# Integrating Blockchains with the IoT: A Review of Architectures and Marine Use Cases
## 3 BioT Architectures and Communication  
When exploring tiered architectures for the BIoT, the model proposed by [PERSON] et al. [2] stands out. Notably, this architecture mirrors the blockchain framework discussed by the same researchers and others ([PERSON] et al. [32], [PERSON] and [PERSON] [34]) mentioned in the previous sections. It is also structured in five distinct layers, which are illustrated in Figure 5.  
Beginning with the foundational \"Physical\" layer (or \"Perception\" layer; see Section 2), IoT devices such as sensors, smart home gadgets, Radio Frequency Identification (RFID) tags, and mobile phones serve as the cornerstone of IoT-blockchain applications. Moving up the hierarchical structure, the \"Network\" layer operates similarly to traditional blockchain networks by facilitating internetworking, routing, and multicasting among IoT devices. By predominantly leveraging P2P networks, this layer ensures efficient communication and data transmission within the IoT ecosystem, supporting decentralized operations [2]. The \"Blockchain\" layer embodies core blockchain functionalities critical to IoT applications, encompassing consensus mechanisms, data storage, and data sharing capabilities. Figure 5: Blockchain–IoT architecture. These different functionalities ensure the integrity and immutability of data records across the distributed network. Diverging from conventional IoT architectures, the \"Middleware\" layer is responsible for managing blockchain operations within the IoT environment. This layer oversees blockchain management, integrates services, and implements the blockchain's security measures. More specifically, the \"Middleware\" layer enhances system efficiency by minimizing the blockchain management overhead (for a detailed presentation and analysis, see [PERSON] et al. [2]). Lastly, the \"Application\" layer is a direct user interface connected to external systems, providing interaction capabilities, abstraction services, and API functionalities adapted to specific BIoT applications. This layer is thus responsible for facilitating the integration of blockchain technology across diverse industrial sectors. Overall, this structured architecture harmonizes the IoT's data generation capabilities with the blockchain's decentralized ledger technology. An alternative framework to the previously mentioned blockchain tiered architecture has been proposed by [PERSON] et al. [43], focusing more on the middleware aspects of a blockchain-based IoT system. This approach closely aligns with the latter layers of the model presented by [PERSON] et al. [2], where the \"Blockchain\", \"Middleware\", and \"Application\" layers correspond to functionalities involving blockchain integration, middleware management, and user interface interactions, respectively. In contrast, [PERSON] et al. [43] focus specifically on the \"Middleware\" layer, emphasizing the blockchain's role as a solution that connects IoT devices with industrial applications. This function is comparable to managing blockchain operations and integrating services within the IoT environment, as discussed by [PERSON] et al. Specifically, [PERSON] et al. [43] provide a detailed analysis of this layer's capabilities, including its role in managing digital currencies, incentivizing participants through rewards, and automating processes via smart contracts. Table 1 compares the functions of different layers, highlighting the key similarities and differences between the general BIoT architecture and the blockchain composite IoT architecture. Although each focuses on different aspects, both studies significantly help in understanding how a blockchain improves industrial IoT applications [2; 43]. By integrating the detailed sub-layers from the \"blockchain-composite\" model into the general architecture proposed by [PERSON] et al. [2], a more complete framework for implementing blockchains in IoT systems emerges. This approach prioritizes incentives and refines network layers, resulting in a more effective strategy for combining blockchains and the IoT.