Achieving High End-to-End Availability in VNF Networks

As software programs, Virtual Network Functions (VNFs) introduce new challenges to network availability due to their potential software failures. Existing models on the availability of VNF networks did not consider all the possible hardware and software failures, making them incapable of analyzing the end-to-end availability of a path. Furthermore, they did not capture the correlation between repeating nodes and links in the path, resulting in inaccurate analytical results. In this paper, we propose a new analytical model, which considers all hardware and software failures as well as the effect of repeating components, to effectively analyze the end-to-end availability of a flow path in VNF networks. On top of the analytical model, we formulate the Highest Availability Path (HAP) problem that finds the flow path with the highest end-to-end availability, and prove its NP-hardness by reduction from the Node-Weighted Steiner Tree problem. Next, we propose two algorithms for HAP: the first one based on a Steiner Tree approximation algorithm, having high time complexity and serving as a performance benchmark; the second one using a dynamic programming approach to search a multi-layer graph in polynomial time. Finally, we present extensive evaluation data to demonstrate the effectiveness of the Layered Search algorithm, which achieves comparable performance as that of the Steiner Tree based algorithm and runs faster by four orders of magnitude.