An Experimental Evaluation of Low Latency Congestion Control for mmWave Links

Applications that require extremely low latency are expected to be a major driver of 5G and WLAN networks that include millimeter wave (mmWave) links. However, mmWave links can experience frequent, sudden changes in link capacity due to obstructions in the signal path. These dramatic variations in link capacity cause a temporary “bufferbloat” condition during which delay may increase by a factor of 2-10. Low latency congestion control protocols, which manage bufferbloat by minimizing queue occupancy, represent a potential solution to this problem, however their behavior over links with dramatic variations in capacity is not well understood. In this paper, we explore the behavior of two major low latency congestion control protocols, TCP BBR and TCP Prague (as part of L4S), using link traces collected over mmWave links under various conditions. Our evaluation reveals potential problems associated with use of these congestion control protocols for low latency applications over mmWave links.