Problem-8

Problem81.TheIEEE802.3standard,knownasEthernet,nowencompassesdataratesof10Mbps,100Mbps,1Gbps,and10Gbps.Forthelowerdatarates,theCSMA/CDMACprotocolisused.Forthe1-Gbpsand10-Gbpsoptions,aswitchedtechniqueisused.2.ThemostimportantofhighspeedLansare:•FastEthernetandGigabitEthernet、FibreChannel、High-speedwirelessLANs.3.Listexamplesofrequirementsthatcallforhigher-speedLANs:•Centralizedserverfarms、Powerworkgroups、High-speedlocalbackbone4.TheearliestofIEEE802.3MediumAccessControltechniquesisALOHA.ThemaximumutilizationofpureALOHAisonlyabout18%.,andthemaximumutilizationofslottedALOHAisonlyabout37%.5.CSMAmeansCarriersensemultipleaccess.ThemaximumutilizationachievableusingCSMAcanfarexceedthatofALOHAorslottedALOHA.Themaximumutilizationdependsonthelengthoftheframeandonthepropagationtime;thelongertheframesortheshorterthepropagationtime,thehighertheutilization.6.For802.3MACframe,•Preambleisa7-octetpatternofalternating0sand1susedbythereceivertoestablishbitsynchronization.•StartFrameDelimiter(SFD)isthesequence10101011,whichindicatestheactualstartoftheframeandenablesthereceivertolocatethefirstbitoftherestoftheframe.•FrameCheckSequence(FCS)isa32-bitcyclicredundancycheck,basedonallfieldsexceptpreamble,SFD,andFCS.7.AtraditionalEthernetishalfduplex:astationcaneithertransmitorreceiveaframe,butitcannotdobothsimultaneously.Withfull-duplexoperation,astationcantransmitandreceivesimultaneously.Ifa100-MbpsEthernetraninfull-duplexmode,thecentralpointinthestarwirecannotbeasimplemultiportrepeaterbutrathermustbeaswitchinghub.Inthiscaseeachstationconstitutesaseparatecollisiondomain.Infact,therearenocollisionsandtheCSMA/CDalgorithmisnolongerneeded.8.Incomputernetworking,GigabitEthernet(GbEor1GigE)isatermdescribingvarioustechnologiesfortransmittingEthernetframesatarateofagigabitpersecond(1,000,000,000bitspersecond),asdefinedbytheIEEE802.3-2008standard.9.ThekeyelementsofaFibreChannelnetworkaretheendsystems,callednodes,andthenetworkitself,whichconsistsofoneormoreswitchingelements.Thecollectionofswitchingelementsisreferredtoasafabric.10.TheIEEEstandardusedforwirelessLANsareinfrared,spreadspectrum,andnarrowbandmicrowaveisTheIEEE802.11.11.ListsomeWirelessLANApplications:•LANextension、Crossbuildinginterconnect、Nomadicaccess、Adhocnetworks.12.Anadhocnetworkisapeer-to-peernetwork(nocentralizedserver)setuptemporarilytomeetsomeimmediateneed.13.AllcurrentwirelessLANproductsfallintooneofthefollowingtransmissioncategories:•Infrared(IR)LANs、SpreadspectrumLANs.14.ThreealternativetransmissiontechniquesareincommonuseforIRdatatransmission•Directed-beamIRcanbeusedtocreatepoint-to-pointlinks.•AnomnidirectionalconfigurationinvolvesasinglebasestationthatiswithinlineofsightofallotherstationsontheLAN.•AdiffusedconfigurationmakealloftheIRtransmittersbefocusedandaimedatapointonadiffuselyreflectingceiling.15.ThesmallestbuildingblockofawirelessLANisabasicserviceset(BSS).Foraccesstothesamesharedwirelessmedium.ABSSmaybeisolatedoritmayconnecttoabackbonenamedthroughanaccesspoint(AP).TheAPfunctionsasabridgeandarelaypoint.WhenallthestationsintheBSSaremobilestations,withnoconnectiontootherBSSs,theBSSiscalledanindependentBSS(IBSS).Anextendedserviceset(ESS)consistsoftwoormorebasicservicesetsinterconnectedbyadistributionsystem.16.TheIEEE802.11MAClayercoversthreefunctionalareas:•reliabledatadelivery,accesscontrol,andsecurity.17.Carriersensemultipleaccesswithcollisionavoidance(CSMA/CA)incomputernetworking,isanetworkmultipleaccessmethodinwhichcarriersensingisused,butnodesattempttoavoidcollisionsbytransmittingonlywhenthechannelissensedtobeidle.ThisprotocoloperatesintheDataLinkLayer(Layer2)oftheOSImodel.