ExLL: An Extremely Low-latency Congestion Control for Cellular Networks
Since the diagnosis of poor latency performance of TCP from overbuffering, namely bufferbloat, in cellular networks, there have been a number of proposals to tackle the problem. However, due to the fundamental challenges involved in the goal of persistently achieving the maximum throughput and the minimum latency at the same time, which are in a trade-off relationship, it was not very successful to have a congestion control that performs very closely to its ideal. To this end, we propose a new congestion control, ExLL that extremely restrain its latency to the level of minimum possible RTT (round trip time) while keeping its throughput in the same level of throughput-oriented congestion control schemes such as TCP Cubic.ExLL properly adjusts CWND without increasing RTT excessively or losing throughput even in a mobility scenario. ExLL records around 30% RTT gap while TCP Cubic and BBR shows 419% and 143% gaps.