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Computer Networking

广西医科大学. Computer Networking. 网络课件. 双语教学. 模拟实验. 计算机网络教研室. DI. 1. 2. 3. CHAPTER 8 TRANSMISSION MEDIA. The first section. Exercises. Online lecture. Chapter 8 Transmission Media. 8.1 INTRODUCTION. Media transmission. Conducted or guided media

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Computer Networking

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  1. 广西医科大学 ComputerNetworking 网络课件 双语教学 模拟实验 计算机网络教研室

  2. DI 1 2 3 CHAPTER 8 TRANSMISSION MEDIA The first section Exercises Online lecture

  3. Chapter 8 Transmission Media 8.1 INTRODUCTION Media transmission Conducted or guided media A type of media that provides some type of physical path, such as wire, cable, or optical fiber, along which the signal moves from end to end . Radiated or unguided media most commonly known today as wireless,such as radio waves,microwaves,or infrared waves,throughair,water,or a vacuum.

  4. Chapter 8 Transmission Media • 8.2 CONDUCTED MEDIA • 8.2.1 Unshielded Twisted Pair Wire Figure 8-1 Twisted pair wires are the most commonly used medium for communications transmission. www.gxmu.edu.cn

  5. Chapter 8 Transmission Media • Twisting a pair of wires together has the effect of electrically canceling the signals radiating from each wire . • The Electrical Industries Association(EIA) has defined six categories of UTP for telephone and data transmission use. P150 www.gxmu.edu.cn

  6. Chapter 8 Transmission Media Cat 3 Cat 5 Wire containing at least three twists per foot and that is about the same as normal telephone cable installed in most office buildings is called CAT 3. CAT 5 cable normally contains four pairs of wires and is the type that is most commonly being installed in new homes and businesses, particularly when it is known that a computer network will be used. Company Logo

  7. Chapter 8 Transmission Media • When UTP is use in a data application it is normally terminated with a RJ-45 jack. P151 • The purpose of a terminating block or a punchdown block is to be responsible for providing and maintaining all wiring within the building. P152 www.gxmu.edu.cn

  8. Chapter 8 Transmission Media Figure 8-2 Wires installed outside may be buried or hung from poles above ground. www.gxmu.edu.cn

  9. Chapter 8 Transmission Media • 8.2.2 Shielded Twisted Pair Wire（STP） • Twisted pair wire is placed inside a thin metallic shielding,similar to aluminum foil and then enclosed in an outer plastic casing. • STP cable is infrequently used because it is difficult to work with. www.gxmu.edu.cn

  10. Chapter 8 Transmission Media 8.2.3Coaxial cable Figure 8-3 Parts of coaxial cable. www.gxmu.edu.cn

  11. Chapter 8 Transmission Media • Coaxial cableis advantageous when taps in the cable need to be made—it is easier to tap than optical fiber. • The most common connector used in networking applications is the British Naval Connector(BNC). www.gxmu.edu.cn

  12. Chapter 8 Transmission Media • 8.3OPTICAL FIBERThe optical fiberis a very thin glass fiber of high purity. • The core of an optical fiber is surrounded by another type of glass called the cladding. • Data are placed on an optical fiber with a light source, either an LED or a laser. • The total diameter of an optical fiber is less than that of a human hair. www.gxmu.edu.cn

  13. Chapter 8 Transmission Media • 8.3OPTICAL FIBER 光发射机原理示意图 光接收机光电转换原理示意图 www.gxmu.edu.cn

  14. Chapter 8 Transmission Media Figure 8-4 Parts of optical fiber cable. Single mode optical fiber is more expensive than multimode fiber. www.gxmu.edu.cn

  15. Chapter 8 Transmission Media Structure of Optical Fiber Cable www.gxmu.edu.cn

  16. Chapter 8 Transmission Media • 8.3OPTICAL FIBER • The characteristic of optical fiber include: • high bandwidth; • difficult to tap and splice; • not subject to electrical interference; • cable is very small diameter and lightweight. • little loss of signal strength; www.gxmu.edu.cn

  17. Chapter 8 Transmission Media • 8.4WIRELESS MEDIA • 8.4.1 Microwave Radio • Microwave radio signals travel in a straight line,andcann’tfollow the curvature of the earth so it is necessary for the transmitting and receiving antennas to be in a direct LOS. www.gxmu.edu.cn

  18. Chapter 8 Transmission Media • 8.4.2 Satellite • Satellites in geosynchronous orbits circle the earth at 22,300 miles. • The radio signal beamed from the Earth at a satellite is called the uplink，where it is received,amplified,and then rebroadcast on a different frequency,called the downlink. www.gxmu.edu.cn

  19. Chapter 8 Transmission Media Figure 8-5 Satellite transmission. www.gxmu.edu.cn

  20. Chapter 8 Transmission Media • Propagation delayis the delay that occurs because light and radio signals only travel at 186,000 miles per second.  • A type of satellite commonly used to send television programming into homes is called a direct broadcast satellite. • Satellites in medium earth orbits(MEO) are approximately 6,000 miles high. • Low earth orbit(LEO) satellites orbit at between 300 and 1000 miles high. www.gxmu.edu.cn

  21. Chapter 8 Transmission Media • 8.4.3 Infrared • Infrared transmissions require the sender and receiver to be in direct line of sight. • 8.4.4 Free Space Optics • The use of modulated laser beams to send data between locations that are within LOS of each other is called Free space optics (FSO). www.gxmu.edu.cn

  22. Chapter 8 Transmission Media • 8.6 SUMMARY OF MEDIA CHARACTERISTICS www.gxmu.edu.cn

  23. Chapter 8 Transmission Media 课后习题 1.The radio signal beamed from the Earth at a satellite is called the （　　）. A A、 uplink √ B、 downlink × C、 data link × × D、 control link Redo Next Answer

  24. Chapter 8 Transmission Media 课后习题 2.The most popular cable for networking being installed in new office buildings is （　）. D × A、 STP × B、 optical fiber × C、 CAT 3 D、 CAT 5 √ Redo Next Answer

  25. Chapter 8 Transmission Media 课后习题 3.Multiplexing on optical fibers is performed by using（　　）. B × A、 FSK √ B、 WDM × C、 FDM × D、 PAM Redo Next Answer

  26. Chapter 8 Transmission Media 课后习题 4. The type of media that provides some type of physical path is called （　　）. D × A、 unguided media × B、 physical media × C、 wireless media D、 conducted media √ Redo Next Answer

  27. Chapter 8 Transmission Media 课后习题 C 5.Twisting a pair of wires together has the effect of（　　）. × A、 shielding the wire from outside interference × B、 strengthening the pair against breakage C、 electrically canceling the signals radiating from each wire √ × D、 amplifying the signal flowing through the wire Redo Next Answer

  28. Chapter 8 Transmission Media 课后习题 • unguided 6.Air is an example of _________ media. Answer 7.The most appropriate media to use when there is a need for very high bandwidth and high security is _____________ . • optical fiber Answer • guided 8.Twisted pair wire is an example of _________ media. Answer

  29. Chapter 8 Transmission Media 课后习题 optical fiber 9.The characteristic of ___________ include: high bandwidth, difficult to tap and splice; not subject to electrical interference, cable is very small diameter and lightweight. Answer 10.A type of satellite commonly used to send television programming into homes is called a _____________________ . direct broadcast satellite Answer

  30. Chapter 8 Transmission Media Thank You ! www.gxmu.edu.cn

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