通信及基础工程7

Unit2TextAMobileWirelessOverviewMobileWirelessOverviewAfast-pacedtechnologicaltransitionisoccurringtodayintheworldofinternetworking.ThistransitionismarkedbytheconvergenceofthetelecommunicationsinfrastructurewiththatofIPdatanetworkingtoprovideintegratedvoice,video,anddataservices.TextTextWordsNotesDiscussionHomeAsthistransitionprogresses,thecorrespondingstandardsarecontinuingtoevolveandmanynewstandardsarebeingdevelopedtoenableandacceleratethisconvergenceoftelecommunicationsandIPnetworkingtomobilizetheinternetandprovidenewmultimediaservices.TextTextWordsNotesDiscussionHome1.IntroductiontoMobileWirelessTechnologyThetechnologiesrelatedtowirelesscommunicationcanbecomplextodifferentiate.Wirelesstechnologyhasbeenaroundforawhile;however,therehasbeenarelativelyrecentandrapidsurgeintheevolutionofnewwirelessstandardstosupporttheconvergenceofvoice,videoanddatacommunication.Muchofthisrapidevolution,orrevolution,isaresultofpeopleseekingubiquitousandimmediateaccesstoinformationandtheassimilationoftheinternetintobusinesspracticesandforpersonaluse.People“onthego”wanttheirinternetaccesstomovewiththem,sothattheirinformationisavailableatanytime,anywhere.TextWordsNotesDiscussionHomeTherearemanyfactorsthatcanbeusedtocharacterizewirelesstechnologies:•Spectrum,ortherangeoffrequenciesinwhichthenetworkoperates•Transmissionspeedssupported•Underlyingtransmissionmechanism,suchasfrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA),orcodedivisionmultipleaccess(CDMA)•Architecturalimplementation,suchasenterprisebased(orin-building),fixed,ormobileTextWordsNotesDiscussionHomeInaddition,themobilewirelesstechnologies[suchasGlobalSystemforMobileCommunications(GSM),TDMA,CDMA]aredifferentiatedbyanumberofdifferentfactors,includingsomeofthefollowing:•Controlofthetransmittedpower•Radioresourcemanagementandchannelallocation•Codingalgorithms•Networktopologyandfrequencyreuse•HandoffmechanismsTextWordsNotesDiscussionHomeAssuggestedbyitsname,mobilewirelesscommunicationaddressesthosewirelesstechnologiesthatsupportmobilityofasubscriber,whichprovideseamlessandreal-timeserviceswithoutinterruption.[1]Mobilewirelesstechnologiessupportnetworkaccesswhethersubscribersroamwithinoroutsidetheirhomewirelesscoveragearea.TextWordsNotesDiscussionHome2.OverviewofBasicNetworkElementsAssociatedwithCellularNetworksandMobileWirelessThissectionprovidesabriefintroductiontoafewofthebasicnetworkcomponentsassociatedwiththeexistingtelecommunicationsinfrastructure.ItspecificallydiscussestheexistingmobilewirelessnetworkinfrastructurecomponentsforTDM-basedwirelessnetworks,someofwhicheventuallywillbereplacedbynewIP-basedcomponents.TextWordsNotesDiscussionHomeIntheearly1980s,supportformobilewirelesscommunicationswasintroducedusingcellularnetworks,whichwerebasedonanalogtechnologiessuchasAMPS[2].Manyofthetelecommunicationsentitiesassociatedwithcellularnetworksstillplayavitalroleintoday’swirelessnetworks.AswirelesscommunicationstechnologiescontinuetoprogressandIPdatanetworkingisfurtherintegratedintotheexistinginfrastructure,someofthefunctionsoftheseentitiesmightstillexistwithinthenetwork,butwillbeimplementedindifferentandmoreeffectiveways.TextWordsNotesDiscussionHomeThefollowingnetworkelementsarepartofatypicalcellulartelecommunicationsnetwork:•PublicSwitchedTelephoneNetwork(PSTN)•MobileSwitchingCenter(MSC)•BaseStation(BS)•RadioAccessNetwork(RAN)•HomeLocationRegister(HLR)•VisitorLocationRegister(VLR)•AuthenticationCenter(AC)

[3]TextWordsNotesDiscussionHome(1)PublicSwitchedTelephoneNetwork(PSTN)ThePSTNisthefoundationandremainsthepredominantinfrastructurethatcurrentlysupportstheconnectionofmillionsofsubscribersworldwide.ThePSTNhasseveralthousandsofmilesoftransmissioninfrastructure,includingfixedlandlines,microwave,andsatellitelinks.Aftertheintroductionofcellulartelephonesystemsintheearlyandmid-1980s,andwiththerapiddevelopmentofmobilewirelesscommunicationservices,thePSTNstillprovidesthefixednetworksupportusingtheSignalingSystemNumber7(SS7)protocoltocarrycontrolandsignalingmessagesinapacket-switchedenvironment.TextWordsNotesDiscussionHome(2)MobileSwitchingCenter(MSC)TheMSC,usuallylocatedattheMobileTelephoneSwitchingOffice(MTSO),ispartofthemobilewirelessnetworkinfrastructurethatprovidesthefollowingservices:•SwitchesvoicetrafficfromthewirelessnetworktothePSTNifthecallisamobile-to-landlinecall,oritswitchestoanotherMSCwithinthewirelessnetworkifthecallisamobile-to-mobilecall.•Providestelephonyswitchingservicesandcontrolscallsbetweentelephoneanddatasystems.TextWordsNotesDiscussionHome•Providesthemobilityfunctionsforthenetworkandservesasthehubforuptoasmanyas100BSs.Morespecifically,theMSCprovidesthefollowingfunctions:•Mobilitymanagementforthesubscribers(toregistersubscribers,toauthenticateandauthorizethesubscribersforservicesandaccesstothenetwork,tomaintaintheinformationonthetemporarylocationofthesubscriberssotheycanreceiveandoriginatevoicecalls).TextWordsNotesDiscussionHomeInGSM,someofthefunctionalityoftheMSCisdistributedtotheBaseStationController(BSC).InTDMA,theBSCandtheMSCareintegrated.•Callsetupservices(callroutingbasedonthecallednumber).ThesecallscanbetoanothermobilesubscriberthroughanotherMSC,ortoalandlineuserthroughthePSTN.•Connectioncontrolservices,whichdeterminehowcallsareroutedandestablishestrunkstocarrythebearertraffictoanotherMSCortothePSTN.TextWordsNotesDiscussionHome•Servicelogicfunctions,whichroutethecalltotherequestedserviceforthesubscriber,suchasan800service,callforwarding,orvoicemail.•Transcodingfunctions,whichdecompressthevoicetrafficfromthemobiledevicegoingtothePSTNandcompressesthetrafficgoingfromthePSTNtothemobiledevice.TextWordsNotesDiscussionHome(3)BaseStation(BS)TheBSisthecomponentofthemobilewirelessnetworkaccessinfrastructurethatterminatestheairinterfaceoverwhichthesubscribertrafficistransmittedtoandfromamobilestation(MS).InGSM-basednetworks,theBSiscalledaBaseTransceiverStation(BTS).TextWordsNotesDiscussionHome(4)RadioAccessNetwork(RAN)TheRANidentifiestheportionofthewirelessnetworkthathandlestheradiofrequencies(RF),RadioResourceManagement(RRM),whichinvolvessignaling,andthedatasynchronizationaspectsoftransmissionovertheairinterface.TextWordsNotesDiscussionHomeInGSM-basednetworks,theRANtypicallyconsistsofBTSsandBaseStationControllers(BSCs).UsersessionsareconnectedfromamobilestationtoaBTS,whichconnectstoaBSC.ThecombinedfunctionsoftheBTSandBSCarereferredtoastheBaseStationSubsystem(BSS)[4].TextWordsNotesDiscussionHome(5)HomeLocationRegister(HLR)TheHLRisadatabasethatcontainsinformationaboutsubscriberstoamobilenetworkthatismaintainedbyaparticularserviceprovider.Inaddition,forsubscribersofaroamingpartner,theHLRmightcontaintheserviceprofilesofvisitingsubscribers.TextWordsNotesDiscussionHomeTheMSCusesthesubscriberinformationsuppliedbytheHLRtoauthenticateandregisterthesubscriber.TheHLRstores“permanent”subscriberinformation(ratherthantemporarysubscriberdata,whichaVLRmanages),includingtheserviceprofile,locationinformation,andactivitystatusofthemobileuser.TextWordsNotesDiscussionHome(6)VisitorLocationRegister(VLR)TheVLRisadatabasethatismaintainedbyanMSC,tostoretemporaryinformationaboutsubscriberswhoroamintothecoverageareaofthatMSC.TheVLR,whichisusuallypartofanMSC,communicateswiththeHLRoftheroamingsubscribertorequestdata,andtomaintaininformationaboutthesubscriber’scurrentlocationinthenetwork.TextWordsNotesDiscussionHome(7)AuthenticationCenter(AC)TheACprovideshandsetauthenticationandencryptionservicesforaserviceprovider.Inmostwirelessnetworkstoday,theACiscollocatedwiththeHLR,andisoftenimplementedaspartoftheHLRcomplex.TextWordsNotesDiscussionHome3.ModelforIPIntegrationintoMobileWirelessThestandardsfortheintegrationofIPdatanetworkingwiththeexistingtelecommunicationsinfrastructurearerapidlydevelopingandbeginningtoberealizedintoday’sproductionnetworks.TextWordsNotesDiscussionHomeFigure1 IPIntegrationPhasesinMobileWirelessTextWordsNotesDiscussionHomeFigure1showsamodelforIPintegrationbaseduponthecurrentindustrydirectionandreflectssomeofthelatestideaswithintheMobileWirelessInternetForum(MWIF).TheMWIFisapre-standardsconsortiumforserviceprovidersandsupplierstocollaborateontheimplementationofIP-basedmobilewirelessnetworks.TheMWIFinfluencesthestandardsbodiessuchas3GPPand3GPP2tosuccessfullyadoptnewimplementations.Inparticular,Figure1showswhereCiscoSystems’GGSNproductforGSMnetworksfitsintothemodel.TextWordsNotesDiscussionHomeThetoptwoquadrantsinFigure1showwherewearetodayinthetelecommunicationsandIPdataservicesinfrastructures.Thefirstquadrantrepresentsthefirstphaseoftheseinfrastructuresbasedoncircuit-switchedvoiceanddataservices.ThebeginningsofacoreIPtransportforvoiceanddataintegrationcanbebuiltusingCiscoSystemsV.110solutions.TextWordsNotesDiscussionHomeThesecondquadrantdepictstheimplementationphaseof2G+technologies,suchasGPRS,supportinghighertransmissionspeeds.Inthisquadrant,theCiscoSystemsGGSNprovidesIPpacketdataservices.ItactsasanIPgatewayforaccesstotheinternetandotherpublicandprivatedatanetworksfortrafficthatisinitiatedinaGSM-basedmobileenvironment.Theservicesanticipatedinthisphaseincludeimplementingalways-ondataservicesandenablingoperatorstochargebypacketratherthanconnecttime.SimilarservicesaresupportedbyPacketDataServicesNode(PDSN),forCDMA-basedwirelessnetworks.TextWordsNotesDiscussionHomeThethirdquadrantrepresentsphasethreeoftheintegrationofIPnetworkingwherevoiceanddataareconsolidatedontoapacket-basedinfrastructurefromtheRANorradionetworkcontrol(RNC)outward.Thisisconsidereda3Gsolution.Phasethreeenablesintegratedvoiceanddataapplicationsandreducescosts.Inaddition,someofthecomponentsorfunctionsoftheMSCaredistributed.TextWordsNotesDiscussionHomeThefourthquadrantrepresentsthefinalphase,whichincludes3GservicesplustheimplementationofIP-basedradioandmobilitycomponentstodevelopatrueend-to-end,all-IPwirelessnetworksolution.TextWordsNotesDiscussionHomeconvergencen.趋同；集收敛；集合，会聚；[气]辐合infrastructuren.基础结构，基础架构；基础设施；基础建设differentiatev.区分，辨别；使不同ubiquitousadj.无所不在的，普遍存在的assimilationn.吸收，消化subscribern.用户，订户WordsWordsTextWordsNotesDiscussionHomeseamlessadj.无缝的；无漏洞的roamv.&n.漫游，漫步cellularadj.蜂窝状的；细胞的analogadj.[电]模拟的；（钟表）有长短针的implementvt.实施，执行；使生效hubn.（电器面板上的）电线插孔；[计]集线器WordsTextWordsNotesDiscussionHomeauthenticatevt.使生效；鉴别encryptionn.编密码；加密decompressvt.解压compressvt.压紧；压缩；精简synchronizationn.同步，使时间互相一致profilen.人物简介；外形，轮廓WordsTextWordsNotesDiscussionHomeconsortiumn.组合，共同体；财团quadrantn.象限仪，四分仪gatewayn.网关；入口；途径WordsTextWordsNotesDiscussionHome[1]Assuggestedbyitsname,mobilewirelesscommunicationaddressesthosewirelesstechnologiesthatsupportmobilityofasubscriber,whichprovideseamlessandreal-timeserviceswithoutinterruption.顾名思义，移动无线通信用以称呼那些支持用户流动性的无线技术，它能够提供无缝连接和不间断的实时业务。TextWordsNotesDiscussionNotesHome[2]AMPS是第一代蜂窝技术，使用单独的频带，或者说“信道”，为每次对话服务。它因此需要相当的带宽来支持一个大数量的用户群体。在通用术语中，AMPS常常被当作更早的“0G”改进型移动通信服务，只不过AMPS使用更多的计算功率来选择频谱、切换到PSTN线路的通话、以及处理登记和呼叫建立。真正将AMPS从更早的0G系统中区分出来的是最后的呼叫建立功能。在AMPS中，蜂窝中心可以根据信号强度灵活地分配信道给每个手持终端，允许相同的频率在完全不同的位置复用，并且不会有干扰。这使得在一个地区内，大数量的手持终端被同时支持成为可能。AMPS的创始者们发明了“蜂窝”这个术语正是因为它在一个系统里使用的都是小的六边形“蜂窝”形状。TextWordsNotesDiscussionHome[3]AuthenticationCenter（AUC）：称为鉴权中心，是GSM系统中的安全管理单元，存储鉴权算法和密钥，保证各种保密参数的安全性，向HLR（归属用户位置寄存器）提供鉴权参数。鉴权参数包括三组：RAND（RandomNumber，随机数），SRES（SignResponse，符号响应），Kc（CipheringKey，加密密钥）。

TextWordsNotesDiscussionHome[4]BaseStationSubsystem（BSS）：指基站子系统，是移动通信系统中与无线蜂窝网络关系最直接的基本组成部分。在整个移动网络中基站主要起中继作用。基站与基站之间采用无线信道连接，负责无线发送、接收和无线资源管理。而主基站与移动交换中心（MSC）之间常采用有线信道连接，实现移动用户之间或移动用户与固定用户之间的通信连接。TextWordsNotesDiscussionHomeQuestionsfordiscussion1.Whatarethebasicelementsofwirelesstechnologies?2.Whatcomponentsisatypicalcellulartelecommunicationsnetworkmadeupof?3.WhatisMSC?Whatdoesitserveasinthemobilewirelessnetworkinfrastructure?4.WhatisHLRandVLR?Whataretheirfunctions?TextWordsNotesDiscussionHomeAnswerstoquestionsfordiscussionTextWordsNotesDiscussionHome1.Whatarethebasicelementsofwirelesstechnologies?Spectrum,ortherangeoffrequenciesinwhichthenetworkoperatesTransmissionspeedssupportedUnderlyingtransmissionmechanism,suchasfrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA),orcodedivisionmultipleaccess(CDMA)Architecturalimplementation,suchasenterprisebased(orin-building),fixed,ormobileTextWordsNotesDiscussionHome2.Whatcomponentsisatypicalcellulartelecommunicationsnetworkmadeupof?Atypicalcellulartelecommunicationsnetworkconsistsofthefollowingcomponents:PublicSwitchedTelephoneNetwork(PSTN)MobileSwitchingCenter(MSC)BaseStation(BS)