2. Computer Networking

3. Department of Computer Networking Application CHAPTER 8 TRANSMISSION MEDIA 1 The first section 2 Exercises 3 Online lecture

4. www.gxmu.edu.cn 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. physical path wire, cable, or optical fiber Media transmission Radiated or unguided media most commonly known today as wireless,such as radio waves,microwaves,or infrared waves,through air,water,or a vacuum. wirelessradio waves,microwaves,or infrared wavesvacuum Chapter 8 Transmission Media 8.1 INTRODUCTION

5. 8.2 CONDUCTED MEDIACONDUCTED MEDIA 8.2.1 Unshielded Twisted Pair WireUnshielded Twisted Pair Wire Figure 8-1 Twisted pair wires are the most commonly used medium for communications transmission. Chapter 8 Transmission Media www.gxmu.edu.cn

6. Twisting a pair of wires together has the effect of electrically canceling the signals radiating from each wire.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. P150The Electrical Industries Association(EIA) Chapter 8 Transmission Media www.gxmu.edu.cn

7. www.themegallery.com Company Logo 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.three twists per foot 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. Cat 3Cat 5 Chapter 8 Transmission Media

8. When UTP is use in a data application it is normally terminated with a RJ-45 jack. P151jack The purpose of a terminating block or a punchdown block is to be responsible for providing and maintaining all wiring within the building. P152terminating block punchdown block Chapter 8 Transmission Media www.gxmu.edu.cn

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

10. 8.2.2 Shielded Twisted Pair Wire STP Shielded Twisted Pair Wire Twisted pair wire is placed inside a thin metallic shielding,similar to aluminum foil and then enclosed in an outer plastic casing.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. Chapter 8 Transmission Media www.gxmu.edu.cn

11. 8.2.3 Coaxial cableCoaxial cable Chapter 8 Transmission Media www.gxmu.edu.cn Figure 8-3 Parts of coaxial cable.

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

13. 8.3 OPTICAL FIBER The optical fiber is a very thin glass fiber of high purity.OPTICAL FIBERa very thin glass fiber of high purity The core of an optical fiber is surrounded by another type of glass called the cladding.cladding Data are placed on an optical fiber with a light source, either an LED or a laser.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. Chapter 8 Transmission Media www.gxmu.edu.cn

14. 8.3 OPTICAL FIBEROPTICAL FIBER Chapter 8 Transmission Media www.gxmu.edu.cn

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

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

17. 8.3 OPTICAL FIBEROPTICAL FIBER The characteristic of optical fiber include:characteristic high bandwidth;high bandwidth difficult to tap and splice;difficult to tap and splice not subject to electrical interference;not subject to electrical interference cable is very small diameter and lightweight.cable is very small diameter and lightweight little loss of signal strength;little loss of signal strength Chapter 8 Transmission Media www.gxmu.edu.cn

18. 8.4 WIRELESS MEDIAWIRELESS MEDIA 8.4.1 Microwave RadioMicrowave Radio Microwave radio signals travel in a straight line,and cannt follow the curvature of the earth so it is necessary for the transmitting and receiving antennas to be in a direct LOS. straight line curvaturetransmitting and receiving antennas to be in a direct LOS. Chapter 8 Transmission Media www.gxmu.edu.cn

19. 8.4.2 SatelliteSatellite Satellites in geosynchronous orbits circle the earth at 22,300 miles.geosynchronous orbits 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.radio signal beamed uplinkamplifieddownlink Chapter 8 Transmission Media www.gxmu.edu.cn

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

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

22. 8.4.3 InfraredInfrared Infrared transmissions require the sender and receiver to be in direct line of sight.in direct line of sight 8.4.4 Free Space Optics 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).modulated laser beams to send data between locations that are within LOS of each other Chapter 8 Transmission Media www.gxmu.edu.cn

23. 8.6 SUMMARY OF MEDIA CHARACTERISTICSSUMMARY OF MEDIA CHARACTERISTICS Chapter 8 Transmission Media www.gxmu.edu.cn

24. A uplink 1.The radio signal beamed from the Earth at a satellite is called the. A B downlink D control link C data link Answer Redo Next × × × Exercises Chapter 8 Transmission Media

25. D CAT 5 2.The most popular cable for networking being installed in new office buildings is. D A STP B optical fiber C CAT 3 Answer Redo Next × × × Exercises Chapter 8 Transmission Media

26. B WDM 3.Multiplexing on optical fibers is performed by using. B A FSK D PAM C FDM Answer Redo Next × × × Exercises Chapter 8 Transmission Media

27. D conducted media 4. The type of media that provides some type of physical path is called. D A unguided media B physical media C wireless media Answer Redo Next × × × Exercises Chapter 8 Transmission Media

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

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

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

31. www.gxmu.edu.cn Chapter 8 Transmission Media