Computer Communication & Networks

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Computer Communication & Networks

Lecture 8Physical Layer: Transmission Media

http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp

Waleed Ejazwaleed.ejaz@uettaxila.edu.pk

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Physical Layer

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Physical Layer Topics to CoverSignals

Digital TransmissionAnalog Transmission

Multiplexing

Transmission Media

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Transmission Medium and Physical Layer

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Twisted-pair Cable

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Categories of unshielded twisted-pair cables

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Twisted Pair Cable

(a) Category 3 UTP(b) Category 5 UTP

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UTP connector

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Twisted Pair Cables (Example) ADSL Ethernet networks

- 10BASE-T

- 100BASE-TX

- 1000BASE-T

- 1000BASE-TX (Cat5e (enhanced))

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UTP Performance

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Twisted Pair Cable (Pros & Cons)Pros: easy to understand mass production - low cost most widely used medium

Cons: prone to electromagnetic interference

in power plants, airport buildings, military facilities, cars…

Note:In-building networks at our university are almost all

twisted pair

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Coaxial cable

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BNC connectors

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Performance Coaxial Cable

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Bending of light ray

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Optical fiber

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Propagation Modes

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Modes

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Fiber types

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Fiber construction

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Fiber-optic Cable Connectors

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Performance Optical Fiber

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Optical Fiber (Pros & Cons)

Pros: Low attenuation Large bandwidth

Cons: Relatively “new” technology “Expensive”

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Comparing optical fiber to UTPPros: Immune to electro-magnetic interference

no crosstalk Reduced need for error detection and correction Enables longer link distances Attenuation unaffected by transmission rate Easier network upgrade Can combine different services: telephony, TV, internet…

Cons: Optical components have higher cost Expensive deploying protocols

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Unguided Media: Wireless

Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication.

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Wireless

Modern wireless digital communication began in the Hawaiian Islands

What is “the best” frequency to use for communication?

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Propagation Methods

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Bands

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Wireless Transmission Waves

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Omni directional Antenna

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Radio waves are used for multicast communications, such as radio and

television, and paging systems.

Note

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Unidirectional Antennas

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Microwaves are used for unicast communication such as cellular telephones, satellite networks,

and wireless LANs.

Note

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Infrared signals can be used for short-range communication in a closed area

using line-of-sight propagation.

Note

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Readings

Chapter 7 (B.A Forouzan) Section 7.1, 7.2

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