# Evaluating the Functioning Quality of Data Transmission Networks in the Context of Cyberattacks
## 1 Introduction  
According to the general global trend of the growth of information needs over the last 15-20 years, modernization of communication networks in the power industry is in progress; outdated networks are being replaced and digital telecommunication systems for processing and data transmission are being created. The result of such modernization should be a unified technological communication system of the power industry, which is necessary for the stable operation of the whole power system and its components [1]. Large-scale implementation of packet telecommunication technologies in the power system largely ensures the cost-effective and uninterrupted functioning of all elements of electrical network, from control centers to substations and high-, medium- and low-voltage distribution devices (Figure 1). A modern digital telecommunication network must meet the requirements of reliability, stability, security and efficiency in any of its segments. The significant impact of the quality of the resources provided by the energy system on the development of most sectors of the national economy determines, on the one hand, high requirements for packet data transmission networks, and on the other hand, increased attention on them by intruders, whose targets are elements of the energy complex. In fuel-power complex companies, the telecommunications network is usually divided into two segments--corporate and technological. The corporate segment is represented by a range of interconnected local area networks. The technological segment consists of the technological data transmission network (DTN). In local area networks, there are workplaces for employees whose activities are not directly related to the management of industrial equipment. After penetration into the company's infrastructure, malefactors are likely to get into this section of the network. Here, malefactors will be interested in computers that store confidential information. However, since the main goal of a cyberattack on the fuel and energy complex is the possibility of influencing production processes, the malefactor will not stop at the corporate segment. He/she will try to intrude into the technological segment, from which industrial systems are controlled, i.e., into the technological DTN. The malefactor will try to find a way to automatically control systems of technological processes, supervisory control and data acquisition (SCADA), industrial controllers, automatic blocking systems, relay protection terminals and other technological resources, depending on the goals of the malefactor. For example, when the malefactor carries out a cyberattack at an electrical substation, his/her intrusion in the behavior of the protective automation, in the case of an abnormal situation, can lead to power cuts for consumers. When the malefactor takes control of the main nodes of the network, he/she will be present secretly in the network until a decision is made to realize the active actions. However, it is possible that after examining reliable ways for access to important objects, the malefactor will leave the network to reduce the risk of his/her detection and return later. Obviously, a technological DTN should be isolated from the corporate segment, but this does not always happen. Remote access to isolated segments can be carried out from dedicated computers of administrators who create special communication channels in order to simply implement their tasks. In some companies, a technological DTN is completely separated from the corporate segment. This fact significantly complicates the implementation of cyberattacks, but does not mean that a malefactor's access to the technological DTN is impossible. In this case,  
Figure 1: The location of the technological data transmission network in the branch electric power complex. malefactor can use other methods.