# Digital Twin Technology-Based Networking Solution in Low Earth Orbit Satellite Constellations
## 6 Simulation and Analysis
### Twin Scenario Construction and Test Verification for \"Phase 2\"  
Simulation tests during construction are necessary to verify the effectiveness of the deployed constellation protocols as the LEO constellation is gradually deployed. Additionally, evaluating the performance of the fully operational semi-physical LEO constellation system based on semi-physical test validation methods for on-orbit scenarios is essential. In response to the verification requirements for the ongoing development of the low Earth orbit constellation network protocol in Phase 2, a semi-physical low Earth orbit constellation twin verification environment is established by introducing physical devices based on the foundation of the fully digital simulated nodes in Phase 1. This environment consists of two parts: a fully digital environment and physical prototypes of on-board routing and switching equipment. In the fully digital environment, 48 simulated low Earth orbit satellites, one gateway station, several broadband terminals, and one controller are simulated. Each low Earth orbit satellite deploys an on-board routing and switching node to forward data within and between satellites by running inter-satellite routing protocols. The satellite terminals simulate the network layer and above functionalities of real user terminal devices, providing functions such as user access, service access, and inter-satellite handover through running user satellite-ground routing protocols. The gateway station deploys a border gateway node to handle the conversion and processing of low Earth orbit feeder link protocols and ground protocols by running feeder satellite-ground routing protocols. The controller is primarily used for the network control of the low Earth orbit constellation. Figure 11: Service transmission performance in the scenario of inter-satellite link failure. Figure 10: Service transmission delay. As shown in Figure 12, there are two physical prototypes of on-board switching equipment, each simulating two physical satellites in one orbital plane. Based on the research results of the twin platform virtual-to-physical interface presented in Section 5.4, the two physical satellites, L0106 and L0107, are connected to the different-orbit satellites L0206 and L0207 and the same-orbit satellites L0105 and L0108 through multiple network interfaces in the fully digital environment. As shown in Figure 13, after initiating the controller and waiting for the convergence of the low Earth orbit constellation routing throughout the network, both the interface and the backend printout indicate that the controller can collect the complete constellation topology of the 50 satellites (including the two physical satellites). Based on the virtual-physical interconnected fully digital low Earth orbit constellation twin verification environment shown in Figure 12, the main focus is on conducting functional tests for the interconnectivity of virtual and physical nodes. The satellite payload source 0106, connected to the physical satellite L0106, sends ping packets to the ground gateway (border gateway) with an IP address of 16.1.123. During ping packet transmission, the inter-satellite topology undergoes periodic changes based on the ephemeris. According to the ping packet display interface from the deployed functional model in the low Earth orbit constellation twin verification environment, the business communication is normal, without packet loss. Additionally, the latency varies dynamically with the relative positions of the satellites, ranging from 32.13 to 40.2 milliseconds, as shown in Figures 14 and 15. The protocol test results conducted in this environment indicate that by constructing a twin verification environment that converges with the actual system and supports virtual-physical interconnection, various virtual-physical interconnected testing and verification scenarios can be created. Building upon the first phase, this approach enables a higher level of maturity in validating the network protocol for low Earth orbit constellations.