The RTDEVSCORBA Environment for Simulation-Based D

TheRTDEVS/CORBAEnvironmentforSimulation-BasedDesignOfDistributedReal-TimeSystemsYoungK.Cho**,XiaolinHu*,andBernardP.Zeigler**ArizonaCenterforIntegrativeModelingandSimulation,Dept.ofElectricalandComputerEngineering,UniversityofArizona,Tucson,AZ,USA85721**RepublicofKoreaAirForce,Nonsancity,Choongnam,Korea320-913AbstractTheincreasingcomplexityoflarge-scaledistributedrealtimesystemsdemandspowerfulrealtimeobjectcomputingtechnologies.Furthermore,systematicdesignapproachesareneededtosupportanalysis,design,test,andimplementationofthesesystems.Inthispaper,wediscussRTDEVS/CORBA,animplementationofDEVSmodelingandsimulationtheorybasedonrealtimeCORBAcommunicationmiddleware.WithRTDEVS/CORBA,thesoftwaremodelofacomplexdistributedrealtimesystemcanbedesignedandthentestedinavirtualtestingenvironmentandfinallyexecutedinarealdistributedenvironment.Thismodelcontinuityandsimulation-baseddesignapproacheffectivelymanagessoftwarecomplexityandconsistencyproblemsforcomplexsystemsandincreasestheflexibilityfortestconfigurationsaswellasreducesthetimeandcostfortesting.Inthepaper,thelayeredarchitectureanddifferentimplementationissuesofRTDEVS/CORBAarestudiedanddiscussed.AnexampleapplicationisthengiventoshowhowRTDEVS/CORBAsupportsaframeworkformodelcontinuityindistributedrealtimemodelingandsimulation.KeyWordsDistributedrealtimesystems,modelingandsimulation,DEVS,CORBA,modelcontinuity,simulation-baseddesign,virtualtestingenvironment1.IntroductionDistributedreal-timeobjectcomputingtechnologieshavebeenattractinglotsofattentioninthereal-timecomputingareaduringrecentyears.Becauseoftheeffectiveobject-orientedmethodologieswhichenableengineerstoreducethedevelopmentcomplexityandmaintenancecostsoflargescalesoftwareapplications,object-orientedcomputingtechnologyhasbeensuccessfullyappliedtonon-real-timesoftwaresystems.However,real-timesystemengineeringtechniqueshavenotfullyadoptedtheconceptofmodulardesignandanalysiswhicharethemainvirtuesofobject-orienteddesigntechnologies.Asaconsequence,thedemandforobject-orientedanalysis,design,andimplementationoflarge-scalereal-timeapplicationshasbeengrowing.ThispaperproposesthataDEVS-basedreal-timemodelingandsimulationenvironmentcanprovidecapabilitiesrequiredbyreal-timesystemengineering.DEVS(DiscreteEventSystemSpecification)isasoundformalmodelingandsimulation(M&S)frameworkbasedongenericdynamicsystemsconcepts[1].DEVSisamathematicalformalismwithwell-definedconceptsofhierarchicalandmodularmodelconstruction,couplingofcomponents,supportfordiscreteeventapproximationofcontinuoussystemsandanobject-orientedsubstratesupportingrepositoryreuse.DEVSisnot,however,ajustmathematicalframeworkbutalsoapracticalM&Stoolimplementedinvariousobject-orientedlanguagessuchasScheme,C++,andJava.RecentlyDEVSmodelingandsimulationenvironmentsalsohavebeencombinedwithmidddlewareslikeHLA(HighLevelArchitecture)RTI(RuntimeInfrastructure)andCORBA(CommonObjectRequestBrokerArchitecture)tosupportfastandeasyconstructionofdistributedmodels,andsimulationofsuchmodels.TheseDEVS-basedmodelingandsimulationenvironmentshavebeenshowntosupportaneffectivemodelingandsimulationmethodologyinvariousapplicationareasincludingdesignandimplementationofreal-timecontrolsystems[2].Real-timesystemsdesignconnotesanapproachtosoftwaredesigninwhichtimeliness(ortimingcorrectness)isasimportantasthecorrectnessoftheoutputs(orlogicalcorrectness)[3,4].Timelinessofresponsedoesnotnecessarilyimplyspeed--although,thismaybeimportant--asmuchaspredictabilityofresponseandreliableconformancetodeadlines.Forrealtimesystems,performanceestimationtoguaranteethesystemunderdesigntomeetperformancerequirementsarecrucial.Performanceanalysisoftenconcernsschedulability,checkingofthetaskscheduleforfeasibilityorconformancewiththerequiredtimingconstraints.Indistributednetworkedsystems,qualityofservice(QoS)characteristics,suchasthetimelydeliveryofeventsbetweensystemcomponentsorpriority-basedbandwidthutilization,mustnecessarilybeincludedinperformanceevaluation.Tosupportthedesignandperformanceevaluationfordistributedrealtimesystem,modelingandsimulationtechnologiesaredeveloped.Real-timeconsiderationsenterintotheworldofmodelingandsimulationinvariousways.Areal-timesimulationisareal-timesystemwheresomeportionoftheenvironmentorportionsofthereal-timesystemitself,arerealizedbysimulationmodels[5].Whenasimulationmodelinteractswithasurroundingenvironment,suchassoftwaremodules,hardwarecomponentsorhumanoperators,thesimulatormusthandleexternaleventsfromitsenvironmentinatimelymanner[6].Inmoregeneralterms,interfacingofabstractmodelswithrealworldprocessesrequiresthatthe(logical)timebaseofthesimulationbesynchronizedascloselyaspossibletotheclocktimeoftheunderlyingcomputersystem[2].Workrelatedtoreal-timesimulationandcontrolincludesearlyresearchinDEVS-Scheme[2],theextensionoftheDiscreteEventSystemSpecification(DEVS)formalismtotheDEVSReal-timeFormalism[6]anditsapplicationtoprocesscontrol[17].CurrentprojectsincludePORTS:AParallel,Optimistic,Real-TimeSimulation[5],OPERA(OperatorsTrainingDistributedReal-TimeSimulation)[7],Ptolemy(ConcurrentDis