Transcript Chap 7
Chapter 7 Transmission Media 7.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transmission Media 7.2 The transmission media lies below the Physcial Layer It can be considered the Level-0 layer in our Network Models. Figure 7.1 Transmission medium and physical layer 7.3 Transmission Media Guided media Unguided media 7.4 Twister pair copper wire Coaxial cable Fiber optic cable Wireless Figure 7.2 Classes of transmission media 7.5 Twisted Pair The twisted pair wire 7.6 One wire carries signal The other wire acts as a ground Twisting cancels out unwanted signal (noise) Figure 7.3 Twisted-pair cable 7.7 Figure 7.4 UTP and STP cables 7.8 Table 7.1 Categories of unshielded twisted-pair cables 7.9 Figure 7.5 UTP connector 7.10 Wire Guage 40 Guages Based on wire diameter Bigger wire guage number implies smaller diameter. n = -39log92( d/.005 ) + 36 7.11 Wire Guage If the diameter of a wire is doubled, The guage decreases by 6. Thin wires have greater resistance 7.12 Similar to a pipe carrying water. Figure 7.6 UTP performance 7.13 Figure 7.7 Coaxial cable 7.14 Coaxial Cable 7.15 The inner conductor carries the signal. The shielding also acts as a ground. Table 7.2 Categories of coaxial cables 7.16 Figure 7.8 BNC connectors 7.17 Figure 7.9 Coaxial cable performance 7.18 Fiber Optic Cable Capable of carrying greater bandwidth compared to copper wire. 7.19 Copper wire carries frequencies below 100KHz Fiber optic carries frequencies beyond 10THz More expensive than copper wire Fiber Optic Cable 7.20 Incident – incoming wave Refraction – transmitted across the boundary Reflection – reflected within the boundary Critical Angle Total internal reflection Index of refraction – a function of density Fiber Optic Cable Cladding – a transparent material less dense than the inner core of an optical cable. 7.21 Prevents refraction which leads to less loss of signal Figure 7.10 Bending of light ray 7.22 Figure 7.11 Optical fiber 7.23 Figure 7.12 Propagation modes 7.24 Figure 7.13 Modes 7.25 Fiber Optic Cable Multimode step-index fiber: 7.26 The sudden change in density between cable and cladding will result in some distortion of the signal. Fiber Optic Cable Multimode graded-index fiber: 7.27 A gradual change in density from the cable center to the outer cladding and will result in less distortion of the signal compared to stepindex fiber. Graded-index fiber is more costly Fiber Optic Cable Single-mode fiber: 7.28 A narrow diameter of low index of refraction step-indexed glass fiber. A very focused beam of coherent light (similar to a laser) passes near parallel to the fiber edges. Table 7.3 Fiber types 7.29 Figure 7.14 Fiber construction 7.30 Figure 7.15 Fiber-optic cable connectors 7.31 Figure 7.16 Optical fiber performance 7.32 Fiber Optic Cable 7.33 High bandwidth measured in THz Less attenuation Immunity to interference Light weight Tapping is more difficult Unidirectional Expensive compared to copper wire. 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 7.34 Figure 7.17 Electromagnetic spectrum for wireless communication 7.35 Figure 7.18 Propagation methods 7.36 Satellite 7.37 Satellite is direct line of sight communication (Covered in chapter 16) Table 7.4 Bands 7.38 Figure 7.19 Wireless transmission waves 7.39 Multicast vs Broadcast 7.40 Broadcast implies a single transmission to all. (Analog radio or analog TV broadcast) Multicast delivers data to a group of destinations simultaneously; creating copies when links to the destinations split. (guided network transmissions) Figure 7.17 Electromagnetic spectrum for wireless communication 7.41 Radio Wave Properties Frequency range from 3KHz-3GHz Radio waves can pass through walls 7.42 FM, AM, TV, Cell Phone, etc. Figure 7.20 Omnidirectional antenna 7.43 Figure 7.21 Unidirectional antennas 7.44 Figure 7.17 Electromagnetic spectrum for wireless communication 7.45 Note Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. 7.46 Microwaves Range from 3GHz to 300GHz High frequency microwaves do not pass through walls The bottom of the frequency range can pass through walls Capable of high bandwidth 7.47 Bluetooth is in the microwave range. Figure 7.17 Electromagnetic spectrum for wireless communication 7.48 Note Infrared signals can be used for shortrange communication in a closed area using line-of-sight propagation. 7.49 Infrared Waves Range from 300GHz to 400THz Do not pass through walls Capable of high bandwidth Lots of bands can be created reducing the likelihood of interference from other infrared devices. 7.50 Remote control devices