# Performance Evaluation of TCP BBRv3 in Networks with Multiple Round Trip Times
## 5 Performance Evaluation
### Intraprotocol Fairness
The results presented in [11; 12; 18] suggest that long RTT flows dominate over short RTT flows; however, in some of these findings, we can observe that the bias towards long RTT flows is less pronounced in shallow buffers. The problem lies in the lack of clarity regarding the precise buffer size, which is typically provided in terms of multiples of BDP. Do we calculate it using the shortest, the longest, or the mean RTT of all paths? With large differences between RTT times, in very shallow buffers, streams with shorter RTTs are indeed able to achieve better throughput. In particular, short RTT BBRv1 flows, which ignore packet loss signals, update their \(BW\) estimates faster and maintain a relatively higher sending rate. This study would anticipate that scenarios with 0.5*baseRTT would demonstrate an inverse pattern compared to those with 2*baseRTT. However, this trend was only observable for sufficiently large buffers of 2*BDP and above. As the buffer size decreased, this correlation diminished, thus confirming that bandwidth allocation is influenced not only by the discrepancies in absolute RTTs but also by the relationship of the maximum RTT to the buffer size. The BBRv1 streams occupied a larger share of the bandwidth in shallow buffer scenarios. This dependency was less pronounced with BBRv3. Summary: With varying path lengths, bandwidth sharing relies less on the ratio of RTT times and more on the buffer size calculated in relation to the RTT of the path. This dependency was particularly evident with BBRv1, while BBRv3 partially mitigated this correlation. If the disparity in the RTT among flows is significant, a buffer size of at least 1-2*BDP calculated using the longest RTT should be provided to ensure high fairness. \begin{table}
\begin{tabular}{|l|l|c|c|c|c|c|c|c|} \hline  & & 0.1*bRTT & 0.2*bRTT & 0.5*bRTT & 0.8*bRT & 1*bRTT & 2*bRTT \\ \hline \multirow{3}{*}{0.1*BDP} & BBRv1 & 1.00 & 0.60 & 0.86 & 0.96 & 0.98 & 0.90 \\ \cline{2-9}  & BBRv2 & 0.82 & 0.53 & 0.95 & 0.62 & 0.75 & 0.79 \\ \cline{2-9}  & BBRv3 & 0.98 & 0.54 & 0.97 & 0.97 & 0.74 & 0.59 \\ \hline \multirow{3}{*}{0.2*BDP} & BBRv1 & 0.97 & 0.69 & 0.87 & 1.01 & 0.99 & 0.84 \\ \cline{2-9}  & BBRv2 & 0.65 & 0.51 & 0.97 & 0.87 & 0.76 & 1.00 \\ \cline{2-9}  & BBRv3 & 0.60 & 0.53 & 0.96 & 0.84 & 1.00 & 0.70 \\ \hline \multirow{3}{*}{0.5*BDP} & BBRv1 & 0.99 & 0.90 & 0.80 & 0.90 & 0.99 & 0.77 \\ \cline{2-9}  & BBRv2 & 0.84 & 0.73 & 0.99 & 0.96 & 0.57 & 0.91 \\ \cline{2-9}  & BBRv3 & 0.96 & 0.77 & 0.72 & 0.87 & 0.99 & 0.58 \\ \hline \multirow{3}{*}{1*BDP} & BBRv1 & 0.90 & 0.99 & 0.98 & 0.97 & 1.00 & 0.92 \\ \cline{2-9}  & BBRv2 & 0.60 & 0.99 & 0.85 & 0.54 & 0.79 & 0.89 \\ \cline{2-9}  & BBRv3 & 0.99 & 0.97 & 1.00 & 0.94 & 1.00 & 0.82 \\ \hline \multirow{3}{*}{2*BDP} & BBRv1 & 0.79 & 0.81 & 0.86 & 0.99 & 1.00 & 0.97 \\ \cline{2-9}  & BBRv2 & 0.79 & 0.83 & 0.93 & 1.00 & 1.00 & 0.52 \\ \cline{1-1} \cline{2-9}  & BBRv3 & 0.84 & 0.87 & 0.95 & 1.01 & 1.00 & 0.98 \\ \hline \end{tabular} Colors are used to emphesize the lowest and highest values.  
\end{table} 
Table 2: [PERSON]’s index for different buffer settings and RTT ratios for all BBR versions; bottleneck link delay = 2 ms.