Accommodating Dynamic Traffic Immediately: A VNF Placement Approach

Network function virtualization has become a promising technology recently. To accommodate dynamic traffic such as burst, NFV can scale virtual network functions (VNFs) across several physical servers, which is known as horizontal scaling, or enlarge the capacity of a VNF leveraging idle resources in one physical server, which is called vertical scaling. Vertical scaling should be used as much as possible to accommodate user traffic increment immediately, and horizontal scaling is only performed when vertical scaling cannot allocate sufficient resource to meet the demand. We find that just to reserve redundant resource is far from sufficient to enable vertical scaling with good performance, and VNF placement plays a crucial role. In this paper, we model the scalable VNF placement problem formally, and prove that the problem is NP-hard. Then, we develop two online heuristic algorithms gradually to solve the problem. The sVNFP algorithm focuses on maximizing the vertical scalability, while the sVNFP-adv algorithm considers path length and server utilization concurrently. Simulation results show that our algorithms can reduce packet loss ratio by 15% to 40%, with a short path length and a high server utilization.