數(shù)據(jù)通信基礎(chǔ)：第7章 傳輸介質(zhì)

1、數(shù)據(jù)通信基礎(chǔ)第7章 (傳輸介質(zhì)) Transmission Media20120312BitLiuJKPage 2 7.1 Guided Media 導(dǎo)向介質(zhì)7.2 Unguided Media 非導(dǎo)向介質(zhì)注意:“Medium” 是單數(shù)形式，而“Media” 是復(fù)數(shù)形式第4章內(nèi)容提要20120312BitLiuJKPage 3 IntroductionIn this chapter, we will discuss the communication channel, or medium.Transmission media can be divided into:Guided media (

2、twisted-pair雙絞線, coaxial cable同軸電纜, fiber-optic光纖)Unguided media (radio無(wú)線電, microwave微波, infrared紅外線)Medium can be wired有線 or wireless無(wú)線.20120312BitLiuJKPage 4 Importance of MediaTransmission media is the communication channel between sender and receiver.Many characteristics of communication system

3、will be determined by the property of the media used for transmission.20120312BitLiuJKPage 5 Classes of MediaTransmission media can be divided into two groups: guided and unguidedGuided media can be further categorized into twisted-pair, coaxial, and fiber-optic cables.20120312BitLiuJKPage 6 Electro

4、magnetic SpectrumWhen we arrange the frequency from low to high, we have the whole electro-magnetic spectrum.This is a very important and limited resource for communication.Only part of it can be used.See next slide.20120312BitLiuJKPage 7 20120312BitLiuJKPage 8 Twisted-Pair Cable雙絞線Coaxial Cable同軸電纜

5、Fiber-Optic Cable光纖/光纜7.1 Guided Media20120312BitLiuJKPage 9 Twisted-PairTwisted-pair is a pair of wires twisted with each other. Each wire contains a conductor surrounded by an insulator.Twisted-pair is commonly used for daily life, such as inside power line and telephone line.20120312BitLiuJKPage

6、10 UTP and STPUTP = Unshielded Twisted PairSTP = Shielded Twisted PairUTP has no metal shield, so it is much cheaper and most used for LAN.20120312BitLiuJKPage 11 Inside of a UTPNormally only FOUR pairs of wires inside the UTP. They are colored with Orange, Blue, Green, Brown.20120312BitLiuJKPage 12

7、 CategoryBandwidthData RateDigital/AnalogUse1very low 100 kbpsAnalogTelephone2 2 MHz2 MbpsAnalog/digitalT-1 lines3 16 MHz 10 MbpsDigitalLANs4 20 MHz 20 MbpsDigitalLANs5 100 MHz 100 MbpsDigitalLANs6 (draft) 200 MHz 200 MbpsDigitalLANs7 (draft) 600 MHz 600 MbpsDigitalLANsTable 7.1 Categories of unshie

8、lded twisted-pair cables20120312BitLiuJKPage 13 UTP ConnectorThe UTP connector for LAN is called RJ-45 in USA.The UTP for telephone is called RJ-11 which has SIX conductors, but only two of them are used.20120312BitLiuJKPage 14 Classes of UTP Conductor20120312BitLiuJKPage 15 Frequency Range for UTPT

9、he frequency range for twisted-pair is considered as up to 5 MHz, but actually only 1 MHz can be used.See the Figure.20120312BitLiuJKPage 16 Coaxial CableCoaxial cable (coax) can carry higher frequency than twisted-pair. Coax has a outer conductor, which is served as a outer shield. Therefore, coax

10、can protect signal from noise. 20120312BitLiuJKPage 17 Coaxial ConnectorBNC = Bayone-Neill-Concelman or Bayonet network connectorThere are BNC connector, BNC T, and BNC terminator.BNC is used in instrument and thin/thick Ethernet.20120312BitLiuJKPage 18 CategoryImpedanceUseRG-5975 WCable TVRG-5850 W

11、Thin EthernetRG-1150 WThick EthernetTable 7.2 Categories of coaxial cables20120312BitLiuJKPage 19 Frequency Range for CoaxFrequency range for coaxial can be up to 500 MHz. Good coaxial can be 1000 MHz, such as the new Cable TV coax.MHz20120312BitLiuJKPage 20 Fiber-Optic CableA fiber-optic cable is m

12、ade of glass or plastic and transmits signal in the form of light. There are two parts of a fiber: core and cladding, with different dense.纖芯和涂覆層外護(hù)套包20120312BitLiuJKPage 21 Nature of LightWhen light goes from more dense material to less dense side, refraction happens. The angle for the input light i

13、s less than the angle for output.When the input angle is greater than Critical angle臨界角, no refraction to the other side. This is called Complete Reflection全反射.20120312BitLiuJKPage 22 Complete ReflectionIn complete reflection, the angle of incidence 入射角 is equal to the angle of reflection 反射角.201203

14、12BitLiuJKPage 23 Principle of Fiber-OpticWhen the angle of incidence is greater than the critical angle, input light is reflected within the core of fiber.With many times reflection, the light goes from sender at one end to receiver at the other end. 20120312BitLiuJKPage 24 Fiber Propagation ModeMu

15、ltimode多模: Multiple beams in the coreMultimode Step-index階躍: constant density in coreMultimode Graded-index漸變: varying density in coreSingle-mode單模: Only one mode exists.20120312BitLiuJKPage 25 Effects of Different Mode20120312BitLiuJKPage 26 TypeCoreCladdingMode50/125 50125Multimode, graded-index62

16、.5/125 62.5125Multimode, graded-index100/125100125Multimode, graded-index7/125 7125Single-modeTable 7.3 Fiber types20120312BitLiuJKPage 27 Fiber Construction塑料包杜邦特氟龍20120312BitLiuJKPage 28 Fiber-Optic Cable Connector20120312BitLiuJKPage 29 Fiber Performance20120312BitLiuJKPage 30 Radio Waves無(wú)線電波Micr

17、owaves微波Infrared紅外線7.2 Unguided Media: Wireless20120312BitLiuJKPage 31 Frequency Range for WirelessWhen signal is transmitted through air, anyone can receiver the signal without need a connection wire.The frequency used for wireless can be radio wave, microwave, or infrared.20120312BitLiuJKPage 32 P

18、ropagation傳輸 ModeThere are three ways for wireless:Ground wave 地波Sky wave 天波(reflected by the Ionosphere)Line-of-Sight 視距傳播(direct transmission within sight)電離層20120312BitLiuJKPage 33 Table 7.4 BandsBand中文RangePropagationApplicationVLF甚低頻330 KHzGroundLong-range radio navigationLF低頻30300 KHzGroundRad

19、io beacons andnavigational locatorsMF中頻300 KHz3 MHzSkyAM radioHF 高頻330 MHzSkyCitizens band (CB),ship/aircraft communicationVHF 甚高頻/短波30300 MHzSky andline-of-sightVHF TV, FM radioUHF 特高頻300 MHz3 GHzLine-of-sightUHF TV, cellular phones, paging, satelliteSHF 超高頻330 GHzLine-of-sightSatellite communicationEHF極高頻30300 GHzLine-of-sightLong-range radio navigation20120312BitLiuJKPage 34 Omni directional antennaThree types of antenna are used for terrestrial microwave communication: omni directional全向, parabolic dish拋物面, and horn喇叭. Omni directional antenna is used for Rad