"Access is the killer app" is the vision of the Daedalus project at U.C. Berkeley. Being able to be connected seamlessly anytime anywhere to the best network still remains an unfulfilled goal. Often, even determining the "best" network is a challenging task because of the widespread deployment of overlapping wireless networks. In this report, we describe a policy-enabled handoff system that allows users to express policies on what is the "best" wireless system at any moment, and make tradeoffs among network characteristics and dynamics such as cost, performance and power consumption. We designed a performance reporting scheme estimating current network conditions, which serves as input to the policy specification. A primary goal of this work is to make it possible to balance the bandwidth load across networks with comparable performance. We identified the problem of handoff instability that may be caused by handoff synchronization, i.e., the scenario of many mobile hosts making the same handoff decision at essentially the same time. We use randomization to break such synchronizations. Given the current "best" network, our system also determines whether the handoff is worthwhile based on the handoff overhead and potential network usage duration.




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