# IIoT System for Intelligent Detection of Bottleneck in Manufacturing Lines
## 2 Literature Review
### Current Reference Architecture for Industry 4.0  
Two primary architecture models were identified within the industrial context of manufacturing. One of them was exposed by the IIC (Industrial Internet Consortium) in 2017 as a common framework, called the IIRA [30] (Industrial Internet Reference Architecture). This architecture defines a high-level reference table with models, sectors, processes, and a series of domains to create an entire base ecosystem. Structurally, this IIRA defines a system through tiers that allow the information technologies model to integrate with the operational technologies model. It includes hardware and software in the physical context of industrial manufacturing, such as PLCs or SCADA systems [31]. This architecture, illustrated by the IIC [30], was partially founded on the principles of edge computing [32]. As we can see in Figure 2, the model comprises three tiers: edge, platform, and enterprise. The edge tier acts as the integration point between the industrial environment  
Figure 1: Example of grouping by dataset. Nodes represent data sources such as sensors, actuators, machine data, production, yields, etc. and information technology, connecting control devices, regulation devices, and sensors. The platform tier, facilitated by the edge gateway, includes components for information transformation, functional scope implementation, and data analytics. This tier establishes a data flow for integration with the enterprise tier, where applications develop business logic, rules, and controls. The key to the model's effectiveness lies in the seamless interaction and communication of data between tiers. Continuous traceability in data communication is highlighted, particularly in real-time scenarios. Additionally, timely acquisition of sensor data is emphasized, as demonstrated in addressing bottlenecks in a production line within the article. RAMI (Reference Architectural Model for Industry 4.0) is the other model proposed internationally by the body Platform Industry 4.0 [33]. As we see in Figure 3, this model proposes a vertical layer stack. The authors have developed a three-dimensional base model to facilitate Industry 4.0 discussions. This model adopts a service-oriented architecture, consolidating all elements and components of information technologies into a unified layer. As illustrated in Figure 4, the hierarchical structure depicts communication among various industrial elements and devices [35]. A key feature is the multiple interconnections among different components,  
Figure 3: RAMI reference (reprinted from [34]). Figure 2: IIRA reference: three-tier IIoT architecture (Reprinted with permission from [30]. Copyright 2023 Object Management Group). emphasizing the importance of considering various protocols for effective linking of diverse devices and components. Comparing the two models, both present division by layers, but the main difference is that the IIRA model presents an alignment between domains and cross-functions, while the RAMI model presents an interconnected system between all its components. Another differential example is assets. The RAMI model sees an asset as any element that can be interrelated, such as a product, raw material, software, or people. In contrast, for the IIRA model, assets are the physical components that are controlled [36; 37]. Given this service architecture, the RAMI model, unlike the IIRA, must have a powerful system of services. In the literature, numerous articles incorporate both Industry 4.0 references. For example, in [38], the authors developed a forensic model for investigating industrial automation environments, utilizing the IIRA benchmark to create an architecture that enables internet access for forensic analysis against remote attacks on industrial control components, such as PLC and SCADA. In [39], the authors proposed a RAMI-based architecture with an additional layer, emphasizing an intelligent federation of components and human-centered intelligent decision support.