Re: [quicwg/base-drafts] No RTT samples, no persistent congestion (#3889)

[Kazuho Oku <[e-mail]>]

@kazuho commented on this pull request.



> @@ -1580,14 +1586,18 @@ Invoked when an ACK frame with an ECN section is received from the peer.
 Invoked when DetectAndRemoveLostPackets deems packets lost.
 
 ~~~
-   InPersistentCongestion(lost_packets):
+   InPersistentCongestion(largest_lost):
+     // Persistent congestion cannot be declared on the
+     // first RTT sample.
+     if (is first RTT sample):
+       return false

I agree with @marten-seemann here.

Consider the case where an endpoint receives the first ACK 10 seconds after sending the first packet (with an RTT of 10ms), then receives the next ACK in 20ms (with RTT of 10ms).

When the second ACK is being processed, the execution would pass through this `if`, and invoke `AreAllPacketsLost`. Because all the packets that were sent during the first few seconds are not acked, persistent congestion would be declared.

I think we can simply remove these lines, and rely on the fact that the comment in the pseudo-code talking about "edges." We can clarify what "edge" means, if necessary.

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