Reliability evaluation for distributed computing networks with imperfect nodes

This paper examines two compensating methods that: (1) account for imperfect nodes, and (2) can be embedded in most symbolic network reliability algorithms that presume perfect nodes. The Aggarwal method can be exponential in time with the number of links, whereas the Torrieri method is always linear. However the Torrieri method can yield incorrect results for some undirected networks. This paper points out such incorrectness and then proposes an efficient reliability evaluation algorithm (ENR/KW) accounting for imperfect nodes in distributed computing networks. Based on the concept of network partition, ENR/KW exploits some simple efficient techniques to handle the unreliable nodes, for directly computing the network reliability expression considering imperfect nodes instead of using any compensating method. The basic idea of ENR/KW is to partition the network directly into a set of smaller disjoint subnetworks by only considering link elements as if all nodes are perfect. Each disjoint subnetwork is generated by maintaining a specific directed graph structure to consider the effect of imperfect nodes. Therefore, the reliability expression for imperfect nodes can be obtained directly from the disjoint subnetwork and the specific directed graph. ENR/KW can be generalized to evaluate various network reliability measures considering imperfect nodes such as terminal-pair reliability, K-terminal reliability, and distributed-program reliability. Many experiments for evaluating the terminal-pair reliability and distributed-program reliability were performed on a SUN workstation to show the efficiency of ENR/KW in terms of the number of generated subnetworks and overall computation time.