# Dynamic Virtual Network Slicing and Orchestration for Selective MEC Services over Wide-Area SDN
## 2 KREONET-S: Wide-Area SDN Infrastructure Development and Deployment  
SDN has attracted much attention as a new network paradigm. Open Network Foundation (ONF) [22] is a founder of SDN and leads the technology development, interface and data model standardization, and SDN commercialization in a joint effort and partnership with major telecommunications and service providers in the world. According to ONF, SDN is defined as follows: \"the data plane and control plane are separated in SDN architecture, and network intelligence and network status information are logically centralized in the control plane. Network infrastructure is abstracted from the perspective of applications.\" The SDN architecture is composed of a data plane, a control plane, and an application plane, which are associated with the southbound interface (SBI) and northbound interface (NBI) on the basis of the aforementioned definition by ONF. Figure 1 shows that the SBI interconnects the data plane and the control plane, and the NBI provides abstracted network information by interconnecting the control plane and the application plane. Moreover, multiple SDN controller instances in the control plane can be clustered as a logically centralized controller by exchanging the network topology view and the state information via eastbound and westbound interfaces (EWBIs). The logically centralized controller is capable of high availability and scalability in regard to reliable SDN operations and management, resulting in efficient handling of massive network traffic generated from large-scale and wide-area SDN environments. According to the fundamental SDN architecture defined by ONF, as shown in Figure 1, four principal layers are designed and developed for the KREONET-S initiative, namely, the infrastructure layer corresponding to the data plane, the control layer corresponding to the control plane, the virtualization layer corresponding to the application plane, and an additional orchestration layer (for network automation and intelligence) also corresponding to the application plane. KREONET-S has several unique features, as compared with other SDN platforms. First of all, KREONET-S provides a native and tunnel-free wide-area SDN infrastructure, adopting the standard OpenFlow protocol as its southbound interface and APIs. Other SD-WAN technologies developed by the commercial vendors generally use overlay and tunneling mechanisms with the proprietary interfaces and APIs applied, which may cause vendor lock-in  
Figure 1: Fundamental software-defined network (SDN) architecture: data, control, and application planes and interfaces [23]. issues, thereby hindering heterogeneous and multi-vendor network deployment and further technology development. Furthermore, KREONET-S is differentiated from other platforms and applications that use ONOS as their SDN controller, mainly considering the VDN (and VDNO) capabilities. The VDN system is a district ONOS-oriented application providing logically isolated and dedicated networks over WAN with high performance and strict end-to-end network security guaranteed, particularly using dynamic flow control and automated end-host/UE awareness. On the other hand, other well-known ONOS virtual network applications are rather focused on the datacenter (overlay) network virtualization or LAN virtualization, for example, SONA (Simplified Overlay Networking Architecture) and VPLS (Virtual Private LAN Service). In addition, the VDNO system coordinates the VDN system and Kubernetes to integrate virtual networking, computing, and storage resources in an automated manner, which is described in detail in Section 3. The layered architecture of KREONET-S is indicated in Figure 2. The infrastructure layer of KREONET-S facilitates OpenFlow-capable core and edge network devices to build a wide-area SDN as a data plane network in five regions in Korea (Daejeon, Seoul, Busan, Gwangju, and Changwon) two regions in the US (Chicago and Seattle), and one region in China (Hong Kong).