-57--58--59-DesignArchitecturesfor3GandWLANIntegrationWeiWeiLiZhao(NationalKeyLabofIntegratedServiceNetworks,XidianUniversity,XiÕan710071)AbstractWereview3GWLANintegrationarchitecturesandinvestigatetwosucharchitecturesinthecasewhentheUMTSnetworkisconnectedtoaWLANnetworkatdifferentintegrationpoint,namelytheSGSNandtheGGSN.AfterexplainingofhowtosimulatethesearchitecturesusingOPNET,wecometotheconclusionoftheirperformance.Keywords3G,WLAN,SGSN,GGSN,OPNET,attachprocedure