简介:Thispaperdealswithadiscrete-timeGeo/Geo/1queueingsystemwithworkingbreakdownsinwhichcustomersarriveatthesysteminvariableinputratesaccordingtothestatesoftheserver.Theservermaybesubjecttobreakdownsatrandomwhenitisinoperation.Assoonastheserverfails,arepairprocessimmediatelybegins.Duringtherepairperiod,thedefectiveserverstillprovidesserviceforthewaitingcustomersatalowerservicerateratherthancompletelystoppingservice.Weanalyzethestabilityconditionfortheconsideredsystem.Usingtheprobabilitygeneratingfunctiontechnique,weobtaintheprobabilitygeneratingfunctionofthesteady-statequeuesizedistribution.Also,variousimportantperformancemeasuresarederivedexplicitly.Furthermore,somenumericalresultsareprovidedtocarryoutthesensitivityanalysissoastoillustratetheeffectofdifferentparametersonthesystemperformancemeasures.Finally,anoperatingcostfunctionisformulatedtomodelacomputersystemandtheparabolicmethodisemployedtonumericallyfindtheoptimumservicerateinworkingbreakdownperiod.