Re: [quicwg/base-drafts] An example ECN validation algorithm (#3320)

Martin Thomson <> Fri, 10 January 2020 02:37 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] An example ECN validation algorithm (#3320)
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martinthomson commented on this pull request.

> +
+The testing period runs for a number of packets or round trip times as
+determined by the endpoint.  During this time, packets sent are marked with
+ECT(0).  The goal is to limit the duration of the testing period, but to ensure
+that enough marked packets are sent that it is likely that ECN counts will
+provide a clear indication of how the path treats marked packets.
+<!-- Do we need a more concrete recommendation here?  For instance, I might say
+"Endpoints could test with packets that amount to between 1 to 2 times the
+initial congestion window over a period between 1 to 2 times the estimated RTT."
+After the testing period ends, the ECN state for the path becomes "unknown".
+From the "unknown" state, successful validation of the ECN counts an ACK frame
+(see {{ecn-ack}}) causes the ECN state for the path to become "capable", unless
+no marked packet has been acknowledged.

I don't think that works without additional constraints or checks as you could exit the testing state before any PTO might occur.

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