Fig. 7

Cost–benefit ratios diagram, higher is better. x axis: number of controllers. y axis: Cost–benefit ratios for optimized average latency. We define a benefit–cost ratio to represent the cost of building the network. This value can reflect the proportional relationship between the communication delay with different number of controllers and the communication delay with one controller. By judging the rake ratio of the numerical value, we can choose the optimal number of controllers so that we can get higher benefits