Chapter 7 Transmission Media

1. Chapter 7 Transmission Media

2. 7 장 Transmission media • Transmission medium and physical layer

3. Transmission media(전송매체) 7.1 Guided Media(유도매체) 7.2 Unguided media(비유도매체) : Wireless

4. Transmission Media(cont’d) ~ Can be divided into two broad categories : 유도매체, 비 유도매체 • Classes of transmission media

5. 7.1 Guided Media(유도매체) • 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

6. 유도매체(cont’d) • Twisted-Pair Cable ~ comes in two forms : unshielded (비차폐) 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

7. 유도매체(cont’d) • Twisted-Pair Cable • consists of two conductors (usually copper), each with its own colored plastic insulation Color-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

8. 유도매체(cont’d) • Effect of noise on parallel lines

9. 유도매체(cont’d) • Effect of noise on twisted-pair lines

10. 유도매체(cont’d) • Advantage of UTP • cheap, flexible, and easy to install. • 2 ~ 12 twists per foot • Cable with 5 unshielded twisted pairs of wires

11. 유도매체(cont’d) • UTP standards has developed to grade by quality

12. 유도매체(cont’d) • UTP connectors • RJ – Registered Jack • keyed connector, can be inserted one way

13. Performance

14. Applications of UTP • telephone lines for voice and data • DSL • LAN – 10Base-T and 100Base-T

15. 유도매체(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

16. 유도매체(cont’d) • 동축 케이블(Coaxial Cable) • carries signals of higher frequency ranges • Frequency range of coaxial cable

17. 유도매체(cont’d) • Coaxial cable

18. 유도매체(cont’d) • Coaxial Cable Standards ~ are categorized by RG(radio government) rating

19. 유도매체(cont’d) • Coaxial Cable Connectors

20. 유도매체(cont’d) • Performance

21. 유도매체(cont’d) • Applications • Cable TV • traditional Ethernet LANs, 10Base-2, 10Base-5

22. 유도매체(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.

23. 유도매체(cont’d) • 굴절(Refraction)

24. 유도매체(cont’d) • 임계각(critical angle) • As the angle of incidence(입사각) increase, it moves away from vertical and closer to the horizontal.

25. 유도매체(cont’d) • 반사(Reflection) • When the angle of incidence becomes greater than the critical angle, a new phenomenon occurs called reflection

26. 유도매체(cont’d) • Optical Fiber

27. 유도매체(cont’d) • Propagation Models • current technology supports two models for propagating light along optical channel.

28. 유도매체(cont’d) • Multimode step-index ~ multiple beams from a light source move through the core in different paths.

29. 유도매체(cont’d) • Multimode graded-index • fiber with varying densities • highest density at the center of the core

30. 유도매체(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.

31. 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 유도매체(cont’d) • Fiber sizes ~ are defined by the ratio of the diameter of their core to the diameter of their cladding.

32. 유도매체(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

33. 유도매체(cont’d) • Cable Composition

34. 유도매체(cont’d) • Applications of Fiber-optic • network backbones • cable TV • LANs, 100Base-FX, 1000Base-X

35. 유도매체(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.

36. 유도매체(cont’d) • Fiber-optic Cable Composition

37. 유도매체(cont’d) • Optical Fiber Performance

38. 유도매체(cont’d) • Advantages of Optical Fiber • Noise resistance • Less signal attenuation • Higher bandwidth • Disadvantages of Optical Fiber • Cost • Installation/maintenance • Fragility

39. 7.2 비유도 매체(Unguided media) • wireless • signals are broadcasted through air

40. 비유도 매체(cont’d) • Radio Frequency Allocation 대류층 전리층

41. 비유도 매체(cont’d) • Propagation of radio waves • Types of propagation

42. 비유도 매체(cont’d) • Type of propagation • Surface Propagation • Radio waves travel through the lowest portion of the 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)

43. 비유도 매체(cont’d) • Ionospheric (전리층) Propagation • High-frequency radio waves radiate upward into the ionosphere where they are reflected back to earth • Line-of-Sight Propagation • Very high frequency signals are transmitted in straight lives directly from antenna to antenna • Space Propagation • Utilizes satellite relays in place of atmospheric refraction

44. 비유도 매체(cont’d)

45. 비유도 매체(cont’d) • Wireless Transmission Waves

46. 비유도 매체(cont’d) • Omnidirectional antennas

47. 비유도 매체(cont’d) • Radio waves are used for multicast communications, such as radio and television, and paging systems.

48. 비유도 매체(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

49. 비유도 매체(cont’d) • Repeaters • To increase the distance served by terrestrial microwave, a system of repeaters can be installed with each antenna.

50. 비유도 매체(cont’d) • Antennas • two types of antenna • Parabolic dish • is based on the geometry of a parabola