for skilled operators, and expensive towers at intervals of 10–30 kilometers (6–20 mi). As a result of competition from the electrical telegraph, Europe's last commercial semaphore line in Sweden was abandoned in 1880.[17]
Telegraph and telephone[edit]
Experiments on communication with electricity, initially unsuccessful, started in about 1726. Scientists of including Laplace, Ampère, and Gauss were involved. A practicalelectrical telegraph was proposed in January 1837 by William Fothergill Cooke, who considered it an improvement on the existing "electromagnetic telegraph"; an improved five-needle, six-wire system developed in partnership with Charles Wheatstone entered commercial use in 1838.[18] Early telegraphs used several wires connected to a number of indicator needles.
Businessman Samuel F.B. Morse and physicist Joseph Henry of the United States developed their own, simpler version of the electrical telegraph, independently. Morse successfully demonstrated this system on 2 September 1837. Morse's most important technical contribution to this telegraph was the simple and highly efficient Morse Code co-developed with his associate Alfred Vail, which was an important advance over Wheatstone's more complicated and expensive system, and required just two wires. The communications efficiency of the Morse Code preceded that of the Huffman code in digital communications by over 100 years, but Morse and Vail developed the code purelyempirically, with shorter codes for more frequent letters.
The first permanent transatlantic telegraph cable was successfully completed on 27 July 1866, allowing transatlantic electrical communication for the first time.[19] An earlier transatlantic cable had operated for a few months in 1859, and among other things, it carried messages of greeting back and forth between President James Buchanan of the United States and Queen Victoria of the United Kingdom.
However that first transatlantic cable soon failed, and the project to lay a replacement line was delayed for five years by theAmerican Civil War. The first transatlantic telephone cable (which incorporated hundreds of electronic amplifiers) was not operational until 1956, only six years before the first commercial telecommunications satellite, Telstar, was launched into space.[20]
The conventional telephone now in use worldwide was first patented by Alexander Graham Bell in March 1876.[21] That first patent by Bell was the master patent of the telephone, from which all other patents for electric telephone devices and features flowed. Credit for the invention of the electric telephone has been frequently disputed, and new controversies over the issue have arisen from time-to-time. As with other great inventions such as radio, television, the light bulb, and the digital computer, there were several inventors who did pioneering experimental work on voice transmission over a wire, who then improved on each other's ideas. However, the key innovators were Alexander Graham Bell and Gardiner Greene Hubbard, who created the first telephone company, the Bell Telephone Company in the United States, which later evolved intoAmerican Telephone & Telegraph (AT&T), at times the world's largest phone company.
The first commercial telephone services were set up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven, Connecticut, and London, England.[22][23]
Radio and television[edit]
In 1832, James Lindsay gave a classroom demonstration of wireless telegraphy viaconductive water to his students. By 1854, he was able to demonstrate a transmission across the Firth of Tay from Dundee, Scotland, to Woodhaven, a distance of about two miles (3 km), again using water as the transmission medium.[24] In December 1901, Guglielmo Marconi established wireless communication between St. John's, Newfoundland and Poldhu, Cornwall (England), earning him the Nobel Prize in Physics for 1909, one which he shared with Karl Braun.[25]
On 25 March 1925, John Logie Baird of Scotland was able to demonstrate thetransmission of moving pictures at the Selfridge's department store in London, England. Baird's system relied upon the fast-rotating Nipkow disk, and thus it became known as the mechanical television. It formed the basis of experimental broadcasts done by the British Broadcasting Corporation beginning 30 September 1929.[26] However, for most of the 20th century, television systems were designed around the cathode ray tube, invented by Karl Braun. The first version of such an electronic television to show promise was produced by Philo Farnsworth of the United States, and it was demonstrated to his family in Idaho on 7 September 1927.[27]
Television, however, is not solely a technology, limited to its basic and practical application. It functions both as an appliance, and also as a means for social story telling and message dissemination. It is a cultural tool that provides a communal experience of receiving information and experiencing fantasy. It acts as a “window to the world” by bridging audiences from all over through programming of stories, triumphs, and tragedies that are outside of personal experiences.[28]
Videotelephony[edit]
Main article: History of videotelephony
The development of videotelephony involved the historical development of several technologies which enabled the use of live video in addition to voice telecommunications. The concept of videotelephony was first popularized in the late 1870s in both the United States and Europe, although the basic sciences to permit its very earliest trials would take nearly a half century to be discovered. This was first embodied in the device which came to be known as the video telephone, or videophone, and it evolved from intensive research and experimentation in several telecommunication fields, notably electrical telegraphy, telephony, radio, and television.
The development of the crucial video technology first started in the latter half of the 1920s in the United Kingdom and the United States, spurred notably by John Logie Baird and AT&T's Bell Labs. This occurred in part, at least by AT&T, to serve as an adjunct supplementing the use of the telephone. A number of organizations believed that videotelephony would be superior to plain voice communications. However video technology was to be deployed in analog television broadcasting long before it could become practical—or popular—for videophones.
Videotelephony developed in parallel with conventional voice telephone systems from the mid-to-late 20th century. Only in the late 20th century with the advent of powerful video codecs and high-speed broadband did it become a practical technology for regular use. With the rapid improvements and popularity of the Internet, it became widespread through the use of videoconferencing and webcams, which frequently utilize Internet telephony, and in business, where telepresence technology has helped reduce the need to travel.
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