"Telecomy" redirects here. For specific telecommunications companies, seeList of telephone operating companies.
Copy ofAlexander Graham Bell's original telephone, at theMusée des Arts et Métiersin Paris
Telecommunicationis the assistedtransmissionofsignalsover a distance for the purpose ofcommunication. In earlier times, this may have involved the use ofsmoke signals,drums,semaphore,flags,Morse Code, orheliograph. In modern times, telecommunication typically involves the use of electronic transmitters such as thetelephone,television,radioorcomputer. Early inventors in the field of telecommunication includeAlexander Graham Bell,Guglielmo MarconiandJohn Logie Baird. Telecommunication is an important part of the world economy and the telecommunication industry's contribution was estimated to be $1.2 trillion in 2006.
2.1.1Analogue or digital
3Society and telecommunication
3.2.1Cellular Telephone Industry
4.2Telegraph and telephone
4.3Radio and television
4.4Computer networks and the Internet
5.2Radio and television
5.4Local area networks
6Telecommunication by region
The wordtelecommunicationwas adapted from the French wordtélécommunication. It is a compound of the Greek prefixtele-(τηλε-), meaning 'far off', and the Latincommunicare, meaning 'to share'.The French wordtélécommunicationwas coined in 1904 by French engineer and novelistÉdouard Estaunié.
A telecommunication system consists of three basic elements:
atransmitterthat takesinformationand converts it to asignal;
atransmission mediumthat carries the signal; and,
areceiverthat receives the signal and converts it back into usable information.
For example, in a radio broadcast thebroadcast toweris the transmitter,free spaceis the transmission medium and theradiois the receiver. Often telecommunication systems are two-way with a single device acting as both a transmitter and receiver ortransceiver. For example, amobile phoneis a transceiver.
Telecommunication over a telephone line is calledpoint-to-point communicationbecause it is between one transmitter and one receiver. Telecommunication through radio broadcasts is calledbroadcastcommunication because it is between one powerful transmitter and numerous receivers.
Analogue or digital
Signals can be eitheranalogueordigital. In an analogue 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 ones and zeros). During transmission the information contained in analogue signals will be degraded by noise. Conversely, unless the noise exceeds a certain threshold, the information contained in digital signals will remain intact. This noise resistance represents a key advantage of digital signals over analogue signals.
A collection of transmitters, receivers or transceivers that communicate with each other is known as anetwork. Digital networks may consist of one or moreroutersthat transmit information to the correct users. An analogue network may consist of one or moreswitchesthat establish a connection between two or more users. For both types of network,repeatersmay be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combatattenuationthat can render the signal indistinguishable fromnoise.
Achannelis a division in a transmission medium so that it can be used to send multiple streams of information. For example, a radio station may broadcast at 96.1 MHz while another radio station may broadcast at 94.5 MHz. In this case, the medium has been divided byfrequencyand each channel has received a separate frequency to broadcast on. Alternatively, one could allocate each channel a recurring segment of time over which to broadcastthis is known astime-division multiplexingand is sometimes used in digital communication.
The shaping of a signal to convey information is known asmodulation. Modulation can be used to represent a digital message as an analogue waveform. This is known askeyingand several keying techniques exist (these includephase-shift keying,frequency-shift keyingandamplitude-shift keying).Bluetooth, for example, usesphase-shift keyingto exchange information between devices.
Modulation can also be used to transmit the information of analogue signals at higher frequencies. This is helpful because low-frequency analogue signals cannot be effectively transmitted over free space. Hence the information from a low-frequency analogue signal must be superimposed on a higher-frequency signal (known as acarrier wave) before transmission. There are several different modulation schemes available to achieve this (two of the most basic beingamplitude modulationandfrequency modulation). An example of this process is aDJ'svoice being superimposed on a 96 MHz carrier wave using frequency modulation (the voice would then be received on a radio as the channel "96 FM").
Society and telecommunication
Telecommunication is an important part of modern society. In 2006, estimates placed the telecommunication industry's revenue at $1.2 trillion or just under 3% of thegross world product(official exchange rate).There exist several economic,socialand sovereignisticimpacts.
An antique radio, aContempra Telephone(Artifact no. 2000 0019) by Northern Electric (Nortel) (Syd Horen,John Tyson,Graham Parson) ca. 1967., a television display system and the first Canadian (Quebec) designed fully electronic digitaltelephone switching boardca. 1972. on display at theMuseum of Science and Technology(Aug 2008).
On the microeconomic scale, companies have used telecommunication to help build global empires. This is self-evident in the case of online retailerAmazon.combut, according to academic Edward Lenert, even the conventional retailerWal-Marthas benefited from better telecommunication infrastructure compared to its competitors.In cities throughout the world, home owners use theirtelephonesto organize many home services ranging frompizza deliveriestoelectricians. Even relatively poor communities have been noted to use telecommunication to their advantage. InBangladesh's Narshingdi district, isolated villagers use cell phones to speak directly to wholesalers and arrange a better price for their goods. InCote d'Ivoire, coffee growers share mobile phones to follow hourly variations in coffee prices and sell at the best price.
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 worldthis is known as thedigital divide.
Cellular Telephone Industry
In 2000, market research groupIpsos MORIreported that 81% of 15 to 24 year-oldSMSusers in the United Kingdom had used the service to coordinate social arrangements.The cellular telephone industry has had significant impact of telecommunications. A 2003 survey by theInternational Telecommunication Union(ITU) revealed that roughly one-third of countries have less than 1 mobile subscription for every 20 people and one-third of countries have less than 1 fixed line subscription for every 20 people. In terms of Internet access, roughly half of all countries have less than 1 in 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,DenmarkandIcelandreceived the highest ranking while the African countriesNiger,Burkina FasoandMalireceived the lowest.
For more details on this topic, seeHistory of telecommunication.
A replica of one of Chappe's semaphore towers.
Early forms of telecommunication includesmoke signalsanddrums. Drums were used by natives inAfrica,New GuineaandSouth Americawhereas smoke signals were used by natives inNorth AmericaandChina. Contrary to what one might think, these systems were often used to do more than merely announce the presence of a camp.
In the Middle Ages, chains ofbeaconswere 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 theSpanish Armada, when a beacon chain relayed a signal fromPlymouthtoLondon.
In 1792,Claude Chappe, a French engineer, built the first fixed visual telegraphy system (orsemaphore line) betweenLilleandParis.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.
Homing pigeonshave occasionally been used through history by different cultures.Pigeon postis thought to have Persians roots and was used by the Romans to aid their military.Frontinussaid thatJulius Ceasarused pigeons as messengers in his conquest ofGaul.TheGreeksalso 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 inJavaandSumatra. And in 1849,Paul Julius Reuterstarted a pigeon service to fly stock prices betweenAachenandBrussels, a service that operated for a year until the gap in the telegraph link was closed.
Telegraph and telephone
SirCharles Wheatstoneand SirWilliam Fothergill Cookeinvented the electric telegraph in 1837.Also, the first commercialelectrical telegraphis purported to have been constructed by Wheatstone and Cooke and opened on 9 April 1839.Both inventors viewed their device as "an improvement to the [existing] electromagnetic telegraph" not as a new device.
Samuel Morseindependently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837.His codewas an important advance over Wheatstone's signaling method. The firsttransatlantic telegraph cablewas successfully completed on 27 July 1866, allowing transatlantic telecommunication for the first time.
The conventional telephone was invented independently byAlexander BellandElisha Grayin 1876.Antonio Meucciinvented the first device that allowed the electrical transmission of voice over a line in 1849. However Meucci's device was of little practical value because it relied upon theelectrophonic effectand 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 ofNew HavenandLondon.
Radio and television
In 1832,James Lindsaygave a classroom demonstration ofwireless telegraphyto his students. By 1854, he was able to demonstrate a transmission across theFirth of TayfromDundee, ScotlandtoWoodhaven, a distance of two miles (3 km), using water as the transmission medium.In December 1901,Guglielmo Marconiestablished wireless communication betweenSt. John's, Newfoundland(Canada) andPoldhu, Cornwall(England), earning him the1909 Nobel Prize in physics(which he shared withKarl Braun).However small-scale radio communication had already been demonstrated in 1893 byNikola Teslain a presentation to the National Electric Light Association.
On 25 March 1925,John Logie Bairdwas able to demonstrate the transmission of moving pictures at the London department storeSelfridges. Baird's device relied upon theNipkow diskand thus became known as themechanical television. It formed the basis of experimental broadcasts done by theBritish Broadcasting Corporationbeginning 30 September 1929.However, for most of the twentieth century televisions depended upon thecathode ray tubeinvented byKarl Braun. The first version of such a television to show promise was produced byPhilo Farnsworthand demonstrated to his family on 7 September 1927.
Computer networks and the Internet
On 11 September 1940,George Stibitzwas able to transmit problems usingteletypeto his Complex Number Calculator inNew Yorkand receive the computed results back atDartmouth CollegeinNew Hampshire.This configuration of a centralized computer ormainframewith remote dumb terminals remained popular throughout the 1950s. However, it was not until the 1960s that researchers started to investigatepacket switching a technology that would allow chunks of data to be sent to different computers without first passing through a centralized mainframe. A four-node network emerged on 5 December 1969; this network would becomeARPANET, which by 1981 would consist of 213 nodes.
ARPANET's development centred around theRequest for Commentprocess and on 7 April 1969,RFC 1was published. This process is important because ARPANET would eventually merge with other networks to form theInternetand many of the protocols the Internet relies upon today were specified through the Request for Comment process. In September 1981,RFC 791introduced theInternet Protocolv4 (IPv4) andRFC 793introduced theTransmission Control Protocol(TCP) thus creating the TCP/IP protocol that much of theInternetrelies upon today.
However, not all important developments were made through the Request for Comment process. Two popular link protocols forlocal area networks(LANs) also appeared in the 1970s. A patent for thetoken ringprotocol was filed byOlof Soderblomon 29 October 1974 and a paper on theEthernetprotocol was published byRobert MetcalfeandDavid Boggsin the July 1976 issue ofCommunications of the ACM.
Optical fiberprovides cheaper bandwidth for long distance communication
In an analogue telephone network, thecalleris connected to the person he wants to talk to by switches at varioustelephone exchanges. The switches form an electrical connection between the two users and the setting of these switches is determined electronically when the callerdialsthe number. Once the connection is made, the caller's voice is transformed to an electrical signal using a smallmicrophonein the caller'shandset. 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 smallspeakerin that person's handset. There is a separate electrical connection that works in reverse, allowing the users to converse.
Thefixed-linetelephones in most residential homes are analogue that is, the speaker's voice directly determines the signal's voltage. Although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting the signals to digital for transmission before converting them back to analogue for reception. The advantage of this is that digitized voice data can travel side-by-side with data from the Internet and can be perfectly reproduced in long distance communication (as opposed to analogue signals that are inevitably impacted by noise).
Mobile phones have had a significant impact on telephone networks. Mobile phone subscriptions now outnumber fixed-line subscriptions in many markets. Sales of mobile phones in 2005 totalled 816.6 million with that figure being almost equally shared amongst the markets of Asia/Pacific (204 m), Western Europe (164 m), CEMEA (Central Europe, the Middle East and Africa) (153.5 m), North America (148 m) and Latin America (102 m).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 asGSMorW-CDMAwith many markets choosing to depreciate analogue systems such asAMPS.
There have also been dramatic changes in telephone communication behind the scenes. Starting with the operation ofTAT-8in 1988, the 1990s saw the widespread adoption of systems based onoptic fibres. The benefit of communicating with optic fibres is that they offer a drastic increase in data capacity. TAT-8 itself was able to carry 10 times as many telephone calls as the last copper cable laid at that time and today's optic 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, optic fibres are physically much smaller than competing technologies. Second, they do not suffer fromcrosstalkwhich 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 optic fibre networks is a protocol known asAsynchronous 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 atraffic contractwith 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 asMultiprotocol Label Switching(MPLS), that perform a similar task and are expected to supplant ATM in the future.
Radio and television
Digital television standards and their adoption worldwide.
In a broadcast system, a central high-poweredbroadcast towertransmits a high-frequencyelectromagnetic waveto numerous low-powered receivers. The high-frequency wave sent by the tower ismodulatedwith a signal containing visual or audio information. Theantennaof the receiver is thentunedso as to pick up the high-frequency wave and ademodulatoris used to retrieve the signal containing the visual or audio information. The broadcast signal can be either analogue (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete values).
The broadcast media industry is at a critical turning point in its development, with many countries moving from analogue to digital broadcasts. This move is made possible by the production of cheaper, faster and more capableintegrated circuits. The chief advantage of digital broadcasts is that they prevent a number of complaints with traditional analogue broadcasts. For television, this includes the elimination of problems such assnowy pictures,ghostingand other distortion. These occur because of the nature of analogue transmission, which means that perturbations due tonoisewill 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. Usingforward error correctiona 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 theATSC,DVBandISDBstandards; the adoption of these standards thus far is presented in the captioned map. All three standards useMPEG-2for video compression. ATSC usesDolby Digital AC-3for audio compression, ISDB usesAdvanced Audio Coding(MPEG-2 Part 7) and DVB has no standard for audio compression but typically usesMPEG-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 theDigital Audio Broadcastingstandard (also known as theEureka 147standard). The exception being the United States which has chosen to adoptHD Radio. HD Radio, unlike Eureka 147, is based upon a transmission method known asin-band on-channeltransmission that allows digital information to "piggyback" on normal AM or FM analogue transmissions.
However, despite the pending switch to digital, analogue receivers still remain widespread. Analogue television is still transmitted in practically all countries. The United States had hoped to end analogue broadcasts on 31 December 2006; however, this was recently pushed back to 17 February 2009.For analogue television, there are three standards in use (see a map on adoptionhere). These are known asPAL,NTSCandSECAM. For analogue radio, the switch to digital is made more difficult by the fact that analogue receivers are a fraction of the cost of digital receivers.The choice of modulation for analogue radio is typically betweenamplitude modulation(AM) orfrequency modulation(FM). To achievestereo playback, an amplitude modulated subcarrier is used forstereo FM.
TheOSI reference model
The Internet is a worldwide network of computers and computer networks that can communicate with each other using theInternet Protocol.Any computer on the Internet has a uniqueIP addressthat 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. In this way, the Internet can be seen as an exchange of messages between computers.
As of2008, 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 ofbroadband access,Iceland(26.7%),South Korea(25.4%) and theNetherlands(25.3%) led the world in2005.
The Internet works in part because ofprotocolsthat 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 anInternet browserto run the same code regardless of whether the computer it is running on is connected to the Internet through anEthernetorWi-Ficonnection. Protocols are often talked about in terms of their place in theOSI 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 theAsynchronous Transfer Mode(ATM) protocol (or a modern equivalent) on top of optic fibre. This is because for most intercontinental communication the Internet shares the same infrastructure as thepublic switched telephone network.
At the network layer, things become standardized with theInternet Protocol(IP) being adopted forlogical addressing. For the world wide web, these "IP addresses" are derived from the human readable form using theDomain Name System(e.g.184.108.40.206is derived fromwww.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 theTransmission Control Protocol(TCP) or theUser Datagram Protocol(UDP). TCP is used when it is essential every message sent is received by the other computer where as 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 carryport numberswith them to specify what application orprocessthe packet should be handled by.Because certain application-level protocols usecertain ports, network administrators can restrict Internet access by blocking the traffic destined for a particular port.
Above the transport layer, there are certain protocols that are sometimes used and loosely fit in the session and presentation layers, most notably theSecure Sockets Layer(SSL) andTransport Layer Security(TLS) protocols. These protocols ensure that the data transferred between two parties remains completely confidential and one or the other is in use when a padlock appears at the bottom of your web browser.Finally, at the application layer, are many of the protocols Internet users would be familiar with such asHTTP(web browsing),POP3(e-mail),FTP(file transfer),IRC(Internet chat),BitTorrent(file sharing) andOSCAR(instant messaging).
Some of the most popular internet telecommunications applications include e-mail, instant messaging, browsing the sites, and the use of various media outlets as well as chat groups. Today just about everyone has at least one e-mail address if not two or three. When the network is not bogged down messages can travel anywhere in the world in a matter of a few seconds or minutes depending on the data and its size (O'Brian,Marakas,2008). Instant messaging is a common and convenient way to communicate with known individuals in real time. There are plenty of browsers that can be used to navigate the internet; some of the popular ones are Internet Explorer and Firefox. You can get news updates as they happen from your favorite news network online.
Local area networks
Despite the growth of the Internet, the characteristics oflocal area networks(computer networks that run at most 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.
In the mid-1980s, several protocol suites emerged to fill the gap between the data link and applications layer of theOSI reference model. These wereAppletalk,IPXandNetBIOSwith the dominant protocol suite during the early 1990s being IPX due to its popularity withMS-DOSusers.TCP/IPexisted at this point but was typically only used by large government and research facilities.As the Internet grew in popularity and a larger percentage of traffic became Internet-related, local area networks gradually moved towards TCP/IP and today networks mostly dedicated to TCP/IP traffic are common. The move to TCP/IP was helped by technologies such asDHCPthat allowed TCP/IP clients to discover their own network address a functionality that came standard with the AppleTalk/IPX/NetBIOS protocol suites.
It is at the data link layer though that most modern local area networks diverge from the Internet. WhereasAsynchronous Transfer Mode(ATM) orMultiprotocol Label Switching(MPLS) are typical data link protocols for larger networks,EthernetandToken Ringare typical data link protocols for local area networks. These protocols differ from the former protocols in that they are simpler (e.g. they omit features such asQuality of Serviceguarantees) and offercollision prevention. Both of these differences allow for more economic set-ups.
Despite the modest popularity ofToken Ringin the 80's and 90's, virtually all local area networks now use wired or wirelessEthernet. At the physical layer, most wired Ethernet implementations usecopper twisted-pair cables(including the common10BASE-Tnetworks). However, some early implementations usedcoaxial cablesand some recent implementations (especially high-speed ones) useoptic fibres. Optic fibres are also likely to feature prominently in the forthcoming10-gigabit Ethernetimplementations.Where optic fibre is used, the distinction must be made between multi-mode fibre and single-mode fibre.Multi-mode fibrecan be thought of as thicker optical fibre that is cheaper to manufacture but that suffers from less usable bandwidth and greater attenuation (i.e. poor long-distance performance).
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Group-calling, similar toconference calling, is a means ofcommunicationwhere the calling party wishes to involve multiple parties. In comparison to conference calling, all parties involved in a call always have the opportunity to participate actively. Alternatively, group calling also functions as a means of leaving voice message to defined groups. The calling initiator calls a number that identifies the caller and inquires the caller as to which of the caller's defined groups the voice message should be sent to. Many US-based group calls now take place using free conference calling services.
1.3Social groups, Clubs and Teams
1.4Prayer groups and Support groups
Group calling offers, as an implication of its functionality, alternative opportunities and new settings for group communication. The concept of group-calling, moves conference calling to a more social and flexible means ofinteraction.
When preparing for an event, such as a party, reunion, or meeting, all of those involved are called at any one time to spread the necessary information or come to an agreement and make decisions together.
A significant amount of coursework is completed in groups. A common problem is having the time and place to assemble the entire group for the purpose of working together. With the concept of group calling, group members need not be together at all times for group work. Agreements upon complicated decisions related to the direction of the assignment are made in a group-call, with all active group members taking part in the conversation actively.
Social groups, Clubs and Teams
Communication in groups is often utilized for the purpose of spreading an important message or agreeing upon decisions that need to be made together. The group-calling concept is applied to groups with the need to involve all or most members at a specific point in time.
Prayer groups and Support groups
Group calling is an alternative to getting together in cases where the need for communication is sudden or more frequent. This calling method is commonly used for groups that wish to communicate together spontaneously, or on a daily basis without having to meet personally, as it is a quick and mobile alternative.
Similar to conference calling, group calling is used in business situations where decisions must be made and the necessary people are not all in one place due to either geographical dispersion or flexible work hours.