# SatScope: A Data-Driven Simulator for Low-Earth-Orbit Satellite Internet
## 4 Simulation Experiment
### Fidelity Comparison  
Based on the Starlink network topology measurements conducted in Europe in 2021 [47], we compared the performance of several network simulation tools. Using the latency measurement results from 2021 as a benchmark, we evaluated and contrasted the latency distributions obtained from continuous simulations using SatScope, StarPerf, Hypatia, and StaryNet. Among them, the latency of StarPerf, Hypatia, and Starnet simulators was derived from the research [5].  
In this simulation experiment, SatScope utilized all V1.0 satellites and the sixth shell layer satellites (referenced in Table 1) as satellite nodes to continuously simulate communications between two ground stations located in Klagenfurt and Vienna, Austria, as illustrated in Figure 9. Given that Starlink's inter-satellite links were in their initial deployment phase during the 2021 network measurements and could not fully support inter-satellite routing, we adopted the sixth shell layer satellites as a theoretical routing scheme to address potential bent-pipe routing failures, thereby assessing the network latency conditions of that year. We made the following basic settings to improve simulation fidelity: The delay between each hop of ground nodes follows a normal distribution with a mean of 1.3 milliseconds and a standard deviation of 1.37 milliseconds. Additionally, since the connection relationship between ground nodes and satellite nodes is re-evaluated every 15 s, the queuing delay cannot be ignored. We conducted a continuous 100 min simulation using SatScope, from which we derived the delay distribution.  
After accounting for the impact of service satellite handovers at ground nodes, the delay distribution calculated by SatScope is higher than that of StarPerf and Hypatia but lower than that of StarryNet in Figure 10. The horizontal axis of Figure 10 shows key metrics: the mean, median, and the points at which the cumulative probability function reaches 70% and 90%. This indicates that, compared to other simulation tools, SatScope achieves acceptable fidelity at a lower cost.  
The aforementioned simulation comparisons do not reflect the network performance of satellite networks with inter-satellite links. To address this, we input all currently orbiting satellites into SatScope and conducted latency analysis based on network measurements. Given that our server nodes are located in Asia, accessing target nodes involves traversing submarine cables, introducing additional delays. After accounting for and removing these extra delays, we obtained the latency distribution for the Starlink network, as shown inFigure 11: The median latency for end-users accessing the internet via the satellite network is 43.2 ms, which aligns closely with the recent latency results published by Starlink [41].  
Figure 10: Latency comparison diagram. Except for the delay simulation results of SatScope, all other results use the point-plotting method, as cited from StarryNet [5].  
Figure 9: Visualization of the route in [47]. The center of the sphere is Greenland. Red spherical points represent satellite nodes, blue spherical points represent ground nodes; red lines indicate in\(-\)plane links of V1.5 satellites, light green lines indicate inter\(-\)plane links between adjacent orbits of V1.5 satellites, and isolated red nodes represent V1.0 satellites. The dark green line indicates the connection between ground nodes and satellite nodes.