## 2 State of the Art
Catering to vast models, it encompasses both qualitative and quantitative examination instruments. * **Fault Tree Analyser** (Demo version available): A segment of ALD's suite tailored for reliability engineering and risk evaluation, this tool offers a visual interface for constructing and scrutinizing FT. It is engineered to deduce the likelihood of a principal event from the probabilities of foundational events. * **Isograph FaultTree+** (7-day trial): Crafted by Isograph, FaultTree+ is a leading application for creating FT and executing qualitative and quantitative FTA. Its user-friendly interface is equipped to manage a range of logic gates and incidents. Industries such as defense, aerospace, nuclear, and rail have integrated Isograph's software suite into their operations. * **Item Toolkit** (30-day trial): This suite offers tools essential for reliability predictions--Failure Modes and Effects Analysis (FMEA), FTA, and other reliability engineering undertakings. Designed for analyzing both rudimentary and advanced systems, it aids engineers across domains, from electronics to mechanics, to gauge their designs' reliability. * **DFTCalc** (Open-source): Essentially a \"DFT Calculator\", DFTCalc specializes in DFT analysis. Differing from conventional FT that employs just AND and OR gates, DFT encapsulates event sequences and intricate interdependencies. Scripted in C++, DFTCalc yields metrics for reliability and availability for such trees. Despite a wealth of research, significant discrepancies in the interpretation of KPI persist across several publications [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. With an intent to address and rectify these inconsistencies, in paper [26], the authors propose a time-dependent reliability analysis tailored for a real critical energy infrastructure use case, which consists of interconnected urban electrical and communication network reliability assessment of highly reliable elements, which leverages exact reliability quantification of highly reliable systems. The software presented in this paper can quantify the reliability of very reliable systems up to \(10^{-45}\), which was demonstrated on a Highly Reliable Markovian System (HRMS) benchmark and also successfully compared with MOCA-RP software [26]. Differentiating from earlier studies, the current investigation of this paper's authors emphasizes a robust reliability quantification, which is applied to the real interconnected energy infrastructure. The interconnected infrastructure is based on the real system located in the Czech Republic and covers two distinct infrastructures: the power grid and the communication network. For illustrative purposes, the paper introduces a novel version of an interconnected infrastructure test network proposed in [27]. Further, in the realm of time-dependent reliability analysis using AG, pertinent algorithms for discrete maintenance optimization of intricate multi-component systems have been presented in [26]. Given the current discourse in the state of the art, there is an unequivocal demand for specialized software tools that can handle the time-dependent reliability of highly reliable interconnected systems. Pursuing this need, the main aim of this paper is to incorporate the computations related to unavailability into a pre-existing simulator, which has been elaborately discussed in [28].