Optimal VNF Scheduling for Minimizing Duration of QoS Degradation.

Network services provisioning with Service Function Chaining (SFC) consists of various controls such as Virtual Network Function (VNF) placement and traffic flow routing, executed dynamically. These controls take time to execute from start to completion (reconfiguration delay), and the reconfiguration delay varies depending on the type of control. When control is executed with a long reconfiguration delay to eliminate Quality of Service (QoS) degradation, it will take longer to complete, resulting in continued degradation. To optimize the network performance, a control method needs to consider the difference in the reconfiguration delay. However, most of existing works do not assume the difference, and aim to optimize QoS only at the completion of controls. In this paper, we assume different reconfiguration delays for each control in SFC provisioning, and propose a control scheduling that optimizes QoS during control execution on the basis of them. We first propose a network model in which the reconfiguration delay of each type of control is different and formulate the scheduling problem of network controls that minimizes the duration of QoS degradation. Then we propose a control scheduling method to solve the problem. Our method develops a stochastic search on the basis of the load degree of VNF instances to obtain a sub-optimal solution with low computational complexity. We also provide a packet-level simulation to verify the performance of our method when QoS degrades due to traffic demand rapidly increasing. Simulation results show that our method reduces the delay degradation and its duration compared with the control scheduling method that optimizes performance at the completion of controls.