## 5 Roles of SDN for Cloud-Fog Enabled 5G and Beyond
### Resource Scheduling in Cloud-Fog  
The authors in [57] proposed an architecture for task scheduling in SDN-based IoT-fog networks, in which the fog devices are clustered into virtual organizations (with each of them representing a fog region), and they are interconnected by SDN switches. The central controller of their scheme is located on the cloud gateway. In this work, the authors considered the fog gateway and the cloud gateway as the SDN switch and the SDN controller, respectively. The study work in [14] proposed an SDN-based cloud-fog architecture for telesurgery in a tactile internet system. Since the performance of robotic telesurgery largely depends on the network performance in terms of latency, jitter and packet loss, the authors used optical network connecting cloud, SDN and fog layers. In the fog layer, a special routing and forwarding method is used for SDN packets. They proposed a scheduling algorithm to meet real-time requirements in the SDN because the traditional algorithms for SDN are not appropriate, effective, or applicable. SAFE, as the next work in this category, is a secure healthcare ecosystems introduced in [58]. At the edge of the network, the healthcare units exits where thousands of the biosensorsors are generating the continuous data streams. The primary purpose of medical data computation is improving decisions for health and fast patient recovery. Due to the physical distance of cloud resources from these real-time applications (biosensors, various other hospital applications), SAFE works as a cloud and edge interplay. It supports the computational demand of ever-increasing medical applications for quality of experience (QoE) and QoS constraints. SAFE leverages the lattice-based cryptosystem and deploys global and virtualized SDN controllers to ensure resource allocation, low latency, and services management for increasing healthcare applications in a distributed/multi-region infrastructure. In [59], the problem of fog node trust is exploited for the security of healthcare unit and patient records. When the cloud-fog is used for smart healthcare, health data need to be securely communicated in a parallel manner. Health data can include various unauthorized intentions, which drives the fog node for biasing behavior and violating the data security policy (e.g., tempering attacks at Fog node, fabricated health records). Data in the healthcare unit are processed mostly at nearby fog nodes, whereas the data heterogeneity and some real-time or delay-intensive healthcare demands can bottleneck the neighboring fog node. The SDN controller deployed in a distributed manner can manage the load by provisioning the resource effectively and ensure the network security edge efficiently. Authors in [59] also presented a case study that proposes secure privacy aware health data computation with the assistance of fog and cloud nodes. [PERSON] et al. [60] also investigated the SDN-enabled edge network for resources and secure services provisioning in a healthcare system. In this paper, a framework is proposed for IoT device authentication that employs the probabilistic k-nearest neighbor (p-KNN). Using p-KNN, an edge server investigates the legitimacy of healthcare IoT devices and SDN performs efficient collaboration among the edge servers that are close computation resources. The research work [61] addressed the problem of services quality for demands by local residential communities at the edge. Required services often include multimedia services, IoT and video gaming applications in distributed edge access networks. The proposed mechanism introduces function chains to support the differentiated treatment for required services. It also includes a control management and a virtualized management network domain. The control plane in this methodology provides the initiation of NFV, service function chains (SFC) and routing for the application of the residential gateway. The SDN control plane also supports mapping different VNFs to the virtualized management network domain, using APIs in the edge cloud.