Abstract
To alleviate the lower performance of Transmission Control Protocol (TCP) congestion control over complex network, especially the high latency and packet loss scenario, Google proposed the Bottleneck Bandwidth and Round-trip propagation time (BBR) congestion control algorithm. In contrast with other TCP congestion control algorithms, BBR adjusted transfer data by maximizing delivery rate and minimizing delay. However, some evaluation experiments have shown that the persistent queues formation and retransmissions in the bottleneck can lead to serious fairness issues between BBR flows with different round-trip times (RTTs). They pointed out that small RTT differences cause unfairness in the throughput of BBR flows and flows with longer RTT can obtain higher bandwidth when competing with the shorter RTT flows. In order to solve this fairness problem, an adaptive congestion window of BBR is proposed, which adjusts the congestion window gain of each BBR flow in network load. The proposed algorithms alleviate the RTT fairness issue by controlling the upper limit of congestion window according to the delivery rate and queue status. In the Network Simulator 3 (NS3) simulation experiment, it shows that the adaptive congestion window of BBR (BBR-ACW) congestion control algorithm improves the fairness by more than 50% and reduces the queuing delay by 54%, compared with that of the original BBR in different buffer sizes.
Highlights
After the observation of Internet congestion collapse in 1986, Jocobson [1] proposed a method to adjust the transmission window of Transmission Control Protocol (TCP) flow by using the loss of packet
Song et al [28] pointed out the problem of Bottleneck Bandwidth and Roundtrip propagation time (BBR) when analyzing the Inter-Protocol Fairness of BBR: BBR only estimates the delivery rate based on BDP and uses a fixed congestion window, without considering the impact of packet loss
The impact of different buffer sizes is considered to avoid increased queuing delay or a large number of packet losses. This paper provides another way, which adaptively adjusts the upper limit of the congestion window (CWND) of each round-trip times (RTTs) flow and moves the operating point of BBR to the position where the buffer is not full
Summary
After the observation of Internet congestion collapse in 1986, Jocobson [1] proposed a method to adjust the transmission window of TCP flow by using the loss of packet. Song et al [28] pointed out the problem of BBR when analyzing the Inter-Protocol Fairness of BBR: BBR only estimates the delivery rate based on BDP and uses a fixed congestion window, without considering the impact of packet loss. It can be seen from the above literature that if the amount of data sent by the BBR exceeds the capacity of the link, it can lead to serious queuing delay and severe network congestion.
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