Abstract: The next generation mobile networks have the development trend of integration of cellular networks and Wireless Local Area Networks (WLAN).Considering the heterogeneous environment, Universal Mobile Telecommunication System (UMTS) of cellular technology and WLAN (over IEEE 802.11) are the most promising networks. Integration of these two networks facilitate user for the seamless communication. Handoff decision making is the main challenging issue in the integration of UMTS and WLAN networks.Efficient vertical handoff algorithms are required to maintain the acceptable level of quality and seamless connectivity in heterogeneous wireless environment. Various metrics have been considered such as bandwidth, energy, traffic, distance, monetary cost to make handoff decision.A novelhandoff decision making algorithm using fuzzy rule for meeting the requirements of heterogeneous networks is proposed in this paper.WLAN and UMTS are considered as two integrated network entities.Handoff decision metrics for the proposed algorithm are energy, traffic and cost. The algorithm allows the mobile terminal to have the seamless connection with most energy efficient and cost effective network weighted with the handoff metrics such as energy, traffic and cost.

Keywords: WLAN, UMTS, Heterogeneous Wireless Networks, Vertical Handoff.