BISCAY: Practical Radio KPI Driven Congestion Control for Mobile Networks

Abstract

Mobile application performance relies heavily on the congestion control design of the underlying transport, which is typically bottlenecked by cellular link and has to cope with rapid cellular link bandwidth fluctuations. We observe that radio KPI measurements from the mobile device chipset can be exploited for precise and timely measurement of available bandwidth on the cellular link. Building on this insight, we propose Biscay, a practical and radio KPI-driven congestion control system design for mobile networks. Biscay leverages OpenDiag, the in-kernel real-time radio KPI extraction tool we introduce in this paper, along with our KPI-based accurate bandwidth determination layer towards dynamically adjusting the congestion window to optimally use the available bandwidth while keeping delay to the minimum. Our solution is practical and deployable, as shown through our implementation of Biscay and OpenDiag on unrooted Android 5G phones. We extensively evaluate Biscay against different state-of-the-art congestion control designs including BBR and CUBIC with emulations driven by real measurement traces as well as real-world experiments spanning diverse 4G and 5G scenarios, and show that it provides significant average and tail delay improvements (typically over 90% reduction) while yielding better or similar throughput. These gains are enabled by 100% improvement in the granularity of on-device radio KPI measurements with OpenDiag compared to existing alternatives like MobileInsight.