By :-

Sudhanshu Kumar Shivam Dubey

Vinay DasPrashant

Contents

Introduction Characteristics Factors affecting data

communication distance of a medium

Reasons for transmission Impairence Types of transmission media Guided Media Twisted Pair Cables

ILLUMINATI 2

Coaxial Cables Optical Fiber Cables Basic Differences Comparision Unguided Medium Radio waves Microwaves Infrared waves Conclusion

ILLUMINATI 3

On any network, the various entities must communicate through some form of media.

Just as humans can communicate through telephone wires or sound waves in the air, computers can communicate through cables, light, and radio waves.

Transmission media enables computers to send and receive messages but do not guarantee that the messages will be understood.

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Introduction

Communication is possible only if information is encoded in a signal, and the signal is carried on a transmission the characteristics of the signal and of the medium both determine the quality of the communication medium.

There are two main groups of transmission media, namely the guided medium and the wireless medium.

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For the guided medium, there is a physical path (such as a cable) for electromagnetic wave propagation.

For the wireless medium, however, the electromagnetic wave is transmitted through air, water, or vacuum.

A wireless medium is also called an unguided medium.

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Characteristics

A good transmission medium should provide communication with good quality at long distance.

For voice communication, quality of communication is determined by the voice quality.

For data communication, however, the quality of communication is mainly determined by the effective data rate of communication.

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Factors Affecting Data Communication of a Medium

Communication bandwidth of the medium

Interference The transmission impairments

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The bandwidth of a medium determines the signal frequencies that can be carried in the medium.

A wide bandwidth, or broadband, usually allows communication at a higher data rate.

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Reasons For Transmission Impairence

Attenuation

Distortion during signal propagation

Noises

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TYPES

of

TRANSMISSION MEDIA

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Guided Media

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Guided media includes everything that ‘guides’ the transmission. That usually takes the form of some sort of a wire. Usually copper, but can also be an optical fiber.

Twisted Pair Cable

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Twisted Pair Cable

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A transmission medium consisting of pairs of twisted copper wires.

We can transmit 1 Mbps over short distances (less than 100m).

They are mainly used to transmit analog signals, but they can be used for digital signals.

Performance

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One way to measure the performance of twisted pair cable is to compare attenuation versus frequency and distance.Gauge is a measure of the thickness of the wire.

Applications

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They are used in telephone lines to provide voice and data channels.

Local area networks , such as 10 Base-T and 100 Base-T also use twisted-pair cables.

Coaxial Cable

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Coaxial Cable

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In its simplest form, coaxial consists of a core made of solid copper surrounded by insulation, a braided metal shielding, and an outer cover.

A transmission medium consisting of thickly insulated copper wire, which can transmit a large volume of data than twisted wire.

Performance

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The performance is same as the twisted pair cable.

The only difference is that the attenuation is much higher in co-axial cable than in twisted pair cable.

Applications

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It is used in cable TV networks

It is used in traditional ethernet LANs.

Optical Fiber

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Optical Fiber

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Optical fiber consists of a glass core, surrounded by a glass cladding with slightly lower refractive index.

In most networks fiber-optic cable is used as the high-speed backbone, and twisted wire and coaxial cable are used to connect the backbone to individual devices.

Performance

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The performance can be measured by plot of attenuation versus wavelength.

Attenuation is flatter than in case of twisted pair cable and co-axial cable.

Applications

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The fiber optic cable is often found in backbone networks because its bandwidth is cost effective.

Used in TV companies.

LAN such as 100 Base-FX Network

Twisted Wire

It is inexpensive and already is in use.

Twisted wires are slow, high-speed transmission causes interference (crosstalk).

Limiting factors: skin effect & radiation effect.

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Coaxial Cable

It is often used in place of twisted wire for important links in a network because it is a faster.

More interference-free transmission medium (speed: 200 megabits per second).

Coaxial cable is thick, is hard to wire in many buildings. It does not support analog conversations.

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Optical Fiber

Optical fibers are faster, lighter, and suitable for transferring large amount of data.

Fiber-optic cable is more difficult to work with, more expensive.

Its difficult to install them.

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Comparison

• Optical fiber cable differs from both these transmission media in that it carries the transmitted information in the form of a fluctuating beam of light in a glass fiber.

• Light transmission has much wider bandwidth, thus enabling the transmission rate of hundreds of megabits per second.

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•Optical transmission is immune to electromagnetic interference and crosstalk. While others are immune to interference.

•Optical fibers have less loss of signal strength than

copper, after every 30 miles we need to use a repeater, whereas in copper, we should insert repeaters at an interval of 2.8 miles .

•Optical fiber is more secure, no easy tapping on the cable, like in copper.

•But optical fibers are more expensive than other two cables.

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Unguided Media

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Unguided media is still ‘media’ (stuff that signal travels though). The trick is that the media is usually not directional, like air, space, etc. Because the effect is usually much wider than with guided media, there have been a lot of regulation, licensing, and standardization of transmissions via unguided media.

Wireless Transmission

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Wireless transmission that sends signals through air or space without any physical wire.

Common uses of wireless data transmission include pagers, cellular telephones, microwave transmissions, communication satellites, mobile data networks, personal digital assistants, television remote controls.

Radio Waves

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Although there is no clear cut demarcation between radio waves and microwaves , electromagnetic waves ranging in frequencies between 3KHz and 1GHz normally called radio waves.

Radio waves are omnidirectional.

Radio waves particularly those waves that propagate in the sky mode , can travel long distances .This makes Radio waves a good candidate for long distance broadcasting such as AM Radio

Applications

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The omnidirectional characteristics of Radio waves make them useful for multicasting, in which there is one sender but many receivers.

AM and FM Radio, television ,maritime radio , cordless phone , and paging are examples of multicasting.

Microwaves

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Electromagnetic waves having frequency between 1 and 300 GHz are called as Micro waves.

Micro waves are unidirectional.Microwave propagation is line of sight.

Very high frequency Micro waves can not penetrate walls.

The microwave band is relatively wide, almost 299 GHz

Applications

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Microwaves due to there unidirectionalproperties are very useful when unicast (one to one ) communication is needed between the sender and the receiver.

They are used in Cellular phones.

They are used in satellite networks.

They are used in wireless LANs.

Infrared Waves

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Infrared waves , with frequencies from 300GHz-400THz can be used for short range communication .

Infrared waves having high frequencies can not penetrate walls.

When we use our Infrared control , we do not interfere with use of the remote by our neighbours.

We cannot use Infrared waves outside a building because the suns rays Contain Infrared waves that can interfere with communication.

Applications

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The infrared band almost 400 THz has an excellent potential for data transmission.

Such a wide bandwidth can be used to transmit digital data with a very high data rate.

Infrared waves is used in communication between devices such as Keyboard, PCs and Printers.

KEY Terms

Bandwidth: The difference between the lowest and highest frequency signals that can be transmitted across a transmission line or communication system.

Interference: The distortion on the signal in transmission due to unwanted signals from outside sources.

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Transmission Impairments: Attenuation, distortion, or noises that will degrade the signal quality during transmission.

Attenuation: The loss of a signal’s energy when the signal is transmitted across a medium.

Signal Distortion: Any change in a signal during signal transmission. 41

Noises: Random signals that can be picked up during signal transmission and result in degradation or distortion of data.

Trunk Circuits: The communication circuits between two switching offices.

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Conclusion In summary, transmission media are

essential for communication systems. Signals that carry information can be transmitted on a transmission medium for communication purposes.Thetransmission characteristics of the medium in use are important because they directly affect the communication quality. Since different types of transmission media have different transmission characteristics and costs, they are used in different (and the most suited) applications.

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