1 Kyung Hee University Chapter 7 Transmission Media

11

Kyung Hee University

Chapter 7

Transmission Media

22


7. Transmission media7. Transmission media

Transmission medium and physical layer

33


Transmission media(Transmission media( 전송매체전송매체 ))

7.1 Guided Media( 유도매체 )

7.2 Unguided media( 비 유도매체 ) : Wireless

44


Transmission Media(cont’d)Transmission Media(cont’d)

Classes of transmission media

55


7-1 GUIDED MEDIA7-1 GUIDED MEDIA

Guided media, which are those that Guided media, which are those that provide a conduit from one device to provide a conduit from one device to another, include twisted-pair cable, coaxial another, include twisted-pair cable, coaxial cable, and fiber-optic cable.cable, and fiber-optic cable.

Twisted-Pair CableCoaxial CableFiber-Optic Cable

Topics discussed in this section:Topics discussed in this section:

66


Figure 7.3 Twisted-pair cable

Two copper conductors

One carriers signals, the other is the ground reference

Receiver operates on the difference between the signals.

This is why they are twisted, to maintain balance

More twists mean better quality

Twisted-Pair Cable Twisted-Pair Cable

77


Twisted-Pair CableTwisted-Pair Cable

Effect of noise on parallel lines

88



Effect of noise on twisted-pair lines

99


Twisted-Pair Cable Twisted-Pair Cable

Twisted-Pair Cable comes in two forms

- Unshielded ( 비차폐 ) twisted pair cable

- Shielded( 차폐 ) twisted pair cable

1010


Table 7.1 Categories of unshielded twisted-pair cables

1111



UTP connectors

• RJ – Registered Jack

• keyed connector, can be inserted one way

1212



1313


Coaxial CableCoaxial Cable

동축 케이블 (Coaxial Cable)

carries signals of higher frequency ranges

Frequency range of coaxial cable

1414


Figure 7.7 Coaxial cable


1515



Coaxial Cable Standards

~ are categorized by RG(radio government) rating

Table 7.2 Categories of coaxial cables

1616



Coaxial Cable Connectors

1717



Performance

1818


Optical Fiber CableOptical Fiber Cable

Optical Fiber( 광섬유 )

~ is made of glass or plastic and transmits signals in the form of light

Nature of Light

~ is a form of electromagnetic energy. It travels at its fastest in a vacuum : 300,000km/s. This speed decreases as the medium through which the light travels become denser.

1919



굴절 (Refraction)

2020



임계각 (critical angle)

As the angle of incidence( 입사각 ) increases, it moves away from vertical and closer to the horizontal.

2121



반사 (Reflection)

When the angle of incidence becomes greater than the critical angle, a new phenomenon occurs called reflection

2222



Optical Fiber

2323



Propagation Models

current technology supports two models for propagating light along optical channel.

2424


Figure 7.13 Modes


2525



Multimode step-index

~ multiple beams from a light source move through the core in different paths.

2626


Optical Fiber CableOptical Fiber Cable Multimode graded-index

fiber with varying densities

highest density at the center of the core

2727



Single Mode

~ uses step-index fiber and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal.

2828



Fiber sizes

~ are defined by the ratio of the diameter of their core to the diameter of their cladding.

Table 7.3 Fiber types

2929



Cable Composition

3030



Fiber-optic Cable Composition

3131



Optical Fiber Performance

Wavelength (μm)

3232



Advantages of Optical Fiber

Noise resistance

Less signal attenuation

Higher bandwidth

Disadvantages of Optical Fiber Cost

Installation/maintenance

Fragility

3333


7.2 UNGUIDED MEDIA: WIRELESS7.2 UNGUIDED MEDIA: WIRELESS

Unguided media transport electromagnetic waves Unguided media transport electromagnetic waves without using a physical conductor. This type of without using a physical conductor. This type of communication is often referred to as wireless communication is often referred to as wireless communication.communication.

Radio WavesMicrowavesInfrared

Topics discussed in this section:Topics discussed in this section:

3434


비유도 매체비유도 매체 (Unguided media)(Unguided media)

wireless

signals are broadcasted through air

Figure 7.17 Electromagnetic spectrum for wireless communication

3535


Wireless TransmissionWireless Transmission

Radio Frequency Allocation

대류층 전리층

3636


비유도 매체비유도 매체 (Unguided media)(Unguided media)

BandBand RangeRange PropagationPropagation ApplicationApplication

VLFVLF 3–30 KHz Ground Long-range radio navigation

LFLF 30–300 KHz GroundRadio beacons and

navigational locators

MFMF 300 KHz–3 MHz Sky AM radio

HF HF 3–30 MHz SkyCitizens band (CB),

ship/aircraft communication

VHF VHF 30–300 MHzSky and

line-of-sight

VHF TV,

FM radio

UHF UHF 300 MHz–3 GHz Line-of-sightUHF TV, cellular phones,

paging, satellite

SHF SHF 3–30 GHz Line-of-sight Satellite communication

EHFEHF 30–300 GHz Line-of-sight Long-range radio navigation

3737


전파경로에 따른 분류전파경로에 따른 분류

지표면 전파 (Ground Propagation)

저주파 사용하며 , 지구를 감싸는 대기의 가장 낮은 부분 통해 전파

전파거리는 신호의 전력량에 비례 ( 직접파 , 대지반사파 , 회절파 )

공중전파 (Sky Propagation)

고주파 사용하며 , 대류권 산란 또는 전리층 반사를 이용

낮은 전력으로 원거리 전파 가능

가시선 전파 (Line of sight Propagation)

초단파의 신호가 안테나에서 안테나로 직접 전송

안테나는 반드시 마주보고 있어야 한다 .

3838


Earth’s AtmosphereEarth’s Atmosphere외기권

열권

중간권

성층권

대류권

3939



Propagation of radio waves

Types of propagation

4040


Table 7.4 Bands


4141



Wireless Transmission Waves

4242


RADIO WAVERADIO WAVE

Electromagnetic waves ranging in frequencies between

3khz and 1Ghz are called Radio wave.

Radio waves are Omni-

directional, they are

propagated in all directions.

Radio waves are

propagated in sky mode,

can travel long distance.

4343


RADIO WAVERADIO WAVE

Radio waves are used for multicast communications, such as radio and

television, and paging systems.

Note

4444


MICRO WAVESMICRO WAVES

Electromagnetic waves having frequencies between 1 and 300Ghz are called Microwaves.

Microwave propagation is line-of-sight. Since the towers with the mounted antennas need to be in direct sight of each other.

Very high-frequency M/W cannot penetrate walls.

The M/W band is relatively wide, almost 299 Ghz.

Therefore wider subbands can be assigned, and a high data rate is possible.

4545


MICRO WAVEMICRO WAVE

Repeaters

To increase the distance served by terrestrial microwave, a system of repeaters can be installed with each antenna.

4646



Antenna – need unidirectional antenna that send out

signals in one direction

parabolic dish antenna horn antenna

4747


Microwaves are used for unicast communication such as cellular telephones, satellite n

etworks,and wireless LANs.


4848


InfraredInfrared

Infrared waves, with frequencies from 300 Ghz to 400 T

hz, can be used for short-range communication.

Infrared waves, having high frequencies, cannot penetra

te walls.

this advantageous characteristic prevents interference between one system and another; a short-range communication system in one room cannot be affected by another system in the next room.

We cannot use infrared waves outside a building becau

se the sun’s rays contain infrared waves that can interfe

re with the communication

4949


Infrared signals can be used for short-range communication in a closed area

using line-of-sight propagation.

InfraredInfrared

5050


Q & AQ & A

Documents

1 Kyung Hee University Chapter 7 Transmission Media