csc 535 communication networks i chapter 3c transmission media (section 3.7) dr. cheer-sun yang

CSC 535Communication Networks I

Chapter 3C Transmission Media (Section 3.7)

Dr. Cheer-Sun Yang

2

OverviewGuided - 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

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Design FactorsBandwidth

Higher bandwidth gives higher data rate

Transmission impairments Attenuation

InterferenceNumber of receivers

In guided media More receivers (multi-point) introduce more

attenuation

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102 104 106 108 1010 1012 1014 1016 1018 1020 1022 1024

Frequency (Hz)

Wavelength (meters)

106 104 102 10 10-2 10-4 10-6 10-8 10-10 10-12 10-14

pow

er &

tele

phon

e

broa

dcas

tra

dio

mic

row

ave

radi

o

infr

ared

ligh

t

visi

ble

ligh

t

ultr

avio

let l

ight

x ra

ys

gam

ma

rays

Figure 3.35

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Electromagnetic Spectrum

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t = 0t = d/c

communication channel

d meters

Figure 3.36

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Guided Transmission MediaTwisted PairCoaxial cableOptical fiber

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Twisted Pair

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Twisted Pair - ApplicationsMost common mediumTelephone network

Between house and local exchange (subscriber loop)

Within buildings To private branch exchange (PBX)

For local area networks (LAN) 10Mbps or 100Mbps

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

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Twisted Pair - Transmission CharacteristicsAnalog

Amplifiers every 5km to 6km

Digital Use either analog or digital signals repeater every 2km or 3km

Limited distanceLimited bandwidth (1MHz)Limited data rate (100MHz)Susceptible to interference and noise

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Unshielded and Shielded TPUnshielded Twisted Pair (UTP)

Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference

Shielded Twisted Pair (STP) Metal braid or sheathing that reduces

interference More expensive Harder to handle (thick, heavy)

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UTP CategoriesCat 3

up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm

Cat 4 up to 20 MHz

Cat 5 up to 100MHz Commonly pre-installed in new office buildings Twist length 0.6 cm to 0.85 cm

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Near End CrosstalkCoupling of signal from one pair to

anotherCoupling takes place when transmit signal

entering the link couples back to receiving pair

i.e. near transmitted signal is picked up by near receiving pair

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Att

enua

tion

(dB

/mi)

f (kHz)

19 gauge

22 gauge

24 gauge

26 gauge

6

12

3

9

15

18

21

24

27

30

1 10 100 1000

Figure 3.37

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Figure 3.38

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ApplicationsAsymmetric digital subscriber line (ADSL)

The system uses existing twisted-pair lines to provide the higher bit rates.

It is asymmetric in that users can transmit upstream at the speeds from 64 kbps (10**3 bits per second) to 640 kbps and receive information at the speed from 1.536 Mbps (10**6 bps) to 6.144 Mbps.

Ethernet

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Coaxial Cable

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Centerconductor

Dielectricmaterial

Braidedouter

conductor

Outercover

Figure 3.39

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35

30

10

25

20

5

15Att

enua

tion

(dB

/km

)

0.01 0.1 1.0 10 100 f (MHz)

2.6/9.5 mm

1.2/4.4 mm

0.7/2.9 mm

Figure 3.40

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Head

end

Unidirectionalamplifier

Figure 3.41

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Head

end

Upstream fiber

Downstream fiber

Fibernode

Coaxialdistribution

plant

Fibernode

BidirectionalSplit-BandAmplifier

Fiber Fiber

Figure 3.42

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Coaxial Cable ApplicationsMost versatile mediumTelevision distribution

Ariel to TV Cable TV

Long distance telephone transmission Can carry 10,000 voice calls simultaneously Being replaced by fiber optic

Short distance computer systems linksLocal area networks

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Coaxial Cable - Transmission CharacteristicsAnalog

Amplifiers every few km Closer if higher frequency Up to 500MHz

Digital Repeater every 1km Closer for higher data rates

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Downstream

54 MH

z

500 MH

zUpstream

Downstream

5 MH

z

42 MH

z

54 MH

z

500 MH

z

550 MH

z

750 MH

z

(a)Currentallocation

(b) Proposedhybridfiber-coaxialallocation

Proposed downstream

Figure 3.43

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Optical Fiber

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Optical Fiber - BenefitsGreater capacity

Data rates of hundreds of Gbps

Smaller size & weightLower attenuationElectromagnetic isolationGreater repeater spacing

10s of km at least

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core

cladding jacket

light

c

(a) Geometry of optical fiber

(b) Reflection in optical fiber

Figure 3.44

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100

50

10

5

1

0.5

0.1

0.05

0.010.8 1.0 1.2 1.4 1.6 1.8

Wavelength (m)

Los

s (d

B/k

m) Infrared absorption

Rayleigh scattering

Figure 3.45

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(a) Multimode fiber: multiple rays follow different paths

(b) Single mode: only direct path propagates in fiber

direct path

reflected path

Figure 3.46

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Optical Fiber - ApplicationsLong-haul trunksMetropolitan trunksRural exchange trunksSubscriber loopsNetwork backboneLANs

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Optical Fiber - Transmission CharacteristicsAct as wave guide for 1014 to 1015 Hz

Portions of infrared and visible spectrum

Light Emitting Diode (LED) Cheaper Wider operating temp range Last longer

Injection Laser Diode (ILD) More efficient Greater data rate

Wavelength Division Multiplexing

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Optical Fiber Transmission Modes

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Optical fiber

Opticalsource

ModulatorElectricalsignal

ReceiverElectrical

signal

Figure 3.47

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Radio TransmissionUnguided mediaTransmission and reception via antennaDirectional

Focused beam Careful alignment required

Omnidirectional Signal spreads in all directions Can be received by many antennae

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104 106 107 108 109 1010 1011 1012

Frequency (Hz)

Wavelength (meters)

103 102 101 1 10-1 10-2 10-3

105

satellite & terrestrial microwave

AM radio

FM radio & TV

LF MF HF VHF UHF SHF EHF104

Cellular& PCS

Wireless cable

Figure 3.48

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Frequencies2GHz to 40GHz

Microwave Highly directional Point to point Satellite

30MHz to 1GHz Omnidirectional Broadcast radio

3 x 1011 to 2 x 1014

Infrared Local

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

39

Satellite MicrowaveSatellite is relay stationSatellite receives on one frequency,

amplifies or repeats signal and transmits on another frequency

Requires geo-stationary orbit Height of 35,784km

TelevisionLong distance telephonePrivate business networks

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Broadcast RadioOmnidirectionalFM radioUHF and VHF televisionLine of sightSuffers from multipath interference

Reflections

41

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

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Required ReadingSection 3.7