# Integrating Blockchains with the IoT: A Review of Architectures and Marine Use Cases
## 2 Architectural Foundations of IoT, Blockchains, and MIoT/IoUT
### Architectures and Implementation of MIoT/IoUT Systems  
There have been various architectures proposed for MIoT/IoUT systems, each designed to address the unique challenges posed by underwater environments ([PERSON] and [PERSON] (2016), [PERSON] et al. (2017), [PERSON] et al. (2018), [PERSON] et al. (2019)). According to [PERSON] and [PERSON] (2016), MIoT network architectures can be organized in several ways, including traditional TCP/IP-based models, data transfer scenario-based architectures, and functionality-based designs. The TCP/IP-based model provides a layered approach that is effective for ensuring reliable communication and data management across various underwater devices. In contrast, data transfer scenario-based architectures focus on specific communication pathways, often involving surface gateways and autonomous underwater vehicles, while functionality-based designs emphasize simplicity, dividing the system into key layers that handle perception, networking, and the application of data ([PERSON] and [PERSON], 2016). Figure 3 illustrates a basic IoUT architecture, which provides a foundational overview of the layers within the system. Each architecture offers different strengths, depending on the system's requirements for data transmission, latency, bandwidth, and security. The \"Named Data Networking\" (NDN) approach, for instance, is well suited to the IoUT due to its data-centric model, which simplifies configuration and addresses challenges such as low data rates and high latency ([PERSON] and [PERSON], 2016). Similarly, \"Delay-Tolerant Networking\" (DTN) is recommended for harsh environments with limited bandwidth as noted by ([PERSON] and [PERSON], 2016) and [PERSON] and [PERSON] (2015, as cited in ([PERSON] and [PERSON], 2016)). DTN manages connectivity gaps by storing data until a reliable path is available, enabling communication across different network types. Among these approaches, the TCP/IP-based model remains one of the most widely utilized. As explained by [PERSON] and [PERSON] (2016), this architecture is typically organized into five layers: \"Application\", \"Transport\", \"Network\", \"Data Link\", and \"Physical\". In some cases, the \"Data Link\" and \"Physical\" layers are combined into a single one, referred to as the \"Network Access\" layer. Figure 4 illustrates the referred-to structure, which connects the entire network, linking every device from underwater sensors to onshore computers, with each layer using specific protocols to manage data exchange efficiently. More specifically, these protocols define how data are formatted, communicated, synchronized, secured, and controlled for errors, allowing for the integration of various protocols that address key aspects of the infrastructure. These aspects include maintaining connectivity, managing latency and the packet size, dealing with signal loss and error rates, and ensuring sufficient bandwidth as well as security. Figure 3: Overview of basic IoUT architecture. In this architecture, the \"Application\" layer serves as the framework that supports different MIoT applications and provides a foundation for defining each device within the system. Furthermore, it organizes these devices, manages data collection and processing, and supports command execution, allowing the system to effectively respond to various situations. In the \"Transport\" layer, data are divided into packets for network transmission, ensuring they arrive in the correct sequence and addressing any potential data loss that might occur. Various routing protocols are employed to optimize communication, as efficient data routing is critical in this layer. For IoUT systems, routing protocols such as opportunistic, on-demand, geographic, table-driven, and multicast-tree-based protocols play a significant role in maintaining the intended Quality of Service (QoS). These protocols determine the paths that data packets follow, ensuring that data are transmitted efficiently even in the challenging underwater environment [25].