还剩1页未读,继续阅读
文本内容:
实验一Ci rcuitSwitching and Packet Switching
一、实验目的
1、扩大通信技术的英语词汇量
2、熟悉电路交换、分组交换等专业术语
3、了解科技文章的表达特点和掌握科技英语的翻译技巧
二、实验内容文章翻译Circuit SwitchingandPacketSwitching Thereare twobasic typesof switchingtechniques:circuit switchingand message switching.In circuit switching,a totalpath ofconnected linesis set up fromthe originto thedestination at the timethe callis made,and thepath remainsallocated to the source-destination pairwhether usedor notuntil it is releasedby thecommunicating parties.The switches,cal ledcircui tswi tchesor officeexchange intelephone jargon,have nocapabi1ity ofstoring ormanipulating usersdata ontheir wayto thedestination.The circuit is setup bya specialsignaling message that findsits waythrough the network,seizing channelsin thepath as it proceeds.Once thepath isestablished,a returnsignal informsthe source to begin transmission.Direct transmissionof datafrom sourceto destinationcan thentake placewithout anyintervention onthe partof thesubnet.In message switching,the transmissionunit isa well-defined blockof datacalled a message.In additionto thetext tobe transmitted,amessagecomprises aheader and a checksum.The headercontains informationregarding thesource anddestination addressesas wellas othercontrol information;the checksumis usedfor errorcontrol purposes.The switchingelement isa computerreferred to as amessage processor,with processingand storagecapabilities.Messages travelindependently andasynchronously,finding theirown wayfrom sourceto destination.First the message istransmitted fromthe hostto the message processorto whichitisattached.Once the message isentirely received,the messageprocessor examinesits header,and accordinglydecides onthe nextoutgoing channelon whichto transmitit.If thisselected channelis busy,the messagewaits in a queueuntil thechannel becomesfree,at whichtime transmissionbegins.At thenext messageprocessor,themessage is againreceived,stored,examined,and transmittedon someoutgoing channel,and thesame processcontinues untilthemessageis deliveredto itsdestination.This transmissiontechnique isalso referredtoasthe store-and-forward transmissiontechnique.A variationof messageswitching ispacket switching.Here themessageisbroken up into severalpieces of a gi venmax imum1ength,called packets.As withmessageswitching,each packetcontains aheader anda checksum.Packets aretransmitted independentlyinastore-and-forward manner.With circuitswitching,there isalways aninitial connectioncost incurredin settingup the circuit.It iscost-effective onlyin thosesituations whereonce thecircuitissetupthere isa guaranteedsteady flowof informationtransfer toamortize theinitial cost.This iscertainly thecase withvoice communicationin thetraditional way,and indeedcircuitswitching is thetechnique usedin thetelephone system.Communication amongcomputers,however,is characterizedas bursty.Burstiness isa resultof thehigh degreeof randomnessencountered inthemessage-generation processand themessage size,and of the lowdelay constraintrequired bythe user.The usersand devicesrequire thecommunication resourcesrelatively infrequently;but whenthey do,they requirea relativelyrapid response.If afixed dedicatedend-to-end circuitwere tobe setup connectingthe endusers,then onemust assignenough transmissionbandwidth tothecircuitin orderto meetthe delayconstraint withthe consequencethat theresulting channel utilization islow.If thecircuit ofhigh bandwidthwere setup andreleased ateach messagetransmission request,then theset-up timewould belarge compared tothetransmission timeof themessage,resulting againin lowchannelutilization.Therefore,for burstyusers whichcan alsobe characterizedby highpeak-to-average dataate requirements,store-and-forward transmissiontechniques offera morecost-effective solution,since amessage occupiesa particularcommunications linkonly forthe durationof itstransmission onthat link;the restof thetime itis storedat someintermediate messageswitch and the linkis availablefor othertransmissions.Thus themain advantage of store-and-forward transmissionover circuitswitchingisthat thecommunication bandwidthis dynamicallyallocated,andtheallocation isdone onthe finebasis ofa particularlink inthenetworkandaparticular messagefor aparticular source-destination pair.Packet switchingachieves thebenefits discussedso farand offersadded features.It providesthe fulladvantageof the dynamicallocation ofthe bandwidth,even whenmessages arelong.Indeed,with packet switching,many packets ofthesame messagemay beintransmissionsimultaneously overconsecutive linksofapath fromsourcetodestination,thus achievinga“pipelining〃effect andreducing considerablythe overalltransmission delayofthemessage ascomparedtomessageswitching.It tendsto requiresmaller storageallocation atthe intermediateswitches.It alsohas bettererror characteristicsand leadsto moreefficient errorrecovery procedures,asitdeals withsmaller entities.Needless tosay,packetswitchingpresents designproblems ofits own,such asthe needto reorderpacketsofa givenmessagethatmay arriveatthedestination nodeout ofsequence.
三、实验步骤及要求
1、首先,打开手机,在应用市场上搜索可以翻译文档的软件,然后将翻译软件先下栽到手机匕然后打开软件软件分为三个功能文档翻译、图片翻译、短句翻译
2、将翻译软件中的翻译参数设置为英译汉,将需要翻译成的语言调整为简体中文
3、利用翻译软件功能,采用一句原文,一句中文的方式进行翻译
4、将翻译后的汉语内容进彳强当的句式调整施帷确、完整、通顿和专业
四、实验设备一部可以装有翻译软件的智能手机
五、实验预习要求阅读实验指导书内容,做好课前预习工作
六、实验报告要求要求对文章进行翻译,书写的翻译内容要通顺、专业。