Evaluating a Dependable Distributed System with Multiple Critical Tasks

The aim of our research is to develop a distributed system that support a variety of tasks. Currently, we are implementing Internet applications on the system, including firewall, web and mail applications. These applications have different levels of dependability requirements. Depending on their criticality, a single task may execute on one, two or more computer nodes. Fault tolerant protocols are used to detect the disagreement among replicas. A reconfiguration protocol is used to identify the faulty nodes according to the fault reports from the fault tolerant protocols. It then isolates the faulty nodes from the system and reallocates their tasks to other working nodes. As a part of the project, this work focuses on the dependability analysis. The dependability attributes under modelling are the reliability of the system and the risk that an unacceptable packet is accepted in the firewall application.