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(QoS)20084(QoS)UDC10497(QoS)TheoreticalResearchofQualityofService(QoS)inComputerNetworks200852008520084I(QoS)QoSIETFQoSQoSQoSTCPQoSQoSQoSQoSQoSQoSQoSIIABSTRACTWiththetechnologyimprovementofcomputercommunicationandmultimediacoding,realtimecommunicationsuchasaudioandvideoisintroducedtonetworksandbecomeadominantwayofcommunication.Buttherearestillquitealotofproblems;wecallthemQualityofServe”(QoS).HowtoprovideQoStocomputercommunicationnetworksisbecomingmoreandmoreimportanttous.There’relotsofresearchworksforprovidingQoS,basedontheseworks,wefirstfocusontheQoSmodelsdefinedbyIETF,andanalyzethecharacteristicsofthem.Sinceasinglemodelalwayshasdrawbacks,soweusuallycombinedthesemodelsinpracticaluse.Followingworksarefocusedonthemechanismsofthenetworknode,whichisaveryimportantpartofthisthesis.Thewordnodewementionedisconsideredasboththeendnodeandthenetworkrouter.Asanendnode,weprovidetheflowcontrolandcongestioncontrolmechanismsbasedonTCPprotocol,whichiswidelyused.Innetworkrouters,wemainlyprovidesomeothermechanismstoguaranteeQoS,includingconnectioncontrol,buffermanagement,trafficshaping,andcongestioncontrol.Finally,weworkontheschedulingmechanismsforQoS-capablerouters.Comparingwithotherreferences,themaindifferenceisthatwetakemostefforttothealgorithmsnotthemodels,andverifiedtheconclusionsbasedonsimulations.Furthermore,thecodingmethodofsimulationissocalled“EventScheduling”,nottheexistingsoftware;therefore,it’sbetterforthedetailedunderstandingofthesealgorithms,whichisanotherdifferencewithotherreferences.Untilnow,QoSisstillanopenfieldforresearching,andthere'restillmanyactivetopicstobediscussed.Intheendofeachchapter,webringforwardtheadvancedworkwe'llbefacingandhopeQoSwillhaveabrightwayincomputercommunicationnetworks.Keywords:QualityofService,QoSmodel,nodeQoScontrol,schedulingalgorithms,inputqueueIIIIV111.1InternetFTPE-mailTCP/IP(QualityofService,QoS)QoSQoS2080SeitzWortendykeARPANETX.25QoSQoS2080B-ISDNATMQoSQoS-AXRMTINA-CTENETIBMHeiProjectInternetInternetQoSIETF19979QoSRFCInternetQoS(integratedservices,IntServ)2(differentiatedservicesDiffServ)QoSQoSQoSQoS1.2QoSQoSQoSRFC2386QoSQoSQoSQoSFTP0.2-10MbpsTelnet=800ms16kbps0-150ms1ms=1e-2=1Gbps()500Mbps()20Mbps()250ms1ms=1e-2()HDTV=1e-11()(QoS)QoS3QoS1.3QoSQoSQoS(Delay)(Throughput)(Droprate)ComplexityQoSQoS1.4QoS4QoSQoSQoSIETFInternetQoS(IntServ)(DiffServ)QoS(ConnectionAdmissionControl)(TrafficShaping)(QueueBufferManagement)TCPQoSQoS(InputQueue/OutputQueue)QoS52InternetFTPEmailQoSQoSQoSQoS(IETF)(IntServ)(DiffServ)2.1IntServ(RSVP)IntServ(RSVP)2.1.1RSVPRSVPIPQoSRSVPRSVPRSVPPATHPATH(T-Spec)RSVP6RSVPPATHPATH(RSVP)CAC(ERROR)RSVPRSVP2-1RSVP2-1RSVPIntServIntServIntServ(Classifier)IP(ConnectionAdmissionControl)7QoSRSVPInternetRSVP(Scheduling)RRWFQVCWRRIntServIntServ(BestEffort)IntServ(GuaranteedServicesGS)GS8(ControlledloadServiceCLS)CLSIntServIntServIntServQoSRSVPRSVPRSVPPATHRSVPIntServQoSunicastmulticastRSVPPATHPATHRSVPIntServIntServRSVPInternet(Hop-By-Hop)QoSRSVPIntServRSVPRSVPREFRESH9QoSIntServRSVPQoSIntServWEBQoSIntServIntServIntServ2.2IntServDiffServ)1998IETFDiffServIntServIntServDiffServDiffServDiffServIPInternet)QoS10DiffServDiffServER:EdgeRouter(CR:CoreRouter)DiffServDiffServIPv4TOS(TypeofService)IPv6TC(TrafficClass)DSDS6bitDSCP(DiffServCodePoint)2bit(CurrentUnused,CU)IPv4(Header)DSCP2-4IPv4DSCP11(ER)DSCPDSCPPHB,PerHopBehaviorDiffServER(InternetServiceProvider,ISP)DSCPDiffServCRDSCPDiffServDSCPDiffServERCRCR(corestateless)DiffServDiffServ2-3DiffServDiffServDiffServDiffServDSCP(PHB)ExpeditedForwardingEF)(AssuredForwardingAF)(BestEffortDefault)EFPHB12EFEFEFPHBQoSDiffServEFPHBDSCPAFPHBAFAFUDPTCPAFDSCPAFPHBDSCPClass1Class2Class3Class4LowDropAF11=001010AF21=010010AF31=011010AF41=100010MedDropAF12=001100AF22=010100AF32=011100AF42=100100HighDropAF13=001110AF23=010110AF33=011110AF43=100110AFPHBAFPHBAFQoSEFDSCP000000IPDiffServDiffServIntServ/RSVPDiffServDiffServDiffServDiffServDiffServDiffServQoS13DiffServDSCPDiffServIntServDiffServQoSDiffServToSQoSDiffServQoSQoS2.3IntServDiffServInternetQoSIntServDiffServIntServDiffServIPDSCP(PHB)QoSQoSIntServDiffServQoS[53][55]QoSQoS143QoSQoS3.1(CAC)CACCAC(1)QoS(2)QoSCACCACCACCACCACQoS≤−∑15(PeakRate)(AverageRate)(Equivalentbandwidth)QoS(CBR)CACPeakRateCACCBRQoSCAC(VBR)CACCACVBRCACQoSQoSCACCAC()ii≤−∑()ii≤−∑16CACCACCACCAC3-1CACCACCACExponentialAveraging)[52]QoSQoSQoS(TrafficShaping)3.2QoS173.2.1(LeakyBucket)(TokenBucket)3-23-2β183.2.2(EventsScheduling)M=20B=10R=2ρ(Events)(arrivalofpacket)(arrivaloftoken)(departure)3-3Tia???193-43-5C(Event)C?11??20voidarrivalofpacket(void){Timedelta;Record*rec;determinedeltaaccordingsomeassumption;schedule(ARRIVAL_PKT,current_time+delta);buffer++;if(buffer=B)nr_pkt_loss++;else{rec=new_record();rec-arrival=current_time;if(queue==NULL)if(nr_token!=NULL){in_list(&queue,rec);schedule(DEPARTURE,current_time+departuretime);}elsein_list(&queue,rec);return;}voidarrivaloftoken(void){Timedelta2;determinedelta2accordingsomeassumption;schedule(ARRIVAL_TOKEN,current_time+delta2);nr_token++;if(nr_token=M)nr_token--;return;}voiddeparture(v