## 3 Key Technology of the A2S Integrated MIoT
### Routing Protocol  
#### 3.3.1 End-to-End Transmission and Cluster Routing  
When it comes to A2S integrated MIoT routing protocols, the common end-to-end transmission and clustered routing structures are two important concepts.  
1. End-to-end transmission: End-to-end transmission refers to the process of transmitting data from the source node to the target node through the network. In the A2S integrated MIoT, wireless sensor networks are usually used for DT [128]. Data start from the source node, passes through various intermediate nodes step by step through multi-hop mode, and finally reaches the target node. The transmission mode allows there to be a certain distance between the nodes in the MIoT and the target node, with data transmission completed through the cooperation of the intermediate nodes [129]. End-to-end transmission needs to consider factors such as energy efficiency, network topology, and communication quality among nodes.
2. Cluster routing: Cluster routing is a commonly used routing mechanism in wireless sensor networks, as shown in Figure 7. Due to the large number of nodes and wide network range, the clustering routing structure can improve the scalability and energy efficiency of the network in the A2S integrated MIoT. The structure divides the nodes into several clusters, each with a cluster-head node responsible for coordinating the communication of the nodes within the group [130]. Cluster-head nodes collect data from surrounding nodes and forward them to other cluster-head nodes or the cloud. Other nodes only need to communicate with the cluster-head node, which reduces the communication and energy consumption among nodes. At the same time, the cluster structure can also improve the stability and fault tolerance of the network. When a node fails, it only affects the communication within the cluster, not the whole network.  
In A2S integrated scenarios, the clustering routing structure is also a common technical means. NASA's Office of Information Science and Technology conducted a research project  
Figure 7: Cluster routing structure.  
called \"Fault-tolerant protocols for wind power\". The aim of this project was to ensure the safety and reliability of data transmission in wind power systems by using a cluster routing structure and fault tolerance mechanism. By dividing nodes into different clusters and repairing data errors through fault tolerance mechanisms, the reliability and performance of wind power systems can be greatly improved [131]. A study by the Indian Institute of Technology has implemented multi-path DT for intelligent transportation systems using clustered routing structures. By dividing nodes into different clusters and establishing a multi-path routing mechanism, the reliability and robustness of DT can be improved, so as to realize the efficient operation of intelligent transportation systems. The University of Hamburg in Germany has used a clustered routing structure to achieve efficient data collection in wireless sensor networks [132]. By dividing nodes into different clusters, and dividing clusters according to the location and function of nodes, efficient data collection and processing of wireless sensor networks can be realized, so as to support various application scenarios of A2S integrated systems.  
Since some of the topics that have been discussed are related to clustering methods, we need to discuss how offering a backup node within the cluster can ensure less latency and further reliability. In [133,134], dynamic self-healing vehicle network organization methods considering the deviation of key network connection components were proposed. The design ideas of these methods can be applied to the A2S integrated MIoT with mobile nodes. Therefore, through the application of end-to-end transmission and clustered routing, the A2S integrated MIoT can achieve effective DT and resource management, improve network reliability and energy efficiency, and meet the needs of various application scenarios of the MIoT.