In this paper, we present an anonymous, stable, communication efficient, stabilizing leader election algorithm that works using anonymous communication primitives. The algorithm offers properties similar to that of the Omega failure detector, with the added property of totally ordering the sequence of proposed leaders. The algorithm does not need to know beforehand the identity or the number of processes in the system, and operates using a constant amount of memory. We present the algorithm, discuss performance issues and optimizations and present experimental results of a prototype implementation.

The paper presents a fail-safe mobility management and a collision prevention platform for a group of asynchronous cooperative mobile robots. The fail-safe platform consists of a time-free collision prevention protocol, which guarantees that no collision can occur between robots, independently of timeliness properties of the system, and even in the presence of timing errors in the environment. The collision prevention protocol is based on a distributed path reservation system. Each robot in the system knows the composition of the group, and can communicate with all robots of the group. A performance analysis of the protocol provides insights for a proper dimensioning of system parameters in order to maximize the average effective speed of the robots.

This paper presents a fully decentralized distributed path reservation system for a group of asynchronous cooperative mobile robots. The protocol assumes a mobile ad hoc network formed by the robots themselves, and takes advantage of the inherent locality of the problem in order to reduce communication. In contrast with other work, our protocol requires neither initial nor complete knowledge of the composition of the group. A performance analysis of the protocol provides insights for a proper dimensioning of system parameters in order to maximize the average effective speed of the robots

End-to-end consensus ensures delivery of the same value to the application layer running in distributed processes. Deliveries that have not been acknowledged by the application before a failure are delivered again. End-to-end primitives are important for applications that need to enforce persistency. We present an algorithm that solves the end-to-end consensus problem. Our approach is to build end-to-end consensus using a new type of communication channels, end-to-end channels

In this paper, we present the SNMP-FD service, a novel failure detection service entirely based on the Simple Network Management Protocol (SNMP). This approach promises better interoperability with external tools and failure information sources, including network equipment and cluster management tools. We first show how the SNMP standard can be used to build a failure detection service. We describe the already standardized interfaces that can be reused and introduce the interfaces that need to be added. SNMP is used extensively in the service for messaging, process status description, configuration, services statistics and delivering failure detection information to applications. We then present our implementation and an evaluation of performance and quality of service

In this paper, we present a performance comparison of database replication techniques based on total order broadcast. While the performance of total order broadcast-based replication techniques has been studied in previous papers, this paper presents many new contributions. First, it compares with each other techniques that were presented and evaluated separately, usually by comparing them to a classical replication scheme like distributed locking. Second, the evaluation is done using a finer network model than previous studies. Third, the paper compares techniques that offer the same consistency criterion (one-copy serializability) in the same environment using the same settings. The paper shows that, while networking performance has little influence in a LAN setting, the cost of synchronizing replicas is quite high. Because of this, total order broadcast-based techniques are very promising as they minimize synchronization between replicas.

Group communication provides communication primitives with various semantics and their use greatly simplifies the development of highly available services. However, despite tremendous advances in research and numerous prototypes, group communication stays confined to small niches and academic prototypes. In contrast, message-oriented middleware such as the Java message service (JMS) is widely used, and has become a de-facto standard. We believe that the lack of a well-defined and easily understandable standard is the reason that hinders the deployment of group communication systems. Since JMS is a well-established technology, an interesting solution is to extend JMS adding group communication primitives to it. Foremost, this requires extending the traditional semantics of group communication in order to take into account various features of JMS, e.g., durable/nondurable subscriptions and persistent/non-persistent messages. The resulting new group communication specification, together with the corresponding API, defines group communication primitives compatible with JMS.

While group communication systems have been proposed for some time, they are still not used much in actual systems. We believe that one reason for this is the lack of standardisation of group communication system interfaces. The paper proposes an architecture, using the standard decomposition into services, where services are based on standard interfaces: both interactions between services and interactions with the application use existing, open standards. A decomposition of the group communication into services is presented, along with a description of applicable standards. As an example, a group membership service based on the LDAP standard is discussed.

Atomic broadcast primitives are often proposed as a mechanism to allow fault-tolerant cooperation between sites in a distributed system. Unfortunately, the delay incurred before a message can be delivered makes it difficult to implement high performance, scalable applications on top of atomic broadcast primitives. Recently, a new approach has been proposed for atomic broadcast which, based on optimistic assumptions about the communication system, reduces the average delay for message delivery to the application. We develop this idea further and show how applications can take even more advantage of the optimistic assumption by overlapping the coordination phase of the atomic broadcast algorithm with the processing of delivered messages. In particular, we present a replicated database architecture that employs the new atomic broadcast primitive in such a way that communication and transaction processing are fully overlapped, providing high performance without relaxing transaction correctness.

Replication is an area of interest to both distributed systems and databases. The solutions developed from these two perspectives are conceptually similar but differ in many aspects: model, assumptions, mechanisms, guarantees provided, and implementation. In this paper, we provide an abstract and "neutral" framework to compare replication techniques from both communities. The framework has been designed to emphasize the role played by different mechanisms and to facilitate comparisons. The paper describes the replication techniques used in both communities, compares them, and points out ways in which they can be integrated to arrive to better, more robust replication protocols.

Data replication is an increasingly important topic as databases are more and more deployed over clusters of workstations. One of the challenges in database replication is to introduce replication without severely affecting performance. Because of this difficulty, current database products use lazy replication, which is very efficient but can compromise consistency. As an alternative, eager replication guarantees consistency but most existing protocols have a prohibitive cost. In order to clarify the current state of the art and open up new avenues for research, this paper analyses existing eager techniques using three key parameters (server architecture, server interaction and transaction termination). In our analysis, we distinguish eight classes of eager replication protocols and, for each category, discuss its requirements, capabilities and cost. The contribution lies in showing when eager replication is feasible and in spelling out the different aspects a database replication protocol must account for.