# Integrating Blockchains with the IoT: A Review of Architectures and Marine Use Cases
## 2 Architectural Foundations of IoT, Blockchains, and MIoT/IoUT
### Background: IoT and Blockchain Architectures  
The IoT architecture outlines a detailed framework that connects physical components such as sensors and actuators (devices that convert energy into motion), communication networks, and functional layers to create cohesive solutions [29]. Due to the wide range of technologies involved, IoT architectures can often differ considerably to meet the unique requirements of each implementation. Despite this diversity, a widely referenced model in the literature is the three-layer architecture, which consists of the \"Perception\", the \"Network\", and the \"Application\" layers [2; 30]. The \"Perception\" layer (also referred to as the \"Devices\" or \"Sensing\" layer) forms the foundation of IoT systems. It consists of various interconnected devices that exchange messages and gather information. This layer handles essential operations such as data generation, identification, tracking, short-range communication, and environmental monitoring [31]. The sensors employed in this layer are designed to capture specific data types according to the purpose of each IoT system [2]. The \"Network\" layer transmits data collected or processed by IoT devices using technologies such as WiFi, 5G, and Bluetooth to send data between nodes, hypervisors, and user applications. It also manages network connectivity tasks, including mobility and security functions, ensuring the cohesive transportation of data [2; 30]. The \"Application\" layer provides services to users based on the collected data, supporting a variety of use cases such as smart homes, smart cities, and health monitoring. It processes information locally or through Application User Interfaces (APIs) to meet user requests [2; 30]. [PERSON] and [PERSON] (2021, as cited in [30]) suggest the introduction of an additional \"Application Support\" layer. Their research indicates that this layer not only improves security through user verification but also ensures efficient data transmission by bridging the gap between the application and network layers, thus supporting a more resilient and adaptable IoT architecture. This \"Application Support\" layer ensures secure data transmission by verifying users and safeguarding information before passing it to the \"Network\" layer. For this purpose, various authentication mechanisms are commonly employed. Moreover, the support layer enhances the efficiency of IoT deployments by facilitating data transmission to the network layer via wireless and wired media [30]. Another alternative approach is the five-layer IoT model, which introduces an additional \"Middleware\" Layer positioned between the \"Network\" and the \"Application\" layers, as shown in Figure 1. This layer resolves compatibility issues related to varying operating systems, data formats, and communication protocols, facilitating cohesive integration and functionality across platforms [2; 31]. The concept of incorporating a \"Mid-dleware\" layer aligns with recommendations from the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) dating back to 2012. As noted by [PERSON] et al. [30], the ITU-T underscored the importance of this layer in IoT architectures, especially for integrating new computing paradigms such as edge and cloud computing. The \"Middleware\" layer is also necessary for improving data processing and management efficiency, effectively supporting current IoT applications and paving the way for future innovations. In this expanded model, the \"Application\" layer is split into \"Application\" and \"Business\" layers. The first manages user access to services via APIs, while the second assumes strategic oversight, encompassing the management of the entire IoT ecosystem. This includes defining business models, conducting data analysis, and guiding decision-making processes within IoT-driven enterprises [2; 31]. The architecture of a blockchain consists of several layers, each serving a specific role in the network's functionality.