CE 4228

CE 4228Data Communications and NetworkingTransmission MediaTransmission Media OutlineGuided mediaTwisted pairCoaxial cableOptical fiberUnguided mediaAntennaPropagationTransmission Media DesignKey concerns are data rate and distanceBandwidthHigher bandwidth gives higher data rateTransmission impairmentsAttenuationInterferenceNumber of receiversIn guided mediaMore multi-point receivers introduce more attenuationTransmission Media GuidedTwisted pairCoaxial cableOptical fiber

Twisted Pair(a) Category 3 UTP(b) Category 5 UTP

Twisted Pair Rationale

Twisted Pair ApplicationsMost common mediumTelephone networksBetween house and local exchangeSubscriber loopWithin buildingsTo private branch exchange or PBXLocal area networksTwisted Pair CharacteristicsAnalog Amplifiers every 5 to 6 kmDigitalUse either analog or digital signalsRepeater every 2 or 3 kmLimited distanceLimited bandwidthLimited data rateSusceptible to interference and noiseTwisted Pair UTP/STPUTPUnshielded twisted pair Ordinary telephone wireCheapestEasiest to installSuffer from external EM interferenceSTPShielded twisted pairMetal braid or sheathing that reduces interferenceMore expensiveThick, heavyHarder to handle

Twisted Pair UTPCategory 3Up to 16 MHzVoice grade found in most officesTwist length of 7.5 cm to 10 cmCategory 4Up to 20 MHzCategory 5Up to 100 MHzCommonly pre-installed in new office buildingsTwist length 0.6 cm to 0.85 cmCategory 5eEnhancedCategory 6Category 7Twisted Pair Categories

Twisted Pair Categories

TelephoneCategory 3Category 5eCategory 6Twisted Pair Category 6 UTP

Twisted Pair Categories/Classes

Category 3 Class C

Category 5 Class D

Category 5E

Category 6 Class E

Category 7 Class F

Bandwidth

16 MHz

100 MHz

100 MHz

200 MHz

600 MHz

Cable Type

UTP

UTP/FTP

UTP/FTP

UTP/FTP

SSTP

Link Cost

0.7

1

1.2

1.5

2.2

Twisted Pair Comparison

Attenuation (dB per 100 m)Near-end Crosstalk (dB)Frequency (MHz)Category 3 UTPCategory 5 UTP150-ohm STPCategory 3 UTPCategory 5 UTP150-ohm STP1

2.6

2.0

1.1

41

62

58

4

5.6

4.1

2.2

32

53

58

16

13.1

8.2

4.4

23

44

50.4

25

10.4

6.2

41

47.5

100

22.0

12.3

32

38.5

300

21.4

31.3

Twisted Pair SummaryCheapEasy to work withLow data rateShort rangeCoaxial Cable

75-ohm cable is widely usedImpedance easily matched with 300-ohm antenna50-ohm cable is sometimes used when intended for digital transmission from the startCoaxial 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 networksCoaxial Cable CharacteristicsAnalogAmplifiers every few km, closer if higher frequencyUp to 500 MHzDigitalRepeater every 1 km, closer for higher data rates500 Mbps or higherFor comparison6 MHz/TV channel1.4 Mbps for CDOptical Fiber

Optical Fiber

Optical FiberOptical Fiber ApplicationsLong-haul trunksMetropolitan trunksRural exchange trunksSubscriber loopsLANs

Optical Fiber FTTH

Optical Fiber CharacteristicsAct as wave guide for 1014 to 1015 Hz Portions of infrared and visible spectrumTheoretical bandwidth of 50 TbpsPractical data rate of 2 GbpsSpeed/distance limited by dispersionTwo types of light sourceLEDLight emitting diodeILDInjection laser diodeWavelength division multiplexingOptical Fiber Light Source

Optical Fiber Modes

Optical Fiber Dispersion

Optical Fiber DispersionDefine the followingD = dispersion rate in s/kmPulse width increased/distanceDepend on types of fiberR = bit rate in bpsL = length of fiber in kmSending 101010 LD T/2 RL 1/2DHence, RL must be less than10 Mbps km for a step-index fiber1 Gbps km for a graded-index fiber200 Gbps km for a single-mode fiberWavelength range (nm)

Frequency range (THz)

Band label

Fiber type

Application

820 to 900

366 to 333

Multimode

LAN

1280 to 1350

234 to 222

S

Single mode

Various

1528 to 1561

196 to 192

C

Single mode

WDM

1561 to 1620

192 to 185

L

Single mode

WDM

Optical Fiber Frequency RangeOptical Fiber Frequency Band

Optical Fiber BenefitsGreater capacityData rates of hundreds of GbpsSmaller size & weightLower attenuationElectromagnetic isolationCan be operated for communications and control networks in close proximity to electrical circuits without problemsGreater repeater spacing10 km or more

Guided Media Characteristics

Frequency Range

Typical Attenuation

Typical Delay

Repeater Spacing

Twisted pair (with loading)0 to 3.5 kHz

0.2 dB/km @ 1 kHz

50 s/km

2 km

Twisted pairs (multi-pair cables)

0 to 1 MHz

0.7 dB/km @ 1 kHz

5 s/km

2 km

Coaxial cable

0 to 500 MHz

7 dB/km @ 10 MHz

4 s/km

1 to 9 km

Optical fiber

186 to 370 THz

0.2 to 0.5 dB/km

5 s/km

40 km

Guided Media Characteristics

Guided Media Attenuation

Electromagnetic Spectrum

Electromagnetic Spectrum

Wireless Frequency Band

Wireless Frequency BandRadio10 kHz to 1 GHzOmnidirectionalBroadcast radioInfrared31011 to 21014 HzLocalMicrowave1 GHz to 40 GHzHighly directionalPoint to pointSatelliteWireless ISM BandIndustrial, scientific, medicalUnlicensed usageLow power only, to avoid interferenceGarage door openers, cordless phones, wireless mice, wireless LANs, Bluetooth

WirelessUnguided transmission mediaSeveral reasons of usagesMobilityAccessibilityModern wireless digital communications began in Hawaii, where conventional landline system was inadequateAntennaTransmissionsRadio frequency energy from transmitterConverted to electromagnetic energy by antennaRadiated into surrounding environmentReceptionsElectromagnetic energy impinging on antennaConverted to radio frequency electrical energyFed to receiverSame antenna often used for both

Antenna Radiation PatternPower radiated in all directionsNot same performance in all directionsIsotropic antenna is theoretical point in spaceRadiate in all directions equallyGive spherical radiation pattern

Antenna Parabolic ReflectiveUsed for terrestrial and satellite microwaveParabola is locus of point equidistant from a line and a point not on that lineFixed point is focusLine is directrixRevolve parabola about axis to get paraboloidCross section parallel to axis gives parabolaCross section perpendicular to axis gives circleAntenna Parabolic ReflectiveSource placed at focus will produce waves reflected from parabola in parallel to axisCreates theoretical parallel beam of light/sound/radioOn reception, signal is concentrated at focus, where detector is placedAntenna Parabolic Reflective

Antenna GainMeasure of directionality of antennaPower output in particular direction compared with that produced by isotropic antennaMeasured in dBResult in loss in power in another directionEffective area relates to size and shapeRelated to gainTerrestrial MicrowaveParabolic dishFocused beamLine of sightHigher frequencies give higher data ratesLong haul telecommunicationsA microwave tower every 50 km

SatelliteSatellite is relay stationSatellite receives on one frequency, amplifies or repeats signal and transmits on another frequencyInherently broadcast mediaCan be deployed almost instantlyMilitaryCost of transmitting is independent of the distanceSatelliteGeostationary orbitHeight of 35,784 kmRelatively large propagation delayTypical value is 270 msec3 sec/km for terrestrial microwave5 sec/km for coaxial cable or optical fiberTelevisionLong distance telephonePrivate business networksSatellite Frequency Band

Satellite Altitude

Satellite Point to Point Link

Satellite Broadcast Link

Satellite VSAT

Broadcast RadioOmnidirectionalFM radioUHF and VHF televisionLine of sightSuffer from multipath interferenceReflections

InfraredModulate noncoherent infrared lightLine of sight or reflectionBlocked by wallsTV remote control, IrDA portPoint to pointCellular SystemReplace high power transmitter/receiver systemsUse lower power, shorter range, more transmittersArea divided into cellsAdjacent cells on different frequencies to avoid crosstalkFrequency reuseHexagonal cellsMost resemble to circular shapeCan be packed without holeCellular System Cells

Cellular System Design FactorFadingTime variation of received signal, caused by changes in transmission pathsMultiple accessFDMATDMACDMAHandoffBase station location

Cellular System Signal Strength

Cellular System Signal Strength

Wireless PropagationSignal travels along three routesGround waveSky waveLine of sightWireless Ground WaveFrequency less than 2 MHzFollow contour of the earthAM radio

Wireless Sky WaveFrequency of 2-30 MHzBBC world, Voice of America, amateur radioSignal reflected, or actually refracted, from ionosphere layerWireless Line of SightFrequency above 30 MHzMay be further than optical line of sight due to refraction

Wireless RefractionVelocity of electromagnetic wave is a function of density of material3108 m/s in vacuum, less in anything elseAs wave moves from one medium to another, its speed changesDirection bending of wave at boundaryTowards more dense mediumIndex of refractionsin(angle of incidence)/sin(angle of refraction)Vary with wavelengthAlso called refractive index

Wireless RefractionMay cause sudden change of direction at transition between mediaMay cause gradual bending if medium density is varyingDensity of atmosphere decreases with heightResult in bending towards earth of radio wavesWireless ImpairmentFree space lossSignal disperses with distanceGreater for higher frequenciesBut consider antenna gain that can compensate, higher frequencies are betterAtmospheric absorptionWater vapour and oxygen absorb radio signalsWater greatest at 22 GHz, less below 15 GHzOxygen greatest at 60 GHz, less below 30 GHzRain and fog scatter radio wavesWireless ImpairmentMultipathBetter to get line of sight if possibleSignal can be reflected causing multiple copies to be receivedMay be no direct signal at allMay reinforce or cancel direct signalRefractionMay result in partial or total loss of signal at receiver

WirelessFree space lossWireless Multipath Interference

Transmission Media ConclusionGuidedUnguidedUnderstanding the properties