1 MULTIMEDIA CAPABILITIES IN DISTRIBUTED REAL-TIME

1MULTIMEDIACAPABILITIESINDISTRIBUTEDREAL-TIMEAPPLICATIONSSubhabrataSen,OscarGonzalez,KrithiRamamritham,JohnA.Stankovic,ChiaShen*andMorikazuTakegaki**DepartmentofComputerScienceUniversityofMassachusettsAmherst,MA01003*AMitsubishiElectricResearchLab**MitsubishiElectricCorporationABSTRACTInthispaper,weconsidertheproblemsandbenetsofdevelopingtheinfrastructureneededtohandlethetimingrequirementsofareal-timeindustrialcontrolapplicationandtheprocessingofmultimediastreams.Inparticular,thispaperexploresvariousapplicationscenarioswhichcanbenetfromareal-timecontrolsystemintegratedwithmultimedia.Weproposeahigh-levelarchitecturebasedonopensystemsandidentifykeyresearchissuesatthesystemanddatabaselevelsthatmustbeaddressedinordertoincorporatemultimediacapabilitiesintoadistributedindustrialcontrolapplication.Areal-timemultimediadatabaseisakeycomponentinthisplatformanditcanaidbothinreal-timecontrolandinthedecisionmakingprocessatthemanagementlevel,potentiallyresultinginreducedcostsandimprovedoperationofanindustrialplant.1INTRODUCTIONDistributedreal-timeindustrialcontrolapplicationscanbenetsignicantlyfromtheincorporationofmultimediainformationintothecontrolenvironment.Potentialbenetsofsuchsystemsincludeenablingmoreintuitivevisualizationofthestateofthecontrolprocess,resultinginimprovedqualityand/orsafetyoftheprocess,betterdecisionmakingatboththemanagementandsupervisoryoperatorlevels,aswellasdistancecollaborativeplanning,designandeective12Chapter1troubleshooting.Thus,theprocessingandanalysisofdierenttypesofmul-timediainformationprovidesawiderrangeofcapabilitiestodierententities(e.g.,operation,maintenance,training,andadministration)withinacompanythanispossiblenow.Recentadvancesincomputertechnology,highspeednetworks,highcapacitystorageandinnovativesensorsmakeitpossibletore-alizesuchenhancedcontrolsystems.Thegoalsofthischapteraretoexaminereal-timecontrolapplicationsthatcanexploitmultimediacapabilitiessoastodeterminetheirrequirements,toidentifykeyresearchissuesatthesystemanddatabaselevels,andtoproposeagenericarchitecturefortheseapplications.1.1InadequaciesofCurrentPracticesWhenwestudywaystoaddmultimediacapabilitiestotoday’scontrolsystems,wequicklyrealizethatmodicationsorextensionstoalargenumberofcurrentdistributedplantcontrolsystemsisnotfeasible.Thesesystemshavebeenbuiltmostlywithproprietarynetworkcomponentsandhostsystems,andreal-timeconstraintsarepartiallymetthroughphysicalisolationofsub-networks.Inordertoguaranteetheplantcontroltimingconstraints,theworkstationssupportingthehumaninterfaceorplantinformationmanagementoftendonotresideonthesamephysicalnetworkasthenetworkinthecontrolledplantsite.Recently,limitedmultimedia(particularlyvideo)capabilitieshavebeenincorporatedinsomeindustrialplantsbytheadditionofaseparatephysicalnetworkforvideotransmissionfromindustrialTVcameras.Figure1portraysatypicalexampleofcurrentindustrialcontrolsystems[7,6].Thenetworkarchitecturecontainstwolayers,acontrollayerandaninformationlayer.ThenetworkbusinthecontrollayerisFDDI-compliant,connectingto-getherproprietarysubsystemssuchasprogrammablelogiccontrollers(PLCs),andoperatorstations(OPs).Aproprietaryprotocol,calledcyclictransmis-sion,isusedtoachieveguaranteedend-to-enddelaysinthecontrollayeramongthesubsystems.Underthisprotocol,eachsubsysteminthecontrollayerhasaxedamountoftimewithinaperiodiccycletobroadcastinformation.Theinformationlayeremploysstandardgeneralpurposecomponentsforlowcost.ThislayercontainsanEthernetLANandanumberofEngineerWorkstations(EWS).TheEWSshandleplantinformationmanagement,plantmaintenance,andreportgeneration.Someoftheproblemswithsuchatwolayersystemarchitectureare:MultimediainDistributedReal-TimeApplications3PLCFieldbusControlbus(FDDIbased)PLCPLCDataloggerGatewayOPSEWSEWSEWSReport-generationMaintenanceSensors/ActuatorsInformationmanagementGeneralpurposeLAN(ex.Ethernet)AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAInformationlayerControllayerEWSMonitoringPost-analysisOperatingFigure1ArchitectureofCurrentIndustrialControlSystemsFixedQualityofService(QoS):TheQoSisxedbythecyclictrans-missionperiodandcannotbealteredaccordingtodynamicapplicationrequirements.Hierarchicallylayerednetwork:Gatewaysareemployedtoconnecttheinformationlayerandthecontrollayer.Thegatewayscanbeasystembottleneckforperformanceandreliability.Additionalinadequaciesofsuchanarchitecturearepointedoutin[7].Conse-quently,thesedistributedplantcontrolsystemsareinexible,expensive,anddiculttomodify.Theintegrationofmultimediaandtraditionalreal-timeapplicationshasbeenattemptedaspartoftheMercuriproject[3]wheredatafromremotevideocam-erasistransferredthroughanATMnetworkanddisplayedusingXwindows,buttheyprovideonlybesteortservices.ThePrestoproject[4]dealswithprovidingsession-basedQoSguaranteestocontinuousmultimediadatabaseap-plicat