Service Function Chaining deployed in an NFV environment: an availability modeling

Nowadays, network and telecommunication operators require flexible and dynamic models to deploy new services in a fast, reliable and cost saving way. The Service Function Chaining (SFC) design is particularly suited to meet such needs, especially in conjunction with the Network Function Virtualization (NFV) paradigm that adds a noteworthy elasticity during the SFC deployment phase. Accordingly, SFC is realized by means of a composition of Virtualized Network Functions (VNFs) aimed at providing some specific services. We consider, from an availability point of view, an SFC-based architecture with an aim to find out the optimal configuration guaranteeing the so-called “five nines” availability requirement, as demanded in the telecommunication systems. The availability analysis is carried out by exploiting a hierarchical model where a Reliability Block Diagram describes high level dependencies in the SFC implementation, while Stochastic Reward Nets are adopted to model the probabilistic behavior of single blocks. In particular, the SFC availability has been evaluated by performing a steady-state analysis, while a sensitivity analysis of some critical parameters allowed us to analyze in depth the whole system robustness.