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 underestimated. 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.