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Lecture 03

Lecture 03 . Conducted and Wireless Media. 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

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Lecture 03

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  1. Lecture 03 Conducted and Wireless Media

  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 existif 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 (to p4) (to p28) (to p65) (to p3) Application examples

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

  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 p5) (to p10) (to p13) (to p27) (to p2)

  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) • 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 ascrosswalk (to p6) (to p9) (to p4)

  6. FIGURE 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 p7) (to p5) (to p8)

  7. (to p6)

  8. (to p6)

  9. (to p5)

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

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

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

  16. Fiber-Optic Cable (continued) • 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 (to p15)

  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 p18) (to p19) (to p20) (to p22) (to p24) (to p25) (to p4)

  18. (to p17)

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

  21. FIGURE 9-10bContinued (to p17)

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

  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. 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 (to p26) Concepts of refraction and reflection (to p17)

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

  27. Conducted Media (to p4)

  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 p29) (to p30) (to p63) (to p2)

  29. Wireless Media (continued) (to p28)

  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 p31) (to p35) (to p43) (to p52) (to p53) (to p56) (to p59) (to p60) (to p61) (to p28)

  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 p32) (to p33) (to p34)

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

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

  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. 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 p36) (to p39)

  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 p37) (to p35)

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

  38. Satellite Transmission (continued) (to p37)

  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. 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. 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 p42) (to p30)

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

  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 p44) (to p45) (to p46)

  44. Cellular Telephones (continued) (to p43)

  45. Cellular Telephones (continued) (to p43)

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

  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. 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. 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. 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)

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