组播与QOS详解.ppt

,湖南电信组播理论培训,湖南创发科技有限责任公司2010年10月,为何使用组播？,可用于发送数据给多个接收者带宽的有效利用减少主机或者路由器的系统资源消耗可用于接收者地址不可知情况可用于一组接收者针对同一数据传输的请求需求,单播vs组播,Multicast优点,提高效率:控制网络通信并且降低服务器的CPU负担优化性能:减少不必要的冗余通信分布式应用:使多点应用成为可能,Multicast缺点,组播基于UDP协议：尽力传输模式:传输丢包是可以预料到的.因为组播应用程序处理数据采用非可靠性传输.没有拥塞回避功能:TCP协议中的滑动窗口机制可以控制网络拥塞.如果有此功能，组播程序便可以检测和避免拥塞.复制功能:一些组播协议架构需要能够支持复制数据包功能，以备不时之需.如果组播程序支持此功能便可实现数据包的复制.队列传输:网络拓扑的改变影响队列传输组播应用程序需要能解决此问题,组播应用程序的类型,点到多模式:单个主机发送数据给多个接收者多到多模式:一组主机发送数据给同一个组播组的成员多到点模式:一批接收者发送返回数据给源(通过单播或组播方式),CorporateBroadcasts,DistanceLearning,Training,Videoconferencing,Whiteboard/Collaboration,MulticastFileTransferDataandFileReplication,Real-TimeDataDeliveryFinancial,Video-on-Demand,LiveTVandRadioBroadcasttotheDesktop,IP组播应用程序,IP组播地址范围,IP组播地址:ClassDaddressRangefromthrough55IANA分配的公有组播地址：Reserveduse:through55(allmulticastsystemsonsubnet)(allroutersonsubnet)(allDVMRProuters)3(allPIMv2routers),,,and0usedbyunicastroutingprotocols,Layer2组播地址,IPMulticastMACAddressMappingEthernet,IGMPv2协议,RFC2236组播查询报文在转发组播数据到subnet子网时，路由器先发送组播查询包用于确认是否有组播成员在该子网中.离开组播消息报文如果主机需要离开所在组播组，它就发送离开报文.,IGMPv2JoiningaGroup,IGMPv2LeavingaGroup,H2发送离开报文.,Router发送组播查询报文.,其他组播成员发送report,所以组播数据传输仍然处于actvie.,Layer2组播帧的Switching解决方法,CiscoGroupManagementProtocol(CGMP):简单,私有;路由器和交换机支持IGMPsnooping:复杂,公共标准;仅交换机支持,Layer2组播帧的SwitchingCGMP,解决方法1:CGMP在交换机和路由器上运行.路由器发送CGMP报文到交换机，使用CGMPmulticastMACaddress0100.0cdd.ddddCGMP报文包含:Typefield:加入或者离开IGMP客户端的MAC地址组播的MAC地址交换机实用CGMP报文中的信息针对特有的组播MAC地址进行添加或者移除进入.,Layer2组播帧的SwitchingIGMPSnooping,解决方法2:IGMPsnooping交换机变成了IGMP的知情者.IGMP报文被CPU或者专用的硬件ASIC所拦截.交换机通过检查IGMP报文中的信息来确定哪个交换端口需要组播数据:IGMPmembershipreportsIGMPleavemessages在交换机上的影响:必须检查所有二层组播数据帧组播数据的传输负载使得管理负担加重需要额外的硬件来维护吞吐量,MulticastProtocolBasics,组播分布树结构的类型基于根的源树;也叫做最短路径树(SPTs)根处于网络中的一个汇聚点;共享树Rendezvouspoint(RP)Core组播协议的类型紧密模式松散模式,Shortest-PathTrees,Shortest-PathorSourceDistributionTree,Shortest-PathTrees(Cont.),Shortest-PathorSourceDistributionTree,SharedDistributionTrees,SharedDistributionTree,SharedDistributionTrees(Cont.),SharedDistributionTree,组播分布树的识别,(S,G)entries从指定的源发送数据到组播组组播数据转发通过最短路径的形式从源出发(*,G)entries(*)任何组播源发送数据到组播组组播数据都经由汇聚点RP来进行发送到组播组,组播转发,组播路由与单播路由是相对的.单播路由关注的是数据包要去哪里.组播路由关注的是数据包来自哪里.组播路由使用逆向路径转发检测来阻止发生转发环路.,PIM-DM（紧密模式）泛洪与修剪,InitialFlooding,PIM-DM（紧密模式）泛洪与修剪(Cont.),PIM-DM（紧密模式）泛洪与修剪(Cont.),ResultsAfterPruning,PIMSparseMode（松散模式）,协议独立:可在任何单播路由协议下运行同时支持基于源树和共享树基于显式加入模式使用一个RP（汇聚点）Sendersandreceivers“meeteachother.”SendersareregisteredwithRPbytheirfirst-hoprouter.Receiversarejoinedtothesharedtree(rootedattheRP)bytheirlocalDR.,PIM-SM共享树的加入,多个RPs方式,SharedDistributionTree,网络质量问题-需要QOS,带宽不够:多种数据流竞争有限带宽资源.端到端时延:数据包必须穿越许多网络设备和链路，整个过程增加了总时延.抖动时延:有时候大量数据传输,导致时延增加.数据包丢失:当链路发生拥塞，数据包不得不被丢弃.,Classification（分类）,基于以下几个方式对数据流进行分类:IncominginterfaceIPprecedenceDSCPSourceordestinationaddressApplication分类是所有基本QOS的程序块.没有分类,所有数据包将同等对待处理.,Marking（标记）,标记是QOS的特性组成部分，针对数据包进行“着色”处理以便能够使数据流与其他数据流区分开来进行不同处理对待.通常的标记方式:链路层:CoS(ISL,802.1p)MPLSEXPbitsFrameRelay网络层:DSCPIPprecedence,ClassificationandMarkingintheLANwithIEEE802.1Q,IEEE802.1p使用的优先级字段叫做CoS.IEEE802.1p支持8个CoS位.IEEE802.1p用于链路直连LAN上，不支持端到端.,ClassificationandMarkingintheEnterprise,DiffServModel,Describesservicesassociatedwithtrafficclasses.Complextrafficclassificationandconditioningisperformedatthenetworkedge,resultinginaper-packetDSCP.Noper-flowstateinthecore.ThecoreonlyperformssimplePHBsontrafficaggregates.ThegoaloftheDiffServmodelisscalability.Widevarietyofservicesandprovisioningpolicies.Decoupleserviceandapplicationinuse.Noapplicationmodification.Nohop-by-hopsignaling.Interoperabilitywithnon-DiffServ-compliantnodes.Incrementaldeployment.,IPPrecedenceandDSCPCompatibility,CompatibilitywithcurrentIPprecedenceusage(RFC1812)Differentiatesprobabilityoftimelyforwarding:(xyz000)=(abc000)ifxyzabc(thatis,ifapackethasDSCPvalueof011000,ithasagreaterprobabilityoftimelyforwardingthanapacketwithDSCPvalueof001000),Per-HopBehaviors,DSCPselectsPHBthroughoutthenetwork:DefaultPHB(FIFO,taildrop)EFPHBAFPHBClass-selectorPHB(IPprecedence),EFPHB,EFPHB:EnsuresaminimumdeparturerateGuaranteesbandwidthclassguaranteedanamountofbandwidthwithprioritizedforwardingPolicesbandwidthclassnotallowedtoexceedtheguaranteedamount(excesstrafficisdropped)DSCPvalueof101110:LookslikeIPprecedence5tonon-DiffServ-compliantdevices:Bits5to7:101=5(same3bitsareusedforIPprecedence)Bits3and4:11=NodropprobabilityBit2:Just0,AFPHB,AFPHB:GuaranteesbandwidthAllowsaccesstoextrabandwidth,ifavailableFourstandardclasses:AF1,AF2,AF3,andAF4DSCPvaluerangeofaaadd0:aaaisabinaryvalueoftheclassddisdropprobability,AFPHB(Cont.),EachAFclassusesthreeDSCPvalues.EachAFclassisindependentlyforwardedwithitsguaranteedbandwidth.Congestionavoidanceisusedwithineachclasstopreventcongestionwithintheclass.,AFPHB(Cont.),EachAFclassusesthreeDSCPvalues.EachAFclassisindependentlyforwardedwithitsguaranteedbandwidth.Congestionavoidanceisusedwithineachclasstopreventcongestionwithintheclass.,DSCPSummary,MappingCoStoNetworkLayerQoS,QoSServiceClass,AQoSserviceclassisalogicalgroupingofpacketsthataretoreceiveasimilarlevelofappliedquality.AQoSserviceclasscanbe:Asingleuser(suchas,MACaddressorIPaddress)Adepartment,customer(suchas,subnetorinterface)Anapplication(suchas,portnumbersorURL)Anetworkdestination(suchas,tunnelinterfaceorVPN),Example:DefiningQoSServiceClass,Remaining15percentisusedformanagement,signaling,androutingtraffic.,ImplementingQoSPolicyUsingaQoSServiceClass,Example:ApplicationServiceClasses,QueuingMethodsCombined,Basicmethodsarecombinedtocreatemoreversatilequeuingmechanisms.,Class-BasedWeightedFairQueuing,CBWFQisamechanismthatisusedtoguaranteebandwidthtoclasses.CBWFQextendsthestandardWFQfunctionalitytoprovidesupportforuser-definedtrafficclasses:Classesarebasedonuser-definedmatchcriteria.Packetssatisfyingthematchcriteriaforaclassconstitutethetrafficforthatclass.Aqueueisreservedforeachclass,andtrafficbelongingtoaclassisdirectedtothatclassqueue.,CBWFQArchitecture,Classification,Classificationusesclassmaps.AvailabilityofcertainclassificationoptionsdependsontheCiscoIOSversion.Someclassificationoptionsdependontypeofinterfaceandencapsulationwhereservicepolicyisused.Forexample:MatchingonFrameRelaydiscard-eligiblebitscanbeusedonlyoninterfaceswithFrameRelayencapsulation.MatchingonMPLSexperimentalbitshasnoeffectifMPLSisnotenabled.MatchingonISLprioritybitshasnoeffectifISLisnotused.,Scheduling,CBWFQguaranteesbandwidthaccordingtoweightsassignedtotrafficclasses.Weightsareinternallycalculatedfrombandwidthoritspercentage.Bandwidthavailabilitycanbedefinedbyspecifying:Bandwidth(inkbps)Percentageofbandwidth(percentageofavailableinterfacebandwidth)PercentageofremainingavailablebandwidthOneservicepolicycannothavemixedtypesofweights.Theshowinterf