## 5 Conclusions  
The Modbus AUDP-RTU gateway proposed in this study significantly reduces the communication delay and effectively solves the problem of the low communication reliability of UDP. The modeling analysis of UDP transmission based on Markov chain provides theoretical support for system performance optimization, and the experimental results show that the success rate of data transmission after applying AUDP is increased to more than 98% compared with 77.4% of Modbus UDP-RTU, and the real-time performance is also significantly improved compared with Modbus TCP-RTU, which proves the advantages of the AUDP mechanism in terms of reliability and real-time performance. The proposed Modbus AUDP-RTU gateway offers significant practical value for IoT applications, enabling the efficient and reliable real-time monitoring and control of equipment in real-world factory settings. This solution not only helps enterprises reduce upgrade costs and improve operational efficiency but also lays a solid foundation for the large-scale adoption of Industry 4.0 technologies.  
Future research will focus on optimizing the AUDP retransmission mechanism and refining state transition models to achieve adaptive retransmission capabilities. This includes dynamically adjusting maximum retransmission attempts based on network conditions while expanding the gateway's protocol support to align with Industry 4.0 and IoT standards. In particular, the integration of OPC UA will be considered to enable semantic interoperability and secure machine-to-machine communication through its information modeling and encryption features, while the adoption of MQTT will facilitate lightweight publish-subscribe messaging, optimize bandwidth usage, and support efficient cloud-edge synchronization in IoT environments. These enhancements are expected to bridge legacy Modbus systems with modern industrial frameworks, thereby improving both real-time reliability and cross-platform scalability. In addition, we will also explore the introduction of a Modbus multi-master mechanism to integrate a multi-master coordination framework, enabling orderly concurrency of multiple services while maintaining compatibility with existing Modbus devices.  
Conceptualization, S.Z.; methodology, S.Z. and Q.Z. (Qinghai Zhang); software, S.Z.; validation, S.Z., Q.Z. (Qingjian Zhao) and S.L.; formal analysis, S.Z., X.Z. and Q.Z. (Qinghai Zhang); investigation, S.Z. and Q.Z. (Qingjian Zhao); resources, Q.Z. (Qinghai Zhang), Y.G. and L.S.; data curation, S.Z.; writing--original draft preparation, S.Z.; writing--review and editing, Q.Z. (Qinghai Zhang) and S.Z.; visualization, Q.Z. (Qinghai Zhang), Y.G. and Z.Z.; supervision, Q.Z. (Qinghai Zhang), Y.G. and Z.Z.; project administration, Q.Z. (Qinghai Zhang), Y.G. and Z.Z.; funding acquisition, Q.Z. (Qinghai Zhang), Y.G. and Z.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Open Fund Project of Shandong Key Laboratory of Space Debris Monitoring and Low-orbit Satellite Networking, NO.CK-2024-0049.  
Not applicable.  
The data in this paper is obtained from real control experiments. Because the laboratory test data is not publicly available, if there is a need for them, contact the corresponding author.  
**Acknowledgments:** The authors acknowledge all contributors to this paper. We also extend our gratitude to the editors and reviewers for their constructive feedback on the manuscript.  
**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.