## 2 Exploring SDN, NFV, Policies, ML, Network Slicing and Telecom Security
### Software Defining Network  
SDN represents a paradigm shift in how networks are designed, operated, and managed [18]. Unlike traditional networks, where control functions are distributed among various devices, SDN centralises network intelligence in a software-based controller, separating the control plane (decision-making) from the data plane (traffic handling), which presents a different type of threat to the network [19]. This architecture allows for more flexible and dynamic network management, enabling administrators to adjust behaviour via software interfaces without modifying physical devices [20]. SDN simplifies network configuration and optimization tasks, reducing the complexity and cost associated with traditional network management [21]. As well, SDN facilitates a programmable network environment where changes are implemented through software controls rather than hardware reconfigurations, promoting a more dynamic and cost-effective network infrastructure [18]. This evolution raises, as in the previous network generations, security concerns. The attacks and threat vectors associated with SDN have been summarised by [22] and present relevance to both 5G and pre-5G networks. Several aspects can be considered regarding the vulnerabilities and defence mechanisms within different layers and interfaces of SDN architecture, and we can delve into the insights of those key points [23]* **Security Challenges in Interfaces:** SDN interfaces [24], particularly the northbound interface (protocol to support communication between controllers and applications or high-level control plane) and the southbound interface (OpenFlow protocol to support communications between controllers and SDN switches), pose significant security challenges [25; 26]. The southbound interface, which uses TLS (Transport Layer Security) and DTLS (Datagram Transport Layer Security), leaves their implementation optional due to configuration complexity, making these interfaces susceptible to attacks like eavesdropping and attacks on the control plane [19; 27].
* **Security Solutions for SDN:** These outline a multidimensional approach to securing SDN, which includes rigorously verifying SDN applications to prevent access by malicious software and implementing security mechanisms like the SE-Floodlight controller for the control plane [28; 29], which provides privilege separation and a secure API.
* **Control Plane Security**: This area is critical due to its central role in network management. Various security enhancements, such as the SE-Floodlight controller, extend the capabilities of existing solutions by providing mechanisms for privilege separation and secure northbound APIs, which act as mediators between the application and data planes.
* **Data Plane Security**: The data plane handles the actual packet forwarding and is secured through trust methods for authentication and authorization [30] to manage which applications can change flow rules in the network's forwarding elements.
* **Security Enhancements through Network Design**: The principles of SDN itself, including centralised network control and enhanced visibility of traffic flows, are used to bolster network security against common threats such as unauthorised access and control plane attacks.
* **Challenges in SDN Controllers**: The central role of SDN controllers makes them prime targets for DoS and DDoS attacks, compromising network integrity.