A Scalable Approach for Service Chain (SC) Mapping with Multiple SC Instances in a Wide-Area Network

Network Function Virtualization (NFV) aims to simplify service deployment using Virtual Network Functions (VNFs). Service deployment involves placement of VNFs and in-sequence routing of traffic flows through VNFs comprising a Service Chain (SC). The joint VNF placement and traffic routing is called SC mapping. In a Wide-Area Network (WAN), where several traffic flows, generated by many distributed node pairs, require the same SC; a single instance (or occurrence) of that SC might not be enough. SC mapping with multiple SC instances for same SC is a very complex problem, since sequential traversal of VNFs has to be maintained while accounting for traffic flows in various directions. Our study is the first to deal with the problem of SC mapping with multiple SC instances to minimize network resource consumption. We propose an Integer Linear Program (ILP), a column-generation-based ILP (CG-ILP) and a two-phase columngeneration- based model (2PhMod) to solve this problem. ILP does not scale to large networks and CG-ILP scalability is limited by quadratic constraints. So, to get results over large network topologies within reasonable computational times, we propose 2PhMod. Using such an approach, we observe that an appropriate choice of only a small set of SC instances leads to a solution very close to minimum bandwidth consumption. Further, this approach also helps us to analyze effects of number of VNF replicas and number of NFV nodes on bandwidth consumption when deploying these minimum number of SC instances.