## 2 VDES Data Link Credibility Monitoring Approach
### Radio Interference Detection Based on Message Characteristics
#### 2.1.1 VDES Message Integrity Verification Method Based on the MD5 Algorithm
Specifically, the VDES data processing module operates on the raw VDES message data stored in the SQL Server database, parsing and extracting relevant field parameters, categorizing them into different data tables, and managing message encapsulation for data exchange and communication with VDES ship stations. The VDES data link integrity monitoring module consists of two key components: first, the radio interference detection module, which includes four sub-modules VDES message format conformity verification, VDES message parameter legitimacy verification, VDES message content integrity verification, and consistency checks of sent and received messages--aimed at monitoring radio interference in the VDES data link. Second, the spoofing source identification and localization module comprises sub-modules for spoofing source identification based on ship-to-shore distance and propagation distance matching analysis, as well as for spoofing source localization using specialized algorithms. This enables the identification of spoofing sources within the VDES data link. Finally, the frontend display layer visualizes user login information, received messages, parsed message parameters, message verification results, distance matching analysis results, spoofing source localization records, and VDES data link integrity monitoring results. This allows users to observe and understand the status of VDES data link integrity and receive timely alerts. Figure 24 depicts the user login interface of the VDES data link integrity monitoring software system. Figure 23: Architectural overview of the VDES data link monitoring system. Figure 24: User login interface for the software system. ### Design of Key Modules

The algorithmic process and overall architecture of the VDES data link integrity monitoring system, as shown in Figures 25 and 26, necessitate the implementation of functions such as communication, message processing, and data link integrity monitoring. This section provides a detailed exposition of the design process for the key modules of the system. #### 3.1.1 VDES Communication Module

Based on the C/S model, this paper designed a VDES communication module, which facilitates the connection between the server and client for data transmission between

Figure 19:0 Functionality verification results of the VDES communication module. Figure 19:1 Structural block diagram of the VDES communication module. systems. The structural diagram of the VDES communication module is illustrated in Figure 19:2

The VDES communication module, as illustrated in Figure 25, utilizes socket communication based on the System.Net.Sockets namespace. On the client side, upon clicking the StartService button, a Socket object named _socket is created and bound to a specified IP address and port to begin listening for connection requests from the VDES base station server. Once the client is initiated, the ListenFunction() is invoked to continuously accept connection requests, adding information about the connected VDES base station to the dicSocket dictionary. A new thread is then launched to receive message data from the VDES base station server. Messages are sent from the client to the VDES base station server via the btrSendToSingle_Click() function. On the server side, when the Connect button is clicked, the VDES base station server connects to the client at the designated IP address and port using the socketClient.Connect(ipe) function. Once the connection is established, the VDES base station server can communicate with the client through the sockClient.Send() function. Upon completion of communication, the socket is closed using the close() function to terminate the connection. To validate the functionality of the VDES communication module, a C/S model is employed as the foundational structure in Visual Studio 2019. The client initiates requests through socket connections, which are received and responded to by the server.