Re: [quicwg/base-drafts] Add note about frequent RTT estimates (#2340)

Martin Thomson <> Wed, 23 January 2019 00:10 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] Add note about frequent RTT estimates (#2340)
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martinthomson commented on this pull request.

> @@ -289,8 +289,15 @@ be subtracted from the RTT as long as the result is larger than the min_rtt.
 If the result is smaller than the min_rtt, the RTT should be used, but the
 ack delay field should be ignored.
-Like TCP, QUIC calculates both smoothed RTT and RTT variance similar to those
-specified in {{?RFC6298}}.
+A sender calculates both smoothed RTT and RTT variance similar to those
+specified in {{?RFC6298}}, see {{on-ack-received}}.
+A sender takes an RTT sample when an ACK frame is received that acknowledges a
+larger packet number than before (see {{on-ack-received}}).  A sender will take
+multiple RTT samples per RTT when multiple such ACK frames are received within
+an RTT.  When multiple samples are generated within an RTT, the smoothed RTT and
+RTT variance may retain inadequate history, as suggested in {{?RFC6298}}.

RTT variance could retain inadequate history, as suggested in {{?RFC6298}}.

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