In this paper, we study dynamic protocol update (DPU). Contrary to local code updates on-the-fly, DPU requires global coordination of local code replacements. We propose a novel solution to DPU. The key idea is to add a level of indirection between the service callers and the service provider. This indirection level facilitates an implementation of simple and efficient algorithms for DPU. For example, we describe an experimental implementation of adaptive group communication middleware. It can switch between different atomic broadcast protocols on-the-fly. All middleware protocols, including those that depend on the updated protocols, provide service correctly and with negligible delay while the global update takes places. The switching algorithm introduces very low overhead that we illustrate by showing example measurement results. 1

In this paper, we address the problem of dynamic protocol update (DPU) that requires global coordination of local code replacements. We propose a novel approach to DPU. The key idea is the use of synchronization facilities of the services that get updated. This solution makes global update simple and efficient. We describe an experimental implementation of adaptable group communication middleware. It can switch between different distributed agreement protocols on-the-fly. All middleware services, including those that depend on the updated protocols, provide service correctly and with negligible delay while the global update takes places. The switching algorithm introduces very low overhead, that we illustrate by showing example measurement results. Key-words: distributed algorithms, group communication, dynamic protocol update, reliable systems, modular composition and protocol frameworks

In this paper we compare two approaches to the design of protocol frameworks – tools for implementing modular network protocols. The most common approach uses events as the main abstraction for a local interaction between protocol modules. We argue that an alternative approach, that is based on service abstraction, is more suitable for expressing modular protocols. It also facilitates advanced features in the design of protocols, such as dynamic update of distributed protocols. We then describe an experimental implementation of a service-based protocol framework in Java.

Abstract. Group communication is a programming abstraction that allows a distributed group of processes to provide a reliable service in spite of the possibility of failures within the group. The goal of the project was to improve the state of the art of group communication in several directions: protocol frameworks, group communication stacks, specification, verification and robustness. The paper discusses the results obtained. 1