## 2 Smart Grid Technology Essentials  
The smart grid is a large-scale and complex networking system, and the National Institute of Standards and Technology (NIST) has therefore developed a conceptual hierarchical smart grid network infrastructure [1]. This conceptual architectural reference model enables us to analyze use cases, to identify interfaces for which interoperability standards are required and to facilitate the development of a cyber-security strategy [1,9]. Figure 1a shows an example of a three-tier hierarchical smart grid network that is organized by wide area networks (WANs), neighbor area networks (NANs) and home area networks (HANs). The HAN is an end-user network that is constructed by the connection between smart household electric appliances. The NAN is a capillary of the smart grid that provides large-scale data communication and connectivity between each household and a WAN. The WAN is a high capacity data network between NAN gateways and the head-end system (HES). In this smart grid network, all devices need to use the same communication policies, such as the routing strategy and quality of service (QoS) properties of the application, in order to provide the 3S autonomous network functions, namely self-configuration, self-healing and self-optimization. Figure 1b shows the layer-based information and power-flow model of the smart grid. In this figure, all objectives between the power facility and end-user system, such as the power generator, substation and AMI, are connected to the wired power grid infrastructure. The information data from each objective is exchanged via the data-communication infrastructure, which can be established using both wired and wireless communication protocols, such as powerline communication (PLC), Ethernet, IEEE 802.11 wireless local area network (WLAN) and the IEEE 802.15.4 family of protocols [8, 9, 10]. In this layered smart grid model, the electric and communication infrastructure support the two-way flow of electricity and information. Note that it is straightforward to understand the concept of the  
Figure 1: (**a**) multi-tier-based smart grid network architecture. (**b**) Abstraction of the information and power flow view of the smart grid infrastructure;  
\"two-way flow of information\". \"Two-way flow of electricity\" implies that the electric energy delivery is no longer unidirectional. The synthesized requirements of the desired smart grid are as follows:  
* The smart information subsystem is responsible for advanced information metering, monitoring and management in the context of the smart grid. * The smart communication subsystem is responsible for communication connectivity and information transmission between systems, devices and applications in the context of the 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 the application and information sub-systems to the communication infrastructure. Currently, the smart grid concept is a relevant critical-use case, which includes the protection, automation and control of electric power systems and which is supported by ICT facilities that must meet the real-time requirements of these applications with high dependability and security [11]. However, the current communication infrastructure may not be able to dynamically adapt to the new business model of the smart grid because of hardware dependencies. According to some smart grid researchers [12, 13, 14, 15], communication technologies first need to be further developed, and they predict that software-defined networking (SDN) will allow information exchange in different network platforms, different layers and provide the adaption of new business models of the smart grid without hardware replacement. In addition, they argue that the SDN-based smart grid will improve the system robustness by enhancing the reliability and optimization of the transmission asset utilization [13, 15].