In current distributed systems, the notion of mobility is emerging in many forms and applications.

Services for locating mobile objects are often organized as a distributed search tree. A potential problem with this organization is that high-level nodes may become a bottleneck, affecting the scalability of the service. A traditional approach to handle such problems is to also distribute the location information managed by a single node across multiple machines.

This paper presents TRAcKER, * a distributed “location management ” middleware which has the ability to manage the location of mobile agents that travel independently the Internet in search of useful information. A major goal for this middleware is to be flexible and effective, to respond to the demands posed by the environment it aims to assist: an environment that deals with users that are accessing the Internet via static or mobile units of limited resources (e.g., palmtops, handheld devices, WAP-phones) and utilizing mobile agents that are moving “autonomously ” and asynchronously around the Internet with small, medium and in many cases high moving frequency. The mechanism we propose is modular, simple, of low overhead and able to serve all the Java based mobile agent platforms. In addition, is quite generic able to dynamically incorporate various location mechanisms. 1.

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

An important issue in the design of a mobile computing system is how to manage the real-time locations of mobile clients. In the existing commercial cellular mobile computing systems, a two-tier architecture is used [13]. However, the two-tier architecture is not scalable and is not suitable to the new mobile computing applications. In the literatures [1, 12], a hierarchical database structure is proposed in which the location information of the mobile clients within a cell is managed by the location database responsible for the cell. The location databases of different cells are organized into a tree structure to facilitate the search of mobile clients. Although this architecture can distribute the update and searching workload amongst the location databases in the system, it has the problem of heavy location update overhead and long search delay. Thus, it is not suitable to the system which is supporting real-time queries. In this paper, we study how to generate location update in...

An important issue in the design of a mobile computing system is how to manage the location information of mobile clients. In the existing commercial cellular mobile computing systems, a twotier architecture is adopted (Mouly and Pautet, 1992). However, the two-tier architecture is not scalable. In the literatures (Pitoura and Samaras, 2001; Pitoura and Fudos, 1998), a hierarchical database structure is proposed in which the location information of mobile clients within a cell is managed by the location database responsible for the cell. The location databases of different cells are organized into a tree-like structure to facilitate the search of mobile clients. Although this architecture can distribute the updates and the searching workload amongst the location databases in the system, location update overheads can be very expensive when the mobility of clients is high. In this paper, we study the issues on how to generate location updates under the distance-based method for systems using hierarchical location databases. A cost-based method is proposed for calculating the optimal distance threshold with the objective to minimize the total location management cost. Furthermore, under the existing hierarchical location database scheme, the tree structure of the location databases is static. It cannot adapt to the changes in mobility patterns of mobile clients. This will affect the total location management cost in the system. In the second part of the paper, we present a re-organization strategy to re-structure the hierarchical tree of location databases according to the mobility patterns of the clients with the objective to minimize the location management cost. Extensive simulation experiments have been performed to investigate the re-organization strategy when our...

The mobile computing paradigm has emerged due to advances in wireless or