Re: [quicwg/base-drafts] ECN verification text (#2752)

Martin Thomson <> Thu, 08 August 2019 14:03 UTC

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From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] ECN verification text (#2752)
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martinthomson commented on this pull request.

> -reduced throughput or other undesirable side-effects.  To reduce this risk, an
-endpoint uses the following steps to verify the counts it receives in an ACK
+To start ECN validation, an endpoint SHOULD do the following when sending
+packets on a new path to a peer:
+* Set the ECT(0) codepoint in the IP header of early outgoing packets sent on a
+  new path to the peer {{!RFC8311}}.
+* If all packets that were sent with the ECT(0) codepoint are eventually deemed
+  lost {{QUIC-RECOVERY}}, validation is deemed to have failed.
+To reduce the chances of misinterpreting congestive loss as packets dropped by a
+faulty network element, an endpoint could set the ECT(0) codepoint in the first
+ten outgoing packets on a path, or for a period of three RTTs, whichever occurs
+first.  Implementations MAY experiment with and use other strategies.  An

A problem here is that the text mandates use of ECT(0), which might preclude use of something like L4S on a strict reading.  Also, we need a reason to mention ECT(1) later.

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