A Fault-Tolerant Mobile Computing Model Based On Scalable Replica

Abstract

The most frequent challenge faced by mobile user is stay connected with online data, while disconnected or poorly connected store the replica of critical data. Nomadic users require replication to store copies of critical data on their mobile machines. Existing replication services do not provide all classes of mobile users with the capabilities they require, which include: the ability for direct synchronization between any two replicas, support for large numbers of replicas, and detailed control over what files reside on their local (mobile) replica. Existing peer-to- peer solutions would enable direct communication, but suffers from dramatic scaling problems in the number of replicas, limiting the number of overall users and impacting performance. Roam is a replication system designed to satisfy the requirements of the mobile user. Roam is based on the Ward Model, replication architecture for mobile environments. Using the Ward Model and new distributed algorithms, Roam provides a scalable replication solution for the mobile user. We describe the motivation, design, and implementation of Roam and report its performance. Replication is extremely important in mobile environments because nomadic users require local copies of important data. Model, a new replication architecture that has been designed especially with mobility in mind, though of course it applies equally well to stationary environments (1). The Ward Model provides a new replication paradigm that is neither strictly peer nor client-server; rather, it is a hybrid model of the two that allows everyone to be effectively a peer while maintaining good scalability in the number of replicas. Additionally, Roam provides a number of new distributed algorithms. For instance, Roam contains new and improved distributed algorithms for garbage collection and for dynamic management of the version vector, the main data structure behind most optimistic replication systems. In this paper we present an approach for data replication that considers the mobility of clients: The data sets which have to be replicated to mobile clients depend often on dynamic parameters like location of the client or time. Therefore, we introduce a generic model for specifying fragments of the global database with respect to such parameters. The increasing availability of mobile devices and wireless