Chapter 7 Transmission Media Kyung Hee University 1

Chapter 7 Transmission Media Kyung Hee University 1

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

Transmission media(전송매체) 7. 1 Guided Media(유도매체) 7. 2 Unguided media(비 유도매체) : Wireless Kyung Hee University 3

Transmission Media(cont’d) o Classes of transmission media Kyung Hee University 4

7 -1 GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted -pair cable, coaxial cable, and fiber-optic cable. Topics discussed in this section: Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable Kyung Hee University 5

Twisted-Pair Cable Figure 7. 3 Twisted-pair cable q Two copper conductors q One carriers signals, the other is the ground reference q Receiver operates on the difference between the signals. q This is why they are twisted, to maintain balance q More twists mean better quality Kyung Hee University 6

Twisted-Pair Cable o. Effect of noise on parallel lines Kyung Hee University 7

Twisted-Pair Cable o. Effect of noise on twisted-pair lines Kyung Hee University 8

Twisted-Pair Cable comes in two forms - Unshielded (비차폐) twisted pair cable - Shielded(차폐) twisted pair cable Kyung Hee University 9

Table 7. 1 Categories of unshielded twisted-pair cables Kyung Hee University 10

Twisted-Pair Cable o UTP connectors • RJ – Registered Jack • keyed connector, can be inserted one way Kyung Hee University 11

Twisted-Pair Cable Kyung Hee University 12

Coaxial Cable o 동축 케이블(Coaxial Cable) v carries signals of higher frequency ranges o Frequency range of coaxial cable Kyung Hee University 13

Coaxial Cable Figure 7. 7 Coaxial cable Kyung Hee University 14

Coaxial Cable o. Coaxial Cable Standards ~ are categorized by RG(radio government) rating Table 7. 2 Categories of coaxial cables Kyung Hee University 15

Coaxial Cable o Coaxial Cable Connectors Kyung Hee University 16

Coaxial Cable o Performance Kyung Hee University 17

Optical Fiber Cable o Optical Fiber(광섬유) ~ is made of glass or plastic and transmits signals in the form of light o Nature of Light ~ is a form of electromagnetic energy. It travels at its fastest in a vacuum : 300, 000 km/s. This speed decreases as the medium through which the light travels become denser. Kyung Hee University 18

Optical Fiber Cable o굴절(Refraction) Kyung Hee University 19

Optical Fiber Cable o임계각(critical angle) v. As the angle of incidence(입사각) increases, it moves away from vertical and closer to the horizontal. Kyung Hee University 20

Optical Fiber Cable o 반사(Reflection) v When the angle of incidence becomes greater than the critical angle, a new phenomenon occurs called reflection Kyung Hee University 21

Optical Fiber Cable o Optical Fiber Kyung Hee University 22

Optical Fiber Cable o Propagation Models vcurrent technology supports two models for propagating light along optical channel. Kyung Hee University 23

Optical Fiber Cable Figure 7. 13 Modes Kyung Hee University 24

Optical Fiber Cable o Multimode step-index ~ multiple beams from a light source move through the core in different paths. Kyung Hee University 25

Optical Fiber Cable o Multimode graded-index v fiber with varying densities v highest density at the center of the core Kyung Hee University 26

Optical Fiber Cable o 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. Kyung Hee University 27

Optical Fiber Cable o Fiber sizes ~ are defined by the ratio of the diameter of their core to the diameter of their cladding. Table 7. 3 Fiber types Kyung Hee University 28

Optical Fiber Cable o Cable Composition Kyung Hee University 29

Optical Fiber Cable o Fiber-optic Cable Composition Kyung Hee University 30

Optical Fiber Cable o Optical Fiber Performance Wavelength (μm) Kyung Hee University 31

Optical Fiber Cable o Advantages of Optical Fiber l Noise resistance l Less signal attenuation l Higher bandwidth o Disadvantages of Optical Fiber Cost l Installation/maintenance l Fragility Kyung Hee University 32

7. 2 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Topics discussed in this section: Radio Waves Microwaves Infrared Kyung Hee University 33

비유도 매체(Unguided media) o wireless o signals are broadcasted through air Figure 7. 17 Electromagnetic spectrum for wireless communication Kyung Hee University 34

Wireless Transmission o. Radio Frequency Allocation 대류층 Kyung Hee University 전리층 35

비유도 매체(Unguided media) Band Range Propagation Application VLF 3– 30 KHz Ground Long-range radio navigation LF 30– 300 KHz Ground Radio beacons and navigational locators MF 300 KHz– 3 MHz Sky AM radio HF 3– 30 MHz Sky Citizens band (CB), ship/aircraft communication VHF 30– 300 MHz Sky and line-of-sight VHF TV, FM radio UHF 300 MHz– 3 GHz Line-of-sight UHF TV, cellular phones, paging, satellite SHF 3– 30 GHz Line-of-sight Satellite communication EHF 30– 300 GHz Line-of-sight Long-range radio navigation Kyung Hee University 36

Earth’s Atmosphere 외기권 열권 중간권 성층권 Kyung Hee University 대류권 38

Wireless Transmission o Propagation of radio waves v. Types of propagation Kyung Hee University 39

Wireless Transmission Table 7. 4 Bands Kyung Hee University 40

Wireless Transmission o Wireless Transmission Waves Kyung Hee University 41

RADIO WAVE o Electromagnetic waves ranging in frequencies between 3 khz and 1 Ghz are called Radio wave. o. Radio waves are Omnidirectional, they are propagated in all directions. o. Radio waves are propagated in sky mode, can travel long distance. Kyung Hee University 42

RADIO WAVE Note Radio waves are used for multicast communications, such as radio and television, and paging systems. Kyung Hee University 43

MICRO WAVES o Electromagnetic waves having frequencies between 1 and 300 Ghz are called Microwaves. o Microwave propagation is line-of-sight. Since the towers with the mounted antennas need to be in direct sight of each other. o Very high-frequency M/W cannot penetrate walls. o The M/W band is relatively wide, almost 299 Ghz. Therefore wider subbands can be assigned, and a high data rate is possible. Kyung Hee University 44

MICRO WAVE o Repeaters v To increase the distance served by terrestrial microwave, a system of repeaters can be installed with each antenna. Kyung Hee University 45

MICRO WAVE v. Antenna – need unidirectional antenna that send out signals in one direction l parabolic dish antenna Kyung Hee University l horn antenna 46

MICRO WAVE Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Kyung Hee University 47

Infrared q Infrared waves, with frequencies from 300 Ghz to 400 Thz, can be used for short-range communication. q. Infrared waves, having penetrate walls. high frequencies, cannot l 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. q We cannot use infrared waves outside a building because the sun’s rays contain infrared waves that can interfere with the communication Kyung Hee University 48

Infrared signals can be used for shortrange communication in a closed area using line-of-sight propagation. Kyung Hee University 49

Q&A Kyung Hee University 50