SmartPacer: Smart Paced Sender for Low-Latency and High-Efficiency Real-Time Communication

Congestion Control Algorithm (CCA) and paced sender play a crucial role in real-time communication (RTC) applications. While CCA has been studied extensively, the paced sender remains largely unexplored. The default paced sender follows a fixed-interval packet-sending schedule, and employs a uniform budget distribution approach, which is not suitable for RTC applications. With a thorough analysis of the default paced sender, we reveal that the end-to-end delay and CPU cost are far from satisfactory in large-scale deployments.In this paper, we propose SmartPacer, a novel approach that ensures both low latency and high efficiency for RTC applications, even in dynamic and fluctuating network environments. SmartPacer is designed with two key components: a hierarchical pacer budget control scheme and an adaptive scheduling strategy. By integrating SmartPacer with some state-of-the-art bandwidth estimation algorithms, we show that SmartPacer helps achieve a 10%–50% reduction for end-to-end delay. Furthermore, we deploy SmartPacer on Douyin, one of the most popular video platforms in China, where 120 million users are involved in the online A/B test. Comprehensive results demonstrate that CPU usage is reduced by 14.4%, and end-to-end delay is reduced by 7.6%. More importantly, the user engagement duration is increased by 1.0%.