7 장 Transmission media( 전송매체 )

1. 7 장 Transmission media(전송매체) 7.1 Guided Media(유도매체) 7.2 Unguided media(비유도매체) 7.3 Performance(성능) 7.4 요약

2. 전송매체(cont’d) ~ Can be divided into two broad categories : 유도매체, 비유도매체 • Classes of transmission media

3. 7.1 Guided Media(유도매체) • Categories of guided media

4. 유도매체(cont’d) • Twisted-Pair Cable ~ comes in two forms : unshielded(비차폐) and shielded(차폐) • UDP(Unshielded Twisted-Pair) Cable ~ is the most common type of telecommunication medium in use today. • Frequency range for twisted-pair cable

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

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

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

8. 유도매체(cont’d) • Advantage of UTP ~ is cheap, flexible, and easy to install. • Cable with 5 unshielded twisted pairs of wires

9. 유도매체(cont’d) • UDP standards has developed to grade by quality • Category 1 : basic twisted-pair cabling (telephone systems) • Category 2 : suitable for voice and for digital data transmission of up to 4 Mbps • Category 3 : ~ used for data transmission of up to 10 Mbps(now standard cable) • Category 4 : possible transmission rate to 16Mbps • Category 5 : ~ used for data transmission up to 100Mbps

10. 유도매체(cont’d) • UTP connectors ~ a type of snap-in plus like that used with telephone jacks.

11. 유도매체(cont’d) • STP(Shielded Twisted-Pair) cable ~ has the same quality consideration as UTP (more expensive, less susceptible to noise)

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

13. 유도매체(cont’d) • Coaxial cable

14. 유도매체(cont’d) • Coaxial Cable Standards ~ are categorized by RG(radio government) • RG-8 (used in Thick Ethernet) • RG-9 (used in Thick Ethernet) • RG-11 (used in Thick Ethernet) • RG-58 (used in Thin Ethernet) • RG-75 (used for TV)

15. 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.

16. 유도매체(cont’d) • 굴절(Refraction) * Fiber-optic technology takes advantage of the properties shown in Figure 7.13b to control the propagation of light through the fiber channel.

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

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

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

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

21. 유도매체(cont’d) • Multimode graded-index

22. 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.

23. 유도매체(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

24. 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

25. 유도매체(cont’d) • Light Sources for optical label • LED(Light-Emitting Diode) : Short distance • ILD(Injection Laser Diode) : Long distance

26. 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.

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

28. 7.2 비유도 매체(Unguided media) • wireless • signals are broadcast through air

29. 비유도 매체(cont’d) • Radio Frequency Allocation

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

31. 비유도 매체(cont’d) • Type of propagation • Surface Propagation ~ Radio wave travel trough the lowest portion of the atmosphere(대기권) • Troposphere(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

32. 비유도 매체(cont’d) • Ionosphere(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 retraction

33. 비유도 매체(cont’d) • Propagation of Specific Signals ~ The type of propagation used in radio transmission depends on the frequency(speed) of the signal • VLF(Very Low Frequency) ~ are propagated as surface waves, usually through air but sometimes through seawater ~ are used mostly for long-range radio navigation and for submarine communication

34. 비유도 매체(cont’d) • LF(Low Frequency) ~ are also propagated as surface waves ~ are used for long-range radio navigation and for radio beacons or navigation locators

35. 비유도 매체(cont’d) • MF(Middle Frequency) • are propagated in the troposphere(대류권) • are absorbed by the ionosphere • uses for MF transmissions include AM radio, maritime radio, radio direction finding(RDF), and emergency frequencies

36. 비유도 매체(cont’d) • HF(High-Frequency) ~ use ionospheric propagation ~ uses of for HF signals include amateur radio(ham radio), CB(Citizen’s band) radio, international broadcasting, military communication, long-distance aircraft and ship communication, telephone, telegraph, and facsimile

37. 비유도 매체(cont’d) • VHF(Most Very High Frequency) ~ use line-of-sight propagation ~ uses for VHF include VHF television, FM radio, aircraft AM radio, and aircraft navigational aid

38. 비유도 매체(cont’d) • UHF(UltraHigh Frequency) ~ always use line-of-sight propagation. ~ uses for UHF include UHF television, mobile telephone, cellular radio, paging , and micro wave links

39. 비유도 매체(cont’d) • SHF(SuperHigh Frequency) ~ are transmitted using mostly line-of-sight and some space propagation. ~ uses for SHF include terrestrial and satellite microwave, and radar communication

40. 비유도 매체(cont’d) • EHF(Externally High Frequency) ~ use space propagation ~ uses for EHF are radar, Satellite, and experimental communication

41. 비유도 매체(cont’d) • Terrestrial microwave ~ require line-of-sight transmission and reception equipment. The distance coverable by a line-of-sight signal depends to a large extent on the height of the antenna : the taller the antenna, the longer the sight distance

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

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

44. 비유도 매체(cont’d) • Horn antenna ~ looks like a gigantic scoop

45. 비유도 매체(cont’d) • Satellite Communication ~ is much like line of sight microwave transmission in which one of the station is a satellite orbiting the earth

46. 비유도 매체(cont’d) • Geosynchronous satellites

47. 비유도 매체(cont’d) • Frequency bands for satellite communication ` Band Downlink Uplink 03.7 - 04.2 GHz 11.7 - 12.2 GHz 17.7 - 21.0 GHz C Ku Ka 05.925 - 06.425 GHz 14.000 - 14.500 GHz 27.500 - 31.000 GHz

48. 비유도 매체(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.

49. 비유도 매체(cont’d) • Cellular System

50. 비유도 매체(cont’d) • Cellular Bands • Tradition cellular transmission is analog. • The FCC has assigned two bands for cellular use.