The convergence of heterogeneous wireless networks combines existing wireless networks. An effective combination of different wireless networks should enable them to complement each other and provide high-speed data rate, wide area coverage, and quality of service (QoS) guarantee. In Next Generation Wireless Systems (NGWS), seamless handoff between different wireless access networks plays a vital role. One of the major challenges for seamless mobility is the creation of a vertical handoff protocol. In this paper, the performance of vertical handoff is studied using the integration of third generation (3G) cellular and wireless local area networks (WLAN). The effect of application-based signal strength threshold (ASST) and path loss exponent on an adaptive lifetime-based vertical handoff (ALIVE-HO) strategy is studied in terms of number of handoffs, aggregated throughput, and packet delay. Therefore the vertical handoff performance can be optimized in wireless and mobile networks. The present work is done for different channel conditions as well as different mobility schemes.