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7/29/2019 Topic 7 - Guided Transmission Media.pdf
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1Sumati J. Singh
TRANSMISSION MEDIA
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Classification2
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Wired Media3
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Twisted Pair
2 conductors (copper) , own insulation , twisted
1 used to carry signal
Other used for ground reference
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ece ver uses e erence e ween em Noise or crosstalk may affect both
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Noise on Parallel Lines5
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Noise on Twisted Lines6
By adding the twist, reduction in the noise effect.1/23/2013Sumati J. Singh
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Twisted Pair Generally color coded twisted pairs of insulated copper wires encased
in plastic sheath
Each wire has a diameter of 0.4 to 0.8 mm
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,
Higher quality
More expensive
Number of twists per foot/meter is called twist ratio.
More twists need more cable, may increase ATTENUATION.
Balance is needed b/w minimizing crosstalk and reducing attenuation
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Twisted Pair Various purposes
Designs vary in twist ratio,grade of copper used, type of
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.
1 to 4200 pairs can bepacked.
Modern networks use 4 pairspacked in together.
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Characteristics
Twisted pair is
Relatively inexpensive
Flexible
Eas to install
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Span significant distance before needing a repeater
Easily accommodates different topologies
Two categories : STP & UTP
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Shielded Twisted Pair Consists of twisted wire pairs that are not only
individually insulated, but also surrounded by a
shielding made of a metallic substance such as foil.
Sometimes braided copper shielding
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Acts as barrier to external EM forces
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Unshielded Twisted Pair Twisted wire pairs (insulated
individually) covered in a plasticsheath
No additional shieldin
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Less expensive
Less resistant to noise
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Standards TIA/EIA finalized specifications in 1991 named
TIA/EIA 568 TIA Telecommunications Industry Standards
EIA Electronic Industries Standards
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Divides twisted pair wiring in several categories
Catfrom 1 to 7
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TIA/EIA 568
Category Bandwidth Data Rate Digital/Analog Use
1 very low < 100 kbps Analog Telephone
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< z ps na og g a - nes
3 16 MHz 10 Mbps Digital LANs
4 20 MHz 20 Mbps Digital LANs
5 100 MHz 100 Mbps Digital LANs
6 200 MHz 200 Mbps Digital LANs
7 600 MHz 600 Mbps Digital LANs1/23/2013Sumati J. Singh
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Cat 3 vs Cat 5Apart from the listed differences, some visual clues
Higher twist ratio in Cat 5 , at-least 12 twists/ foot Cat 3 has 3 twists/foot
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Cat 3 jacket is loose than Cat 5
Cat 5 can support only a small amount of untwistingbefore termination.
Cat 5 provides better throughput. 1/23/2013Sumati J. Singh
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STP and UTP Cost STP is generally more expensive and also requires grounding
and installation charges. UTP 6 is costly too.
Throughput Ranges from 10 to 1000 Mbps depending on type ofwire.
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Connector Both use RJ-45 and RJ-11 connectors
Noise immunity STP is more resistant than UTP UTP may use filtering and balancing to offset the effects of noise
Size & Scalability Max segment length is 100 m or 328 ft. OnEthernet support 1 Mbps to 10 Gbps with max 1024 nodes.
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UTP Performance16
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Terminating Twisted Pair18
Cross over cable1/23/2013Sumati J. Singh
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Coaxial Cable Also called coax
Single core (copper wire) enclosed in insulating sheath,encased in outer conductor metal foil / braid /
combination.
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This outer wrap is used to shield and acts second conductorfor ground
Outer conductor is insulated
Covered in plastic sheath
Insulator is PVC/Teflon 1/23/2013Sumati J. Singh
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Coaxial Cable20
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Characteristic High resistance to noise
Carry signals to larger distances than twisted pair More expensive
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STANDARDS Radio Guide Used to guide radio frequencies in broadband
Different types provide different impedance,
attenuation and throughput Size of core is in AWG ( American Wire Gauge ). High
AWG smaller the diameter
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RG - 6 Impedance of 75 ohms
contains an 18 AWG conducting core.
to deliver broadband cable Internet service and
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over long distances
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RG - 8 50-ohm impedance
10 AWG core.
the medium for the first Ethernet networks
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o owe e ase- s an ar
10 max throughput 10 Mbps
baseband transmission
maximum segment length of 500 meters. known as Thicknet
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RG - 58 50-ohm impedance
24 AWG core
Popular Ethernet network medium in 80s
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ma er ame er an - , more ex e, easy o
install & handle
10Base-2
Thinner than RG-8, also called Thinnet
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RG-59 75 ohm impedance
20 or 22 AWG core
Made of braided copper
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ess expns ve, u grea er a enua on
Used for short connections
RG-6 and RG-59 are commonly used
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Connector F-type
Attach in a way so that the pin in the center of theconnector is the conducting core of the cable
Compressed to attach to cable, connectors are
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threaded and screw together like a nut and boltassembly
Mostly used for RG-6
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Connector BNC (Bayonet Neill-Concelman)
Crimped, compressed and twisted on cable Connects to another BNC via turning & locking
Do not use core of coax have their own conductin in
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Used with RG 59 commonly
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Applications Analog telephone networks
Single cable carries 10000 voice signals
Later used in digital data, carry upto 600 Mbps
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Refraction29
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Critical Angle30
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Reflection31
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Fiber Optic Cable Glass fibers at the core
Covered by glass or plastic cladding Cladding should be of different density as of core
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opaque, prevent light from escaping
Strands of Kevlar (polymeric fiber) surrounds
Plastic sheath
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Fiber Modes33
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SMF Narrow core ( less than 10 microns)
Highly focused, expensive Limits beam to smaller range of angles, close to
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Lower density material , critical angle close enough
to 90 degree
Propagation almost horizontal
Delays are negligible
Allows high bandwidth & longest distances (of all
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SMF35
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MMF Multiple beams travel
Larger diameter 50 to 115 microns Used as backbone like router to switch /server
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eams rave a eren ang es rom source o
destination
Short distances
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Step Index37
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Graded Index38
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Benefits of Fiber More Reliable
Extremely high throughput Very high resistance to noise
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xce en secur y
Ability to carry signals to larger distances
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Disadvantage Expensive
CablesNICs
Connectors
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hubs
Special equipment to splice
Skilled labor
Connecting two fibers is specialized task
Repairing time is difficult in limited time/resources
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Connectors 10 different types are available
4 are commonly used ST (straight tip)
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LC (local connector)
MT-RJ (mechanical transfer registered jack)
Existing networks generally use SC & ST
With latest technology, LC and MT_RJ are used
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Connectors
LC & MT-RJ are smaller and allow higher density of
connections
-
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multimode fiber in single ferrule ( a short tubewithin, that encircles the fiber to properly align )
Two strands provide for duplex signaling
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Connectors43
STSC
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LC
MT-RJ