Monday, June 3, 2019

Computer Networks And Wireless Transmissions

Computer Ne iirks And Wireless TransmissionsIn telecommunications, wireless communication may be use to transfer information everyplace improvident distances or long distance. The term is often shortened to wireless. it encompasses various types of fixed , mobile, cellular teleph hotshots etc. at present -a days people who need to be online all the time. For these mobile users, twisted pair, coax, and fiber optics be of no use. They need to get their hits of data for their laptop, notebooks, shirt sackful or wrist watch computers without being tethered to the terrestrial communication infrastructure. For these users, wireless communication is the answer.THE ELECTROMAGNETIC SPECTRUMWireless transmission can provide specific services and conveniences to people, much(prenominal) as connection to the internet or other networks without connecting to wire directly. It can also facilitate the creation of networks in limited situations, such as terrain that is unfri completionly to ground cables. Wireless communication began, in fact, in the Hawaiian island precisely the problem of terrain separated by large stretched of ocean. governmental organizations determine which sections of the spectrum of light ar all to which wireless transmission purpose. Because the existing organizations are always in agreement with current practice or with individually other, approximately products manufactured for one country may not work in another.RADIO TRANSMISSIONRadio waves are easy to generate and are omnidirectional, but have low transmission rates. Also, dep displaceing on their frequency, radio waves either cannot run low very far, or are absorbed by the earth. In some cases, though, high frequency waves are reflected back to earth by the ionosphere. Ionosphere is a layer of the atmosphere.MICROWAVE TRANSMISSIONMicrowave transmission is popular for its ability to give-up the ghost in heterosexual person lines. A source can be directly focused on its destination w ithout interfering with neighboring transmissions. Because they travel in straight lines, though, the curvature of the earth can interrupt with the microwave transmitters. The solution to this is the addition of repeaters in between the source and destination to redirect the data path. Microwaves are used for long distance communication like cellular phones, garage door openers and so on..INFRARED AND MILLIMETER WAVESInfrared light is used for close- range communication, such as remote controls, because if does not pass through objects well up. This is also a plus because infrared communications in one room de not interfere with the infrared communications in another room. Infrared communication is more secure than other option, such as radio, but it cannot be used away(p) due to interference by the sun.LIGHTWAVE TRANSMISSIONLasers can be used for wireless communication. It is a relatively low cost way to connect two buildings LAN, but it has drawbacks. The laser is difficult to target on the destinations receiver because the beam is so small. Laser light also diffuses easily in poor atmospherical conditions like rain, fog and so on.TERMS OF WIRELESS TRANSMISSIONThe theoretical basis for data communicationTransmission mediaWireless transmissionThe telephone clayNarrowband ISDNBroadband ISDN and ATMTHE THEORETICAL BASIS FOR DATA COMMUNICATIONHarmonicsAn infinite series, such as a Fourier series, is just the addition of an infinite number of toll. all(prenominal) term is called a harmonic.BaudSignals are used to s difference data over a write. If we want to indicate a data change, there is a corresponding signal change on the wire. The upper limit possible number of signal changes per second is called the baud.Fourier SeriesA periodic function is one that repeats itself over time. Sine and cowickedness are periodic functions. Fourier proved that any reasonably behaved periodic function could be written as a sum of sine and cosine functions. This is importa nt because sine and cosine are easily represented and recreated. The Fourier series allows periodic signals to be sent over a wire.Voice-Grade LineA voice-grade line has certain restrictions that limits the maximum number of signal changes per second.Signal-To-Noise Ratio DecibelsA way to measure to measure the thermal hitch that is present on a wire.TRANSMISSION MEDIAHere more than ten terms are there so I am expiration to explain five termsMagnetic MediaMaterial on which to store data. It is used in diskettes and magnetic tape. Magnetic media is a common way to transport data quickly.Twisted pas de deuxThe oldest and still most common transmission medium. Two insulated copper wires. Twisting the wires reduces electrical interferences from nearby wires. It also counters the antenna effect caused by parallel wires.Head-EndIn a dual cable system, there are two cables which only transmit data in one direction each. At one end of the network, data is collection from one line for re- transmission on the line going the opposite direction. The end of the network responsible for the data collection and retransmission is called the head-end.SubsplitWhen two cables are not used, but there is need for simulation of dual cable system, bandwidth on a single cable can be split up, with one portion representing one cable, and the other portion representing the second cable. Splitting the frequencies so that the lower frequencies are used for one purpose and the higher for another is called a subsplit system.ModeCharacteristic of a light wave associated with the reflection of the wave through the silica fiber.WIRELESS TRANSMISSIONFrequency (F)Light and electricity travel in the form of waves. Waves are periodic in that they repeat themselves, so the frequency of a wave is just the number of times the wave repeats itself in one second.Hertz (Hz)The unit of measure of frequency. The name comes from the german physicist who first produced electromagnetic waves.Wavelength (Lam bda)Wavelength is the measure of the length of a wave that is it is used ti fix the distance between two consecutive maxima or minima.Speed Of Light (C)The speed that electromagnetic waves travel in a vacuum approximately 3*108 m/sec. electromagnetic waves do not travel as fast through a medium as they do through a vacuum. blossom SpectrumA pattern for EM transmission which is popular in the military for its ability to avoid jamming. The transmitter hops from frequency to frequency across a wide frequency band.THE TELEPHONE SYSTEMIn this there are more than ten terms so here I am going to explain six termsPublic Switched Telephone NetworkThe currently existing network used for telephone communication. It was designed specifically for voice, and is not well suited for use by computers for transmitting data to one another.End OfficeThe place to which your telephones lines connect to receive the telephone service. The distance from the telephone to the end office is usually small aro und 1 to 10km).Toll OfficesSwitching centers that connect several end offices.Tandem OfficesSimilar to the toll office, except it connects the end offices that are within the same local area.Toll Connecting TrunksThe hardware which connects the end office to the toll of offices.NARROWBAND ISDNIntegrated Services Digital Network fully digital, circuit switched telephone system that is designed to accommodate both voice and data services.Digital Bit PipeA bi-directional logical pipe which provide pass bits on from source to destination without concern about whether they are voice.NT1Device placed between the user and the nearest end office allows ISDN connection. sphere Old Telephone Exchange or NT2Device placed between the end user which can provide a variety of ISDN services.Narrowband ISDNISDN services on 64-kbps channels.BROADBAND ISDN AND ATMBroadband ISDNIt is more recent design for a digital network on which data can travel rates of 155Mbps. It is base on ATM technology.Perma nent Virtual CircuitsVirtual circuits that remains in place for extended periods of time.Switched Virtual CircuitsVirtual circuits that remains in place for short periods of time, typically related to the session time.Head-Of-Line BlockingIf a questionable cell tries to come into ATM switch, it will be stalled, effectively stalling the cells behind it unfairly. This is called head-of -line blocking. spectator SwitchTo solve the head-of-line blocking problem, queuing on the output side has been proposed. The knockout switch does just this, by stimulating a single output align by having several output queues that are activated on a round- robin type basis.FORMULAETHE THEORETICAL BASIS FOR DATA COMMUNICATIONBaud sayThe baud rate is NOT the same as the data rate. Baud tells how many signals are sent per second, but there are ways of encode more than one bit per signal change. AVOID getting this confused.Baud= number of signal changes/secondMaximum Data Rate Of A groove (Nyquists The orem)Max data rate=2 Hlog2 VH=bandwidth in HZV=discrete levelsThis verbal expression shows the maximum number of bits that can be sent per second on a data line with a bandwidth of H, is V bits are sent per signal. The max data rate should be in bits per second.Signal-To-Noise Ratio10log10(S/N)S=signal powerN=noise powerThis figure is used to quantify the quality of a line. It is not usually presented as a ratio, but instead it is given in the units decibels.Maximum Number of Bits Per Second (Shannons Result)Max number of bits per second=H log2 (1+(S/N))This formula shows the maximum achievable data rate on a noisy line. The difference between shannons result and Nyquists theorem is that Shannons result takes the noise on a line into consideration. The noise can drastically reduce a lines capacity to send data. It is measured in bits per second.TRANSMISSION MEDIAAttenuation10 log10 (transmitted power/ received power)Attenuation is a way to measure the amount of power lost in a sig nals strength from when it was sent to when it was received. Attenuation is measured in decibels.WIRELESS TRANSMISSIONThis formula is used to find the relationship between frequency, wavelength, and the speed of light.Lambda f=cLambda=wavelengthF=frequencyC=speed of lightTHE TELEPHONE SYSTEMThis formula is used to fine the bits per second.Bits per second= number of bits per signal change*

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