## 4 Evolution of the Smart Grid Infrastructure: SDN-Enabled Smart Grid
### Candidate SDN Application for the Smart Grid
The experimental result of the SEMDS shows that the number of request messages and response delay time of the situational-awareness system are reduced compared to the traditional pre-defined profile-based demand response smart grid system [33]. * System and network monitoring: In traditional smart grid communication infrastructure, the service provider cannot monitor the network status without an additional packet inspection device. IEC 61850 focuses on device monitoring automation and not on network-wide monitoring. Thus, the service provider cannot determine the accrueable reason for the instability of the communication infrastructure without using a network-monitoring device. Further, it may be difficult for the network system administrator to determine the actual problem leading to the loss of application packets, because the network stack cannot open the application packet itself. Thus, the system administrator can only identify the end-to-end perspective problem, even if the packet-loss problem occurred during packet transmission in the link layer (hop-by-hop). However, in the SDN-enabled smart grid, the service provider can not only monitor the device, but can also monitor the network status, such as the real-time throughput, dropped packets, topology and link-connection stability between devices. To realize application and network monitoring in SDN, the smart grid application characteristics and network parameters should be handled by an SDN controller. In 2014, [PERSON], [PERSON] et al. proposed a smart grid SDN management application for an IEC 61850-based smart grid system [12]. In this system, they presented a substation configuration description (SCD) information-mapping algorithm for SDN. In traditional smart grid infrastructure, the communication system cannot utilize these types of information for network optimization and monitoring. The SCD is an application profile of the IEC 61850 system and indicates various metering application profiles, such as monitoring intervals, attributes and types. However, in this scheme, the SCD profile is converted to the OpenFlow flow structure. The converted flow structure from the SCD is inserted into the OpenFlow entry table, and the SDN controller maintains the smart grid data flow using its monitoring application. Thus, the system administrator can simplify the access and management of both the application (service) and network using a single SDN controller. The experimental result of the IEC 61850 and OpenFlow achieves automated network monitoring as a real-time topology view, link bandwidth, traffic flow and address information of the substation network. Further, the authors can easily detect service denial attacks using the application and network monitoring SDN application without the need for additional network monitoring devices, such as firewalls [44]. * Neighbor discovery and routing: Optimal network configurations, such as routing and network topologies, are key to providing stable smart grid data communication links between HES and IEDs, but they cannot be dynamically configured by service providers in traditional networks. For example, the neighbor-discovery message interval cannot be dynamically configured in a traditional smart grid, even if the communication environment is very stable. Therefore, the service application may suffer from excessive control message overheads. In addition to the topology construction overhead, excessive routing-control message overheads may lead to a low QoS in resource-constrained AMI network environments [45]. SDN provides a flow-based forwarding strategy that employs combined neighbor discovery and routing SDN applications. [PERSON] et al. proposed a multi-layered SDN4 smart grid architecture in 2014 [34]. In this architecture, the routing path between the central server and devices was constructed using a centralized SDN controller instead of the distributed routing protocol of the devices in the network.