Generalised unavailability and generalised nines and their use in designing services for maximum profit

This paper introduces two related concepts of “Generalised Unavailability” and “Generalised Nines” as the foundation of a versatile framework for modelling customer satisfaction. A service is modelled as a network of maintained components. The annual cost of providing a service is modelled as a simple function of the reliability and resilience of every component. The performance of a service is modelled as a function of network architecture, and the reliability and resilience of each component. Hence, the causal chain from cost to service performance to customer satisfaction to anticipated revenue is modelled, and a method for maximising the profit of providing the service is developed. Necessary conditions on the reliability and resilience of each component are derived. Simple analytic results are derived for special cases. A simple cloud computing service is studied. A small pilot study indicates that customers give greater weighting to resilience than to reliability. Hence the design method is used to optimise profit according to the sampled customer preferences.