7502ICT advanced networking technology

Added on - 08 Nov 2019

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ADVANCED NETWORKINGEncoding TechniquesAuthors NameAffiliationInstitutionCourse and UnitAbstractThis paper discusses and critically analyzestechniques for data encoding. The paper reviews the concept ofdata and signal transmission over networks through encoding.Encoding can be achieved through two level or three levelmethods. Signals are transmitted using a continuous signal thatvaries in phase, amplitude, or other property in direct proportionto that of a variable. Encoding can be analog to analog (AM, FM,PSM), digital to digital (NRZ, NRZI, ME), analog to analog, anddigital to digital (ASK FSK PSK QAM). Some of the significantrecent developments include Orthogonal frequency divisionmultiplexing and MultiplexingKeywords—discusses; critical analysis; encoding; techniques;I.INTRODUCTIONCommunication in networks requires at least two parties;the sender and recipient, along with the medium fortransmission and the message/ data to be transmitted. Allcommunications start with the sender, who must figure outhow to encode the data/ information to be sent, so as to conveymeaning. Encoding refers to the process of putting a charactersequence, such as numbers, symbols, and letters into a specialformat to enable efficient transmission and in some cases,storage. The encoded information is then decoded at therecipient end where the encoded information is encoded(converted) back into the original character sequence. Theencoding aims at producing a signal from the encoded datastream to be transmitted over a specific medium; the encodingmust take into consideration the medium for transmission.Encoding is the process of using a code to convert originalinformation/ data into a form usable by an external process.The process of encoding defines the way that signals arerepresented on a given (physical) line of communication;hence, there is a need to have a format that is standard forseamless communication [1]. The encoded signal ismanipulated in such a way that the sender and the recipient canrecognize the changes (encoding) made. Information to be sentover a network can be analog (such as voice and video data) ordigital.II.LITERATUREREVIEWNetworks have become more complex and highlyinterconnected; for instance, the World Wide Web is amongthe biggest network of interconnected computers and servers.Copious volumes of data are exchanged at any given timewithin networks, hence the need for encoding. Further, newtransmission models, such as fiber optic have been developed,requiring a standardized method of transmitting informationover different mediums until they reach their destination in adesirable format [2]. To ensure transmission is optimized, asignal has to be encoded to facilitate transmission over aphysical medium that can be a copper cable, a network cable,or a fiber cable; wireless mediums also necessitate encoding.Encoding is essential in keeping the lines balanced even if thedata keeps changing its state often enough and to make itdistinguishable from a line that is dead. For instance, if the datastream has uneven 1s and 0s, an unbalanced offset voltage willbe developed by the receiver. Encoding also ensures that long1s or 0s strings are eliminated and that over time, the totalnumber of 1s and 0s remains balanced all the time. Further,signals cannot be sent just in the forms of 0s or 1s; the signalshave to be encoded into signals having two states, such as;The absence or presence of current in a wireTwo different voltage levels relative to the earthDifference in voltage between two mediums(wires)The absence or presence of lightThere are two main ways in which encoding can beachieved; two level encoding and three level encoding. In two-level encoding, the signal is encoded in such a way that it canonly take on a value that is either strictly positive (+x) orstrictly negative (-x), where x is a value of the physicalquantity that is being used to transport signals (the physicalmedium). In three level encoding, the signal can take on avalue that is strictly positive (+x), strictly negative (-x), or null(0). There are various methods for signal encoding, asdiscussed in the next section [3].III.CRITICALANALYSISOFENCODINGThe network uses standard protocols for the transmissionand delivery of data over a distance, with the network designedin layers, each performing a specific function. The standardnetwork has various layers including the physical layer (layer1), the data link layer (layer 2), and the presentation layer(layer 3). The Transmission of data is based on the TCP(Transmission Control Protocol) and it is found in layer one(physical layer), where cannel coding takes place. Data
transmission refers to the transfer of data over a point toanother point or multipoint communication channels. Thechannels used for transmissions include optical fiber, copperwires, computer buses, wireless communication channels, andstorage media. The data being transmitted is presented in theform of electromagnetic signals, for example radio waves,microwaves, infrared signals, or electrical voltages. There arevarious kinds of data transmission, including analogtransmission where data, voice, image, video information orsignals are transmitted using a continuous signal that varies inphase, amplitude, or other property in direct proportion to thatof a variable [2]. The messages are represented by a set oflimited continuous varying wave forms (a process termed passband transmission) through digital modulation, or by a pulsesequence using a line code (a method termed basebandtransmission). Modem equipment undertakes the process ofpassband modulation and its corresponding demodulation. Thebit streams represented by both passband and basebandtransmission are both considered digital transmission. Thetransmitted data can be an analog source, such as from video orphone call digitized into bit stream signals or digital such asfrom a keyboard. Before being transmitted over networks,information/ data must be encoded before being transportedacross a given media such as copper or fiber optic. This impliesthat the current or voltage waveform pattern used forrepresenting 1s and 0s are encoded by adjusting them. Thereare various ways in which encoding of signals for transmissionover networks can be achieved;Analog to digitalDigital to analogAnalog to analogDigital to digital [4]The chosen mechanism for encoding depends largelyon the technology available at a given time and the applicationneeds.IV.ANALOG TO ANALOG ENCODINGThis is one of the oldest methods for encoding and entailsconverting analog data into digital signals and was (is)employed in telephony to transmit voice data over telephone(copper) lines. Analog data is represented in their baseband asanalog frequencies. For instance, when using a telephone,there are two ways in which the data is sent; the analog voicesignal is transmitted at the baseband signal. Alternatively, thedata can be transmitted by combining the signals into anothersignal which acts as the carrier and the combined signalstransmitted at a different frequency. When the pitch of a signalwave is modified, its termed frequency modulation; modifyinga wave’s strength is termed amplitude modulation, whilemodifying its (wave) natural flow is termed phase modulation[4]A.Amplitude ModulationAM works by having the data/ message encoded in theamplitude of a signal pulse series; the amplitudes of carrierpulses train are varied based on the sample value of the data/message signal. The bulk of carrier signals and and a waveformin the baseband with the lower sideband being slightly lowerthan the frequency of the carrier while the upper side band isslightly higher [5]. AM can is expressed as;s(t) = [1+na x(t)] cos 2 πfc tThe resulting signal envelope is 1+na x (t)As long as na <1, the envelope becomes the originalsignal’s exact reproduction. If na >= 1, the standard AMmodulator will fail since as the wave envelop negativeexcursions cannot fall below zero; therefore, the receivedmodulation becomes distorted. Because of its nature, the authorfeels it’s more suited for wide area applications but unsuitablefor situations where quality is required as it has levels of noise.Further, it’s unsuitable for data or multimedia because of alimited bandwidth and has a weaker signalB.Frequency modulation (FM)Is an analog data encoding method in which data isencoded into an alternating current (AC) wave throughchanging the waves instantaneous frequency and can beused for encoding either digital or analog data. In digitalFM, the data is in the form of 0s and 1s, and there areabrupt signal changes of the carrier frequency. The numberof carrier frequencies is represented in powers of two (2),corresponding with the ON/OFF frequency states. AnalogFM has a continuous/ smooth AC carrier wave that can berepresented as a sine wave [6]. If the baseband signal is x m(t) and the sinusoidal carrier wave isXc (t) = Ac cos (2 π fc t)Where fc is the base frequency of the carrier andAc is its amplitude the modulator combines thebaseband data signal with the carrier to obtain thetransmitted signal;The author feels FM is suitable for data transfers over shortdistances due to a larger bandwidth, low noise, is more
efficient as it requires less amplification during transmissionand compression (photo-acoustic) can be applied to it.However, it requires complicated demodulators due to the needfor amplitude limiter.C.Phase Shift Modulation (PSM)This involves conveying digital signals by shifting phases;this technique is basically used for satellite communication anddigital signaling. The phase numbers used in representing theinformation being transmitted can significantly impact theamount of transmitted information. When more than twophases are used, it is termed multi-level signaling [7]. This, onfurther evaluation, is an easier encoding method compared toFM and more information such as Doppler can be obtainedwith PSM. However, extending its modulation beyond 180degrees results in phase ambiguity and it requires frequencymultipliers, limiting its application for modern data transferneedsV.DIGITALTODIGITALENCODINGThis is a method of encoding that is at present, commonlyused in transmitting data over digital facilities, such ascomputer data over networks. This model uses less complexequipment as well as being less expensive, compared tomethods such as digital to analog. Digital signals are discretesequences of discontinuous voltage pulses with every pulsehaving a signal element. It entails encoding binary data bit intosignal elements in order to transmit data. The encoding schemeentails mapping signal elements from data bits; a mark is thebinary digit 1 while the binary digit 0 signifies a space. Thecommon techniques used in digital to digital encoding includeNRZ (no return to zero) encoding, NRZI (no return to zeroinverted) encoding, Bipolar AMI (alternate mark inversion),and Manchester Encoding.A.NRZ EncodingThis is among the simplest and earliest used encodingsystems for digital to digital encoding; it entails transformingthe 1s into -X and the 0s into +X resulting into a bipolarencoding where the signal can never be null. As a consequence,the recipient of the message/ data can determine easily whetherthere is a signal present or not. NRZ is often used in slow speedtype of communications interfaces for asynchronous andsynchronous data transmissions [13]. I think this techniquemakes synchronization difficult and causes higher power lossesfor transmitted DC power and adds costs to transmission as thelines must be DC coupled. Further, it’s difficult to achieveclock recovery from signals and errors may be introduced overlong distancesB.NRZI EncodingThis type of digital to digital encoding entails the signalchanging state after ticking of the clock when the bit value is 1.When value of the bit is 0, there is no change in state of thesignal value. This type of encoding is advantageous because itenables detecting whether there is a signal or not and thetransmission current is low voltage, albeit with the problem ofcontinuous current during sequences of 0s [8]. This method issuitable for data transmissions over long distances becausemany transitions can be introduced to enable clock recoveryfrom the signal and so limit errors; a clear advantage overNZR.C.Manchester Encoding (ME)This is a digital to digital encoding where transitions fromone logical state to another state represents data bits and eachdata bit length is set by default. It entails an exclusiveperformance of the OR (XOR) of a signal with the clock signalthat results into a raising edge when the value of the bit is 0 anda falling edge in the opposite case. The direction of thetransition determines the state of a bit. Data encoded usingManchester Encoding contains frequent transition levels thatallow the extraction of the clock signal by the receiver usingthe DPLL (digital phase locked loop) [8]. Manchester encodingworks based on the rules shown below;TABLE I.Original dataSent valueLogic 11 to 0; downward transitionat the bit center
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