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1、附录一：英文技术资料翻译英文原文ROUTINGANDSWITCHING1. LOCALAREANETWORKS(LANS)OrRftnizntionsoftenneednetworkstoconnectRfiogrnphicnllycloseresources,suchasPCslocatedinthesamecollegeclassroomorbusinessoffice.SuchnetworksareknownaslocalareanetworksorLANs.MostLANsareoftheclient-serverorpeer-to-peervariety.Themostwidespr
2、eadtopologyforLANsdesignedtofunctionasdatacommunicationfortheinterconnectionofIocnlComputeabasedequipmentisstartopology,inwhichthemajorequipmentusedtoconnectavarietyofcomputer-baseddevicesarehubsorswitches.TypicnlI-ANproductofusingthestarloj)ologyisthemostfamousEthernetwhichdominatestheLANworldtoday
3、.EthernetIEIiEH02.3supportsnLANstandardoriginallydevelopedbyXeroxandlaterextendedbyajointventurebetweenDigitalEquipmentCmporntion5IntelCorporation,IntelCorporationandXerox.ThiswascnlledEthernet.2. SwitchSwitchesnrebasicallymulti-portbridges,butsharesomecharacteristicswithrouters.Likerouters,switches
4、workbydividingupthenetworkintoanumberofsegments.Switchingisperformedntlayer2ofthesever-layermodel-thesameasbridging.Sinceitperformedatlayer2,theMACnddressisused,whichisindependentofprotocolnddress.Likeahridge,nswitchIearnswhichnddressresideoneachofitsportsandthenswitchesdataappropriately.Aswitchcanb
5、edesignedusingConventionnlmicroprocessorsordedicatedASIC(Application-SpecificIntegratedCircuit)technology.3. RouterRoutershnvebeenknownbySevernInames.BackinancienttimpswhenwhatisnowInternetwascalledARPANET,routerswerecalledIMPs,forinternetmessageprocessorsMorerecently,routercalledgntownystremnantsof
6、thisnomenclaturesti11befoundintermssuchasBorderGatewayProtocoI(BGP)andInteriorGatewayRoutingProtocol(K;RP).IntheOpenSystemInterconnection(OSI)world,routersareknownasIntermediateSystem(IS).Router,asaname,isprobablythemostdescriptiveofwhatthemodernversionofthesedevicesdo.Aroutersendsinformationalongar
7、oute-apath-betweentwonetworks.Thispathmaytraverseasinglerouterormanyrouters.Furthermore,ininter-networksthathnvemultiplebestroute.Shouldthntroutebecomelessthnnoptimalorentirelyunusable,therouterselectsthenext-bestpath.Theproceduresusedbytheroutertodeterminenndselectthebestrouteandtoshareinformationa
8、boutnetworkreachabilityandstatuswithotherroutersarereferredtocollectivelyasaroutingprotocol.Justasadntfilinkmaydirectlyconnecttwodevices,arouteralsocleatsaconnectionbetweentwodevices.Thedifferenceisthat,asFig.shows,whereasthecommunicationpathbetweentwodevicesShnrinRncommondntnlinkisaphysicalpath,the
9、communicationpathprovidedbyroutersbetweentwodevicesondifferentnetworkisahigher-level,logicalpath.Thisconceptisvitallyimportantunderstandingaroutersfunction.Noticethatthelogicpath,orroute,betweenthedevicesinFig.4-6traversestypesofdatalinks:anEthernet,nnH)l)lring,aseriallink,anda Token Ring, physicnl
10、path of a data finmft, a sort of digital the logical path of encnpsulnted; the digitnlAsnotedearlier,tobedeliveredonthelink,datamustheencapsulatedwithinaenvelope.Likewise,tobedeliveredacrossarouted-inter-network,datamustalsoenvelopebeusedbyroutersispacket.4. ThreeroutingtechnologyExchnnRenetworkrout
11、ingtechnology,therenrethree,thefirstofwhichisthemostconservativeapproach,themethodofcombiningofthothirdInyerrouterswithliyer2switches,layer2switchesstrictrestrictionsonthebridgestructuretordataexchangebetweendifferentnodeswithinthesamevirtualnetwork,virtualLANfeaturesinthesecondlayeroftheOSIreferenc
12、emodel,thedatalinklayer,thethirdlayerfunctionlefttotheroutertoachievedatatransferhotwftenthevirtunlnetworkconnectionwiththeestablishmentofiJNnndCorporntehnckbonorouter.Thesecondmethodusesadistributedroutingtechnology.ItsChnrncteristiesisthntitusesmulti-layerswitch,combinedwithasecondlayerofthebridge
13、withthethirdlayerroutingsomeliteraturealsocalledmulti-layerswitchtothethirdlayerswitch.IthasroutingcapabilitiestosupportvirtunlLANs,andsupportsmostofthesamevirtualnetworkorvirtualnetworknodecommunicatiotnndreducethenumberofroutersbetweenworkgroupsnnddepartments.Butitissti11notcompletelyfreefromtheus
14、eoftraditionalrouters,thisisbecausethemulti-layerswitchescanonlyprovidehigh-endroutercanprovidetheprotocol,security,trafficmanagementandWANconnectivity,asubsetof.CISCO1s7000seriesrouterscanhandle12kindsofagreementsandsupportspoint-to-point,circuitswitchingandcelIswitching,widenrennetwork,thetheAlant
15、ccproductionPowerhubmultilayerswitchcanonlyhandlethreeprotocols:DECnet,IPandIPX,andThereisnoWANinterface.Therefore,themultilayerswitchnetworkneedtousetherouterasthogntewnyoftheWAN.andtocreatemorecomplexroutingfunctions.Thethirdintheswitchingnetworkroutingtechnologywithanewstructure:thpcombinationofr
16、outingserverandtheboundaryswitch.Weknowthatatraditionalrouterpacketforwardingandroutingthetwotasks.Routingserver-basednetworksfromtwoseparatedevicesofthpsetwofunctions:theboundaryswitchtocompletethepacketforwarding,routinginformationisidentifiedbythemoreexpensiveroutingserver.Boundaryswitchonlytonot
17、findtheaddressofthedestinntionnodfiwhentheaccessrouteserverintheaddresstable,therouterontheresponsetoacorrectaddress,theswitchandthenthncachestnndby.Shouldbenotfidthatthecommunicationprotocolbetweentheroutingserverandtheswitchisnotuniform,notcompatiblewithproductsfromdifferentmanufacturers.5. Compar
18、isonandEvaluationHavetheirowncharacteristicsofthethreeroutingtechnology,networkdesigncanbeselectedaccordingtotheactualsituation.Tomakethemabelterunderstandingofthefollowingfourtocomparethem.1 1)networksizeThesizeofthenetworkisthedecisivefactorinthechoiceofroutingtechnologynetwork.Thesecondlayerswitc
19、hesandroutercombinationofapproachesforsmallernetworks,whichischaracterizedbyeconomicandpractical.Butwhenthebackboneisextendedintoalargernetwork,theoverheadofthesecondlayerofthevirtualLANwillbesignificantlyincreased.Withtheexpansionofthebackbone,intelligentmultilayerswitchadvantagesintofullplay,itiso
20、nlyforwardedtothosewhobelongtoaparticularsubnetsegmentbroadcasting,thusreducingthenumberofbackbonebroadcasttraffic.Virtualnetworkofmulti-layerswitchwithfilteringcapabilities,andcansavethebandwidthofthebackboneandthesidesiteoftheclock,virtualnetworksecurityisbetter.Inaddition,itiscomparedwiththefirst
21、method,theswitchcanworkwithinthescopeoftheworkgroupanddepartmentisalsoresponsibleforswitchingandroutingselecteddiameter,thereforesavingthenumberoftraditionalroutersuse.Distributedroutermethodandroutingserverisalsomoreapplicabletolarge-scaledistributednetwork.2 DelayTheincreaseinnetworkdelaywillleadt
22、oadeclineinnetworkperformance,thesizeofthenetworkdelayisgenerallyproportionaltothesizeandoperatingequipmentmustbeaddressedbeforeforwardingtraffic.IntermsofIhesecondlayeroftheEthernetswitch,usethebridgeduetothenatureofthesecondlayerofvirtualnetworkwithoutusingarouter,sotherelativespeed,whentoperforma
23、simpleMACaddresstofindaninformationpacket(64bytes)delayoflessthan100microseconds.Theuseoflayer3routerheadandthesubjectoflookingforandtheimplementationofthealgorithm,thusgreatlyincreasingthepacketdelay,thedelaytimeofupto5ms.Visible,whentheflowoftrafficthroughtherouterfromaswitchtoanotherswitchforLaye
24、r2switchesandlayer3routers,combinedwithanetworkhasaverygoodperformancewhenthetrafficthroughtheswitch;poorperformance.AlmostalltheLayer2switchesandsoftwareusedinconjunctionwithallthenodestoformavirtualnetwork(broadcastdomain),andimprovenetworkperformance.Exchangebetweennodeswithinthesamevirtualnetwor
25、ktrafficattheMAClayerdelaysmaller.Nodestoexchangeinformationbetweenthedifferentvirtualnetwork,thepacketspasstogothroughtherouter,thenthenetworklatency.DistributionofroutingtechnologyallowstheswitchtothevirtualgatewayofthesubnetIDofthethirdlayerprotocoltotransmitinformationtobeabletoovercomethebottle
26、neckformedbytheaboverouter.Boundaryswitchroutingservermethodtousetomakethechoiceofthepath.Occasionallyintheboundaryswitchesdonotknowtosendthedestinationaddresstotheroutingserveraskingforinformationpacketstoappearroutingdelay.Undernormalcircumstances,theswitchescanbedirectlyinthecacheaddresstabletofi
27、ndtheaddress,thenpacketscanbeforwardeddirectlydelayinthiscasethedelayisbasicallythesamewithMAClayerswitches.3ManagementTheroutinginformationstoredateachrouterinthenetwork,eachprotocolhasacorrespondingtablecolumn.Networkmanagementpersonnelmustbeindividuallyconfiguredontherouter,includingthesettingsof
28、thefilter,add,modifyroutingtable.Combinedwithman-machineinterfaceistext-basedinterface,whentheenterprisenetworkisextendedtolarge-scale,managementandconfigurationoftherouterisverytimeconsuming.Distributedroutingtechnology,thedownsideisitsmanagementoverheadandrouting,andincreasethenumberofswitchingtab
29、leexponentialincreasetrend.Toovercomethisshortcoming,theproductionbusinesseswilladoptthefollowingmeasures:thedevelopmentoftrafficcontrolstrategiesinthecenterconsole,andautomaticallypropagatedthroughthenetwork,thusavoidingonebyoneconfigurationforeachdevice,andincreasethegraphicalmanmachineinterface.T
30、hecharacteristicsoftheroutingserveriseasytoadminister,justaroutingserverconfigurationcanprovidehighqualityservicesandmanagementofvirtualnetwork.ManagementproceduressuchasCabletroncompanySecurefastallowsadministratorstotakeadvantageofthescreen,assignaccessprivilegestodifferentgroupsofusersaccessright
31、sthroughtheimplementationofthesoftwarewillnotifyalloftheswitches.Anotheradvantageoftheroutingservermethodallowsadministratorstotransparentlydeveloptrafficmanagementstrategies,donotcareaboutthetypeoftheusersendstation.Forexample,networkmanagementPerSOnnIwillbetooontheswitchnodeandATMserverisassignedt
32、oavirtuallocalareanetwork,withouthavingtoentertheEthernetnodesMACorIPaddressdonothavetoentertheATMnodetheVPI/VCI.4PriceThepriceisanothermajorfactortoconsiderpeoplenetworking.Followingtheauthorgivestheproductionofseveralcompanies50,250,500portthreeroutingproductsperportpricecomparison(seeTable1-2).Th
33、epriceofeachportistoremovetheportnumberofthetotalpriceoftheresultsofnetworkequipment,networkdevicesincludingEthernetswitches,ATMswitches,routingserverandrouter.RoutingservernetworkingNewbridgeonlycompanygiventheprice,theaveragepriceofits50250.500-portdevicesperportfor1920J520and1435U.S.dollars.Canbe
34、seenfromthedatagivenabove,thecheapestprice-basedLayer2switchingnetworkwiththerouterthewaytheprogram,distributedroutingnetworkprice,whilethemoderatepriceofnetworkroutingserverapproach.Fromwhichwecanfind,theuseofLayer2switchesandlayer3routernetwork,withtheexpansionofthenetworksize,theaveragepriceforea
35、chportgettingsmallerandsmaller,similarroutingservernetworking.Distributedrouternetworkingper-portpriceofthenetworksizehaslittleeffect.路由与交换技术1 .腐域网技术叭位通常把位酋卜.比兹近的资源，如放在学院的教4中成企仆的办公中中的PC连在一fc前构成M格.这荧网络tt被称网(LAN).尺名数W城网煨箕户-服务S成对竦方式.胫广的、nrr本地计销机设备4连，以进行数职通怕的R域网沁扑圮叩咿结构.在这神结构中以果线器成义换机作力主典的联网没济.改极各神ir浑机没格
36、*使川这种拓扑络构的W域M的典型产品足著名的以太先也它作全世界域网中Pi统泊地位，以人网IEEERo2.3克由施乐公nhP来由数据没备公川、英特尔扣施乐公灼联介开发的W城网标批，被称力以人网2 .交换机交换机雄木上足多瑙口M桥.莱芭路由热的特性.像路由SWW.交换机足把M格分成很名的本地、卜务郁不公对儿他网K产1:优.交换技木甩在七仗躲彻的论上实现的一5M桥技术相W为它作弟二足上实现.典使用MAf地址.b协议地址无关保M桥一作，交换机记常驻作每个优口的邓芝地址*并且对数你近行相应的交换文换*4以使用常规的微处埠器戌专用ASIC技术进行设计3 .略由器赂山器己抒介几个乞卞了.回到过去称为ARPA
37、NET的那个时代，路山28称为4:联网很文处理机(IMP),ft近路由SX被称为网关：这个术珞的痕进仍可在边界网关协议(BGP)和内部M关路由协议(TfiRP)中兑判作开放武系统互联领域被称力中阀系统.赂山器圾能农达设ft的功能，路山器沿两个网络之问的路山一路择代送伯息.这条路择可以经过一个路由成成行史多个路由器.if;作有很多条路松指K4),一H的地的互状M中，现代路山器叶mw并去决定并使用描件路彳h如果这一路“不ffl圮报件或宪仝不ffl,赂由器会选择K一条最伴路由路由器使用的，用丁确定和选择帝伴路择，并与其他路由器共络可达性和状态W息的ft!序.称为路由选择协议，正如数袱链路可以议技连接
38、两个设济一柞，路ihS也在两个设备之间it立一个迂技，不同的足，如果共阜一系公共数袱琏路的两个没ft之如通W路碎义一条物性路肉由路rtiWW供作小W的M格上的两个没齐之阀的通伯路碎纪逻W路碎，一个以人网，一个FDDl环网，一个申行tt路和一个令牌网，to前所说，数据在数据略1:传送，必须舛装faR一个M*I楼,数据要在通过路由的、符网讲逻辑路役上传送，也必须W装，路山器使m数t封装堪分汛4 .三种路由技术3lW交换M络中的路由技术打三神，其中第一种为保守的方法.即第一层的路由器与访二戊交换机相钻介的方法讯二Ci交换仇严格构，一廉拟网内的不同作点之叫的数抛义换.在OSl衫C揆型的第JiJ.即数榭
39、链路文现虚拟LAN的功能.将第的功能ffl纷路由器尖现.由路由器究成虚拟网格之阀的数裾传输AjaALAN4企业主千网连接的工作访.神方法采用分布式路由技术.次特点圮它使用多y交换机.将耸二足的桥4第的WiiIfXf?在一*起，介的文献也将交换机称之力第三C!交换HL它本4所具叙的路山功能支持虚拟LAN,并支恃人多数冏一虚拟网内成不闷虚拟网之问节点的通侑，减少了1作组4部门之叫所使用的路由器的数H.但它仍然个H全摆脱使叫传统路由.这足W为客位交换机n能提供岛朽路山器所能提供的协议、安今、交通矜理及与*AN途技功能的T集.如CISCO公埼7000系列路由器能够处理12种协议并支持点对点、电路交换与
40、俏元交换的广域网通仍，肉AIanlW!公Hj生产的Pownrhub多足交换机却只能处理7神协议：WiCnct.IP与IPX拼fl没柒IWAN接门，闵此，多S交换机网络中8TS使用路由H作为广域M的M关，并完成较为门取的路由功能，交换M中的饥三种路山技本则采用了一种今新的洁构:路山服齐ffi与边界文换机我们知道，传统的路山S宪成佑息包的技发与路山选抒叫项一作，ifih味r路山服务JK的网烙则由两个独：的没茶分月丁成上述内项功能:边界义换机完成ViSfC!的K发，刑路由记总的确定山价格较货的路山服务器充成.边W交换机JUi在fid的地址农中找不到B标节点的地址时才访问路由服务器，此时路由辨对之响应
41、一个正确的地址.交换机W将iMWftS/fM4兀5ifi出的姑，H前路山服务器勺交换机之间的通估协议还不统一，不网厂家的产品还不兼料5 .比较与评价h述三种路由技术托有特色，网络设计人员叫根据实标悄况加以选用.为使人们对它们有史好的我们分以下（A）个方曲对它们进行比较.1 .组M规模M络的人小足选择时种略山技水组网的决定性闽东.访二J7!交换机与传统路山2S相结合的办法适用于权小规揆的M络，点记经济实用但当主干网ifW成比较大的M格时.羽二C虚拟LAN的JFW将明火，i-:iM的扩版，交换机的矜能优铃相到允分发抨，山T它仪向那咚屈r站一特定的MftK发广播*W此少/主干M上广播义迎的数ffi由
42、于多记义换机组成的虚似M格过滤功能，并W:竹？7b:l网的带宽与埔站点的时钟，闵此庞拟网烙的安今件好，Ji外，它M第一种方法相比，由子交换机町在丁作组与郁门范由内M时负班交换与路由选校下作.故口Wf传统路由器使用的数分布武路由挂卜法b路由服务掰也比较适用于大羽的分布式2 .延迟M格延迟的增加穴导致网络性能的卜降，网洛延迟的人小一般与设济在讨发交通之前所必须处即的作收的人小成正比.对r第二C!的以人交换机柬讲，山丁浓二G廉拟网本切卜.使用桥而十便用路由W,W此相对速哎狡快.当执仃一个冏中的MAC地址、/找时.个MS包（64卞节）的延迟小EOO微抄，泊三C路山器的使川增加了尖标的？J找及父咚解法的
43、执行，W此大大增加f伯息包的延迟，其延圮时间岛达S奄杪可见.对于由笫.雌机4笫路由部络合组成的网饼.当义通经由义换机时只有相气好的性能交通从一个交换机矜山路山器流向另一个交换机时性能较飨儿乎所ff的第交换机y软ftftd合使Mj都能将W点组成虚拟M络（广捕域）.外以此改再M络的性能*拟M内点之问的义迎作MAC足近行义换.延迟较小，个叫虚拟M之问的节点交换信息时，佑息包传通要行过路山器，此时网格延迟较人.分布路山技术允许交换机在汾iC!协议了网11）虚拟MM传递估息，能克服h述路山器所形成的瓶效KWh服务器法使用边界交换机做出路检的选择.偶ifti在边界交换机不知道发送Bh:地址时，才内路由版务
44、器发沏问此时才会出异松的延迟.正常惆况下.交换机可以优孩在级存地址农中孜找地址.之接转发M总包.此神怙况下产生的延迟5MAC足交换机的延迟本WR）.路山伯息介放r网络中冷个路山器中，甸种协议swi相W的ZX列，网竹人员必须达个刈路ill进行配,其中色括城波S的设也_、修改路由农等.加之人机界面是林于文本的W此当企业M扩W到狡大规ffi时.路由热的讶现13以迓足相当费时的，分布穴赂山技术不利的一而AUt竹瑚的汗粕与路山及交换ZX数IJ的W加研衍数增加趋Vh为f克眼这一缺点*生产商来拟采用以下拟盹:在中心控金|台制定交通开策略.并iflilM络白动传播，从而祖免对每个没抓逐一MS.并川加1*1形人
45、机界曲*赂山服务器的特点圮wr竹瑚，一个路山服务器的依貌4提供岛渍母的版务与虚拟M络的行理*如Cft行理权序就能够允邙人M利用W描.对不闷组的用户分访问权限，通过执行该软件将访问权H通知所红的交换机赂山服齐器方法的另一个优点姑，允许网忏人进明地制定交通矜坪策略，不必关心响站用户的类*例如M界人W可将以太交换机上的W点5ATM上的服务热分ft!给IHj一个虚拟W城M,而不必输入以人节点的MACHUP地址，也不必翰入ATM节点的VPI/VC1,1价格价格是人们组W考感的另一个主因索以卜作雌出几个公5J生产的50、250、500个端I种路山方式产品的T均好个SilI价格的对比悄况V见农卜2h这取每个埔Il的价格拈叫瑙口的数H%W络没抓总价格所得的结果*网饼没Ittl括以太交换HUATM义换机、赂由服务S与第三苗路曲3,略由廉务器组M方式只打NeWbridge公司给出价格50.250,500个口没备每个煤口的平均价格分别为1920、1520与1435美元.从卜.而沿出的数据V以苻出，J*r坊二C!交挟与路山器方式汛网的方案价格僧便TG分布式路由技术组M价格圾岛,而路由服务器方武组网价格适中，从我们还可发现.使川第二戊文换机与汾土略山SfIl网时，Mi右网络规昧的扩人，T均每个斓H的价格越柬越小.路山服务器组M的沽况与之类似，（U分布式路山器组网方人工均每个响11的价格受网格规模影嘛不大.
