# Artificial Intelligence Enabled Routing in Software Defined Networking
## 1 Introduction  
### Software-Defined Networking  
The revolutionary technology of radio access network (RAN) in each generation is obvious from the first generation of mobile communications (1G) to the fifth generation of mobile communications (5G) and beyond, but the revolution is not in core network (CN) technology. Only the 3G era has experienced a major change from circuit switching to packet switching. Considering that global operators have invested huge funds in the previous CN technology, the CN technology revolution at the 3G stage allows the two switching modes to coexist and make the operators freely choose to adopt circuit or packet switching mode until the 4G era comes, which is officially integrated into the all-IP (Internet Protocol) packet switching core network system. With the growing demands for wireless mobile communications in the Internet of things (IoT) society after 2020, 5G is regarded as a revolutionary technology with great hopes and an innovation in the RAN technology. As to the CN technology in 5G, it is expected to meet the needs of the rapid development of various services that include a wide range of data and connections in the future, and to ultimately meet theuser-centric wireless communications. One of the most important key to networking requirements is the development of two technologies, software-defined networking (SDN) and network-function virtualization (NFV) [1]. SDN is a kind of control signaling and user data separation, centralized control of network functions, and open application interface (API). After the introduction of SDN, the new challenges are how to reconstruct network functions, how to design new interface protocols, and then optimize the architecture and end-to-end signaling process based on SDN. Similar to some concepts of SDN, NFV uses cloud virtualization-based information technologies to transform 4G/5G core network, using general purpose platform (GPP) to build the basic telecommunications environment. Focusing on applying artificial intelligence (AI) technology to CN routing, this paper presents an AI-enabled routing scheme specifically for SDN because the core concepts of both SDN and NFV technologies are quite similar and the two have high conditions for complementary integration. Based on SDN architecture, several works have been proposed to successfully overcome the limitations regarding the de-facto standard simulator, Mininet [2], or the implementation of multi-domain connectivity services [3; 4; 5; 6; 7]. SDN is an emerging networking architecture that consists of three layers [8; 9], namely, the application, control, and data planes (see Figure 1). SDN is programmable through logically centralized management to simplify complex network tasks, such as route optimization, traffic engineering and so on for increasingly diversified network deployment. The SDN control plane is required to discover a network topology of the entire SDN infrastructure mainly for configuring data transmission paths between any source-to-destination pairs in the data plane. However, discovering a network topology is challenging due to frequent migration of the virtual machines in the data plane, lack of authentication standards, and so on. For the purpose, the authors of [10] have presented a comprehensive survey of the topology discovery and the associated security implications in SDNs. The application programming interface that resides between the control and application planes is called the northbound interface, where a set of network services such as quality of service (QoS), intrusion detection, and monitoring functions can be implemented. Communication interface between the control and data planes is called the southbound interface, where the OpenFlow protocol [11] is commonly used to exchange control messages with forwarding devices, referred to as OpenFlow switches. An OpenFlow switch comprises one or more flow tables, a group table, and an OpenFlow channel for the external controller.