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Transmission Media

Name: SuhaibPresented To:

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Transmission Media

Any thing that carry information from one location to another is known as Transmission

Media. Example Air.

In data communication it may be defined as means by which Signals(information) are

carried from one system to another.

Transmission MediaTransmission Media and Physical Layer

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Classification of Transmission media

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Radio/Microwave

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GUIDED MEDIA

In Bounded Media physical links are established to transmit information from one device to another. It includes twisted-pair cable, coaxial cable, and fiber-optic cable.

•Twisted pair and coaxial cable use copper conductors and transmits signals in the form of electric current.

•Optical fiber transports signals in the form of light.

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Guide Media - Twisted Pair

Twisted pair consists of two conductors (copper).Each wire has its own insulation and are twisted

together.

Twisted pairOne of the wires carries

signal, the other is used only as a ground reference.

The receiver uses the difference b/w the two.

Twisting increases possibility that both wires are equally affected by Noise, thus the difference at the receiver remains same.

Therefore, number of twists per unit length determines the quality of the cable.

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Unshielded Versus Shielded Twisted-Pair Cable

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Unshielded Twisted Pair (UTP)It was invented by

Alexander Graham Bell.

Most common cable used in computer networking and Telephone systems

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Shielded Twisted Pair (STP)It has a Metal foil

or sheathing that reduces the noise and thus improves the quality of Cable.

Used only by IBMMore expensiveHarder to handle

(thick, heavy)

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Guided Media – UTPUTP Connector

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Twisted Pair - Pros and ConsMost preferred mediumCheapestEasiest to installFor local area networks (LAN)

Suffers from external EM interference Less Bandwidth Short range

Guided Media – Coaxial CableCoaxial Cable

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Coaxial Cable

Coaxial cable was invented by English engineer and mathematician H.Oliver in 1880.

Instead of two wires it has one central core conductor.

Coaxial cableInner conductor is

a solid wire outer conductor serves as conductor as well as shield against noise.

Whole cable is protected by a plastic cover.

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Attenuation is much higher in coaxial cable and thus Repeaters are required frequently.

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Coaxial Cable Pros and ConsIts versatile mediumTelevision distributionLong distance telephone transmissionCan carry 10,000 voice calls simultaneouslyLocal area networks

Coaxial cable insulation may degrade, requiring replacement of the cable.

Despite being shielded, interference can occur on coaxial cable lines.

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Guided Media – Coaxial CableBNC Connectors

BNC connectorsBNC = Bayone-Neill-

ConcelmanBNC Connector is

used to connect the end of the cable to a device

BNC T is used in networks to branch out a cable for connection to a computer or other device

BNC Terminator is used at the end of the cable to prevent the reflection of signal.

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Guided Media – Fiber-Optic Cable

Bending of light ray

It works on the principle of total internal reflection

Fiber-optic cable transmit signals in the form of light.

Bending of light rayAngle of Incidence

(I): the angle the ray makes with the line perpendicular to the interface between the two substances

Critical Angle: the angle of incidence which provides an angle of refraction of 90-degrees.

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Guided Media – Fiber-Optic Cable

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Optical Fiber

An optical fiber cable has a cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket.

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OPTICAL FIBER CONSTRUCTION

a) Core: Thin glass center of the fiber where light travels (high refractive index). The core has a diameter in the range of 8 to 50 µm..

b) Cladding: Outer optical material surrounding the core (low refractive index).

c) Buffer Coating: Plastic coating that protects

the fiber.

Buffer coating

claddingcore

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Transmitters

light-emitting diodes (LEDs)

laser diodes

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Receivers

The main component of an optical receiver is

a photodetector that converts light into

electricity through the photoelectric effect.

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Fiber-Optic Cable Two popular connectors used with fiber-optic cable:

ST connectors (Straight Tip) used for networking devices SC connectors (Standard / Subscriber) used for cable TV

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Areas of Applicationa) Telecommunicationsb) Local Area Networksc) Cable TVd) CCTVe) Medical Education

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Advantages of Optical Fibrea) Thinnerb) Higher Carrying Capacityc) Less Signal Degradation d) Light Signalse) Non-Flammablef) Light Weight

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Disadvantages of fiber optics

Unidirectional propagation.

Expensive over short distance.

Requires highly skilled installers.

Adding additional nodes is difficult.

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Guided Media – Fiber-Optic CablePropagation

Modes

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Guided Media – Fiber-Optic Cable

Propagation Modes

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STEP-INDEX

In step-index fiber the density of central core

remains uniform . An outside cladding that

also has a uniform refractive index surrounds

the core;

However, the refractive index of the cladding

is less than that of the central core which

result in abrupt change .

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GRADED-INDEX

In graded-index fiber, the density of the core

varies continuously. Density is highest at the

center of core.

This causes light rays to bend smoothly as

they approach the cladding, rather than

reflecting abruptly from the core-cladding

boundary.

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Optical Fiber Transmission Modes

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Electromagnetic Spectrum

• Data communication and Networking By : BEHROUZ A FOROUZAN

References