# A Trustworthy Communication Hub for Cyber-Physical Systems
## 1 Introduction
It is also well known that some application ecosystems have very much the same types of challenges to collaborate. For example, Apple's iPhone is tightly coupled with its cloud storage service iCloud, Android smart phones with Google Drive, and Windows ecosystem with OneDrive. Accordingly, wearables, home automation devices, machines, and so on are tightly coupled to operate with the specific SPs' clouds. These realities cause significant barriers for smart communications between CPSs required by the owners. The owners require trustworthy and secure communications, and data/information exchange exposed from their owned CPS entities with the other owners without compromising their privacy. This means that the owners need to manage access rights across several SPs that host their CPS entities. Currently, there is lack of proper means for owners to monitor and control the policies used to regulate access to their CPS entities and exposed data. Furthermore, each SP usually uses its own specific solution for access control. This requires owners to redefine their policies for each SP system, which causes difficulty in synchronizing them across multiple SPs. The situation becomes even more challenging when owners want to share their CPS entities with other owners who are not registered to the same SP, and SPs do not have any means of verifying authorizations for unknown users. However, owners require more and more trustworthy, smart, and interoperable operation from their SPs, which is in line with their own collaboration agreements, and their regulated privacy and ownership rights related to the data/information exposed from their physical CPS entities (resources). The selected research method is experimental/constructive relying on hybrid simulation based prototyping and systematic evaluation of the solution constructions. The hybrid simulation refers to a method in which simulated entities and models are executed together with selected real entities in order to validate the operation as much as possible representing real system behavior [1]. The results from the preceding steps of this research, the dynamic communication spaces concept, are applied as an essential starting point for this research [2]. Accordingly, it is expected here that each user/owner has its own communication space, which consist of links to the services, networks, content, and devices of the specific user. In the preceding steps, the required capabilities as separate functionalities for enabling the concept were studied; however, the challenges related to trust and security were not considered and any proper design of the communication spaces solution was not proposed. In this research step, we focus on solving these challenges and prototyping a novel solution realizing the concept, which is especially targeted to fulfill the needs of energy flexibility and traffic accident cases. As the result, we provide a trustworthy communication hub for CPS (CPS hub), describe its' main conceptual enhancements with design of building blocks, and clarify the evaluations. Special novelty arises from the combined trust and communications process when dynamic resources owned by different stakeholders are exchanging information. The solutions provided are developed in a step-by-step manner and evaluated accordingly in the energy flexibility and traffic accident cases. The reminder of this paper is organized as follows. Related works of this research are discussed in Chapter 2. The main concepts of the CPS communications hub are provided in Chapter 3. The building blocks of CPS communication hub are described in Chapter 4, and respective solutions in Chapter 5. The evaluation results are clarified in Chapter 6. Finally, the conclusions are presented in Chapter 7.