Availability Modeling and Analysis for Software Defined Networks

Software Defined Network (SDN) is an emerging paradigm for flexible network design and implementation. Availability metric of SDNs is critically demanding further studies. This paper aims to propose hierarchical models to assess the availability of SDNs. We incorporate various failure modes and recovery behaviors in the SDN including (i) link failures at network level, and (ii) software and hardware failures at network device level. We use hierarchical models in which a Reliability Graph (RG) is used to represent the reachability of hosts (and switches) in the SDN at the upper level and Stochastic Reward Net (SRN)s are used to represent the detailed failure and recovery of network devices at the lower level, respectively. We incorporate the programmable capability of the SDN at the upper level (i.e., the RG). We perform numerical analysis to assess the availability of the SDN in terms of steady state availability and downtime in minutes per year, and we also show the sensitivity analysis.