# A Method for Building a Mixed-Reality Digital Twin of a Roadheader Monitoring System
## 3 Construction of the Digital Twin Monitoring System
### Construction of the Exchange System Twin Data
#### 3.2.2 Network Connection Module  
The network connection module is the information hub in the twin data exchange processing program. Its essence is a socket communication server, and its framework and performance directly determine the communication efficiency performance between client application programs.  
The network connection module is divided into four parts: the network service layer, the business logic layer, the data access layer, and the user interaction layer, as shown in Figure 13.  
The network service layer is mainly used for monitoring socket connections, creating sockets, receiving messages, sending messages, and closing connections. To ensure real-time synchronization between the physical roadheader and its virtual model, a timestamp synchronization mechanism is implemented. Each transmitted data packet is tagged with a timestamp, allowing the business logic layer to align incoming data with its respective time marker, reducing discrepancies between the physical and virtual states.  
In addition, two key mechanisms are incorporated into the data transmission process to improve system performance. First, a data lightweighting algorithm is employed to reduce the volume of data being transmitted, improving transmission efficiency and reducing bandwidth consumption. Second, a lightweight error correction algorithm is used to detect and correct errors in data packets. This ensures the integrity of the transmitted data. Error correction includes the use of checksums and cyclic redundancy checks (CRC) for verifying data integrity, along with a forward error correction (FEC) approach to recover lost or corrupted packets, thereby enhancing the robustness and reliability of bidirectional interactions.  
The network service layer transfers the content of the fragmented information segments to the business logic layer. After receiving the content of the information segments, the business logic layer parses the information and then proceeds to the corresponding processing flow. Due to the differences in the types of clients connected to the server, the network service layer of the twin data processing program does not actively send information. The network service layer provides interface functions for sending messages for the business logic layer to call. The operation of sending information is controlled by the business logic layer. The business logic layer integrates and encodes the information according to different data protocols based on the specific business applications of different clients and different information segment formats and calls the information sending interface to send the data to the designated client. The function of the data access layer is the data interaction between the server and the database. Separating the data access layer from the network service layer reduces the coupling of the programs within the network connection module. Multi-threaded programming is used to achieve the parallel operation of the network service layer and the data access layer, saving the waste of CPU cycles and improving the efficiency of the application program.  
Figure 13: Architecture of network connection module.