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This patch estimates the connection RTT using EventBasedExponentialMovingAverage. The half time is set to 500 but can be modified using field trials. This new metric is currently unused, but will be used for exploration of of whether it can be used instead of the existing metric. Bug: webrtc:11140 Change-Id: I9db93e9b9eb932e3cd18935cd4ce0d90fc1cb293 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/161000 Commit-Queue: Jonas Oreland <jonaso@webrtc.org> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29944}
82 lines
2.7 KiB
C++
82 lines
2.7 KiB
C++
/*
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* Copyright 2019 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "rtc_base/numerics/event_based_exponential_moving_average.h"
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#include <cmath>
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#include "rtc_base/checks.h"
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namespace {
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// For a normal distributed value, the 95% double sided confidence interval is
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// is 1.96 * stddev.
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constexpr double ninetyfive_percent_confidence = 1.96;
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} // namespace
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namespace rtc {
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// |half_time| specifies how much weight will be given to old samples,
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// a sample gets exponentially less weight so that it's 50%
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// after |half_time| time units has passed.
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EventBasedExponentialMovingAverage::EventBasedExponentialMovingAverage(
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int half_time) {
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SetHalfTime(half_time);
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}
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void EventBasedExponentialMovingAverage::SetHalfTime(int half_time) {
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tau_ = static_cast<double>(half_time) / log(2);
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Reset();
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}
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void EventBasedExponentialMovingAverage::Reset() {
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value_ = std::nan("uninit");
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sample_variance_ = std::numeric_limits<double>::infinity();
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estimator_variance_ = 1;
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last_observation_timestamp_.reset();
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}
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void EventBasedExponentialMovingAverage::AddSample(int64_t now, int sample) {
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if (!last_observation_timestamp_.has_value()) {
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value_ = sample;
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} else {
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// TODO(webrtc:11140): This should really be > (e.g not >=)
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// but some pesky tests run with simulated clock and let
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// samples arrive simultaneously!
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RTC_DCHECK(now >= *last_observation_timestamp_);
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// Variance gets computed after second sample.
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int64_t age = now - *last_observation_timestamp_;
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double e = exp(-age / tau_);
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double alpha = e / (1 + e);
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double one_minus_alpha = 1 - alpha;
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double sample_diff = sample - value_;
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value_ = one_minus_alpha * value_ + alpha * sample;
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estimator_variance_ =
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(one_minus_alpha * one_minus_alpha) * estimator_variance_ +
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(alpha * alpha);
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if (sample_variance_ == std::numeric_limits<double>::infinity()) {
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// First variance.
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sample_variance_ = sample_diff * sample_diff;
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} else {
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double new_variance = one_minus_alpha * sample_variance_ +
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alpha * sample_diff * sample_diff;
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sample_variance_ = new_variance;
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}
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}
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last_observation_timestamp_ = now;
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}
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double EventBasedExponentialMovingAverage::GetConfidenceInterval() const {
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return ninetyfive_percent_confidence *
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sqrt(sample_variance_ * estimator_variance_);
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}
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} // namespace rtc
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