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1、DQDBNetworkswithandwithoutBandwidthBalancingEllenL.Hahne,Member,IEEE,AbhijitK.Choudhury,Member,IEEE,andNicholasF.Maxemchuk,Fellow,IEEE.Ab.struct-Thispaperexplainswhylongdistributedqueuedualbus(DQDB)networkswithoutbandwidthbalancingcanhavefairnessproblemswhenseveraln
2、odesareperforminglargefiletransfers.Theproblemsarisebecausethenetworkcontrnlinformationissubjecttopropagationdelaysthataremuchlongerthanthetransmissiontimeofadatasegment.Bandwidthbalancingisthenpresentedasasimplesolution.Byconstraining~C'Deachnodetotakeonlyacertainf
3、ractionofthetransmissionopportunitiesofferedtoitbythebasicDQDRprotocol,band-e-.cwidthbalancinggraduallyachievesafairallocationofbandwidthamongsimultaneousfiletransfers.Wealsoproposetwowaystoextendthisprocedureeffectivelytomultiprioritytraffic.'1tromtromBCDCDToAI.IYT
4、RODUCTIONFig.1.DQDBnetworkarchikclureHEdistributedqueuedualbus(DQDB)[l]?[2]isaTmetropolitanareanctworkthathasrecentlybeenstan-dardizedbytheIEEE[3].Thedual-bustopologyisidcnticaltoasexplainedinSectionII.TheaimofDQDB'sreservationsthatusedinFasnet[4]andisdepictedinFig.
5、1.Thetwobusesistoimproveaccessfairnesswithoutthehandwidthwastagesupportunidirectionalcommunicationsinoppositedirections.ofacirculatingtoken.Moreover,byassociatingprioritylevelsNodesareconnectedtobothbusesandcommunicatebywiththesereservations,DQDBcanoffermultipriorit
6、yservice.selectingtheproperbus.InbothDQDBandFasnetaspecialUnfortunately.theDQDBreservationprocessisimperfect.unitatthehead-endofeachbusgeneratesslots:howcvcr,theThenetworkspan(upto50km),thetransmissionrate(as-protocolsforacquiringslotsdiffersignificantly.Fasnetusesa
7、sumedtobe150Mbpsinthispaper),andthcslotsize(53protocolsimilartothatofatokenring,whereeachstationisbytes)ofDQDBallowmanyslotstobeintransitbetweenthegivenanopportunitytotransmitinorder.DQDBresemblesnodes.Therefore,thenodescanhaveinconsistentviewsoftheaslottedringwithf
8、reeacccss,wherestationstransmitinreservationprocess.Ifthishappens,andiftheaccessprotocoleveryemptyslotiftheyhavedata.Bothtokenacccssandfre
