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A cloudlet is a small-scale data centre or a cluster of computing devices designed to provide cloud services to primarily constrained devices close to it (Babar et al., 2021). The industrial IoT system is made up of many heterogeneous nodes that are connected using different wired and wireless networks (Lou et al., 2021). An industrial system has at least three levels of network hierarchy. The lowest level comprises sensors and actuators, while the second level comprises programmable logic controllers and computerized numerical control systems; the third level generally includes complex computing devices that can form edge devices in IoT systems. Industrial IoT systems are an ideal application for a localised cloudlet architecture as they guarantee data privacy, security, and predictable latency jitters (Fernández-Caramés et al., 2018). The proposed cloudlet system is a low-cost solution that is easily adaptable to small-scale and medium-scale industries. This solution is also scalable for large-scale industries since the architecture and the network protocol provide a consistent performance irrespective of the number of nodes that are part of the cloudlet system. The complete cloudlet architecture is shown in Figure 1.
Figure 1. The Complete Architecture of Cloudlet
The solution eliminates the need to pay for higher-cost, less secure cloud services that may be inaccessible due to connectivity issues. Most industrial complexes are situated at the periphery of cities, so the network connectivity may need to be more consistent. Also, cloudlet systems solve the significant and unpredictable jitter in task execution by allowing tasks with hard real-time deadlines to be scheduled on a priority basis (Ramasubbareddy & Sasikala, 2021). Tasks with long-running and soft real-time deadlines may be transferred to the cloud. Generally, industrial networks have three levels of hierarchy, as shown in Figure 2.
Figure 2. Hierarchical Model of Industrial Networks
- 1.
The device level, i.e., the network of sensors and actuators. The primary function at the device level is data acquisition and control.
- 2.
The field level, which is made up of controllers and programmable logic controllers. This level controls the manufacturing process or industrial equipment. The processing capabilities required are high because complex control functions are implemented at this level.
- 3.
The plant level comprises two or more complex computing devices that form the edge of the IoT system. We propose replacing level 3 with a cloudlet system comprising distributed system on chips (SoCs) connected in an ad-hoc network.
The cloudlet system meets the requirements of industrial IoT: responsiveness, scalability, usability, flexibility, and security (Ren et al., 2019).
The cloudlet system collects industrial data in real time from the end devices in Levels 1 and 2.