## 5 Discussing Open Issues and Challenges
Nevertheless, apart from semantic modelling and simulation of interoperability issues, trustworthiness of universal interoperability which resides in cybersecurity domain, affects every interconnected device above and below the surface. UUVs and their applications result in many vulnerabilities. Collaborative tasks and heterogeneous devices demand real-time information exchange, adding even more obstacles in establishing a secure underwater network. Although traditional operating systemsdiffer from those in underwater communications, threats, and risks from the cybersecurity aspect, remain almost the same, with the main challenge being the protection of the CIA triad. However, countermeasures for regular WSNs are not directly applicable to UWSNs. For example, nodes, a critical asset for a robust underwater network, are the most vulnerable to cyber threats. Acting as transponders of information, they may distribute data packets for the whole operation. The eavesdropping of such communication or a DDoS attack are challenging threats that may be encountered. Moreover, as underwater assets incorporate electro-acoustic transducers to receive and transmit sound signals [124], adversaries exploit emerged vulnerabilities from a native characteristic of water, i.e., latency, which delays the distribution of this huge volume of data (and generated alerts from cyber incidents) as well as their inspection and analysis. Hence, the classification of attacks differs also. Security measures should be implemented and must be a precondition for the start of a mission. Simulations act as catalytic agents for the implementation of these measures, supporting even further the scientific community. Simulation tools are a key factor for the successful evaluation of a task. Based on our extensive research, the lack of specifically designed simulation tools for underwater security communications with the utilization of semantic modelling, was identified. Initially, the selection of a tool should be based on specific requirements, with the most important being (a) capability of heterogeneous data integration using ontologies/semantic knowledge, (b) support of multiple UUVs (swarms) simulation, (c) support of modeling and simulation of sensors and network interfaces, and (d) support of visualization for realistic scenario representation. Furthermore, in order to reuse an existed simulation tool or develop a new one, there is a high need for important extensions to be implemented in order to be compatible with the various emerging technologies, and thus to be more efficient. As we have already proposed in our preliminary work [125], introducing a high-level architecture model, these extensions include: (i) a compatible framework for integration of semantic data in various formats, (ii) the ability to analyze and integrate the huge amount of exchanged data to extract infer new knowledge, (iii) the enrichment of such integrated knowledge with underwater protocols and libraries of cybersecurity frameworks. The secure interconnection and interoperability between the devices and the vehicle or the vehicle and a central platform are resolved by using a semantic approach/ontology, especially if combined with a standardized middleware architecture to establish a common \"language\", regardless of the arrangement of heterogeneous components of IoUT. Concluding, what is needed today is an overall integrated approach for automated threat modeling, semantic knowledge representation, and robust simulation of the cybersecurity and interoperability challenges using an ontological model, to support the efficient prediction of the impact of rapid decision-making in critical situations such as military and SAR ones.