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OverviewOverview
guided – copper twisted pair, coaxial cable optical fiber
unguided – wireless; through air, vacuum, or water
characteristics and quality determined by medium and transmitted signalin unguided media - bandwidth of signal
produced by the antenna is more importantin guided media - medium is more important
key concerns are data rate and distance
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Design FactorsDesign Factors
A number of design factors relating to the transmission media and the signal determine the data rate and distance
1. bandwidth higher bandwidth gives higher data rate
2. transmission impairments e.g. attenuation limit the distance
3. Interference from other signals in overlapping frequency bands
4. number of receivers in guided media more receivers introduces more attenuation
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Transmission Characteristics of Transmission Characteristics of Guided mediaGuided media
186 to 370 THz
0.2 to 0.5 dB/km
Frequency Range
Typical Attenuatio
n
Typical Delay
Repeater Spacing
Twisted pairs (multi-pair cables)
0 to 1 MHz 0.7 dB/km @ 1 kHz
5 µs/km 2 km
Coaxial cable
0 to 500 MHz
7 dB/km @ 10 MHz
4 µs/km 1 to 9 km
Optical fiber 5 µs/km 40 km
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Twisted pairTwisted pair
Twisting tends to decrease the crosstalk interference between adjacent pairs in a cable.
Neighboring pairs in a bundle typically have somewhat different twist lengths to reduce the crosstalk interference
On long-distance links, the twist length varies from 5 to 15 cm
Twisted Pair: Transmission Twisted Pair: Transmission CharacteristicsCharacteristics
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Analog Transmissionneeds amplifiers every 5km to 6km
Digital Transmissioncan use either analog or digital signalsneeds a repeater every 2-3km
Limited distanceLimited bandwidth (1MHz)Limited data rate (few Mbps)Susceptible to interference and noise
e.g., 50/60 Hz power line frequencyLess expensive that coaxial cables and fiber
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Unshielded vs Shielded twisted pairsUnshielded vs Shielded twisted pairs
Unshielded Twisted Pair (UTP)ordinary telephone wirecheapesteasiest to installsuffers from external Electromagnetic (EM) interference
Shielded Twisted Pair (STP)metal braid or sheathing that reduces interferencemore expensiveharder to handle (thick, heavy)
In a variety of categories - see the Electronic Industry Association standard EIA-568
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Twisted Pair Categories and 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 (Cat 5 =1)
0.7 1 1.2 1.5 2.2
UTP = Unshielded Twisted Pair
FTP = Foil Twisted Pair (Foil قصدير)
SSTP = Shielded Screen Twisted Pair
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Comparison Between Unshielded and Shielded Twisted Pair
Attenuation (dB per 100 m)
Frequency(MHz)
Category 3UTP
Category 5UTP 150-ohm STP
1 2.6 2.0 1.1
4 5.6 4.1 2.2
16 13.1 8.2 4.4
25 — 10.4 6.2
100 — 22.0 12.3
300 — — 21.4
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Coaxial Cable: Transmission characteristics
superior frequency characteristics to TPperformance limited by attenuation &
noiseanalog signals
amplifiers every few Kmcloser when using higher frequenciesup to 500MHz
digital signalsrepeater every 1kmcloser for higher data rates
Coaxial Cable : Applications
Television Distribution (cable TV)Long distance telephone transmissionShort-run computer system linksLocal area networks
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Optical Fiber: Benefits
greater capacitydata rates of hundreds of Gbps
smaller size & weightlower attenuationelectromagnetic isolationgreater repeater spacing
10s of km at least
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Optical Fiber: Transmission Characteristics
uses total internal reflection to transmit lighteffectively acts as wave guide for 1014 to 1015 Hz
can use several different light sourcesLight Emitting Diode (LED)
cheaper, wider operating temp range, lasts longerInjection Laser Diode (ILD)
more efficient, has greater data rate
relation of wavelength, type & data rate
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Frequency Utilization for Fiber Application
Wavelength (invacuum) range
(nm)
FrequencyRange (THz)
BandLabel
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
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Optical Fiber : Applications
Long-haul trunks (1500Km, high capacity: typically 20000-60000 voice channels)
Metropolitan trunks (12 Km, 100000 voice channel in a trunk group)
Rural exchange trunks (40-160 Km, 5000 voice channels)
Subscriber loops (replace twisted pair and coaxial cables, carry voice, data, image and video)
Local area networks (100Mbps-10Gbps)