# 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
This section draws from key research to outline how these layers interact to form a cohesive blockchain network. At the core of blockchain architecture is the \"Data\" layer (or \"Physical\" layer), which stores crucial blockchain information, including block timestamps, transaction details, and Merkle roots [2; 32]. Blocks consist of a header and a body, with headers containing the previous block hash, timestamp, and Merkle root, ensuring a tamper-proof, chronological order. Merkle roots facilitate quick transaction verification by eliminating the need to review entire blocks [32; 33]. In this way, the \"Data\" layer essentially provides the groundwork for the blockchain. Above is the \"Network\" layer, which facilitates decentralized, peer-to-peer (P2P) communication between nodes. This approach not only enhances fault tolerance but also reduces the risk of network failure, keeping the system operational even if some nodes are compromised [2]. To achieve this, the \"Network\" layer relies on data transmission protocols that ensure the accurate exchange of information [32; 34]. The \"Consensus\" layer ensures that all network participants agree on the blockchain's current state. Various consensus mechanisms validate transactions and maintain network consistency, including Proof of Work (PoW), Proof of Stake (PoS), and Byzantine Fault  
Figure 1: IoT architectural layers. Tolerance (BFT), as well as alternatives like Delegated Proof of Stake (DPoS) and Practical Byzantine Fault Tolerance (PBFT) [2; 32; 34]. Each mechanism employs a distinct approach to achieving network consensus: PoW requires significant computational effort to validate transactions, PoS depends on cryptocurrency staked as collateral, and BFT focuses on addressing Byzantine failures, including malicious node activity. These mechanisms are vital to ensuring the blockchain remains secure and reliable [32; 33]. Closely tied to the \"Consensus\" layer is the \"Incentives\" layer, which motivates participants to contribute to the blockchain's security by offering rewards [34]. In PoW systems, miners compete to solve cryptographic puzzles, earning cryptocurrency for validating transactions. Similarly, PoS systems reward validators based on their staked cryptocurrency [32; 33]. While certain blockchain designs treat the \"Incentives\" and \"Consensus\" layers as separate entities, they are frequently integrated into a unified layer [32; 34]. The \"Contract\" layer enables the creation and execution of smart contracts, which are self-executing agreements that automate processes based on predefined conditions [32; 34]. Smart contracts play a key role in facilitating secure transactions and support the development of decentralized applications (dApps) that operate independently on the blockchain [32]. Finally, the \"Application\" layer bridges blockchain technology with real-world applications, enabling interoperability across networks and fostering adaptable frameworks. This allows different blockchain networks to interact and supports a wide range of innovative solutions in various sectors [2; 32].The structure of these layers is depicted in Figure 2 below.