Media Concept and

classification of Media

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Presenter:

Purushottam Dahal

https://www.facebook.com/puru.BIM

Contents

Guided Media

Twisted pair overview

Coaxial cable overview

Fiber optics overview

Unguided Media

VSAT

Satellite

Transmission Characteristics

Attenuation

Noise

Signal to Noise Ratio

Propagation Delay 1/19/2015

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Guided Transmission Media

Purpose is to transfer raw bit stream

Related with physical layer

Various physical medias can be used

Magnetic media, removable medias

Transfer rate, depends upon distance and media

used. Same media may contain various transfer

rates with high degree of variation.

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Twisted Pair

Bandwidth characteristics of Magnetic tape and other removable

media is excellent, the delay characteristics is very poor.

Transmission time is measured in minutes or hours, not milliseconds.

One of the oldest and still most common transmission media is twisted

pair

A cable made by intertwining two separate insulated wires together

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Types of Twisted Pair

UTP STP

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Name Type Bandwidth Applications

Level 1 0.4 MHz Telephone and modem lines

Level 2 4 MHz Older terminal systems, e.g. IBM 3270

Cat3 UTP 16 MHz 10BASE-T and 100BASE-T4 Ethernet

Cat4 UTP 20 MHz 16 Mbit/s Token Ring

Cat5 UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet

Cat5e UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet

Cat6 UTP 250 MHz 10GBASE-T Ethernet

Cat6a 500 MHz 10GBASE-T Ethernet

Class F S/FTP 600 MHzTelephone, CCTV, 1000BASE-TX in the

same cable. 10GBASE-T Ethernet.

Class Fa 1000 MHzTelephone, CATV, 1000BASE-TX in the

same cable. 10GBASE-T Ethernet.1/19/2015

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Co-axial Cable

It has better shielding than twisted pairs, so it can span longer

distances at higher speeds.

Two kinds of coaxial cable are widely used.

One kind, 50-ohm cable, is commonly used when it is intended for

digital transmission from the start. The other kind, 75-ohm cable, is

commonly used for analog transmission and CATV, but is becoming

more important with the advent of Internet over cable.

The construction and shielding of the coaxial cable give it a good

combination of high bandwidth and excellent noise immunity.

The bandwidth possible depends on the cable quality, length, and

signal-to-noise ratio of the data signal.

Modern cables have a bandwidth of close to 1 GHz.

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Coaxial Cable Cut away View1/19/2015

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Fiber Optics

A technology that uses glass (or plastic) threads (fibers) to transmit data. Afiber optic cable consists of a bundle of glass threads, each of which iscapable of transmitting messages modulated onto light waves.

An optical transmission system has three key components: the light source,the transmission medium, and the detector.

Conventionally, a pulse of light indicates a 1 bit and the absence of lightindicates a 0 bit.

The transmission medium is an ultra-thin fiber of glass. The detectorgenerates an electrical pulse when light falls on it.

By attaching a light source to one end of an optical fiber and a detectorto the other, we have a unidirectional data transmission system thataccepts an electrical signal, converts and transmits it by light pulses, andthen reconverts the output to an electrical signal at the receiving end.

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CONT……..

Fiber optics has several advantages over traditional metal

communications lines:

Fiber optic cables have a much greater bandwidth than metal

cables. This means that they can carry more data.

Fiber optic cables are less susceptible than metal cables to

interference.

Fiber optic cables are much thinner and lighter than metal wires.

Data can be transmitted digitally (the natural form for computer

data) rather than analogically.

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A Bundle of Optical Fibers

The structure of a typical

single-mode fiber.

1. Core: 8 µm diameter

2. Cladding: 125 µm dia.3. Buffer: 250 µm dia.

4. Jacket: 400 µm dia

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VSAT

A very small aperture terminal (VSAT), is a two-way satellite ground

station or a stabilized maritime VSAT antenna with a dish antenna that

is smaller than 3 meters.

The majority of VSAT antennas range from 75 cm to 1.2 m.

Data rates range from 4 Kbit/s up to 4 Mbit/s; some upgraded

modules can even reach a max downlink of up to 16 Mbit/s.

VSATs access satellites in geosynchronous orbit to relay data from

small remote earth stations (terminals) to other terminals (in mesh

topology) or master earth station "hubs" (in star topology).

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Satellite

A satellite is an artificial object which has been intentionally placed

into orbit.

Such objects are sometimes called artificial satellites to distinguish

them from natural satellites such as the Moon.

Satellite is a specialized wireless receiver/transmitter that is launched

by a rocket and placed in orbit around the earth.

There are hundreds of satellites currently in operation. They are used

for such diverse purposes as weather forecasting, television broadcast,

amateur radio communications, Internet communications, and the

Global Positioning System(GPS).

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Attenuation

Attenuation is a general term that refers to any reduction in the

strength of a signal.

Attenuation is a general term that refers to any reduction in the

strength of a signal.

Attenuation occurs with any type of signal, whether digital or

analog.

Sometimes called loss, attenuation is a natural consequence of

signal transmission over long distances.

The extent of attenuation is usually expressed in units called

decibels (dBs).

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Noise

Noise is unwanted electrical or electromagnetic energy that degrades the quality of signals and data.

Noise occurs in digital and analog systems, and can affect files and communications of all types, including text, programs, images, audio, and telemetry.

In a hard-wired circuit such as a telephone-line-based Internet hookup, external noise is picked up from appliances in the vicinity, from electrical transformers, from the atmosphere, and even from outer space.

Normally this noise is of little or no consequence. However, during severe thunderstorms, or in locations were many electrical appliances are in use, external noise can affect communications.

In an Internet hookup it slows down the data transfer rate, because the system must adjust its speed to match conditions on the line. In a voice telephone conversation, noise rarely sounds like anything other than a faint hissing or rushing.

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Signal-to-Noise Ratio

In analog and digital communications, signal-to-

noise ratio, often written S/N or SNR, is a measure of

signal strength relative to background noise.

The ratio is usually measured in decibels (dB).

Communications engineers always strive to

maximize the S/N ratio.

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Propagation Delay

Propagation delay is the amount of time it takes for the head of the

signal to travel from the sender to the receiver.

Propagation delay refers to the time lag between the departure of

a signal from the source and the arrival of the signal at the

destination.

It can be computed as the ratio between the link length and the

propagation speed over the specific medium.

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“

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THANK YOU

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