# Development of a Novel Open Control System Implementation Method under Industrial IoT
## 1 Introduction
Compared to the components, services are platform-independent and highly interoperable since they interact via standard messages. Therefore, services are used to develop control tasks. In service-based open control prototypes, control services are often deployed on a cloud platform and publish their functions via exposing the uniform resource locators (URLs) over the network, which formalizes a Control-as-a-Service (CaaS) paradigm [6; 7]. But, this faces an urgent challenge: how to satisfy the time determinacy of control systems in the context of the indeterminacy of the network (e.g., latency, packet loss, etc.). A common solution is to distribute control services across cloud and edge platforms in light of their time sensitivity. That is, control services with high time sensitivity are placed on the edge platform, which connects actuators via real-time communication approaches, such as the field bus and real-time Ethernet, while control services with low time sensitivity are deployed on the cloud platform. In this case, openness is implemented by changing the URLs of control services. However, service-based open control prototypes fail to reach a high level of openness as well. In addition to the lack of a control task granularity standard, the reasons attributed to the deployment pattern of control services is relatively static since it is defined in light of the control service's time sensitivity, which is often invariable. Figure 1: The closed architecture of modern control systems. Overall, according to the open system's definition and the openness criteria, the key to implementing open control systems is the independence of control tasks. Here, independence has two meanings: one is the independence among control tasks, and the other is the independence between control tasks and infrastructures. Current open control prototypes attempt to deal with the first independence by defining a standard control task granularity. However, it is hard to define such a granularity standard, especially since the complexity and scale of control software are increasing rapidly. Regarding the second independence, current open control prototypes often develop control tasks in the form of components or services. But, this is incompetent with respect to heterogeneous infrastructures in the environment of the industrial IoT. This paper, therefore, suggests a new method for implementing open control systems in the environment of the industrial IoT. Specifically, the formal description of the control domain is introduced to cope with the first independence rather than defining a control task granularity standard. Virtualization technology is adopted to isolate control tasks from infrastructures to tackle the second independence. The rest of this paper is organized as follows: Section 2 presents related work about the formal description of the control domain and the virtualization of control tasks; Section 3 overviews the proposed open control system implementation method, with a corresponding demonstration that implements an open CNC system presented in Section 4; Section 5 concludes this paper and presents future work.