## 4 Results: State-of-the-Art Approaches
### Simulation of Cybersecurity and Interoperability in IoUT  
Assuming that an underwater network has been established taking into consideration the cybersecurity and interoperability aspects, we should be able to ensure its robustness, effectiveness, and operability. Simulation software allows engineers and scientists to predict the outcome of operational scenarios using data from the real-world. For example, companies take advantage of simulation software to design their products in the digital world, without the need for repetition of expensive and time-consuming physical representations. To realize the benefits of simulation, we can think of the designing of a UUV/AUV with specific requirements and characteristics, based on the hazardous environment it operates in. Simulation engineers can change environmental conditions unlimited times in a protected and monitored area, in order to measure its durability in various situations or to reach the limits of the system's endurance and extract quickly, accurately and cost-efficiently, its failure points. Especially in the IoUT domain, where danger is a major factor, and heterogeneity exists in plethora, simulation facilitates procedures tremendously, without affecting the accuracy of results. In this review, we mainly focus on the simulation of trajectories of UUVs/AUVs and their cooperation, as well as on the cybersecurity issues that appear. To achieve efficient simulation in different domains, several tools need to be available. Co-simulation of these tools is a very challenging research topic, due to their heterogeneity. Co-simulation is the joint simulation of loosely coupled stand-alone sub-simulators, taking into consideration their heterogeneity [94]. One of the goals of our research is to simulate the underwater environment in which underwater assets will interoperate, as well as assets' communication. Qualnet Network Simulation Software ([[https://www.scalable-networks.com/products/qualnet-network-simulat](https://www.scalable-networks.com/products/qualnet-network-simulat)]([https://www.scalable-networks.com/products/qualnet-network-simulat](https://www.scalable-networks.com/products/qualnet-network-simulat)) ion-software, accessed on 20 November 2022) is a scalable simulation tool for replicating live networks; it is used for commercial and military purposes, as well as by governments and educational organizations around the world. In addition, Qualnet provides a wide range of libraries and popular protocols, such as the Military and Radios library and Network (ARP, IPv4) and internet protocols (FTP, HTTP). It can run accurate simulations and analyze networks efficiently. This tool is utilized in related work [95], in which the simulation of an SDN ([[https://sdn.ieee.org/outreach/resources](https://sdn.ieee.org/outreach/resources)]([https://sdn.ieee.org/outreach/resources](https://sdn.ieee.org/outreach/resources)), accessed on 20 November 2022) IoUT was successfully established. Furthermore, it can model numerous nodes and supports the designing of new protocol models and the optimization of existing models. WOSS (World Ocean Simulation System, [[http://telecom.dei.unipd.it/ns/woss/](http://telecom.dei.unipd.it/ns/woss/)]([http://telecom.dei.unipd.it/ns/woss/](http://telecom.dei.unipd.it/ns/woss/)), accessed on 20 November 2022) is another open-source simulation tool, developed in C++, which enables the integration of existing underwater channel simulator (NS-2, [https://ns2 simulator.com/ns2-download/20](https://ns2 simulator.com/ns2-download/20) November 2022, NS-3, [https://ns3 simulation.com/network-simulator-software/](https://ns3 simulation.com/network-simulator-software/), accessed on 20 November 2022, etc. ); the user can input environmental data and as an output can have a channel realization.