# Internet of Things for Modern Energy Systems: State-of-the-Art, Challenges, and Open Issues
## 2 Key Features in the Energy Internet
### Communication Infrastructure  
Communication infrastructure is deemed as the backbone of the communications system upon which different broadcasting and telecommunication services are operated [45]. Many architectures are designed in respect of Information and Communication Technology (ICT), based on the need of the system and valid facilities. Generally, communication infrastructures are divided into two categories: (a) wired communication systems like Asymmetric Digital Subscriber Line (ADSL), PLC, and Ethernet; and (b) wireless communication systems like WiFi, Cellular, and Satellite [46]. The main goal of every communication system is to obtain, collect, process, and save the information from each component of the system. In this manner, information sensing and processing are defined as a part of communication infrastructure in energy systems [31]. After sensing information and processing it, the next step is to send commands from decision-makers to low-level parts of the system; this means that bi-directional or two-way communication systems are needed to handle data exchange among components. The whole process of receiving, processing, and sending back the data is affected by the stochastic nature of the loads. This means that uncertainty in the energy demand affects the designed structure of the communication system. Therefore, stochastic nature of loads should be considered in planning of the communication system [47]. To overcome this drawback, in [47], two robust applications based on multi-layer and mixed-line-rate network design are introduced for the communication network in order to deal with uncertain input parameters. Talking about collecting information in an energy system, which can be considered as a key part of communication infrastructure, gateways are needed to overcome this part, for which they are responsible to reach information from sensors and send it to data collectors [48]. In addition, in some cases, information could be shared with some parts of the system. However, what is understood from every communication system is that a well-designed architecture is needed for the communication system, so each component of the system can be named in a level [49]. In the IoT perspective, communication infrastructure is mostly included in network layers that provide networking supports and data transfer using wireless and wired network for industries [50]. In the IoT-based systems, communication networks face challenges like scalability of the system, quality of the service requirements, and optimizing communication related power consumption. In addition, as in this system, things are supposed to communicate with each other with minimal human intervention; then, each subsystem, in this case the communication system, should be able to be organized and healed by themselves. In this manner, standards and protocols need to be agreed by the society in order to have a mutual perception. To do so, in [51], communication protocols are categorized in three main classes that are contention-based, contention-free, and hybrid protocols. More details about communication infrastructures could be found in [51; 52]. Machine-Type Communication (MTC) is defined as the data exchange and processing among machines with the minimum intervention of human, which is generally used in IoT-based systems. To establish data connection among things in MTC, several steps must be followed: first of all, things that are supposed to be connected should establish a session between them (Figure 2). In this step, the flow and direction of data flow need to be controlled. Depending on the nature of the application, full duplex, half duplex, or simplex communication mode will be established. In this manner, applications must know when and how long they should send information. For this step, International Organization for Standardization (ISO) introduces a detailed protocol in order to establish the connection between objects in communication systems [53]. In the second step, they may exchange their main information.