Meeting SLA Availability Guarantees through Engineering Margin

This research deals with availability of Service Level Agreements (SLA) between information technology service providers, such as carriers, and user corporations. A combination of different reliability/maintainability scenarios and time intervals have been used to generate availability distributions in order to assess the efficacy of availability guarantees. Markov and semi-Markov models are used to provide a comparative analysis of the availability distributions and probability of service level violation. In the semi-Markov model, long tail and short tail lognormal distributions are used for the repair time. A Monte Carlo simulation program is developed and from the generated distributions it is found that there are significant chances of SLA violation, given a wide range of different reliability/maintainability levels used to achieve typical goals such as 0.99999 availability for a variety of time intervals. The results are fairly sensitive to the tail of the repair distribution, meaning it is essential to understand repair distribution in order to assess chances of SLA violation. Results indicate that the way to dramatically decrease the probability of SLA violation is through availability engineering margin. Delivering availability beyond 0.99999 through redundancy and responding more rapidly to failures greatly diminishes the chances of violating a 0.99999 SLA.