1. 1 Lecture 03 Conducted and Wireless Media

2. 2 Introduction Communications are conducted through a medium, –For example, we talked, our voice transmitted through air Thus, the world of computer networks would not exist if there were no medium by which to transfer data The two major categories of media include: –Conducted media –Wireless media How to subscribe them for organizations? –Selection criteria Application examples (to p4) (to p28) (to p65) (to p3)

3. 3 Application examples Conducted –Example 1Example 1 –Example 2Example 2 Wireless –Example 1Example 1 –Example 2Example 2 –Example 3Example 3 (to p71) (to p75) (to p74) (to p77) (to p73)

4. 4 Conducted media Physical connection between source and sink points Three common media: –i) wire –ii) coaxial cable –iii) optical fiber –Comparison between their transmission speeds (to p10) (to p13) (to p5) (to p27) (to p2)

5. 5 i) wire –usually made of copper with a pair of wire Or called twisted pair of wire –the pairs of wires are almost insulated with plastic coating and twisted together -- known as twisted pair wires –(see Figure 9-6)Figure 9-6 –Categorizations –the twisting has the effect of electrically canceling the signals radiating form each wire ---- prevents the signals on one pair of wires from interfering the adjacent pair –the effect is known as crosswalk ( to p6) ( to p9) ( to p4)

6. 6 FIGURE 9-6 Twisted pair wires are the most commonly used medium for communications transmissionFIGURE 9-6 Twisted pair wires are the most commonly used medium for communications transmission. ( to p5) -As to oppose different layout as shown in Figure 3.2 -Different ways of twisted pair way adopted in industries ( to p8) ( to p7) ( to p5)

7. 7 ( to p6)

8. 8

9. 9 ( to p5)

10. 10 ii) coaxial cable –Cable that made of several layers of material around a central core, which often a copper wire –(see Figure 9-8)Figure 9-8) –has a very wide bandwidth (400 Mhz to 600 Hhz), thus carries a very high data capacity –one coaxial cable carries up to 10,800 voice conversations or over 50 television channles –Its max capacity is dependent on the thickness of the copper wire –Two main applications ( to p12) ( to p11)

11. 11 ii) coaxial cable (cont.) It has two main applications: –1) Baseband coaxial technology uses digital signaling in which the cable carries only one channel of digital data –2) Broadband coaxial technology transmits analog signals and is capable of supporting multiple channels Disadv: it is easy to tape and thus lack of a high security measure ( to p4)

12. 12 FIGURE 9-8 Parts of a coaxial cableFIGURE 9-8 Parts of a coaxial cable. ( to p10)

13. 13 iii) optical fiber –Is a new media for comm –is a very thin glass fiber; which core provides the transmission capability –the core is surrounded by another type of glass called cladding, which protected by a plastic coating –(see Figure 9-9) (to p14)Figure 9-9 –data is placed on with a light source or a laser. Light source stays in the core as the cladding has a low refractive index ( to p17)

14. 14 FIGURE 9-9 Parts of optical fiber cable. Alternative view ( to p13) ( to p15)

15. 15 Thin vs. Thick fiber optic cable ( to p16) ( to p13)

16. 16 Fiber-optic cable is capable of supporting millions of bits per second for 1000s of meters Thick cable (62.5/125 microns) causes more ray collisions, so you have to transmit slower. This is step index multimode fiber. Typically use LED for light source, shorter distance transmissions Thin cable (8.3/125 microns) – very little reflection, fast transmission, typically uses a laser, longer transmission distances; known as single mode fiber Fiber-Optic Cable (continued) ( to p15)

17. 17 iii) optical fiber (cont.) –Two primary types of fiber: a) single mode b) multi mode How more lights can be traveled together –Layout of optical fiber worldwide –Fiber optic cable is difficult to splice - requires a reflectometer to detect such work –SONET concept –Adv –Disv ( to p19) ( to p20) ( to p22) ( to p4) ( to p18) ( to p25) ( to p24)

18. 18 ( to p17)

19. 19 Wavelength division Wavelength division multiplexing –A technique which allows many light beams of different wavelengths can travel along a single fiber simultaneously without interfering with one another ( to p17)

20. 20 FIGURE 9-10a The world’s undersea cable network. ( to p21)

21. 21 FIGURE 9-10b Continued ( to p17)

22. 22 SONET Synchronous Optical Network –A technique facilitates easy to connect carriers that using different brands/products of their optical networks –It is a standard for the ANSI (American National Standard Institute) –Transmission rate at Gpbs –Data speed for different networks ( to p23) ( to p17)

23. 23 FIGURE 9-11 Comparative data rates for the SONET and ITU-T optical fiber transmission standards. ( to p22)

24. 24 iii) optical fiber (cont.) –Advantages: 1) do not radiate signal as all electrical devices do 2) fiber is of light weight 3) cost of fibers is getting cheaper 4) high bandwidth - high data capability 5) little lost of signal strength 6) excellent isolation between parallel fiber - crossed-talk between fiber does not exist 7) very secure, difficult to tape ( to p17)

25. 25 Disv Because fiber-optic cable is susceptible to reflection (where the light source bounces around inside the cable) and refraction (where the light source passes out of the core and into the surrounding cladding), thus Fiber-optic cable is not perfect either. Noise is still a potential problem Concepts of refraction and reflection ( to p26) ( to p17)

26. 26 Fiber-Optic Cable (continued) ( to p25)

27. 27 Conducted Media ( to p4)

28. 28 Wireless media Technically speaking – in wireless transmissions, space is the medium Radio, satellite transmissions, and infrared light are all different forms of electromagnetic waves that are used to transmit data Their frequencies of transmission Different types of applications Comparisons ( to p2) ( to p63) ( to p30) ( to p29)

29. 29 Wireless Media (continued) ( to p28)

30. 30 Applications –i) microwave radio –ii) satellite –iii) cellular phones –Iv) Infrared Transmissions –v) Wireless Application Protocol (WAP) –Broadband Wireless Systems –Bluetooth –Wireless Local Area Networks –Free Space Optics and Ultra-Wideband ( to p28) ( to p61) ( to p60) ( to p59) ( to p56) ( to p53) ( to p52) ( to p43) ( to p35) ( to p31)

31. 31 iv) microwave radio –Is a medium most common carriers for long distance comm (how it looks like ) –transmit in the range of 4-28 Ghz freq range –up to 6000 voice circuits are carried in a 30 Mhz wide radio channel –travel in a straight line - ie must transmit and receive in a direct line of sight, and signals will not pass through solid objects –requirement ( to p34) ( to p33) ( to p32)

32. 32 Terrestrial Microwave Transmission (continued) ( to p31)

33. 33 Terrestrial Microwave Transmission (continued) ( to p31)

34. 34 iv) microwave radio (cont.) –requires to set up an antenna in the range of 20 to 30 miles –Capable to carry either analog and digital form –Disadv may interfere by the weather condition (why?) ( to p30)

35. 35 v) satellite –Use of microwave radio, the signal travels from a ground station on earth to a satellite and back to another ground station –Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, and HEO) –radio signal is beamed to the satellite on a specific frequency called uplink; where rebroadcast on a different frequency called downlink ( to p39) ( to p36)

36. 36 Satellite Microwave Transmission (continued) LEO (Low-Earth-Orbit) – 100 to 1000 miles out –Used for wireless e-mail, special mobile telephones, pagers, spying, videoconferencing MEO (Middle-Earth-Orbit) – 1000 to 22,300 miles –Used for GPS (global positioning systems) and government GEO (Geosynchronous-Earth-Orbit) – 22,300 miles –Always over the same position on earth (and always over the equator) –Used for weather, television, government operations HEO (Highly Elliptical Earth orbit) – satellite follows an elliptical orbit –Used by the military for spying and by scientific organizations for photographing celestial bodies Their positions on the orbit ( to p35) ( to p37)

37. 37 Satellite Microwave Transmission (continued) ( to p38) ( to p36)

38. 38 Satellite Transmission (continued) ( to p37)

39. 39 v) satellite (cont.) –Due to the security reason, information that being sent is first encrypted so that tapping and interpret its content is difficult –there exists a delay of receiving information -- - called propagation delay, is called as distance apart of comm device = ----------------------------------------- speed in which data is transmitted –example ( to p40)

40. 40 v) satellite (cont.) –If satellite is 22,300 mile from the ground and speed sending data is 186,000 miles per second, then 2 x 22,300 Propagation delay = ---------------- 18,6000 = 0.2398 sec –Classifications by their configuration ( to p41)

41. 41 Satellite (continued) Satellite microwave can also be classified by its configuration: –Bulk carrier configuration –Multiplexed configuration –Single-user earth station configuration (e.g. VSAT) Their semantic view ( to p30) ( to p42)

42. 42 Satellite Microwave Transmission (continued) ( to p41)

43. 43 Cellular Telephones Wireless telephone service, also called mobile telephone, cell phone, and PCS To support multiple users in a metropolitan area (market), the market is broken into cells Each cell has its own transmission tower and set of assignable channels Different generations of MP ( to p46) ( to p45) ( to p44)

44. 44 Cellular Telephones (continued) ( to p43)

45. 45 Cellular Telephones (continued) ( to p43)

46. 46 Cellular Phones 1 st generation 2 nd generation 2.5 generation 3 rd generation ( to p30) ( to p50) ( to p48) ( to p49) ( to p47)

47. 47 Cellular Telephones (continued) 1st Generation –AMPS (Advanced Mobile Phone Service) – first popular cell phone service; used analog signals and dynamically assigned channels –D-AMPS (Digital AMPS) – applied digital multiplexing techniques on top of AMPS analog channels ( to p46)

48. 48 Cellular Telephones (continued) 2nd Generation –PCS (Personal Communication Systems) – essentially all-digital cell phone service –PCS phones came in three technologies: TDMA – Time Division Multiple Access CDMA – Code Division Multiple Access GSM – Global System for Mobile Communications ( to p46)

49. 49 Cellular Telephones (continued) 2.5 Generation –AT&T Wireless, Cingular Wireless, and T- Mobile now using GPRS (General Packet Radio Service) in their GSM networks (can transmit data at 30 kbps to 40 kbps) –Verizon Wireless, Alltel, U.S.Cellular, and Sprint PCS are using CDMA2000 1xRTT (one carrier radio- transmission technology) (50 kbps to 75 kbps) –Nextel uses IDEN technology ( to p46)

50. 50 Cellular Telephones (continued) 3rd Generation –UMTS (Universal Mobile Telecommunications System) – also called Wideband CDMA The 3G version of GPRS UMTS not backward compatible with GSM (thus requires phones with multiple decoders) –1XEV (1 x Enhanced Version) –3G replacement for 1xRTT Will come in two forms: –1xEV-DO for data only –1xEV-DV for data and voice ( to p46)

51. 51

52. 52 Infrared Transmissions Transmissions that use a focused ray of light in the infrared frequency range Very common with remote control devices, but can also be used for device-to-device transfers, such as PDA to computer ( to p30)

53. 53 Wireless Application Protocol (WAP) WAP is a set of protocols that allows wireless devices such as cell phones, PDAs, and two- way radios to access the Internet WAP is designed to work with small screens and with limited interactive controls WAP incorporates Wireless Markup Language (WML) which is used to specify the format and presentation of text on the screenWireless Markup Language Their applications ( to p54) ( to p55)

54. 54 Wireless Application Protocol (WAP) (continued) ( to p53)

55. 55 Wireless Application Protocol (WAP) (continued) WAP may be used for applications such as: –Travel directions –Sports scores –E-mail –Online address books –Traffic alerts –Banking and news Possible short-comings include low speeds, security, and very small user interface ( to p30)

56. 56 Broadband Wireless Systems Delivers Internet services into homes and businesses Designed to bypass the local loop telephone line, in a metropolitan areametropolitan area Transmits voice, data, and video over high frequency radio signals Past and future trends ( to p58) ( to p57)

57. 57 Broadband Wireless Systems (continued) ( to p56)

58. 58 Broadband Wireless Systems (continued) Multichannel multipoint distribution service (MMDS) and local multipoint distribution service (LMDS) looked promising a few years ago but died off Now companies are eyeing Wi-Max, an IEEE 802.16 standard; initially 300 kbps to 2 Mbps over a range of as much as 30 miles; forthcoming standard (802.16e) will allow for moving devicesWi-Max ( to p30)

59. 59 Bluetooth Bluetooth is a specification for short-range, point-to-point or point-to-multipoint voice and data transferBluetooth Bluetooth can transmit through solid, non-metal objects Its typical link range is from 10 cm to 10 m, but can be extended to 100 m by increasing the power Bluetooth will enable users to connect to a wide range of computing and telecommunication devices without the need of connecting cables Typical uses include phones, pagers, modems, LAN access devices, headsets, notebooks, desktop computers, and PDAsTypical uses ( to p30)

60. 60 Wireless Local Area Networks (IEEE 802.11) This technology transmits data between workstations and local area networks using high-speed radio frequencies Current technologies allow up to 54 Mbps (theoretical) data transfer at distances up to hundreds of feet Three popular standards: IEEE 802.11b, a, g More on this in Chapter Seven (LANs) ( to p30)

61. 61 Free Space Optics and Ultra- Wideband Free space optics –Uses lasers, or more economically, infrared transmitting devices –Line of sight between buildingsLine of sight between buildings –Typically short distances, such as across the street –Newer auto-tracking systems keep lasers aligned when buildings shake from wind and traffic –Current speeds go from T-3 (45 Mbps) to OC-48 (2.5 Gbps) with faster systems in development –Major weakness is transmission thru fog –A typical FSO has a link margin of about 20 dB –Under perfect conditions, air reduces a system’s power by approximately 1 dB/km –Scintillation is also a problem (especially in hot weather) ( to p62)

62. 62 Free Space Optics and Ultra-Wideband (continued) Ultra-wideband –UWB not limited to a fixed bandwidth but broadcasts over a wide range of frequencies simultaneouslybroadcasts over a wide range of frequencies simultaneously –Many of these frequencies are used by other sources, but UWB uses such low power that it “should not” interfere with these other sources –Can achieve speeds up to 100 Mbps but for small distances such as wireless LANs –Proponents for UWB say it gets something for nothing, since it shares frequencies with other sources. Opponents disagree –Cell phone industry against UWB because CDMA most susceptible to interference of UWB –GPS may also be affected –One solution may be to have two types of systems – one for indoors (stronger) and one for outdoors (1/10 the power) ( to p30)

63. 63 Wireless Media (continued) more ( to p64)

64. 64 Wireless Media (continued) ( to p28)

65. 65 Media Selection Criteria 1.Cost 2.Speed 3.Distance and expandability 4.Environment 5.Security ( to p66) ( to p67) ( to p68) ( to p69) ( to p70) ( to p2)

66. 66 Cost Different types of costs –Initial cost – what does a particular type of medium cost to purchase? To install? –Maintenance / support cost ROI (return on investment) – if one medium is cheaper to purchase and install but is not cost effective, where are the savings? ( to p65)

67. 67 Speed Two different forms of speed: –Propagation speed – the time to send the first bit across the medium This speed depends upon the medium Airwaves and fiber are speed of light Copper wire is two thirds the speed of light –Data transfer speed – the time to transmit the rest of the bits in the message This speed is measured in bits per second ( to p65)

68. 68 Expandability and Distance Certain media lend themselves more easily to expansion Don’t forget right-of-way issue ( to p65)

69. 69 Environment Many types of environments are hazardous to certain media ( to p65)

70. 70 Security If data must be secure during transmission, it is important that the medium not be easy to tap ( to p65)

71. 71 Conducted Media in Action: Example 1 First example – simple local area network –Hub typically used –To select proper medium, consider: Cable distance Data rate –Layout ( to p72)

72. 72 Conducted Media in Action: Example 1 ( to p3)

73. 73 Conducted Media in Action: Example 2 Second example – company wishes to transmit data between buildings that are one mile apart –Is property between buildings owned by company? If not consider using wireless When making decision, need to consider: –Cost –Speed –Expandability and distance –Environment –Security ( to p3)

74. 74 Wireless Media In Action: Example 1 First example – you wish to connect two computers in your home to Internet, and want both computers to share a printer –Can purchase wireless network interface cards –May consider using Bluetooth devices ( to p3)

75. 75 Example 2 Second example – company wants to transmit data between two locations, such as Beijing and Shanghai –Company considering two-way data communications service offered through VSAT satellite system –Layout ( to p3) ( to p76)

76. 76 Wireless Media In Action: Three Examples (continued) ( to p3)

77. 77 Wireless Media In Action: Example 3 Third example – second company wishes to transmit data between offices two miles apart –Considering terrestrial microwave system –Layout ( to p78)

78. 78 Wireless Media In Action: Three Examples (continued) ( to p3)