lecture3 dcn
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Physical Media
PHYSICAL MEDIA
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Physical Media
Physical Media
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Physical MediaMagnetic Media/optical discs etc.
CopperCoaxial Cable Baseband and broadbandUnshielded Twisted Pair - CAT 3,4,5,5e&6
Optical FiberMultimodeSinglemode
WirelessRadio waveIR waveMicrowaveSatellite
Physical Media
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Copper Media: Coaxial CableCoaxial cable is a copper-cored cable surroundedby a heavy shielding andis used to connectcomputers in a network.
Outer conductor shieldsthe inner conductor frompicking up stray signalfrom the air.
High bandwidth but lossychannel.
Repeater is used toregenerate the weakenedsignals.
Physical Media
Category Impedance Use
RG-59 75 Cable TV
RG-58 50Thin
Ethernet
RG-11 50Thick
Ethernet
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Copper Media: Twisted PairTwisted-pair is a type ofcabling that is used fortelephone communicationsand most modern Ethernetnetworks.
A pair of wires forms acircuit that can transmitdata. The pairs are twistedto provide protection
against crosstalk, the noisegenerated by adjacent pairs.
There are two basic types,shielded twisted-pair (STP)and unshielded twisted-pair
(UTP).
Physical Media
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Shielded Twisted Pair (STP)
Physical Media
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Unshielded Twisted Pair (UTP)
Physical Media
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Unshielded Twisted Pair (UTP)Consists of 4 pairs (8 wires) ofinsulated copper wires typicallyabout 1 mm thick.
The wires are twisted together in ahelical form.
Twisting reduces the interferencebetween pairs of wires.
High bandwidth and High attenuationchannel.
Flexible and cheap cable.Category rating based on number oftwists per inch and the material used
CAT 3, CAT 4, CAT 5, Enhanced CAT5 and now CAT 6.
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Categories of UTPUTP comes in several categories that are based onthe number of twists in the wires, the diameter of thewires and the material used in the wires.
Category 3 is the wiring used primarily for telephone
connections.Category 5e and Category 6 are currently the mostcommon Ethernet cables used.
Physical Media
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Categories of UTP: CAT 3
Bandwidth 16 Mhz
11.5 dB Attenuation
100 ohms ImpedanceUsed in voice applications and 10baseT (10Mbps)Ethernet
Physical Media
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Categories of UTP: CAT 4
20 MHz Bandwidth
7.5 dB Attenuation
100 ohms ImpedanceUsed in 10baseT (10Mbps) Ethernet
Physical Media
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Categories of UTP: CAT 5
100 MHz Bandwidth
24.0 dB Attenuation
100 ohms ImpedanceUsed for high-speed data transmission
Used in 10BaseT (10 Mbps) Ethernet & Fast Ethernet(100 Mbps)
Physical Media
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Categories of UTP: CAT 5e
150 MHz Bandwidth
24.0 dB Attenuation
100 ohms ImpedanceTransmits high-speed data
Used in Fast Ethernet (100 Mbps), Gigabit Ethernet(1000 Mbps) & 155 Mbps ATM
Physical Media
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Categories of UTP: CAT 6
250 MHz Bandwidth
19.8 dB Attenuation
100 ohms ImpedanceTransmits high-speed data
Used in Gigabit Ethernet (1000 Mbps) & 10 GigEthernet (10000 Mbps)
Physical Media
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Fiber Media
Optical fibers use lightto send informationthrough the optical
medium.It uses the principal oftotal internal reflection.
Modulated lighttransmissions are usedto transmit the signal.
Physical Media
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Fiber MediaLight travels through the optical media by the way oftotal internal reflection.
Modulation scheme used is intensity modulation.
Two types of Fiber media :MultimodeSinglemode
Multimode Fiber can support less bandwidth thanSinglemode Fiber.
Singlemode Fiber has a very small core and carryonly one beam of light. It can support Gbps datarates over > 100 Km without using repeaters.
Physical Media
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Propagation of Signals inOptical Fiber
Advantages Low loss ~0.2dB/km at1550nm Enormous bandwidth at least 25THz Light weight Flexible Immunity to interferencesDisadvantages and Impairments Difficult to handle dispersion Absor tion &Ra lei h Scatterin
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Single and Multimode FiberSingle-mode fiber
Carries light pulsesalong single pathUses Laser Light
SourceMultimode fiberMany pulses of lightgenerated by LEDtravel at different
angles
Physical Media
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A fiber optic ring LAN
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Fiber MediaThe bandwidth of the fiber is limited due to thedispersion effect.
Distance Bandwidth product of a fiber is almost aconstant.
Fiber optic cables consist of multiple fibers packedinside protective covering.
Physical Media
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Fiber-Optic CableContains one or severalglass fibers at its core
Surrounding the fibers isa layer called cladding
Physical Media
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Fiber Optic CableFO Cable may have 1 toover 1000 fibers
Physical Media
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Wireless MediaVery useful in difficultterrain where cablelaying is not possible.
Provides mobility to
communication nodes.Right of way and cablelaying costs can bereduced.
Susceptible to rain,atmospheric variationsand Objects intransmission path.
CLASS NOTES
Physical Media
h i l di
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Frequency Bands
Physical Media
Band RangePropagatio
nApplication
VLF 3 30 KHz Ground Long-range radio navigation
LF 30 300 KHz Ground Radio beacons andnavigational locators
MF 300 KHz 3 MHz Sky AM radio
HF 3 30 MHz Sky Citizens band (CB),ship/aircraft communication
VHF 30 300 MHz Sky andline-of-sight
VHF TV,FM radio
UHF 300 MHz 3 GHz Line-of-sight
UHF TV, cellular phones,paging, satellite
SHF 3 30 GHz Line-of-sight
Satellite communication
EHF 30 300 GHz Line-of-sight Long-range radio navigation
Ph i l M di
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Wireless LAN
Physical Media
Internet Router Switch
Access Point
Access Point
PC
PC
Ph i l M di
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Terrestrial MicrowaveMicrowaves do notfollow the curvature ofearth
Line-of-Sight
transmissionHeight allows thesignal to travel farther
Two frequencies fortwo waycommunicationRepeater is used toincrease the distanceHop-by-Hop
Physical Media
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Ph i l M di
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Satellite Communication
Physical Media
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+ CLASS NOTES-------------
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