ThispaperproposesaformalapproachtoprotocolperformancetestingbasedontheextendedconcurrentTTCN,Tomeettheneedsofprotocolperformancetesting,concurrentTTCNisextended,andtheextendedconcurrentTTCN'soperationalsemanticsisdefinedintermsofInput-OutputLabeledTransitionSystem.Anarchitecturedesignofprotocolperformancetestsystemisdescribed,andanexampleoftestcasesanditstestresultaregiven.