Investigating WebRTC BBR as an alternative to GCC for live video streaming

Google Congestion Control (GCC) is the default congestion control algorithm for WebRTC, a popular web application used for live video streaming. BBR, also developed at Google, is commonly used for streaming pre-recorded video on services like YouTube. However, BBR has not been widely deployed for real-time applications like live video streaming. It was implemented for WebRTC in 2018, but it was later deprecated due to poor performance. While GCC performs well under most network conditions, it can be starved by a loss-based TCP flow using the same bottleneck link. In this work, we investigate the possibility of using BBR as an alternative to GCC for WebRTC congestion control. We test it under a variety of network conditions and find that it performs better than GCC when competing with TCP, and it achieves bitrates comparable to GCC’s in isolation, except when bandwidth is restricted and the bottleneck buffer is deep. We find that this is because of bandwidth overestimation, a problem which also exists in TCP BBR. While modifying WebRTC BBR’s bandwidth estimation fails to improve performance in our experiments, we do find that disabling its recovery state, a unique loss response, improves WebRTC BBR’s performance in under-provisioned networks.