1.
Communication system
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The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in union. Telecommunications is a method of communication, a communications subsystem is a functional unit or operational assembly that is smaller than the larger assembly under consideration. An optical communication system is any form of telecommunication that uses light as the transmission medium, fiber-optic communication systems transmit information from one place to another by sending light through an optical fiber. The light forms a signal that is modulated to carry information. A radio communication system is composed of several communications subsystems that give exterior communications capabilities, power line communication systems operate by impressing a modulated carrier signal on power wires. Different types of powerline communications use different frequency bands, depending on the signal characteristics of the power wiring used. Since the power wiring system was intended for transmission of AC power. The propagation problem is a factor for each type of power line communications. Mail Gmail imo Snapchat Instagram A duplex communication system is a composed of two connected parties or devices which can communicate with one another in both directions. The term duplex is used when describing communication between two parties or devices, an Antenna is basically a small length of a qwert conductor that is used to radiate or receive electromagnetic waves. Several types of antenna are used in communication, examples of communications subsystems include the Defense Communications System. These systems are designed to integrate the cross-communication of messages between are variety of communication technologies. An Automatic call distributor is a system that automatically queues, assigns. This is used often in service, ordering by telephone. These types of sensors are called input transducers in modern analog, at the end of the circuit is an antenna, the point at which the signal is released as electromagnetic waves. A communication channel is simply referring to the medium by which a signal travels, there are two types of media by which electrical signals travel, i. e. guided and unguided. Guided media refers to any medium that can be directed from transmitter to receiver by means of connecting cables, in optical fiber communication, the medium is an optical fiber. Other guided media might include coaxial cables, telephone wire, twisted-pairs, the other type of media, unguided media, refers to any communication channel that creates space between the transmitter and receiver
2.
Point-to-point (telecommunications)
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In telecommunications, a point-to-point connection refers to a communications connection between two nodes or endpoints. An example is a call, in which one telephone is connected with one other. This is contrasted with a point-to-multipoint or broadcast connection, in which many nodes can receive information transmitted by one node, other examples of point-to-point communications links are leased lines, microwave relay links, and two way radio. Point-to-point is sometimes abbreviated as P2P and this usage of P2P is distinct from P2P referring to peer-to-peer for file sharing networks. A traditional point-to-point data link is a medium with exactly two endpoints and no data or packet formatting. The host computers at either end had to take responsibility for formatting the data transmitted between them. The connection between the computer and the medium was generally implemented through an RS-232 or similar interface. Computers in close proximity may be connected by wires directly between their interface cards, when connected at a distance, each endpoint would be fitted with a modem to convert analog telecommunications signals into a digital data stream. When the connection used a telecommunications provider, the connections were called a dedicated, leased, the ARPANET used leased lines to provide point-to-point data links between its packet-switching nodes, which were called Interface Message Processors. In, the term point-to-point telecommunications relates to fixed wireless communications for Internet or voice over IP via radio frequencies in the multi-gigahertz range. The Telecommunications Industry Associations engineering committees develop U. S. standards for point-to-point communications, online tools help users find if they have such line of sight. The telecommunications signal is typically bi-directional, either time division multiple access or channelized, in hubs and switches, a hub provides a point-to-multipoint circuit which divides the total bandwidth supplied by the hub among each connected client node. Within many switched telecommunications systems, it is possible to establish a permanent circuit, one example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. Nailing down a switched connection saves the cost of running a circuit between the two points. The resources in such a connection can be released when no longer needed, for example, a television circuit from a parade route back to the studio
3.
Telephone
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A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice and this instrument was further developed by many others. The telephone was the first device in history that people to talk directly with each other across large distances. Telephones rapidly became indispensable to businesses, government, and households, the essential elements of a telephone are a microphone to speak into and an earphone which reproduces the voice in a distant location. Until approximately the 1970s most telephones used a dial, which was superseded by the modern DTMF push-button dial. The receiver and transmitter are usually built into a handset which is held up to the ear, the dial may be located either on the handset, or on a base unit to which the handset is connected. The transmitter converts the sound waves to electrical signals which are sent through the network to the receiving phone. The receiving telephone converts the signals into audible sound in the receiver, telephones permit duplex communication, meaning they allow the people on both ends to talk simultaneously. The first telephones were connected to each other from one customers office or residence to another customers location. Being impractical beyond just a few customers, these systems were replaced by manually operated centrally located switchboards. For greater mobility, various systems were developed for transmission between mobile stations on ships and automobiles in the middle 20th century. Hand-held mobile phone]s was introduced for personal service starting in 1973, by the late 1970s several mobile telephone networks operated around the world. In 1983, the Advanced Mobile Phone System was launched, offering a standardized technology providing portability for users far beyond the residence or office. These analog cellular system evolved into digital networks with better security, greater capacity, better regional coverage, the public switched telephone network, with its hierarchical system of many switching centers, interconnects telephones around the world for communication with each other. With the standardized international numbering system, E.164, each line has an identifying telephone number. Although originally designed for voice communications, convergence has enabled most modern cell phones to have many additional capabilities. Since 1999, the trend for mobile phones is smartphones that integrate all mobile communication, a traditional landline telephone system, also known as plain old telephone service, commonly carries both control and audio signals on the same twisted pair of insulated wires, the telephone line. The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial, the ringer, or beeper, light or other device, alerts the user to incoming calls
4.
Walkie-talkie
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A walkie-talkie is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been credited to Donald L. Hings, radio engineer Alfred J. Gross. First used for infantry, similar designs were created for field artillery and tank units, typical walkie-talkies resemble a telephone handset, with a speaker built into one end and a microphone in the other and an antenna mounted on the top of the unit. They are held up to the face to talk, a walkie-talkie is a half-duplex communication device, multiple walkie-talkies use a single radio channel, and only one radio on the channel can transmit at a time, although any number can listen. The transceiver is normally in receive mode, when the user wants to talk he presses a button that turns off the receiver. The walkie-talkie was developed by the US military during World War 2, the first radio transceiver to be widely nicknamed Walkie-Talkie was the backpacked Motorola SCR-300, created by an engineering team in 1940 at the Galvin Manufacturing Company. The team consisted of Dan Noble, who conceived of the design using frequency modulation, Henryk Magnuski, who was the principal RF engineer, Marion Bond, Lloyd Morris, the first hand-held walkie-talkie was the AM SCR-536 transceiver also made by Motorola, named the Handie-Talkie. The terms are often confused today, but the original walkie-talkie referred to the back mounted model, both devices used vacuum tubes and were powered by high voltage dry cell batteries. Canadian inventor Donald Hings is also credited with the invention of the walkie-talkie and he called the system a packset, but it later became known as the walkie-talkie. In 2001, Hings was formally decorated for its significance to the war effort, Hings model C-58 Handy-Talkie was in military service by 1942, the result of a secret R&D effort that began in 1940. Following World War II, Raytheon developed the SCR-536s military replacement, the AN/PRC-6 circuit used 13 vacuum tubes, a second set of 13 tubes was supplied with the unit as running spares. The unit was set with one crystal which could be changed to a different frequency in the field by replacing the crystal. It used a 24 inch whip antenna, there was an optional handset H-33C/PT that could be connected to the AN/PRC-6 by a 5-foot cable. An adjustable strap was provided for carrying and support while operating, the AN/PRC-68 was first produced in 1976 by Magnavox, was issued to the Marines in the 1980s, and was adopted by the US Army as well. Public safety or commercial users generally refer to their handhelds simply as radios, surplus Motorola Handie Talkies found their way into the hands of ham radio operators immediately following World War II. Motorolas public safety radios of the 1950s and 1960s, were loaned or donated to ham groups as part of the Civil Defense program, to avoid trademark infringement, other manufacturers use designations such as Handheld Transceiver or Handie Transceiver for their products. Some cellular telephone networks offer a push-to-talk handset that allows operation over the cellular network. However, the provider must be accessible
5.
Push-to-talk
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For example, an air traffic controller usually talks on one radio frequency to all aircraft under his/her supervision. Those under the frequency can hear others transmissions while using procedure words such as over. In doing so, they are aware of others actions and intentions. Similar considerations apply to radio, the use of business band radios on construction sites. Citizens Band is another example of classic push-to-talk operation, the PTT switch is most commonly located on the radios handheld microphone, or for small hand-held radios, directly on the radio. For heavy radio users, a PTT foot switch may be used, less commonly, a separate hand-held PTT switch may be used. This type of switch was historically called a pressel, in situations where a user may be too busy to handle a talk switch, voice operated switches are sometimes employed. Some systems use PTT ID to identify the speaker, push-to-talk over cellular is a service option for a cellular phone network that enables subscribers to use their phones as walkie-talkies with unlimited range. A typical push-to-talk connection connects almost instantly, a significant advantage of PTT is the ability for a single person to reach an active talk group with a single button press, users need not make several telephone calls to coordinate with a group. Push-to-talk cellular calls similarly provide half-duplex communications — while one person transmits and this combines the operational advantages of PTT with the interference resistance and other virtues of mobile phones. Mobile push-to-talk services, offered directly some mobile carriers as well as independent companies, adds PTT functionality to smartphones, in addition to mobile handsets, some services also work on a laptop, desktop, and tablet computers. Recent development in PTT communications is the appearance of apps on smartphones, wireless carrier-grade PTT systems have adapted to and adopted the smartphone platform by providing downloadable apps that support their PTT systems across many mobile platforms. Over-the-top applications are not dependent on a carrier and nearly as fast as carrier implementations. Talk-IP, Twisted Pair, Wave, Zello, Talko, Orion Labs, and Voxer may offer similar services to carriers.0 –26 February 2008
6.
Simplex communication
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Simplex communication is a communication channel that sends information in one direction only. The International Telecommunication Union definition is a channel that operates in one direction at a time, but that may be reversible. A duplex communication channel requires two simplex channels operating in opposite directions, for example, in TV and radio broadcasting, information flows only from the transmitter site to multiple receivers. A pair of walkie-talkie two-way radios provide a circuit in the ITU sense, only one party at a time can talk. The transmission medium can carry information in one direction. The same definition for a radio channel was used by the National Fire Protection Association in 2002
7.
Broadcasting
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Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, all forms of communication were one-to-one, with the message intended for a single recipient. Over the air broadcasting is usually associated with radio and television, the receiving parties may include the general public or a relatively small subset, the point is that anyone with the appropriate receiving technology and equipment can receive the signal. The field of broadcasting includes both government-managed services such as radio, community radio and public television, and private commercial radio. The U. S. Code of Federal Regulations, title 47, part 97 defines broadcasting as transmissions intended for reception by the general public, private or two-way telecommunications transmissions do not qualify under this definition. For example, amateur and citizens band radio operators are not allowed to broadcast, as defined, transmitting and broadcasting are not the same. Transmissions using a wire or cable, like television, are also considered broadcasts. In the 2000s, transmissions of television and radio programs via streaming digital technology have increasingly been referred to as broadcasting as well, the earliest broadcasting consisted of sending telegraph signals over the airwaves, using Morse code, a system developed in the 1830s by Samuel F. B. Morse, physicist Joseph Henry and Alfred Vail and they developed an electrical telegraph system which sent pulses of electric current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, Morse therefore developed the forerunner to modern International Morse code. Audio broadcasting began experimentally in the first decade of the 20th century, by the early 1920s radio broadcasting became a household medium, at first on the AM band and later on FM. Television broadcasting started experimentally in the 1920s and became widespread after World War II, satellite broadcasting was initiated in the 1960s and moved into general industry usage in the 1970s, with DBS emerging in the 1980s. Originally all broadcasting was composed of signals using analog transmission techniques but in the 2000s. In general usage, broadcasting most frequently refers to the transmission of information, Analog audio vs. HD Radio Analog television vs.9 zettabytes. This is the equivalent of 55 newspapers per person per day in 1986. Historically, there have been several methods used for broadcasting electronic media audio and/or video to the public, Telephone broadcasting. Telephone broadcasting also grew to include telephone services for news and entertainment programming which were introduced in the 1890s. These telephone-based subscription services were the first examples of electrical/electronic broadcasting, Radio broadcasting, audio signals sent through the air as radio waves from a transmitter, picked up by an antenna and sent to a receiver
8.
Garage door opener
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A garage door opener is a motorized device that opens and closes garage doors. Most are controlled by switches on the wall, as well as by remote controls carried by the owner. The electric overhead garage door opener was invented by C. G, johnson in 1926 in Hartford City, Indiana. As in an elevator, the motor does not provide most of the power to move a heavy garage door. Instead, most of doors weight is offset by the springs attached to the door. In a typical design, torsion springs apply torque to a shaft, the electric opener provides only a small amount of force to control how far the door opens and closes. In most cases, the door opener also holds the door closed in place of a lock. The typical electric garage door opener consists of a unit that contains the electric motor. The power unit attaches to a track, a trolley connected to an arm that attaches to the top of the garage door slides back and forth on the track, thus opening and closing the garage door. The trolley is pulled along the track by a chain, belt, a quick-release mechanism is attached to the trolley to allow the garage door to be disconnected from the opener for manual operation during a power failure or in case of emergency. Limit switches on the unit control the distance the garage door opens. The entire assembly hangs above the garage door, the power unit hangs from the ceiling and is located towards the rear of the garage. The end of the track on the end of the power unit attaches to a header bracket that is attached to the header wall above the garage door. The power head is supported by punched angle iron. Recently another type of opener, known as the opener, has become more popular. This style of opener was used frequently on commercial doors but in recent years has been adapted for residential use and this style of opener consists of a motor that attaches to the side of the torsion rod and moves the door up and down by simply spinning the rod. These openers need a few extra components to function safely for residential use and these include a cable tension monitor, to detect when a cable is broken, and a separate locking mechanism to lock the door when it is fully closed. These have the advantage that they free up ceiling space that an ordinary opener and these also have the disadvantage that the door must have a torsion rod to attach the motor to
9.
Baby monitor
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A baby monitor, also known as a baby alarm, is a radio system used to remotely listen to sounds made by an infant. An audio monitor consists of a unit, equipped with a microphone. It transmits the sounds by radio waves to a unit with a speaker carried by, or near to. Some baby monitors provide two-way communication which allows the parent to speak back to the baby, some allow music to be played to the child. A monitor with a camera and receiver is often called a baby cam. One of the uses of baby monitors is to allow attendants to hear when an infant wakes. Although commonly used, there is no evidence that these monitors prevent SIDS, infants and young children can often be heard over a baby monitor in crib talk, in which they talk to themselves. This is a part of practising their language skills. The first baby monitor was the Radio Nurse in 1937, some baby monitors also use a video camera to show pictures on the receiver, either by plugging the receiver into a television or by including a portable LCD screen. This type of camera is often called a baby cam. Some baby cams can work at night with low light levels, most video baby monitors today have a night vision feature. Infrared LEDs attached on the front of the camera allow a user to see the baby in a dark room, video baby monitors that have night vision mode will switch to this mode automatically in the dark. Some advanced baby cams now work over Wi-Fi so parents can watch babies through their smartphone or computer, baby monitors continue to evolve and now also can utilize features such as night lights and built-in lullabies. These are not available in all monitors, some include temperature and movement monitoring devices to sit underneath a mattress or close to the baby within a cot. A baby movement monitor uses sensor pads placed under the mattress to detect movement. Baby monitors generally use wireless systems, but can also use wires or may operate over existing household wiring such as X10, wireless systems use radio frequencies that are designated by governments for unlicensed use. For example, in North America frequencies near 49 MHz,902 MHz or 2.4 GHz are available, digital audio wireless systems using DECT, are resistant to interference and have a range up to 300 m. Digital transmission such as Frequency-hopping spread spectrum provides a level of protection from casual interception, some wireless baby monitors support multiple cameras on one handheld monitor-receiver
10.
Wireless microphone
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A wireless microphone is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. The other audio equipment is connected to the unit by cable. There are many different standards, frequencies and transmission used to replace the microphones cable connection. They can transmit, for example, in radio waves using UHF or VHF frequencies, FM, AM, some low cost models use infrared light. Infrared microphones require a line of sight between the microphone and the receiver, while costlier radio frequency models do not. Some models operate on a fixed frequency, but the more advanced models operate on a user selectable frequency to avoid interference. Various individuals and organizations claim to be the inventors of the wireless microphone, from about 1945 there were schematics and hobbyist kits offered in Popular Science and Popular Mechanics for making a wireless microphone that would transmit the voice to a nearby radio. Moores affixed the wireless transmitter to the costume of the character Abanazar, Moores did not patent his idea, as he was illegally using the radio frequency 76 MHz. In 1972 Moores donated his 1947 prototype to the Science Museum in London, the transmitter was strapped to the umpires back. Macs brother was Harold M. McClelland, the chief architect of the U. S. Air Force. Shure Brothers claims that its Vagabond system from 1953 was the first wireless system for performers. Its field of coverage was a circle of approximately 700 square feet, in 1957, the German audio equipment manufacturer Sennheiser, at that time called Lab W, working with the German broadcaster Norddeutscher Rundfunk, exhibited a wireless microphone system. From 1958 the system was marketed through Telefunken under the name of Mikroport, the pocket-sized Mikroport incorporated a dynamic moving-coil cartridge microphone with a cardioid pickup pattern. It transmitted at 37 MHz with a range of 300 feet. The first recorded patent for a microphone was filed by Raymond A. His U. S. patent number 3134074 was granted in May 1964, two microphone types were made available for purchase in 1959, hand-held and lavalier. The main transmitter module was a device which weighed 7 ounces. The Federal Communications Commission granted Litke twelve frequencies at his approval hearing and it was first tested at the Olympic trials held at Stanford University in 1959
11.
Closed-circuit television
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Closed-circuit television, also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may point to point, point to multipoint. Videotelephony is seldom called CCTV but the use of video in distance education, Surveillance of the public using CCTV is common in many areas around the world. In recent years, the use of body worn video cameras has been introduced as a new form of surveillance, video surveillance has generated significant debate about balancing its use with individuals right to privacy even when in public. In industrial plants, CCTV equipment may be used to observe parts of a process from a control room. CCTV systems may operate continuously or only as required to monitor a particular event, a more advanced form of CCTV, utilizing digital video recorders, provides recording for possibly many years, with a variety of quality and performance options and extra features. More recently, decentralized IP cameras, some equipped with sensors, support recording directly to network-attached storage devices. There are about 350 million surveillance cameras worldwide as of 2016, about 65% of these cameras are installed in Asia. The growth of CCTV has been slowing in recent years, the first CCTV system was installed by Siemens AG at Test Stand VII in Peenemünde, Nazi Germany in 1942, for observing the launch of V-2 rockets. The noted German engineer Walter Bruch, Wayne Cox, and Tashara Arnold were responsible for the technological design, in the U. S. the first commercial closed-circuit television system became available in 1949, called Vericon. Very little is known about Vericon except it was advertised as not requiring a government permit, marie Van Brittan Brown invented the home security system. The patent was granted in 1969, browns system had a set of 4 peep-holes and a camera that could slide up and down to look through each one. The system included a device that enabled a homeowner to use a set to view the person at the door. The earliest video surveillance systems involved constant monitoring because there was no way to record, the development of reel-to-reel media enabled the recording of surveillance footage. Due to these shortcomings, video surveillance was not widespread, VCR technology became available in the 1970s, making it easier to record and erase information, and use of video surveillance became more common. During the 1990s, digital multiplexing was developed, allowing cameras to record at once, as well as time lapse. This increased savings of time and money and the led to an increase in the use of CCTV, recently CCTV technology has been enhanced with a shift toward Internet-based products and systems, and other technological developments. In September 1968, Olean, New York was the first city in the United States to install video cameras along its main street in an effort to fight crime
12.
Bandwidth (signal processing)
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Bandwidth is the difference between the upper and lower frequencies in a continuous set of frequencies. It is typically measured in hertz, and may refer to passband bandwidth, sometimes to baseband bandwidth. Passband bandwidth is the difference between the upper and lower frequencies of, for example, a band-pass filter, a communication channel. In the case of a filter or baseband signal, the bandwidth is equal to its upper cutoff frequency. A key characteristic of bandwidth is that any band of a given width can carry the amount of information. For example, a 3 kHz band can carry a telephone conversation whether that band is at baseband or modulated to some higher frequency, Bandwidth is a key concept in many telecommunications applications. In radio communications, for example, bandwidth is the range occupied by a modulated carrier signal. An FM radio receivers tuner spans a range of frequencies. A government agency may apportion the regionally available bandwidth to broadcast license holders so that their signals do not mutually interfere, each transmitter owns a slice of bandwidth. For different applications there are different precise definitions, which are different for signals than for systems. One definition of bandwidth, for a system, could be the range of frequencies over which the system produces a level of performance. A less strict and more practically useful definition will refer to the frequencies beyond which frequency response is small, small could mean less than 3 dB below the maximum value, or more rarely 10 dB below, or it could mean below a certain absolute value. As with any definition of the width of a function, many definitions are suitable for different purposes, in some contexts, the signal bandwidth in hertz refers to the frequency range in which the signals spectral density is nonzero or above a small threshold value. That definition is used in calculations of the lowest sampling rate that will satisfy the sampling theorem, the threshold value is often defined relative to the maximum value, and is most commonly the 3dB point, that is the point where the spectral density is half its maximum value. The word bandwidth applies to signals as described above, but it could apply to systems. To say that a system has a certain bandwidth means that the system can process signals of that bandwidth, or that the system reduces the bandwidth of a white noise input to that bandwidth. If the maximum gain is 0 dB, the 3 dB bandwidth is the range where the gain is more than −3 dB. This is also the range of frequencies where the gain is above 70. 7% of the maximum amplitude gain
13.
Communication channel
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A channel is used to convey an information signal, for example a digital bit stream, from one or several senders to one or several receivers. A channel has a capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second. Communicating data from one location to another requires some form of pathway or medium and these pathways, called communication channels, use two types of media, cable and broadcast. Cable or wire line media use physical wires of cables to transmit data, twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass. In information theory, a channel refers to a theoretical channel model with certain error characteristics, in this more general view, a storage device is also a kind of channel, which can be sent to and received from. Examples of communications include, A connection between initiating and terminating nodes of a circuit. A single path provided by a transmission medium via either physical separation, such as by multipair cable or electrical separation, a path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths. A storage which can communicate a message over time as well as space The portion of a medium, such as a track or band. A buffer from which messages can be put and got, see Actor model and process calculi for discussion on the use of channels. In a communications system, the physical or logical link that connects a data source to a data sink, a specific radio frequency, pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement. Examples, Marine VHF radio uses some 88 channels in the VHF band for two-way FM voice communication, Channel 16, for example, is 156.800 MHz. In the US, seven additional channels, WX1 - WX7, are allocated for weather broadcasts, television channels such as North American TV Channel 2 =55.25 MHz, Channel 13 =211.25 MHz. Each channel is 6 MHz wide, besides these physical channels, television also has virtual channels. Wi-Fi consists of unlicensed channels 1-13 from 2412 MHz to 2484 MHz in 5 MHz steps, the radio channel between an amateur radio repeater and a ham uses two frequencies often 600 kHz apart. For example, a repeater that transmits on 146.94 MHz typically listens for a ham transmitting on 146.34 MHz, all of these communications channels share the property that they transfer information. The information is carried through the channel by a signal, a channel can be modelled physically by trying to calculate the physical processes which modify the transmitted signal. For example, in wireless communications the channel can be modelled by calculating the reflection off every object in the environment, a sequence of random numbers might also be added in to simulate external interference and/or electronic noise in the receiver. Statistical and physical modelling can be combined, for example, in wireless communications the channel is often modelled by a random attenuation of the transmitted signal, followed by additive noise
14.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
15.
Mobile phone
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A mobile phone is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area. The radio frequency link establishes a connection to the systems of a mobile phone operator. Most modern mobile telephone services use a network architecture, and, therefore. Mobile phones which offer these and more general computing capabilities are referred to as smartphones, the first handheld mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing c.4.4 lbs. In 1983, the DynaTAC 8000x was the first commercially available mobile phone. From 1983 to 2014, worldwide mobile phone subscriptions grew to seven billion, penetrating 100% of the global population. In first quarter of 2016, the top smartphone manufacturers were Samsung, Apple, a handheld mobile radio telephone service was envisioned in the early stages of radio engineering. In 1917, Finnish inventor Eric Tigerstedt filed a patent for a pocket-size folding telephone with a thin carbon microphone. Early predecessors of cellular phones included analog radio communications from ships, the race to create truly portable telephone devices began after World War II, with developments taking place in many countries. These 0G systems were not cellular, supported few simultaneous calls, the first handheld mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing c.4.4 lbs. The first commercial automated cellular network was launched in Japan by Nippon Telegraph and this was followed in 1981 by the simultaneous launch of the Nordic Mobile Telephone system in Denmark, Finland, Norway, and Sweden. Several other countries followed in the early to mid-1980s. These first-generation systems could support far more simultaneous calls but still used analog cellular technology, in 1983, the DynaTAC 8000x was the first commercially available handheld mobile phone. In 1991, the digital cellular technology was launched in Finland by Radiolinja on the GSM standard. This sparked competition in the sector as the new operators challenged the incumbent 1G network operators, ten years later, in 2001, the third generation was launched in Japan by NTT DoCoMo on the WCDMA standard. This was followed by 3. 5G, 3G+ or turbo 3G enhancements based on the high-speed packet access family, allowing UMTS networks to have data transfer speeds. By 2009, it had become clear that, at point, 3G networks would be overwhelmed by the growth of bandwidth-intensive applications. Consequently, the industry began looking to data-optimized fourth-generation technologies, with the promise of speed improvements up to ten-fold over existing 3G technologies
16.
Cordless telephone
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A cordless telephone or portable telephone is a telephone in which the handset is portable and communicates with the body of the phone by radio, instead of being attached by a cord. The base station is connected to the network through a telephone line as a corded telephone is. The range is limited, usually to the building or some short distance from the base station. The base station on subscriber premises is what differentiates a cordless telephone from a mobile telephone, in specialized models, base stations are maintained by a commercial mobile network operator and users subscribe to the service. In 1994, digital cordless phones in the 900 MHz frequency range were introduced, Digital signals allowed the phones to be more secure and decreased eavesdropping—it was relatively easy to eavesdrop on analog cordless phone conversations. In 1995, digital spread spectrum was introduced for cordless phones, unlike a corded telephone, a cordless telephone needs mains electricity to power the base station. The cordless handset is powered by a battery, which is charged when the handset is stored in its cradle. In 1968, she sold her rights to the phone to a manufacturer who modified it for practical use. Bell Labs Lineless Telephone 1963-1967 Beginning in 1963, a team of Bell Laboratories engineers were given the task of developing a practical. Clemency, M. Rosenthal, and W. Zinsmeister, under the direction of W. D. Goodale, by 1964, breadboard models were working in the lab. During 1964-65 these were refined and packaged to test around the Bell Labs Holmdel N. J. building, the system operated under an experimental license on crystal controlled channels in the 35 and 43 MHz bands using FM modulation, a low power transmitter and a sensitive superhet receiver. Full supervision of all functions, including on-off hook and dialing was provided via an out of band tone supervision system. The user end of the system was packaged to look like a telephone handset. The other end – the base station was a small box connected to the telephone network. About 50 units were built in a Western Electric model shop in Andover Mass. for field trails in two Bell System locations in the Boston and Phoenix area, the overall project was described in the Bell Laboratories Record, Volume 45, pages 202-203. He was awarded US3449750 in June 1969 He, sweigert was an active proponent for directly coupling consumer electronics to the AT&T-owned telephone lines in the late 1960s. The original cordless phones, like the Carterfone, were connected to the Public Switched Telephone Network. A single logic tone is transmitted and detected for all logical control for ring signals, on-hook and off-hook signals, in the United States, seven frequency bands have been allocated by the Federal Communications Commission for uses that include cordless phones
17.
Hybrid coil
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A hybrid coil is a transformer that has three windings, and which is designed to be configured as a circuit having four ports that are conjugate in pairs. A signal arriving at one port is divided equally between the two adjacent ports but does not appear at the opposite port, in the schematic diagram, the signal into W splits between X and Z, and no signal passes to Y. Similarly, signals into X split to W and Y with none to Z, correct operation requires matched characteristic impedance at all four ports. Hybrids are a class of directional coupler in which the input power is split equally between the two output ports. Forms of hybrid other than transfomer coils are possible, any format of directional coupler can be designed to be a hybrid and these formats include transmission lines and waveguides. The primary use of a hybrid coil is to convert between 2-wire and 4-wire operation in sequential sections of a communications circuit, for example in a four-wire terminating set. Such conversion was necessary when repeaters were introduced in a 2-wire circuit, without hybrids, the output of one amplifier feeds directly into the input of the other, resulting in a howling situation. By using hybrids, the outputs and inputs are isolated, resulting in correct 2-wire repeater operation, late in the century, this practice became rare but hybrids continued in use in line cards. Two versions of transformer hybrids were used, the transformer version providing unbalanced outputs with one end grounded. For use in 2-wire repeaters, the transformer version suffices. X, Y, and Z share a common ground, as shown at left, signal into W, the 2-wire port, will appear at X and Z. But since Y is bridged from center of coil to center of X and Z, signal into X will appear at W and Y. But signal at Z is the difference of what appears at Y and, through the coil, at W. Similar reasoning proves both pairs, W & Y, X & Z, are conjugates, when both the 2-wire and the 4-wire circuits must be balanced, double transformer hybrids are used, as shown at right. Signal into port W splits between X and Z, but due to reversed connection to the windings, cancel at port Y, signal into port X goes to W and Y. But due to reversed connection to ports W and Y, Z gets no signal, thus the pairs, W & Y, X & Z, are conjugates. Telephone hybrids are used in telephone exchanges to convert the 4-wire appearance to the 2-wire last mile connection to the subscribers telephone, a different kind of hybrid is used in telephone handsets to convert the four wires of the transmitter and receiver to the 2-wire line connection. This kind of hybrid is commonly called an induction coil due to its derivation from high-voltage induction coils
18.
Telephone hybrid
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A telephone hybrid is the component at the ends of a subscriber line of the public switched telephone network that converts between two-wire and four-wire forms of bidirectional audio paths. When used in broadcast facilities to enable the airing of telephone callers, the need for hybrids comes from the nature of analog plain old telephone service home or small business telephone lines, where the two audio directions are combined on a single two-wire pair. Within the telephone network, switching and transmission are almost always four-wire circuits with the two signals being separated, in older analog networks, conversion to four-wire was required so that repeater amplifiers could be inserted in long-distance links. In todays digital systems, each speech direction must be processed and transported independently, the line cards in a telephone central office switch that are interfaced to analog lines include hybrids that adapt the four-wire network to the two-wire circuits that connect most subscribers. The search for better telephone hybrids and echo cancelers was an important motive for the development of DSP algorithms and hardware at Bell Labs, NEC, the fundamental principle is that of impedance matching. The incoming signal is applied to both the line and a balancing network that is designed to have the same impedance as the line. The outgoing signal is derived by subtracting the two, thus canceling the incoming signal from the outgoing signal, early hybrids were made with transformers configured as hybrid coils that had an extra winding that could be connected out of phase. The name hybrid comes from these special mixed-winding transformers, an effective hybrid would have high trans-hybrid loss, which means that relatively little of the incoming audio would appear on the outgoing port. Too much leakage can cause echoes when there is a delay in the path, as there is with satellite, mobile phone. This is a result of a talkers voice traversing to the far-end hybrid, ITU-T Recommendation G.131 describes the relationship of echo delay vs. amplitude to listener annoyance. At 100ms,45 dB return loss is required for less than 1% of test subjects to express dissatisfaction, good cancellation depends upon the balancing network having a frequency-vs. -impedance characteristic that accurately matches the line. Since telephone line impedances vary depending upon many factors and the relationship is not always smooth and these may reach greater than 30 dB trans-hybrid loss, measured with white noise as the send signal. DSP hybrids are called line echo cancellers. Hybrids and cancellers are sometimes combined with echo suppressors and these work on the assumption that usually only one of the two parties to a conversation is speaking at a given time. The suppressor switches a loss into the inactive speech path, thus enhancing the effect of the hybrid at the expense of simultaneous two-way conversation. Despite being inherently four-wire, VoIP systems require hybrids when they interface to two-wire lines, a VoIP-to-Telco gateway used to interface a VoIP PBX to analog lines would contain hybrids to perform the required conversion. End-end VoIP needs no hybrids unless adaptation to a line is required. These devices often include processing in addition to the function, such as dynamics control, filtering
19.
Ethernet
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Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE802.3, over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a medium, while the newer Ethernet variants use twisted pair. Over the course of its history, Ethernet data transfer rates have increased from the original 2.94 megabits per second to the latest 100 gigabits per second. The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet, systems communicating over Ethernet divide a stream of data into shorter pieces called frames. As per the OSI model, Ethernet provides services up to, since its commercial release, Ethernet has retained a good degree of backward compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols, the primary alternative for some uses of contemporary LANs is Wi-Fi, a wireless protocol standardized as IEEE802.11. Ethernet was developed at Xerox PARC between 1973 and 1974 and it was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, in 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. Metcalfe left Xerox in June 1979 to form 3Com and he convinced Digital Equipment Corporation, Intel, and Xerox to work together to promote Ethernet as a standard. The so-called DIX standard, for Digital/Intel/Xerox, specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and it was published on September 30,1980 as The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications, version 2 was published in November,1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the time and resulted in the publication of IEEE802.3 on June 23,1983. Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus, in the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, an Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced for a time, with drivers for DOS, by the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was sped up with the introduction of 10BASE-T and its relatively small modular connector. Since then, Ethernet technology has evolved to meet new bandwidth, in addition to computers, Ethernet is now used to interconnect appliances and other personal devices
20.
Twisted pair
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It was invented by Alexander Graham Bell. In balanced pair operation, the two wires carry equal and opposite signals, and the destination detects the difference between the two and this is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields, the noise thus produces a common-mode signal which is canceled at the receiver when the difference signal is taken. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles, one pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged, providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges, the twist rate makes up part of the specification for a given type of cable. When nearby pairs have equal twist rates, the conductors of the different pairs may repeatedly lie next to each other. For this reason it is specified that, at least for cables containing small numbers of pairs. In contrast to shielded or foiled twisted pair, UTP cable is not surrounded by any shielding, UTP is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables. The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits, in the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, as electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, within a few years, the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles, in this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, such open-wire balanced lines with periodic transpositions still survive today in some rural areas. Twisted-pair cabling was invented by Alexander Graham Bell in 1881, by 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. UTP cables are found in many Ethernet networks and telephone systems, for indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T Corporation. A typical subset of these colors shows up in most UTP cables, for urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into small but identical bundles. Each bundle consists of twisted pairs that have different twist rates, the bundles are in turn twisted together to make up the cable
21.
Point-to-multipoint communication
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Point-to-multipoint is often abbreviated as P2MP, PTMP, or PMP. Point-to-multipoint telecommunications is most typically used in wireless Internet and IP telephony via gigahertz radio frequencies, P2MP systems have been designed both as single and bi-directional systems. A central antenna or antenna array broadcasts to several receiving antennas, Point to Multipoint is the most popular approach for wireless communications that have a large number of nodes, end destinations or end users. Point to Multipoint generally assumes there is a central Base Station to which remote Subscriber Units or Customer Premises Equipment, connections between the Base Station and Subscriber Units can be either Line of Sight or for lower-frequency radio systems Non-Line-of-Sight where link budgets permit. Generally, lower frequencies can offer non-Line-of Sight connections, various software planning tools can be used to determine feasibility of potential connections using topographic data as well as link budget simulation. Often the point to multipoint links are installed to reduce the cost of infrastructure and increase the number of CPEs, Point to Multipoint wireless networks employing directional antennas are affected by the hidden node problem in case they employ a CSMA/CA medium access control protocol. The negative impact of the hidden node problem can be mitigated using a TDMA based protocol or a polling protocol rather than the CSMA/CA protocol, the telecommunications signal in a Point to Multipoint system is typically bi-directional, either time division multiple access or channelized. Systems using Frequency Division Duplexing offer full duplex connections between base station and remote sites, and Time Division Duplex systems offer half duplex connections, Point to Multipoint systems can be implemented in Licensed, Semi-licensed or Unlicensed frequency bands depending on the specific application. The Base Station may have a single Omnidirectional antenna or multiple Sector Antennas which is used to increase both range and capacity. All-to-all communication Multipoint microwave distribution system Point-to-point Wireless Communications Wireless Access Point List of emerging technologies Backhaul
22.
Cellular network
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A cellular network or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called cells, each served by at least one fixed-location transceiver and this base station provides the cell with the network coverage which can be used for transmission of voice, data and others. A cell might use a different set of frequencies from neighboring cells, to avoid interference, when joined together these cells provide radio coverage over a wide geographic area. This allows mobile phones and mobile computing devices to be connected to the switched telephone network. Private cellular networks can be used for research or for large organizations and fleets, each of these cells is assigned with multiple frequencies which have corresponding radio base stations. The group of frequencies can be reused in other cells, provided that the frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference. If there is a single transmitter, only one transmission can be used on any given frequency. Unfortunately, there is some level of interference from the signal from the other cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a one cell gap between cells which reuse the same frequency, in the simple case of the taxi company, each radio had a manually operated channel selector knob to tune to different frequencies. As the drivers moved around, they would change from channel to channel, the drivers knew which frequency covered approximately what area. When they did not receive a signal from the transmitter, they would try other channels until they found one that worked, the taxi drivers would only speak one at a time, when invited by the base station operator. With TDMA, the transmitting and receiving time slots used by different users in each cell are different from each other, with FDMA, the transmitting and receiving frequencies used by different users in each cell are different from each other. In a simple system, the taxi driver manually tuned to a frequency of a chosen cell to obtain a strong signal. The principle of CDMA is more complex, but achieves the same result, time division multiple access is used in combination with either FDMA or CDMA in a number of systems to give multiple channels within the coverage area of a single cell. The key characteristic of a network is the ability to re-use frequencies to increase both coverage and capacity. The elements that determine frequency reuse are the distance and the reuse factor. The reuse distance, D is calculated as D = R3 N, cells may vary in radius from 1 to 30 kilometres. The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells, the frequency reuse factor is the rate at which the same frequency can be used in the network
23.
Time-division multiplexing
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It is used when the data rate of the transmission medium exceeds that of signal to be transmitted. Time-division multiplexing was first developed for applications in telegraphy to route multiple transmissions simultaneously over a transmission line. In the 1870s, Émile Baudot developed a system of multiple Hughes telegraph machines. The communication was by a microwave system throughout Long Island, the experimental TDM system was developed by RCA Laboratories between 1950 and 1953. In 1962, engineers from Bell Labs developed the first D1 channel banks, a channel bank sliced a 1.544 Mbit/s digital signal into 8,000 separate frames, each composed of 24 contiguous bytes. Each byte represented a single telephone call encoded into a constant bit rate signal of 64 kbit/s, channel banks used the fixed position of one byte in the frame to identify the call it belonged to. The time domain is divided into several recurrent time slots of fixed length, a sample byte or data block of sub-channel 1 is transmitted during time slot 1, sub-channel 2 during time slot 2, etc. One TDM frame consists of one time slot per sub-channel plus a synchronization channel and sometimes error correction channel before the synchronization. After the last sub-channel, error correction, and synchronization, the cycle all over again with a new frame, starting with the second sample, byte or data block from sub-channel 1. The Basic Rate Interface and Primary Rate Interface for the Integrated Services Digital Network, TDM allows transmitting and receiving telephone switches to create channels within a transmission stream. A standard DS0 voice signal has a bit rate of 64 kbit/s. A TDM circuit runs at a higher signal bandwidth, permitting the bandwidth to be divided into time frames for each voice signal which is multiplexed onto the line by the transmitter. If the TDM frame consists of n voice frames, the bandwidth is n*64 kbit/s. Each voice time slot in the TDM frame is called a channel, in European systems, standard TDM frames contain 30 digital voice channels, and in American systems, they contain 24 channels. Both standards also contain extra bits for signaling and synchronization bits, multiplexing more than 24 or 30 digital voice channels is called higher order multiplexing. Higher order multiplexing is accomplished by multiplexing the standard TDM frames, for example, a European 120 channel TDM frame is formed by multiplexing four standard 30 channel TDM frames. At each higher order multiplex, four TDM frames from the lower order are combined, creating multiplexes with a bandwidth of n*64 kbit/s. There are three types of synchronous TDM, T1, SONET/SDH, and ISDN, plesiochronous digital hierarchy was developed as a standard for multiplexing higher order frames
24.
Asymmetry
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Asymmetry is the absence of, or a violation of, symmetry. Symmetry is an important property of physical and abstract systems and it may be displayed in precise terms or in more aesthetic terms. The absence of or violation of symmetry that are expected or desired can have important consequences for a system. Due to how cells divide in organisms, asymmetry in organisms is fairly usual in at least one dimension, louis Pasteur proposed that biological molecules are asymmetric because the cosmic forces that preside over their formation are themselves asymmetric. While at his time, and even now, the symmetry of physical processes are highlighted, it is known there are fundamental physical asymmetries. Asymmetry is an important and widespread trait, having evolved numerous times in many organisms, in other examples, division of function between the right and left half may have been beneficial and has driven the asymmetry to become stronger. Such an explanation is given for mammal hand or paw preference. Training the neural pathways in a skill with one hand may take less effort than doing the same with both hands, nature also provides several examples of handedness in traits that are usually symmetric. The following are examples of animals with obvious left-right asymmetries, Fiddler crabs have one big claw, the narwhals tusk is a left incisor which can grow up to 10 feet in length and forms a left-handed helix. Flatfish have evolved to swim with one side upward, and as a result have both eyes on one side of their heads, several species of owls exhibit asymmetries in the size and positioning of their ears, which is thought to help locate prey. Many animals have asymmetric male genitalia, the evolutionary cause behind this is, in most cases, still a mystery. Certain disturbances during the development of the organism, resulting in birth defects, injuries after cell division that cannot be biologically repaired, such as a lost limb from an accident. Since birth defects and injuries are likely to indicate poor health of the organism, in particular, a degree of facial symmetry is associated with physical attractiveness, but complete symmetry is both impossible and probably unattractive. Pre-modern architectural styles tended to place an emphasis on symmetry, except where extreme conditions or historical developments lead away from this classical ideal. To the contrary, modernist and postmodern architects became more free to use asymmetry as a design element. Some asymmetrical structures There are no a and b such that a < b and b < a and this form of asymmetry is an asymmetrical relation. Certain molecules are chiral, that is, they cannot be superposed upon their mirror image, chemically identical molecules with different chirality are called enantiomers, this difference in orientation can lead to different properties in the way they react with biological systems. Asymmetry arises in physics in a number of different realms, the original non-statistical formulation of thermodynamics was asymmetrical in time, it claimed that the entropy in a closed system can only increase with time
25.
Beamforming
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Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity, the improvement compared with omnidirectional reception/transmission is known as the directivity of the element. Beamforming can be used for radio or sound waves and it has found numerous applications in radar, sonar, seismology, wireless communications, radio astronomy, acoustics and biomedicine. Adaptive beamforming is used to detect and estimate the signal-of-interest at the output of an array by means of optimal spatial filtering. When receiving, information from different sensors is combined in a way where the pattern of radiation is preferentially observed. The same thing can be carried out in air using loudspeakers, receive beamforming can also be used with microphones or radar antennas. With narrow-band systems the time delay is equivalent to a shift, so in this case the array of antennas. A narrow band system, typical of radars, is one where the bandwidth is only a fraction of the center frequency. With wide band systems this approximation no longer holds, which is typical in sonars, in the receive beamformer the signal from each antenna may be amplified by a different weight. Different weighting patterns can be used to achieve the desired sensitivity patterns, a main lobe is produced together with nulls and sidelobes. As well as controlling the main lobe width and the sidelobe levels and this is useful to ignore noise or jammers in one particular direction, while listening for events in other directions. A similar result can be obtained on transmission, for the full mathematics on directing beams using amplitude and phase shifts, see the mathematical section in phased array. This process may be carried out in either the time or the frequency domain, as the name indicates, an adaptive beamformer is able to automatically adapt its response to different situations. Some criterion has to be set up to allow the adaption to proceed such as minimizing the total noise output, because of the variation of noise with frequency, in wide band systems it may be desirable to carry out the process in the frequency domain. Sonar phased array has a data rate low enough that it can be processed in real-time in software, which is flexible enough to transmit or receive in several directions at once. In contrast, radar phased array has a rate so high that it usually requires dedicated hardware processing. However, newer field programmable gate arrays are fast enough to handle data in real-time
26.
UMTS
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The Universal Mobile Telecommunications System is a third generation mobile cellular system for networks based on the GSM standard. UMTS uses wideband code division multiple access radio access technology to offer greater spectral efficiency, UMTS specifies a complete network system, which includes the radio access network, the core network and the authentication of users via SIM cards. The technology described in UMTS is sometimes referred to as Freedom of Mobile Multimedia Access or 3GSM. Unlike EDGE and CDMA2000, UMTS requires new base stations and new frequency allocations, UMTS supports maximum theoretical data transfer rates of 42 Mbit/s when Evolved HSPA is implemented in the network. Users in deployed networks can expect a transfer rate of up to 384 kbit/s for Release 99 handsets, since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High-Speed Downlink Packet Access, sometimes known as 3. 5G. Currently, HSDPA enables downlink transfer speeds of up to 21 Mbit/s, work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access. The first national consumer UMTS networks launched in 2002 with a emphasis on telco-provided mobile applications such as mobile TV. UMTS combines three different terrestrial air interfaces, GSMs Mobile Application Part core, and the GSM family of speech codecs, the air interfaces are called UMTS Terrestrial Radio Access. All air interface options are part of ITUs IMT-2000, in the currently most popular variant for cellular mobile telephones, W-CDMA is used. Please note that the terms W-CDMA, TD-CDMA and TD-SCDMA are misleading, while they suggest covering just a channel access method, they are actually the common names for the whole air interface standards. W-CDMA or WCDMA, along with UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface found in 3G mobile telecommunications networks. W-CDMA uses the DS-CDMA channel access method with a pair of 5 MHz wide channels, in contrast, the competing CDMA2000 system uses one or more available 1.25 MHz channels for each direction of communication. W-CDMA systems are criticized for their large spectrum usage, which delayed deployment in countries that acted relatively slowly in allocating new frequencies specifically for 3G services. The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base, in the US, 1710–1755 MHz and 2110–2155 MHz are used instead, as the 1900 MHz band was already used. Some carriers such as T-Mobile use band numbers to identify the UMTS frequencies, in the late 1990s, W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network FOMA. Later NTT DoCoMo submitted the specification to the International Telecommunication Union as a candidate for the international 3G standard known as IMT-2000. The ITU eventually accepted W-CDMA as part of the IMT-2000 family of 3G standards, as an alternative to CDMA2000, EDGE, later, W-CDMA was selected as an air interface for UMTS. As NTT DoCoMo did not wait for the finalisation of the 3G Release 99 specification, however, this has been resolved by NTT DoCoMo updating their network
27.
LTE (telecommunication)
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In telecommunication, Long-Term Evolution is a standard for high-speed wireless communication for mobile phones and data terminals, based on the GSM/EDGE and UMTS/HSPA technologies. It increases the capacity and speed using a different radio interface together with core network improvements, the standard is developed by the 3GPP and is specified in its Release 8 document series, with minor enhancements described in Release 9. LTE is the path for carriers with both GSM/UMTS networks and CDMA2000 networks. The different LTE frequencies and bands used in different countries mean that only multi-band phones are able to use LTE in all countries where it is supported. LTE is commonly marketed as 4G LTE, but it does not meet the criteria of a 4G wireless service, as specified in the 3GPP Release 8 and 9 document series. The requirements were set forth by the ITU-R organization in the IMT Advanced specification. The LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced, to differentiate LTE Advanced and WiMAX-Advanced from current 4G technologies, ITU has defined them as True 4G. LTE stands for Long Term Evolution and is a trademark owned by ETSI for the wireless data communications technology. However, other nations and companies do play an role in the LTE project. The goal of LTE was to increase the capacity and speed of data networks using new DSP techniques. A further goal was the redesign and simplification of the architecture to an IP-based system with significantly reduced transfer latency compared to the 3G architecture. The LTE wireless interface is incompatible with 2G and 3G networks, LTE was first proposed by NTT DoCoMo of Japan in 2004, and studies on the new standard officially commenced in 2005. Initially, CDMA operators planned to upgrade to rival standards called UMB and WiMAX, the evolution of LTE is LTE Advanced, which was standardized in March 2011. Services are expected to commence in 2013, additional evolution known as LTE Advanced Pro have been approved in year 2015. The LTE specification provides downlink peak rates of 300 Mbit/s, uplink peak rates of 75 Mbit/s, LTE has the ability to manage fast-moving mobiles and supports multi-cast and broadcast streams. LTE supports scalable carrier bandwidths, from 1.4 MHz to 20 MHz, the simpler architecture results in lower operating costs. In 2004, NTT DoCoMo of Japan proposes LTE as the international standard, in September 2006, Siemens Networks showed in collaboration with Nomor Research the first live emulation of an LTE network to the media and investors. As live applications two users streaming an HDTV video in the downlink and playing a game in the uplink have been demonstrated
28.
4G
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4G is the fourth generation of wireless mobile telecommunications technology, succeeding 3G. A 4G system must provide capabilities defined by ITU in IMT Advanced, potential and current applications include amended mobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing, and 3D television. The first-release Long Term Evolution standard has been deployed in Oslo, Norway. It has, however, been debated whether first-release versions should be considered 4G, since the first-release versions of Mobile WiMAX and LTE support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers. According to operators, a generation of the network refers to the deployment of a new non-backward-compatible technology, as opposed to earlier generations, a 4G system does not support traditional circuit-switched telephony service, but all-Internet Protocol based communication such as IP telephony. The peak bit rate is improved by smart antenna arrays for multiple-input multiple-output communications. New mobile generations have appeared about ten years since the first move from 1981 analog to digital transmission in 1992. In the mid-1990s, the ITU-R standardization organization released the IMT-2000 requirements as a framework for what standards should be considered 3G systems, in 2008, ITU -R specified the IMT - Advanced requirements for 4G systems. In theory speeds up to 672 Mbit/s are possible, but have not been deployed yet, the fastest 3G-based standard in the CDMA2000 family is the EV-DO Rev. B, which is available since 2010 and offers 15.67 Mbit/s downstream. This article refers to 4G using IMT-Advanced, as defined by ITU-R, an IMT-Advanced cellular system must fulfill the following requirements, Be based on an all-IP packet switched network. Have peak data rates of up to approximately 100 Mbit/s for high mobility such as mobile access, be able to dynamically share and use the network resources to support more simultaneous users per cell. Use scaleable channel bandwidths of 5–20 MHz, optionally up to 40 MHz. Rumney, IMT-Advanced, 4G Wireless Takes Shape in an Olympic Year. Have peak link spectral efficiency of 15-bit/s/Hz in the downlink, and 6. 75-bit/s/Hz in the up link, system spectral efficiency is, in indoor cases, 3-bit/s/Hz/cell for downlink and 2. 25-bit/s/Hz/cell for up link. In September 2009, the proposals were submitted to the International Telecommunication Union as 4G candidates. Basically all proposals are based on two technologies, LTE Advanced standardized by the 3GPP802. The latters standard versions were ratified in spring 2011, but are far from being implemented. The first set of 3GPP requirements on LTE Advanced was approved in June 2008, LTE Advanced was to be standardized in 2010 as part of Release 10 of the 3GPP specification. LTE Advanced will be based on the existing LTE specification Release 10, a summary of the technologies that have been studied as the basis for LTE Advanced is included in a technical report
29.
3G
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3G, short for third generation, is the third generation of wireless mobile telecommunications technology. Later 3G releases, often denoted 3. 5G and 3. 75G, also mobile broadband access of several Mbit/s to smartphones. This ensures it can be applied to voice telephony, mobile Internet access, fixed wireless Internet access, video calls. A new generation of cellular standards has appeared approximately every year since 1G systems were introduced in 1981/1982. Each generation is characterized by new bands, higher data rates. The first 3G networks were introduced in 1998 and fourth generation 4G networks in 2008, several telecommunications companies market wireless mobile Internet services as 3G, indicating that the advertised service is provided over a 3G wireless network. Services advertised as 3G are required to meet IMT-2000 technical standards, including standards for reliability, to meet the IMT-2000 standards, a system is required to provide peak data rates of at least 200 kbit/s. However, many services advertised as 3G provide higher speed than the technical requirements for a 3G service. Recent 3G releases, often denoted 3. 5G and 3. 75G, also mobile broadband access of several Mbit/s to smartphones. The cell phones are typically UMTS and GSM hybrids, several radio interfaces are offered, sharing the same infrastructure, The original and most widespread radio interface is called W-CDMA. The TD-SCDMA radio interface was commercialized in 2009 and is offered in China. The latest UMTS release, HSPA+, can provide data rates up to 56 Mbit/s in the downlink in theory and 22 Mbit/s in the uplink. The CDMA2000 system, first offered in 2002, standardized by 3GPP2, used especially in North America and South Korea, the cell phones are typically CDMA2000 and IS-95 hybrids. The latest release EVDO Rev B offers peak rates of 14.7 Mbit/s downstream, the above systems and radio interfaces are based on spread spectrum radio transmission technology. It is based on the three times as efficient 8PSK modulation scheme as supplement to the original GMSK modulation scheme, EDGE is still used extensively due to its ease of upgrade from existing 2G GSM infrastructure and cell-phones. However, in practice EDGE is seldom marketed as a 3G system, EDGE was also a mode in the IS-136 TDMA system, today ceased. Evolved EDGE, the latest revision, has peaks of 1 Mbit/s downstream and 400 kbit/s upstream, the Universal Mobile Telecommunications System, created and revised by the 3GPP. The family is a revision from GSM in terms of encoding methods and hardware
30.
Digital Enhanced Cordless Telecommunications
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Digital Enhanced Cordless Telecommunications, usually known by the acronym DECT, is a standard primarily used for creating cordless telephone systems. It originated in Europe, where it is the standard, replacing earlier cordless phone standards, such as 900 MHz CT1. Beyond Europe, it has been adopted by Australia, and most countries in Asia, North American adoption was delayed by United States radio frequency regulations. This forced development of a variation of DECT, called DECT6.0, the technology is nearly identical, but the frequency difference makes the technology incompatible with systems in other areas, even from the same manufacturer. DECT has almost universally replaced other standards in most countries where it is used, DECT was originally intended for fast roaming between networked base stations and the first DECT product was Net3 wireless LAN. DECT can also be used for other than cordless phones, such as baby monitors. DECT ULE is a variant tailored for home security and automation, the DECT standard includes a common interoperability profile for simple telephone capabilities, called GAP, which most manufacturers implement. GAP-conformance enables DECT handsets and bases from different manufacturers to interoperate at the most basic level of functionality, New Generation DECT standard, marketed as CAT-iq by the DECT Forum, provides a common set of advanced capabilities for handsets and base stations. CAT-iq allows interchangeability across base stations and handsets from different manufacturers and it also requires mandatory support for wideband audio. The DECT standard was developed by ETSI in several phases, the first of that took place between 1988 and 1992 when the first round of standards were published. These were the ETS 300-175 series in 9 parts defining the air interface, a technical report, ETR-178, was also published to explain the standard. Subsequent standards were developed and published by ETSI to cover interoperability profiles, in 1995, due to its more global usage, the name was changed from European to Enhanced. DECT is recognized by the ITU as fulfilling the IMT-2000 requirements, within the IMT-2000 group of technologies, DECT is referred to as IMT-2000 Frequency Time. DECT was developed by ETSI but has since adopted by many countries all over the World. The original DECT frequency band is used in all countries in Europe, outside Europe, it is used in most of Asia, Australia and South America. S. New Generation DECT standard was first published in 2007, it was developed by ETSI with guidance from the Home Gateway Initiative through the DECT Forum, the ETSI TS102527 series come in 5 parts and cover wideband audio and mandatory interoperability features. DECT Ultra Low Energy standard was announced in January 2011 and the first commercial products were launched later that year by Dialog Semiconductor, the standard has been created to enable home automation, security, healthcare and energy monitoring applications that are battery powered. Like DECT, DECT ULE standard uses the 1.9 GHz band, and so suffers less interference than Zigbee, Bluetooth, Wi-Fi, from microwave ovens, which all operate in the ISM unlicensed 2.4 GHz band
31.
Packet switched
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Packet switching increases network efficiency and robustness, and enables technological convergence of many applications operating on the same network. Packets are composed of a header and payload, Information in the header is used by networking hardware to direct the packet to its destination where the payload is extracted and used by application software. This concept contrasted and contradicted then-established principles of pre-allocation of network bandwidth, the new concept found little resonance among network implementers until the independent work of British computer scientist Donald Davies at the National Physical Laboratory in the late 1960s. Packet mode communication may be implemented with or without intermediate forwarding nodes, in case of a shared physical medium, the packets may be delivered according to a multiple access scheme. In the late 1950s, the US Air Force established a wide area network for the Semi-Automatic Ground Environment radar defense system and they sought a system that might survive a nuclear attack to enable a response, thus diminishing the attractiveness of the first strike advantage by enemies. Report P-2626 described a general architecture for a large-scale, distributed, Barans work was known to Robert Taylor and J. C. R. Licklider at the Information Processing Technology Office, who advocated wide area networks, starting in 1965, Donald Davies at the National Physical Laboratory, UK, independently developed the same message routing methodology as developed by Baran. He called it packet switching, a more accessible name than Barans and he gave a talk on the proposal in 1966, after which a person from the Ministry of Defence told him about Barans work. A member of Davies team met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles, Davies had chosen some of the same parameters for his original network design as did Baran, such as a packet size of 1024 bits. In 1966, Davies proposed that a network should be built at the laboratory to serve the needs of NPL, the NPL Data Communications Network entered service in 1970. In 1974, Vint Cerf and Bob Kahn published the specifications for Transmission Control Protocol, Packet switching may be classified into connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. Examples of connectionless protocols are Ethernet, Internet Protocol, and the User Datagram Protocol, connection-oriented protocols include X.25, Frame Relay, Multiprotocol Label Switching, and the Transmission Control Protocol. In connectionless mode each packet includes complete addressing information, the packets are routed individually, sometimes resulting in different paths and out-of-order delivery. Each packet is labeled with an address, source address. It may also be labeled with the number of the packet. At the destination, the original message/data is reassembled in the correct order, connection-oriented transmission requires a setup phase in each involved node before any packet is transferred to establish the parameters of communication. The packets include a connection identifier rather than address information and are negotiated between endpoints so that they are delivered in order and with error checking, the signaling protocols used allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated, routing a packet requires the node to look up the connection id in a table
32.
Ethernet hub
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It has multiple input/output ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the layer of the OSI model. Repeater hubs also participate in collision detection, forwarding a jam signal to all if it detects a collision. In addition to standard 8P8C ports, some hubs may also come with a BNC or Attachment Unit Interface connector to allow connection to legacy 10BASE2 or 10BASE5 network segments, hubs are now largely obsolete, having been replaced by network switches except in very old installations or specialized applications. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE802.3, a network hub is an unsophisticated device in comparison with a switch. As a multiport repeater it works by repeating bits received from one of its ports to all other ports. It is aware of physical layer packets, that is it can detect their start, a hub cannot further examine or manage any of the traffic that comes through it, any packet entering any port is rebroadcast on all other ports. A hub/repeater has no memory to store any data in – a packet must be transmitted while it is received or is lost when a collision occurs, due to this, hubs can only run in half duplex mode. Consequently, due to a larger collision domain, packet collisions are frequent in networks connected using hubs than in networks connected using more sophisticated devices. The need for hosts to be able to detect collisions limits the number of hubs, for 10 Mbit/s networks built using repeater hubs, the 5-4-3 rule must be followed, up to five segments are allowed between any two end stations. For 10BASE-T networks, up to five segments and four repeaters are allowed between any two hosts, for 100 Mbit/s networks, the limit is reduced to 3 segments between any two end stations, and even that is only allowed if the hubs are of Class II. Most hubs detect typical problems, such as collisions and jabbering on individual ports. Thus, hub-based twisted-pair Ethernet is generally more robust than coaxial cable-based Ethernet, to pass data through the repeater in a usable fashion from one segment to the next, the framing and data rate must be the same on each segment. This means that a repeater cannot connect an 802.3 segment,100 Mbit/s hubs and repeaters come in two different speed grades, Class I delay the signal for a maximum of 140 bit times and Class II hubs delay the signal for a maximum of 92 bit times. In the early days of Fast Ethernet, Ethernet switches were relatively expensive devices, hubs suffered from the problem that if there were any 10BASE-T devices connected then the whole network needed to run at 10 Mbit/s. Therefore, a compromise between a hub and a switch was developed, known as a dual-speed hub and these devices make use of an internal two-port switch, bridging the 10 Mbit/s and 100 Mbit/s segments. When a network device becomes active on any of the physical ports and this obviated the need for an all-or-nothing migration to Fast Ethernet networks. These devices are considered hubs because the traffic between devices connected at the speed is not switched
33.
Wireless LAN
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This gives users the ability to move around within a local coverage area and yet still be connected to the network. A WLAN can also provide a connection to the wider Internet, most modern WLANs are based on IEEE802.11 standards and are marketed under the Wi-Fi brand name. Wireless LANs have become popular for use in the home, due to their ease of installation and they are also popular in commercial complexes that offer wireless access to their customers. Norman Abramson, a professor at the University of Hawaii, developed the worlds first wireless communication network, ALOHAnet. The system included seven computers deployed over four islands to communicate with the computer on the Oahu Island without using phone lines. Wireless LAN hardware initially cost so much that it was used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards, beginning in 1991, a European alternative known as HiperLAN/1 was pursued by the European Telecommunications Standards Institute with a first version approved in 1996. This was followed by a HiperLAN/2 functional specification with ATM influences accomplished February 2000, in 2009802. 11n was added to 802.11. It operates in both the 2.4 GHz and 5 GHz bands at a data transfer rate of 600 Mbit/s. Most newer routers are able to utilise both wireless bands, known as dualband and this allows data communications to avoid the crowded 2.4 GHz band, which is also shared with Bluetooth devices and microwave ovens. The 5 GHz band is wider than the 2.4 GHz band, with more channels. Not all channels are available in all regions, a HomeRF group formed in 1997 to promote a technology aimed for residential use, but it disbanded at the end of 2002. All components that can connect into a medium in a network are referred to as stations. All stations are equipped with wireless network interface controllers, Wireless stations fall into two categories, wireless access points, and clients. Access points, normally wireless routers, are base stations for the wireless network and they transmit and receive radio frequencies for wireless enabled devices to communicate with. The basic service set is a set of all stations that can communicate with other at PHY layer. Every BSS has an identification called the BSSID, which is the MAC address of the access point servicing the BSS, there are two types of BSS, Independent BSS, and infrastructure BSS. An independent BSS is an ad hoc network that contains no access points, an extended service set is a set of connected BSSs
34.
Bluetooth
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Bluetooth is a wireless technology standard for exchanging data over short distances from fixed and mobile devices, and building personal area networks. Invented by telecom vendor Ericsson in 1994, it was conceived as a wireless alternative to RS-232 data cables. It can connect up to seven devices, overcoming problems that older technologies had when attempting to connect to each other. Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 30,000 member companies in the areas of telecommunication, computing, networking, the IEEE standardized Bluetooth as IEEE802.15.1, but no longer maintains the standard. The Bluetooth SIG oversees development of the specification, manages the qualification program, a manufacturer must meet Bluetooth SIG standards to market it as a Bluetooth device. A network of patents apply to the technology, which are licensed to individual qualifying devices, the development of the short-link radio technology, later named Bluetooth, was initiated in 1989 by Nils Rydbeck, CTO at Ericsson Mobile in Lund, Sweden, and by Johan Ullman. The purpose was to develop wireless headsets, according to two inventions by Johan Ullman, SE 8902098-6, issued 1989-06-12 and SE9202239, issued 1992-07-24, Nils Rydbeck tasked Tord Wingren with specifying and Jaap Haartsen and Sven Mattisson with developing. Both were working for Ericsson in Lund, the specification is based on frequency-hopping spread spectrum technology. The idea of this name was proposed in 1997 by Jim Kardach who developed a system that would allow mobile phones to communicate with computers, at the time of this proposal he was reading Frans G. Bengtssons historical novel The Long Ships about Vikings and King Harald Bluetooth. The implication is that Bluetooth does the same with communications protocols, the Bluetooth logo is a bind rune merging the Younger Futhark runes and, Haralds initials. Bluetooth operates at frequencies between 2402 and 2480 MHz, or 2400 and 2483.5 MHz including guard bands 2 MHz wide at the end and 3.5 MHz wide at the top. This is in the globally unlicensed Industrial, Scientific and Medical 2.4 GHz short-range radio frequency band, Bluetooth uses a radio technology called frequency-hopping spread spectrum. Bluetooth divides transmitted data into packets, and transmits each packet on one of 79 designated Bluetooth channels, each channel has a bandwidth of 1 MHz. It usually performs 800 hops per second, with Adaptive Frequency-Hopping enabled, Bluetooth low energy uses 2 MHz spacing, which accommodates 40 channels. Originally, Gaussian frequency-shift keying modulation was the modulation scheme available. Since the introduction of Bluetooth 2. 0+EDR, π/4-DQPSK and 8DPSK modulation may also be used between compatible devices, devices functioning with GFSK are said to be operating in basic rate mode where an instantaneous data rate of 1 Mbit/s is possible. The term Enhanced Data Rate is used to describe π/4-DPSK and 8DPSK schemes, the combination of these modes in Bluetooth radio technology is classified as a BR/EDR radio. Bluetooth is a protocol with a master-slave structure
35.
IEEE 802.16
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IEEE802.16 is a series of wireless broadband standards written by the Institute of Electrical and Electronics Engineers. The IEEE Standards Board established a group in 1999 to develop standards for broadband for wireless metropolitan area networks. The Workgroup is a unit of the IEEE802 local area network, although the 802.16 family of standards is officially called WirelessMAN in IEEE, it has been commercialized under the name WiMAX by the WiMAX Forum industry alliance. The Forum promotes and certifies compatibility and interoperability of products based on the IEEE802.16 standards, the 802. 16e-2005 amendment version was announced as being deployed around the world in 2009. The version IEEE802. 16-2009 was amended by IEEE802. 16j-2009, projects publish draft and proposed standards with the letter P prefixed. Once a standard is ratified and published, that P gets dropped and replaced by a trailing dash, the 802.16 standard essentially standardizes two aspects of the air interface – the physical layer and the media access control layer. This section provides an overview of the employed in these two layers in the mobile 802. 16e specification. 802. 16e uses scalable OFDMA to carry data, supporting channel bandwidths of between 1.25 MHz and 20 MHz, with up to 2048 subcarriers, in intermediate conditions,16 QAM and QPSK can also be employed. Although the standards allow operation in any band from 2 to 66 GHz, mobile operation is best in the bands which are also the most crowded. Further features of the MAC layer include power saving mechanisms and handover mechanisms, a key feature of 802.16 is that it is a connection-oriented technology. The subscriber station cannot transmit data until it has allocated a channel by the base station. This allows 802. 16e to provide support for quality of service. Quality of service in 802. 16e is supported by allocating each connection between the SS and the BS to a specific QoS class. In 802. 16e, there are 5 QoS classes, The BS, because the IEEE only sets specifications but does not test equipment for compliance with them, the WiMAX Forum runs a certification program wherein members pay for certification. WiMAX certification by this group is intended to guarantee compliance with the standard, the mission of the Forum is to promote and certify compatibility and interoperability of broadband wireless products. WiBro WiMAX WiBAS WiMAX MIMO Wireless mesh network 4G LTE The IEEE802.16 Working Group on Broadband Wireless Access Standards, get IEEE802 official standards download
36.
WiMAX
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WiMAX is a family of wireless communication standards based on the IEEE802.16 set of standards, which provide multiple physical layer and Media Access Control options. The forum describes WiMAX as a standards-based technology enabling the delivery of last mile broadband access as an alternative to cable. IEEE802. 16m or WirelessMAN-Advanced was a candidate for the 4G, WiMAX was initially designed to provide 30 to 40 megabit-per-second data rates, with the 2011 update providing up to 1 Gbit/s for fixed stations. WiMAX refers to implementations of the IEEE802.16 family of wireless-networks standards ratified by the WiMAX Forum. The original IEEE802.16 standard was published in 2001, WiMAX adopted some of its technology from WiBro, a service marketed in Korea. Mobile WiMAX is the revision that was deployed in many countries, WiMAX is sometimes referred to as Wi-Fi on steroids and can be used for a number of applications including broadband connections, cellular backhaul, hotspots, etc. It is similar to Long-range Wi-Fi, but it can enable usage at much greater distances, the bandwidth and range of WiMAX make it suitable for the following potential applications, Providing portable mobile broadband connectivity across cities and countries through various devices. Providing a wireless alternative to cable and digital subscriber line for last mile broadband access, Providing data, telecommunications and IPTV services. Providing Internet connectivity as part of a continuity plan. Smart grids and metering WiMAX can provide at-home or mobile Internet access across whole cities or countries, in many cases this has resulted in competition in markets which typically only had access through an existing incumbent DSL operator. Additionally, given the low costs associated with the deployment of a WiMAX network. Mobile WiMAX was a replacement candidate for cellular phone technologies such as GSM and CDMA, fixed WiMAX is also considered as a wireless backhaul technology for 2G, 3G, and 4G networks in both developed and developing nations. In North America, backhaul for urban operations is provided via one or more copper wire line connections. In other regions, urban and rural backhaul is usually provided by microwave links, WiMAX has more substantial backhaul bandwidth requirements than legacy cellular applications. Consequently, the use of wireless microwave backhaul is on the rise in North America, capacities of between 34 Mbit/s and 1 Gbit/s are routinely being deployed with latencies in the order of 1 ms. In many cases, operators are aggregating sites using wireless technology, WiMAX in this application competes with microwave radio, E-line and simple extension of the fiber network itself. WiMAX directly supports the technologies that make triple-play service offerings possible and these are inherent to the WiMAX standard rather than being added on as Carrier Ethernet is to Ethernet. The new company hopes to benefit from combined services offerings and network resources as a springboard past its competitors, the cable companies will provide media services to other partners while gaining access to the wireless network as a Mobile virtual network operator to provide triple-play services
37.
PACTOR
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PACTOR is a radio modulation mode used by amateur radio operators, marine radio stations, and radio stations in isolated areas to send and receive digital information via radio. A robust network of PACTOR stations has been established to relay data between stations and the Internet, extending Internet access to sea based and other isolated users. PACTOR utilizes a combination of simple FSK modulation, and the ARQ protocol for robust error detection, generational improvements to PACTOR include PACTOR II, PACTOR III, and PACTOR IV which are capable of higher speed transmission. Pactor modes other than level 1 are not open source and therefore cannot be decoded by anyone who hasnt invested in a proprietary modem, PACTOR was developed by Special Communications Systems GmbH and released to the public in 1991. It was developed in order to improve the reception of data when the received signal was weak or noisy. PACTOR is an evolution of both AMTOR and packet radio, its name is a portmanteau of two technologies. PACTOR combines the bandwidth efficiency of packet radio with the error-correction, Amateur radio operators were instrumental in developing and implementing these digital modes. PACTOR is most commonly used on frequencies between 1 MHz and 30 MHz, PACTOR is a set of standardized modes used by Amateur and Marine radio operators for FSK radioteletype transfer of digital information over shortwave bands. PACTOR radio equipment consists of an HF transceiver, a computer, software running on the computer drives the terminal node controller. The most commonly used Amateur program for this purpose is Airmail, PACTOR is used by Amateur Bulletin Board operators to exchange public messages, and open conversations across the world. It is also used by the NTSD portion of the ARRLs National Traffic System to pass digital ARRL Radiograms, newer PACTOR modes are used to transfer large binary data files and Internet E-mail, particularly via the Winlink global E-mail system. The SailMail network transfers E-mail on behalf of Marine stations, HF data transmission by radio amateurs uses medium power over long distances. Effective radio-frequency communications over long distances over hostile radio paths require that special attention be paid to the rate at which data is repeated. To reduce the amount of data sent, on-line data compression is utilized, by combining these open technologies, PACTOR achieves a power efficiency much greater than that of older protocols such as packet, AMTOR, or RTTY. PACTOR has a very narrow waveform and occupies the same space as analog 300 baud packet. PACTOR utilizes very rapid Time-Division Duplexing, giving PACTOR communications its characteristic cricket-like chirping sound when listened through a single-sideband receiver. Depending on the version of PACTOR protocol used and the radio-frequency conditions, the ITU Emission Designators, Pactor I is 304HF1B. Cost is an important consideration when choosing PACTOR equipment, PACTOR I is open technology and modems can be purchased in the $50-$150 price range and are in ample supply
38.
G.fast
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G. fast is a digital subscriber line protocol standard for local loops shorter than 500 m, with performance targets between 150 Mbit/s and 1 Gbit/s, depending on loop length. High speeds are only achieved over very short loops, formal specifications have been drafted as ITU-T G.9700 and G.9701, with approval of G.9700 granted in April 2014 and approval of G.9701 granted on December 5,2014. Development was coordinated with the Broadband Forums FTTdp project, the name G. fast is an acronym for fast access to subscriber terminals, the letter G stands for the ITU-T G series of recommendations. Limited demonstration hardware was demonstrated in mid-2013, the first chipsets were introduced in October 2014, with commercial hardware introduced in 2015, and first deployments started in 2016. In G. fast, data is modulated using discrete multi-tone modulation, as in VDSL2, G. fast modulates up to 12 bit per DMT frequency carrier, reduced from 15 in VDSL2 for complexity reasons. The first version of G. fast will specify 106 MHz profiles, with 212 MHz profiles planned for future amendments, compared to 8.5,17.664, or 30 MHz profiles in VDSL2. This spectrum overlaps the FM broadcast band between 87.5 and 108 MHz, as well as military and government radio services. To enable co-existence with ADSL2 and the various VDSL2 profiles, the frequency can be set to 2.2,8.5,17.664, or 30 MHz. G. fast uses time-division duplexing, as opposed to ADSL2 and VDSL2, support for symmetry ratios between 90/10 and 50/50 is mandatory, 50/50 to 10/90 is optional. This optional discontinuous operation allows a trade-off between throughput and power consumption, the forward error correction scheme using trellis coding and Reed–Solomon coding is similar to that of VDSL2. FEC does not provide protection against impulse noise. To that end, the impulse noise protection data unit retransmission scheme specified for ADSL2, ADSL2+, to respond to abrupt changes in channel or noise conditions, fast rate adaptation enables rapid reconfiguration of the data rate. Performance in G. fast systems is limited to an extent by crosstalk between multiple wire pairs in a single cable. Self-FEXT cancellation, also called vectoring, is mandatory in G. fast, vectoring technology for VDSL2 was previously specified by the ITU-T in G.993.5, also called G. vector. The first version of G. fast will support a version of the linear precoding scheme found in G. vector. Since all current G. fast implementations are limited to 106 MHz, instead, current efforts to deliver a gigabit are focusing on bonding, power and more bits per hertz. On older, unshielded cable, aggregate data rates of 500 Mbit/s were achieved at 100 m, a A straight loop is a subscriber line without bridge taps. B The listed values are aggregate data rates, the Broadband Forum is investigating architectural aspects of G. fast and has, as of May 2014, identified 23 use cases
39.
Digital subscriber line
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Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line, DSL service can be delivered simultaneously with wired telephone service on the same telephone line. This is possible because DSL uses higher frequency bands for data, on the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency interference to enable simultaneous use of the voice and DSL services. Bit rates of 1 Gbit/s have been reached in trials, in ADSL, the data throughput in the upstream direction is lower, hence the designation of asymmetric service. In symmetric digital subscriber line services, the downstream and upstream data rates are equal, researchers at Bell Labs have reached speeds of 10 Gbit/s, while delivering 1 Gbit/s symmetrical broadband access services using traditional copper telephone lines. These higher speeds are lab results, however, a 2012 survey found that DSL continues to be the dominant technology for broadband access with 364.1 million subscribers worldwide. For a long time it was thought that it was not possible to operate a conventional phone-line beyond low-speed limits, in the 1950s, ordinary twisted-pair telephone-cable often carried four megahertz television signals between studios, suggesting that such lines would allow transmitting many megabits per second. One such circuit in the UK ran some ten miles between the BBC studios in Newcastle-upon-Tyne and the Pontop Pike transmitting station and it was able to give the studios a low quality cue feed but not one suitable for transmission. However, these cables had other impairments besides Gaussian noise, preventing such rates from becoming practical in the field, the 1980s saw the development of techniques for broadband communications that allowed the limit to be greatly extended. A patent was filed in 1979 for the use of existing telephone wires for both telephones and data terminals that were connected to a computer via a digital data carrier system. Joseph W. Lechleiders contribution to DSL was his insight that an asymmetric arrangement offered more than double the capacity of symmetric DSL. ADSL supports two modes of transport—fast channel and interleaved channel, fast channel is preferred for streaming multimedia, where an occasional dropped bit is acceptable, but lags are less so. Interleaved channel works better for file transfers, where the data must be error-free. Older ADSL standards delivered 8 Mbit/s to the customer over about 2 km of unshielded twisted-pair copper wire, distances greater than 2 km significantly reduce the bandwidth usable on the wires, thus reducing the data rate. But ADSL loop extenders increase these distances by repeating the signal, until the late 1990s, the cost of digital signal processors for DSL was prohibitive. All types of DSL employ highly complex digital signal processing algorithms to overcome the inherent limitations of the twisted pair wires. Due to the advancements of very-large-scale integration technology, the cost of the equipment associated with a DSL deployment lowered significantly, the two main pieces of equipment are a digital subscriber line access multiplexer at one end and a DSL modem at the other end. A DSL connection can be deployed over existing cable, such deployment, even including equipment, is much cheaper than installing a new, high-bandwidth fiber-optic cable over the same route and distance
40.
Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
41.
Radio receiver
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In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna, the antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The information produced by the receiver may be in the form of sound, a radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar form of radio receiver is a broadcast receiver, often just called a radio, the sound is produced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power, provided either by batteries inside the radio or a cord which plugs into an electric outlet. All radios have a control to adjust the loudness of the audio. The frequency of radio stations is usually listed prominently in their advertising, in order to select a particular station to receive, the radio is adjusted to the frequency of the desired transmitter. In some radios this is done by the user turning a tuning knob until the station is heard in the radios loudspeaker. In most countries radio broadcasting is permitted using two different methods of modulation, that is, methods of adding the signal to the radio wave, AM and FM. In amplitude modulation the strength of the signal is varied by the audio signal. AM broadcasting is permitted on AM broadcast bands between 148 and 283 kHz in the low range and 526 and 1706 kHz in the medium frequency range of the radio spectrum. In frequency modulation the frequency of the signal is varied slightly by the audio signal. FM broadcasting is permitted in the FM broadcast bands between about 65 and 108 MHz in the high frequency range. The exact frequency ranges vary somewhat in different countries, radios sold in each receive the correct frequency range for that country. Most broadcast radios, called AM/FM radios, can receive both AM and FM bands, and have a switch to select which band to receive. Limited AM broadcasting is permitted in parts of the high frequency band called the shortwave band. Shortwave listening requires a receiver that can receive these bands, called a shortwave receiver, at these frequencies, radio waves transmitted into the sky can reflect from a layer in the atmosphere called the ionosphere, returning to earth at transcontinental distances. So shortwaves are used for long distance international broadcasting, often by governmental public service broadcasting organizations like the BBC, due to their lower frequency, AM radio stations can often be received at longer distances than FM stations, at hundreds of miles
42.
Amateur radio
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The amateur radio service is established by the International Telecommunication Union through the International Telecommunication Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with a call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics, according to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are regularly involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 followed by IARU Region 3 with about 750,000 stations, a significantly smaller number, about 400,000, are located in IARU Region 1. The origins of amateur radio can be traced to the late 19th century, the First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains a list of amateur radio stations. This radio callbook lists wireless telegraph stations in Canada and the United States, as with radio in general, amateur radio was associated with various amateur experimenters and hobbyists. Amateur radio enthusiasts have significantly contributed to science, engineering, industry, research by amateur operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency. Ham radio can also be used in the classroom to teach English, map skills, geography, math, science, the term ham radio was first a pejorative that mocked amateur radio operators with a 19th-century term for being bad at something, like ham-fisted or ham actor. It had already used for bad wired telegraph operators. Subsequently, the community adopted it as a moniker, much like the Know-Nothing Party, or other groups. Other, more entertaining explanations have grown up throughout the years, the many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and then combine other personal interests to make pursuit of the hobby rewarding, some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, and computer networking. Amateur radio operators use various modes of transmission to communicate, the two most common modes for voice transmissions are frequency modulation and single sideband. FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. Radiotelegraphy using Morse code, also known as CW from continuous wave, is the extension of landline telegraphy developed by Samuel Morse. Morse, using internationally agreed message encodings such as the Q code, a similar legacy mode popular with home constructors is amplitude modulation, pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology. Demonstrating a proficiency in Morse code was for years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in regulations in 2003, countries are no longer required to demand proficiency
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Repeater
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In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover distances or be received on the other side of an obstruction. Some types of repeaters broadcast a signal, but alter its method of transmission, for example. A broadcast relay station is a used in broadcast radio. When an information-bearing signal passes through a channel, it is progressively degraded due to loss of power. The longer the wire is, the power is lost. So with a long enough wire the call will not be audible at the other end, similarly, the farther from a radio station a receiver is, the weaker the radio signal, and the poorer the reception. A repeater is a device in a communication channel that increases the power of a signal and retransmits it. Since it amplifies the signal, it requires a source of electric power, the term repeater originated with telegraphy in the 19th century, and referred to an electromechanical device used to regenerate telegraph signals. Use of the term has continued in telephony and data communications and this is used to increase the range of telephone signals in a telephone line. They are most frequently used in trunklines that carry long distance calls, since the telephone is a duplex communication system, the wire pair carries two audio signals, one going in each direction. So telephone repeaters have to be bilateral, amplifying the signal in both directions without causing feedback, which complicates their design considerably, telephone repeaters were the first type of repeater and were some of the first applications of amplification. The development of telephone repeaters between 1900 and 1915 made long distance phone service possible, however most telecommunications cables are now fiber optic cables which use optical repeaters. Submarine cable repeater This is a type of telephone used in underwater submarine telecommunications cables. This is used to increase the range of signals in a fiber optic cable, digital information travels through a fiber optic cable in the form of short pulses of light. The light is made up of particles called photons, which can be absorbed or scattered in the fiber, however, optical amplifiers are being developed for repeaters to amplify the light itself without the need of converting it to an electric signal first. Some repeaters have been powered by light energy transmitted down the fiber with the signal and this is used to extend the range of coverage of a radio signal. A radio repeater usually consists of a receiver connected to a radio transmitter
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Lag
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In online gaming, lag is a noticeable delay between the action of players and the reaction of the server in a video game. The tolerance for lag depends heavily on the type of game, however, the specific characteristics of the game matter. For example, fast chess is a game that is fast action. Also, some games can be designed such that only events that dont impact the outcome of the game introduce lag. As such, the client has no control over the central game state and may only send change requests to the server. This need to communicate causes a delay between the clients and the server, and is the cause behind lag. Hardware related issues cause lag due to the structure of the game architecture. Generally, games consist of a sequence of states, or frames. During each frame, the game accepts user input and performs necessary calculations, when all processing is finished, the game will update the game state and produce an output, such as a new image on the screen and/or a packet to be sent to the server. The frequency at which frames are generated is often referred to as the frame rate, as the central game state is located on the server, the updated information must be sent from the client to the server in order to take effect. In addition, the client must receive the information from the server in order to fully update the state. Generating packets to send to the server and processing the received packets can only be done as often as the client is able to update its local state. Although packets could theoretically be generated and sent faster than this, a low frame rate would therefore make the game less responsive to updates and may force it to skip outdated data. Conversely, the same true for the server. The frame rate of the server determines how often it can process data from clients and this type of problem is difficult to predict and compensate for. Apart from enforcing minimum hardware requirements and attempting to optimize the game for better performance, perhaps the most common type of lag is caused by network performance problems. Losses, corruption or jitter may all cause problems, but these problems are rare in a network with sufficient bandwidth. Instead, the involved in transmitting data between clients and server plays a significant role
