# A Trustworthy Communication Hub for Cyber-Physical Systems
## 3 Concepts of the CPS Communication Hub  
### Conceptual Model for Cyber-Physical Systems  
A view of the structure of cyber-physical systems (CPS) is visualized in Figure 1, and shortly clarified in the following. The CPS system usually consists of subsystems such as a capillary network, gateway, infrastructure, and service systems, which are usually hosted by different stakeholders such as service providers, infrastructure providers, mobile connectivity providers, and asset providers. Each of these stakeholders usually have a number of agreements based relationship with their customers. This means that they usually have their own database of allowed users (their customers) in their service systems, which they do not necessarily want to open for the other SPs because of business reasons. However, multiple SPs can have agreements with a single user. When looking at the system from the referred customers/users' point of view, another complex dimension of the system pops up. This is because usually CPS entities (devices) may belong to a user, group of users, or an organization (_owner_). It is obvious that the owners want to use all the services relying on their own M2M asset devices/resources and the extracted M2M data/information based services in a smart way. As the result from these needs and recent new GDPR (General Data Protection Regulation (EU) 2016/679) regulations, it is envisioned that the requirements of owners shall be an essential starting point for establishment of future smart interoperable cyber-physical systems. Therefore, it is seen that the agreements between owners establish the rules according to which the access rights can or cannot be established. When looking at the agreements of an individual owner, it is obvious that there can be agreements with multiple service providers. For example, in the energy sector, the owner can have an agreement, for example, with an energy seller, energy  
Figure 1: A view of the structure of a cyber-physical system (CPS). aggregator, distribution network provider, and charging operator. The same owner can have also agreements, for example, with health and wellness service providers, among others. In addition, when looking at the relationships of the referred owner on a more detailed level, the owner can have an agreement level relationship with family/organization members and reliable friends/partners. However, it is obvious that such relationships can be under continuous change/maintenance processes. In addition, the trustability of the relationships may be fuzzy from an individual owner point of view. Therefore, there is the need for continuous monitoring of trust level. This reasoning has led us to the assumption that the future cyber-physical systems shall be structured in a new way by taking the _ownership and trust_ related requirements as the key starting point. The respective conceptual architecture model created as a part of this research and clarified in the work of [24]. According to it, the CPS system has been divided into set of CPS architectural zones according to horizontal abstraction levels of the system, system evolution perspectives, access rights, and roles of related stakeholders in the typical CPS value network. The defined architectural zones are vertical enterprises, IoT platform, demilitarized, mobility, physical resources, and authorization and trust zones; see the left side of Figure 2. The _vertical enterprises zone_ consists of CPS service providers' (SP) services and their service cloud systems targeted to support domain/sector/business specific services of individual SP. The _IoT platforms zone_ consists of horizontal service platforms, their components, and cloud systems of platform providers, which can be applied in multiple domains/sectors/businesses in vertical enterprises zone. The _demilitarized zone_ contains Internet type of networks, which can be open or limited for special use only. The _mobility zone_ consists of services of mobile access/connectivity providers such as mobile telecom operators.