Experimenting with Ledbat++: Fairness, Flow Scalability and LBE Compliance

The Ledbat++ protocol has been recently introduced as the evolution of Ledbat, a congestion control algorithm for background traffic. Ledbat++ encompasses improved congestion control mechanisms to mitigate inherent Ledbat issues stemming mainly from falsely estimated delays and resulting in degraded inter-flow fairness or undesired aggressiveness. However, the performance evaluation of Ledbat++ remains rather limited to date. In this paper, we introduce an ns-3-based Ledbat++ implementation which allows us to evaluate for the first time the protocol performance under realistic conditions with an increasing number of competing flows. To better assess the protocol's impact on regular TCP traffic we consider well-suited scenarios including competition with various congestion control algorithms. Our findings indicate that Ledbat++ satisfies its design goals in the sense that it solves the problems original Ledbat is inherently susceptible to, but also efficiently backs off and allows TCP flows to prevail, serving the ‘less-than-best-effort’ principle. We also found that Ledbat++ flows achieve throughput close to its competing flows only when competing with other bulk transfer-oriented algorithms, such as TCP Low Priority.