BBR Bufferbloat in DASH Video
BBR Bufferbloat in DASH Video
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DOI：
10.1145/3442381.3450061
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发表时间：
2021-04
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影响因子：
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通讯作者：
Santiago Vargas;Rebecca Drucker;Aiswarya Renganathan;A. Balasubramanian;Anshul Gandhi
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作者：
Santiago Vargas;Rebecca Drucker;Aiswarya Renganathan;A. Balasubramanian;Anshul Gandhi
BBR是一种新的拥塞控制算法，正在被越来越多的人采用，特别是在视频流量方面。BBR解决了传统的基于丢失的拥塞控制算法中的缓冲区膨胀问题，当路由器缓冲区较深时，应用程序性能会显著下降。BBR调整流量，使路由器队列不会增加，从而在保持高吞吐量的同时避免缓冲区膨胀问题。然而，我们的分析表明，在深度缓冲下使用BBR时，视频应用程序的性能明显较差。事实上，我们发现，由于路由器上的长队列，视频流量会出现延迟过大的情况，最终会降低视频性能。为了理解这种二分法，我们研究了BBR和DASH视频之间的交互作用。我们的研究表明，在深度缓冲和高网络突发度的情况下，BBR严重高估了可用带宽并且没有收敛到稳定状态，这两者都会导致BBR向网络发送大量的数据，从而导致队列堆积。BBR下数据包发送速率的提高最终是由路由器吸收突发流量的能力造成的，这破坏了BBR的带宽估计，并覆盖了BBR退出启动阶段的预期逻辑。我们设计了一种新的带宽估计算法，并将其应用于BBR(以及仍未发布的BBR的较新版本BBR2)。我们改进的BBR和BBR2即使在深度缓冲下也能显著改善视频QOE。
BBR is a new congestion control algorithm and is seeing increased adoption especially for video traffic. BBR solves the bufferbloat problem in legacy loss-based congestion control algorithms where application performance drops considerably when router buffers are deep. BBR regulates traffic such that router queues don’t build up to avoid the bufferbloat problem while still maintaining high throughput. However, our analysis shows that video applications experience significantly poor performance when using BBR under deep buffers. In fact, we find that video traffic sees inflated latencies because of long queues at the router, ultimately degrading video performance. To understand this dichotomy, we study the interaction between BBR and DASH video. Our investigation reveals that BBR under deep buffers and high network burstiness severely overestimates available bandwidth and does not converge to steady state, both of which results in BBR sending substantially more data into the network, causing a queue buildup. This elevated packet sending rate under BBR is ultimately caused by the router’s ability to absorb bursts in traffic, which destabilizes BBR’s bandwidth estimation and overrides BBR’s expected logic for exiting the startup phase. We design a new bandwidth estimation algorithm and apply it to BBR (and a still-unreleased, newer version of BBR called BBR2). Our modified BBR and BBR2 both see significantly improved video QoE even under deep buffers.