Persistent congestion pseudocode to match text

draft-ietf-quic-recovery.md

@@ -1504,6 +1504,13 @@ ssthresh:
   the mode is slow start and the window grows by the number of bytes
   acknowledged.
 
+first_rtt_sample:
+: The time that the first RTT sample was obtained.
+
+pc_lost:
+: Lost packets from all packet number spaces that are used in determining
+  persistent congestion.
+
 
 ## Initialization
 
@@ -1515,6 +1522,7 @@ congestion_window = kInitialWindow
 bytes_in_flight = 0
 congestion_recovery_start_time = 0
 ssthresh = infinite
+first_rtt_sample = 0
 for pn_space in [ Initial, Handshake, ApplicationData ]:
   ecn_ce_counters[pn_space] = 0
 ~~~
@@ -1541,19 +1549,25 @@ InCongestionRecovery(sent_time):
   return sent_time <= congestion_recovery_start_time
 
 OnPacketsAcked(acked_packets):
+  if (first_rtt_sample == 0):
+    first_rtt_sample = now()
+
   for acked_packet in acked_packets:
     OnPacketAcked(acked_packet)
 
 OnPacketAcked(acked_packet):
   // Remove from bytes_in_flight.
   bytes_in_flight -= acked_packet.sent_bytes
+
   // Do not increase congestion_window if application
   // limited or flow control limited.
   if (IsAppOrFlowControlLimited())
     return
+
   // Do not increase congestion window in recovery period.
   if (InCongestionRecovery(acked_packet.time_sent)):
     return
+
   if (congestion_window < ssthresh):
     // Slow start.
     congestion_window += acked_packet.sent_bytes
@@ -1605,26 +1619,37 @@ ProcessECN(ack, pn_space):
 Invoked when DetectAndRemoveLostPackets deems packets lost.
 
 ~~~
-InPersistentCongestion(largest_lost):
-  // Persistent congestion cannot be declared on the
-  // first RTT sample.
-  if (is first RTT sample):
-    return false
+InPersistentCongestion(lost_packets):
+  // Consider lost packets across all packet number spaces.
+  pc_lost.append(lost_packets)
+
+  // Disregard packets sent prior to getting an RTT sample.
+  assert(first_rtt_sample != 0)
+  for lost in pc_lost:
+    if lost.time_sent <= first_rtt_sample:
+      pc_lost.remove(lost)
+
+  // Find the duration of the largest contiguous set of lost
+  // packets that starts and ends with an ack-eliciting packet.
+  // Note: Indexing pc_lost by time_sent rather than packet
+  // number might simplify implementation.
+  pc_duration = FindLargestLossPeriod(pc_lost)
+
+  // Declare persistent congestion if these packets span
+  // a period longer than the persistent congestion period.
   pto = smoothed_rtt + max(4 * rttvar, kGranularity) +
     max_ack_delay
-  congestion_period = pto * kPersistentCongestionThreshold
-  // Determine if all packets in the time period before the
-  // largest newly lost packet, including the edges and
-  // across all packet number spaces, are marked lost.
-  return AreAllPacketsLost(largest_lost, congestion_period)
+  return pc_duration > pto * kPersistentCongestionThreshold
 
 OnPacketsLost(lost_packets):
   // Remove lost packets from bytes_in_flight.
   for lost_packet in lost_packets:
     bytes_in_flight -= lost_packet.sent_bytes
   OnCongestionEvent(lost_packets.largest().time_sent)
-  // Collapse congestion window if persistent congestion
-  if (InPersistentCongestion(lost_packets.largest())):
+
+  // Collapse congestion window on persistent congestion.
+  if (InPersistentCongestion(lost_packets)):
+    pc_lost.clear()
     congestion_window = kMinimumWindow
 ~~~