In the era of fifth generation (5G) telecommunication systems, a flexible, cost saving and reliable deployment of the network infrastructures appears to be a crucial issue. The European Telecommunications Standard Institute jointly with a group of telecom providers, proposed a novel networking paradigm considered as an enabler for future 5G networks: the Network Function Virtualization (NFV) paradigm that, taking inspiration from classical virtualization concepts, allows to implement virtualized versions of standard network appliances (Routers, Switches, Firewalls etc.) called Virtualized Network Functions (VNFs). A network infrastructure that can take advantages of such a virtualization criteria is the IP Multimedia Subsystem (IMS), the framework in charge of managing the multimedia services in the next generation networks. By merging the IMS and NFV concepts, we propose a virtualized IMS architecture modeled by a three-level hierarchical approach that mixes different types of formalism relyingon: i) Reliability Block Diagrams to model network modules; ii) Fault Trees to consider the state of a system (top event) in terms of the states of its subsystems (basic events); iii) Continuous-Time Markov Chains (CTMCs) to model single subsystems. Furthermore, we propose an availability evaluation of the virtualized IMS infrastructure by performing a steady-state analysis in order to pinpoint the best configuration guaranteeing the “five nines” requirement for 5G telecommunication systems.
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