## 5 Experimental Evaluation
### Evaluation and Benchmarking of AQM Algorithms
#### 5.1.4 FQ-PIE  
In experiments (16)-(19), The internal parameters of FQ-PIE were configured with target = 15 ms, tupdate = 15 ms, alpha = 0.125, beta = 1.25, max-burst = 150 ms, max-ecuth = 0.1, quantum = 1514 bytes, limit = 10,240 packets, and flows = 6 queues.  
**Scenario 1 (Bandwidth = 10 Mbps, Delay = 20 ms)**: We evaluated the performance of FQ-PIE in two cases: (i) Case 1 is with enabled ECN; the results are shown in Figure 16, and (ii) Case 2: ECN is disabled, and the results are in Figure 17.  
Similarly to PIE, The FQ-PIE algorithm drops packets instead of merely marking them when the drop probability exceeds the configurable parameter'max_ecuth'. This behavior  
Figure 14: Case 1: FQ-CoDel (ECN enabled)—Scenario 2 with Bandwidth = 1 Mbps, Delay = 20 ms. (a) Throughput; (b) Congestion Window; (c) Smoothed TCP RTT.  
Figure 13: Case 2: FQ-CoDel (ECN disabled)—Scenario 1 with Bandwidth = 10 Mbps, Delay = 20 ms. (a) Throughput; (b) Congestion Window; (c) Smoothed TCP RTT.  
Figure 15: Case 2: FQ-CoDel (ECN disabled)—Scenario 2 with Bandwidth = 1 Mbps, Delay = 20 ms. (a) Throughput; (b) Congestion Window; (c) Smoothed TCP RTT.  
ensures that the congestion control optimally sets _cwnd_ sizes, leveraging its high variability characteristics whether ECN is enabled or disabled, as illustrated in Figures 16b and 17b.  
This conservative behavior results in near consistent throughput and RTT values across multiple TCP connections, regardless of enabling ECN, though only after it starts dropping packets in the case of ECN, causing a slight delay in its reduction of _cwnd_ to optimal levels. It results in low RTTs and stable bandwidth sharing, as depicted in Figures 8c, 9c and 8a, 9a, respectively. Upon closer examination, Figure 16c shows higher RTT when ECN is enabled, as illustrated. Subsequently, Figure 16a illustrates a higher throughput and more unfairness when compared to its counterpart in Figure 17a. This outcome stems from NewReno's conservative approach in reducing its _cwnd_ size when ECN is enabled. In contrast, NewReno instantly halves its _cwnd_ upon detecting packet loss and then enters fast-recovery mode.  
In Figure 16c, we see a bit more instability than in Figure 17c.  
**Scenario 2 (Bandwidth = 1 Mbps, Delay = 20 ms)**: We evaluated the performance of FQ-PIE in two cases, Case 1 with ECN enabled and Case 2 with ECN disabled, for comparison. Figures 18 and 19 present the results for the two cases.  
The FQ-PIE algorithm exhibits consistent behavior in low-bandwidth environments as in high-bandwidth environments, characterized by slight unfairness and slightly elevated RTTs, especially when ECN is enabled.  
Compared to the high-bandwidth environment in scenario 1, scenario 2 demonstrates notably more exaggerated RTT, particularly in TCP connection 2. This increase in RTT directly results from lower available bandwidth and increased waiting time due to congestion and packet loss. The resulting diminished performance of throughput and _cwnd_ due to lower bandwidth is as expected in such scenarios.  
Figure 16: Case 1: FQ-PIE (ECN enabled)—Scenario 1 with Bandwidth = 10 Mbps, Delay = 20 ms. (a) Throughput; (b) Congestion Window; (c) Smoothed TCP RTT.  
Figure 17: Case 2: FQ-PIE (ECN disabled)—Scenario 1 with Bandwidth = 10 Mbps, Delay = 20 ms. (a) Throughput; (b) Congestion Window; (c) Smoothed TCP RTT.