《計(jì)算機(jī)專(zhuān)業(yè)英語(yǔ)》課件第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.企業(yè)packetn.信息包c(diǎn)onventionaladj.常規(guī)的layern.層reliableadj.可靠的errorfreeadj.無(wú)誤的techniquen.技術(shù)interceptv.截取destinev.注定predictv.預(yù)測(cè)overwhelmv.崩潰embedv.使嵌入intelligencen.智能quickenv.加速pacen.速度identifyv.確定dictatev.指示virtualadj.虛擬的cachen.緩存consistentlyadv.一貫地destinationn.目標(biāo)problematicadj.有疑問(wèn)的indistinguishableadj.無(wú)法辨識(shí)的headern.頁(yè)眉segmentn.片段routern.路由器datagramn.數(shù)據(jù)包payloadn.有效載荷replicatev.復(fù)制rotationn.旋轉(zhuǎn)ensurev.保證traversev.橫貫PhrasesandExpressions

electroniccommerceservice電子商務(wù)服務(wù)dependon依靠webtraffic網(wǎng)絡(luò)流量asaresult因此armwith配備associatewith使連接portnumber端口編碼keeptrackof追蹤inconstrast相反地lookinto調(diào)查T(mén)heExplanationofDifficultStatements

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

分析:其中“ArmedwithURLload-balancingcapabilities,NetworkAddressTranslation,andembeddedDomainNameSystemintelligence”為過(guò)去分詞作狀語(yǔ)表示原因。

句意:由于這些交換機(jī)配備了統(tǒng)一資源定位符(URL)負(fù)荷平衡功能,網(wǎng)絡(luò)地址轉(zhuǎn)換和嵌入式域名系統(tǒng)智能,故它們能利用復(fù)雜的算法來(lái)管理和加快Web流量。

2.WebswitchesareabletoquickenthepaceofWebtrafficbecausetheyuseURLs,inadditiontoIPaddresses,tomakeswitchingdecisions.

分析:其中“inadditiontoIPaddresses”為插入語(yǔ),譯為“除了……還有”,相當(dāng)于“aswellas”。

句意:因?yàn)閃eb交換機(jī)除了使用IP地址外還使用URL作為交換決策的依據(jù),故它們能加快Web站點(diǎn)的流量。

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

分析:此句中“insteadofviewingtheIPaddressassociatedwiththeURLasthenetworkaddress”為介詞短語(yǔ),其中“associatedwiththeURLasthenetworkaddress”為過(guò)去分詞作定語(yǔ),修飾“IPaddress”;“which”所引導(dǎo)的從句為非限制性定語(yǔ)從句,修飾“Webswitch”。

句意:因此,并不是把與該URL有關(guān)的IP地址看成網(wǎng)絡(luò)地址,該地址指向Web交換機(jī)的虛擬IP地址(VIP),它起到緩存或內(nèi)容流量管理器的作用。

4.BylookingintotheHTTPpayloaddowntotheURLandcookie,aWebswitchknowswhatcontentisbeingrequested.

分析:其中“whatcontentisbeingrequested”為賓語(yǔ)從句,whatcontent在從句中作主語(yǔ),其語(yǔ)序?yàn)殛愂鼍湔Z(yǔ)序。

句意:通過(guò)檢查HTTP負(fù)載一直到URL和cookie(個(gè)人化上網(wǎng)信息塊),Web交換機(jī)知道什么內(nèi)容被請(qǐng)求了。

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

分析:此句中的三個(gè)由“which”所引導(dǎo)的從句均為“determine”的并列賓語(yǔ)(從句)。

句意:有了這個(gè)知識(shí),用戶定義的和/或預(yù)先設(shè)定的政策就決定了實(shí)施哪個(gè)流安全規(guī)則,允許或拒絕哪些內(nèi)容,以及對(duì)具體的內(nèi)容或用戶,需要哪種QoS要求。

6.WebswitchesalsodynamicallyreplicatehotcontenttoWebcacheandbringthecacheintotheload-balancingrotation,ensuringthatusersgettheinformationtheyneednomatterhowmuchtrafficistraversingthesite.

分析:“nomatterhowmuchtrafficistraversingthesite.”句中的“nomatterhow”相當(dāng)于“however”,引導(dǎo)狀語(yǔ)從句。類(lèi)似的如:nomatterwhat,nomatterwhich,nomatterwhere,nomatterwhen。

句意:Web交換機(jī)也動(dòng)態(tài)地把熱門(mén)的內(nèi)容復(fù)制到高速緩存中,使高速緩存進(jìn)入負(fù)荷平衡循環(huán),保證用戶得到他們所需的信息,而不管有多少流量通過(guò)網(wǎng)站。GrammarTranslationSkills狀語(yǔ)從句的翻譯方法

1.時(shí)間狀語(yǔ)從句的翻譯

時(shí)間狀語(yǔ)從句可以放在句首、句中或句末,譯成漢語(yǔ)時(shí)通常放在主句之前,但由until或till引導(dǎo)的從句在翻譯時(shí)一般放在主句之后,譯為“直到……為止”,“not...until”譯為“直到……才”。例如:

Anelectromagnetisonlyamagnetwhileacurrentisflowing.

只有電流通過(guò)時(shí),電磁鐵才有磁性。

Thedevelopmentstagelastsaslongasitneedsto,untiltheworkingdevicehasbeenconstructedandtested.研制階段持續(xù)的時(shí)間根據(jù)需要可長(zhǎng)可短,直到運(yùn)行的裝置得以建造和試驗(yàn)為止。

2.地點(diǎn)狀語(yǔ)從句的翻譯表示處所的地點(diǎn)從句譯成漢語(yǔ)時(shí)多放在主句之前。例如:

Whereverpeopleonearthgothereisalwaysgravitytokeepusfromfallingoff.無(wú)論地球上的人走在哪里,總有地心吸力使我們不致從地球上掉下去。

3.條件狀語(yǔ)從句的翻譯

條件狀語(yǔ)從句可以放在句首、句中或句末,通常由if,aslongas,provided,providing(假如),unless等詞引導(dǎo)。翻譯時(shí),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年很可能受到嚴(yán)重的污染。

4.原因狀語(yǔ)從句的翻譯

(1)由because和as引導(dǎo)的原因狀語(yǔ)從句翻譯時(shí),可以放在主句之前或之后。例如:

Asheatmakesthingsmove,itisaformofenergy.由于熱能使物體運(yùn)動(dòng),所以它是能量的一種形式。

(2)連詞since或nowthat表示已知的原因,常譯成“既然”,翻譯時(shí)從句通常放在主句之前。例如:

Whycananairplaneflyupsinceitismuchheavierthanair?

既然飛機(jī)比空氣重得多,為什么能飛上天空呢？

5.結(jié)果狀語(yǔ)從句的翻譯

結(jié)果狀語(yǔ)從句由連詞sothat,so...that,such...that引導(dǎo)。翻譯時(shí),從句譯在主句之后,例如:

Thetemperatureofthegasrises,sothatitexpandsinthecylinder.氣體的溫度升高,因而它在汽缸中膨脹。

6.目的狀語(yǔ)從句的翻譯

(1)由that,sothat或inorderthat引導(dǎo)的目的狀語(yǔ)從句通常與may或can等詞連用。翻譯時(shí),從句如放在主句之前則譯成“為了”,如放在主句之后則譯成“以便”。例如:

Inorderthatanelectriccurrentcanbeproducedinaconductor,anelectricfieldmustbebuiltinit.為使在導(dǎo)體中產(chǎn)生電流,必須在其中建立電場(chǎng)。

(2)由lest或forfearthat引導(dǎo)的狀語(yǔ)從句多使用虛擬語(yǔ)氣。翻譯時(shí),從句放在主句之后。例如:

Coalminerswearsafetyhelmetsforfearthatfallingrocksshouldhurtthem.煤礦工人頭戴安全帽,以免被落下的巖石砸傷。

7.比較狀語(yǔ)從句的翻譯

(1)用than引導(dǎo)的比較狀語(yǔ)從句多為省略句,譯成“比……”。翻譯時(shí),可以把省略的成分補(bǔ)充完整。例如:

Whenamanisworkinghisbodyproducesmoreheatthanwhenheisatrest.當(dāng)一個(gè)人工作時(shí),他的身體產(chǎn)生的熱比他在靜止?fàn)顟B(tài)時(shí)產(chǎn)生的熱要多。

(2)結(jié)構(gòu)“as...as”翻譯成“和…一樣”,其否定形式——“notso/as...as”譯成“不如……一樣”。例如:

Thebodymustdissipateheatasfastasitproducesit.身體排出熱量的速度必須和產(chǎn)生熱的速度一樣快。

(3)句型“themore...,themore...”翻譯成“越……,越……”。例如:

Thegreateranobject’squality,themoredifficultitistospeedituporslowitdown.物體的質(zhì)量越大,要使它加速或減速就越困難。

8.讓步狀語(yǔ)從句的翻譯

(1)用though或although引導(dǎo)的讓步狀語(yǔ)從句譯為“雖然”、“盡管”。翻譯時(shí),通常放在主句之前,主句中可用“但是”、“然而”等與之呼應(yīng)。例如:

Althoughonlyrelativelysmallexpansionsarenormallyencountered,theymustbetakenintoaccount.盡管通常遇到的膨脹比較少,然而卻必須加以考慮。

(2)用as引導(dǎo)的讓步狀語(yǔ)從句通常是部分倒裝,即把形容詞或副詞放在as之前,一般譯在主句之前。例如:

Smallasanatomis,itconsistsofsmallerparticles.原子盡管很小,它卻由更小的粒子組成。

(3)由whether引導(dǎo)的狀語(yǔ)從句,通常譯為“不管是……還是……”,翻譯時(shí),既可放在主句前,也可放在主句之后。例如:

Theinitialcostofbuildingapipeline,whetheritbeundergroundoraboveground,ishigh.鋪設(shè)管道的初始成本很高,不管是在地下還是地上。

9.方式狀語(yǔ)從句的翻譯

(1)由as引導(dǎo)的狀語(yǔ)從句出現(xiàn)在主句之后,翻譯時(shí),一般放在主句之后或主句的主語(yǔ)之后,譯為“如”。例如:

Solidsexpandandcontractasliquidsdo.固體像液體一樣熱脹冷縮。

(2)由justas引起的方式狀語(yǔ)從句比由as引導(dǎo)的從句強(qiáng)調(diào)的程度更大。翻譯時(shí),一般放在主句之前,譯為“正如”。例如:

Justasthedesignofacomputerismostcomplicatedmatter,sotooisitsmanufacture.正如計(jì)算機(jī)的設(shè)計(jì)極其復(fù)雜一樣,計(jì)算機(jī)的制造也十分復(fù)雜。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.防火墻buzzword時(shí)髦詞語(yǔ)vendorn.銷(xiāo)售商unveilvt.向公眾透露tool-setn.工具組Questions(1)WhichisoneofthefastestgrowingareasinInternetapplications?(2)InIntranet,thetwokeytypessoftwarearewhat?FromInternettoIntranet(Ⅱ)

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