Comparative Performability Assessment of SFCs: The case of Containerized IP Multimedia Subsystem

The failure of a single network element composing a Service Function Chain (SFC) unavoidably leads to some degradation in terms of availability (ability of guaranteeing working conditions), and/or performance (ability of sustaining a certain workload) for the whole SFC. By considering both of these aspects, we propose, as a case study, a joint analysis of availability and performance (a.k.a. performability) of IP Multimedia Subsystem, an SFC infrastructure which plays a key role in the all-IP convergence of telecommunication services, especially as per prospects of $5{G}$ . We refer to an implementation of IMS based on container technology (containerized IMS, or cIMS) which allows to decouple the application layer from the underlying hardware infrastructure more efficiently than classic virtualization schemes. We model the probabilistic behavior of a cIMS by means of Stochastic Reward Networks (SRN) and Reliability Block Diagram (RBD) formalisms to take into account failure and repair events. Then, with the assistance of a designed-from-scratch algorithm (OptChains+), we carry on a performability analysis: i) to evaluate and compare series/parallel cIMS configurations (or settings), and ii) to find settings with minimum cost and maximum availability, given a performance level. The proposed assessment lends itself to a sensitivity analysis, here demonstrated by examples, useful for robustness evaluation.