Real-time TTCN for testing real-time and

Real-timeTTCNfortestingreal-timeandmultimediasystemsThomasWalterSwissFederalInstituteofTechnologyZurich,ComputerEngineeringandNetworksLaboratory(TIK)CH-8092Zurich,Switzerland,Tel:[phone],Fax:[phone],e-mail:[e-mail]iversityofLübeck,InstituteforTelematicsRatzeburgerAllee160,D-23538Lübeck,Germany,Tel:[phone],Fax:[phone],e-mail:[e-mail]efinereal-timeTTCNandapplyittoseveralapplications.Inreal-timeTTCN,statementsareannotatedwithtimelabelsthatspecifytheirearliestandlatestexecutiontimes.ThesyntacticalextensionsofTTCNarethedefinitionofatableforthespecificationoftimenamesandtimeunits,andtwonewcolumnsinthedynamicbehaviourdescriptiontablesfortheannotationofstatementswithtimelabels.Wedefineanoperationalsemanticsforreal-timeTTCNbymappingreal-timeTTCNtotimedtransitionsystems.Alternatively,weintroducearefinedTTCNsnapshotsemanticsthattakestimeannotationsintoaccount.KeywordsConformancetesting,TTCN,testcases,real-timetesting1INTRODUCTIONTesting,ortobepreciseconformancetesting,isthegenerallyappliedprocessinval-idatingcommunicationsoftware.Aconformancetestingmethodologyandframe-work(ISO9646-11994)havebeenestablishedwithinthestandardizationbodiesofISOandITU.Anessentialpartofthismethodologyisanotation,calledTTCN(TreeandTabularCombinedNotation)(ISO9646-31996),forthedefinitionofconfor-mancetestcases.TTCNhasbeendesignedfortestingsystemsforwhichingeneraltimingbetweencommunicatingentitieshasnotbeenanissue.Testcasesarespeci-fiedassequencesoftesteventswhichareinputandoutputeventsofabstractserviceprimitives(ASP)orprotocoldataunits(PDU).Therelativeorderingoftesteventsisdefinedinatestcasebehaviourdescription.Thesituationischangingnow.Wecanidentifytwomainnewkindsofdistributedsystems:firstly,real-timesystemswhichstemfromtheuseofcomputersforcon-trollingphysicaldevicesandprocesses.Forthesesystems,real-timecommunicationisessentialfortheircorrectbehaviour.Secondly,multimediasystemswhichinvolvethetransmissionofseveralcontinuousstreams(ofbits)andtheirtimelyreproduction(e.g.,synchronizationofaudioandvideo).However,aspointedoutin,e.g.,(Atesetal.1996),TTCNisnotanappropriatetestnotationfortestingreal-timeandmulti-mediasystems:Firstly,testeventsinTTCNareformessage-basedsystemsandnotforstream-basedsystems.Secondly,inTTCNreal-timecanonlybeapproximated.Inthispaperwedefineareal-timeextensionofTTCNasacontributionforsolvingthesecondproblem.OurextensionofTTCNtoreal-timeTTCNisonasyntacticalandasemanticallevel.Thesyntacticalextensionisthatweallowanannotationoftesteventswithanearliestexecutiontime(EET)andalatestexecutiontime(LET).Informally,atesteventmaybeexecutedifithasbeenenabledforatleastEETunitsanditmustbeexecutedifithasbeenenabledforLETunits.Forthedefinitionofanopera-tionalsemanticsofreal-timeTTCNweusetimedtransitionsystems(Henzingeretal.1991).Anumberoftechniquesforthespecificationofreal-timeconstraintshavebeenproposedwhicharebesidesothers:timePetriNets(Berthmieuetal.1991,Merlinetal.1976)andextensionsofLOTOS(Bowmanetal.1994,Hogrefeetal.1992,Léonardetal.1994,Quemadaetal.1987),SDL(Hogrefeetal.1992,Leue1995)andESTELLE(Fischer1996).Asinthecitedliterature,ourapproachallowsthetim-ingofactionsrelativetotheoccurrenceofpreviousactions.Thedifferencebetweenthecitedapproachesandoursisthatreal-timeTTCNisahybridmethodusedforthespecificationofpropertiesoftestsystemsandrequirementsonimplementationsundertest(IUT).Section2givesabriefintroductiontoTTCN.Section3explainsreal-timeTTCN.TheapplicabilityofourapproachisshowninSection4.Section5concludesthepaperwithanassessmentofourworkandthediscussionofopenissues.2TTCN-TREEANDTABULARCOMBINEDNOTATIONTTCNisanotationforthedescriptionoftestcasestobeusedinconformancetesting.ForthepurposeofthispaperwerestrictourattentiontoTTCNconceptsrelatedtothedescriptionofthedynamictestcasebehaviour.FurtherdetailsonTTCNcanbefoundin:(BaumgartenandGiessler1994,BaumgartenandGattung1996,ISO9646-31996,Kristoffersenetal.1996,Linn1989,Probertetal.1992,Sarikaya1989).2.1AbstracttestingmethodsandTTCNAtestcasespecifieswhichoutputsfromanIUTcanbeobservedandwhichinputstoanIUTcanbecontrolled.Inputsandoutputsareeitherabstractserviceprimi-tives(ASPs)orprotocoldataunits(PDUs).Ingeneral,severalconcurrentlyrunningdistributedtestcomponents(TC)participateintheexecutionofatestcase.TCsareinterconnectedbycoordinationpoints(CPs)throughwhichtheyasynchronouslyex-changecoordinationmessages(CMs).TCsandIUTlogicallycommunicatebyex-changingPDUswhichareembeddedinASPsexchangedatpointsofcontrolandobservation(PCOs),whichareinterfacesaboveandbelowtheIUT.SinceinmostcasesthelowerboundaryofanIUTdoesnotprovideadequatePCOinterfaces,TCsandIUTcommunicatebyusingservicesofanunderlyingserviceprovider.2.2TestcasedynamicbehaviourdescriptionsThebehaviourdescriptionofaTCconsistsofstatementsandverdictassignments.AverdictassignmentisastatementofeitherPASS,FAILorINCONCLUSIVE,concerningtheconformanceofanIUTwithrespecttothesequenceofeventswhichhasbeenperformed.TTCNstatementsaretestevents(SEND,IMPLICITSEND,RECEIVE,OTHERWISE,TI