Analyzing the impact of bufferbloat on latency-sensitive applications

Delay-sensitive applications, such as live and interactive video, are mainstream in today´s Internet, and set to increase with the emergence of web-based video conference. For such applications quality cannot be captured solely by a flow´s throughput: interactive video needs to avoid fluctuations in both visual quality and delay. This is far more valuable than achieving a fleeting increase in throughput. Emerging real-time protocols are being designed with these goals in mind, but it is important to evaluate these methods when sharing the network with real-world traffic. Much of today´s Internet traffic uses TCP CUBIC, we therefore quantify its impact on interactive video experience (visual quality and delay): we measure the degradation imposed to interactive video when sharing a network bottleneck with TCP CUBIC traffic. To understand this impact, we compare performance when two delay-based congestion control schemes are used, one for interactive video and another for file transfer and show that these algorithms can assure good video experience and appropriate download time to their respective users. In contrast, we suggest that achieving such a “low-delay coexistence” with TCP CUBIC would require use of Active Queue Management (AQM) techniques. The paper therefore provides quantitative evidence that AQM can force loss-based TCP and delay-sensitive flows to reach a stable equilibrium point that is similar to the one naturally achieved when TCP flows are governed by delay-based mechanisms.