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  1. 1. Chapter 7 Transmission Media 7.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. Figure 7.1 Transmission medium and physical layer It can be defined as any thing that carry information from a source to destination 7.2
  3. 3. Figure 7.2 Classes of transmission media 7.3
  4. 4. 7-1 GUIDED MEDIA Guided media, which are those that provide a conduit ‫ قناة‬from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Topics discussed in this section: Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable 7.4
  5. 5. Figure 7.3 Twisted-pair cable One to carry the signal and the other as a ground. The receiver uses the difference between the two Interference and crosstalk may affect the wires and create unwanted signals Twisting makes it probable that both wires are equally affected by external influences, it means that the receiver which calculate the difference between the two receives no unwanted signals. 7.5
  6. 6. Figure 7.4 UTP and STP cables The metal case prevent noise or crosstalk, quality is improved. 7.6
  7. 7. Table 7.1 Categories of unshielded twisted-pair cables by EIA 7.7
  8. 8. Figure 7.5 UTP connector RJ ( registered jack) It’s a key connector which means that it can can be inserted in only one way 7.8
  9. 9. Figure 7.6 UTP performance (Attenuation vs frequency & distance) Gauge is a measure of the wire thickness Applications Telephone lines DSL lines LAN 10 base T 7.9
  10. 10. Figure 7.7 Coaxial cable It carries signals of higher frequency ranges 7.10
  11. 11. Table 7.2 Categories of coaxial cables RG radio governments 7.11
  12. 12. Figure 7.8 BNC connectors Bayone-Neill-Concelman To prevent signal reflection 7.12
  13. 13. Figure 7.9 Coaxial cable performance The attenuation is much higher than the twisted –pair cable, but it has a much higher bandwidth but we need a frequent use of repeaters. Its used in analog tel. It carry up to 10000 voice signal and in digital network to carry data up to 600 Mbps, now it is replaced by the fiber optic. 7.13
  14. 14. Figure 7.10 Bending of light ray Fiber optic cable is made of glass or plastic ,, transform signals in form of light I (angle of incidence) Light travel in a straight lines, as long as it moves through a single uniform substance, if more than one the ray changes its direction( different density) So the critical angle is defined as the angle of incidence which provides an angle of refraction of 90-degrees . 7.14
  15. 15. Figure 7.11 Optical fiber A glass or plastic core is surrounded by a cladding of less dense glass or plastic 7.15
  16. 16. Figure 7.12 Propagation modes 7.16
  17. 17. Figure 7.13 Modes Multimodal : multiple beams from a light source move through the core in different paths. Step index : suddenness of changing the beam angle at the surface between the core and cladding material, core material of the same density. Graded index : core of a varying density, index refers to refraction, density is high at the center, and decreases gradually at the edge Single :Highly focused source of light that limits beams to a small range of angles. 7.17
  18. 18. Table 7.3 Fiber types 7.18
  19. 19. Figure 7.14 Fiber construction PVC or Teflon 7.19
  20. 20. Figure 7.15 Fiber-optic cable connectors Sc subscriber channel St straight-tip Advantages : Higher bandwidth, less signal attenuation ( still up to 50 Km), Immunity against electromagnetic interference, resistance to corrosive materials 7.20
  21. 21. Figure 7.16 Optical fiber performance 7.21
  22. 22. Advantages & Disadvantages of Optical fibers Advantages 1- higher Bandwidth ( but limited due to the trans. & receive. Technology 2- Less signal Attenuation ( signal can run up to 50Km without regeneration 3- Immunity to Electromagnetic interference. 4- Resistance to corrosive materials. 5- Light weight. 6- Greater immunity to tapping. Disadvantages 1- Installation and maintenance 2- unidirectional light propagation 3- Cost 7.22
  23. 23. 7-2 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Topics discussed in this section: Radio Waves Microwaves Infrared 7.23
  24. 24. Figure 7.17 Electromagnetic spectrum for wireless communication 7.24
  25. 25. Figure 7.18 Propagation methods 7.25
  26. 26. Table 7.4 Bands 7.26
  27. 27. Figure 7.19 Wireless transmission waves Radio Waves: 3kHz – 1 GHz Omni directions, signal propagates in all directions, travelling long distances AM&FM radios television Microwave : 1GHz-3GHz uni-direction Infrared : 3GHz7.27
  28. 28. Figure 7.20 Omnidirectional antenna 7.28
  29. 29. Note Radio waves are used for multicast communications, such as radio and television. 7.29
  30. 30. Figure 7.21 Unidirectional antennas Advantages: A Pair of antennas can be aligned without interfering with another pair. Microwave propagation is a line of sight. -wider sub bands are assigned ( wide band) , high data rate . Disadvantages: can’t penetrate walls, certain portions of the band requires permission fro authorities. 7.30
  31. 31. Note Microwaves are used for unicast (One to one) communication such as cellular telephones, satellite networks, and wireless LANs. 7.31
  32. 32. Note Infrared signals can be used for shortrange communication in a closed area using line-of-sight propagation. 7.32