<Paper No.>/1 A Smart Decision Model for Vertical Handoff Ling-Jyh Chen * , Tony Sun * , Benny Chen * , Venkatesh Rajendran † , Mario Gerla * * Department of Computer Science, University of California at Los Angeles, Los Angeles, CA 90095, USA † Department of Computer Engineering, University of California at Santa Cruz, Santa Cruz, CA 95064, USA {cclljj, tonysun, cudokido, gerla}@cs.ucla.edu, venkat@soe.ucsc.edu Abstract – As mobile computing increases in prevalence and popularity, it is becoming increasingly important to have a vertical handoff solution, which can perform a vertical handoff seamlessly and smartly. In this paper, we propose a Smart Decision Model to decide the “best” network interface and “best” time moment to handoff. A score function is utilized in the model to make the smart decision based on various factors, such as the properties of available network interfaces, the system information, and the user preferences. A USHA based testbed is created to evaluate this model in various scenarios, and the results show that our model is feasible and helpful in mobile computing scenarios. Additionally, this model is simple and also applicable to other vertical handoff approaches. Key-Words – seamless handoff, vertical handoff, smart decision, policy-based handoff, mobile computing 1 Introduction As mobile computing increases in prevalence and popularity, more and more mobile hosts nowadays are equipped with multiple network interfaces which are capable of connecting to the Internet. As a result, an interesting problem surfaced on how to decide the “best” network interface to use any given moment. It is apparent to us that the decision should be based on various considerations such as the capacity of each network link, ISP charge of each network connection, power consumption of each network interface, and battery status of the mobile device. A similar policy-based handoff scheme has been proposed in [18], where the authors designed a cost function to decide the “best” moment and interface for vertical handoff. However, the cost function presented in this paper is very preliminary and not able to handle more sophisticated configurations. The logarithmic function used in the cost function will also have difficulty in representing the cost value while the value of the constraint factor is zero (e.g. the connection is free of charge). Another scheme proposed in [1] models the handoff with HTTP traffic, but it may have problems with other types of traffic, such as video and audio streaming, where the bandwidth demand is much higher than HTTP traffic. In this study, we propose a Smart Decision Model to smartly perform vertical handoff among available network interfaces. Using a well-defined score function, the proposed model can properly handoff to the “best” network interface at the “best” moment according to the properties of available network interfaces, system configurations/information, and user preferences. A Smart Decision Model implementation is employed on the top of the Universal Seamless Handoff Architecture (USHA), which is a simple and practical seamless handoff solution [2], and a set of experiments are performed to evaluate the feasibilities of the model. The results show that the proposed smart decision model can adequately perform vertical handoff to the “best” interface at the “best” moment. The rest of the paper is organized as follows: Section 2 describes the handoff overview and a simple seamless handoff approach, USHA. Section 3 presents our proposed Smart Decision Model. Section 4 demonstrates the model using a detailed example. Finally, section 5 concludes the work. 2 Background In this section, we present the background of this study. Section 2.1 clarifies the difference of vertical and horizontal handoff, and defines the seamless handoff. In section 2.2, we describe a simple and practical handoff approach: USHA, which will be used in the following discussions and testbed experiments. 2.1 Handoff Handoff occurs when the user switches between different network access points. Handoff techniques have been well studied and deployed in the domain of cellular system and are gaining a great deal of momentum in the wireless computer networks, as IP-based wireless networking increases in popularity. Differing in the number of network interfaces involved during the process, handoff can be characterized into either vertical or horizontal [16], as depicted in Figure 1. A vertical handoff involves two different network interfaces, which usually represent different technologies. For example, when a mobile device moves out of an 802.11b network and into a 1xRTT network, the handoff event