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Access loss recovery state in congestion control pseudocode #4174

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Oct 1, 2020
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Access loss recovery state in congestion control pseudocode #4174

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0549911
Access loss recovery state in congestion control pseudocode
martinthomson Sep 30, 2020
530f5fa
Reorder variable descriptions
martinthomson Oct 1, 2020
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19 changes: 10 additions & 9 deletions draft-ietf-quic-recovery.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1242,6 +1242,9 @@ min_rtt:
: The minimum RTT seen in the connection, ignoring acknowledgment delay, as
described in {{min-rtt}}.

first_rtt_sample:
: The time that the first RTT sample was obtained.

max_ack_delay:
: The maximum amount of time by which the receiver intends to delay
acknowledgments for packets in the Application Data packet number
Expand Down Expand Up @@ -1282,6 +1285,7 @@ latest_rtt = 0
smoothed_rtt = kInitialRtt
rttvar = kInitialRtt / 2
min_rtt = 0
first_rtt_sample = 0
for pn_space in [ Initial, Handshake, ApplicationData ]:
largest_acked_packet[pn_space] = infinite
time_of_last_ack_eliciting_packet[pn_space] = 0
Expand Down Expand Up @@ -1385,10 +1389,11 @@ OnAckReceived(ack, pn_space):


UpdateRtt(ack_delay):
if (is first RTT sample):
if (first_rtt_sample == 0):
min_rtt = latest_rtt
smoothed_rtt = latest_rtt
rttvar = latest_rtt / 2
first_rtt_sample = now()
return

// min_rtt ignores acknowledgment delay.
Expand Down Expand Up @@ -1637,9 +1642,8 @@ 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.

The congestion control pseudocode also accesses some of the variables from the
loss recovery pseudocode.

## Initialization

Expand All @@ -1651,7 +1655,6 @@ 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
~~~
Expand Down Expand Up @@ -1682,9 +1685,6 @@ 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)

Expand Down Expand Up @@ -1759,7 +1759,8 @@ OnPacketsLost(lost_packets):
// Reset the congestion window if the loss of these
// packets indicates persistent congestion.
// Only consider packets sent after getting an RTT sample.
assert(first_rtt_sample != 0)
if (first_rtt_sample == 0):
return
pc_lost = {}
for lost in lost_packets:
if lost.time_sent > first_rtt_sample:
Expand Down