# Advances in Improving Energy Efficiency of Fiber-Wireless Access Networks: A Comprehensive Overview
## 6 Implementation of SDN-Based Energy Conservation Concepts in the FiWi Networks
The simulation results showed that various trade-offs should be considered when evaluating the EE of the system. In order to minimize power consumption without adding additional delay in the 5G EPONs, the authors in ref. [101] proposed a framework based on the SDN and NFV paradigms (Table 5). The authors proposed an SDN 5G EPON network design that reduces the complexity of managing and operating the network, while improving the usage of network resources. The suggested solution extends the multipoint MAC control sub-layer in the OLT and divides its responsibilities between the OLT and the SDN controller. The management and control functions of the OLT and RAN were moved to the SDN controller, while the other functional components remained in the OLT and were integrated with the OpenFlow switch. Therefore, the functions that operate on longer time scales were transferred to the SDN controller, while those related to shorter time scales were kept in the OLT and RAN. This design allowed for the integration of EPON and RAN energy conservation techniques and additionally enabled the minimization of CAPEX costs. Nevertheless, the authors in ref. [101] emphasized the need for further evaluation of the proposed solution in order to clarify levels of energy savings. The authors in ref. [102] proposed the PS scheme for FiWi networks based on an SDN approach (Table 5). The scheme is based on the OpenFlow protocol and a newly introduced controller that manages ONU's working and sleeping states based on the traffic flow threshold. According to the simulation results, such a proposed centralized energy-saving approach based on SDN has a significant advantage. These advantages are mainly due to the central management provided by the introduced controllers. The controllers enable fair distribution of available resources, which results in greater energy savings. The authors demonstrated that the proposed SDN-based energy-saving scheme in the FiWi networks is effective and has practical value. To achieve energy-efficient computing in a specific environment such as cloud-edge FiWi networks, it is crucial to coordinate the actions of edge servers and cloud servers in order to reduce energy consumption. Therefore, the authors in ref. [103] presented a solution for reducing energy consumption in such an environment by improving the cooperation between edge servers and cloud servers (Table 5). The proposed solution, called energy-efficient workload allocation (EEWA), was tested on an SDN testbed to demonstrate its feasibility. In addition, simulations were conducted to find the best possible outcomes for a set of task requests. The simulation results indicated that the EEWA scheme significantly decreased the network blocking probability and the average energy consumption in edge-cloud FiWi networks. While implementation of SDN in RAN shows potential for improving EE of the FiWi networks, much work remains to be done within the areas of algorithms, standardization, architectures and interfaces.