Network-Aware Availability Modeling of an End-to-End NFV-Enabled Service

Abstract

Network Function Virtualization (NFV) represents a key shift in nowadays network service provisioning by entailing higher flexibility, elasticity, and programmability of network services. Dependability is one of the main aspects that need to be investigated and tackled in order to profitably use NFV in the future. The main objective of this paper is to propose a comprehensive approach to estimate the end-to-end NFV-deployed service availability and present a quantitative assessment of the network factors that affect the availability of the service provided by an NFV architecture. To achieve this goal, we adopted a two-level availability model where i) the low level considers the network topology structure and NFV connectivity requirements through the definition of the system structure function based on minimal-cut sets and ii) the higher level examines dynamics and failure modes of network and NFV elements through stochastic activity networks. By using the proposed model, we have carried out an extensive sensitivity analysis to identify the impact on the service availability of the different service elements involved in the delivery, and their deployment across the network. The results highlight the significant impact that network nodes have on the end-to-end network service. Less robust network nodes may reduce the availability of an NFV-enabled service by more than one order of magnitude even though NFV elements like VNFs or MANO are provided with redundancy. Moreover, the results show that adopting an SDN-integrated network degrades the service availability and increases the vulnerability of the network service to SDN controllers unless adequately protected.