Re: [quicwg/base-drafts] Persistent Congestion Time Threshold (#2365)

[MikkelFJ <[e-mail]>]

mikkelfj commented on this pull request.



> -When an ACK frame is received that establishes loss of all in-flight packets
-sent prior to a threshold number of consecutive PTOs (pto_count is more than
-kPersistentCongestionThreshold, see {{cc-consts-of-interest}}), the network is
-considered to be experiencing persistent congestion, and the sender's congestion
-window MUST be reduced to the minimum congestion window (kMinimumWindow).  This
-response of collapsing the congestion window on persistent congestion is
-functionally similar to a sender's response on a Retransmission Timeout (RTO) in
-TCP {{RFC5681}}.
+## Persistent Congestion
+
+The network is considered to be experiencing persistent congestion when the
+sender goes a period of time without receiving any ACK frames for its in-flight,
+ack-eliciting packets.  Generally, this can be calculated as a number of
+consecutive PTOs (pto_count is more than  kPersistentCongestionThreshold, see
+{{cc-consts-of-interest}}), but since a PTO only occurs if no other
+ack-eliciting packets have been sent, an explicit time out must be used to

```suggestion
ack-eliciting packets have been sent, an explicit timeout must be used to
```

> -sent prior to a threshold number of consecutive PTOs (pto_count is more than
-kPersistentCongestionThreshold, see {{cc-consts-of-interest}}), the network is
-considered to be experiencing persistent congestion, and the sender's congestion
-window MUST be reduced to the minimum congestion window (kMinimumWindow).  This
-response of collapsing the congestion window on persistent congestion is
-functionally similar to a sender's response on a Retransmission Timeout (RTO) in
-TCP {{RFC5681}}.
+## Persistent Congestion
+
+The network is considered to be experiencing persistent congestion when the
+sender goes a period of time without receiving any ACK frames for its in-flight,
+ack-eliciting packets.  Generally, this can be calculated as a number of
+consecutive PTOs (pto_count is more than  kPersistentCongestionThreshold, see
+{{cc-consts-of-interest}}), but since a PTO only occurs if no other
+ack-eliciting packets have been sent, an explicit time out must be used to
+account for those cases where PTOs don't occur.

```suggestion
account for those cases where PTOs do not occur.
```

> @@ -1132,6 +1144,8 @@ increases bytes_in_flight.
 
 ~~~
    OnPacketSentCC(bytes_sent):
+     if (bytes_in_flight == 0):

if (ack_eliciting && bytes_in_flight == 0):

> @@ -1132,6 +1144,8 @@ increases bytes_in_flight.
 
 ~~~
    OnPacketSentCC(bytes_sent):
+     if (bytes_in_flight == 0):
+       probe_start_time = Now()

`if (ack_eliciting)` is used elsewhere.

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