R-TCP: A Framework to Optimize TCP Performance Over Rate-Limiting Networks

Many mobile operators provide subscription plans that include a data quota for full-speed access, beyond which the service will be throttled to a low data rate — rate-limited service. This is designed to control costs and to motivate users to upgrade. Our recent measurements in a country-scale service suggested that the proportion of TCP flows subjected to rate limiting can be as high as 28%. More importantly, TCP flows under rate limiting can exhibit excessive retransmission rates, exceeding 20% in many cases. The extra bandwidth costs incurred by the retransmissions for large service providers are very significant, not to mention bandwidth wastage. This work develops a novel R-TCP framework to mitigate the excessive retransmissions problems in various TCP designs (e.g., Cubic and BBR) under rate limiting networks. R-TCP is specifically designed and optimized for sender-side kernel implementation with minimal overheads. It has been implemented into Linux where extensive experiments in real-world networks and applications show that it can substantially reduce excessive retransmissions by up to 88% with negligible tradeoff in goodput and application-layer performance.