Abstract
This paper shows the inefficiency of TCP BBR in exploiting the Wi-Fi bandwidth. This limitation of BBR has been observed with both IEEE 802.11n and IEEE 802.11ac, where the mechanism of frame aggregation is used to boost the throughput of data transmission. In the last years, many TCP variants have been introduced to limit the bufferbloat phenomena and bound the latency through a reduction of the queue backlog injection rate. However, this mechanism impacts on the Wi-Fi frame aggregation logic, impeding TCP congestion controls to reach the full throughput potential of a Wi-Fi interface. While this problem can be solved with TCP Cubic by allowing the sender node to enqueue more packets, for TCP BBR the fix is not the same, as it has a customized pacing algorithm. With this contribution we propose BBRp, a new BBR version that allows for fine-tuning the congestion control pace, achieving between four and six times more throughput over IEEE 802.11n and IEEE 802.11ac channels, at the cost of an increased latency that is however always less than the latency obtainable with loss-based TCP congestion controls.
Highlights
The increase of Wi-Fi users is demanding new optimized standards, as well as refinements in the current ones [1]–[3]
Google has introduced a new mechanism called TCP Small Queues (TSQ) that limits the number of packets that a TCP socket can push down in the stack until packets have been truly dispatched by the Network
This paper showed the inefficiency of TCP BBR over IEEE 802.11n and IEEE 802.11ac, the two most used Wi-Fi technologies
Summary
The increase of Wi-Fi users is demanding new optimized standards, as well as refinements in the current ones [1]–[3]. Even if the TSQ performance over wired links is remarkable, this is not the case for WLAN environments in which TSQ could break the frame aggregation logic, impeding all the TCP variants to discover the full link potential correctly. This limitation has been discovered and solved for TCP Cubic, and it led to a new solution for boosting BBR v2.0 throughput on Wi-Fi paths [11]–[13]. We demonstrated the ability of BBRp to discover the full Wi-Fi bandwidth reaching almost optimal throughput values, outperforming the standard BBR algorithm, while still maintaining better latency performance when compared to TCP Cubic.
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