Modeling the Software Dependability For a SDN/NFV Controller

The software defined network (SDN) is a new approach to building telecommunication networks, which can significantly increase the efficiency of telecommunication equipment and the entire network as a result of network functions virtualization (NFV). Removing separate functionality from network elements and its addition to a controller that manages a software defined network makes the it independent of equipment manufacturers. In this case, the problem of assessing the reliability of a software defined network, and in particular of a controller, becomes more important and valuable. An increase in the volume of software and its complication contributes to an increase in the number of errors at the stage of software development and leads to serious economic and reputational damage to the network service providers. Software reliability assessment deserves special attention, since it has significant differences from hardware reliability assessment. The paper discusses the main differences between software and hardware failures and examples of faults that can lead to SDN/NFV controller failure. An analytical model of the SDN/NFV controller operation in the conditions of software failures is presented. Two cases of failures are considered: with one critical state and with three critical states with different levels of failures criticality. Depending on these, the reliability indicators of the controller are determined: the availability factor and the unavailability factor. The model is based on the matrix method of describing the functioning of long-term use systems.