《计算机专业英语》课件第23章

WebSwitches

Inenterprisenetworks,thenameofthegameisgettingpacketsfrompointAtopointBfast.ByspeedingIPpacketforwarding,conventionalLayer3and4switcheshavegreatlyimprovednetworkperformance.ButbusinesssuchasWebandcontenthosting,andelectroniccommerceservices,dependonfast,reliable,error-freeWebperformance.

EnteratechniquecalledWebswitching.WebswitchingisdesignedtoaddresstherequirementsofWebtraffic.Webswitchesinterceptalltrafficdestinedforaparticularsite.Asaresult,theseswitcheshavetheabilitytotrackcontentrequestsandpredictheavytrafficloadsbeforeserversbecomeoverwhelmed.

1ArmedwithURLload-balancingcapabilities,NetworkAddressTranslation,andembeddedDomainNameSystemintelligence,theswitchesusecomplexpoliciestomanageandspeedWebtrafficflow.

2WebswitchesareabletoquickenthepaceofWebtrafficbecausetheyuseURLs,inadditiontoIPaddresses,tomakeswitchingdecisions.URLsprovideamethodofidentifyingcontentwhereveritisontheInternet.AURLidentifiesonlythecontentrequesteditdoesnotdedicatewherethecontentmightbefound.3SoinsteadofviewingtheIPaddressassociatedwiththeURLasthenetworkaddress,thisaddresspointstothevirtualIPaddress(VIP)oftheWebswitch,whichfunctionsasacacheorcontenttrafficmanager.Theresult:aconsistentlypositiveperformanceforWebsiteusers.

Currentload-balancingserversordevices,includingLayer4switches,routeincomingpacketsbasedonthedestinationIPaddressorthecombinationofdestinationIPaddress,protocolIDandtransportportnumber.ThiscanbeproblematicinaWebenvironment.Toalayer4load-balancingdevice,WebapplicationsappeartobeusingTCPport80thetypicalTCPportforHTTPtraffic-makingWebapplicationtrafficindistinguishablefromHTTPtraffic.

PortnumberisastapleofTCP/IPcommunications.Becauseseveralapplicationprogramsmayberunningononemachineandusingasinglenetworkinterface,TCPneedstokeeptrackofwhatdatagoestowhichprogram.ThisisdonebyassigningaportnumbertoeveryTCPconnection.EachTCPsessionhasadestinationportnumberintheTCPheader.WhenaTCPsegmentisreceived,theTCProuterknowswhichporttopassittobylookingattheportnumberintheTCPheader.Somestandardportnumbersare:Telnet,port23;SimpleMailTransferProtocolMail,Port25andPostOfficeProtocol3Mail,Port110.

TypicallywithLayer4switchingaCommonGatewayInterfacerequestlooksnodifferentthanaWeb-enabledSAPapplicationorstreamingaudiorequest,eventhoughalloftheserequestshaveverydifferentqualityofservice(QoS)requirements.

Incontrast,WebswitcheduseURLstorouteincomingTCPorUserDatagramProtocol(UDP)flowstotargetedservers.4BylookingontotheHTTPpayloaddowntotheURLandcookie,aWebswitchknowswhatcontentisbeingrequested.5Withthisknowledge,user-definedand/orpre-setpoliciesdeterminewhichflow-securityrulesareenforced,whichQoSrequirementsareneededforspecificcontentorusers.

6WebswitchesalsodynamicallyreplicatehotcontenttoWebcacheandbringthecacheintotheload-balancingrotation,ensuringthatusersgettheinformationtheyneednomatterhowmuchtrafficistraversingthesite.NewWords

enterprisen.企业packetn.信息包conventionaladj.常规的layern.层reliableadj.可靠的errorfreeadj.无误的techniquen.技术interceptv.截取destinev.注定predictv.预测overwhelmv.崩溃embedv.使嵌入intelligencen.智能quickenv.加速pacen.速度identifyv.确定dictatev.指示virtualadj.虚拟的cachen.缓存consistentlyadv.一贯地destinationn.目标problematicadj.有疑问的indistinguishableadj.无法辨识的headern.页眉segmentn.片段routern.路由器datagramn.数据包payloadn.有效载荷replicatev.复制rotationn.旋转ensurev.保证traversev.横贯PhrasesandExpressions

electroniccommerceservice电子商务服务dependon依靠webtraffic网络流量asaresult因此armwith配备associatewith使连接portnumber端口编码keeptrackof追踪inconstrast相反地lookinto调查TheExplanationofDifficultStatements

1.ArmedwithURLload-balancingcapabilities,NetworkAddressTranslation,andembeddedDomainNameSystemintelligence,theswitchesusecomplexpoliciestomanageandspeedWebtrafficflow.

分析:其中“ArmedwithURLload-balancingcapabilities,NetworkAddressTranslation,andembeddedDomainNameSystemintelligence”为过去分词作状语表示原因。

句意:由于这些交换机配备了统一资源定位符(URL)负荷平衡功能,网络地址转换和嵌入式域名系统智能,故它们能利用复杂的算法来管理和加快Web流量。

2.WebswitchesareabletoquickenthepaceofWebtrafficbecausetheyuseURLs,inadditiontoIPaddresses,tomakeswitchingdecisions.

分析:其中“inadditiontoIPaddresses”为插入语,译为“除了……还有”,相当于“aswellas”。

句意:因为Web交换机除了使用IP地址外还使用URL作为交换决策的依据,故它们能加快Web站点的流量。

3.SoinsteadofviewingtheIPaddressassociatedwiththeURLasthenetworkaddress,thisaddresspointstothevirtualIPaddress(VIP)oftheWebswitch,whichfunctionsasacacheorcontenttrafficmanager.

分析:此句中“insteadofviewingtheIPaddressassociatedwiththeURLasthenetworkaddress”为介词短语,其中“associatedwiththeURLasthenetworkaddress”为过去分词作定语,修饰“IPaddress”;“which”所引导的从句为非限制性定语从句,修饰“Webswitch”。

句意:因此,并不是把与该URL有关的IP地址看成网络地址,该地址指向Web交换机的虚拟IP地址(VIP),它起到缓存或内容流量管理器的作用。

4.BylookingintotheHTTPpayloaddowntotheURLandcookie,aWebswitchknowswhatcontentisbeingrequested.

分析:其中“whatcontentisbeingrequested”为宾语从句,whatcontent在从句中作主语,其语序为陈述句语序。

句意:通过检查HTTP负载一直到URL和cookie(个人化上网信息块),Web交换机知道什么内容被请求了。

5.Withthisknowledge,user-definedandpre-setpoliciesdeterminewhichflow-securityrulesareenforced,whichcontentisallowedordenied,andwhichQoSrequirementsareneededforspecificcontentorusers.

分析:此句中的三个由“which”所引导的从句均为“determine”的并列宾语(从句)。

句意:有了这个知识,用户定义的和/或预先设定的政策就决定了实施哪个流安全规则,允许或拒绝哪些内容,以及对具体的内容或用户,需要哪种QoS要求。

6.WebswitchesalsodynamicallyreplicatehotcontenttoWebcacheandbringthecacheintotheload-balancingrotation,ensuringthatusersgettheinformationtheyneednomatterhowmuchtrafficistraversingthesite.

分析:“nomatterhowmuchtrafficistraversingthesite.”句中的“nomatterhow”相当于“however”,引导状语从句。类似的如:nomatterwhat,nomatterwhich,nomatterwhere,nomatterwhen。

句意:Web交换机也动态地把热门的内容复制到高速缓存中,使高速缓存进入负荷平衡循环,保证用户得到他们所需的信息,而不管有多少流量通过网站。GrammarTranslationSkills状语从句的翻译方法

1.时间状语从句的翻译

时间状语从句可以放在句首、句中或句末,译成汉语时通常放在主句之前,但由until或till引导的从句在翻译时一般放在主句之后,译为“直到……为止”,“not...until”译为“直到……才”。例如:

Anelectromagnetisonlyamagnetwhileacurrentisflowing.

只有电流通过时,电磁铁才有磁性。

Thedevelopmentstagelastsaslongasitneedsto,untiltheworkingdevicehasbeenconstructedandtested.研制阶段持续的时间根据需要可长可短,直到运行的装置得以建造和试验为止。

2.地点状语从句的翻译表示处所的地点从句译成汉语时多放在主句之前。例如:

Whereverpeopleonearthgothereisalwaysgravitytokeepusfromfallingoff.无论地球上的人走在哪里,总有地心吸力使我们不致从地球上掉下去。

3.条件状语从句的翻译

条件状语从句可以放在句首、句中或句末,通常由if,aslongas,provided,providing(假如),unless等词引导。翻译时,一般放在句首。例如:

Unlessmeasuresaretakenatonce,thereisagoodchancethatalltheoceansoftheworldwouldbeheavilypollutedbytheyear2000.若不立即采取措施,全世界的海洋到2000年很可能受到严重的污染。

4.原因状语从句的翻译

(1)由because和as引导的原因状语从句翻译时,可以放在主句之前或之后。例如:

Asheatmakesthingsmove,itisaformofenergy.由于热能使物体运动,所以它是能量的一种形式。

(2)连词since或nowthat表示已知的原因,常译成“既然”,翻译时从句通常放在主句之前。例如:

Whycananairplaneflyupsinceitismuchheavierthanair?

既然飞机比空气重得多,为什么能飞上天空呢？

5.结果状语从句的翻译

结果状语从句由连词sothat,so...that,such...that引导。翻译时,从句译在主句之后,例如:

Thetemperatureofthegasrises,sothatitexpandsinthecylinder.气体的温度升高,因而它在汽缸中膨胀。

6.目的状语从句的翻译

(1)由that,sothat或inorderthat引导的目的状语从句通常与may或can等词连用。翻译时,从句如放在主句之前则译成“为了”,如放在主句之后则译成“以便”。例如:

Inorderthatanelectriccurrentcanbeproducedinaconductor,anelectricfieldmustbebuiltinit.为使在导体中产生电流,必须在其中建立电场。

(2)由lest或forfearthat引导的状语从句多使用虚拟语气。翻译时,从句放在主句之后。例如:

Coalminerswearsafetyhelmetsforfearthatfallingrocksshouldhurtthem.煤矿工人头戴安全帽,以免被落下的岩石砸伤。

7.比较状语从句的翻译

(1)用than引导的比较状语从句多为省略句,译成“比……”。翻译时,可以把省略的成分补充完整。例如:

Whenamanisworkinghisbodyproducesmoreheatthanwhenheisatrest.当一个人工作时,他的身体产生的热比他在静止状态时产生的热要多。

(2)结构“as...as”翻译成“和…一样”,其否定形式——“notso/as...as”译成“不如……一样”。例如:

Thebodymustdissipateheatasfastasitproducesit.身体排出热量的速度必须和产生热的速度一样快。

(3)句型“themore...,themore...”翻译成“越……,越……”。例如:

Thegreateranobject’squality,themoredifficultitistospeedituporslowitdown.物体的质量越大,要使它加速或减速就越困难。

8.让步状语从句的翻译

(1)用though或although引导的让步状语从句译为“虽然”、“尽管”。翻译时,通常放在主句之前,主句中可用“但是”、“然而”等与之呼应。例如:

Althoughonlyrelativelysmallexpansionsarenormallyencountered,theymustbetakenintoaccount.尽管通常遇到的膨胀比较少,然而却必须加以考虑。

(2)用as引导的让步状语从句通常是部分倒装,即把形容词或副词放在as之前,一般译在主句之前。例如:

Smallasanatomis,itconsistsofsmallerparticles.原子尽管很小,它却由更小的粒子组成。

(3)由whether引导的状语从句,通常译为“不管是……还是……”,翻译时,既可放在主句前,也可放在主句之后。例如:

Theinitialcostofbuildingapipeline,whetheritbeundergroundoraboveground,ishigh.铺设管道的初始成本很高,不管是在地下还是地上。

9.方式状语从句的翻译

(1)由as引导的状语从句出现在主句之后,翻译时,一般放在主句之后或主句的主语之后,译为“如”。例如:

Solidsexpandandcontractasliquidsdo.固体像液体一样热胀冷缩。

(2)由justas引起的方式状语从句比由as引导的从句强调的程度更大。翻译时,一般放在主句之前,译为“正如”。例如:

Justasthedesignofacomputerismostcomplicatedmatter,sotooisitsmanufacture.正如计算机的设计极其复杂一样,计算机的制造也十分复杂。ExercisesⅠ.Fillintheblanksaccordingtothetext:(1)______________isdesignedtoaddresstherequirementsofWebtraffic.(2)Armedwith______________,NetworkAddressTranslation,andembeddedDomainNameSystemintelligence,theswitchesusecomplexpoliciestomanageandspeedWebtrafficflow.(3)A______________identifiesonlythecontentrequesteditdoesnotdedicatewherethecontentmightbefound.(4)WhenaTCPsegmentisreceived,the______________knowswhichporttopassittobylookingattheportnumberintheTCPheader.(5)Webswitchesareabletoquicken______________becausetheyuseURLs,inadditiontoIPaddresses,tomakeswitchingdecisions.Ⅱ.Decidewhethereachofthefollowingstatementsistrueorfalseaccordingtothetext:(1)BusinesssuchasWebandcontenthosting,andelectroniccommerceservices,dependonfast,reliable,error-freeWebperformance.(2)Asaresult,theseswitcheshavetheabilitytotrackcontentrequestsandpredictheavytrafficloadsafterserversbecomeoverwhelmed.(3)Becauseseveralapplicationprogramsmayberunningononemachineandusingasinglenetworkinterface,TCPneedstokeeptrackofwhatdatagoestowhichprogram.(4)Currentload-balancingserversordevicesrouteincomingpacketsonlybasedonthedestinationIPaddressorthecombinationofdestinationIPaddress.(5)Toalayer4load-balancingdevice,WebapplicationsappeartobeusingTCPport70.Ⅲ.TranslatethefollowingsentencesintoChinese:(1)Thenormaltemperatureforahumanbeingisabout37℃,nomatterinwhatpartoftheworldhelived.(2)Becauseseveralapplicationprogramsmayberunningononemachineandusingasinglenetworkinterface,TCPneedstokeeptrackofwhatdatagoestowhichprogram.(3)URLsprovideamethodofidentifyingcontentwhereveritisontheInternet.(4)WhenaTCPsegmentisreceived,theTCProuterknowswhichporttopassittobylookingattheportnumberintheTCPheader.(5)TypicallywithLayer4switchingaCommonGatewayInterfacerequestlooksnodifferenthanaWeb-enabledSAPapplicationorstreamingaudiorequest,eventhoughalloftheserequestshaveverydifferentqualityofservice(QoS)requirements.Ⅳ.TranslatethefollowingparagraphintoChinese:

OneofthemostoftenquotedcriticismofInternetwhenbeingconsideredforseriousbusinessapplicationsisitssecurityrisk,oritsperceivedinadequacyofsecurityfeatures.ManyfeelthattheInternetisdistributedand“uncontrolled”.Byitsveryownnature,thereisnosingleorganizationowningtheInternet,runningitorcanbeheldresponsibleforitintheconventionalsense.Intrusionmaycomefromanywhereintheworld.Tofurthercomplicatethematter,legislationandlawenforcementconcerningelectroniccrimesvarygreatlyfromonecountrytoanother.ThispresentsgreatchallengesintheprosecutionofcrimescommittedusingtheInternet.ReadingMaterials

FromInternettoIntranet(Ⅰ)

OneofthefastestgrowingareasinInternetapplicationsistheadoptionofInternettechnologiesforthedevelopmentofcorporatenetworksandbusinesssolutions.Manypublicsectorandcommercialorganizationsthroughouttheworld,areacceleratingtheirpacesinbuildingcorporatenetworksbasedonInternettechnologies,particularlytheWorldWideWeb,allowingthemtorollouttheirprivate“Intranets”.TheseIntranetsareusedtosupportenterpriseapplicationsandcommunications,bothinsideandoutsidethecorporatefirewall.

Intranetisthenewbuzzwordreferringtotheuseoffastgrowingandrelativelyin-expensiveInternettechnologiesforthedevelopmentofenterpriseinformationandcommunicationsystems.Itgenerallyinvolvestwokeytypesofsoftware:the“browser”whichallowuserstoscanthenetworkforusefulinformationandthe“server”whichstoresandorganizestheinformation.MajorITvendorshaveannouncedorareplanningtoannounceproductsandserviceswhichwillhelptheircustomersinrealizingthecompetitiveadvantagesmadepossiblebythesenewtechnologies.Forexample,OracleandSybasehaveunveiledtheirplanstointroducebrowsersthatincludesapplicationdevelopmenttoolsbasedonJava,aprogramminglanguagelicensedfromSunMicrosystemsInc.Thesenewtool-setswillallowdeveloperstowritenetwork-connection-ready,web-enabledapplicationsthatlinktocorporatedatabases.NewWordsandExpressions

corporaten.公司rolloutvt.突破firewalln.防火墙buzzword时髦词语vendorn.销售商unveilvt.向公众透露tool-setn.工具组Questions(1)WhichisoneofthefastestgrowingareasinInternetapplications?(2)InIntranet,thetwokeytypessoftwarearewhat?FromInternettoIntranet(Ⅱ)

ThecreationofprivateIntranetsprovidesopportunitiesforcompaniestousetheWebasacomplementoranalternativefortraditionalinternalnetworking,applicationdevelopmenttoolsandgroup-wareproducts.Amongmanyothers,companieslikeUSWest,aBabyBellcompanyofmorethan15,000employees,MorganStanleyandTurnerBroadcastinghavesuccessfullyimplementedtheirownIntranetswhichallowtheiremployeestoshareinformation,collaborateonprojects,helptorealizetheconceptofvirtualoffices,andtocreateveryeffectivew