# Digital Twin Technology-Based Networking Solution in Low Earth Orbit Satellite Constellations
## 6 Simulation and Analysis
### Twin Scenario Construction and Test Verification for \"Phase 3\"  
The finalized LEO constellation digital twin system must undergo verification to ensure its capability to achieve the closed-loop control and optimization of the physical system. This verification process involves observing real-time changes in the twin system as the network state of the physical system fluctuates, through simulation data validation on the LEO constellation twin verification platform. In order to meet the parallel formation flight requirements during the operational phase of the low Earth orbit constellation network in Phase 3, additional functionalities have been implemented based on the virtual-physical interconnected low Earth orbit constellation twin verification environment established in Phase 1. These new functionalities include the construction of a unified representation of the virtual-physical integrated network twin database, virtual-physical mapping interaction, and network digital twin visualization. These additions aim to fulfill the needs for the fine-grained monitoring of network elements and network operational situations, the visualization of low Earth orbit constellation network management, real-time closed-loop control, and the optimization of the network. Regarding the Phase 3 digital twin prototype verification system shown in Figure 16, for the simulation of the physical low Earth orbit constellation network system, as the current stage is in the technical verification phase and there is no actual constellation system, it is not feasible to construct a physical low Earth orbit constellation scenario with such a large scale and frequent dynamic changes in network topology in a ground laboratory. Therefore, the simulation of the physical system directly utilizes the results obtained from the construction of the twin system in Phase 1, as shown in the right figure. The physical satellite network elements and protocol characteristics of the actual physical low Earth orbit constellation network are simulated through digitization. Similarly, for the simulation of the twin low Earth orbit constellation network system, a digitization approach is also employed, as shown in the left figure. The synchronization of network states in the virtual-physical environment is achieved through a database. A unified representation of the virtual-physical integrated network twin database is established between the physical system and the twin system. This database is used for the unified representation, storage, and cleansing of the data collected from the physical system. It also enables the twin system to read and use these data in near-real time to recreate the real network states, including the network topology, link latency changes, node failures, network traffic, and business conditions. Based on the reproduced network states, network prediction and optimization functionalities are realized in the digital twin environment. Both the physical system and the twin system scenarios consist of 50 low Earth orbit satellites, 6 ground gateways, several satellite terminals, and 1 controller. Each low Earth orbit satellite deploys an onboard 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 and achieve user access, service access, and inter-satellite handover functionalities by running user satellite-ground routing protocols. The ground gateways deploy border gateway nodes to handle the conversion and processing of low Earth orbit feeder link satellite-side link layer protocols and ground-side protocols by running feeder link satellite-ground routing protocols. Additionally, in the physical system, collection agent functional models are deployed at the satellites, ground gateways, and satellite terminals to collect information such as the device status, port rates, queue conditions, and specific business flow information from various network element nodes.