1 kyung hee university prof. choong seon hong transmission media
TRANSCRIPT
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Kyung Hee University
Prof. Choong Seon HONG
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
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Transmission Media(cont’d)Transmission Media(cont’d)
~ Can be divided into two broad categories :
유도매체 , 비 유도매체
Classes of transmission media
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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
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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
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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
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유도매체유도매체 (cont’d)(cont’d)
Effect of noise on parallel lines
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유도매체유도매체 (cont’d)(cont’d)
Effect of noise on twisted-pair lines
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유도매체유도매체 (cont’d)(cont’d)
Advantage of UTP
cheap, flexible, and easy to install.
2 ~ 12 twists per foot
Cable with 5 unshielded twisted pairs of wires
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유도매체유도매체 (cont’d)(cont’d)
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
4 20 MHz 20 Mbps Digital LANs
5 100 MHz 100 Mbps Digital LANs
6 (draft) 200 MHz 200 Mbps Digital LANs
7 (draft) 600 MHz 600 Mbps Digital LANs
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유도매체유도매체 (cont’d)(cont’d)
UTP connectors
• RJ – Registered Jack
• keyed connector, can be inserted one way
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PerformancePerformance
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Applications of UTPApplications of UTP
telephone lines for voice and data
DSL
LAN – 10Base-T and 100Base-T
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유도매체유도매체 (cont’d)(cont’d)
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
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유도매체유도매체 (cont’d)(cont’d)
동축 케이블 (Coaxial Cable)
carries signals of higher frequency ranges
Frequency range of coaxial cable
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유도매체유도매체 (cont’d)(cont’d)
Coaxial cable
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유도매체유도매체 (cont’d)(cont’d)
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
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유도매체유도매체 (cont’d)(cont’d)
Coaxial Cable Connectors
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유도매체유도매체 (cont’d)(cont’d)
Performance
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유도매체유도매체 (cont’d)(cont’d)
Applications
Cable TV
traditional Ethernet LANs, 10Base-2, 10Base-5
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유도매체유도매체 (cont’d)(cont’d)
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.
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유도매체유도매체 (cont’d)(cont’d)
굴절 (Refraction)
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유도매체유도매체 (cont’d)(cont’d)
임계각 (critical angle)
As the angle of incidence( 입사각 ) increase, it moves away from vertical and closer to the horizontal.
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유도매체유도매체 (cont’d)(cont’d)
반사 (Reflection)
When the angle of incidence becomes greater than the critical angle, a new phenomenon occurs called reflection
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유도매체유도매체 (cont’d)(cont’d)
Optical Fiber
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유도매체유도매체 (cont’d)(cont’d)
Propagation Models
current technology supports two models for propagating light along optical channel.
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유도매체유도매체 (cont’d)(cont’d)
Multimode step-index
~ multiple beams from a light source move through the core in different paths.
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유도매체유도매체 (cont’d)(cont’d)Multimode graded-index
fiber with varying densities
highest density at the center of the core
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유도매체유도매체 (cont’d)(cont’d)
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.
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유도매체유도매체 (cont’d)(cont’d)
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
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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
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유도매체유도매체 (cont’d)(cont’d)
Cable Composition
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유도매체유도매체 (cont’d)(cont’d)
Applications of Fiber-optic
network backbones
cable TV
LANs, 100Base-FX, 1000Base-X
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유도매체유도매체 (cont’d)(cont’d)
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.
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유도매체유도매체 (cont’d)(cont’d)
Fiber-optic Cable Composition
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유도매체유도매체 (cont’d)(cont’d)
Optical Fiber Performance
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유도매체유도매체 (cont’d)(cont’d)
Advantages of Optical Fiber
Noise resistance
Less signal attenuation
Higher bandwidth
Disadvantages of Optical Fiber
Cost
Installation/maintenance
Fragility
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7.2 7.2 비유도 매체비유도 매체 (Unguided media)(Unguided media)
wireless
signals are broadcasted through air
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비유도 매체비유도 매체 (cont’d)(cont’d)
Radio Frequency Allocation
대류층 전리층
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비유도 매체비유도 매체 (cont’d)(cont’d)
Propagation of radio waves
Types of propagation
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비유도 매체비유도 매체 (cont’d)(cont’d)
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)
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비유도 매체비유도 매체 (cont’d)(cont’d)
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
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비유도 매체비유도 매체 (cont’d)(cont’d)
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
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비유도 매체비유도 매체 (cont’d)(cont’d)
Wireless Transmission Waves
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비유도 매체비유도 매체 (cont’d)(cont’d)
Omnidirectional antennas
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비유도 매체비유도 매체 (cont’d)(cont’d)
• Radio waves are used for multicast communications, such as radio and television, and paging systems.
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비유도 매체비유도 매체 (cont’d)(cont’d)
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
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비유도 매체비유도 매체 (cont’d)(cont’d)
Repeaters
To increase the distance served by terrestrial microwave, a system of repeaters can be installed with each antenna.
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비유도 매체비유도 매체 (cont’d)(cont’d)
Antennas
two types of antenna
Parabolic dish
is based on the geometry of a parabola
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비유도 매체비유도 매체 (cont’d)(cont’d)
Horn antenna
looks like a gigantic scoop
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비유도 매체비유도 매체 (cont’d)(cont’d)
Satellite Communication
is much like line of sight microwave transmission in which one of the station is a satellite orbiting the earth
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비유도 매체비유도 매체 (cont’d)(cont’d)
Geosynchronous (geostationary) satellites
@ the view from the North Pole
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비유도 매체비유도 매체 (cont’d)(cont’d)
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
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비유도 매체비유도 매체 (cont’d)(cont’d)
Cellular telephony
is designed to provide stable communications connections between two moving device or between one mobile unit and one stationary(land) unit.
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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
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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