Analytical Model for Assessing Unavailability in Middleboxes with Multiple Backup Servers under Shared Protection

This paper proposes an analytical model that deter-mines the unavailability of middle box functions, where multiple backup servers protect one or more functions, which we call a multiple-backup shared protection strategy. Middlebox functions as software are implemented on a general-purpose server through the utilization of network function virtualization. The metric of unavailability in middleboxes carries significant importance, underscoring the necessity for streamlined and efficient protection strategies. While existing approaches tackle this problem, they often become complex, or only exceptional cases are considered, prompting new model development. In our model, we enable each function to be protected by multiple backup servers to ensure function availability, and each backup server can recover at most one function simultaneously. We employ a Markov chain to an-alyze state transitions and establish equilibrium-state equations, providing an analytical foundation for assessing the performance of the multiple-backup shared protection strategy. Numerical results show that the multiple-backup shared protection strategy reduces the unavailability by 7.80-72.3 % compared to the single-backup shared protection strategy in our examined cases.