Vicente Chirivella

A New Reliability Model for Interconnection Networks

The traditional approach to study fault-tolerance in multicomputer interconnection networks consists of determining the worst possible combination of faulty components that causes a network failure, and then assuming that this will occur. But the worst possible combination does not always occur, and the routing algorithm allows the network to work in the presence of a greater number of failures. Thus network reliability parameters computed according to the traditional approach will be underestimated. In this paper we propose a new methodology to compute accurately the reliability function. The reliability parameters have been computed for an interconnection network with mesh topology, taking into account size, routing algorithm, failure and repair rates of the network channels and coverage.

Dependability Analysis of a Fault-Tolerant Network Reconfiguring Strategy

Fault tolerance mechanisms become indispensable as the number of processors increases in large systems. Measuring the effectiveness of such mechanisms before its implementation becomes mandatory. Research toward understanding the effects of different network parameters on the dependability parameters, like mean time to network failure or availability, becomes necessary. In this paper we analyse in detail such effects with a methodology proposed previously by us. This methodology is based on Markov chains and Analysis of Variance techniques. As a case study we analyse the effects of network size, mean time to node failure, mean time to node repair, mean time to network repair and coverage of the failure when using a 2D mesh network with a fault-tolerant mechanism (similar to the one used in the BlueGene/L system), that is able to remove rows and/or columns in the presence of failures.

Studying the effect of the design parameters on the interconnection network performance in NOWs

With the increasing use of network of workstations (NOWs) as an alternative to huge parallel computers it has become essential to design high-performance interconnection networks for the communication between the nodes of these clusters. A large number of studies have been carried out to achieve this objective. Most of them propose a new technique that affects one of the parameters that characterize the interconnection network. These techniques are completely new or inspired in the techniques previously used in multiprocessor systems. The impact of the proposal is studied (in most cases using simulation), and an analysis is made of the effect of the new technique over the system performance versus those currently in existence. In this kind of study most of the network parameters are fixed and usually only a few parameters are varied. This paper presents a more general study of the interconnection network performance. This study consists in showing the effect of different design parameters over the network performance, and the interaction between them. This study would not be viable with the traditional techniques due to the number of simulations required. The alternative of the experimental design is used to carry out the study.

Improving the Accuracy of Reliability Models for Direct Interconnection Networks

Fault-tolerance in multicomputer interconnection networks has been traditionally studied by determining the worst possible combination of faulty components that causes a network failure and then assuming that this will occur. But, the worst possible combination may occur with low probability and the routing algorithm may allow the network to work, even when there is a large number of faults. Thus, the network dependability parameters computed according to this approach will be underestimated. In a previous paper [3], we have proposed a new methodology, based on Markov chains, for evaluating interconnection network dependability. Using this methodology, we can accurately compute the network reliability behavior. In this paper we apply it to evaluate dependability parameters in a 2-D mesh, taking into account network size, routing algorithm, failure and repair rates of nodes and coverage. Finally, we compare the computed results under traditional and our approach.

An accurate analysis of reliability parameters in meshes with fault-tolerant adaptive routing

The traditional approach to study fault-tolerance in multicomputer interconnection networks consists of determining the worst possible combination of faulty components that causes a network failure, and then assuming that this will occur. But the worst possible combination does not always occur, and the routing algorithm allows the network to work in the presence of a greater number of failures. The network reliability parameters computed according to the traditional approach will be under-estimated. In this paper we use a new methodology to compute accurately the reliability and availability functions. The reliability parameters have been computed for a network with mesh topology, taking into account size, routing algorithm, failure and repair rates of the network channels and coverage.