csc 535 communication networks i chapter 3c transmission media (section 3.7) dr. cheer-sun yang
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CSC 535Communication Networks I
Chapter 3C Transmission Media (Section 3.7)
Dr. Cheer-Sun Yang
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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
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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
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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