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Open AccessArticle

BBR-ACD: BBR with Advanced Congestion Detection

School of Electronics Engineering, Kyungpook National University, Daegu 41566, Korea
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Electronics 2020, 9(1), 136; https://doi.org/10.3390/electronics9010136
Received: 2 December 2019 / Revised: 30 December 2019 / Accepted: 7 January 2020 / Published: 10 January 2020
(This article belongs to the Section Networks)
With the aim of improved throughput with reduced delay, Google proposed the bottleneck bandwidth and round-trip time (BBR) congestion control algorithm in 2016. Contrasting with the traditional loss-based congestion control algorithms, it operates without bottleneck queue formation and packet losses. However, we find unexpected behaviour in BBR during testbed experiments and network simulator 3 (NS-3) simulations. We observe huge packet losses, retransmissions, and large queue formation in the bottleneck in a congested network scenario. We believe this is because of BBR’s nature of sending extra data during the bandwidth probing without considering the network conditions, and the lack of a proper recovery mechanism. In a congested network, the sent extra data creates a large queue in the bottleneck, which is sustained due to insufficient drain time. BBR lacks a proper mechanism to detect such large bottleneck queues, cannot comply with the critical congestion situation properly, and results in excessive retransmission problems. Based on these observations, we propose a derivative of BBR, called “BBR with advanced congestion detection (BBR-ACD)”, that reduces the excessive retransmissions without losing the merits. We propose a novel method to determine an actual congestion situation by considering the packet loss and delay-gradient of round-trip time, and implement a proper recovery mechanism to handle such a congestion situation. Through extensive test and NS-3 simulations, we confirmed that the proposed BBR-ACD could reduce the retransmissions by about 50% while improving the total goodput of the network. View Full-Text
Keywords: BBR; congestion control; actual congestion detection; retransmissions; TCP BBR; congestion control; actual congestion detection; retransmissions; TCP
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Mahmud, I.; Kim, G.-H.; Lubna, T.; Cho, Y.-Z. BBR-ACD: BBR with Advanced Congestion Detection. Electronics 2020, 9, 136.

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