# Cybersecurity of Microgrid: State-of-the-Art Review and Possible Directions of Future Research
## 2 The Microgrid Architecture
### Communication Protocols and Standards of Microgrid  
To better understand microgrid communication protocols, research on the design of its communication network has focused on the interaction between several components of the microgrid for control and monitoring purposes. A review shows that numerous types of communication networks are used in microgrid systems, as depicted in Table 1. As standard communication protocols, the IEC 61850, Distributed Network Protocol 3.0 (DNP 3.0), Modbus, Profibus, Wi-Fi, and the TCP/IP are extensively used in microgrid operations [16; 17; 18; 19]. We present a brief description of the commonly used communication protocols in microgrid electrical systems in the following subsections. * IEC 61850 IEC 61850 is the most widely used standard of communication owing to its speed, excellent reliability, and security. The IEC 61850 standard is an international standard developed for substation automation. It is composed of three levels, namely, the process, bay, and substation. The IEC 61850 is built with different data attributes and functionalities to ensure interoperability, introducing some latencies in communication. This protocol is suitable to be applied in a microgrid, particularly in distribution automation [20]. * Modbus As reported in [21], Modbus is widely used in microgrids due to its simplicity. It can be transmitted over the different physical networks of RS 485, RS 232, and the Ethernet TCP/IP. However, the Modbus protocol is inefficient for large-scale data transmission from/to the network. It has high latency, making it unsuitable for a communication system, especially one involving emergency control. Such microgrid architectures such as PrInCE Lab use hard-wired networks if long delays occur in communication [16]. * Distributed Network Protocol 3.0 (DNP3) DNP3 is a power communication protocol originally developed by General Electric that was made public in 1993. Use in SCADA applications was the initial purpose for the design of DNP3. It is used mainly in the oil and gas, security, water infrastructure, and electrical industries in Asia, North America, South America, Australia, and South Africa [22]. The initial design of DNP3 comprises four layers: the transport, application, data link, and physical layers. Serial communication protocols such as the RS-232, RS-422, and RS-485 became the basis for designing the original physical layer. The DNP3 has been moved over to the TCP/IP layer to support current communication technologies. Therefore, it can be considered a three-layer network protocol that operates on the TCP/IP layer [22] in supporting end-to-end communication. Contrary to Modbus, the slave of DNP3 can produce feedback with unsolicited responses to the master. Single DNP3 messages can demonstrate time-stamped tasks and information on data quality and various data types [17]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Study** & **Year** & **Media** & **Protocol** & **Advantages** & **Limitations** \\ \hline Korea- KEPRI Microgrid [18] & 2014, 2017 & Optical fiber & N.A. & High-speed communication, low latency time, & Cover short distances \\  & & & high reliability & & \\  & & & & high reliability & \\  & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A summary of the advantages and limitations of microgrid communication protocols based on selected related works. DNP3 is to be replaced by IEC 61850 in substation communication. The general belief is that in future power systems, IEC 61850 has the potential for usage outside substation communication, although its use is presently limited within a power substation [30]. Due to the absence of any security mechanism in the initial design of DNP3 and IEC 61850, the microgrid network can easily intercept or falsify messages sent through them, resulting in either incorrect operation of power devices or information leakage.