## 4 Evolution of the Smart Grid Infrastructure: SDN-Enabled Smart Grid  
The smart grid technologies employed for industrial and mission-critical environments require new network management technologies to provide simple system management between smart grid sub-layers from applications, information sub-systems and communication infrastructure. Currently, the smart grid concept is a relevant critical use case that includes the protection, automation and control of electric power systems and which is supported by ICT facilities that must meet the real-timerequirements of these applications with high dependability and security. However, the current communication infrastructure may not dynamically adapt to the new business model of the smart grid due to its hardware dependability. For example, in the traditional network paradigm, each network device, such as switches (AMI meter), individually manages its routing table by using a pre-defined routing protocol. In this architecture, the pre-defined routing protocol of the network device cannot be flexibly changed or configured to adapt network dynamicity. From a service (application) perspective, the system administrator cannot dynamically manage the network system because the network and service layer are isolated from each other. Thus, the service administrator would not be able to directly identify a network problem even when the application service is down due to network instability. Further, a new application profile of the utility service or network function needs to be added to legacy AMI infrastructure, and all AMI devices need to be replaced or upgraded with service interruption. According to smart grid researchers, smart grid communication technologies are required to evolve in order to solve these various complexity problems affecting the large-scale smart grid system. In addition, they predict that SDN will allow information exchange across different network platforms and different layers and will enable the adaption of a new business model of the smart grid system [27,28]. Meanwhile, SDN-enabled smart grid architecture has been considered for various companies, such as Fujitsu and Cisco [46].  
SDN is a next-generation network architecture that provides simplified and flexible network-management services through the abstraction of lower-level functionality, such as packet filtering, switching and monitoring. In SDN, to isolate the control and data plane of the network, a centralized network controller manages the control plane of the network instead of individual network switches. The incoming packet information (flow) of each switch is reported to the SDN controller when a packet is not listed in its flow table. The SDN controller decides and publishes the flow entry of the requested flow from the network switches using an SDN application that can be directly programmed by the system administrator. This separated control is implemented in the application layer through an application-network interconnection interface, such as OpenFlow API [29]. Thus, the service administrator manages and monitors not only the service (business) application status, but also the communication system without the need for an additional network management system. Moreover, each resource-constrained AMI device does not need to maintain its routing strategy, which is maintained using the SDN controller. The network design and potential advantages of the SDN-enabled smart grid are discussed below.