Dependability modelling of homogeneous and heterogeneous distributed systems

In the past few years we have developed an experimental distributed system that supports multi-task applications with different levels of criticality. Software implemented fault-tolerant protocols are used to support dependable computing. This paper first presents Markov models of a distributed system under the occurrence of faults, reconfiguration and repair. As a part of our overall project, these models are intended for solving our particular problems, like assessing the merits of redundant schemes, task allocation and reallocation policies, and fault handling used in our experimental system. However, these models are developed in a generic way. They can also be used in evaluating individual task's reliability, risk and availability under various redundant schemes in any homogeneous distributed system. Then, we extend our study in analysing the dependability of the heterogeneous system consisting of a number homogeneous distributed systems connected through gateways.