Lecture Chapter7 Media Transmisi

8/19/2019 Lecture Chapter7 Media Transmisi

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Chapter 7

Transmission MediaSignals (that represent data) are transmitted from

one device to another in the form of electromagnetic

energy

Electromagnetic signals travel through transmission

media (metal cables, air/space, fiber-optic, etc).


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Guided Media

cables that provide a conduit from one device

to another.


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Guided Media

Twisted-air !able two conductors each surrounded by an insulator

the most common type of telecommunicationmedium in use.

e.g. telephone system

suitable for voice and

data color-banded for

identification


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Guided Media

Twisted-air !able " effect of noise if on parallel line

the wire closest to the source of noise gets more

interference (high voltage level) " uneven load anddamaged signals


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Guided Media

Twisted-air !able " noise on twisted-pair line

twisted wires at regular intervals (#-$# twists/foot),

the cumulative effect of the interference is e%ual onboth wires

significantly reduce

the impact of noise


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Guided Media

&nshielded Twisted-air (&T) !able cheap, fle'ible, easy to install


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Guided Media

&nshielded Twisted-air (&T) !able E categories of &T !ables

Cat. 1 " used in old telephone system, fine for voice andlow-speed data transmission.

Cat. 2 " suitable for voice, data transmission up to * +bps.

Cat. 3 " now standard cable for most telephone systems,

data transmission up to $ +bps.

Cat. 4 " data transmission up to $ +bps. Cat. 5 " data transmission up to $ +bps.


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Guided Media

&T !able !onnectors snap-in plug lie telephone acs

male (plug), female (receptacle)

popular, 01*2

(* twisted pairs "

3 conductors)

01$$

(# pairs "* conductors)


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Guided Media

Shielded Twisted-air (ST) !able has a metal foil or braided mesh covering each pair of

insulated conductors

prevents penetration of electromagnetic noise and crosstal

(undesired effect of one circuit on another circuit).

more e'pensive

than &T but

less susceptible

to noise


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Guided Media

!oa'ial (!oa') !able has a central core conductor of solid or stranded wire

(copper) enclosed in an insulating sheath, which is in turn,

encased in an outer conductor of metal foil,

braid or combination.

The outer conductor

serves as a shield

against noise and thesecond conductor.


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Guided Media

!oa' !able 0adio 4overnment (04) ratings for coa' cables

04-3, 04-5, 04$$ " used in thic Ethernet 04-23 " used in thin Ethernet

04-25 " used for T6


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Guided Media

!oa' !able !onnectors 78! (bayonet networ connector) " pushes on

and loc into place with a half turn the most popular

T-connectors " allow cables to branch from a main

line used in thin Ethernet

Terminators " re%uired for bus topologies to

absorb the wave at the end and eliminate echo-

bac.


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Guided Media

9iber-optic !able made of glass or plastic and transmits signals in the form of

light.

nformation is encoded onto a beam of light as a series of

on-off flashes that represent $ and bits.

ropagation modes multimode

single mode


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Guided Media

9iber-optic !able " +ultimode Step-nde' multiple beams from a light source move through the core in

different path.

the density of the core remains constant from the center to

the edges.

some beams in the

middle travel in

straight lines through

the core and reach

the destination.


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Guided Media

9iber-optic !able " +ultimode Step-nde' (cont) some beams strie the interface of the core bouncing bac and

forth until they reach destination.

as these different beams are recombined at the receiver, they

result in a signal that is no longer an e'act replica of the signal

that was transmitted.

The distortion limits the

available data rate.


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Guided Media

9iber-optic !able " +ultimode 4raded-nde' multiple beams from a light source move through the core in

different path.

variable core density " density is highest at the center and

decrease gradually to its lowest at the edge.

a series of constantly

changing density

causes each beam

to refract into a curve

the reconstructed

signal allows

greater precision.


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Guided Media

9iber-optic !able " Single +ode a highly focused source of light that limits beams close to

hori:ontal

smaller diameter than multimode fibers

all beams arrive

;together< and can

be recombined

;without< distortion

to the signal


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Guided Media

9iber-optic !able " si:es

= single mode

Fiber Type Core (microns) Cladding (microns)

#.2/$#2

2/$#2

$/$*

3.>/$#2 =

#.2

2.

$.

3.>

$#2

$#2

$*

$#2


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Guided Media

9iber-optic !able " !able !onstruction fiber " made of either glass or plastic of different densities,

ultrapure (material, si:e, shape).

buffer " protects from moisture.

outer acet " teflon coating, plastic coating, fibrous plastic,

etc, choice depends on

where the cable is to be

installed


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Guided Media

9iber-optic !able " ?ight Sources ?E@ (light emitting diode)

cheaper, unfocused light, short distance use

?@ (inection laser diode) focused, preserve signal over considerable distance

9iber-optic !able " !onnectors precise and easy to use

(popular) barrel shape in male and female versions


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Guided Media

dvantages of Aptical 9iber noise resistance

less signal attenuation (loss of energy) " can run miles

without re%uiring regenaration

higher bandwidth (and data rates)

@isadvantages of Aptical 9iber cost

installation/maintenance

fragility " glass fiber is easily broen


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Unguided Media

wireless communication " transport electromagneticwave without using physical conductorB e.g. air.

0adiocommunication

bands


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Unguided Media

Types of ropagation

tmosphereC troposphere " about

> miles from earth

surface, air

ionosphere " above

troposphere


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Unguided Media

Types of ropagation " Surface radio waves travel through the lowest portion of the

atmosphere

signals emanate in all directions follow the curvature of the

planet

6?9 (very low fre%uency) wave " do not suffer

much attenuation in transmission but susceptible

to the high levels of atmospheric noiseB used

mostly for long-range radio and submarinecommunication

?9 (low fre%uency) wave " similar to 6?9B

attenuation is greater during daytime


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Unguided Media

Types of ropagation " Tropospheric signal can be directed in a straight line from antenna to

antenna (line-of-sight) re%uires placement of the receiver and the transmitter within

line of sight distance

also signal can be broadcast at an angle into

the upper layers of troposphere where it is

reflected bac to earth greater distance covered

+9 (middle fre%uency) transmissionB

for + radio, etc.


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Unguided Media

Types of ropagation " onospheric waves radiate upward into ionosphere where there are

reflected bac to the earth

even greater distance than tropospheric propagation with

lower power output

D9 (high fre%uency) transmissionB

for aircraft comm., military comm.,

telephone


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Unguided Media

Types of ropagation " ?ine-of-sight signals are transmitted in straight line directly from antenna

to antenna

6D9 (very high fre%uency)B for 6D9 television, 9+ radio, etc.

&D9 (ultra high fre%uency)B &D9 television,

mobile telephone, paging, etc.


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Unguided Media

Types of ropagation " Space utili:e satellite relays

a broadcast signal is received by an orbiting satellite, which

rebroadcasts the signal to the intended receiver bac on

earth

the satellite is lie super-high-gain antenna and dramatically

increases the distance covered

SD9 (super high fre%uency)

ED9 (e'tremely high fre%uency)B

predominantly for scientific, radar,

satellite, e'perimental comm.


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Satellite Communication

satellite acting acting as a supertall antenna and repeater

+alaysian +EST

http://www.measat.com/http://www.measat.com/


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4eosynchronous Satellites it taes a minimum of three satellites e%uidistant to provide

full global transmission

remain fi'ed above a

certain spot


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9re%uency bands for satellite communications uplin " transmission from the earth to the satellite

downlin " transmission from the satellite to the earth

+EST Technical Specifications

Band Downlink Uplink

!

u

a

>.F to *.# 4D:

$$.F to $#.# 4D:

$F.F to #$ 4D:

2.5#2 to .*#2 4D:

$* to $*.2 4D:

#F.2 to >$ 4D:

http://www.measat.com/html/system.htmlhttp://www.measat.com/html/system.html


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Cellular Telephony

the service provider must

be able to locate and trac

the caller, assign a channel

to the call, and transfer the

signal from channel to

channel as the caller

moves out of the range of

one channel into the range

of another


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Transmission

ImpairmentThe imperfection of transmission medium cause

impairment in the signal what is sent is not what is received


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Transmission

Impairment ttenuation loss of energy during transmission due to

resistance of the medium.

amplifiers are used to compensate the lost.


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Transmission

Impairment@istortion signal changes its form or shape.

occurs in a composite signal which made ofdifferent fre%uencies.


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Transmission

Impairment8oise thermal noise (random motion of electrons creates an

e'tra signal), induced noise (comes from outside

source), crosstal (effect on one wire on the other )


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Performance

Transmission media performance can be

measured


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Performance

Throughput the time - how fast data can pass through a point

bits per second


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Performance

ropagation Speed the distance " how far a signal (or a bit) can travel

through a medium e.g. light in a vacuum G twisted pair H > ' $3 m/s

coa'ial G fiber optic H # ' $3 m/s


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Performance

ropagation Time time re%uired for a signal (or a bit) to travel from

one point of the transmission medium to another ropagation time H @istance/ropagation speed


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Wavelength

The distance a simple signal can travel in one period wavelength H propagation speed ' period

H propagation speed ' ($ / fre%uency)

H propagation speed / fre%uency


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Media Comparison

+edium !ost Speed ttenuation E+ Security

&T

ST!oa'

Aptical fiber

0adio

+icrowave

Satellite

!ellular

?ow

+oderate+oderate

Digh

+oderate

Digh

Digh

Digh

$-$ +bps

$-$2 +bps$ +bps " $4bps

$ +bps " # 4bps

$-$ +bps

$ +bps " $ 4bps

$ +bps " $ 4bps

5.-$5.# bps

Digh

Digh+oderate

?ow

?ow-Digh

6ariable

6ariable

?ow

Digh

+oderate+oderate

?ow

Digh

Digh

Digh

+oderate

?ow

?ow?ow

Digh

?ow

+oderate

+oderate

?ow

Lecture Chapter7 Media Transmisi

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