# A Trustworthy Communication Hub for Cyber-Physical Systems
## 6 Evaluation
### CPS Hub with External Authorization Service in the Traffic Accident Case  
The traffic accident case is described in the work of [24], and overviewed shortly in the following (Figure 27). A person does his exercise on the road, and monitors the performance via the smart watch. The smart watch is able to receive warnings from environmental conditions such as CO\({}_{2}\) level, because the owner of the CO\({}_{2}\) measurements has allowed delivering the measurement reports directly to him. Simultaneously, another person is hunting in the nearby forest with his dog. The dog has a tracker that makes it possible to follow the dog on a map. If the dog runs too near the road, the location of the dog is detected by the nearby street lamp, which thus increases the intensity of lightning and starts blinking. However, a vehicle collides with the hunting dog, causing an accident. A person sees the accident and calls the alarm center. The alarm results in authorized changes in the information delivery process according to the profiles of the persons and stakeholders on the road. For example, authorities such as the police and medics are able to receive information from multiple devices and stakeholders according to their alarm-related profiles and see the situation online. Figure 26: The CPS hub with streams based M2M service platform. Figure 27: Structure of the smart mobility in the emergency case. The capabilities of the CPS hub to operate with several heterogeneous stakeholders' systems and resources of multiple owners so that the security policies of the owners can be taken into concern were tested in this evaluation step. This considered the evaluation of the scalability of the CPS hub to support presence management of a larger set of resources owned by different stakeholders; evaluation of the trust checker of CPS hub for taking care of the dynamic grid of agreements dynamically negotiated between the parties/resources; evaluation of the trust checker negotiation with SAFAX in a simple security policies case dealing with alarm type of event; and evaluation of the trusted publish/subscribe type of information sharing between resources, so that the delivery of subscribed content happens only if it is allowed. The operation capabilities of the trust checker of the CPS hub to collaborate with policy based authorization, extensible authorization framework as a service (SAFAX), were especially focused on in this evaluation step. In addition, the capabilities of trust checker to take into concern the policies of the owners in the information delivery process were tested as the part of the traffic accident case. First, a simple security policy for the owner \"IMEC\" and \"Polar\" was done so that they allow delivery of the CO\({}_{2}\) measurement information between each other. In addition, a special system status information to a specific location area was defined to indicate the \"alarm\" type of condition. It was seen that only an authorized stakeholder, which was simulated in this case, can define such an \"alarm\". Then, the security policies for the owners \"Polar\", \"Imec\", \"Starhome\", and \"Bittium\" were defined so that the information from their resources can be delivered to authorized stakeholder, \"LiveU\", if an alarm happens. After these actions, the alarm situation was executed together with the physical resources attached to the CPS hub. The trust relationship between the owners before the alarm event, the traffic accident, has happened is visualized in Figure 28. The respective situation after the accident has happened is shown in Figure 29.  
Figure 28: Trust relationship between owners before the alarm event, the traffic accident, has happened. The visualization screenshot shows that after the alarm event has happened, the trust relationships between the owners are updated according to their policies.