Telecommunications

Source: Wikipedia, the free encyclopedia.
(Redirected from
Electronic communications
)

"Telecommunication" redirects here. For the A Flock of Seagulls song, see Telecommunication (song).
Earth station at the satellite communication facility Raisting Earth Station in Raisting, Bavaria
, Germany

Telecommunication, often used in its plural form, is the transmission of information with an immediacy comparable to face-to-face communication. As such, slow communications technologies like

coded drumbeats, the blowing of horns, and whistles. Long-distance technologies invented during the 20th and 21st centuries generally use electric power, and include the telegraph, telephone
, television, and radio.

Early telecommunication networks used metal wires as the medium for transmitting signals. These networks were used for

Edwin Armstrong and Lee de Forest, as well as inventors of television like Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth
.

Since the 1960s, the proliferation of digital technologies has meant that voice communications have gradually been supplemented by data. The physical limitations of metallic media prompted the development of optical fibre.[3][4][5] The Internet, a technology independent of any given medium, has provided global access to services for individual users and further reduced location and time limitations on communications.

Etymology

Telecommunication is a compound noun of the Greek prefix tele- (τῆλε), meaning distant, far off, or afar,[6] and the Latin verb communicare, meaning to share. Its modern use is adapted from the French,[7] because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié.[8][9] Communication was first used as an English word in the late 14th century. It comes from Old French comunicacion (14c., Modern French communication), from Latin communicationem (nominative communication), noun of action from past participle stem of communicare, "to share, divide out; communicate, impart, inform; join, unite, participate in," literally, "to make common", from communis".[10]

History

Further information: History of telecommunication

At the 1932 Plenipotentiary Telegraph Conference and the International Radiotelegraph Conference in Madrid, the two organizations merged to form the International Telecommunication Union (ITU).[11] They defined telecommunication as "any telegraphic or telephonic communication of signs, signals, writing, facsimiles and sounds of any kind, by wire, wireless or other systems or processes of electric signaling or visual signaling (semaphores)."

The definition was later reconfirmed, according to Article 1.3 of the

electromagnetic
systems".

Beacons and pigeons

semaphore towers

Persian roots and was later used by the Romans to aid their military. Frontinus claimed Julius Caesar used pigeons as messengers in his conquest of Gaul.[12]
The
Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed.[14]

In the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London.[15]

In 1792,

semaphore line) between Lille and Paris.[16] However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres (six to nineteen miles). As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880.[17]

Telegraph and telephone

On July 25, 1837, the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke and English scientist Sir Charles Wheatstone.[18][19] Both inventors viewed their device as "an improvement to the [existing] electromagnetic telegraph" and not as a new device.[20]

Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on September 2, 1837. His code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was successfully completed on July 27, 1866, allowing transatlantic telecommunication for the first time.[21]

The conventional telephone was patented by

New Haven and London.[24][25]

Radio and television

In 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the then-newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean.[26] This was the start of wireless telegraphy by radio. On 17 December 1902, a transmission from the Marconi station in Glace Bay, Nova Scotia, Canada, became the world's first radio message to cross the Atlantic from North America. In 1904, a commercial service was established to transmit nightly news summaries to subscribing ships, which incorporated them into their onboard newspapers.[27]

World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated the development of radio for the wartime purposes of aircraft and land communication, radio navigation, and radar.[28] Development of stereo FM broadcasting of radio began in the 1930s in the United States and the 1940s in the United Kingdom,[29] displacing AM as the dominant commercial standard in the 1970s.[30]

On March 25, 1925,

cathode ray tube 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.[32] 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

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.[34]

In the 1940s, the invention of

solid-state 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,

industrial laboratories, such as the local area network (LAN) developments of Ethernet (1983), Token Ring (1984)[citation needed]and Star network
topology.

Growth of transmission capacity

The effective capacity to exchange information worldwide through two-way telecommunication networks grew from 281

exabytes (EB) in 2000 to 65 EB in 2007.[37] This is the informational equivalent of two newspaper pages per person per day in 1986, and six entire newspapers per person per day by 2007.[38] Given this growth, telecommunications play an increasingly important role in the world economy and the global telecommunications industry was about a $4.7 trillion sector in 2012.[39][40] The service revenue of the global telecommunications industry was estimated to be $1.5 trillion in 2010, corresponding to 2.4% of the world's gross domestic product (GDP).[39]

Technical concepts

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
    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

power amplifier is the transmitter and the broadcasting antenna is the interface between the power amplifier and the free space channel. The free space channel is the transmission medium and the receiver's antenna is the interface between the free space channel and the receiver. Next, the radio receiver
is the destination of the radio signal, where it is converted from electricity to sound.

Telecommunication systems are occasionally

nanowatts
. Hence, transceivers have to be carefully designed and built to isolate their high-power circuitry and their low-power circuitry from each other to avoid interference.

Telecommunication over fixed lines is called

point-to-point communication because it occurs between a transmitter and a receiver. Telecommunication through radio broadcasts is called broadcast communication because it occurs between a powerful transmitter and numerous low-power but sensitive radio receivers.[41]

Telecommunications in which multiple transmitters and multiple receivers have been designed to cooperate and share the same physical channel are called multiplex systems. The sharing of physical channels using multiplexing often results in significant cost reduction. Multiplexed systems are laid out in telecommunication networks and multiplexed signals are switched at nodes through to the correct destination terminal receiver.

Analogue versus digital communications

Communications signals can be sent by

additive noise
, with the understanding that the noise can be negative or positive at different instances.

Unless the additive noise disturbance exceeds a certain threshold, the information contained in digital signals will remain intact. Their resistance to noise represents a key advantage of digital signals over analogue signals. However, digital systems

quantization noise
to the output. This can be reduced, but not eliminated, only at the expense of increasing the channel bandwidth requirement.

Communication channels

Main article: Communication channel

The term "channel" has two different meanings. In one meaning, a channel is the physical medium that carries a signal between the transmitter and the receiver. Examples of this include the

ultraviolet light, and radio waves. Coaxial cable types are classified by RG type or "radio guide", terminology derived from World War II. The various RG designations are used to classify the specific signal transmission applications.[43] This last channel is called the "free space channel". The sending of radio waves from one place to another has nothing to do with the presence or absence of an atmosphere between the two. Radio waves travel through a perfect vacuum
just as easily as they travel through air, fog, clouds, or any other kind of gas.

The other meaning of the term "channel" in telecommunications is seen in the phrase

kHz (kilohertz), centred at frequencies such as the above, which are called the "carrier frequencies"
. Each station in this example is separated from its adjacent stations by 200 kHz, and the difference between 200 kHz and 180 kHz (20 kHz) is an engineering allowance for the imperfections in the communication system.

In the example above, the "free space channel" has been divided into communications channels according to frequencies, and each channel is assigned a separate frequency bandwidth in which to broadcast radio waves. This system of dividing the medium into channels according to frequency is called "frequency-division multiplexing". Another term for the same concept is "wavelength-division multiplexing", which is more commonly used in optical communications when multiple transmitters share the same physical medium.

Another way of dividing a communications medium into channels is to allocate each sender a recurring segment of time (a "time slot", for example, 20

milliseconds out of each second), and to allow each sender to send messages only within its own time slot. This method of dividing the medium into communication channels is called "time-division multiplexing
" (TDM), and is used in optical fibre communication. Some radio communication systems use TDM within an allocated FDM channel. Hence, these systems use a hybrid of TDM and FDM.

Modulation

Main article: Modulation

The shaping of a signal to convey information is known as modulation. Modulation can be used to represent a digital message as an analogue waveform. This is commonly called "keying"—a term derived from the older use of Morse Code in telecommunications—and several keying techniques exist (these include phase-shift keying, frequency-shift keying, and amplitude-shift keying). The "Bluetooth" system, for example, uses phase-shift keying to exchange information between various devices.[44][45] In addition, there are combinations of phase-shift keying and amplitude-shift keying which is called (in the jargon of the field) "quadrature amplitude modulation" (QAM) that are used in high-capacity digital radio communication systems.

Modulation can also be used to transmit the information of low-frequency analogue signals at higher frequencies. This is helpful because low-frequency analogue signals cannot be effectively transmitted over free space. Hence the information from a low-frequency analogue signal must be impressed into a higher-frequency signal (known as the "carrier wave") before transmission. There are several different modulation schemes available to achieve this [two of the most basic being amplitude modulation (AM) and frequency modulation (FM)]. An example of this process is a disc jockey's voice being impressed into a 96 MHz carrier wave using frequency modulation (the voice would then be received on a radio as the channel "96 FM").[46] In addition, modulation has the advantage that it may use frequency division multiplexing (FDM).

Telecommunication networks

Main article: Telecommunications network

A telecommunications network is a collection of transmitters, receivers, and

switches that establish a connection between two or more users. For both types of networks, repeaters may be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combat attenuation that can render the signal indistinguishable from the noise.[47]
Another advantage of digital systems over analogue is that their output is easier to store in memory, i.e., two voltage states (high and low) are easier to store than a continuous range of states.

Societal impact

Telecommunication has a significant social, cultural and economic impact on modern society. In 2008, estimates placed the

telecommunication industry's revenue at US$4.7 trillion or just under three per cent of the gross world product (official exchange rate).[39]
Several following sections discuss the impact of telecommunication on society.

Microeconomics

On the

Amazon.com but, according to academic Edward Lenert, even the conventional retailer Walmart has benefited from better telecommunication infrastructure compared to its competitors.[48] In cities throughout the world, home owners use their telephones to order and arrange a variety of home services ranging from pizza deliveries to electricians. Even relatively poor communities have been noted to use telecommunication to their advantage. In Bangladesh's Narsingdi District, isolated villagers use cellular phones to speak directly to wholesalers and arrange a better price for their goods. In Côte d'Ivoire, coffee growers share mobile phones to follow hourly variations in coffee prices and sell at the best price.[49]

Macroeconomics

On the macroeconomic scale, Lars-Hendrik Röller and Leonard Waverman suggested a causal link between good telecommunication infrastructure and economic growth.[50][51] Few dispute the existence of a correlation although some argue it is wrong to view the relationship as causal.[52]

Because of the economic benefits of good telecommunication infrastructure, there is increasing worry about the inequitable access to telecommunication services amongst various countries of the world—this is known as the digital divide. A 2003 survey by the International Telecommunication Union (ITU) revealed that roughly a third of countries have fewer than one mobile subscription for every 20 people and one-third of countries have fewer than one land-line telephone subscription for every 20 people. In terms of Internet access, roughly half of all countries have fewer than one out of 20 people with Internet access. From this information, as well as educational data, the ITU was able to compile an index that measures the overall ability of citizens to access and use information and communication technologies.[53] Using this measure, Sweden, Denmark and Iceland received the highest ranking while the African countries Niger, Burkina Faso and Mali received the lowest.[54]

Social impact

Telecommunication has played a significant role in social relationships. Nevertheless, devices like the telephone system were originally advertised with an emphasis on the practical dimensions of the device (such as the ability to conduct business or order home services) as opposed to the social dimensions. It was not until the late 1920s and 1930s that the social dimensions of the device became a prominent theme in telephone advertisements. New promotions started appealing to consumers' emotions, stressing the importance of social conversations and staying connected to family and friends.[55]

Since then the role that telecommunications has played in social relations has become increasingly important. In recent years,[

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 organising social engagements to courtship.[56]

Prior to social networking sites, technologies like

short message service (SMS) and the telephone also had a significant impact on social interactions. In 2000, market research group Ipsos MORI reported that 81% of 15- to 24-year-old SMS users in the United Kingdom had used the service to coordinate social arrangements and 42% to flirt.[57]

Entertainment, news, and advertising

News source preference of Americans in 2006.[58]
Local TV 59%
National TV 47%
Radio 44%
Local paper 38%
Internet 23%
National paper 12%
Survey permitted multiple answers

In cultural terms, telecommunication has increased the public's ability to access music and film. With television, people can watch films they have not seen before in their own home without having to travel to the video store or cinema. With radio and the Internet, people can listen to music they have not heard before without having to travel to the music store.

Telecommunication has also transformed the way people receive their news. A 2006 survey (right table) of slightly more than 3,000 Americans by the non-profit Pew Internet and American Life Project in the United States the majority specified television or radio over newspapers.

Telecommunication has had an equally significant impact on advertising.

TNS Media Intelligence reported that in 2007, 58% of advertising expenditure in the United States was spent on media that depend upon telecommunication.[59]

Advertising expenditures in US in 2007
Medium Spending
Internet 7.6% $11.31 billion
Radio 7.2% $10.69 billion
Cable TV 12.1% $18.02 billion
Syndicated TV 2.8% $4.17 billion
Spot TV 11.3% $16.82 billion
Network TV 17.1% $25.42 billion
Newspaper 18.9% $28.22 billion
Magazine 20.4% $30.33 billion
Outdoor 2.7% $4.02 billion
Total 100% $149 billion

Regulation

See also: List of telecommunications regulatory bodies

Many countries have enacted legislation which conforms to the International Telecommunication Regulations established by the International Telecommunication Union (ITU), which is the "leading UN agency for information and communication technology issues".[60] In 1947, at the Atlantic City Conference, the ITU decided to "afford international protection to all frequencies registered in a new international frequency list and used in conformity with the Radio Regulation". According to the ITU's Radio Regulations adopted in Atlantic City, all frequencies referenced in the International Frequency Registration Board, examined by the board and registered on the International Frequency List "shall have the right to international protection from harmful interference".[61]

From a global perspective, there have been political debates and legislation regarding the management of telecommunication and broadcasting. The history of broadcasting discusses some debates in relation to balancing conventional communication such as printing and telecommunication such as radio broadcasting.[62] The onset of World War II brought on the first explosion of international broadcasting propaganda.[62] Countries, their governments, insurgents, terrorists, and militiamen have all used telecommunication and broadcasting techniques to promote propaganda.[62][63] Patriotic propaganda for political movements and colonization started the mid-1930s. In 1936, the BBC broadcast propaganda to the Arab World to partly counter similar broadcasts from Italy, which also had colonial interests in North Africa.[62] Modern political debates in telecommunication include the reclassification of broadband Internet service as a telecommunications service (also called net neutrality),[64][65] regulation of phone spam,[66][67] and expanding affordable broadband access.[68]

Modern media

Worldwide equipment sales

According to data collected by Gartner[69][70] and Ars Technica[71] sales of main consumer's telecommunication equipment worldwide in millions of units was:

Equipment / year 1975 1980 1985 1990 1994 1996 1998 2000 2002 2004 2006 2008
Computers 0 1 8 20 40 75 100 135 130 175 230 280
Cell phones N/A N/A N/A N/A N/A N/A 180 400 420 660 830 1000

Telephone

Optical fibre
provides cheaper bandwidth for long-distance communication.

In a telephone network, the caller is connected to the person to whom they wish to talk by switches at various

telephone exchanges. The switches form an electrical connection between the two users and the setting of these switches is determined electronically when the caller dials the number. Once the connection is made, the caller's voice is transformed to an electrical signal using a small microphone in the caller's handset. This electrical signal is then sent through the network to the user at the other end where it is transformed back into sound by a small speaker
in that person's handset.

As of 2015[update], the landline telephones in most residential homes are analogue—that is, the speaker's voice directly determines the signal's voltage.[72] Although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting the signals to digital signals for transmission. The advantage of this is that digitized voice data can travel side by side with data from the Internet and can be perfectly reproduced in long-distance communication (as opposed to analogue signals that are inevitably impacted by noise).

Mobile phones have had a significant impact on telephone networks. Mobile phone subscriptions now outnumber fixed-line subscriptions in many markets. Sales of mobile phones in 2005 totalled 816.6 million with that figure being almost equally shared amongst the markets of Asia/Pacific (204 m), Western Europe (164 m), CEMEA (Central Europe, the Middle East and Africa) (153.5 m), North America (148 m) and Latin America (102 m).

W-CDMA with many markets choosing to deprecate analog systems such as AMPS.[75]

There have also been dramatic changes in telephone communication behind the scenes. Starting with the operation of

crosstalk which means several hundred of them can be easily bundled together in a single cable.[77] Lastly, improvements in multiplexing have led to an exponential growth in the data capacity of a single fibre.[78][79]

Assisting communication across many modern optical fibre networks is a protocol known as

data transmission mentioned in the second paragraph. It is suitable for public telephone networks because it establishes a pathway for data through the network and associates a traffic contract with that pathway. The traffic contract is essentially an agreement between the client and the network about how the network is to handle the data; if the network cannot meet the conditions of the traffic contract it does not accept the connection. This is important because telephone calls can negotiate a contract so as to guarantee themselves a constant bit rate, something that will ensure a caller's voice is not delayed in parts or cut off completely.[80] There are competitors to ATM, such as Multiprotocol Label Switching (MPLS), that perform a similar task and are expected to supplant ATM in the future.[81][82]

Radio and television

Main articles: Radio, Television, and Broadcasting
Digital television standards and their adoption worldwide

In a broadcast system, the central high-powered

demodulator is used to retrieve the signal containing the visual or audio information. The broadcast signal can be either analogue (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete values).[41][83]

The

forward error correction a receiver can correct a handful of bit errors in the resulting message but too much noise will lead to incomprehensible output and hence a breakdown of the transmission.[84][85]

In digital television broadcasting, there are three competing standards that are likely to be adopted worldwide. These are the

Eureka 147 standard). The exception is the United States which has chosen to adopt HD Radio. HD Radio, unlike Eureka 147, is based upon a transmission method known as in-band on-channel transmission that allows digital information to "piggyback" on normal AM or FM analog transmissions.[88]

However, despite the pending switch to digital, analog television remains being transmitted in most countries. An exception is the United States that ended analog television transmission (by all but the very low-power TV stations) on 12 June 2009

stereo FM, and quadrature amplitude modulation is used for stereo AM or C-QUAM
.

Internet

OSI reference model

The Internet is a worldwide network of computers and computer networks that communicate with each other using the Internet Protocol (IP).[91] Any computer on the Internet has a unique IP address that can be used by other computers to route information to it. Hence, any computer on the Internet can send a message to any other computer using its IP address. These messages carry with them the originating computer's IP address allowing for two-way communication. The Internet is thus an exchange of messages between computers.[92]

It is estimated that 51% of the information flowing through two-way telecommunications networks in the year 2000 were flowing through the Internet (most of the rest (42%) through the

broadband access, Iceland (26.7%), South Korea (25.4%) and the Netherlands (25.3%) led the world.[94]

The Internet works in part because of

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.[95]

For the Internet, the physical medium and data link protocol can vary several times as packets traverse the globe. This is because the Internet places no constraints on what physical medium or data link protocol is used. This leads to the adoption of media and protocols that best suit the local network situation. In practice, most intercontinental communication will use the Asynchronous Transfer Mode (ATM) protocol (or a modern equivalent) on top of optic fibre. This is because for most intercontinental communication the Internet shares the same infrastructure as the public switched telephone network.

At the network layer, things become standardized with the Internet Protocol (IP) being adopted for

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.[96]

At the transport layer, most communication adopts either the Transmission Control Protocol (TCP) or the

port numbers with them to specify what application or process the packet should be handled by.[97] Because certain application-level protocols use certain ports, network administrators can manipulate traffic to suit particular requirements. Examples are to restrict Internet access by blocking the traffic destined for a particular port or to affect the performance of certain applications by assigning priority
.

Above the transport layer, there are certain protocols that are sometimes used and loosely fit in the session and presentation layers, most notably the

BitTorrent (file sharing) and XMPP
(instant messaging).

synchronous voice communications. The data packets are marked as voice-type packets and can be prioritized by the network administrators so that the real-time, synchronous conversation is less subject to contention with other types of data traffic which can be delayed (i.e., file transfer or email) or buffered in advance (i.e., audio and video) without detriment. That prioritization is fine when the network has sufficient capacity for all the VoIP calls taking place at the same time and the network is enabled for prioritization, i.e., a private corporate-style network, but the Internet is not generally managed in this way and so there can be a big difference in the quality of VoIP calls over a private network and over the public Internet.[99]

Local area networks and wide area networks

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

TCP/IP existed at this point, but it was typically only used by large government and research facilities.[100]

As the Internet grew in popularity and its traffic was required to be routed into private networks, the TCP/IP protocols replaced existing local area network technologies. Additional technologies, such as

DHCP, allowed TCP/IP-based computers to self-configure in the network. Such functions also existed in the AppleTalk/ IPX/ NetBIOS protocol sets.[101]

Whereas Asynchronous Transfer Mode (ATM) or Multiprotocol Label Switching (MPLS) are typical data-link protocols for larger networks such as WANs; Ethernet and Token Ring are typical data-link protocols for LANs. These protocols differ from the former protocols in that they are simpler, e.g., they omit features such as quality of service guarantees, and offer medium access control. Both of these differences allow for more economical systems.[102]

Despite the modest popularity of Token Ring in the 1980s and 1990s, virtually all LANs now use either wired or wireless Ethernet facilities. At the physical layer, most wired Ethernet implementations use

10BASE-T networks). However, some early implementations used heavier coaxial cables and some recent implementations (especially high-speed ones) use optical fibres.[103] When optic fibres are used, the distinction must be made between multimode fibres and single-mode fibres. Multimode fibres can be thought of as thicker optical fibres that are cheaper to manufacture devices for, but that suffer from less usable bandwidth and worse attenuation—implying poorer long-distance performance.[104]

See also

References

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Bibliography

External links

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