1 Kyung Hee University Transmission Media. 2 Kyung Hee University 7 장 Transmission media o Transmission medium and physical layer

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Kyung Hee University

Transmission MediaTransmission Media

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7 7 장 장 Transmission mediaTransmission media

Transmission medium and physical layer

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Transmission media(Transmission media( 전송매체전송매체 ))

7.1 Guided Media( 유도매체 )

7.2 Unguided media( 비유도매체 ) : Wireless

44


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

~ Can be divided into two broad categories :

유도매체 , 비 유도매체

Classes of transmission media

55


7.1 Guided Media(7.1 Guided Media( 유도매체유도매체 ))

Twisted-Pair Cable

• two copper conductors• one carries signals, the other is the ground reference• interference may affect both wires• receiver operates on the difference between the signals• this is why they are twisted, to maintain balance• more twists mean better quality

66


유도매체유도매체 (cont’d)(cont’d)

Twisted-Pair Cable

~ comes in two forms : unshielded ( 비 차 폐 ) and shielded( 차폐 )

UTP(Unshielded Twisted-Pair) Cable

~ is the most common type of telecommunication medium in use today.

Frequency range for twisted-pair cable

77


유도매체유도매체 (cont’d)(cont’d) Twisted-Pair Cable

consists of two conductors (usually copper), each with its own colored plastic insulation Color-banded for identificationColor-banded for identification

PVC : polyvinyl chloride

• two copper conductors• one carries signals, the other is the ground reference• interference may affect both wires• receiver operates on the difference between the signals• this is why they are twisted, to maintain balance• more twists mean better quality

88



Effect of noise on parallel lines

99



Effect of noise on twisted-pair lines

1010



Advantage of UTP

cheap, flexible, and easy to install.

2 ~ 12 twists per foot

Cable with 5 unshielded twisted pairs of wires

1111



UTP standards has developed to grade by quality

Category Bandwidth Data Rate Digital/Analog Use

1 very low < 100 kbps Analog Telephone

2 < 2 MHz 2 Mbps Analog/digital T-1 lines

3 16 MHz 10 Mbps Digital LANs



6 (draft) 200 MHz 200 Mbps Digital LANs

7 (draft) 600 MHz 600 Mbps Digital LANs

1212



UTP connectors

• RJ – Registered Jack

• keyed connector, can be inserted one way

1313


PerformancePerformance

1414


Applications of UTPApplications of UTP

telephone lines for voice and data

DSL

LAN – 10Base-T and 100Base-T

1515



STP(Shielded Twisted-Pair) cable

has the same quality consideration as UTP (more expensive, less susceptible to noise)

eliminating most of the effects of crosstalk

1616



동축 케이블 (Coaxial Cable)

carries signals of higher frequency ranges

Frequency range of coaxial cable

1717



Coaxial cable

1818



Coaxial Cable Standards

~ are categorized by RG(radio government) rating

Category Impedance Use

RG-59RG-59 75 Cable TV

RG-58RG-58 50 Thin Ethernet

RG-11RG-11 50 Thick Ethernet

1919



Coaxial Cable Connectors

2020



Performance

2121



Applications

Cable TV

traditional Ethernet LANs, 10Base-2, 10Base-5

2222



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.

2323



굴절 (Refraction)

2424



임계각 (critical angle)

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

2525



반사 (Reflection)

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

2626



Optical Fiber

2727



Propagation Models

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

2828



Multimode step-index

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

2929


유도매체유도매체 (cont’d)(cont’d)Multimode graded-index

fiber with varying densities

highest density at the center of the core

3030



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.

3131



Fiber sizes

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

Fiber Type Core(microns) Cladding(microns)

62.5/125

50/125

100/140

8.3/125

62.5

50

100

8.3

125

125

140

125

3232


유도매체유도매체 (cont’d)(cont’d)Cable Composition

Fiber can be made of either glass or plastic

Inner core must be ultrapure and completely regular in size and shape

Outer jacket can be made Teflon coating, plastic coating, fibrous plastic, metal tubing, and metal mesh

3333



Cable Composition

3434



Applications of Fiber-optic

network backbones

cable TV

LANs, 100Base-FX, 1000Base-X

3535



Fiber-Optic Connectors

must be as precise as the cable itself.

All of the popular connector are barrel( 원통 ) shaped and come in male and female versions.

3636



Fiber-optic Cable Composition

3737



Optical Fiber Performance

3838



Advantages of Optical Fiber

Noise resistance

Less signal attenuation

Higher bandwidth

Disadvantages of Optical Fiber

Cost

Installation/maintenance

Fragility

3939


7.2 7.2 비유도 매체비유도 매체 (Unguided media)(Unguided media)

wireless

signals are broadcasted through air

4040


비유도 매체비유도 매체 (cont’d)(cont’d)

Radio Frequency Allocation

대류층 전리층

4141



Propagation of radio waves

Types of propagation

4242



Type of propagation

Surface Propagation Radio waves travel through the lowest portion of t

he atmosphere( 대기권 )

Tropospheric ( 대류권 ) Propagation can work two ways( signal can be directed in a

straight line from antenna to antenna. It can be broadcast at an angle into the upper layers of troposphere where it is reflected back down to the earth’s surface)

4343



Ionospheric ( 전리층 ) Propagation High-frequency radio waves radiate upward into t

he ionosphere where they are reflected back to earth

Line-of-Sight Propagation Very high frequency signals are transmitted in str

aight lives directly from antenna to antenna

Space Propagation Utilizes satellite relays in place of atmospheric ref

raction

4444



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

4545



Wireless Transmission Waves

4646



Omnidirectional antennas

4747



• Radio waves are used for multicast communications, such as radio and television, and paging systems.

4848



Terrestrial microwaves

require line-of-sight transmission and reception equipment. The distance coverable by a line-of-sight signal depends on a large extent on the height of the antenna : the taller the antenna, the longer the sight distance

4949



Repeaters

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

5050



Antennas

two types of antenna

Parabolic dish

is based on the geometry of a parabola

5151



Horn antenna

looks like a gigantic scoop

5252



Satellite Communication

is much like line of sight microwave transmission in which one of the station is a satellite orbiting the earth

5353



Geosynchronous (geostationary) satellites

@ the view from the North Pole

5454



Frequency bands for satellite communication

`

Band Downlink Uplink

C

Ku

Ka

03.7 - 04.2 GHz

11.7 - 12.2 GHz

17.7 - 21.0 GHz

05.925 - 06.425 GHz

14.000 - 14.500 GHz

27.500 - 31.000 GHz

5555



Cellular telephony

is designed to provide stable communications connections between two moving device or between one mobile unit and one stationary(land) unit.

5656


Cellular and PCS telephonyCellular and PCS telephony

서비스 별 비교

항목 IS-95A IS-95B IS-95C(CDMA2000 1X) IMT2000(MC3X)

주파수대역 셀룰러 800MHz 대역 , PCS 1.7 ~ 1.8GHz 1.9 ~ 2.1GHz

단말기 대기시간 1( 기준 ) 1.3~1.5 3 3 이상

데이터 속도 14.4Kbps 64Kbps 144Kbps 384Kbps ~ 2Mbps

A4 100 장 전송 55 초 12 초 6 초 2.5 초 미만

동영상통화 불 가 가 능

IS : Interim StandardIS : Interim Standard

5757


Wireless TransmissionWireless Transmission

Radio waves are used for multicast communic

ations, such as radio and television, and paging

systems

Microwaves are used for unicast communicatio

n such as cellular telephones, satellite network

s, and wireless LANs.

Infrared signals can be used for short-range co

mmunication in a closed area using line-of-sigh

t propagation

Documents

1 Kyung Hee University Transmission Media. 2 Kyung Hee University 7 장 Transmission media o Transmission medium and physical layer