Download - Lecture3 DCN

8/13/2019 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

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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).

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Shielded Twisted Pair (STP)

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Unshielded Twisted Pair (UTP)

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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.

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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

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20 MHz Bandwidth

7.5 dB Attenuation

100 ohms ImpedanceUsed in 10baseT (10Mbps) Ethernet

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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)

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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

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250 MHz Bandwidth

19.8 dB Attenuation

100 ohms ImpedanceTransmits high-speed data

Used in Gigabit Ethernet (1000 Mbps) & 10 GigEthernet (10000 Mbps)

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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.

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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.

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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

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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.

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Fiber-Optic CableContains one or severalglass fibers at its core

Surrounding the fibers isa layer called cladding

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Fiber Optic CableFO Cable may have 1 toover 1000 fibers

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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

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Wireless LAN

Physical Media

Internet Router Switch

Access Point

Access Point

PC

PC

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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

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Ph i l M di


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Satellite Communication

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+ CLASS NOTES-------------