Why architecture matters here

BBR wins on lossy long-haul links but can starve co-existing CUBIC. Architecture matters because phases + fairness + kernel compose.

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The architecture: every piece explained

The top strip is model. min RTT filter. max BW filter. BDP. Pacing rate.

The middle row is phases. STARTUP. DRAIN. PROBE_BW. PROBE_RTT.

The lower rows are ops. vs CUBIC. Metrics. Ops — kernel + tuning + rollout.

BBR — bandwidth + RTT + probe phasesmodel-based congestion controlmin RTT filter10s windowmax BW filter10 RTT windowBDPBW * min_RTTPacing rate= BW * gainSTARTUP2/ln(2) gainDRAINreduce inflightPROBE_BW8-phase cyclePROBE_RTTsample min RTTvs CUBICloss vs model basedMetricsthroughput + latencyOps — kernel version + tuning + rolloutgrowdrainprobesamplecomparewatchwatchoperateoperate
BBR probes bandwidth + RTT to set pacing rate.
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End-to-end flow

End-to-end: new flow starts STARTUP, doubles rate each RTT until BW plateau. DRAIN reduces inflight. PROBE_BW cycles 1.25x, 0.75x, then 1x×6 to fairness-share. PROBE_RTT every 10s dips inflight to sample.