Date: Thu, 17 Jan 2019 13:49:14 -0800
From: ianswett <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Add note about frequent RTT estimates (#2340)
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ianswett commented on this pull request.



> @@ -289,8 +289,14 @@ 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 will commonly receive ACK frames that acknowledge larger packet numbers
+than before.  A sender might therefore take multiple samples per RTT (see

Suggestion: replace "A sender..." on with: "When multiple samples are generated within an RTT, the smoothed RTT may retain inadequate RTT history, as suggested in {{?RFC6298}}.  Utilizing multiple RTT samples per RTT in smoothed RTT and RTT variance in a different way is currently an open research question."

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<p><b>@ianswett</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/quicwg/base-drafts/pull/2340#discussion_r248854185">draft-ietf-quic-recovery.md</a>:</p>
<pre style='color:#555'>&gt; @@ -289,8 +289,14 @@ 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 will commonly receive ACK frames that acknowledge larger packet numbers
+than before.  A sender might therefore take multiple samples per RTT (see
</pre>
<p>Suggestion: replace "A sender..." on with: "When multiple samples are generated within an RTT, the smoothed RTT may retain inadequate RTT history, as suggested in {{?RFC6298}}.  Utilizing multiple RTT samples per RTT in smoothed RTT and RTT variance in a different way is currently an open research question."</p>

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