Re: [quicwg/base-drafts] Rework section on persistent congestion (#3961)

[Jana Iyengar <[e-mail]>]

@janaiyengar commented on this pull request.



> +This design does not use consecutive PTO events to establish persistent
+congestion, since application patterns impact PTO expirations. For example, a
+sender that sends small amounts of data with silence periods between them
+restarts the PTO timer every time it sends, potentially preventing the PTO timer
+from expiring for a long period of time, even when no acknowledgments are being
+received. The use of a duration enables a sender to establish persistent
+congestion without depending on the occurrence of PTOs.
+
+### Establishing Persistent Congestion
+
+A sender establishes persistent congestion on receiving an acknowledgement if at
+least two ack-eliciting packets are declared lost, and:
+
+* a prior RTT sample existed when both packets were sent;
+
+* the duration between the send times of these two packets exceeds the

That's still not correct. The point here is that there's a contiguous period that is long enough, and the duration has to be between two packets that were marked lost, not necessarily the oldest and the newest packets. For example, consider that 
- packets 1-10 were sent,
- all odd packets were marked lost: 1, 3, 5, 7, 9.
- the duration between 1 and 9 was greater than the persistent congestion duration.

According to the existing design, this should not be considered persistent congestion, but with your proposed text, it will be.



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