Re: [quicwg/base-drafts] Document TCP RTO vs QUIC PTO (#3441)

ianswett <> Sat, 07 March 2020 11:41 UTC

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Date: Sat, 07 Mar 2020 03:41:02 -0800
From: ianswett <>
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Subject: Re: [quicwg/base-drafts] Document TCP RTO vs QUIC PTO (#3441)
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ianswett commented on this pull request.

> @@ -228,6 +228,25 @@ QUIC endpoints measure the delay incurred between when a packet is received and
 when the corresponding acknowledgment is sent, allowing a peer to maintain a
 more accurate round-trip time estimate (see Section 13.2 of {{QUIC-TRANSPORT}}).
+### Probe Timeout Replaces RTO and TLP
+QUIC uses a probe timeout (see {{pto}}), with a timer based on TCP's RTO
+computation.  QUIC's PTO includes the peer's maximum expected acknowledgement
+delay instead of using a fixed minimum timeout. Unlike TCP, which collapses
+the congestion window upon expiry of an RTO, QUIC does not collapse the
+congestion window until persistent congestion {{persistent-congestion}} is
+declared and instead allows probe packets to temporarily exceed the congestion
+window whenever the timer expires.  In practice, this is similar to TCP with
+F-RTO, but it does allow more packets to be sent when the congestion window was

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