现代通信网络4课件

现代通信网络

ModernTelecommunicationNetworkLecture4PS分组交换与IP互联网电话：现代通信网络4CommunicationNetworks【通信网络的分类】CommunicationNetworkSwitched

CommunicationNetworkVirtualCircuitNetwork:MPLSBroadcast

CommunicationNetwork广播，电视，卫星PacketSwitch(PS)-分组交换DatagramNetwork:InternetCircuit-Switched(CS)-电话现代通信网络4PS:PacketSwitch

分组交换网原理现代通信网络4SimpleSwitchedNetwork现代通信网络4PacketSwitching(PS)PrinciplesCircuitswitchingdesignedforvoice

Resourcesdedicatedtoaparticularcall

Muchofthetimeadataconnectionisidle

DatarateisfixedBothendsmustoperateatthesamerate现代通信网络4PS：BasicOperation【基本操作原理】DatatransmittedinsmallpacketsTypically1000octetsLongermessagessplitintoseriesofpacketsEachpacketcontainsaportionofuserdataplussomecontrolinfoControlinfo【控制信息】

Routing(addressing)infoPacketsarereceived,storedbriefly(buffered)

andpastontothenextnode

Storeandforward现代通信网络4PS：UsingPackets现代通信网络4PS：Advantages【优点】LineefficiencySinglenodetonodelinkcanbesharedbymanypacketsovertimePacketsqueuedandtransmittedasfastaspossibleDatarateconversionEachstationconnectstothelocalnodeatitsownspeedNodesbufferdataifrequiredtoequalizeratesPacketsareacceptedevenwhennetworkisbusyDeliverymayslowdownPrioritiescanbeused现代通信网络4PS：SwitchingTechnique【交换技术】StationbreakslongmessageintopacketsPacketssentoneatatimetothenetworkPacketshandledintwowaysDatagram【数据报】VirtualCircuit【虚电路】

PVC:PermanentVirtualCircuit【永久虚电路】

SVC:SwitchVirtualCircuit【交换虚电路】现代通信网络4PS：Datagram【数据报】EachpackettreatedindependentlyPacketscantakeanypracticalroutePacketsmayarriveoutoforderPacketsmaygomissingUptoreceivertore-orderpacketsandrecoverfrommissingpackets现代通信网络4PS：DatagramApproach现代通信网络4PS：VirtualCircuit【虚电路】PreplannedrouteestablishedbeforeanypacketssentCallrequestandcallacceptpacketsestablishconnection(handshake)EachpacketcontainsavirtualcircuitidentifierinsteadofdestinationaddressNoroutingdecisionsrequiredforeachpacketClearrequesttodropcircuitNotadedicatedpath现代通信网络4SVC：SwitchVirtualCircuit–连接建立【可交换的虚电路】现代通信网络4SVC：SwitchedVirtualCircuit–数据传输【可交换的虚电路】现代通信网络4SVC：SwitchedVirtualCircuit–连接释放【可交换的虚电路】现代通信网络4VirtualCircuitsvDatagramVirtualcircuitsNetworkcanprovidesequencinganderrorcontrolPacketsareforwardedmorequicklyNoroutingdecisionstomakeLessreliableLossofanodeloosesallcircuitsthroughthatnodeDatagramNocallsetupphaseBetteriffewpacketsMoreflexibleRoutingcanbeusedtoavoidcongestedpartsofthenetwork现代通信网络4虚电路举例：FrameRelay【帧中继】DLCI(DataLinkConnectionIdentifier)-identificationofavirtualcircuit【虚电路】DLCI-oflocal(foragivenport)meaningtherecanbemax.976VCsonaninterfaceuser-networkDLCIvalues:0-LMIchannel,1-15-reserved,16-991-availableforVCs,992-1007-layer2managementofFRservice,1008-1022-reserved,1023-inchannellayermanagementABCToA:DLCI121ToB:DLCI243ToA:DLCI182ToC:DLCI121现代通信网络4TimingofDatagramPacketSwitchingPacket3Packet3Packet1Packet2Packet1Packet2Packet1Packet2Packet3processing

delayofPacket1atNode2Host1Host2Node1Node2propagationdelaybetweenHost1andNode2transmissiontimeofPacket1atHost1现代通信网络4三种交换的比较

P1P2P3P4P1P2P3P4P3P4报文报文报文ABCDABCDABCD报文交换电路交换分组交换t连接建立数据传送报文P2P1连接释放数据传送的特点比特流直达终点报文报文报文分组分组分组存储转发存储转发存储转发存储转发现代通信网络4【独享】–【共享】

虚电路概念在

TD-SCDMA网络：空间接口的应用现代通信网络43GPP-HSDPA概述为了更好地发展数据业务，3GPP对空中接口作了改进，在R5版本中引入高速下行分组接入（HSDPA）技术;HSDPA(高速下行分组接入，HighSpeedDownlinkPackagesAccess)技术，是3GPP在R5协议中为了满足上下行数据业务不对称的需求提出来的，它可以在不改变已经建设的系统网络结构的基础上，大大提高用户下行数据业务速率(理论上单载波最大值可达2.8Mbps)现代通信网络4基站侧物理资源有限，HSDPA资源不可以同时分配给R4业务使用，比如，当系统为3个上行时隙与3个下行时隙的比例配置时，其中2个下行时隙分配给HSDPA使用，则下行业务时隙就剩下1个时隙，此时如果大量用户的业务需求是普通R4业务，则系统会受限于资源而决绝新用户的接入所以当业务小区内普通R4业务较多时，可以减少或者取消HSDPA资源配置，将大部分时隙资源分配给普通R4业务使用；当业务小区内大部分用户需要使用高速下载的数据业务，则可以将大部分业务时隙分配给HSDPA使用灵活的载波配置可以满足运营商网络规划中的不同的需求

HSDPA载波配置现代通信网络4TD-SCDMA无线帧结构

现代通信网络4物理层复用与调度算法用户被调度是HSDPA业务区别于普通R4业务的一个主要特征普通R4用户会【“独享”】一部分物理资源，直到其业务被释放掉，即使此时并没有在进行数据传输，资源也是被占用的，形成了一种浪费（类似：电路交换中的实电路）而HSDPA业务，可以让多用户【共享】整个HSDPA资源，采取的方式是分时分码复用，也就是在每一个TTI内部分或者全部资源为一个用户而用，下一个TTI，资源又给另一个用户使用，这样数据需求量大的用户就可以获得较高的被调用的几率，从而获得较高速率，节省了资源。灵活的调度算法也可以满足运营商不同的需求。现代通信网络4PS应用：IP-Internet

分组交换网-IP因特网现代通信网络47.1IP互联网结构现代通信网络4InternetworkingTerms(1)CommunicationsNetworkFacilitythatprovidesdatatransferserviceThe

Internet【因特网】-noteuppercaseITheglobalcollectionofthousandsofindividualmachinesandnetworksIntranet【内联网

】CorporateinternetoperatingwithintheorganizationUsesInternet(TCP/IPandhttp)technologytodeliverdocumentsandresources现代通信网络4TelecommuterResidentialCableInternetBackbonexDSL,FTTH,DialAggregationISP’sEnterpriseEnterpriseIP-InternetArchitectureTransportControlProtocol(TCP)InternetProtocol(IP)现代通信网络4InternetworkingTerms-2EndSystem(ES)DeviceattachedtooneofthenetworksofaninternetSupportsend-userapplicationsorservicesIntermediateSystem(IS)DeviceusedtoconnecttwonetworksPermitscommunicationbetweenendsystemsattachedtodifferentnetworks现代通信网络4InternetworkingTerms-3BridgeISusedtoconnecttwoLANsusingsimilarLANprotocolsAddressfilterpassingonpacketstotherequirednetworkonlyOSIlayer2(DataLink)RouterConnectstwo(possiblydissimilar)networksUsesinternetprotocolpresentineachrouterandendsystemOSILayer3(Network)现代通信网络4USA-InternetInfrastructure现代通信网络4InternetInfrastructureTheinfrastructureoftheInternetconsistsofafederationofconnectednetworksthatareeachindependentlymanaged(“autonomoussystem”)Note:Each“autonomoussystemmayconsistofmultipleIPnetworksAutonomoussystemshaveanumber(ASnumber)Hierarchyofnetworkserviceproviders(NSPs)Tier-1:nationorworldwidenetwork(US:lessthan20)Tier-2:regionalnetworks(inUS:lessthan100)Tier-3:localInternetserviceprovider(inUS:severalthousand)现代通信网络4InternetInfrastructure-2Locationwhereanetwork(ISP,corporatenetwork,orregionalnetwork)getsaccesstotheInternetiscalledaPoint-of-Presence(POP).

Locations(Tier-1orTier-2)networksareconnectedforthepurposeofexchangingtrafficarecalledpeeringpoints.Publicpeering:Trafficissinaspecificlocation,calledInternetexchangepoints(IXPs)Privatepeering:Twonetworksestablishadirectlinktoeachother.现代通信网络4Internetstructure:

roughlyhierarchicalatcenter:“tier-1”ISPs(e.g.,UUNet,BBN/Genuity,Sprint,AT&T),national/internationalcoveragetreateachotherasequalsTier1ISPTier1ISPTier1ISPTier-1providersinterconnect(peer)privatelyNAPTier-1providersalsointerconnectatpublicnetworkaccesspoints(NAPs)Interconnect–互联互通（不同公司，不同国家，等）

现代通信网络4【美国】Tier-1ISP:e.g.,SprintSprintUSbackbonenetworkSeattleAtlantaChicagoRoachdaleStocktonSanJoseAnaheimFortWorthOrlandoKansasCityCheyenneNewYorkPennsaukenRelayWash.DCTacomaDS3(45Mbps)OC3(155Mbps)OC12(622Mbps)OC48(2.4Gbps)…to/fromcustomerspeering

to/frombackbone….………POP:point-of-presence现代通信网络4CERNET【中国教育网-AS：4538】

徐闻长春哈尔滨乌鲁木齐拉萨西宁兰州银川呼和浩特台北沈阳南昌西安徐州武汉合肥郑州石家庄北京南宁广州福州杭州上海南京天津贵阳海口三亚湛江无锡大连太原济南烟台成都长沙重庆黄梅九江昆明青岛汕头唐山汉中宜昌珠海深圳惠州柳州百色厦门BackboneRegionalGigaPopPop桂林深圳现代通信网络4

五类线核心层业务层汇聚层接入层城域骨干网BRASMANSRDSLAM楼道交换机铜缆汇聚交换机/MSTP/RPR(可级连）CN2SRCN2骨干网ChinaNet骨干网宽带接入网核心路由器（可级连）骨干网园区交换机CPE终端城域网IP：国家骨干网-城域网：网络结构

现代通信网络47.2IP网协议的体系结构和协议地址7.2.1IP网协议的体系结构现代通信网络4IP网络:地址结构

现代通信网络4TCP/IPConcepts现代通信网络4TCP/IP地址系统现代通信网络4IPv4PacketFormat：地址格式现代通信网络4HeaderFields(20Bytes)VersionCurrently4：【IPv6：6】IPv6-seelaterInternetheaderlengthIn32bitwordsIncludingoptionsTotallengthOfdatagram,inoctetsProtocolNexthigherlayertoreceivedatafieldatdestination现代通信网络4InternetAddress：地址概念层次Internet：地址结构Internet网络1网络nIP地址网络号主机号2.编址方式

IPaddress=(netid+hostid）3.表示方法:

二进制表示、点分十进制IPaddress=

1000001001Thenetworknumberpart【netid】oftheIPaddressiscentrallyadministeredbytheInternetNetworkInformationCenter(theInterNIC)andisuniquethroughouttheInternet.现代通信网络4ClassesofInternetAddresses:【分类IP地址】现代通信网络47.2.2.互联网的协议地址

地址类型A类：0-8位网络号首字节1–126B类：10-16位网络号首字节128–191C类：110-24位网络号首字节192–223D类：1110-组播地址首字节224–239E类：11110-（保留未用）首字节240-247特殊IP地址广播地址：主机号全‘1’有限广播地址：32位全‘1’；回送地址：127.*.*.*，网络软件测试及本机进程间的通信。IP地址的实质：IP地址标识的不一定是一台主机，实质上标识的是到一个网络的一条连接。现代通信网络4Broadcastaddress现代通信网络4LimitedBroadcastAddress现代通信网络4All0Address现代通信网络4IPAddressSpace【IP地址空间问题】Originally,3ClassesA,B,CProblem【问题所在】Classestoorigid(刚性的)(Ctoosmall,Atoobig)ClassAwasoverkillwithmorethan16millionhostsClassChadtoofewhostspernetworkClassBisafairbalancebetweenthenumberofnetworksandthenumberofhostsSolution【解决方案】

Subnetting【子网】ClasslessInterdomainRouting(CIDR)：【无分类IP地址】现代通信网络43.子网的划分－SubnetclassificationAllowarbitrarycomplexityofinternetworkedLANswithinorganizationHostportionofaddresspartitionedintosubnetnumberandhostnumber【IP地址的主机地址部分划分为：子网码：主机码】现代通信网络4SubnetsandSubnetMasks【子网掩码】Insulate【隔离】overallinternetfromgrowthofnetworknumbersandroutingcomplexitySitelookstorestofinternetlikesinglenetworkEachLANassignedsubnetnumber【子网号码】LocalroutersroutewithinsubnettednetworkSubnetmask【子网掩码】indicateswhichbitsaresubnetnumberandwhicharehostnumber现代通信网络4IP地址的各字段和子网掩码

145.13.3.10两级IP地址子网号为3的网络的网络号三级IP地址主机号子网掩码net-idhost-id子网的网络地址1111111111111111

11111111000000000net-idsubnet-idhost-id145.13.145.13.33.10现代通信网络40目的网络地址子网掩码下一跳282828接口0接口1R23H1子网1：网络地址

子网掩码2830R1

的路由表（未给出默认路由器）R11R2子网2：网络地址28

子网掩码28H2380129H3子网3：网络地址

子网掩码2【例】已知互联网和路由器R1

中的路由表。主机H1向H2发送分组。试讨论R1收到H1

向H2发送的分组后查找路由表的过程。现代通信网络40目的网络地址子网掩码下一跳282828接口0接口1R2H1子网1：网络地址

子网掩码2830R11R2子网2：网络地址28

子网掩码28H23380129H3子网3：网络地址

子网掩码2主机H1

首先将本子网的子网掩码28

与【toH2】分组的

IP

地址38逐比特相“与”(AND

操作)

28AND38的计算255就是二进制的全1，因此255ANDxyz=xyz，这里只需计算最后的128AND138即可。128→10000000138→10001010逐比特AND

操作后：10000000→12828128.30.33.138128.30.33.128逐比特AND

操作

H1

的网络地址现代通信网络4路由器R1再用路由表中第2个项目的

子网掩码和38逐比特AND

操作0目的网络地址子网掩码下一跳282828接口0接口1R2R1

的路由表（未给出默认路由器）3H1子网1：网络地址

子网掩码2830R11R2子网2：网络地址28

子网掩码28H2380129H3子网3：网络地址

子网掩码228AND38=28匹配!这表明子网2就是收到的分组所要寻找的目的网络R1

收到的分组的目的IP地址：38一致!现代通信网络4

CIDP-ClasslessInter-DomainRouting

【无分类IP地址】CIDRisintroducedtoovercomethefollowingproblemsexhaustingofclassBnetworkexplosionofinternetroutingtable【路由表爆炸增长】CIDRallowsanylengthofsubRouterssummarizednetmaske.g.ChinaTelecom.canassign2classCnetworks(subnetmasklength=23)toacompanyifhehasonly300hosts=>efficientforIPaddressallocationRoutercanaggregateseveralroutestoabigroutewithlessmasklength=>reducecorerouter’sroutingtablesize现代通信网络4LookupsMustbeFast

【路由表搜索必须快】12540Gb/s200331.2510Gb/s20017.812.5Gb/s19991.94622Mb/s199740Bpackets(Mpkt/s)LineRateYearlookupmechanismmustbesimple,easytoimplementmemoryaccesstimelong-termbottleneck现代通信网络4RouteAggregationbyCIDRCIDRpermitsrouteaggregation

reducetheInternetroutingtable现代通信网络4IPAddressLookup：【IP地址搜索】

CIDRandLongestPrefixMatchingroutingtablescontain(prefix,nexthop)pairsaddressinpacketcomparedtostoredprefixes,startingatleftprefixthatmatcheslargestnumberofaddressbitsisdesiredmatchpacketforwardedtospecifiednexthop01*5110*31011*50001*010*700010*1001100*21011001*31011010*501011*701001100*410110011*810011000*1001011001*90100110*6prefixnext

hoproutingtableaddress:101100101000Problem-largeroutermayhave

100,000prefixesinitslist现代通信网络4NAT/PAT

NAT–NetworkAddressTranslation

PAT–PortAddressTranslation现代通信网络4IPPrivateAddressesNotwomachinesthatconnecttoapublicnetworkcanhavethesameIPaddressbecausepublicIPaddressesareglobalandstandardizedPrivateIPaddressesareasolutiontotheproblemoftheexhaustionofpublicIPaddresses.AddressesthatfallwithintheserangesarenotroutedontheInternetbackbone:ConnectinganetworkusingprivateaddressestotheInternetrequirestheusageofNAT现代通信网络4现代通信网络42.IP地址与物理地址ARP-TheAddressResolutionProtocolisresponsibleforconvertingthehigher-levelprotocoladdresses(IPaddresses)tophysicalnetworkaddresses.SuchasEthernetAddress(MAC)现代通信网络4ARP协议ARP的协议过程XYABARP请求IP=PA=?IP=PA=XXXIP=PA=YYYIP=PA=AAAIP=PA=BBBARP应答PA=YYY现代通信网络4C:\>arp-aInterface:06---0x2InternetAddressPhysicalAddressType2900-01-30-bd-e9-a0dynamic3200-04-96-05-47-0adynamic3300-04-96-05-47-15dynamic3400-04-96-05-34-f7dynamic3500-04-96-05-47-0edynamic3600-04-96-05-35-11dynamic3700-04-96-05-47-d6dynamic3800-04-96-05-34-ecdynamic3900-04-96-05-48-96dynamic4000-04-96-05-34-70dynamicC:\>现代通信网络4IP（internet）网络

工作原理现代通信网络4RouterandtheOSIModel现代通信网络4IPNetwork:DesignIssues【设计因素】Routing【IP路由选择】Datagramlifetime【生命周期】Fragmentationandre-assemblyErrorcontrolFlowcontrol现代通信网络4IPRouting【IP选路原理】Endsystemsandroutersmaintainroutingtables路由表IndicatenextroutertowhichdatagramshouldbesentStatic【静态：路由表】MaycontainalternativeroutesDynamic【动态：路由表】FlexibleresponsetocongestionanderrorsSourcerouting【发端路由器选路】SourcespecifiesrouteassequentiallistofrouterstobefollowedSecurityPriorityRouterecording现代通信网络4H1H2R1R5R2R3R4IP路由表设计原理

路径：H1-R1-R2-R4-H2设计需要考虑到问题(4个)：路由器（Routers）的路由表如何获取？为什么选择这条路径？假设R2与R4的连接断掉，如何通知R1？在Internet中，是否每个路由器都必须了解其它路由器的情况？现代通信网络4IP网络：

路由器（Routers）的路由表如何获取？

现代通信网络4IP路由表的建立和维护-静态配置静态配置：管理员手工配置和更新路由表适用环境：拓扑相对稳定，路由器个数较少优点：节省路由器的处理时间、存储空间以及网络带宽缺陷：对于链路故障及拓扑结构变化的响应速度慢H1H2R1R5R2R3R4现代通信网络4H1H2R1R5R2R3R4IP路由表的建立和维护–

动态配置动态配置：利用路由协议交换路由信息，并根据拓扑结构的变化动态更新路由表适用环境：路由器较多的大规模网络优点：自动适应链路故障及拓扑结构的变化缺陷：耗费路由器的处理时间、存储空间以及网络带宽现代通信网络47.3IP路由表：选路原理1、选路方式：

表驱动：每个主机和路由器都有一张路由表，指明去往某信宿应该走哪条路径。选路时，查询路由表。2、路由表格式【IPDestination:信宿】信宿地址去往信宿的路径不是主机地址，而是网络地址不是完整路径，而是(nexthop)下一跳地址目标网络1的网络号到达网络1的下一跳路由器IP目标网络2的网络号到达网络2的下一跳路由器IP………现代通信网络4网

1网

4网

3网

2目的主机所在的网络下一跳地址直接交付，接口1直接交付，接口0路由器R2

的路由表链路

4链路

3链路

2链路

1R2R3R101R2R3R1在路由表中，对每一条路由，最主要的是（目的网络地址，下一跳地址）现代通信网络4IP网络结构：AS系统设置

AS-AutonomousSystems

自治系统现代通信网络4WhatisAutonomousSystems(AS)GroupofroutersExchangeinformationCommonroutingprotocolSetofroutersandnetworksmanagedbysingleorganizationAconnectednetworkThereisatleastoneroutebetweenanypairofnodes现代通信网络4现代通信网络4InteriorRouterProtocol(IRP)PassesroutinginformationbetweenrouterswithinASMaybemorethanoneASininternetRoutingalgorithmsandtablesmaydifferbetweendifferentASIRPneedsdetailedmodel现代通信网络4ExteriorRoutingProtocol(ERP)RoutersneedsomeinfoaboutnetworksoutsidetheirASUsedexteriorrouterprotocol(ERP)ERPsupportssummaryinformationonreachability(网络可达性)现代通信网络4ApplicationofIRPandERP现代通信网络4CERNET【中国教育网-AS：4538】

徐闻长春哈尔滨乌鲁木齐拉萨西宁兰州银川呼和浩特台北沈阳南昌西安徐州武汉合肥郑州石家庄北京南宁广州福州杭州上海南京天津贵阳海口三亚湛江无锡大连太原济南烟台成都长沙重庆黄梅九江昆明青岛汕头唐山汉中宜昌珠海深圳惠州柳州百色厦门BackboneRegionalGigaPopPop桂林深圳现代通信网络4IPRoutingAlgorithms【路由算法】RoutingalgorithmsareusedtobuildandmaintaintheIProutingtableonadevice.Therearetwoprimarymethodsusedtobuildtheroutingtable:Staticrouting:Staticroutingusepreprogrammeddefinitionsrepresentingpathsthroughthenetwork.Dynamicrouting:Dynamicroutingalgorithmsallowrouterstoautomaticallydiscover(learn)andmaintainawarenessofthepathsthroughthenetwork.Thisautomaticdiscoverycanuseanumberofcurrentlyavailabledynamicroutingprotocols.现代通信网络4IP路由表原理

Dynamicrouting:【动态路由】现代通信网络4DynamicRouting【算法原理】Distancevectorrouting矢量-距离算法：以跳数（hop）作为度量值，通过交换路由表，计算出所有已知的最短路由，更新路由表。Linkstaterouting【链路状态算法】通过交换链路状态，让AS中的每个路由器都有一张该AS的网络拓扑结构图。使用Dijkstra算法求最短路径，计算该路由器到其它目的站的最短路径，然后更新路由表。现代通信网络4DistanceVectorRouting

矢量-距离算法现代通信网络4Whatis【DistanceVectorRouting]】Theprinciplebehinddistancevectorroutingissimple.Eachrouterintheinternetworkmaintainsthedistanceorcost

fromitselftoeveryknowndestination.Thisvaluerepresentstheoveralldesirabilityofthepath.Pathsassociatedwithasmallercostvaluearemoreattractivetousethanpathsassociatedwithalargervalue.Thepathrepresentedbythesmallestcostbecomesthepreferredpathtoreachthedestination.现代通信网络4WhatisDistanceVectorRoutingThisinformationismaintainedinadistancevectortable.Thetableisperiodicallyadvertisedtoeachneighboringrouter.Eachrouterprocessestheseadvertisementstodeterminethebestpathsthroughthenetwork.RIPandBGParetwopopularexamplesofdistancevectorroutingprotocols.现代通信网络4DistanceVectorRouting【矢量-距离算法】Eachrouterperiodicallysharesitsknowledgeabouttheentirenetworkwithitsneighbors.Knowledgeaboutthewholenetwork.Routingonlytoneighbors.Informationsharingatregularintervals.Basedonhopcount现代通信网络4ExampleofanInternet现代通信网络4ConceptofDistanceVectorRouting现代通信网络4DistanceVectorRoutingTable路由表Aroutercandiscovertowhichnetworksitisconnectedbyexaminingitsownlogicaladdresses现代通信网络4OriginalRoutingTableDistribution现代通信网络4UpdatingRoutingTableforRouterA现代通信网络4UpdatingRoutingTableforRouterC现代通信网络4UpdatedRoutingTables现代通信网络4UpdatingRoutingTableforRouterF1-1-4B78

1-+ONEHOP=2A2A5A782A2A2A5A1-921-555A现代通信网络4NewUpdatedRoutingTables现代通信网络4FinalRoutingTables现代通信网络4Linkstaterouting

【链路状态算法】

使用Dijkstra算法求最短路径现代通信网络4Whatis【Linkstaterouting】Thealgorithmsareusedintheprincipleofalinkstateistodeterminenetworktopology.Alinkstateisthedescriptionofaninterfaceonarouter(forexample,IPaddress,subnetmask,typeofnetwork)anditsrelationshiptoneighboringrouters.Thecollectionoftheselinkstatesformsalinkstatedatabase.Eachrouteridentifiesallotherroutingdevicesonthedirectlyconnectednetworks.Eachrouteradvertisesalistofalldirectlyconnectednetworklinksandtheassociatedcostofeachlink.Thisisperformedthroughtheexchangeoflinkstateadvertisements(LSAs)withotherroutersinthenetwork.LSAs-linkstateadvertisements现代通信网络4Usingtheseadvertisements,eachroutercreatesadatabasedetailingthecurrentnetworktopology.Thetopologydatabaseineachrouterisidentical.Eachrouterusestheinformationinthetopologydatabasetocomputethemostdesirableroutestoeachdestinationnetwork.ThisinformationisusedtoupdatetheIProutingtable.

TheSPFalgorithmisusedtoprocesstheinformationinthetopologydatabase.Itprovidesatree-representationofthenetwork.ThedevicerunningtheSPFalgorithmistherootofthetree.Theoutputofthealgorithmisthelistofshortest-pathstoeachdestinationnetwork.

TheOSPFprotocolisapopularexampleofalinkstateroutingprotocol.Whatis【Linkstaterouting】-2现代通信网络4LinkStateRoutingSendknowledgeabouttheneighborhoodonlyToallrouters(flooding：泛洪)Informationsharingwhenthereisachange.现代通信网络4ConceptofLinkStateRouting现代通信网络4PacketCostCostisaweightedvaluebasedonavarietyoffactorssuchassecuritylevels,traffic,orthestateofthelink.Costisappliedonlybyroutersandnotbyanyotherstationsonanetwork.Costisappliedasapacketleavestherouterratherthanasitenters.现代通信网络4CostsinLinkStateRouting现代通信网络4LinkStatePacket(LSP)Whenarouterfloodsthenetworkwithinformationaboutitsneighborhood,itissaidtobeadvertising.Aroutergetsitsinformationaboutitsneighborsbyperiodicallysendingthemashortgreetingpacket.现代通信网络4Flooding【泛洪】ofA’sLSP现代通信网络4FloodingofB’sLSP现代通信网络4LinkStateDatabase现代通信网络4最短路由选择算法–byE.DijkstraD(u)isthedistanceofsourcenode1toanynodeu.现代通信网络4Dijkstra’sAlgorithmDefinitionsFindshortestpathsfromgivensourcenodetoallothernodes,bydevelopingpathsinorderofincreasingpathlengthN

= setofnodesinthenetworks= sourcenodeT

= setofnodessofarincorporatedbythealgorithmw(i,j)

= linkcostfromnodeitonodejw(i,i)=0w(i,j)=

ifthetwonodesarenotdirectlyconnectedw(i,j)

0ifthetwonodesaredirectlyconnectedL(n)

=

costofleast-costpathfromnodestonodencurrentlyknownAttermination,L(n)iscostofleast-costpathfromston现代通信网络4现代通信网络4Dijkstra’sAlgorithm：分析Step5：{1,2,3,4,5,6}Node1Node2:距离D：2，直连；Node1Node3:距离D：3，经由节点：{4,5}现代通信网络4CostsinDijkstraAlgorithm现代通信网络4FourstepstodiscovertheshortestpathtreeThealgorithmbeginstobuildthetreebyidentifyingitsroot.Nodesandarcsaretemporary.Thealgorithmcomparesthetree’stemporaryarcsandidentifiesthearc(弧)withthelowestcumulativecost.Thealgorithmexaminesthedatabaseandidentifieseverynodethatcanbereachedfromitschosennode.Thelasttwostepsarerepeateduntileverynodeinthenetworkhasbecomeapermanentpartofthetree.现代通信网络4ShortestPathCalculation现代通信网络4ShortestPathCalculation现代通信网络4ShortestPathCalculation现代通信网络4ShortestPathCalculation现代通信网络4ShortestPathCalculation现代通信网络4ShortestPathCalculation现代通