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1 Chapter 7. Transmission Media Contents 1. Introduction 2. 유선전송매체 (Guided Media) 3. 무선전송매체 (Unguiede Media) Yoon-Seok Nam Dept. of Information and Communication Engineering Dongguk University 707 Sukjang-Dong, Gyeongju-City, Gyeongsangbuk-Do, , Korea Phone : (Lab), (Office), (fax), (CP) ysnam@dongguk.ac.kr 데이터통신 (Data Communications) 1

2 1. Introduction 전송매체 송신기와수신기간의물리적경로 : Physical Layer 의제어를받음. Layer 0(?) Guided, Bounded wire Unguided, Unbounded wireless Characteristics and quality of data transmission are determined by characteristics of medium and signal For guided media, medium characteristics is more important.( 왜? 선택할..) For unguided media, the bandwidth produced by the antenna is more important( 왜? 매체는선택불가. 따라서신호의대역을제어 ) 주파수, 대역폭 : 타전송매체와의영향을배제 Key concerns are data rate and distance!!! 데이터통신 (Data Communications) 2

3 Figure 7.2: Classes of transmission media 데이터통신 (Data Communications) 3

4 Electromagnetic Spectrum 데이터통신 (Data Communications) 4

5 2. Guided Transmission Media 종류 Twisted Pair(TP) 24-gauge : 직경 0.5mm 26-gauge : 직경 0.4mm AWG=American Wire Gauge 전선의지름 11.68mm=AWG mm=AWG 36 AWG 0~40 으로구분 Coaxial cable 외경 ( 외부도체의안지름 ) : (3/8) =0.95cm, 5.6mm, 4.4mm Optical fiber 주파수범위, 감쇠, Repeater 간격 유도매체의감쇠 데이터통신 (Data Communications) 5

6 (1) Twisted Pair(TP) 독립적으로절연 2 가닥씩꼬임대부분케이블에다발로구성빌딩건설당시에구축됨. Twist Length : 5~15cm(?) 1 인치당꼬인횟수로 TP 구분전선의굵기 ( 직경 ) : 0.4~0.9mm 데이터통신 (Data Communications) 6

7 Twisted Pair - 응용 Most common medium Telephone network Between house and local exchange (subscriber loop) 빌딩내 To private branch exchange (PBX) 교환기 ----(analog)---pbx---(analog) 교환기 ----(digital)---pbx---(analog) For local area networks (LAN) RJ-45 Connector 사용 10Mbps or 100Mbps Twisted Pair 장, 단점 Cheap( 저렴 ) Easy to work with( 작업용이 ) Low data rate( 저속 ) Short range( 단거리 ) (a) 핀번호 (b) 측면 RJ-45 Connector(female, male) 케이블을꼬는이유전선은외부잡음원에의해발생한전자기적간섭에의해잡음이유발되며, 잡음원에근접할수록높은잡음신호가유도된다. 꼬인쌍의경우, 잡음에영향받는시간의반은잡음원과가깝고반은멀어지게되어잡음원으로부터누적된갑섭은두꼬인선에동일하게됨. 따라서꼬인선에 Differential 형태로신호가전송되면잡음의영향은 0 이된다. 데이터통신 (Data Communications) 7

Twisted Pair 전송특성 Analog : Amplifiers every 5km to 6km Digital : Use either analog or digital signals.

꼬임 : 저주파에서의간섭영향감소 Limited bandwidth (1MHz) Limited data rate : 수 Mbps(PTP), 100Mbps( 짧은거리 ), 1Gbps

Suffers from external EM interference(emi) UTP 쌍을집합시킨케이블심을 shield 하여도 UTP 로불린다.

8 Twisted Pair 전송특성 Analog : Amplifiers every 5km to 6km Digital : Use either analog or digital signals. repeater every 2km or 3km Limited distance Susceptible to interference and noise( 간섭, 잡음에민감 ) 60Hz 전력선, 충격잡음 꼬임 : 저주파에서의간섭영향감소 Limited bandwidth (1MHz) Limited data rate : 수 Mbps(PTP), 100Mbps( 짧은거리 ), 1Gbps Unshielded and Shielded TP Unshielded Twisted Pair (UTP) Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference(emi) UTP 쌍을집합시킨케이블심을 shield 하여도 UTP 로불린다. Shielded Twisted Pair (STP) 간섭을줄이기위해그물망또는외장을사용 More expensive Harder to handle (thick, heavy) 플라스틱피복 구리도선외부피복금속박막 UTP STP 데이터통신 (Data Communications) 8

9 UTP 케이블 5 개의비차폐 (UTP) 꼬임쌍선으로된케이블 데이터통신 (Data Communications) 9

MHz 20 Mbps Digital LANs 5 100 MHz 100Mbps Digital LANs 6(draft) 200 MHz 200 Mbps

10 UTP 의종류 Category Bandwidth Data Rate Digital/Analo g Use 1 Very low <100 Kbps Analog Telephone 2 <2 MHz 2 Mbps Analog/digita l T-1 lines 3 16 MHz 10 Mbps Digital LANs 4 20 MHz 20 Mbps Digital LANs MHz 100Mbps Digital LANs 6(draft) 200 MHz 200 Mbps Digital LANs 7(draft) 600 MHz 600 Mbps Digital LANs 전화선케이블 : RJ11 데이터통신 (Data Communications) 10

11 Figure 7.6: UTP Performance 데이터통신 (Data Communications) 11

12 (2) Coaxial Cable 동축케이블 원통형중심도선 ( 내부절연체 ) 금속박, 꼬인끈등으로된외부절연체 각절연체는외피로보호 전체플라스틱은플라스틱피복에의해보호 외부잡음에강하다. 영상전송이나계측기의 Lead 선등에폭넓게사용 LAN 에서는버스형배선에사용 BNC 라는원통형커넥터사용하여노드연결 바다밑이나땅속에묻어도성능에큰지장이없음 데이터통신 (Data Communications) 12

13 Coaxial Cable 전송특성 Analog Amplifiers every few km Closer if higher frequency Up to 500MHz Digital Repeater every 1km Closer for higher data rates Thick Cable 외부직경 11mm, 10Base5 에사용 황색케이블 특성 impedance : 50 ohm 내부도체 : 2.17 mm 감쇠량 : 10 MHz 시 500 미터길이에서 8.5 db 이하 Thin Cable 외부직경 5mm, 10Base2 에사용 특성 impedance : 50 ohm 내부도체 : 0.9 mm 감쇠량 : 10 MHz 시 185 미터길이에서 8.5 db 이하 양끝단에터미네이터부착해야함 데이터통신 (Data Communications) 13

14 Table 7.2 Categories of coaxial cables Figure 7.8: BNC connectors 데이터통신 (Data Communications) 14

수십 ~100 km at least (AT&T 광전송시스템 : 318km, 3.

15 (3) Optical Fiber 코팅클래딩코어 광케이블 (Optical-fiber Cable) 유리나플라스틱으로만들어지며빛의형태로신호전송 중앙은실리카 (SiO 2 ) 로구성된 core 가위치하고있으며외벽은반사벽역할을하는실리카 Cladding 으로구성 전기적인간섭을받지않음 (Electromagnetic isolation) Greater capacity Data rates of hundreds of Gbps Greater repeater spacing 수십 ~100 km at least (AT&T 광전송시스템 : 318km, 3.5Gbps) Smaller size & weight, Lower attenuation 구조 코어 (core) : 높은굴절률의투명한덮개로빛이통과하는통로역할 클래딩 (cladding) : 코어보다낮은굴절률의투명한덮개로코어외부를싸고있으며빛을반사 코팅 (coating) : 코어와클래딩을보호하기위해합성수지로만든피복을이용해외부를감쌈 데이터통신 (Data Communications) 15

16 Optical fiber 전송원리 total internal reflection 원리에근거 If β>α, medium B (water) has a higher optical density than medium A (air) 굴절계수 (Index of refraction) = sin( 입사각 )/sin( 굴절각 ) =cos(α)/cos(β) In case the index of refraction < 1 (α > β), if α is less than a certain critical angle, there is no refracted light. I.e., all the light is reflected. This is what makes fiber optics work. The cladding surrounding the core is also glass but is optically less dense than the core 빛은코어에서클래드로진행. 코어밀도 > 클래드밀도 코어에입사한빛이코어와클래드의경계면에서전반사되어코어내에빛을가두어전달 Incident light( 입사광 ) Reflected light( 반사광 ) A B α β α Interface between two media A and B Refracted light( 굴절광 ) 데이터통신 (Data Communications) 16

17 Optical Fiber 원리 : 전반사를쉽게하기위하여 입사매질밀도 가 굴절매질밀도 보다크게설계 데이터통신 (Data Communications) 17

18 데이터통신 (Data Communications) 18

19 데이터통신 (Data Communications) 19

20 Optical Fiber Transmission Mode A B A travels a greater distance but faster than B 데이터통신 (Data Communications) 20

21 Figure 7.14: Fiber connection Figure 7.15: Fiber-optic cable connector 데이터통신 (Data Communications) 21

22 Optical Fiber - 응용 Long-haul trunks Subscriber loops : 현재는 FTTH 가실현되는단계 (EPON 이서비스중 ). LANs 광원 (Lighting Source) Light Emitting Diode (LED) 저렴. 동작온도범위가넓다. 오랜수명 Injection Laser Diode (ILD) 더효율적 더높은전송율을얻을수있다. 파장 (Wave Length) 가시광선 : 400~700 nm 850, 1300, 1550 nm 범위의광원을사용 ( 적외선영역 ) 파장이클수록손실은적다.( 주파수가클수록손실이크다.) 단거리 (850 nm LED), 장거리 (1300 LED or ILD), 원거리 (1500 nm ILD) 데이터통신 (Data Communications) 22

23 유선매체의장단점 매체의종류장점단점응용 꼬임쌍선케이블 동축케이블 광섬유 가격이저렴 사용이용이 음성주파수대역에서 감쇄가작음 높은대역폭으로케이블 당채널수가많음 감쇠나신호지연의변화 가적음 잡음 / 간섭에대한저항력 이강함 신호감쇠가적음 대역폭이높음 안정성이떨어짐 외부조건에영향을 많이받음 단단하여설치가쉽지 않음 크기가크고가격이 비쌈 가격이매우비쌈 설치및유지보수가 어려움 Unidirectional propagation Local loop ( 전화선, DSL line) T-1 LAN Cable TV Thin Ethernet Thick Ethernet SONET Backbone Network Fast Ethernet FTTx 데이터통신 (Data Communications) 23

24 Attenuation in Guided Media 데이터통신 (Data Communications) 24

25 3. 무선전송매체 무선전송매체 공간 무선방식은전파를사용해공중으로신호를전파함 유선과달리신호를보호할대비가없어잡음, 간섭, 왜곡에쉽게노출되는점이특징 따라서무선전송에서는다양한무선채널의특성과노이즈특성, 페이딩에대한연구가필요함 신호간충돌을대비해통신방식별로사용되는주파수대역을지정해놓음 데이터통신 (Data Communications) 25

26 신호의종류 Radio wave and microwave Infrared Light wave 3KHz 300 GHz 라디오파 3KHz에서 1GHz 사이의파 무지향성안테나를통해방사되는파 마이크로파 1GHz에서 300GHz 사이의파 단방향성으로전파되는특징 적외선 300GHz에서 400THz 사이의파 단거리통신에주로사용됨 400 THz 900 THz 데이터통신 (Data Communications) 26

27 Figure 7.18: Propagation methods 데이터통신 (Data Communications) 27

28 Table 7.4: Bands 데이터통신 (Data Communications) 28

29 주파수사용대역 Radio wave 항공, 해상에서이용 AM 라디오 (535~1 605kHz) HAM (1850~2000k Hz) FM 라디오 (88.1MHz~ 107.9MHz) TV 방송 (VHF) (54~216MHz) 지상파 DMB (204~210MHz) 셀룰러이동통신 (836/881MHz) PCS ( ~ MHz) 3G (1885~2200MHz) 휴대인터넷 (2.3GHz 대역 ) 무선랜 (802.11b/g : 2.4GHz 대역 ) 위성 DMB (2.630~2.655GHz 대역 ) 무선랜 (802.11a : 5GHz) 디지털위성방송 (12GHz) 우주연구및위성사용대역 9~300kHz VLF 300kHz~3MHz MF 3MHz~30MHz HF 30MHz~300MHz VHF 300MHz~3GHz UHF 3GHz~30GHz SHF 30GHz~300GHz EHF 현재대한민국주파수분배현황 ( 출처 : 중앙전파관리소 ) VLF: Very Low Frequency MF: Medium Frequency HF: High Frequency VHF: Very High Frequency UHF: Ultra High Frequency SHF: Super High Frequency EHF: Extremely Frequency 데이터통신 (Data Communications) 29

Radio Waves Although there is no clear-cut demarcation between radio waves and microwaves, electromagnetic waves ranging in frequencies between 3 khz and 1 GHz are normally called radio waves; waves

30 Radio Waves Although there is no clear-cut demarcation between radio waves and microwaves, electromagnetic waves ranging in frequencies between 3 khz and 1 GHz are normally called radio waves; waves ranging in frequencies between 1 and 300 GHz are called microwaves. However, the behavior of the waves, rather than the frequencies, is a better criterion for classification. Figure 7.19: Omnidirectional antenna 데이터통신 (Data Communications) 30

31 Microwaves Electromagnetic waves having frequencies between 1 and 300 GHz are called microwaves. Microwaves are unidirectional. When an antenna transmits microwaves, they can be narrowly focused. This means that the sending and receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas. 데이터통신 (Data Communications) 31

32 Figure 7.20: Unidirectional antenna 데이터통신 (Data Communications) 32

33 Infrared Infrared waves, with frequencies from 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm), can be used for shortrange communication. Infrared waves, having high frequencies, cannot penetrate 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. When we use our infrared remote control, we do not interfere with the use of the remote by our neighbors. 데이터통신 (Data Communications) 33

34 Antennas Electrical conductor( 안테나 ) 을통하여 electromagnetic energy 를 radiate( 송신 ) 또는 collect( 수신 ) Transmission Radio frequency electrical energy from transmitter Converted to electromagnetic energy by antenna Radiated into surrounding environment Reception Electromagnetic energy impinging on antenna Converted to radio frequency electrical energy Fed to receiver Same antenna often used for both Electrical energy Electromagnetic Electrical energy energy transmitter Antenna Antenna Receiver 데이터통신 (Data Communications) 34

35 Terrestrial Microwave( 지상마이크로파 ) 지상마이크로파 (Terrestrial Microwave) 장거리의수십 Mbps 의데이터전송속도를제공하며주로장거리통신서비스용으로전송매체의설치가불가능하거나설치비용이비쌀때사용 Mocrowave(2~40GHz) 특성 접시형안테나를사용하며고지대에위치 장거리에대해높은데이터전송률을제공 장거리통신서비스용, TV나음성전송용동축케이블대용가능 동축케이블에비해훨씬적은증폭기와리피터가필요 지구대기를통한가시거리마이크로웨이브통신은 50Km 이상가능 높은구조물이나기상조건에영향을받음 데이터통신 (Data Communications) 35

36 케이블을설치하기어려운경우에적합 Parabolic dish shaped antenna ( 10 ft dia= 직경 3m) transmits/receives electromagnetic waves in the 2-40 GHz range Travels in a straight line (line-of-sight propagation) 안테나간의최대거리 K : 굴절율을고려한조정치 d = 7.14 Kh = 7.14 (4 3)h h : 안테나높이 d는안테나간최대거리 안테나의길이 : 반파장, ¼ 파장 높은주파수를사용하면안테나가더작아진다. ( 예, AM/FM 안테나 ) Incoming signals Incoming signals Parabola s focus (receiver) Parabolic arc (reflector) 데이터통신 (Data Communications) 36

37 Satellite Microwave( 위성마이크로파 ) 물리적특성 통신위성 : 마이크로파중계국. 지구국과통신 Satellite receives on one frequency(uplink), amplifies or repeats signal and transmits on another frequency(downlink) Point-to-Point 위치및방향이고정 Uses satellite in geo-stationary orbit (Height of 35,784km) 동일주파수를사용하는근접한두위성의경우 신호간섭을배제하기위하여전송방향을 3~4도간격 ( 지상에서본각도 ) 으로유지 위성의수는제한됨. 데이터통신 (Data Communications) 37

38 전송특성 Optimum transmission in 1-10 GHz range; Bandwidth of 100 s MHz 4/6 GHz 대역 Uplink : 5.925~6.425 GHz Downlink : 3.7~4.2 GHz 1~10GHz 대역가운데최적대역. 사용이포화상태 12/14 GHz 대역 (Ku band) Uplink : 14~14.5 GHz Downlink : 11.7~14.2 GHz 감쇠가문제 19/29 GHz 대역 (Ka band) Uplink : 27.5~31.0 GHz Downlink : 17.7~21.2 GHz 위성통신에서의 Significant propagation delay 270ms 데이터통신 (Data Communications) 38

39 위성의분류 고도에의한분류 LEO(Low Earth Orbit: 저궤도 ) 600~1,500Km, MEO에비해저소비전력 안테나크기가작고, 짧은지연 공전주기는약 90분에서수시간정도 커버리지영역이좁아지표면전체를위해위성이 48~288개필요 위성을이용한지상셀룰러네트워크지원 ( 모토롤러이리듐사업 ) MEO(Medium Earth Orbit: 중궤도 ) 10,000~20,000Km, GPS와 GLONASS 등합법위성에사용 많이사용되지않음 GEO(Geo-synchronous Earth Orbit: 지구동기궤도 ) 적도상공에위치 (35,786Km) 하는경사궤도 위성의공전속도와지구의자전속도가일치 GSO(Geo-stationary Orbit: 지구정지궤도 ) 지상에서관찰되는위성은항상같은지점궤도모양에의한분류 원궤도, 타원궤도 : Closed Orbit, 인공위성 쌍곡선, 포물선궤도 : Open Orbit 데이터통신 (Data Communications) 39

40 Refraction( 굴절 ) Velocity of electromagnetic wave is a function of density of material ~3 x 10 8 m/s in vacuum, less in anything else As wave moves from one medium to another, its speed changes Causes bending of direction of wave at boundary Towards more dense medium Index of refraction (refractive index) is sin(angle of incidence)/sin(angle of refraction) Varies with wavelength May cause sudden change of direction at transition between media May cause gradual bending if medium density is varying Density of atmosphere decreases with height Results in bending towards earth of radio waves 데이터통신 (Data Communications) 40

Optical & Radio Horizons d = 3. 57 h d = 3.

41 Optical & Radio Horizons d = h d = Kh 빛의가시거리 : d: 안테나와지평선간의거리 (Km) h: 안테나의높이 (m) 전파의가시거리 : h1=h2=h라면, 두안테나간의최대거리 d = h d = Kh d = 3.57( Kh + Kh 2) 1 = 7.14 Kh 데이터통신 (Data Communications) 41

42 LOS(Line of Sight) Transmission Free space loss Signal disperses with distance Greater for lower frequencies (longer wavelengths) Atmospheric Absorption Water vapour and oxygen absorb radio signals Water greatest at 22GHz, less below 15GHz Oxygen greater at 60GHz, less below 30GHz Rain and fog scatter radio waves Multipath Better to get line of sight if possible Signal can be reflected causing multiple copies to be received May be no direct signal at all May reinforce or cancel direct signal Refraction May result in partial or total loss of signal at receiver 데이터통신 (Data Communications) 42

43 참고문헌 1. 데이타통신과네트워킹 (Data Communications and Networking), Behrouz A. Forouzan 저, 이재광, 김중규, 박동선, 홍충선공역, 교보문고, 데이터통신및컴퓨터통신, Stallings, 김종상역 ), 사이텍미디어, 2013 데이터통신 (Data Communications) 43

Chapter 4 - William Stallings, Data and Computer Communications, 8/e

Chapter 4 - William Stallings, Data and Computer Communications, 8/e Data and Computer Communications Chapter 4 Transmission Media Design Factors Characteristics and quality determined by medium and signal Key concerns are data rate and distance Higher bandwidth gives higher