IT2101: Communication Technology

5.Transmission/ Network Media

Program: BSCS I (January Semester – 2014)Lecturer: Rebecca Asiimwe

Email: rasiimwe@technology.ucu.ac.ug

Network Media

2

• 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.

Transmission Media

• Numerous transmission media types are used for Data Communication

• Generally categorized as:

1. Guided

2. Unguided (Wireless)

3

The Basics of Transmission

4

• The Transmitter generates and encodes data as energy which is transmitted through a medium.

• Transmitted energy is carried through some medium

• The medium can be copper, glass, air, etc

• At the destination the energy is decoded back into data that can be used by the destination device.

• Energy can be electrical, light, radio etc.

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

5

Fundamental Limits of Transmission Media

6

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.

7

ii) All channels are subject to background

noise (noise is unwanted electrical or

electromagnetic energy that degrades the

quality of signals and the data received).

Fundamental Limits of Transmission Media

8

• 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.

Fundamental Limits of Transmission Media

b) Near-End Crosstalk

9

• 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 is affected.

c) Impulse noise

10

• 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

Thermal noise (white noise):

11

• 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.

Additional Limitations of Transmission Media

12

iii) Signal Attenuation: Is the phenomenon where the Amplitude/

strength 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.

Media Types

13

Two categories a) 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.

Also known as Bound

Media Types

14

• Guided Transmission Media include:

– Fiber optics

– Twisted pair cables

– Coaxial cables

1) Twisted-Pair Cable

15

• 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.

Twisted pair cable

16

• Can be

a) Unshielded Twisted Pair (UTP)

b) Shielded Twisted Pair (STP)

a) UTP

17

• UTP cable is a medium that is composed of pairs of wires.

• Used in a variety of networks.

• Each of the eight individual copper wires in UTP cable is covered by an insulating material.

18

UTP Cont’d

19

• 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).

b) Shielded Twisted-Pair (STP)

20

• 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.

21

22

STP

UTP

Merits of the twisted pair technology

23

• 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

Demerits of the twisted pair technology

24

• 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-45 connector

2) Coaxial Cable

25

• 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

26

Coaxial cable

27

Coaxial Cable

28

3) Fiber-Optic Cable

29

• 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

Parts of fiber optics

30

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

How fiber optics operate

31

• The 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.

32

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 . 33

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

34

Fiber-Optic Cable

35

Two types of fiber-optic cables

36

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).

Multimode

37

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)

Advantages

38

• 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.

Disadvantages

39

• They are quite difficult to install

• Its an expensive technology - expensive to

install.

• Very delicate / fragile.

b) Unguided Media-Wireless Communication

40

• 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.

Wireless communication

41

• 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.

Example of unguided media

42

1. Radio wave transmission

2. Micro wave transmission

3. Light wave transmission

1. Radio transmission

43

• 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.

Characteristics of radio transmission

44

•Easily generated

•Omni-directionally travel a long distance

•Can penetrate building

•Frequency dependant

•Relatively low bandwidth for data

communication

•Tightly licensed by governments

i) Ground Wave Propagation

45

• 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.

46

ii) Ionospheric Propagation

47

• 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

48

iii) Line of Sight Propagation

49

• 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.

50

2. Microwaves Transmission

51

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.

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.

52

53

54

3. Bluetooth and infrared

55

• Bluetooth 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 802.15.1) and infrared.

Infra-red

56

• 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.

4.Light wave transmission

57

• 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.

Advantages of wireless communication

58

– 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.

Disadvantages

59

•?

The choice of medium depends on:

• Distance to be covered.

• Desired Bit Rate (in bits per second, bps)

• Cost Considerations

60

Review Questions

61

• 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?

• What are the applications of Radio wave?

Q & A