Themis: Toward Stable Near-Zero Queuing Delay in Congestion Control for Low-Latency Interactive Video Streaming

Low-latency interactive video streaming services critically depend on robust congestion control algorithms (CCA). However, existing CCAs often exhibit frequent self-induced oscillations from unconstrained probing, causing periodic heavy queuing and degrading the user experience. We propose Themis, a novel end-to-end CCA designed to achieve stabilized near-zero queuing delay with high bitrate. By precisely quantifying the trade-off between bitrate and queuing delay within a utility feedback mechanism, Themis effectively controls the amplitude and frequency of probing while ensuring fairness. In parallel, Themis incorporates the awareness of the queuing state through an adaptive-pacing method, combined with utility feedback to guide a three-phase bitrate adjustment strategy. This enables rapid and stable convergence to the optimal utility. We implemented Themis in QUIC, evaluated it on the Mahimahi and conducted a 90-day large-scale A/B test in a real-world network. Compared to state-of-the-art CCAs, Themis effectively suppresses self-induced oscillations, increases the average frame bitrate by 66.8%, and reduces the average frame delay by 13.5%, demonstrating a superior trade-off between high bitrate and low queuing delay.