數(shù)據(jù)通信的基礎(chǔ)知識概述

數(shù)據(jù)通信的基礎(chǔ)知識概述數(shù)據(jù)通信是通信技術(shù)和計算機技術(shù)相結(jié)合而產(chǎn)生的一種新的通信方式。要在兩地間傳輸信息必須有傳輸信道，根據(jù)傳輸媒體的不同，有有線數(shù)據(jù)通信與無線數(shù)據(jù)通信之分。但它們都是通過傳輸信道將數(shù)據(jù)終端與計算機聯(lián)結(jié)起來，而使不同地點的數(shù)據(jù)終端實現(xiàn)軟、硬件和信息資源的共享。

數(shù)據(jù)通信的交換方式及適用范圍

1．?dāng)?shù)據(jù)通信的交換方式

通常數(shù)據(jù)通信有三種交換方式：

（1）電路交換

電路交換是指兩臺計算機或終端在相互通信時，使用同一條實際的物理鏈路，通信中自始至終使用該鏈路進行信息傳輸，且不允許其它計算機或終端同時共亨該電路。

（2）報文交換

報文交換是將用戶的報文存儲在交換機的存儲器中（內(nèi)存或外存），當(dāng)所需輸出電路空閑時，再將該報文發(fā)往需接收的交換機或終端。這種存儲—轉(zhuǎn)發(fā)的方式可以提高中繼線和電路的利用率。

（3）分組交換

分組交換是將用戶發(fā)來的整份報文分割成若于個定長的數(shù)據(jù)塊（稱為分組或打包），將這些分組以存儲—轉(zhuǎn)發(fā)的方式在網(wǎng)內(nèi)傳輸。第一個分組信息都連有接收地址和發(fā)送地址的標識。在分組交換網(wǎng)中，不同用戶的分組數(shù)據(jù)均采用動態(tài)復(fù)用的技術(shù)傳送，即網(wǎng)絡(luò)具有路由選擇，同一條路由可以有不同用戶的分組在傳送，所以線路利用率較高。

2．各種交換方式的適用范圍

（1）電路交換方式通常應(yīng)用于公用電話網(wǎng)、公用電報網(wǎng)及電路交換的公用數(shù)據(jù)網(wǎng)（cSPDN）等通信網(wǎng)絡(luò)中。前兩種電路交換方式系傳統(tǒng)方式；后一種方式與公用電話網(wǎng)基本相似，但它是用四線或二線方式連接用戶，適用于較高速率的數(shù)據(jù)交換。正由于它是專用的公用數(shù)據(jù)網(wǎng)，其接通率、工作速率、用戶線距離、線路均衡條件等均優(yōu)于公用電話網(wǎng)。其優(yōu)點是實時性強、延遲很小、交換成本較低；其缺點是線路利用率低。電路交換適用于一次接續(xù)后，長報文的通信。

（2）報文交換方式適用于實現(xiàn)不同速率、不同協(xié)議、不同代碼終端的終端間或一點對多點的同文為單位進行存儲轉(zhuǎn)發(fā)的數(shù)據(jù)通信。由于這種方式，網(wǎng)絡(luò)傳輸時延大，并且占用了大量的內(nèi)存與外存空間，因而不適用于要求系統(tǒng)安全性高、網(wǎng)絡(luò)時延較小的數(shù)據(jù)通信。

（3）分組交換是在存儲—轉(zhuǎn)發(fā)方式的基礎(chǔ)上發(fā)展起來的，但它兼有電路交換及報文交換的優(yōu)點。它適用于對話式的計算機通信，如數(shù)據(jù)庫檢索、圖文信息存取、電子郵件傳遞和計算機間通信等各方面，傳輸質(zhì)量高、成本較低，并可在不同速率終端間通信。其缺點是不適宜于實時性要求高、信息量很大的業(yè)務(wù)使用。

數(shù)據(jù)通信的分類

1．有線數(shù)據(jù)通信

（1）數(shù)字數(shù)據(jù)網(wǎng)（DDN）

數(shù)字數(shù)據(jù)網(wǎng)由用戶環(huán)路、DDN節(jié)點、數(shù)字信道和網(wǎng)絡(luò)控制管理中心組成。DDN是利用光纖或數(shù)字微波、衛(wèi)星等數(shù)字信道和數(shù)字交叉復(fù)用設(shè)備組成的數(shù)字數(shù)據(jù)傳輸網(wǎng)。也可以說DDN是把數(shù)據(jù)通信技術(shù)、數(shù)字通信技術(shù)、光纖通信技術(shù)以及數(shù)字交叉連接技術(shù)結(jié)合在一起的數(shù)字通信網(wǎng)絡(luò)。數(shù)字信道應(yīng)包括用戶到網(wǎng)絡(luò)的連接線路，即用戶環(huán)路的傳輸也應(yīng)該是數(shù)字的，但實際上也有普通電纜和雙絞線，但傳輸質(zhì)量不如前。

（2）分組交換網(wǎng)

分組交換網(wǎng)（PSPDN）是以ccITTＸ．2５建議為基礎(chǔ)的，所以又稱為Ｘ.25網(wǎng)。它是采用存儲—轉(zhuǎn)發(fā)方式，將用戶送來的報文分成具用一定長度的數(shù)據(jù)段，并在每個數(shù)據(jù)段上加上控制信息，構(gòu)成一個帶有地址的分組組合群體，在網(wǎng)上傳輸。分組交換網(wǎng)最突出的優(yōu)點是在一條電路上同時可開放多條虛通路，為多個用戶同時使用，網(wǎng)絡(luò)具有動態(tài)路由選擇功能和先進的誤碼檢錯功能，但網(wǎng)絡(luò)性能較差。

（3）幀中繼網(wǎng)

幀中繼網(wǎng)絡(luò)通常由幀中繼存取設(shè)備、幀中繼交換設(shè)備和公共幀中繼服務(wù)網(wǎng)3部分組成。幀中繼網(wǎng)是從分組交換技術(shù)發(fā)展起來的。幀中繼技術(shù)是把不同長度的用戶數(shù)據(jù)組均包封在較大的幀中繼幀內(nèi)，加上尋址和控制信息后在網(wǎng)上傳輸。

2．無線數(shù)據(jù)通信

無線數(shù)據(jù)通信也稱移動數(shù)據(jù)通信，它是在有線數(shù)據(jù)通信的基礎(chǔ)上發(fā)展起來的。有線數(shù)據(jù)通信依賴于有線傳輸，因此只適合于固定終端與計算機或計算機之間的通信。而移動數(shù)據(jù)通信是通過無線電波的傳播來傳送數(shù)據(jù)的，因而有可能實現(xiàn)移動狀態(tài)下的移動通信。狹義地說，移動數(shù)據(jù)通信就是計算機間或計算機與人⑥LAN與LAN的互聯(lián)。

⑦遠程計算機輔助設(shè)計/制造文件的傳送、圖像查詢以及圖像監(jiān)視、會議電視等2．無線數(shù)據(jù)通信的應(yīng)用

無線數(shù)據(jù)通信也稱為移動數(shù)據(jù)通信。它的業(yè)務(wù)范圍很廣，也有廣泛的應(yīng)前景。（1）移動數(shù)據(jù)通信在業(yè)務(wù)上的應(yīng)用。移動數(shù)據(jù)通信的業(yè)務(wù)，通常分為基本數(shù)據(jù)業(yè)務(wù)和專用數(shù)據(jù)業(yè)務(wù)兩種：基本數(shù)據(jù)業(yè)務(wù)的應(yīng)用有電子信箱、傳真、信息廣播、局域網(wǎng)（LAN）接入等。專用業(yè)務(wù)的應(yīng)用有個人移動數(shù)據(jù)通信、計算機輔助調(diào)度、車、船、艦隊管理、ＧPS汽車衛(wèi)星定位、遠程數(shù)據(jù)接入等。（2）移動數(shù)據(jù)通信在工業(yè)及其它領(lǐng)域的應(yīng)用。

移動數(shù)據(jù)通信在這些領(lǐng)域的應(yīng)用可分為固定式應(yīng)用、移動式應(yīng)用和個人應(yīng)用三種類型。

①固定式應(yīng)用是指通過無線接入公用數(shù)據(jù)網(wǎng)的固定式應(yīng)用系統(tǒng)及網(wǎng)絡(luò)。如邊遠山區(qū)的計算機入網(wǎng)、交警部門的交通監(jiān)測與控制、收費停車場、加油站以及災(zāi)害的遙測和告警系統(tǒng)等。

②移動式應(yīng)用是指野外勘探、施工、設(shè)計部門及交通運輸部門的運輸車、船隊和快遞公司為發(fā)布指示或記錄實時事件，通過無線數(shù)據(jù)網(wǎng)絡(luò)實現(xiàn)業(yè)務(wù)調(diào)度、遠程數(shù)據(jù)訪問、報告輸入、通知聯(lián)絡(luò)、數(shù)據(jù)收集等均需采用移動式數(shù)據(jù)終端。移動數(shù)據(jù)終端在公安部門的刑警、巡警、交警也開始應(yīng)用。

③個人應(yīng)用是指專業(yè)性很強的業(yè)務(wù)技術(shù)人員、公安外線偵察破案人員等需要在外辦公時，通過無線數(shù)據(jù)終端進行遠程打印、傳真、訪問主機、數(shù)據(jù)庫查詢、查證。股票交易商也可以通過無線數(shù)據(jù)終端隨時隨地跟蹤查詢股票信息，即使度假也可以從遠程參加股票交易。RudimentaryknowledgesummaryofdatacommunicationThecommunicationtechnologyandcomputertechnologythatdatacommunicationiscombinebutakindofnewcommunicationwaythatproduce.Musttransmitthechannelwhiletransmittinginformationbetweentwoplaces,accordingtotransmittingthedifferenceofmedias,differenceofwireddatacommunicationandwirelessdatacommunication.Buttheyallconnectdataterminalandcomputerthroughtransmittingthechannel,andmakethedataterminalofdifferentplacesrealizethesharingofsoftwareandhardwareandinformationresources.Thepatternofexchangingofdatacommunicationandscopeofapplication1.Usuallytherearethreekindsofpatternsofexchangingindatacommunicationforthepatternofexchangingofdatacommunication:(1)ThecircuitexchangingItmeanstwocomputersorterminalstationsarewhilecommunicatingeachotherthatthecircuitexchangesthecircuitandexchanges,usethesamerealphysicschain,usethischaintocarryontheinformationtransmissionfromstarttofinishincommunication,allowothercomputerorterminalstationhenriesofthiscircuitaltogetheratthesametime.(2)Newspaperdocumentexchangenewspaperdocumentexchangeisitstoreamongmemoryofexchangernewspaperdocumentofusertoexchange(whethermemoryoroutsidedeposit),asisitwhencircuitidle,mailexchangerorterminalstationreceivedtoneedtothisnewspaperdocumentandthentooutputwhilebeingnecessary.Thiskindofmemory-thewaytotransmitcanimprovetheutilizationratioofjunctionlineandcircuit.(3)Dividingintogroupsexchangesitmakelongdatapieceonpiecetocutwholecopiesofnewspaperdocumentthatusersendapartintotoexchangetodivideintogroupstoexchangetodivideintogroups(isitdivideintogroupsorbaletocall),divideintogroupsinordertostorethese-waythattransmittransmitinnetwork.Thefirstmessageofdividingintogroupshasidentificationsreceivingtheaddressandsendingtheaddressinsuccession.Inthepacketswitchingnetwork,differentusers'groupingdataadoptthetechnologytransferthatisrepliedanduseddynamically,namelythenetworkhasroutestochoose,therecanbedifferentusers'groupingtoconveyinthesameroute,sotheutilizationratioofthecircuitisrelativelyhigh.2.Scopeofapplicationofdifferentpatternsofexchanging(1)Circuitpatternofexchangingapplypublictelephonenetwork,publictelegramnetworkandpublicdatumnetwork(cSPDN)thatcircuitexchange,etc.amongthecommunicationnetworksusually.Department'straditionalwayofpatternofexchangingoffirsttwokindsofcircuit;Thelastwayandpublictelephonenetworkaresimilarbasically,butitjoinsusersinLinefourorwayofLinetwo,suitableforthedatainterchangeofhigherspeed.Datanetworknotpubliconitistobespecial-purposeinit,puttingthroughrate,speed,theuserlinenotworkingofitfrom,circuittermsnotbalanced,etc.lasttelephonenetworknotpublic.Itsadvantageisthatreal-timecharacterisstrong,delayverysmallandexchangingthecostrelativelylow;Itsshortcomingisthatautilizationratioofacircuitislow.Thecircuitexchangesandissuitableforonceaftercontinuing,thecommunicationofthelongmessage.(2)Thegentlepatternofexchangingofthenewspaperissuitableforrealizingdifferentspeed,differentagreements,terminalstationsortheonepointtomanypointone,withstoringthedatacommunicationthatistransmittedfortheunitgentliesofdifferentcodesterminalstation.Becauseofwaythis,networkprolongheavywhentransmitting,takealargeamountofmemoryandoutsidecheckspace,notsuitabletoprolongwhilerequiringthesystemsecurityhigh,networksmallerdatacommunication.(3)Isitstore-transmitfoundationofthewaynottodeveloptoexchangetodivideintogroups,butithasadvantagethatcircuitexchangesandthenewspaperdocumentexchangeconcurrently.Itissuitableforconversationalcompunication,forinstancethedatabaseissearched,pictureandtextinformationdeposittingandwithdraw,E-mailtransmittingandsuchdifferentfieldsascommunication,etc.amongthecomputers,itisrelativelylowtotransmitthecosthighinquality,andinthecommunicationamongdifferentspeedterminalstation.Itsshortcomingisnottosuitableforexpectingmuch,businessuseverygreatinamountofinformationofreal-timecharacter.1.Wireddatacommunication(1)DigitalDataNet(DDN)DigitalDataNetiscontrolledtheadministrativecentertomakeupbyusercycle,DDNnode,digitalchannelandnetwork.DDNutilizessuchdigitalchannelsasopticfibreordigitalmicrowave,satellite,etc.andfiguretoreplythedigitaldatatransmissionnetmadeupofequipmentalternately.WecansaytooDDNconnectdatacommunicationtechnology,digitalcommunicationtechnology,fiberopticcommunicationtechnologyandfigurealternatelydigitalcommunicationnetworksthattechnologyconbinedtogether.Thedigitalchannelshouldincludeuserstotheconnectioncircuitofthenetwork,thetransmissionofthenamelyuserscycleshouldbethethefigureone,butthereareordinarycablesandpairedlineinfact,butbeforetransmittingqualityandisnotsogoodas.(2)Thepacketswitchingnetworkpacketswitchingnetwork(PSPDN)iswithccITTX.Basedon25suggestions,soalsocalledX.25networks.Itadoptsstoring-transmittheway,dividesthenewspaperdocumentwhichuserssenthereintohavingdatasectionwhichusescertainlength,controlinformationonthesectionineachdata,formagroupingwithaddressmakethecolonyup,transmitonthenet.Packetswitchingnetworkmostoutstandingadvantagetocanopenlargetimidthoroughfaresatthesametimeatonecircuit,useatthesametimeforalotofuser,networkhavedynamicroutechoosefunctionandaadvancedoneyardexaminefunctionbymistakebymistake,buttheperformanceofthenetworkisrelativelybad.(3)Framerelayingnetworkframerelayingnetworkdepositandwithdrawbyframerelayingequipment,framerelayingexchangeequipmentandpublicframerelayingservicenetwork3partmakeupusually.Theframerelayingnetworkisdevelopedfromtheswapperofdividingintogroups.Framerelayingtechnologypairsofdifferentuserdatagroupinbiggerframerelayingframesealoflength,inaddition,transmitonthenetafterseekingthelocationandcontrollinginformation.2.Wirelessdatacommunicationwirelessdatacommunicationcallthemobiledatacommunicationtoo,itdevelopsonthebasisofwireddatacommunication.Wireddatacommunicationdependsontransmittingwiredly,isonlysuitableforthecommunicationbetweenregularterminalstationandthecomputerorthecomputer.Andthemobiledatacommunicationconveyedthedatathroughthespreadoftheradiowave,thereforemayrealizemovingmobilecommunicationunderthestate.Narrowsensesaymobiledatacommunicationcomputercomputerandwirelesscommunicationofpeoplesometimes.Itpasseswiththewireddatanetworkinterconnectedly,expandstheapplicationofthenetworkingofthewireddatatomovingandportableusers.1.Computernetwork(ComputerNetwork),entangletelephonewireorhave,wirelesschanneltwotheabove-mentionedcomputerinterconnectedsetthroughopticalcable,pair.Canrealizenetworkresource-sharingthroughnetworkeveryuser,forinstancefile,procedure,printerandmodem,etc..Computernetworkdivideaccordingtogeographicalposition,candivideintoInternet,WAN,citylandnetworkandLAN4kinds.InternetisthebiggestInternetintheworld;WANgenerallymeansthatjoinsthenetworkofeachareainacountry,WANisgenerallydistributedinthedistanceamong100-1000kilometers;Citylandnetiscallcitynet,itscoverageisgen