# Optimizing Time-Sensitive Traffic Scheduling in Low-Earth-Orbit Satellite Networks
## 4 Simulation Analysis
### Performance Results Analysis  
We first validated the optimality of introducing three queues in TPC-CQF. Under a load of 0.8 and an ISL buffer size of 153.6 KB, it is observed that TPC-CQF achieves the optimal trade-off among packet loss rate, latency, and throughput. It is noteworthy that for the ISL buffer size, primarily selected as 153.6 KB to simulate payload-constrained satellite scenarios, this capacity satisfies moderate burst traffic requirements. A buffer \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Number of satellites & 64 \\ Number of orbits & 8 \\ Satellites per orbit & 8 \\ Orbit altitude & 550 km \\ ISL bandwidth & 1 Gbps \\ Uplink bandwidth per user & 100 Mbps \\ Queue buffer capacity & 32 KB \\ CQF time slot & 500 microseconds \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Constellation parameters. size of 51.2 KB was employed to verify the algorithm's robustness under more stringent resource constraints. Table 2 clearly demonstrates the critical impact of queue count on TPC-CQF performance. While the dual-queue configuration achieves the lowest latency (1.82 ms), it exhibits excessively high TSF packet loss rate (14.8%) and timeout rate (7%). The five-queue configuration suffers from comprehensive performance degradation due to fragmentation (9.6% packet loss, 43% timeout rate, with throughput gain plummeting to +5%). The four-queue solution delivers intermediate performance (16% throughput gain, 2.1% packet loss) but remains significantly inferior to the three-queue design. This validates that the three-queue architecture represents the optimal balance between mitigating onboard buffer fragmentation effects (Equation (9)) and satisfying differentiated scheduling requirements for multi-level time-sensitive flows. To evaluate the forwarding capability for time-sensitive flows, we analyzed the service timeout ratio, defined as the proportion of packets that fail to reach the target node before their deadline. Figure 6 shows that as the load increases, the timeout ratio of TPC-CQF is significantly lower than that of traditional CQF and ES, and demonstrates robust performance under both 153.6 KB and 51.2 KB ISL buffer sizes. This is attributed to TPC-CQF's introduction of a three-queue dynamic priority mechanism (Q\({}_{6}\), Q\({}_{7}\), Q\({}_{8}\)), which enables temporary storage of overloaded packets with delay tolerance and forwards them in the next time slot. This mechanism effectively utilizes the delay redundancy of time-sensitive flows (e.g., a deadline of 6T), significantly reducing timeout occurrences. Under the same buffer size, TPC-CQF's timeout ratio is 10-18% lower than that of CQF, with a more pronounced advantage at high loads. The traditional Ethernet switch (ES) struggles to ensure timely packet transmission. As the load increases, the timeout ratio of ES exceeds 0.2. \begin{table}
\begin{tabular}{c c c c c} \hline
**Queue Count** & **TSF Packet Loss Rate** & **Average Latency (ms)** & **Throughput Gain** & **Timeout Rate** \\ \hline
2 & 0.148 & 1.82 & Baseline & 7\% \\
3 & 0.001 & 2.05 & +28\% & 6.7\% \\
4 & 0.021 & 2.91 & +16\% & 12\% \\
5 & 0.096 & 3.72 & +5\% & 43\% \\ \hline \end{tabular}
\end{table} 
Table 2: Impact of queue count on scheduling performance. Figure 6: Timeout ratio. The packet loss ratio is a key metric for evaluating network reliability, with packet losses occurring in both ISLs and STLs due to buffer overflow. We calculated two types of packet loss rates: one for the total traffic and one specifically for TSFs. As shown in Figure 7, TPC-CQF exhibits a lower packet loss ratio for TSFs compared to CQF and ES across various loads, maintaining relatively stable performance under different ISL buffer sizes. Additionally, TPC-CQF demonstrates the best performance in terms of packet loss ratio for total traffic.