Re: [quicwg/base-drafts] Don't verify ECN counts for out of order ACKs (#2215)

[Martin Thomson <[e-mail]>]

martinthomson requested changes on this pull request.

I really don't like adding a hard coupling like this to the design.  I would be comfortable with a SHOULD NOT, explaining that if you don't do that, you might disable ECN unnecessarily in some rare cases.

> @@ -3065,6 +3064,10 @@ to be greater than the number of packets acknowledged in an ACK frame.  When
 this happens, and if verification succeeds, the local reference counts MUST be
 increased to match the counts in the ACK frame.
 
+Processing counts out of order can result in verification failure.  An endpoint
+MUST NOT perform this verification if the ACK frame is received in a packet with
+packet number lower than a previously received ACK frame.

With the proposed change, add:

> Verifying based on ACK frames that arrive out of order can result in disabling ECN unnecessarily.

> @@ -3065,6 +3064,10 @@ to be greater than the number of packets acknowledged in an ACK frame.  When
 this happens, and if verification succeeds, the local reference counts MUST be
 increased to match the counts in the ACK frame.
 
+Processing counts out of order can result in verification failure.  An endpoint
+MUST NOT perform this verification if the ACK frame is received in a packet with

```suggestion
SHOULD NOT perform this verification if the ACK frame is received in a packet with
```

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