komunikasi data dan jaringan komputer (bagian 1)

Komunikasi Data dan Jaringan Komputer(Bagian 1)Dr. Tb. Maulana [email protected]://staffsite.gunadarma.ac.id/mkusumaInternet dan Jaringan Komputer

Magister Manajemen Sistem Informasi

ReferensiW. Stallings, Data and Computer Communications, 4ed, Macmillan, 1994.

F. Halsall, Data Communications, Computer Networks and Open Systems, Addison Wesley, 1996.


A Communications ModelSourcegenerates data to be transmittedTransmitterConverts data into transmittable signalsTransmission SystemCarries dataReceiverConverts received signal into dataDestinationTakes incoming data


Simplified Communications Model - Diagram


Simplified Data Communications Model


Key Communications TasksTransmission System UtilizationInterfacingSignal GenerationSynchronizationExchange ManagementError detection and correctionAddressing and routingRecoveryMessage formattingSecurityNetwork Management


Communications StandardMany types of connection media : telephone lines, optical fibers, cables, radios, etc.Many different types of machines and operating systemsMany different network applications


What Standard means?How many volts pulse is a 0 and 1 ? How to determine the end of a message ? How to handle lost messages ? How many bits for different data types ? Integers/Strings, etc.; are ASCII chars ?How machines are identified ?How to find the way to reach a machine ?How applications speaks together through the network ?


Standard BodiesInternational Telecommunications Union Telecommunications Sector (ITU-T)Institute of Electrical and Electronics Engineers (IEEE)International Organization for Standardization (ISO)Electronic Industries Alliance (EIA)dll


The ISO/OSI ModelISO (the International Standards Organization) has developed a reference model for communications, called theOSI(Open Systems Interconnection)

OPEN SYSTEM means that it can communicate with any other system that follows the specified standards, formats and semantics.


OSI Networking Model


OSI Layers (1)PhysicalPhysical interface between devicesMechanicalElectricalFunctionalProceduralData LinkMeans of activating, maintaining and deactivating a reliable linkError detection and controlHigher layers may assume error free transmission


OSI Layers (2)NetworkTransport of informationHigher layers do not need to know about underlying technologyNot needed on direct linksTransportExchange of data between end systemsError freeIn sequenceNo lossesNo duplicatesQuality of service


OSI Layers (3)SessionControl of dialogues between applicationsDialogue disciplineGroupingRecoveryPresentationData formats and codingData compressionEncryptionApplicationMeans for applications to access OSI environment


Transmission MediumGuided - wireUnguided - wirelessCharacteristics and quality determined by medium and signalFor guided, the medium is more importantFor unguided, the bandwidth produced by the antenna is more importantKey concerns are data rate and distance


Guided Transmission MediaTwisted PairCoaxial cableOptical fiber


Twisted pair - INEXPENSIVETwo wires twisted together.Makes them less susceptible to acting like an antenna and picking up radio frequency information or appliance noise.Telephone company uses twisted-pair copper wires to link telephones.

Twisted Pair


Twisted Pair


Twisted Pair - ApplicationsMost common mediumTelephone networkBetween house and local exchange (subscriber loop)Within buildingsTo private branch exchange (PBX)For local area networks (LAN)10Mbps or 100Mbps


Twisted Pair - Pros and ConsCheapEasy to work withLow data rateShort range


Twisted Pair - Transmission CharacteristicsAnalog Amplifiers every 5km to 6kmDigitalUse either analog or digital signalsrepeater every 2km or 3kmLimited distanceLimited bandwidth (1MHz)Limited data rate (100MHz)Susceptible to interference and noise


Unshielded and Shielded TPUnshielded Twisted Pair (UTP)Ordinary telephone wireCheapestEasiest to installSuffers from external EM interferenceShielded Twisted Pair (STP)Metal braid or sheathing that reduces interferenceMore expensiveHarder to handle (thick, heavy)


UTP CategoriesCat 3up to 16MHzVoice grade found in most officesTwist length of 7.5 cm to 10 cmCat 4up to 20 MHzCat 5 or Cat 6up to 100MHzCommonly pre-installed in new office buildingsTwist length 0.6 cm to 0.85 cm


Coaxial Cable (1)Coaxial cableAlso two wires: One of the wires is woven of fine strands of copper forming a tube. The wire mesh surrounds a solid copper wire that runs down the center. Space between has a non-conducting material.Makes them more impervious to outside noise.Use this when1. Long distances2. Lots of interference


Coaxial Cable (2)


Coaxial Cable (3)


Coaxial Cable ApplicationsMost versatile mediumTelevision distributionAerial to TVCable TVLong distance telephone transmissionCan carry 10,000 voice calls simultaneouslyBeing replaced by fiber opticShort distance computer systems linksLocal area networks


Coaxial Cable - Transmission CharacteristicsAnalogAmplifiers every few kmCloser if higher frequencyUp to 500MHzDigitalRepeater every 1kmCloser for higher data rates


Optical Fiber (1)


Optical Fiber (2)


Optical Fiber (3)Fiber-optic cable (BIG JOBS + EXPENSIVE)Light is electromagnetic.Can transmit more information down a single strand. It can send a wider set of frequencies.Each cable can send several thousand phone conversations or computer communications.


Optical Fiber - Spectrum


Optical Fiber - BenefitsGreater capacityData rates of hundreds of GbpsSmaller size & weightLower attenuationElectromagnetic isolationGreater repeater spacing10s of km at least


Optical Fiber - ApplicationsLong-haul trunksMetropolitan trunksRural exchange trunksSubscriber loopsLANs


Optical Fiber - Transmission CharacteristicsAct as wave guide for 1014 to 1015 Hz Portions of infrared and visible spectrumLight Emitting Diode (LED)CheaperWider operating temp rangeLast longerInjection Laser Diode (ILD)More efficientGreater data rateWavelength Division Multiplexing (WDM)


Optical Fiber Transmission Modes


Wireless TransmissionUnguided mediaTransmission and reception via antennaDirectionalFocused beamCareful alignment required Omni-directionalSignal spreads in all directionsCan be received by many antenna


Frequencies2GHz to 40GHzMicrowaveHighly directionalPoint to pointSatellite30MHz to 1GHzOmni-directionalBroadcast radio3 x 1011 to 2 x 1014InfraredLocal


Terrestrial MicrowaveParabolic dishFocused beamLine of sightLong haul telecommunicationsHigher frequencies give higher data rates


Satellite MicrowaveSatellite is relay stationSatellite receives on one frequency, amplifies or repeats signal and transmits on another frequencyRequires geo-stationary orbitHeight of 35,784kmTelevisionLong distance telephonePrivate business networks


Broadcast RadioOmni-directionalFM radioUHF and VHF televisionLine of sightSuffers from multi-path interference


InfraredModulate non-coherent infrared lightLine of sight (or reflection)Blocked by wallse.g. TV remote control, IRD port


Terminology (1)TransmitterReceiverMediumGuided mediume.g. twisted pair, optical fiberUnguided mediume.g. air, water, vacuum


Terminology (2)Direct linkNo intermediate devicesPoint-to-pointDirect link Only 2 devices share linkMulti-pointMore than two devices share the link


Terminology (3)SimplexOne directione.g. TelevisionHalf duplexEither direction, but only one way at a timee.g. police radioFull duplexBoth directions at the same timee.g. telephone


Terminology (4)Bits per second (bps).The number of bits (0s and 1s) that travel down the channel per second.Baud rateThe number of bits that travel down the channel in a given interval.The number is given in signal changes per second, not necessarily bits per second.


Terminology (5)Asynchronous transmission Information is sent byte by byte.Cheaper and more commonly used.Synchronous transmission Data is sent in large blocks rather than in small pieces.Preceded by special information, concerning error detection and block size.These modems are expensive but very fast.


Analog and Digital Data TransmissionData Entities that convey meaningSignalsElectric or electromagnetic representations of dataTransmissionCommunication of data by propagation and processing of signals


DataAnalogContinuous values within some intervale.g. sound, videoDigitalDiscrete valuese.g. text, integers


Data and SignalsUsually use digital signals for digital data and analog signals for analog dataCan use analog signal to carry digital dataModemCan use digital signal to carry analog data Compact Disc audio


SignalsType of signal communicated (analog or digital).Analog: Those signals that vary with smooth continuous changes.A continuously changing signal similar to that found on the speaker wires of a high-fidelity stereo system.Digital: Those signals that vary in steps or jumps from value to value. They are usually in the form of pulses of electrical energy (represent 0s or 1s).


Analog Signals Carrying Analog and Digital Data


Digital Signals Carrying Analog and Digital Data


Analog TransmissionAnalog signal transmitted without regard to contentMay be analog or digital dataAttenuated over distance Use amplifiers to boost signalAlso amplifies noise


Digital TransmissionConcerned with contentIntegrity endangered by noise, attenuation etc.Repeaters usedRepeater receives signalExtracts bit patternRetransmitsAttenuation is overcomeNoise is not amplified


Advantages of Digital TransmissionDigital technologyLow cost LSI/VLSI technologyData integrityLonger distances over lower quality linesCapacity utilizationHigh bandwidth links economicalHigh degree of multiplexing easier with digital techniquesSecurity & PrivacyEncryptionIntegrationCan treat analog and digital data similarly


Transmission ImpairmentsSignal received may differ from signal transmittedAnalog - degradation of signal qualityDigital - bit errorsCaused byAttenuation and attenuation distortionPropagation delayNoiseInterference


AttenuationSignal strength falls off with distanceDepends on mediumReceived signal strength:must be enough to be detectedmust be sufficiently higher than noise to be received without errorAttenuation is an increasing function of frequency


Propagation DelayThe time required for a signal to travel from one point to another. Propagation velocity varies with frequency.


Noise (1)Additional signals inserted between transmitter and receiverThermalDue to thermal agitation of electronsWhite noiseInter-modulationSignals that are the sum and difference of original frequencies sharing a medium


Noise (2)CrosstalkA signal from one line is picked up by anotherImpulseIrregular pulses or spikese.g. External electromagnetic interferenceShort durationHigh amplitude


Channel CapacityData rateIn bits per secondRate at which data can be communicatedBandwidthIn cycles per second of HertzConstrained by transmitter and medium


Modulation Techniques


Adaptive Modulation


Data Rate and BandwidthAny transmission system has a limited band of frequenciesThis limits the data rate that can be carried


Multiplexing


Time Division MultiplexingData rate of medium exceeds data rate of digital signal to be transmittedMultiple digital signals interleaved in timeMay be at bit level of blocksTime slots pre-assigned to sources and fixedTime slots allocated even if no dataTime slots do not have to be evenly distributed amongst sources


Time Division Multiplexing


TDM System


Frequency Division MultiplexingFDMUseful bandwidth of medium exceeds required bandwidth of channelEach signal is modulated to a different carrier frequencyCarrier frequencies separated so signals do not overlap (guard bands)e.g. broadcast radioChannel allocated even if no data


Frequency Division MultiplexingDiagram


FDM System


Increasing Network Capacity OptionsFaster Electronics(TDM)Higher bit rate, same fiberElectronics more expensiveMore Fibers(SDM)Same bit rate, more fibersSlow Time to MarketExpensive EngineeringLimited Rights of WayDuct ExhaustWDMSame fiber & bit rate, more lsFiber CompatibilityFiber Capacity ReleaseFast Time to MarketLower Cost of OwnershipUtilizes existing TDM Equipment


Fiber NetworksTime division multiplexingSingle wavelength per fiberMultiple channels per fiber4 OC-3 channels in OC-124 OC-12 channels in OC-4816 OC-3 channels in OC-48Wave division multiplexingMultiple wavelengths per fiber4, 16, 32, 64 channels per systemMultiple channels per fiberSingle Fiber (One Wavelength)Channel 1Channel nSingle Fiber(Multiple Wavelengths)l1l2ln


Types of WDMCoarse WDM (CWDM)Uses 3000GHz (20 nm) spacing.Up to 18 channels.Distance of 50 km on a single mode fiber.

Dense WDM (DWDM)Uses 200, 100, 50, or 25 GHz spacing.Up to 128 or more channels.Distance of several thousand kilometres with amplification and regeneration.


TDM and DWDM ComparisonTDM (SONET/SDH)Takes sync and async signals and multiplexes them to a single higher optical bit rateE/O or O/E/O conversion (D)WDM Takes multiple optical signals and multiplexes onto a single fiberNo signal format conversionDS-1DS-3OC-1OC-3OC-12OC-48OC-12cOC-48cOC-192cFiberDWDMOADMSONETADMFiber


Why DWDMThe Business CaseTERMTERMTERMConventional TDM Transmission10 Gbps1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTRTERM40km1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTRTERM1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTRTERM1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTR1310RPTRTERM120 kmOC-48OAOAOAOA120 km120 kmOC-48OC-48OC-48OC-48OC-48OC-48OC-48DWDM Transmission10 Gbps1 Fiber Pair4 Optical AmplifiersTERM4 Fibers Pairs 32 Regenerators40km40km40km40km40km40km40km40km


Optical Transmission Bands


Characteristics of a WDM NetworkSub-wavelength Multiplexing or MuxPondingAbility to put multiple services onto a single wavelength


Transmission EffectsAttenuation: Reduces power level with distanceDispersion and nonlinear effects: Erodes clarity with distance and speedNoise and Jitter:Leading to a blurred image


As the need for more capacity increased over the years, first for voice traffic, today mostly for internet traffic, different solutions have been adopted.The simplest one is Space Division Multiplexing: it simply means to deploy and use more links of the same type. This approach is very expensive since it uses up all available resources and asks for infrastructure upgradesA more efficient solution came in with TDM technologies. In this case, we keep the same transmission medium but we increase the bit rate over it. If you go back a few years, SDH/SONET equipment, and routers as well, was transmitting at 155 Mbps, then 622 Mbps, finally 2.5 Gbps and just recently 10 Gbps. It is true that the transmission medium is always the same, but the transmission equipment is getting more and more complicated and expensive. Additionally, the maximum transported capability over a fiber pair is iin the range of a few Gbps.The way to scale to higher transported capacity is WDM. This technology keeps the same fiber, the same bit rate, but uses multiple colours to multiply transported capacity.

The majority of DWDM systems today operate in the C-Band. Moving into L next, then potentially S. CWDM operates primarily across S-C-L, with Extended Band fibers (like Allwave and SMF-28e) opening up the 1360-1460 window to support additional CWDM wavelengths.So in summary we have attenuation that reduced power level over distance, and we have dispersion and non linear effects eroding signal clarity with distance and speed. Additionally we have noise and jitter leading to a blurred image

komunikasi data dan jaringan komputer (bagian 1)

Documents

different data types

computer communications

controlhigher layers

different types of machines

reference model

computer networks

specified standards

reliable linkerror detection