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

ianswett <> Mon, 11 February 2019 19:51 UTC

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Subject: Re: [quicwg/base-drafts] Persistent Congestion Time Threshold (#2365)
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ianswett 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}}.
+sent over a long enough period of time, the network is considered to be
+experiencing persistent congestion.  Commonly, this can be established by
+consecutive PTOs, but since the PTO timer is reset when a new ack-eliciting
+packet is sent, an explicit duration must be used to account for those cases
+where PTOs do not occur or are substantially delayed.  This duration is the
+equivalent of kPersistentCongestionThreshold consecutive PTOS, and is computed

equivalent of kPersistentCongestionThreshold consecutive PTOs, and is computed

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