While studies specifying generic integration architectures are abundant, little or no studies are dedicated for applications performance over such heterogeneous networks. The purpose of this research is to evaluate the performance of integrated UMTS and WLAN network by using two types of standard integrated models proposed by 3GPP,open coupling and loose coupling together with network layer mobility management scheme such as Mobile IP.In this research we calculate the different application‘s traffic our concluded results shows that page response time is smaller for loose coupling scheme as compare to open coupling scheme although difference is not so much wide, pageresponse time increases with the passage of time because number of users increases as the time passes. Same is In case for FTP, download response time for FTP is smaller in case of loose coupling scheme. We have also calculated the WLAN performance parameters (delay and throughput) and UMTS downlink traffic sent and received. We have discussed in detail architecture and functionalities of UMTS and WLAN, mobile IP, standard interworked UMTS and WLAN models proposed by 3GPP.