Problem-7

Problem71.ALANconsistsofasharedtransmissionmediumandasetofhardwareandsoftwareforinterfacingdevicestothemediumandregulatingtheorderlyaccesstothemedium.2.ThetopologiesthathavebeenusedforLANsarering,bus,tree,andstar.3.PersonalComputerLANsisacommonLANconfigurationthatsupportspersonalcomputers.4.Backendnetworksareusedtointerconnectlargesystemssuchasmainframes,supercomputers,andmassstoragedevices.Thekeyrequirementhereisforforbulkdatatransferamongalimitednumberofdevicesinasmallarea.5.ASANisaseparatenetworktohandlestorageneedswhichdetachesstoragetasksfromspecificserversandcreatesasharedstoragefacilityacrossahigh-speednetwork.6.ThekeyelementsofaLANareTopology,Transmissionmedium,Wiringlayout,Mediumaccesscontrol.7.Inthecontextofacommunicationnetwork,thetermtopologyreferstothewayinwhichtheendpoints,orstations,attachedtothenetworkareinterconnected.Busischaracterizedbytheuseofamultipointmedium.Thetreetopologyisageneralizationofthebustopology.Thetransmissionmediumisabranchingcablewithnoclosedloops.RingTopologyconsistsofasetofrepeatersjoinedbypoint-to-pointlinksinaclosedloop.StarTopologyInthestarLANtopology,eachstationisdirectlyconnectedtoacommoncentralnode.8.Thechoiceoftopologydependsonavarietyoffactors,includingreliability,expandability,andperformance.9.Thechoiceoftransmissionmediumisdeterminedbyanumberoffactors.Itis,weshallsee,constrainedbythetopologyoftheLAN.Otherfactorscomeintoplay,including•Capacity:tosupporttheexpectednetworktraffic•Reliability:tomeetrequirementsforavailability•Typesofdatasupported:tailoredtotheapplication•Environmentalscope:toprovideserviceovertherangeofenvironmentsrequired10.ProtocolsdefinedspecificallyforLANandMANtransmissionaddressissuesrelatingtothetransmissionofblocksofdataoverthenetwork.Thephysicallayerprovidesfunctionsas•Encoding/decodingofsignals•Preamblegeneration/removal(forsynchronization)•Bittransmission/receptionMediumaccesscontrol(MAC)providesfunctionsas•Ontransmission,assembledataintoaframewithaddressanderrordetectionfields.•Onreception,disassembleframe,andperformaddressrecognitionanderrordetection.•GovernaccesstotheLANtransmissionmedium.logicallinkcontrol(LLC)layerprovidesaninterfacetohigherlayersandperformflowanderrorcontrol.11.Thekeyparametersinanymediumaccesscontroltechniquearewhereandhow.Wherereferstowhethercontrolisexercisedinacentralizedordistributedfashion.Thesecondparameter,how,isconstrainedbythetopologyandisatradeoffamongcompetingfactors,includingcost,performance,andcomplexity.Theapproachcanbefurthersubdividedintothreecategories:roundrobin,reservation,andcontention.12.ThefieldsofMACframeareMACControl,DestinationMACAddress,SourceMACAddress,LLC,CRC.13.IntheIEEEaddressingscheme,eachaddressconsistsof48bits.TheIEEEaddressingsupportsthreetypesofaddresses:unicast,broadcast,multicast.14.WecanuseASCIIcharactersettheStartOfHeader(SOH)charactermarksthebeginningofaMACframeandtheEndOfTransmission(EOT)charactermarkstheend.15.Physicalnetworksegmentwheredatapacketscancollidewithoneanotherifmorethanonestationsendpackets.Segmentsconnectedbyrepeatersareinthesamecollisiondomain.16.AbridgeisamechanismthatconnectstwoLANsegmentswhichlistensinpromiscuousmodeoneachsegment.Mostbridgesarecalledbecausetheylearnthelocationsofcomputersautomatically.17.BroadcastDomainsmeansphysicalnetworkinwhichallnodescanreacheachotherbybroadcastatthedatalinklayer.Anetworkformedbyrepeaters,hubs,bridges,layer2switcheshasthesamebroadcastdomain.Bridgesandswitchesdividethecollisiondomain.Routersdividethebroadcastdomain.18.ALayer2switchisadeviceusedonacomputernetworktophysicallyconnectdevicestogether.Twotypesoflayer2switchesareavailableascommercialproducts:Store-and-forwardswitch,Cut-throughswitch.19.Virtuallocalareanetworks(VLANs)areGroupofdevicesononeormoreLANsthatareconfigured(usingmanagementsoftware)sothattheycancommunicateasiftheywereattachedtothesamesegment,wheninfacttheyarelocatedonanumberofdifferentLANsegments.20.Layer3switchesarerouterswithfastforwardingdoneviahardware.TheroutersrunroutingprotocolssuchasOpenShortestPathFirst(OSPF)orRoutingInformationProtocol(RIP)tocommunicatewithotherLayer3switchesorroutersandbuildtheirroutingtables.