NewWordsandExpressionsethernet ['iθ?n?t]n.以太網(wǎng)LANLocalAreaNetworks

局域網(wǎng)cable['ke?b(?)l] n.電纜，纜繩alternative[??l't??n?t?v]n.二中擇一，供替代的選擇popularity[p?pj?'l?r?t?]n.普及，流行wirelessnetwork

無線網(wǎng)絡(luò)WANWideAreaNetworks

廣域網(wǎng)airlinesystem

航線系統(tǒng)NewWordsandExpressionsmatured [m?'t???d]v.成熟，到期（mature的過去分詞）Megabit['meɡ?b?t]n.兆位，兆比特（縮寫MB）Gigabit ['g?g?b?t]n.千兆位，千兆比特（縮寫GB）EthernetTopologiesandProtocols

以太網(wǎng)的拓?fù)浣Y(jié)構(gòu)和協(xié)bustopology

總線構(gòu)造，總線拓?fù)鋐ooter['f?t?]n.頁腳bytes[baits]n.字節(jié)，字節(jié)數(shù)（byte的復(fù)數(shù)）broadcast ['br??dkɑ?st]vt.播送，播放NewWordsandExpressionsadapter[?'d?pt?] n.適配器hardware ['hɑ?dwe?]n.計(jì)算機(jī)硬件preliminary[pr?'l?m?n(?)r?]adj.初步的，開始的，預(yù)備的simultaneously[,s?ml'te?n??sl?]adv.同時(shí)trade-off ['treid?f] n.權(quán)衡，平衡，交換，交易algorithm ['?lg?r?e(?)m]n.算法，運(yùn)算法則random ['r?nd?m]adj.隨機(jī)的，任意的hub [h?b]n.集線器NewWordsandExpressionsrouter['ru?t?(r)] n.路由器console[k?n's??l] n.控制臺，操縱臺sophisticatedkit

先進(jìn)的裝備migrate['ma?gre?t]vt.使移居，使移植terminal['t??m?n(?)l]n.終端機(jī)，末端，終點(diǎn)IntroductiontoEthernetEthernetisacomputernetworkingtechnologythattypicallyconnectsLANnetworks.LANstandsforLocalAreaNetworks,andreferstoanycomputernetworkthatinvolvesmorethanonecomputer.LANnetworksareusuallyconnectedusingEthernetcables.Ethernetisasystemofcablesusedtoconnectnetworks.ItwasinvestedbyBobMetcalfeandhasbeenaroundsince1973inoneformoranother.ItisbyfarthemostwidelyusedstandardusedtoconnectLANnetworks.ThereareotheralternativesbutEthernetistheclearleaderintermsofpopularity.EthernetCardsWearenowinthetimesofthewirelessnetwork,meaningthatinmanycaseslargenumbersofcablesarenotnecessary.LANconnectionsandinternetconnectioncanoftenbeachievedusingwirelesssystemsnow.Thismeansitispossibletogainaccesstothenetworkanywherewithinacertainarea,dependingonthereachofthewirelessnetwork.Thismeansuserscanbemoremobileanddon’thavetobesittingattheirdeskinthesameplaceallofthetimewithacablepluggedin.Inthecaseofinternetaccessthismeansuserscanmovearoundtheofficeortheirhome(orevengarden)whilestillgainingaccesstoit.Forwirelessnetworks,Ethernetcardsareoftenused.TheseessentiallydothesamejobasanEthernetcablebutwithoutthenecessityortheconstraintsofthecables.WANNetworksWANstandsforWideAreaNetworks,whicharenetworksthatstretchoveramuchwiderareathanLAN’s,sometimesconnectingsystemsthroughouttheworld(WAN就是廣域網(wǎng)，其覆蓋范圍比局域網(wǎng)大得多，有的能夠覆蓋全球范圍).TheinternetisanexampleofaWAN.TheEthernetstandardisnowalsousedforWAN’sinmuchthesamewayasforLAN’s.AirlinesystemthatareusedinairportsaroundtheworldisagoodexampleofaWideAreaNetwork.FastEthernetandGigabitEthernetInthemid-1990s,FastEthernettechnologymaturedandmetitsdesigngoalsofa)increasingtheperformanceoftraditionalEthernetwhileb)avoidingtheneedtocompletelyre-cableexistingEthernetnetworks.WhileFastEthernetimprovedtraditionalEthernetfrom10Megabitto100Megabitspeed,GigabitEthernetboaststhesameorder-of-magnitudeimprovementoverFastEthernetbyofferingspeedsof1000Megabits(1Gigabit)(雖然快速以太網(wǎng)將傳統(tǒng)的以太網(wǎng)從10MB提高到100MB，但千兆以太網(wǎng)通過提供1000MB（1GB）的速度，擁有與快速以太網(wǎng)相同的量級改進(jìn)).GigabitEthernetwasfirstmadetotraveloveropticalandcoppercabling,butthe1000Base-Tstandardsuccessfullysupportsitaswell.WhereasregularEthernetcarriestrafficatarateof10Mbit/s,FastEthernetcarriestraffictentimesfasterat100Mbit/s.EthernetTopologiesandProtocolsTraditionalEthernetemploysabustopology,meaningthatalldevicesorhostsonthenetworkusethesamesharedcommunicationline.EachdevicepossessesanEthernetaddress,alsoknownasMACaddress.SendingdevicesuseEthernetaddressestospecifytheintendedrecipientofmessages.DatasentovertheEthernetexistsintheformsofframes.AnEthernetframecontainsaheader,adatasection,andafooterhavingacombinedlengthofnomorethan1518bytes.TheEthernetheadercontainstheaddressesofboththeintendedrecipientandthesender.EthernetTopologiesandProtocolsDatasentovertheEthernetisautomaticallybroadcasttoalldevicesonthenetwork.BycomparingtheirEthernetaddressagainsttheaddressintheframeheader,eachEthernetdevicetestseachframetodetermineifitwasintendedforthemandreadsordiscardstheframeasappropriate(通過將它們的以太網(wǎng)地址與幀頭中的地址進(jìn)行比較，每個以太網(wǎng)設(shè)備都會測試每個幀，以確定是否適合它們，并根據(jù)需要讀取或丟棄幀).Networkadaptersincorporatethisfunctionintotheirhardware.DeviceswantingtotransmitontheEthernetfirstperformapreliminarychecktodeterminewhetherthemediumisavailableorwhetheratransmissioniscurrentlyinprogress.IftheEthernetisavailable,thesendingdevicetransmitsontothewire.It’spossible,however,thattwodeviceswillperformthistestatapproximatelythesametimeandbothtransmitsimultaneously.EthernetTopologiesandProtocolsBydesign,asaperformancetrade-off,theEthernetstandarddoesnotpreventmultiplesimultaneoustransmissions.Theseso-calledcollisions,whentheyoccur,causebothtransmissionstofailandrequirebothsendingdevicestore-transmit.Ethernetusesanalgorithmbasedonrandomdelaytimestodeterminetheproperwaitingperiodbetweenre-transmissions.Thenetworkadapteralsoimplementsthisalgorithm(以太網(wǎng)使用基于隨機(jī)延遲時(shí)間的算法來確定重新傳輸之間的適當(dāng)?shù)却龝r(shí)間。網(wǎng)絡(luò)適配器也實(shí)現(xiàn)了這個算法).IntraditionalEthernet,thisprotocolforbroadcasting,listening,anddetectingcollisionsisknownasCSMA/CD(CarrierSenseMultipleAccess/CollisionDetection).SomenewerformsofEthernetdonotuseCSMA/CD.Instead,theyusetheso-calledfullduplexEthernetprotocol,whichsupportspoint-to-pointsimultaneoussendsandreceiveswithnolisteningrequired.Figure1ShipboardNetworkMoreaboutEthernetDevicesAsmentionedearlier,Ethernetcablesarelimitedintheirreach,andthosedistances(asshortas100meters)areinsufficienttocovermedium-sizedandlargenetworkinstallations.ArepeaterinEthernetnetworkingisadevicethatallowsmultiplecablestobejoinedandgreaterdistancestobespanned.AbridgedevicecanjoinanEthernettoanothernetworkofadifferenttype,suchasawirelessnetwork.OnepopulartypeofrepeaterdeviceisanEthernethub.Otherdevicessometimesconfusedwithhubsareswitchesandrouters.Ethernetnetworkadaptersalsoexistinmultipleforms.Newerpersonalcomputersandgameconsolesfeatureabuilt-inEthernetadapter.USB-to-EthernetadaptersandwirelessEthernetadapterscanalsobeconfiguredtoworkwithmanynewerdevices.MoreaboutEthernetDevicesShipboardLANbegantoemergeinthe1980’sasship-to-shorecommunicationincreased,anditwasrecognizedthatvoyageandmachinerydataneededtobeintegratedintosship’ssystems.Thegrowthofsatellitetechnologyaswellasthekindofsophisticatedkitthatappearedonresearchandsurveyshipsincreasedthescopeofwhatcouldbe