Congestion window reduced on ACK

draft-ietf-quic-recovery.md

@@ -955,10 +955,14 @@ packets might cause the sender's bytes in flight to exceed the congestion window
 until an acknowledgement is received that establishes loss or delivery of
 packets.
 
-If a threshold number of consecutive PTOs have occurred (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.
+When an ACK frame is received that establishes loss after 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}}.
+
 
 ## Pacing
 
@@ -1030,15 +1034,12 @@ kLossReductionFactor:
   The RECOMMENDED value is 0.5.
 
 kPersistentCongestionThreshold:
-: Number of consecutive PTOs after which network is considered to be
+: Number of consecutive PTOs after which network might be considered to be
   experiencing persistent congestion.  The rationale for this threshold is to
   enable a sender to use initial PTOs for aggressive probing, similar to Tail
-  Loss Probe (TLP) in TCP {{TLP}} {{RACK}}.  Once the number of consecutive PTOs
-  reaches this threshold - that is, persistent congestion is established - the
-  sender responds by collapsing its congestion window to kMinimumWindow, similar
-  to a Retransmission Timeout (RTO) in TCP {{RFC5681}}.  The RECOMMENDED value
-  for kPersistentCongestionThreshold is 2, which is equivalent to having two
-  TLPs before an RTO in TCP.
+  Loss Probe (TLP) in TCP {{TLP}} {{RACK}}.  The RECOMMENDED value for
+  kPersistentCongestionThreshold is 2, which is equivalent to having two TLPs
+  before an RTO in TCP.
 
 ### Variables of interest {#vars-of-interest}