Network Media Network media is the actual path over which an electronic signal travels as it moves from one component to another or one device to another

Network Media

Network media is the actual path over

which an electronic signal travels as it

moves from one component to another or

one device to another.

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BIT 1102: Communications Technology & the Internet

The choice of medium depends on: -Distance to be covered.

-Desired Bit Rate (in bits per second, bps)-Cost Considerations

Generally categorized as:-Guided-Unguided (Wireless).

Numerous transmission media types are used for Data

Communication

2BIT 1102: Communications Technology & the Internet

The Basics of Transmission

The Transmitter generates and encodes data as energy which it (energy) transmits through medium.

Transmitted energy is carried through some a medium

Media can be copper, glass, air, etc

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At the destination the energy is decoded back into data (Caustic data).

Energy can be electrical, light, radio etc.

Note: Each form of energy has different properties and requirements for transmission.


Fundamental Limits of Transmission Media

i) All channels allow only a limited set of frequencies to be passed. This limit is called bandwidth of that channel.

Bandwidth: Is the data transfer rate - the amount of data that can be carried from one point to another in a given time period (usually a second).

I.e., How much data is allowed to move through a medium usually per second.

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Fundamental Limits of Transmission Media cont’d

ii) All channels are subject to

background noise (noise is unwanted

electrical or electromagnetic energy

that degrades the quality of signals and

data).

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Fundamental Limits of Transmission Media cont’d

NB: Sources of noise include:

a) crosstalk: A signal on one line is picked up by adjacent lines as a small

noise signal

– For crosstalk, both cables / wires have the same strength.

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b) Near-End Crosstalk (NEXT)

Caused when a strong transmitter output signal interferes with a much weaker incoming receiver signal.

A strong wire Vs a weak energy wire so, the weak /lower strength cable ie the one with low bandwidth or carrying less data is affected

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c) Impulse noise

Caused by external activity or equipment which generates electrical impulses.

Can be caused by voltage spikes in equipment, lightening flashes, during thunderstorms and a wide variety of other phenomenon

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Thermal noise (white noise):

Caused by the thermal agitation of electrons associated with each atom in the device or transmission line material.

Eg , electrical (“UMEME wire”) running parallel but near with the telephone wire. So, the thermal signals from the electrical wire might disorganize the telephone wire.

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Additional Limitations of Transmission Media cont’dAdditional Limitations of Transmission Media cont’d

iii) Signal Attenuation: Is the phenomenon whereby the Amplitude of a signal decreases as it propagates along a transmission line.-Attenuation is a function of distance and frequency of signal-Repeaters are used to increase the power of the signal at appropriate intervals.

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Research about-

Shannon Channel Capacity


Media Types

Two categoriesa) Guided media.

b) Unguided.

a)Guided Transmission Media uses a "cabling" system that guides the data signals along a specific path. The data signals are bound by the "cabling" system. Guided Media

Also known as Bound

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Media Types.

Guided Transmission Media include:Fiber opticsTwisted pair cablesCoaxial cables

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1) Twisted-Pair Cable

Twisted-pair cable: Two of wires form a circuit that can transmit data. Cables are twisted to provide protection against crosstalk.

When two wires in an electrical circuit are placed close together, the magnetic fields are the exact opposite of each other.

The two magnetic fields cancel each other out. They also cancel out any outside magnetic fields. Twisting the wires can enhance this cancellation effect.

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Twisted pair cable

Can be

a) Unshielded Twisted Pair (UTP)

b) Shielded Twisted Pair (STP)

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a) UTP

Unshielded Twisted Pair: UTP cable is a medium that is composed of pairs of wires.

UTP cable is used in a variety of networks. Each of the eight individual copper wires in UTP cable is covered by an insulating material.

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UTP cont’d

UTP cable relies solely on the cancellation effect produced by the twisted wire pairs to limit signal degradation caused by electromagnetic interference (EMI) and radio frequency interference (RFI).

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b) Shielded Twisted-Pair (STP)

Combines the techniques of shielding, cancellation, and wire twisting. Each pair of wires is wrapped in a metallic foil). The four pairs of wires then are wrapped in an overall metallic braid or foil.

Has a cancellation effect and a shield to prevent it from attacks like EMI

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STP

UTP

The general merits of the twisted pair technology

It is rather cost effective in comparison to other technologies like the fiber optic.

It is extremely easy to terminate.

Its thin and flexible and can be strung around walls

More lines can be run through the same connection ducts

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The demerits of the twisted pair technology

It is prone to external interference.

They require many repeaters for relatively long distances which makes it expensive.

NB: The twisted pair technology uses A Registered Jack (RJ 45) in connections.

THE RJ-4525


2) Coaxial Cable

Consists of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements, located in the center of the cable, is a copper conductor.

NB: e.g. those used on TV sets

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Coaxial cable28


Coaxial Cable29


3) Fiber-Optic Cable

Uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages as light waves

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Parts of fiber optics

Core - Thin glass center of the fiber where the light travels

Cladding - Outer optical material surrounding the core that reflects the light back into the core

Buffer coating - Plastic coating that protects the fiber from damage and moisture

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How fiber optics operateThe light in a fiber-optic cable travels through

the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances

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Transmission is through electroluminescence

(an optical phenomenon and electrical

phenomenon in which a material emits

light in response to the passage).

The emitted light is incoherent with a relatively

wide spectral width of 30-60 nm.Receivers- the main component of an optical

receiver is a photo-detector that converts light into electric-signal through the photoelectric effect .


Transmitter-the most commonly-used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes.

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Fiber-Optic Cable36


Two types of fiber-optic cables

a) Single-mode

Allows only one mode of light to propagate through the fiber. Capable of higher bandwidth, and it is often used as a backbone - (10kms).

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Multimode

Multimode fiber cable allows multiple modes of light to propagate through the fiber. It uses light-emitting diodes (LEDs) as a light-generating device (2km)

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Advantages

Fibers do not leak light and are quite difficult to tap (Secure).

Handles much higher bandwidth than copper wires.The loss of signal in optical fiber is less than in

copper wire. Repeaters are needed at 30 km Vs 5 for copper.

Not affected by electromagnetic interference. Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable.

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Disadvantages

They are quite difficult to install Its an expensive technology. Its expensive to

install.Very delicate / fragile.


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b) Unguided Media-Wireless Communication

Unguided Transmission Media refers to data signals that flow through the air. They are not guided or bound to a channel to follow.

Unguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum and sea-water.

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Wireless communication

Is the transfer of information over a distance with the use of electromagnetic waves.

Electromagnetic waves are formed when an electric field couples with a magnetic field.

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Example of unguided media

1. Radio wave transmission

2. Micro wave transmission

3. Light wave transmission

4. Infrared and bluetooth


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1. Radio transmission

The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave

There are 3 types of RF (Radio Frequency) Propagation: Ground Wave, Ionospheric and Line of Sight (LOS) Propagation.

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Xtics of radio transmission 45


i) Ground Wave Propagation

Follows the curvature of the Earth. Ground Waves have carrier frequencies up to 2 MHz. AM radio is an example of Ground Wave Propagation.

Radio, television and micro-waves are types of electromagnetic waves. They differ from each other in wavelength.

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ii) Ionospheric Propagation

Bounces off of the Earths Ionospheric Layer in the upper atmosphere. It is sometimes called Double Hop Propagation. It operates in the frequency range of 30 - 85 MHz

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iii) Line of Sight Propagation

Line of Sight Propagation transmits exactly in the line of sight. The receive station must be in the view of the transmit station. It is sometimes called Space Waves or Tropospheric Propagation.

Examples of Line of Sight Propagation are: FM Radio, Microwave and Satellite.

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Wavelength is the distance between one wave crest to the next.


Frequencies

Gamma Rays (above 30GHz) X-RaysUltra-Violet Light Visible Light Infrared Light EHF - Extremely High Frequencies 30 GHz Radar

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SHF - Super High Frequencies 3 GHz Satellite & Microwaves

UHF - Ultra High Frequencies 300 MHz, UHF TV

VHF - Very High Frequencies 30 MHz FM & TV

HF - High Frequencies 3 MHz Short Wave Radio


MF – Medium Frequencies 300 kHz (kilo = 10^3) AM Radio

LF - Low Frequencies 30 kHz Navigation VLF - Very Low Frequencies 3 kHz

Submarine Communications VF - Voice Frequencies 300 Hz Audio ELF - Extremely Low Frequencies 30 Hz

Power Transmission


2. Microwaves Transmission

Frequency of above 100MHz, Travel in straight lines Can be narrowly focused.Use a parabolic antenna. Both the transmitting and the receiving

antennas should be accurately aligned with each other.

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Its used for long distance communication,

Can not easily pass through strong buildings and can easily be absorbed by the rain.

• Affected by rain, vapor, dust, snow, clouds, mist and fog, heavy moisture, depending on chosen frequency.

• It’s used for long distance communication.


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3. Bluetooth and infraredBluetooth uses radio to transmit between

microchip devices like mobile phone and a Hands free device.

Infrared (IR) uses electromagnetic waves for transmission as a smaller wavelength than radio. A TV remote control is an example of an Infrared application.

Wireless Personal Area Networks (WPANs) are able to communicate using technologies like Bluetooth (IEEE 8.2.15.1) and infrared.

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Infra-red

Infrared signals can be used for short range communication. Infrared signals, having high frequencies, cannot penetrate walls. This helps to prevent interference between one system and another.

There are a number of computer devices which are used to send the data through infrared medium e.g. keyboard mice, PCs, phones and printers. There are some manufacturers who provide a special part called the IrDA (Infrared Data Association) port that allows a wireless keyboard to communicate with the pc.


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4.Light wave transmission

Unguided optical signal such as laser.Connect 2 LANS in two buildings via a laser

mounted on their roof.Unidirectional, easy to install, don’t require

license.Laser beams can be used for communication but

can not penetrate rain or thick fog.Laser beams can easily be diverted by turbulent

air.

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Advantages associated to wireless communication

• It’s ideal for non-reachable places.• It’s ideal for temporary network setups.• It supports more users unlike the wired

ones.• It’s neat and easy to install.• It’s flexible/can be moved easily.• It’s cheaper to maintain.

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Disadvantages

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Review Questions

Discuss the different types of network media with an in depth study of fiber optics and shielded twisted pair giving their advantages and disadvantages.

Explain the advantages associated with wireless communication .

How do guided differ from unguided media?What is the purposes of cladding in an optical

fiber?Define Shannon capacity and mention its

functions?What are the applications of Radio wave?

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Thank you

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Documents

Network Media Network media is the actual path over which an electronic signal travels as it moves from one component to another or one device to another