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

[ianswett <[e-mail]>]

@ianswett approved this pull request.



> +This duration is intended to allow a sender to use initial PTOs for aggressive
+probing, as TCP does with Tail Loss Probe (TLP; see {{RACK}}), before

```suggestion
This duration is intended to allow a sender to use one or more PTOs for
probing, as TCP does with Tail Loss Probe (TLP; see {{RACK}}), before
```

>  max_ack_delay irrespective of the packet number spaces in which losses are
 established.
 
+This duration is intended to allow a sender to use initial PTOs for aggressive
+probing, as TCP does with Tail Loss Probe (TLP; see {{RACK}}), before
+establishing persistent congestion, as TCP does with a Retransmission Timeout
+(RTO; see {{?RFC5681}}).
+
+The RECOMMENDED value for kPersistentCongestionThreshold is 3, which is
+approximately equivalent to two TLPs before an RTO in TCP.
+
+This design uses an explicit duration instead of consecutive PTO events since
+the PTO timer is restarted every time an ack-eliciting packet is sent. An
+application that trickles data restarts the PTO timer repeatedly, preventing the

nit: Is everyone going to understand trickle in this context?

> +The RECOMMENDED value for kPersistentCongestionThreshold is 3, which is
+approximately equivalent to two TLPs before an RTO in TCP.
+
+This design uses an explicit duration instead of consecutive PTO events since
+the PTO timer is restarted every time an ack-eliciting packet is sent. An
+application that trickles data restarts the PTO timer repeatedly, preventing the
+PTO timer from expiring for a potentially long period of time. A consequence of
+this design is that persistent congestion can be established without the
+occurrence of any PTOs.
+
+### Declaring Persistent Congestion
+
+A sender declares persistent congestion on receiving an acknowledgement, if the
+following conditions are true:
+
+* there are at least two ack-eliciting packets that are declared lost;

How could this not be true given other requirements?
Also should this be kPersisentCongestion - 1?

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