# Performance Evaluation of TCP BBRv3 in Networks with Multiple Round Trip Times
## 5 Performance Evaluation
### RTT Fairness and Access Link Scenario  
In this scenario, each of the nine paths had a unique RTT. All link rates were set to 100 Mbps, while the propagation delay between routers A and B was set to 2 ms. The one-way propagation delays were distributed across the range from 0 ms to 75 ms. The RTT values for all connections are compiled in Table 4, thus aligning with the representative distribution of RTTs on the central link, as reported by [25]. Buffer sizes were determined as multiples of BDP and relative to the mean RTT, thus resulting in a size of 900 packets. The flows were initiated randomly within the first second of the simulation. The disparity in throughput among the various flows was considerable, and it mainly depended on both the RTT and the buffer size. The buffer size, denoted as a multiplication of the BDP, is calculated in reference to the average RTT, which was set at 100 ms. Therefore, for very short and very lengthy paths, it becomes considerably deeper or shallower. The overall throughput, Jain's index, drop ratio, and average queue size with the standard deviation of the queue size for all simulation runs are presented in Table 5.  
The throughput results for all BBRv1 flows are presented in Table 6. BBRv1 provided very high fairness when the buffer size ranged between 1 and 2*BDP. Consistently across \begin{table}
\begin{tabular}{|l|c|c|c|c|c|} \hline N1–N4 & 8 & N2–N4 & 32 & N3–N4 & 58 \\ \hline N1–N5 & 78 & N2–N5 & 102 & N3–N5 & 128 \\ \hline N1–N6 & 154 & N2–N6 & 178 & N3–N6 & 204 \\ \hline \end{tabular}
\end{table} 
Table 4: Values of RTT [ms] between all node pairs. \begin{table}
\begin{tabular}{|l|l|c|c|c|c|} \hline  & & **0.5*bRTT** & **1*bRTT** & **2*bRTT** & **5*bRTT** \\ \hline \multirow{3}{*}{2*BDP} & BBRv1 & 0.86 & 1.00 & 0.97 & 0.97 \\ \cline{2-5}  & BBRv2 & 0.92 & 1.00 & 0.52 & 0.76 \\ \cline{2-5}  & BBRv3 & 0.96 & 1.00 & 0.98 & 0.86 \\ \hline \multirow{3}{*}{5*BDP} & BBRv1 & 0.87 & 1.00 & 0.82 & 0.97 \\ \cline{2-5}  & BBRv2 & 0.92 & 1.00 & 0.85 & 0.97 \\ \cline{2-5}  & BBRv3 & 0.96 & 1.00 & 0.91 & 0.99 \\ \hline \multirow{3}{*}{10*BDP} & BBRv1 & 0.87 & 1.00 & 0.82 & 0.97 \\ \cline{2-5}  & BBRv3 & 0.96 & 1.00 & 0.91 & 0.99 \\ \hline \multirow{3}{*}{10*BDP} & BBRv1 & 0.87 & 1.00 & 0.82 & 0.97 \\ \cline{2-5}  & BBRv2 & 0.92 & 1.00 & 0.85 & 0.97 \\ \cline{1-1} \cline{2-5}  & BBRv3 & 0.96 & 1.00 & 0.91 & 0.99 \\ \hline \end{tabular}
\end{table} 
Table 3: [PERSON]’s index for different buffer settings and RTT ratios for all BBR versions; bottleneck link delay = 10 ms. \begin{table}
\begin{tabular}{|l|c|c|c|c|c|} \hline  & & **(1)** & **(2)** & **(3)** & **(4)** \\ \hline \multirow{3}{*}{0.5*BDP} & BBRv1 & 90 & 0.84 & 4.55 & 279 [185] \\ \cline{2-5}  & BBRv2 & 92 & 0.51 & 0.29 & 347 [132] \\ \cline{2-5}  & BBRv3 & 92 & 0.70 & 0.70 & 238 [114] \\ \hline \multirow{3}{*}{1*BDP} & BBRv1 & 92 & 0.95 & 4.22 & 637 [310] \\ \cline{2-5}  & BBRv2 & 93 & 0.54 & 0.27 & 601 [316] \\ \cline{2-5}  & BBRv3 & 93 & 0.62 & 0.29 & 612 [255] \\ \hline \multirow{3}{*}{2*BDP} & BBRv1 & 93 & 0.98 & 2.56 & 1218 [615] \\ \cline{2-5}  & BBRv2 & 93 & 0.70 & 0.21 & 1073 [492] \\ \cline{1-1} \cline{2-5}  & BBRv3 & 93 & 0.81 & 0.11 & 521 [251] \\ \hline \multirow{3}{*}{10*BDP} & BBRv1 & 91 & 0.49 & 0.00 & 2448 [883] \\ \cline{2-5}  & BBRv2 & 93 & 0.80 & 0.48 & 2534 [1512] \\ \cline{1-1} \cline{2-5}  & BBRv3 & 94 & 0.86 & 0.04 & 5308 [1993] \\ \hline \end{tabular}
\end{table} 
Table 5: (1) Overall throughput [Mbps]. (2) Jain’s index. (3) Drop ratio [%]. (4) Queue size [pkts] and standard deviation of queue size for different buffer settings. these scenarios, the packet loss ratio remained notably high. Analysis of both the average queue length and the standard deviation reveals considerable oscillations induced by BBRv1, thus contributing to a lack of queue stability. In scenarios with a buffer size of 0.5*BDP, streams with the shortest RTTs tend to monopolize the majority of available bandwidth--three flows utilized almost 50% of the available capacity.