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/*
* Copyright 2018 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "modules/congestion_controller/goog_cc/link_capacity_estimator.h"
#include <algorithm>
#include <cmath>
#include "api/units/data_rate.h"
#include "rtc_base/numerics/safe_minmax.h"
namespace webrtc {
LinkCapacityEstimator::LinkCapacityEstimator() {}
DataRate LinkCapacityEstimator::UpperBound() const {
if (estimate_kbps_.has_value())
return DataRate::KilobitsPerSec(estimate_kbps_.value() +
3 * deviation_estimate_kbps());
return DataRate::Infinity();
}
DataRate LinkCapacityEstimator::LowerBound() const {
if (estimate_kbps_.has_value())
return DataRate::KilobitsPerSec(
std::max(0.0, estimate_kbps_.value() - 3 * deviation_estimate_kbps()));
return DataRate::Zero();
}
void LinkCapacityEstimator::Reset() {
estimate_kbps_.reset();
}
void LinkCapacityEstimator::OnOveruseDetected(DataRate acknowledged_rate) {
Update(acknowledged_rate, 0.05);
}
void LinkCapacityEstimator::OnProbeRate(DataRate probe_rate) {
Update(probe_rate, 0.5);
}
void LinkCapacityEstimator::Update(DataRate capacity_sample, double alpha) {
double sample_kbps = capacity_sample.kbps();
if (!estimate_kbps_.has_value()) {
estimate_kbps_ = sample_kbps;
} else {
estimate_kbps_ = (1 - alpha) * estimate_kbps_.value() + alpha * sample_kbps;
}
// Estimate the variance of the link capacity estimate and normalize the
// variance with the link capacity estimate.
const double norm = std::max(estimate_kbps_.value(), 1.0);
double error_kbps = estimate_kbps_.value() - sample_kbps;
deviation_kbps_ =
(1 - alpha) * deviation_kbps_ + alpha * error_kbps * error_kbps / norm;
// 0.4 ~= 14 kbit/s at 500 kbit/s
// 2.5f ~= 35 kbit/s at 500 kbit/s
deviation_kbps_ = rtc::SafeClamp(deviation_kbps_, 0.4f, 2.5f);
}
bool LinkCapacityEstimator::has_estimate() const {
return estimate_kbps_.has_value();
}
DataRate LinkCapacityEstimator::estimate() const {
return DataRate::KilobitsPerSec(*estimate_kbps_);
}
double LinkCapacityEstimator::deviation_estimate_kbps() const {
// Calculate the max bit rate std dev given the normalized
// variance and the current throughput bitrate. The standard deviation will
// only be used if estimate_kbps_ has a value.
return sqrt(deviation_kbps_ * estimate_kbps_.value());
}
} // namespace webrtc