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[quicwg/base-drafts] persistent congestion can never happen (#2208)

Marten Seemann <notifications@github.com> Wed, 19 December 2018 06:31 UTC

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Date: Wed, 19 Dec 2018 06:31:10 +0000
From: Marten Seemann <notifications@github.com>
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Subject: [quicwg/base-drafts] persistent congestion can never happen (#2208)
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The collapse of the congestion window (which used to happen after an RTO was verified) happens in `CongestionEvent`, if `pto_count > kPersistentCongestionThreshold`.
`CongestionEvent` is called from `OnPacketsLost`, which is called from `DetectLostPackets`, which in the case of a tail is only called when a new ACK is received from `OnAckReceived`. However, `OnAckReceived` resets the `pto_count` to 0 *before* calling `DetectLostPackets`, so the condition that leads to the collapse of the congestion window can never occur.

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