To provide service anywhere and at anytime, there is a strong demand for integration of two promising technologies; UMTS and WLAN. By integrating these two, the user can have the benefits of using both technologies. The WLAN is capable of providing high data rate at low cost. However, its services are limited to a small geographical area. UMTS networks coverage area is wider, however, cost is high and the data rate provided does not fulfill the requirements of bandwidth intensive applications. Integration of these two technologies can provide ubiquitous connectivity and high data rate to wireless clients. This paper focuses on the different integration mechanisms of tight coupling i.e. connecting WLAN with GGSN and SGSN at the UMTS core packet based network. Moreover, it has been observed that the performance of G GSN-WLAN integration is better than SGSN-WLAN integration mechanism for all the applied services. © 2010 IEEE.