IP Multimedia Subsystem in an NFV environment: availability evaluation and sensitivity analysis

The Network Function Virtualization (NFV) paradigm is giving impetus to novel telecommunication infrastructures that readily benefit from virtualized environments. One of the most interesting implications consists in turning traditional network appliances (e,g, routers, switches, firewalls) into virtual applications also known as Virtual Network Functions (VNFs). Same virtualization concepts can be applied to complex network systems, such as IP Multimedia Subsystem (IMS), where constitutive network elements can be recasted in a set of chained VNFs, thus resulting in a virtualized IMS infrastructure (or vIMS). Starting from this challenging environment, in this work we propose an availability assessment of a vIMS divided in two stages: i) a preparatory modeling phase by means of two formalisms: Reliability Block Diagram and Stochastic Reward Networks; ii) a numerical analysis aimed at characterizing both the optimal vIMS configuration satisfying an high availability condition (availability evaluation), and the robustness of the system as some parameters deviate from their nominal values (sensitivity analysis).