## 6 Evaluation
### Experiment Result and Analysis  
(1) The increase of the length of interval and flow rate will improve DRW. DRW greatly affects the judgment of network status. In Figure 7a, we set the packet loss rate as 5%, the average delay jitter as 20 ms and the flow rate as 1 M/s, 10 M/s and 20 M/s in different interval length to evaluate the detection rate of watermark based on sparsity of packet. As shown in Figure 8, the increase of the length of interval and the flow rate will improve DRW; thus, we set length of interval as 500 ms and flow rate as 10 M/s to evaluate the performance of network congestion detection based on flow watermarking. (2) DRW in different packet delays and packet loss rates. In order to evaluate the detection ability of watermark in different packet delays and packet loss rates, we evaluate DRW in three scenes. In Figure 7a, we set the average delay jitter as 0-500 ms, the length of interval as 500 ms and the average packet loss rate as 0-20%. From Figure 9, it can be concluded that with the increase of packet delay and packet loss rate, the DRW of three watermarks decrease accordingly. Compared with the other two watermarks, the watermark based on sparsity of packet has a larger change, which can better reflect the changes in network status. Figure 8: The DRW in different intervals and flow rates. Figure 9: The DRW in different packet delays and packet loss rates. In order to make evaluation in line with real network status, we simulate a more real network environment by adding interference flows to create congestion. In Figure 7b,c, we set the length of interval as 500 ms, the flow rate of the encoded flow as 10 M/s, the limit rate of shared link C2-C3 as 20 M/s, and the rate of the interference flow as 5 M/s, 10 M/s, 15 M/s, and 20 M/s, respectively, and evaluate the DRW of the encoded flow in C4. When the rate of interference flow increases gradually, the packet loss rate of the encoded flow increases accordingly. As shown in Figure 10, as the packet loss rate of the encoded flow increases, the DRW decreases. In Figure 7c, because the encoded flow and the interference flow share the transmission path of C2-C4 and the decoder port of C4, the DRW is slightly lower than the DRW in Figure 7b. It be concluded that the watermark will change when network packet delay and packet loss occur. The greater the packet delay and packet loss rate, the lower the DRW; however, the change of the DRW is small when the changes in network status is slight. For example, in Figure 7a, when the packet loss rate is 1% and 5%, the DRW is about 93%, which is easy to cause confusion in the analysis of the changes in network status. Therefore, it is necessary to combine the fine-grained network congestion detection algorithm for further judgment. We evaluate the performance of fine-grained network congestion detection algorithm in three scenes. (3) Evaluation of fine-grained network congestion detection algorithms in three scenes. In Figure 7a, we set the length of interval as 500 ms and the average delay jitter as 0-200 ms to evaluate the Crps of four codes. Figure 11 shows the Crps in different packet delays; it can be concluded that with the increase of packet delay, the Crps change accordingly, and there is a certain range of change when small packet delay occurs. Compared with the DRW, the Crps have larger variation. During the packet delay of 200 ms, the DRW changes by 20%, but the average Crps change by 50%; thus, the Crps can better show the changes in network status. In Figure 7b, we set the length of interval as 500 ms, the rate of the encoded flow as 10 M/s, the limited rate of shared link C2-C3 as 20 M/s, and the rate of interference flow as 5 M/s, 10 M/s, 15 M/s, 20 M/s, respectively, to evaluate the Crps of four codes in C4. As shown in Figure 12, the same conclusion can be drawn. As the packet loss rate increases, the Crps change accordingly, and there are certain changes when small packet loss occurs. Compared with the DRW, some Crps have a greater variation.