Modeling of Hierarchical Distributed Systems with Fault-Tolerance.

This paper addresses some fault-tolerant issues pertaining to hierarchically distributed systems. Since each of the levels in a hierarchical system could have various characteristics, different fault-tolerance schemes could be appropriate at different levels. In this paper, we use stochastic Petri nets (SPN's) to investigate various fault-tolerant schemes in this context. The basic SPN is augmented by parameterized subnet primitives to model the fault-tolerant schemes. Both centralized and distributed fault-tolerant schemes are considered in this paper. These two schemes are investigated by considering the individual levels in a hierarchical system independently. In the case of distributed fault-tolerance, we consider two different checkpointing strategies. This first scheme is called the arbitrary checkpointing strategy. Each process in this scheme does its checkpointing independently; thus, the domino effect may occur. The second scheme is called the planned strategy. Here, process checkpointing is constrained to ensure no domino effect. Our results show that, under certain cases, an arbitrary checkpointing strategy can perform better than a planned strategy. Finally, we have studied the effect of integration on the fault-tolerant strategies of the various levels of a hierarchy. [ABSTRACT FROM AUTHOR]