Large-scale hybrid networks that include wireless, wired, and satellite based communications are becoming common in both military and commercial situations. This paper describes a scalable simulation environment called GloMoSim (for Global Mobile Information System Simulator) that effectively utilizes parallel execution to reduce the simulation time of detailed high-fidelity models of large communication networks. The paper also presents a set of case studies that evaluate the performance of large wireless networks with thousands of nodes and compares the impact of different lower layer protocols on the performance of typical applications. 1.

Abstract Nomadic users require replication to store copies of critical data on their mobile machines while disconnected or poorly connected. 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. Mobile users must adapt their behavior to match the level of service provided by today's replication systems, thereby hindering mobility and costing additional time, money, and systems management. Roam is a replication system designed to satisfy the requirements of the mobile user. Roam is based on the Ward Model, a 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.

Mobile computers often suffer from limited connectivity, or even complete lack of network access. Moreover, in wireless networks some machines are often more accessible to mobile computers than others are. Ideally, nomadic users want the same quality and speed of database access as when they are well connected to the network. Replicated databases meet this need by allowing each mobile machine to carry its own copy of key data. But existing replicated systems are not well suited for all nomadic scenarios. Certain important mobile computing situations require optimistic peer-oriented database replication. The Bengal Database Replication System has these characteristics and was designed to operate in difficult nomadic conditions. This paper presents the design assumptions of the system, describes its architecture, presents performance data on its operation, and discusses future enhancements for the system. The paper also contrasts the system to other replicated databases, concentrating on their suitability for nomadic computing. The Bengal technology can play an important role in the development of highly scalable, highly available, fault-tolerant database systems. Keywords: distributed, optimistic, database, replication, peer-to-peer 1.

Clique is a HP Labs Grenoble project. The goal is to develop a novel peer-to-peer, server-less distributed file system based on optimistic replication algorithms, which transparently integrates into users' native file systems. Some properties of the Clique system are epidemic replication, a no lost updates consistency model and conflict management, as well as disconnected operation and replica convergence. These properties ensure that updates done by any peer of the group will never be lost, and also that they will converge on all the group member machines. The system is well adapted to highly disconnected environments, network partitions, and variable join/leave rates. Even under adverse connectivity conditions, over time, assuming intermittent point-to-point connectivity between each peer and at least one other peer in the group, the local file system view at each node converges towards a consistent global view. The reconciliation protocol used is stateless and has no notion of group me mbership, in order to achieve a linear worst-case scalability in the order of N, the number of peers in the network.

We propose and evaluate a mobile, peer-to-peer Information Retrieval system. Such a system can, for example, support medical care in a disaster by allowing access to a large collections of medical literature. In our system, documents in a collection are replicated in an overlapping manner at mobile peers. This provides resilience in the face of node failures, malicious attacks, and network partitions. We show that our design manages the randomness of node mobility. Although nodes contact only direct neighbors (who change frequently) and do not use any ad hoc routing, the system maintains good IR performance. This makes our design applicable to mobility situations where routing partitions are common. Our evaluation shows that our scheme provides significant savings in network costs, and increased access to information over ad-hoc routing-based approaches; nodes in our system require only a modest amount of additional storage on average.