## 3 ICT Sub-Systems of the Smart Grid
### Communication Infrastructure  
The smart grid is a combination of ICTs and the electrical power grid. It is expected to affect all segments of the current electrical grid system, including generation, transmission and distribution. However, these segments will not function well without an effective data communication networking system. In other words, designing a communication architecture that meets the requirements of the power grid is key to the successful implementation of the smart grid, because power grid implementation has long been established. Based on the requirements of smart grid, it initially implies a need for bidirectional, real-time communication networks for data collection and processing [17]. From a communication technology point of view, information exchange in the upper grid levels for SCADA applications is usually covered by existing communication networks belonging to utilities or grid operation [3]. A smart grid communication infrastructure also includes HANs, building area networks (BANs), industrial area networks (IANs) and a WAN. A HAN is a communication network comprising appliances and devices within a home. A NAN is a network of multiple HANs that delivers the metering data to data concentrators and delivers control data to HANs. A WAN is the largest network for communications to/from data control centers. In a HAN, appliances (such as meters for electricity, gas, water, heat and solar panels) can be equipped with smart meters; these meters also connect smart appliances (_i.e._, appliances with communications and remote control functions, such as smart dishwashers, dryers and ovens). In addition, these meters connect to a metering gateway. In a NAN, many metering gateways of HANs are connected to each other to form a wireless mesh network [6]. A WAN connects smart metering gateways with utilities and the distribution control system. These networks are often based on fiber-optic links that are installed in parallel to the high-voltage grid and connect primary substations, large power plants and control rooms. Furthermore, they are mostly based on Internet technologies. Today, the challenge regarding interconnection lies in the medium- and low-voltage levels required, which are usually not reachable (or only to a small extent) by utility-owned communication infrastructures. To bridge this gap, several communication protocols are provided. PLC systems overcome traditional electronic communication technologies. The PLC channel is problematic, because it is time varying and depends greatly on the actual network topology and the connected electrical loads. To ensure connectivity from a communication viewpoint, network elements, such as transformers, need to be bridged with phases coupled, which requires additional equipment that is expensive at the higher voltage levels. Furthermore, regulation of the frequency bands used for data transmission is fragmented worldwide and remains unclear. The implementation of PLC is considered to be both economically and technically challenging and is still in its infancy compared to other communication technologies. However, it is a promising possibility that is currently being investigated. The use of wireless networks is an alternate option, because they are flexible and can be used to build utility-owned networks. However, typical broadband computer network technologies, such as worldwide interoperability for microwave access (WiMAX) and WLANs, are problematic with respect to their limited transmission range and reachability, especially in urban areas. Hence, they may serve only as communication subsystems for small clusters of devices, such as meters. For long-distance transmission, trunked radio systems, such as terrestrial trunked radio (TTR) or trans-European trunked radio (TETRA), are becoming popular in some countries. Installation costs are moderate, even though the frequencies used are not license free.