# Modeling and Performance Analysis of Satellite Network Moving Target Defense System with Petri Nets
## 4 SPN-Based Modeling and Performance Analysis
### Modeling and Analysis of Traditional Satellite Network with SPN  
As shown in Figure 3, a typical satellite network communication system usually consists of two parts: the space segment and the ground segment. The space segment consists of all satellites in the outer space of the Earth. The ground segment can be divided into two parts: the ground base station (including ground uplink station, ground receiving station, measurement and control station, etc.) and the user segment. The former is responsible for the communication access of user terminals in the communication service area, and undertakes the interface function between the satellite communication system and the terrestrial communication network (such as public telephone exchange network, public exchange data network, Internet). The user segment includes all kinds of user terminals (vehicle terminals, ship terminals, etc.) with communication needs. The communication satellite is the core of the entire system. Its main function is to act as a relay station connecting two or more terrestrial base stations, amplifying and relaying signals from terrestrial or other satellites, thus providing rich and colorful communication services with worldwide coverage and meeting the communication needs of users. The links connecting these devices are called communication links, including \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Research Field** & **Reference** & **Method** & **Content** \\ \hline \multirow{8}{*}{Traditional Network} & Ref. [20] & PN & Application mapping assessment \\  & Ref. [21] & CPN & Evaluation of IEEE802.11e protocol \\  & Ref. [22] & SPN & Performance evaluation of Honeyot technology \\  & Ref. [23] & STCPN & Modeling of CR networks \\  & Ref. [24] & PTPN & Robustness research on railway transportation \\  & Ref. [25] & CPN & Network security interconnection verification \\ \cline{2-4}  & Ref. [26] & GSPN & Evaluate the reliability and performance of the protocols \\  & Ref. [27] & CPN & Protocol consistency check \\  & Ref. [28] & PN & LEO satellite collision prediction \\ \cline{2-4}  & Ref. [29] & CPN & Navigation satellite availability analysis \\  & Ref. [30] & PN & Reliability assessment \\  & Ref. [31] & PN & Satellite constellation system availability analysis \\ \cline{2-4}  & Ref. [32] & CPN & Simulation of satellite communication network \\  & Ref. [33] & PN & Fault diagnosis of satellite remote control subsystem \\ \cline{2-4}  & Ref. [34] & PN & Data processing effectiveness evaluation of satellite \\  & & & information application chain \\ \cline{2-4}  & Ref. [35] & SPN & Two-layer satellite network performance analysis \\  & Ref. [36] & SPN & Three-layer satellite network performance analysis \\  & Ref. [37] & SPN & Calculation of vulnerability and uncertainty \\  & Ref. [38] & SPN & Performance comparison between single user and dual user \\  & Ref. [39] & TPN & Modeling of microsatellite system \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of research literature based on Petri Nets. uplink, downlink, and inter-satellite link. In satellite communication, the link from the earth station to the satellite is an uplink, and, conversely, the link from the satellite to the earth station is a downlink. The inter-satellite link refers to the radio link connecting satellites. Its function is to connect individual satellites into a space-based network to realize the intercommunication between them, and thus enable the collection, processing, transmission, and distribution of information. The typical communication process for satellite network is shown in Figure 4. More specifically, it can be described as follows:  
1. The user terminal sends a service request to the satellite L1 through base station and waits for the service response;
2. Obtaining link bandwidth resources and L1 responds to the service request;
3. Sending data to L1 through the uplink;
4. L1 forwards the received data via the inter-satellite link to L2, which is responsible for the communication of user segment B;
5.