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The 3rd Generation Partnership Project (3GPP) has adopted an interworking architecture between Universal Mobile Telecommunication System (UMTS) and Wireless Local Area Networks (WLANs). This architecture imposes a set of security requirements on subscribers connecting from within interworked WLANs to be able to access their 3G home packet-switched services. Providing seamless handoff and session continuity of ongoing communication is a critical task in UMTS/WLAN integrated networks. However, the 3GPP does not specify how mobility can be supported. This paper provides a performance evaluation for the three candidate solutions: Mobile IP (MIP), Session Initiation Protocol (SIP), and mobile Stream Control Transmission Protocol (mSCTP) that may be used to provide session continuity in the integrated network. The vertical handoff delay figure is analyzed using simulations for different WLAN speeds and its major components due to the involved signaling procedures are quantified. The results are derived from our developed OPNET based simulation model that accounts for the detailed prescribed signaling procedures as per the related standards and Request for Comments (RFCs) documents, and the main network entities in the adopted architecture. The presented analysis provides insight into the potential performance bottlenecks in the integrated network. Major findings of the work show that the security related signaling and the signaling pertaining to obtaining a new Internet Protocol (IP) address, each contribute about 40% of the total delay for all the three solutions. Enhancements targeting these procedures will help reduce the overall delay while supporting seamless handoff between the two networks.