# Improving Energy Efficiency on SDN Control-Plane Using Multi-Core Controllers
## 5 Conclusions and Future Work  
This study shows that an SDN controller can have an improved energy efficiency by lowering its operating frequency using the parallel nature and availability of current multicore processors. The results obtained for the Communication Network Energy Efficiency (CNEE) (see Figure 11) show that the single-core or the dual-core scenarios use more energy to deliver the same number of bits. This improves the DC overall energy efficiency. The reduction of energy consumption, as shown in Figures 8-10, is due to the lower operating frequency and parallel implementation. This indicates that a focus on leveraging parallelism on network applications, especially SDN controller, can improve not only performance but also energy-efficiency. It is shown that a well-implemented parallel controller can leverage its efficiency by distributing tasks, keeping a guaranteed level of service, such as the industry-standard service level agreement. The reduction of energy consumption on the control plane is a novel strategy for energy-aware SDN, where most researchers have focused on the data plane. As the number of applications using network programmability start to increase, the energy demand on controllers will follow. Exploiting the parallel nature of the controller is key to keep this component's energy consumption in balance. Essentially, this solution can be applied to any SDN controller with an off-the-shelf multicore processor with no conflict with others solutions focused on data-plane, improving the overall efficiency of the network. Future Works  
To extend the findings in this paper, we shall evaluate how replacing the constant \(CPUutil\) in (5) by a function of the number of cores and their frequency, i.e., \(f_{cpu}(ActiveCores,\)\(Frequency)\), can further improve energy efficiency. This may help to decide in which traffic  
Figure 15: Accumulated energy consumption for different number of cores during network average latency test with 5 ms limit. load scenarios it is useful to have more cores with a reduced frequencies or fewer cores with higher frequencies. An energy-aware controller may change its processor frequency to go up during the network's bursts or go down on low demand automatically. This can be measured as a function of a predefined network parameter such as minimum throughput, packets per second or any other metric on a user's service level agreement. Openflow protocol defines ways for a switch to deliver accountancy data to its controller. This information can fine-tune the processor frequency on the controller as the demand on the data-plane changes. All authors contributed equally to this work. Conceptualization, T.F.O., S.X.-d.-S. and L.F.S. ; Formal analysis, T.F.O., S.X.-d.-S. and L.F.S. ; Investigation, T.F.O., S.X.-d.-S. and L.F.S. ; Methodology, T.F.O., S.X.-d.-S. and L.F.S. ; Software, T.F.O., S.X.-d.-S. and L.F.S. ; Writing--original draft, T.F.O., S.X.-d.-S. and L.F.S., and Writing--review and editing, T.F.O., S.X.-d.-S. and L.F.S. All authors have read and agreed to the published version of the manuscript. This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (CAPES)-Finance Code 001. Not applicable. The software used on experiments in this study are openly available in Zenodo at doi:10.5281/zenodo.4653312 [41]. The authors declare no conflict of interest. The following abbreviations are used in this manuscript: \begin{tabular}{l l} SDN & Software Defined Network \\ DC & Data Center \\ ICT & Information and Communications Technology \\ PUE & Power Usage Effectiveness \\ NPUE & Network Power Usage Effectiveness \\ CNEE & Communication Network Energy Efficiency \\ TCAM & Ternary Content-Addensable Memory \\ SLA & Service Level Agreement \\ API & Application Programming Interface \\ REST & Representational State Transfer \\ CPU & Central Processing Unit \\ RAPL & Running Average Power Limit \\ MSR & Model-Specific Register \\ OS & Operating System \\ ICMP & Internet Control Message Protocol \\ \end{tabular}