# Cyber Physical Systems Dependability Using CPS-IOT Monitoring
## 3 The CPS Dependability Model
### The CPS Orchestration Model  
In Figure 2 an inner feedback loop reveals the interactions between the cyber and physical spaces and how the CPS is monitored through an inbound surveillance and an outbound actuation process. The figure also reveals: (1) A physical-to-cyber flow of information originating in the physical space and translated into services at higher levels in the cyber space and (2) a cyber-to-physical flow of information, initiated by the processing of information in the cyber space to achieve actuation, both within the sensor network and on physical objects in the physical space. In essence, information flowing from the physical to the cyber space includes: \"Sensor data\" obtained from the sensing of physical objects and \"sensor network monitoring data\", which are extracted from sensor network surveillance. Information flowing from the cyber to the physical space on the other hand contain \"control signals\" for actuating physical devices within the environment and \"control messages\" required for re-optimisation and reconfiguration of the sensor network. In the proposed CPS management model, the key processes are sequentially iterated in a loop as follows:  
Sensing: This is initiated in the physical space to sense the environment for further processing in the cyber space. It generates \"sensing data\", which are routed over paths created by CTPs. These sensing data are used to analyse the diffusion of information in the CPS-IoT subsystem, for the purpose of monitoring the performance of the subsystem and and anomaly detection.  
Communication: The communication process is initiated at the physical space where IoT protocols such as LoRa, ZigBee, and BLE are used to move data from sensors to sink nodes and finally to gateways at the edge layer. Communication processes can also extend to the cyber space where other protocols are used to move data from the gateways to the fog layer for further processing.  
Inbound surveillance: This is the first process initiated in the cyber space and is used to assess the integrity and performance of the CPS's IoT subsystem as well as detect anomalies before and during data processing.  
Data + Control: Filters data and control information and stores the information into databases for batch or stream processing. In batch processing, data are stored in databases for a longer period of time while streamed information are processed in real time to produce data analytics for decision making.  
Data processing: Here various analytics and simulations are applied to the data (both batch and stream) to support decision systems.  
Figure 2: CPS orchestration model.  
Observation center: The observation center is an entity of the CPS management infrastructure where the results are observed by the operation specialists for decision-making purposes (storage or actuation).  
Outbound actuation: The outbound actuation is the last process implemented at the cyber space. It involves adjusting the operating parameters of the IoT subsystem based on the inbound surveillance to restore the CPS's optimal settings whenever necessary.  
Actuation: Initiated in the physical space to either restore the network to its optimal operational level or perform actuation on physical objects in the environment as a result of the data analytics or decision(s) made at the observation center.  
As described above, the CPS orchestration model includes an adaptive control loop similar to the MAPE-K structure [33; 34; 35; 36; 37] where (i) \"Monitoring\" is achieved through the sensing process, (ii) the \"Analysis\" is done by the inbound surveillance, (iii) \"Planing\" is performed through the Data processing process, (iv) the \"Execute\" is achieved by the outbound actuation process, and (v) the \"Knowledge\" acquired in the observation center is used to support decision making.