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// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
use crate::{
packet::number::PacketNumberSpace, time::Timestamp, transport::parameters::MaxAckDelay,
};
use core::{
cmp::{max, min},
time::Duration,
};
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.2
//# When no previous RTT is available, the initial RTT
//# SHOULD be set to 333 milliseconds. This results in handshakes
//# starting with a PTO of 1 second, as recommended for TCP's initial
//# RTO; see Section 2 of [RFC6298].
pub const DEFAULT_INITIAL_RTT: Duration = Duration::from_millis(333);
/// The lowest RTT value that the RTT Estimator is capable of tracking
pub const MIN_RTT: Duration = Duration::from_micros(1);
const ZERO_DURATION: Duration = Duration::from_millis(0);
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//# The RECOMMENDED value of the timer granularity (kGranularity) is 1 millisecond.
pub const K_GRANULARITY: Duration = Duration::from_millis(1);
//= https://www.rfc-editor.org/rfc/rfc9002#section-7.6.1
//# The RECOMMENDED value for kPersistentCongestionThreshold is 3, which
//# results in behavior that is approximately equivalent to a TCP sender
//# declaring an RTO after two TLPs.
const K_PERSISTENT_CONGESTION_THRESHOLD: u64 = 3;
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct RttEstimator {
/// Latest RTT sample
latest_rtt: Duration,
/// The minimum value observed over the lifetime of the connection
min_rtt: Duration,
/// An exponentially-weighted moving average
smoothed_rtt: Duration,
/// The variance in the observed RTT samples
rttvar: Duration,
/// The maximum amount of time by which the receiver intends to delay acknowledgments for
/// packets in the ApplicationData packet number space. The actual ack_delay in a received
/// ACK frame may be larger due to late timers, reordering, or lost ACK frames.
max_ack_delay: Duration,
/// The time that the first RTT sample was obtained
first_rtt_sample: Option<Timestamp>,
}
impl Default for RttEstimator {
/// Creates a new RTT Estimator with default initial values
fn default() -> Self {
RttEstimator::new(DEFAULT_INITIAL_RTT)
}
}
impl RttEstimator {
/// Creates a new RTT Estimator with the given `initial_rtt`
///
/// `on_max_ack_delay` must be called when the `max_ack_delay` transport
/// parameter is received to initialize the `max_ack_delay` value.
#[inline]
pub fn new(initial_rtt: Duration) -> Self {
Self::new_with_max_ack_delay(Duration::ZERO, initial_rtt)
}
/// Creates a new RTT Estimator with the provided initial values using the given `max_ack_delay`.
#[inline]
fn new_with_max_ack_delay(max_ack_delay: Duration, initial_rtt: Duration) -> Self {
debug_assert!(initial_rtt >= MIN_RTT);
let initial_rtt = initial_rtt.max(MIN_RTT);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# Before any RTT samples are available for a new path or when the
//# estimator is reset, the estimator is initialized using the initial RTT;
//# see Section 6.2.2.
//#
//# smoothed_rtt and rttvar are initialized as follows, where kInitialRtt
//# contains the initial RTT value:
//
//# smoothed_rtt = kInitialRtt
//# rttvar = kInitialRtt / 2
let smoothed_rtt = initial_rtt;
let rttvar = initial_rtt / 2;
Self {
latest_rtt: initial_rtt,
min_rtt: initial_rtt,
smoothed_rtt,
rttvar,
max_ack_delay,
first_rtt_sample: None,
}
}
/// Creates a new RTT Estimator with the `max_ack_delay` from the current instance
pub fn for_new_path(&self, initial_rtt: Duration) -> Self {
Self::new_with_max_ack_delay(self.max_ack_delay, initial_rtt)
}
/// Gets the latest round trip time sample
#[inline]
pub fn latest_rtt(&self) -> Duration {
self.latest_rtt
}
/// Gets the weighted average round trip time
#[inline]
pub fn smoothed_rtt(&self) -> Duration {
self.smoothed_rtt
}
/// Gets the minimum round trip time
#[inline]
pub fn min_rtt(&self) -> Duration {
self.min_rtt
}
/// Gets the variance in observed round trip time samples
#[inline]
pub fn rttvar(&self) -> Duration {
self.rttvar
}
/// Gets the timestamp of the first RTT sample
#[inline]
pub fn first_rtt_sample(&self) -> Option<Timestamp> {
self.first_rtt_sample
}
/// Gets the max_ack_delay
#[inline]
pub fn max_ack_delay(&self) -> Duration {
self.max_ack_delay
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//# The PTO period is the amount of time that a sender ought to wait for
//# an acknowledgement of a sent packet.
#[inline]
pub fn pto_period(&self, pto_backoff: u32, space: PacketNumberSpace) -> Duration {
// We operate on microseconds rather than `Duration` to improve efficiency.
// See https://godbolt.org/z/osEd9rj9a
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//# When an ack-eliciting packet is transmitted, the sender schedules a
//# timer for the PTO period as follows:
//#
//# PTO = smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay
let mut pto_period = self.smoothed_rtt().as_micros() as u64;
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//# The PTO period MUST be at least kGranularity, to avoid the timer
//# expiring immediately.
pto_period += max(
self.rttvar_4x().as_micros() as u64,
K_GRANULARITY.as_micros() as u64,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//# When the PTO is armed for Initial or Handshake packet number spaces,
//# the max_ack_delay in the PTO period computation is set to 0, since
//# the peer is expected to not delay these packets intentionally; see
//# Section 13.2.1 of [QUIC-TRANSPORT].
if space.is_application_data() {
pto_period += self.max_ack_delay.as_micros() as u64;
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//# Even when there are ack-eliciting packets in flight in multiple
//# packet number spaces, the exponential increase in PTO occurs across
//# all spaces to prevent excess load on the network. For example, a
//# timeout in the Initial packet number space doubles the length of
//# the timeout in the Handshake packet number space.
pto_period *= pto_backoff as u64;
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//# The PTO period is the amount of time that a sender ought to wait for
//# an acknowledgement of a sent packet.
Duration::from_micros(pto_period)
}
/// Sets the `max_ack_delay` value from the peer `MaxAckDelay` transport parameter
pub fn on_max_ack_delay(&mut self, max_ack_delay: MaxAckDelay) {
self.max_ack_delay = max_ack_delay.as_duration()
}
/// Updates the RTT estimate using the given `rtt_sample`
#[inline]
pub fn update_rtt(
&mut self,
mut ack_delay: Duration,
rtt_sample: Duration,
timestamp: Timestamp,
is_handshake_confirmed: bool,
space: PacketNumberSpace,
) {
self.latest_rtt = rtt_sample.max(MIN_RTT);
if self.first_rtt_sample.is_none() {
self.first_rtt_sample = Some(timestamp);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.2
//# min_rtt MUST be set to the latest_rtt on the first RTT sample.
self.min_rtt = self.latest_rtt;
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# On the first RTT sample after initialization, smoothed_rtt and rttvar
//# are set as follows:
//#
//# smoothed_rtt = latest_rtt
//# rttvar = latest_rtt / 2
self.smoothed_rtt = self.latest_rtt;
self.rttvar = self.latest_rtt / 2;
return;
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.2
//# min_rtt MUST be set to the lesser of min_rtt and latest_rtt
//# (Section 5.1) on all other samples.
self.min_rtt = min(self.min_rtt, self.latest_rtt);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# when adjusting an RTT sample using peer-reported
//# acknowledgment delays, an endpoint:
//#
//# * MAY ignore the acknowledgment delay for Initial packets, since
//# these acknowledgments are not delayed by the peer (Section 13.2.1
//# of [QUIC-TRANSPORT]);
if space.is_initial() {
ack_delay = ZERO_DURATION;
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# To account for this, the endpoint SHOULD ignore
//# max_ack_delay until the handshake is confirmed, as defined in
//# Section 4.1.2 of [QUIC-TLS].
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# * SHOULD ignore the peer's max_ack_delay until the handshake is
//# confirmed;
if is_handshake_confirmed {
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# * MUST use the lesser of the acknowledgement delay and the peer's
//# max_ack_delay after the handshake is confirmed; and
ack_delay = min(ack_delay, self.max_ack_delay);
}
let mut adjusted_rtt = self.latest_rtt;
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# * MUST NOT subtract the acknowledgement delay from the RTT sample if
//# the resulting value is smaller than the min_rtt.
if self.min_rtt + ack_delay < self.latest_rtt {
adjusted_rtt -= ack_delay;
} else if !is_handshake_confirmed {
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# Therefore, prior to handshake
//# confirmation, an endpoint MAY ignore RTT samples if adjusting the RTT
//# sample for acknowledgement delay causes the sample to be less than
//# the min_rtt.
return;
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//# On subsequent RTT samples, smoothed_rtt and rttvar evolve as follows:
//#
//# ack_delay = decoded acknowledgment delay from ACK frame
//# if (handshake confirmed):
//# ack_delay = min(ack_delay, max_ack_delay)
//# adjusted_rtt = latest_rtt
//# if (latest_rtt >= min_rtt + ack_delay):
//# adjusted_rtt = latest_rtt - ack_delay
//# smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * adjusted_rtt
//# rttvar_sample = abs(smoothed_rtt - adjusted_rtt)
//# rttvar = 3/4 * rttvar + 1/4 * rttvar_sample
// this logic has been updated to follow the errata reported in https://www.rfc-editor.org/errata/eid7539
let rttvar_sample = abs_difference(self.smoothed_rtt, adjusted_rtt);
self.rttvar = weighted_average(self.rttvar, rttvar_sample, 4);
self.smoothed_rtt = weighted_average(self.smoothed_rtt, adjusted_rtt, 8);
}
/// Calculates the persistent congestion threshold used for determining
/// if persistent congestion is being encountered.
#[inline]
pub fn persistent_congestion_threshold(&self) -> Duration {
// Since K_GRANULARITY is 1ms, we operate on milliseconds rather than `Duration` to improve efficiency.
// See https://godbolt.org/z/4o71WPods
//= https://www.rfc-editor.org/rfc/rfc9002#section-7.6.1
//# The persistent congestion duration is computed as follows:
//#
//# (smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay) *
//# kPersistentCongestionThreshold
//#
//# Unlike the PTO computation in Section 6.2, this duration includes the
//# max_ack_delay irrespective of the packet number spaces in which
//# losses are established.
//#
//# This duration allows a sender to send as many packets before
//# establishing persistent congestion, including some in response to PTO
//# expiration, as TCP does with Tail Loss Probes [RFC8985] and an RTO
//# [RFC5681].
Duration::from_millis(
(self.smoothed_rtt.as_millis() as u64
+ max(
self.rttvar_4x().as_millis() as u64,
K_GRANULARITY.as_millis() as u64,
)
+ self.max_ack_delay.as_millis() as u64)
* K_PERSISTENT_CONGESTION_THRESHOLD,
)
}
#[inline]
pub fn loss_time_threshold(&self) -> Duration {
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//# The time threshold is:
//#
//# max(kTimeThreshold * max(smoothed_rtt, latest_rtt), kGranularity)
let mut time_threshold = max(
self.smoothed_rtt().as_nanos() as u64,
self.latest_rtt().as_nanos() as u64,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//# The RECOMMENDED time threshold (kTimeThreshold), expressed as an
//# RTT multiplier, is 9/8.
time_threshold += time_threshold / 8;
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//# To avoid declaring
//# packets as lost too early, this time threshold MUST be set to at
//# least the local timer granularity, as indicated by the kGranularity
//# constant.
let time_threshold = max(time_threshold, K_GRANULARITY.as_nanos() as u64);
Duration::from_nanos(time_threshold)
}
/// Allows min_rtt and smoothed_rtt to be overwritten on the next RTT sample
/// after persistent congestion is established.
#[inline]
pub fn on_persistent_congestion(&mut self) {
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.2
//# Endpoints SHOULD set the min_rtt to the newest RTT sample after
//# persistent congestion is established.
self.first_rtt_sample = None;
}
#[inline]
fn rttvar_4x(&self) -> Duration {
// Operate on micros instead, as it's more efficient and we don't need the precision Duration gives
Duration::from_micros(4 * self.rttvar.as_micros() as u64)
}
}
#[inline]
fn abs_difference<T: core::ops::Sub + PartialOrd>(a: T, b: T) -> <T as core::ops::Sub>::Output {
if a > b {
a - b
} else {
b - a
}
}
/// Optimized function for averaging two durations with a weight
/// See https://godbolt.org/z/65f9bYEcs
#[inline]
fn weighted_average(a: Duration, b: Duration, weight: u64) -> Duration {
let mut a = a.as_nanos() as u64;
// it's more accurate to multiply first but it risks overflow so we divide first
a /= weight;
a *= weight - 1;
let mut b = b.as_nanos() as u64;
b /= weight;
Duration::from_nanos(a + b)
}
#[cfg(test)]
mod test {
use super::*;
use crate::{
packet::number::PacketNumberSpace,
path::INITIAL_PTO_BACKOFF,
time::{Clock, Duration, NoopClock},
transport::parameters::MaxAckDelay,
varint::VarInt,
};
/// Test the initial values before any RTT samples
#[test]
fn initial_rtt_across_spaces() {
let rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(10), DEFAULT_INITIAL_RTT);
assert_eq!(rtt_estimator.min_rtt, DEFAULT_INITIAL_RTT);
assert_eq!(rtt_estimator.latest_rtt(), DEFAULT_INITIAL_RTT);
assert_eq!(rtt_estimator.smoothed_rtt(), DEFAULT_INITIAL_RTT);
assert_eq!(rtt_estimator.rttvar(), DEFAULT_INITIAL_RTT / 2);
assert_eq!(
rtt_estimator.pto_period(INITIAL_PTO_BACKOFF, PacketNumberSpace::Initial),
Duration::from_millis(999)
);
assert_eq!(
rtt_estimator.pto_period(INITIAL_PTO_BACKOFF, PacketNumberSpace::Handshake),
Duration::from_millis(999)
);
assert_eq!(
rtt_estimator.pto_period(INITIAL_PTO_BACKOFF, PacketNumberSpace::ApplicationData),
Duration::from_millis(1009)
);
}
/// Test a zero RTT value is treated as 1 µs
#[test]
fn zero_rtt_sample() {
let mut rtt_estimator = RttEstimator::new(DEFAULT_INITIAL_RTT);
let now = NoopClock.get_time();
rtt_estimator.update_rtt(
Duration::from_millis(10),
Duration::from_millis(0),
now,
false,
PacketNumberSpace::ApplicationData,
);
assert_eq!(rtt_estimator.min_rtt, MIN_RTT);
assert_eq!(rtt_estimator.latest_rtt(), MIN_RTT);
assert_eq!(rtt_estimator.first_rtt_sample(), Some(now));
assert_eq!(
rtt_estimator.pto_period(INITIAL_PTO_BACKOFF, PacketNumberSpace::Initial),
Duration::from_micros(1001)
);
}
#[test]
fn for_new_path() {
let mut rtt_estimator = RttEstimator::default();
let max_ack_delay = Duration::from_millis(10);
rtt_estimator.on_max_ack_delay(max_ack_delay.try_into().unwrap());
let new_path_rtt_estimator = rtt_estimator.for_new_path(DEFAULT_INITIAL_RTT);
assert_eq!(max_ack_delay, new_path_rtt_estimator.max_ack_delay)
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# * MUST use the lesser of the acknowledgement delay and the peer's
//# max_ack_delay after the handshake is confirmed;
#[test]
fn max_ack_delay() {
let mut rtt_estimator = RttEstimator::default();
assert_eq!(Duration::ZERO, rtt_estimator.max_ack_delay);
rtt_estimator.on_max_ack_delay(MaxAckDelay::new(VarInt::from_u8(10)).unwrap());
assert_eq!(Duration::from_millis(10), rtt_estimator.max_ack_delay);
let now = NoopClock.get_time();
rtt_estimator.update_rtt(
Duration::from_millis(0),
Duration::from_millis(100),
now,
true,
PacketNumberSpace::ApplicationData,
);
// Update when the handshake is confirmed
rtt_estimator.update_rtt(
Duration::from_millis(1000),
Duration::from_millis(200),
now,
true,
PacketNumberSpace::ApplicationData,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# * MUST use the lesser of the acknowledgement delay and the peer's
//# max_ack_delay after the handshake is confirmed; and
assert_eq!(
rtt_estimator.smoothed_rtt,
7 * Duration::from_millis(100) / 8 + Duration::from_millis(200 - 10) / 8
);
assert_eq!(rtt_estimator.first_rtt_sample(), Some(now));
let prev_smoothed_rtt = rtt_estimator.smoothed_rtt;
// Update when the handshake is not confirmed
rtt_estimator.update_rtt(
Duration::from_millis(50),
Duration::from_millis(200),
now,
false,
PacketNumberSpace::ApplicationData,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# To account for this, the endpoint SHOULD ignore
//# max_ack_delay until the handshake is confirmed, as defined in
//# Section 4.1.2 of [QUIC-TLS].
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# * SHOULD ignore the peer's max_ack_delay until the handshake is
//# confirmed;
assert_eq!(
rtt_estimator.smoothed_rtt,
7 * prev_smoothed_rtt / 8 + Duration::from_millis(200 - 50) / 8
);
}
/// Test several rounds of RTT updates
#[test]
fn update_rtt() {
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(10), DEFAULT_INITIAL_RTT);
let now = NoopClock.get_time();
let rtt_sample = Duration::from_millis(500);
assert!(rtt_estimator.first_rtt_sample.is_none());
rtt_estimator.update_rtt(
Duration::from_millis(10),
rtt_sample,
now,
true,
PacketNumberSpace::ApplicationData,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.2
//= type=test
//# min_rtt MUST be set to the latest_rtt on the first RTT sample.
assert_eq!(rtt_estimator.min_rtt, rtt_sample);
assert_eq!(rtt_estimator.latest_rtt, rtt_sample);
assert_eq!(rtt_estimator.smoothed_rtt, rtt_sample);
assert_eq!(rtt_estimator.rttvar, rtt_sample / 2);
assert_eq!(rtt_estimator.first_rtt_sample, Some(now));
let prev_smoothed_rtt = rtt_estimator.smoothed_rtt;
let rtt_sample = Duration::from_millis(800);
let ack_delay = Duration::from_millis(10);
rtt_estimator.update_rtt(
ack_delay,
rtt_sample,
now + Duration::from_secs(1),
true,
PacketNumberSpace::ApplicationData,
);
let adjusted_rtt = rtt_sample - ack_delay;
assert_eq!(rtt_estimator.min_rtt, prev_smoothed_rtt);
assert_eq!(rtt_estimator.latest_rtt, rtt_sample);
assert_eq!(
rtt_estimator.smoothed_rtt,
7 * prev_smoothed_rtt / 8 + adjusted_rtt / 8
);
assert_eq!(rtt_estimator.first_rtt_sample, Some(now));
// This rtt_sample is a new minimum, so the ack_delay is not used for adjustment
let prev_smoothed_rtt = rtt_estimator.smoothed_rtt;
let rtt_sample = Duration::from_millis(200);
let ack_delay = Duration::from_millis(10);
rtt_estimator.update_rtt(
ack_delay,
rtt_sample,
now + Duration::from_secs(2),
true,
PacketNumberSpace::ApplicationData,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.2
//= type=test
//# min_rtt MUST be set to the lesser of min_rtt and latest_rtt
//# (Section 5.1) on all other samples.
assert_eq!(rtt_estimator.min_rtt, rtt_sample);
assert_eq!(rtt_estimator.latest_rtt, rtt_sample);
assert_eq!(
rtt_estimator.smoothed_rtt,
7 * prev_smoothed_rtt / 8 + rtt_sample / 8
);
assert_eq!(rtt_estimator.first_rtt_sample, Some(now));
assert_eq!(
rtt_estimator.pto_period(INITIAL_PTO_BACKOFF, PacketNumberSpace::ApplicationData),
Duration::from_micros(1620466)
);
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# * MUST NOT subtract the acknowledgement delay from the RTT sample if
//# the resulting value is smaller than the min_rtt.
#[test]
fn must_not_subtract_acknowledgement_delay_if_result_smaller_than_min_rtt() {
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(200), DEFAULT_INITIAL_RTT);
let now = NoopClock.get_time();
rtt_estimator.min_rtt = Duration::from_millis(500);
rtt_estimator.smoothed_rtt = Duration::from_millis(700);
rtt_estimator.first_rtt_sample = Some(now);
let rtt_sample = Duration::from_millis(600);
let prev_smoothed_rtt = rtt_estimator.smoothed_rtt;
rtt_estimator.update_rtt(
Duration::from_millis(200),
rtt_sample,
now,
true,
PacketNumberSpace::ApplicationData,
);
assert_eq!(
rtt_estimator.smoothed_rtt,
7 * prev_smoothed_rtt / 8 + rtt_sample / 8
);
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# Therefore, prior to handshake
//# confirmation, an endpoint MAY ignore RTT samples if adjusting the RTT
//# sample for acknowledgement delay causes the sample to be less than
//# the min_rtt.
#[test]
fn prior_to_handshake_ignore_if_less_than_min_rtt() {
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(200), DEFAULT_INITIAL_RTT);
let now = NoopClock.get_time();
let smoothed_rtt = Duration::from_millis(700);
rtt_estimator.min_rtt = Duration::from_millis(500);
rtt_estimator.smoothed_rtt = smoothed_rtt;
rtt_estimator.first_rtt_sample = Some(now);
let rtt_sample = Duration::from_millis(600);
rtt_estimator.update_rtt(
Duration::from_millis(200),
rtt_sample,
now,
false,
PacketNumberSpace::ApplicationData,
);
assert_eq!(rtt_estimator.smoothed_rtt, smoothed_rtt);
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.3
//= type=test
//# * MAY ignore the acknowledgment delay for Initial packets, since
// these acknowledgments are not delayed by the peer (Section 13.2.1
// of [QUIC-TRANSPORT]);
#[test]
fn initial_space() {
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(10), DEFAULT_INITIAL_RTT);
let now = NoopClock.get_time();
let rtt_sample = Duration::from_millis(500);
rtt_estimator.update_rtt(
Duration::from_millis(10),
rtt_sample,
now,
true,
PacketNumberSpace::Initial,
);
let prev_smoothed_rtt = rtt_estimator.smoothed_rtt;
let rtt_sample = Duration::from_millis(1000);
rtt_estimator.update_rtt(
Duration::from_millis(100),
rtt_sample,
now,
true,
PacketNumberSpace::Initial,
);
assert_eq!(
rtt_estimator.smoothed_rtt,
7 * prev_smoothed_rtt / 8 + rtt_sample / 8
);
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-7.6.1
//= type=test
//# The persistent congestion duration is computed as follows:
//#
//# (smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay) *
//# kPersistentCongestionThreshold
#[test]
fn persistent_congestion_duration() {
let max_ack_delay = Duration::from_millis(10);
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(max_ack_delay, DEFAULT_INITIAL_RTT);
rtt_estimator.smoothed_rtt = Duration::from_millis(100);
rtt_estimator.rttvar = Duration::from_millis(50);
// persistent congestion period =
// (smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay) * kPersistentCongestionThreshold
// = (100 + max(4*50, 1) + 10) * 3 = 930
assert_eq!(
Duration::from_millis(930),
rtt_estimator.persistent_congestion_threshold()
);
rtt_estimator.rttvar = Duration::from_millis(0);
//= https://www.rfc-editor.org/rfc/rfc9002#section-7.6.1
//= type=test
//# The RECOMMENDED value for kPersistentCongestionThreshold is 3, which
//# results in behavior that is approximately equivalent to a TCP sender
//# declaring an RTO after two TLPs.
// persistent congestion period =
// (smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay) * kPersistentCongestionThreshold
// = (100 + max(0, 1) + 10) * 3 = 333
assert_eq!(
Duration::from_millis(333),
rtt_estimator.persistent_congestion_threshold()
);
}
#[test]
fn set_min_rtt_to_latest_sample_after_persistent_congestion() {
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(10), DEFAULT_INITIAL_RTT);
let now = NoopClock.get_time();
let mut rtt_sample = Duration::from_millis(500);
rtt_estimator.update_rtt(
Duration::from_millis(10),
rtt_sample,
now,
true,
PacketNumberSpace::Initial,
);
assert_eq!(rtt_estimator.min_rtt(), rtt_sample);
rtt_sample = Duration::from_millis(200);
rtt_estimator.on_persistent_congestion();
rtt_estimator.update_rtt(
Duration::from_millis(10),
rtt_sample,
now,
true,
PacketNumberSpace::Initial,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-5.2
//= type=test
//# Endpoints SHOULD set the min_rtt to the newest RTT sample after
//# persistent congestion is established.
assert_eq!(rtt_estimator.min_rtt(), rtt_sample);
assert_eq!(rtt_estimator.smoothed_rtt(), rtt_sample);
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.2.1
//= type=test
//# The PTO period MUST be at least kGranularity, to avoid the timer
//# expiring immediately.
#[test]
fn pto_must_be_at_least_k_granularity() {
let space = PacketNumberSpace::Handshake;
let now = NoopClock.get_time();
let mut rtt_estimator = RttEstimator::new(DEFAULT_INITIAL_RTT);
// Update RTT with the smallest possible sample
rtt_estimator.update_rtt(
Duration::from_millis(0),
Duration::from_nanos(1),
now,
true,
space,
);
let pto_period = rtt_estimator.pto_period(INITIAL_PTO_BACKOFF, space);
assert!(pto_period >= K_GRANULARITY);
// pto_period should have microsecond precision
assert_eq!(pto_period, Duration::from_micros(1001))
}
#[test]
#[cfg_attr(kani, kani::proof, kani::unwind(3), kani::solver(cadical))]
#[cfg_attr(miri, ignore)] // This test is too expensive for miri to complete in a reasonable amount of time
fn weighted_average_test() {
bolero::check!()
.with_type::<(u32, u32)>()
.for_each(|(a, b)| {
let a = Duration::from_nanos(*a as _);
let b = Duration::from_nanos(*b as _);
let weight = 8;
// perform the unoptimized version
let expected = ((weight - 1) * a) / weight + b / weight;
let actual = super::weighted_average(a, b, weight as _);
// assert that the unoptimized result matches the optimized to the nearest `weight` nanos
assert!(
super::abs_difference(expected.as_nanos(), actual.as_nanos()) as u32 <= weight,
"expected: {:?}; actual: {:?}",
expected,
actual
);
})
}
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//= type=test
//# The RECOMMENDED time threshold (kTimeThreshold), expressed as an
//# RTT multiplier, is 9/8.
#[test]
fn time_threshold_multiplier_equals_nine_eighths() {
let mut rtt_estimator =
RttEstimator::new_with_max_ack_delay(Duration::from_millis(10), DEFAULT_INITIAL_RTT);
rtt_estimator.update_rtt(
Duration::from_millis(10),
Duration::from_secs(1),
NoopClock.get_time(),
true,
PacketNumberSpace::Initial,
);
assert_eq!(
Duration::from_millis(1125), // 9/8 seconds = 1.125 seconds
rtt_estimator.loss_time_threshold()
);
}
#[test]
fn timer_granularity() {
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//= type=test
//# The RECOMMENDED value of the
//# timer granularity (kGranularity) is 1 millisecond.
assert_eq!(Duration::from_millis(1), K_GRANULARITY);
let mut rtt_estimator = RttEstimator::default();
rtt_estimator.update_rtt(
Duration::from_millis(0),
Duration::from_nanos(1),
NoopClock.get_time(),
true,
PacketNumberSpace::Initial,
);
//= https://www.rfc-editor.org/rfc/rfc9002#section-6.1.2
//= type=test
//# To avoid declaring
//# packets as lost too early, this time threshold MUST be set to at
//# least the local timer granularity, as indicated by the kGranularity
//# constant.
assert!(rtt_estimator.loss_time_threshold() >= K_GRANULARITY);
}
}