BBR拥塞控制状态机分析

最新推荐文章于 2025-03-31 23:26:00 发布

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最新推荐文章于 2025-03-31 23:26:00 发布 · 3.3k 阅读

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本文详细解析了BBR拥塞控制算法的工作原理，包括其四个核心状态：STARTUP、DRAIN、PROBE_BW及PROBE_RTT，并阐述了各状态间的转换条件。深入探讨了BBR如何实现高效带宽探测、链路缓存排空及公平带宽共享。

BBR 源码文件的描述

* A BBR flow starts in STARTUP, and ramps up its sending rate quickly.
* When it estimates the pipe is full, it enters DRAIN to drain the queue.
* In steady state a BBR flow only uses PROBE_BW and PROBE_RTT.
* A long-lived BBR flow spends the vast majority of its time remaining
* (repeatedly) in PROBE_BW, fully probing and utilizing the pipe's bandwidth
* in a fair manner, with a small, bounded queue. *If* a flow has been
* continuously sending for the entire min_rtt window, and hasn't seen an RTT
* sample that matches or decreases its min_rtt estimate for 10 seconds, then
* it briefly enters PROBE_RTT to cut inflight to a minimum value to re-probe
* the path's two-way propagation delay (min_rtt). When exiting PROBE_RTT, if
* we estimated that we reached the full bw of the pipe then we enter PROBE_BW;
* otherwise we enter STARTUP to try to fill the pipe.