Unit I -Transmission Media

8/9/2019 Unit I -Transmission Media

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Transmission Media


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Transmission medium and physical layer


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Classes of transmission media


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GUIDED MEDIAGUIDED MEDIA

Guided media, which are those that provide a conduitGuided media, which are those that provide a conduit

from one device to another, include twisted-pair cable, from one device to another, include twisted-pair cable,

coaxial cable, and fiber-optic cable.coaxial cable, and fiber-optic cable.

Twisted-Pair Cable

Coaxial Cable

Fiber-Optic Cable


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Twisted-pair cable


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UTP and STP cables


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Cateories of unshielded twisted-pair cables


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UTP connector


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Coaxial cable


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Cateories of coaxial cables


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!endin of liht ray


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"ptical fiber


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Propaation modes


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$iber types


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$iber construction


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$iber-optic cable connectors


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"ptical fiber performance


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UNGUIDED MEDIA: WIRELESSUNGUIDED MEDIA: WIRELESS

Unuided media transport electromanetic wavesUnuided media transport electromanetic waveswithout usin a physical conductor. This type ofwithout usin a physical conductor. This type of

communication is often referred to as wirelesscommunication is often referred to as wireless

communication.communication.

Radio Waves

Microwaves

Infrared


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%lectromanetic spectrum for wireless communication


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Propaation methods


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!ands


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&ireless transmission waves


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Unidirectional antennas


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•Radio waves are used for multicast

communications, such as radio andtelevision, and paging systems.•Microwaves are used for unicast

communication such as cellulartelephones, satellite networks,

and wireless LANs•Infrared signals can e used for short!

range communication in a closed area

using line!of!sight propagation.


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"igital Transmission

Representing digital data by using digitalRepresenting digital data by using digital

signals involves three techniques:signals involves three techniques:

•Line codingLine coding•Block coding Block coding •ScramblingScrambling

Line coding is always needed; block codingLine coding is always needed; block coding

and scrambling may or may not be needed.and scrambling may or may not be needed.


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Line coding and decoding


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Signal element versus data element

) l "


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A signal is carrying data in which one data

element is encoded as one signal element r ! "#.

$% the bit rate is "&& kbps' what is the average

value o% the baud rate i% c is between & and "(

Solution

We assume that the average value of c is 1/2 . The baud

rate is then

)*ample "

)*ample /


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+he ma*imum data rate o% a channel see ,hapter

-# is ma* ! / 0 B 0 log / L de%ined by the yquist

%ormula#. 1oes this agree with the previous

%ormula %or ma* (

Solution A signal with L levels actually can carry log 2 L bits per

level. If each level corresponds to one signal element and

we assume the average case (c = 1/2), then we have

)*ample /


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Although the actual andwidth of a

digital signal is infinite, the effective

andwidth is finite.


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)%%ect o% lack o% synchroni2ation

)*ample


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$n a digital transmission' the receiver clock is &."

percent %aster than the sender clock. 3ow many

e*tra bits per second does the receiver receive i%

the data rate is " kbps( 3ow many i% the data rate

is " 4bps( Solution

At 1 kbps, the receiver receives 1001 bps instead of 1000

bps.

)*ample

At " 4bps' the receiver receives "'&&"'&&& bpsinstead o% "'&&&'&&& bps.


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Line coding schemes


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5nipolar R6 scheme


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7olar R68L and R68$ schemes


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•In NR#!L the level of the voltage determines

the value of the it.

•In NR#!I the inversion or the lack of inversion

determines the value of the it.

•NR#!L and NR#!I oth have an average signal

rate of N$% &d.

•NR#!L and NR#!I oth have a "' component

prolem.

)*ample


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A system is using R68$ to trans%er "&84bps data.

9hat are the average signal rate and minimum

bandwidth(

SolutionThe average signal rate is S = N/2 = 500 kbaud. The

minimum bandwidth for this average baud rate is Bmin =

S = 500 kHz.

)*ample


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7olar R6 scheme


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7olar biphase: 4anchester and

1i%%erential 4anchester schemes


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•In Manchester and differential Manchester

encoding, the transition at the middle of theit is used for synchroni(ation.

•The minimum andwidth of Manchester and

differential Manchester is % times that ofNR#.


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Bipolar schemes: A4$ and pseudoternary

•In ipolar encoding, we use three levels)

positive, (ero, and negative.


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In m&nL schemes, a pattern of m data

elements is encoded as a pattern of n

signal elements in which %m * Ln.

4ultilevel encoding


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4ultilevel: /B" scheme


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4ultilevel:


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4ultilevel: 187A4> scheme


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4ultitransition: 4L+8- scheme


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Summary o% line coding schemes


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&lock coding

Block coding is referred as m&$n& coding Replaces each m-bit group with an

n-bit group.


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Block coding concept


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5sing block coding B?>B with

R68$ line coding scheme

B?>B mapping codes


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B?>B mapping codes


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Substitution in B?>B block coding

)*ample >


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9e need to send data at a "84bps rate. 9hat is

the minimum required bandwidth' using a

combination o% B?>B and R68$ or 4anchester

coding( Solution

First 4B/5B block coding increases the bit rate to 1.25

Mbps. The minimum bandwidth using NRZ-I is N/2 or

625 kHz. The Manchester scheme needs a minimum

bandwidth of 1 MHz. The first choice needs a lower bandwidth, but has a DC component problem; the second

choice needs a higher bandwidth, but does not have a DC

component problem.

)*ample >


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A4$ used with scrambling


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+wo cases o% B


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1i%%erent situations in 31B- scrambling technique

/"&0 sustitutes four consecutive (eros with --- or

&-- depending on the numer of non(ero pulses after

the last sustitution.

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Unit I -Transmission Media