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 UDP(Unshielded 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) Frequency range of 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) Nature of Light
~ 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 Fiber Type Core(microns) Cladding(microns)
~ 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
140

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 Line-of-Sight 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 VLF(Very Low Frequency)
~ 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 Parabolic dish ~ two types of antenna
~ 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 C Ku Ka
GHz
GHz
GHz
GHz
GHz
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.

51. 비유도 매체(cont’d) Transmitting
The caller enter a code of 7 or 10 digits(phone number)
Press the send button
The mobile phone then scans the band, seeking a setup channel with a strong signal
Sends the data(phone number) to the closest cell office
Cell office relays the data to the MOS0
MTS0 send data on to the telephone central office

52. 비유도 매체(cont’d) Receiving
Telephone central office sends the number to the MTSO
MTSO search for the location of the mobile phone
Mobile phone is found, the MTSO transmits a ringing signal
When the mobile phone is answered, assigns a voice channel to the call, allowing voice communication to begin

53. 비유도 매체(cont’d) Handoff
During a conversation, the mobile phone moves from one cell to another
Signal may become weak
MTSO monitors the level of the signal every few seconds
MTSO seeks a new cell that can accommodate the communication better
Handoff one performed so smoothly that most of the time they are not observed by the users

54. 비유도 매체(cont’d)
Digital
Integration with Satellites and PCs

55. 7.3 Performance Cost Speed Attenuation
EMI(Electromagnetic Interference)
Security

56. Performance(cont’d) Transmission media performance Medium Cost Speed
Attenuation
EMI
Security
UTP
STP
Coax
Optical fiber
Radio
Microwave
Satellite
Cellular
Low
Moderate
High
Mbps
Mbps
1 Mbps - 1 Gbps
10 Mbps - 2 Gbps
Mbps
1 Mbps - 10 Gbps
Kbps
High
Moderate
Low
Low-high
Variable
High
Moderate
Low
Low
High
Moderate

57. 7.4 요약