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1延迟容忍网络及其应用DTNandItsApplication天津大学计算机科学与技术学院张钢教授gzhang@tju.edu.cn2009-7西藏民族学院新技术讲座2RelatedConcept相关概念•互联网Internet•无线局域网WLAN(WirelessLAN)•无线自组织网络MANET(mobileadhocnetwork)•延迟容忍网络DTN(delaytolerantnetwork)•机会网络Oppnets(OpportunisticNetworks)3SomeNetworks几种网络•FundamentallydifferentwayoflookingatnetworksInternetWiredLANWirelessLANCelltowerInfrastructure=Celltower,LAN,Accesspoint4Internet互联网5Internet互联网•TheusabilityoftheInternetdependsonsomeimportantassumptions几个重要假设–Continuous,bidirectionalend-to-endpath连续、双向端到端通路–Shortround-trips往返时间短–Symmetricdatarates对称数据传输率–Lowerrorrates低错误率6SomeSpecialCases互联网中的特殊情况•Intermittentconnectivity间歇连接•Longorvariabledelay长延迟/不定延迟•Asymmetricdatarates非对称数据传输率•Higherrorrates高出错率•如果互联网出现这些特殊情况会怎样？78WirelessLANorWLAN无线局域网9MANET无线自组织网络MobileAdhocNetworking(MANET)10MANET无线自组织网络•MobileAdhocNetworking(MANET)–Rapidlydeployable,selfconfiguring快速部署，自配置–Noneedforexistinginfrastructure不需要基础设施–Wirelesslinks无线链路–Nodesaremobile,topologycanbeverydynamic结点移动、拓扑动态–Nodesmustbeabletorelaytrafficsincecommunicatingnodesmightbeoutofrange结点必须能转发消息–AMANETcanbeastandalonenetworkoritcanbeconnectedtoexternalnetworks(Internet)可以是独立的网络/可以连接到外部网络11MANET无线自组织网络•MobileAdhocNetworking(MANET)–Tosupportrobustandefficientoperationinmobilewirelessnetworksbyincorporatingroutingfunctionalityintomobilenodes路由功能合并到每个移动节点中–Suchnetworksareenvisionedtohavedynamic,sometimesrapidly-changing,random,multihoptopologieswhicharelikelycomposedbyrelativelybandwidth-constrainedwirelesslinks带宽受限的无线链路12MANET无线自组织网络•Goal目标–toextendmobilityintotherealmofautonomous,mobile,wirelessdomains,whereasetofnodes–whichmaybecombinedroutersandhosts–themselvesformthenetworkroutinginfrastructureinanadhocfashion把移动性扩展到自治、移动、无线领域13MANET无线自组织网络•Characteristics特点–Dynamictopologies动态拓扑–Bandwidth-constrainedvariablecapacitylinks带宽受限–Energy-constrainedoperations能量受限–Limitedphysicalsecurity物理安全有限–Theneedforscalability可扩展14MANET无线自组织网络•MANET要求–任一节点对之间存在至少一条完整的端到端通信路径•可能导致网络不能连通问题–节点移动–节点稀疏–射频关闭–障碍物obstruction15DTN延迟容忍网络•Disruption/Delay-TolerantNetworking(DTN)介绍•最初是为星际网络IPN(interplanetarynetwork)通信提出来的•其主要目标是支持具有间歇性连通、延迟大、错误率高的不同网络的互联和互操作–如互联Internet和传感器网络、移动自组织网络等16InterPlanetaryInternet星际网络161718192021AnInterplanetaryInternetExample22WhatDoesIPDo?•End-to-Endprotocolsfailandclosetheconnectionduringextendeddisruptions在长时间的中断期间，端到端协议失败并关闭链接•Theydonothandledisruptiongracefully23WhatIsDTN?–ConnectsHop-by-Hop,NotEnd-to-End（点到点）–ForwardsOverOutgoingLinks（流出链路）Opportunistically–HoldsDatainPersistentStorage（持久存储器）WhenOutgoingLinksareDown•NetworkProtocolsthatProvideReliableMessageDeliveryacrossintermittent/disrupted/dynamicnetworks提供跨越间歇/中断/动态网络的可靠消息传递的网络协议24DTN延迟容忍网络•DTN网络体系由多个底层运行独立通信协议的DTN域组成•域间网关利用“存储-转发”的模式工作–如果去往目标DTN域的链路存在，则转发消息–否则,将消息存储在本地持久存储器中等待可用链路25TheBundleLayer–BundledData&ControlMinimizeNetworkTraversals捆绑的数据和控制使网络往返移动最小化•AvoidsProtocolChattiness–MinimalDependenceonRemoteInformation最小依赖于远程信息26TheBundleLayer27TheBundleLayer保管者保管者28Step1:BundleCreationatSource29Step2:TransmissionbySource30Step3:First-HopBundleProcessingandForwarding31Step4:Second-HopBundleProcessingandForwarding32Step5:BundleReceptionbyDestination33OpportunisticNetworks机会网络•Inopportunisticnetworkingnoassumptionismadewithregardtotheexistenceofacompletepathbetweentwonodeswishingtocommunicate.在机会网络中并不假设在希望通信的两个结点之间存在完整的通路•Nevertheless,opportunisticnetworkingtechniquesallowsuchnodestoexchangemessagesbetweenthem.然而，机会网络技术允许这样的结点之间交换信息34OpportunisticNetworks机会网络•DifferentlyfromDTNs,inopportunisticnetworkseachsinglenodeactsasagateway.与DTN网络不同的是，在机会网络中每个结点都是网关35OpportunisticNetworks机会网络•Anetworkconnectionbetweenthetwowomenneverexistsbut,byopportunisticallyexploitingcontactsamongheterogeneousdevices,themessageisdeliveredhop-by-hopclosertothedestination,andeventuallytothedestinationitself.36OpportunisticNetworks机会网络•Anoppnetgrowsfromitsseed—theoriginalsetofnodesemployedtogetheratthetimeoftheinitialoppnetdeployment.•Theseedgrowsintoalargernetworkbyextendinginvitationstojointheoppnettoforeigndevices,nodeclusters,ornetworksthatitisabletocontact.37OpportunisticNetworks机会网络•Themainfocusofresearchonopportunisticnetworkshasbeenonroutingandforwardingissues路由和向前推进问题•Becausefindingroutestowardsthedesireddestinationinsuchdisconnectedenvironmentsisregardedasthemostcompellingissue.最引人注目的问题38OpportunisticNetworks机会网络•机会网络可以看成是具有一般DTN网络特征的无线自组网•方法1：源节点必须缓存数据直到进入目标节点通信范围内才允许传输数据39OpportunisticNetworks机会网络•方法2：源节点将消息传输给邻居中继节点,该节点缓存消息再将消息转发给目标节点或遇到的其他中继节点40OpportunisticNetworks机会网络41OpportunisticNetworks机会网络42WhynotdeployInfrastructure?为什么不部署基础设施？•Infrastructureexpensivetodeploy•ProvidingInternetconnectivitytodevelopingregionsKioskNetinWaterloo,DigitalGangeticProjectinIndia43DTN/OppnetApplicationsDTN/机会网络应用•Inter-PlanetaryNetwork(IPN)星际网络–Terrestrialandinterplanetarylinks.LONGdelaysandepisodicconnectivity陆地和星际链路，长延迟和断续连通性•ZebraNet斑马网络–Collectsinformationaboutdispersedzebrapopulations收集分散的斑马数量信息4344DTN/OppnetApplicationsDTN/机会网络应用•DataMules数据骡子–Randomlymoveandcollectdatafromlow-powersensors随意移动并从低能量传感器收集数据•VillageNetworks