Distributed Location Databases for Tracking Highly Mobile Objects

In current distributed systems, the notion of mobility is emerging in many forms and applications. Increasingly many users are not tied to a fixed access point but instead use wireless communications or dial-up services to access data independent of their physical location. Furthermore, mobile software, a popular example being mobile agents, is frequently used as a new form of building distributed network-centric applications. Tracking mobile objects, i.e. identifying their current location, is central to such settings. In this paper, we exploit the use of hierarchical distributed location databases, where each database site covers a specific geographical region and contains location information about all objects residing in it. For highly mobile objects, a scheme based on forwarding pointers enhanced with auxiliary caching techniques is presented, to reduce the cost of the overall network and database traffic generated by frequent location updates. The scheme is extended to support concurrency and failure recovery. Performance is demonstrated through a number of simulation experiments for a range of call to mobility ratios and for a variety of moving and calling behaviors.