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* Copyright (c) 2014 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 <stdint.h>
#include "absl/types/optional.h"
#include "api/transport/network_types.h"
#include "api/transport/webrtc_key_value_config.h"
#include "api/units/data_rate.h"
#include "api/units/timestamp.h"
#include "modules/congestion_controller/goog_cc/link_capacity_estimator.h"
#include "modules/remote_bitrate_estimator/include/bwe_defines.h"
#include "rtc_base/experiments/field_trial_parser.h"
namespace webrtc {
// A rate control implementation based on additive increases of
// bitrate when no over-use is detected and multiplicative decreases when
// over-uses are detected. When we think the available bandwidth has changes or
// is unknown, we will switch to a "slow-start mode" where we increase
// multiplicatively.
class AimdRateControl {
explicit AimdRateControl(const WebRtcKeyValueConfig* key_value_config);
AimdRateControl(const WebRtcKeyValueConfig* key_value_config, bool send_side);
// Returns true if the target bitrate has been initialized. This happens
// either if it has been explicitly set via SetStartBitrate/SetEstimate, or if
// we have measured a throughput.
bool ValidEstimate() const;
void SetStartBitrate(DataRate start_bitrate);
void SetMinBitrate(DataRate min_bitrate);
TimeDelta GetFeedbackInterval() const;
// Returns true if the bitrate estimate hasn't been changed for more than
// an RTT, or if the estimated_throughput is less than half of the current
// estimate. Should be used to decide if we should reduce the rate further
// when over-using.
bool TimeToReduceFurther(Timestamp at_time,
DataRate estimated_throughput) const;
// As above. To be used if overusing before we have measured a throughput.
bool InitialTimeToReduceFurther(Timestamp at_time) const;
DataRate LatestEstimate() const;
void SetRtt(TimeDelta rtt);
DataRate Update(const RateControlInput* input, Timestamp at_time);
void SetInApplicationLimitedRegion(bool in_alr);
void SetEstimate(DataRate bitrate, Timestamp at_time);
void SetNetworkStateEstimate(
const absl::optional<NetworkStateEstimate>& estimate);
// Returns the increase rate when used bandwidth is near the link capacity.
double GetNearMaxIncreaseRateBpsPerSecond() const;
// Returns the expected time between overuse signals (assuming steady state).
TimeDelta GetExpectedBandwidthPeriod() const;
enum class RateControlState { kRcHold, kRcIncrease, kRcDecrease };
friend class GoogCcStatePrinter;
// Update the target bitrate based on, among other things, the current rate
// control state, the current target bitrate and the estimated throughput.
// When in the "increase" state the bitrate will be increased either
// additively or multiplicatively depending on the rate control region. When
// in the "decrease" state the bitrate will be decreased to slightly below the
// current throughput. When in the "hold" state the bitrate will be kept
// constant to allow built up queues to drain.
void ChangeBitrate(const RateControlInput& input, Timestamp at_time);
DataRate ClampBitrate(DataRate new_bitrate) const;
DataRate MultiplicativeRateIncrease(Timestamp at_time,
Timestamp last_ms,
DataRate current_bitrate) const;
DataRate AdditiveRateIncrease(Timestamp at_time, Timestamp last_time) const;
void UpdateChangePeriod(Timestamp at_time);
void ChangeState(const RateControlInput& input, Timestamp at_time);
DataRate min_configured_bitrate_;
DataRate max_configured_bitrate_;
DataRate current_bitrate_;
DataRate latest_estimated_throughput_;
LinkCapacityEstimator link_capacity_;
absl::optional<NetworkStateEstimate> network_estimate_;
RateControlState rate_control_state_;
Timestamp time_last_bitrate_change_;
Timestamp time_last_bitrate_decrease_;
Timestamp time_first_throughput_estimate_;
bool bitrate_is_initialized_;
double beta_;
bool in_alr_;
TimeDelta rtt_;
const bool send_side_;
const bool in_experiment_;
// Allow the delay based estimate to only increase as long as application
// limited region (alr) is not detected.
const bool no_bitrate_increase_in_alr_;
// Use estimated link capacity lower bound if it is higher than the
// acknowledged rate when backing off due to overuse.
const bool estimate_bounded_backoff_;
// Use estimated link capacity upper bound as upper limit for increasing
// bitrate over the acknowledged rate.
const bool estimate_bounded_increase_;
absl::optional<DataRate> last_decrease_;
FieldTrialOptional<TimeDelta> initial_backoff_interval_;
FieldTrialFlag link_capacity_fix_;
} // namespace webrtc