Re: [quicwg/base-drafts] Add some MUSTs to congestion control (#3978)

[mirjak <[e-mail]>]

@mirjak commented on this pull request.



> @@ -767,20 +767,22 @@ While in slow start, QUIC increases the congestion window by the
 number of bytes acknowledged when each acknowledgment is processed, resulting
 in exponential growth of the congestion window.
 
-QUIC exits slow start upon loss or upon increase in the ECN-CE counter.
-When slow start is exited, the congestion window halves and the slow start
-threshold is set to the new congestion window.  QUIC re-enters slow start
-any time the congestion window is less than the slow start threshold,
-which only occurs after persistent congestion is declared.
+QUIC MUST exit slow start and enter congestion avoidance upon loss or upon
+increase in the ECN-CE counter. When slow start is exited, the congestion
+window halves and the slow start threshold is set to the new congestion

Also for TCP it was always possible to send new data because of the packet conservation principle as when you receive an ACK that doesn't ack new data you still know that at least one packet was received and you can reduce your bytes_in_flight by one packet. The thing that TCP does by reducing the cwnd gradually over the recovery RTT is that you don't have the effect you describe above where your don't send anything for half an RTT and then keep sending with exactly the same rate as previously for the second half on the RTT and overload the network again. This is a feature that should be conserved with QUIC as well.

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