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diff --git a/third_party/libwebrtc/modules/congestion_controller/goog_cc/loss_based_bwe_v2.h b/third_party/libwebrtc/modules/congestion_controller/goog_cc/loss_based_bwe_v2.h
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+/*
+ *  Copyright 2021 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.
+ */
+
+#ifndef MODULES_CONGESTION_CONTROLLER_GOOG_CC_LOSS_BASED_BWE_V2_H_
+#define MODULES_CONGESTION_CONTROLLER_GOOG_CC_LOSS_BASED_BWE_V2_H_
+
+#include <vector>
+
+#include "absl/types/optional.h"
+#include "api/array_view.h"
+#include "api/field_trials_view.h"
+#include "api/transport/network_types.h"
+#include "api/units/data_rate.h"
+#include "api/units/data_size.h"
+#include "api/units/time_delta.h"
+#include "api/units/timestamp.h"
+
+namespace webrtc {
+
+// State of the loss based estimate, which can be either increasing/decreasing
+// when network is loss limited, or equal to the delay based estimate.
+enum class LossBasedState {
+  kIncreasing = 0,
+  // TODO(bugs.webrtc.org/12707): Remove one of the increasing states once we
+  // have decided if padding is usefull for ramping up when BWE is loss
+  // limited.
+  kIncreaseUsingPadding = 1,
+  kDecreasing = 2,
+  kDelayBasedEstimate = 3
+};
+
+class LossBasedBweV2 {
+ public:
+  struct Result {
+    ~Result() = default;
+    DataRate bandwidth_estimate = DataRate::Zero();
+    // State is used by goog_cc, which later sends probe requests to probe
+    // controller if state is kIncreasing.
+    LossBasedState state = LossBasedState::kDelayBasedEstimate;
+  };
+  // Creates a disabled `LossBasedBweV2` if the
+  // `key_value_config` is not valid.
+  explicit LossBasedBweV2(const FieldTrialsView* key_value_config);
+
+  LossBasedBweV2(const LossBasedBweV2&) = delete;
+  LossBasedBweV2& operator=(const LossBasedBweV2&) = delete;
+
+  ~LossBasedBweV2() = default;
+
+  bool IsEnabled() const;
+  // Returns true iff a BWE can be calculated, i.e., the estimator has been
+  // initialized with a BWE and then has received enough `PacketResult`s.
+  bool IsReady() const;
+
+  // Returns true if loss based BWE is ready to be used in the start phase.
+  bool ReadyToUseInStartPhase() const;
+
+  // Returns `DataRate::PlusInfinity` if no BWE can be calculated.
+  Result GetLossBasedResult() const;
+
+  void SetAcknowledgedBitrate(DataRate acknowledged_bitrate);
+  void SetMinMaxBitrate(DataRate min_bitrate, DataRate max_bitrate);
+  void UpdateBandwidthEstimate(
+      rtc::ArrayView<const PacketResult> packet_results,
+      DataRate delay_based_estimate,
+      bool in_alr);
+
+  // For unit testing only.
+  void SetBandwidthEstimate(DataRate bandwidth_estimate);
+
+ private:
+  struct ChannelParameters {
+    double inherent_loss = 0.0;
+    DataRate loss_limited_bandwidth = DataRate::MinusInfinity();
+  };
+
+  struct Config {
+    double bandwidth_rampup_upper_bound_factor = 0.0;
+    double rampup_acceleration_max_factor = 0.0;
+    TimeDelta rampup_acceleration_maxout_time = TimeDelta::Zero();
+    std::vector<double> candidate_factors;
+    double higher_bandwidth_bias_factor = 0.0;
+    double higher_log_bandwidth_bias_factor = 0.0;
+    double inherent_loss_lower_bound = 0.0;
+    double loss_threshold_of_high_bandwidth_preference = 0.0;
+    double bandwidth_preference_smoothing_factor = 0.0;
+    DataRate inherent_loss_upper_bound_bandwidth_balance =
+        DataRate::MinusInfinity();
+    double inherent_loss_upper_bound_offset = 0.0;
+    double initial_inherent_loss_estimate = 0.0;
+    int newton_iterations = 0;
+    double newton_step_size = 0.0;
+    bool append_acknowledged_rate_candidate = true;
+    bool append_delay_based_estimate_candidate = false;
+    bool append_upper_bound_candidate_in_alr = false;
+    TimeDelta observation_duration_lower_bound = TimeDelta::Zero();
+    int observation_window_size = 0;
+    double sending_rate_smoothing_factor = 0.0;
+    double instant_upper_bound_temporal_weight_factor = 0.0;
+    DataRate instant_upper_bound_bandwidth_balance = DataRate::MinusInfinity();
+    double instant_upper_bound_loss_offset = 0.0;
+    double temporal_weight_factor = 0.0;
+    double bandwidth_backoff_lower_bound_factor = 0.0;
+    double max_increase_factor = 0.0;
+    TimeDelta delayed_increase_window = TimeDelta::Zero();
+    bool not_increase_if_inherent_loss_less_than_average_loss = false;
+    double high_loss_rate_threshold = 1.0;
+    DataRate bandwidth_cap_at_high_loss_rate = DataRate::MinusInfinity();
+    double slope_of_bwe_high_loss_func = 1000.0;
+    bool not_use_acked_rate_in_alr = false;
+    bool use_in_start_phase = false;
+    int min_num_observations = 0;
+    double lower_bound_by_acked_rate_factor = 0.0;
+    double hold_duration_factor = 0.0;
+    bool use_byte_loss_rate = false;
+    TimeDelta padding_duration = TimeDelta::Zero();
+  };
+
+  struct Derivatives {
+    double first = 0.0;
+    double second = 0.0;
+  };
+
+  struct Observation {
+    bool IsInitialized() const { return id != -1; }
+
+    int num_packets = 0;
+    int num_lost_packets = 0;
+    int num_received_packets = 0;
+    DataRate sending_rate = DataRate::MinusInfinity();
+    DataSize size = DataSize::Zero();
+    DataSize lost_size = DataSize::Zero();
+    int id = -1;
+  };
+
+  struct PartialObservation {
+    int num_packets = 0;
+    int num_lost_packets = 0;
+    DataSize size = DataSize::Zero();
+    DataSize lost_size = DataSize::Zero();
+  };
+
+  struct PaddingInfo {
+    DataRate padding_rate = DataRate::MinusInfinity();
+    Timestamp padding_timestamp = Timestamp::MinusInfinity();
+  };
+
+  static absl::optional<Config> CreateConfig(
+      const FieldTrialsView* key_value_config);
+  bool IsConfigValid() const;
+
+  // Returns `0.0` if not enough loss statistics have been received.
+  double GetAverageReportedLossRatio() const;
+  double GetAverageReportedPacketLossRatio() const;
+  double GetAverageReportedByteLossRatio() const;
+  std::vector<ChannelParameters> GetCandidates(bool in_alr) const;
+  DataRate GetCandidateBandwidthUpperBound() const;
+  Derivatives GetDerivatives(const ChannelParameters& channel_parameters) const;
+  double GetFeasibleInherentLoss(
+      const ChannelParameters& channel_parameters) const;
+  double GetInherentLossUpperBound(DataRate bandwidth) const;
+  double AdjustBiasFactor(double loss_rate, double bias_factor) const;
+  double GetHighBandwidthBias(DataRate bandwidth) const;
+  double GetObjective(const ChannelParameters& channel_parameters) const;
+  DataRate GetSendingRate(DataRate instantaneous_sending_rate) const;
+  DataRate GetInstantUpperBound() const;
+  void CalculateInstantUpperBound();
+  DataRate GetInstantLowerBound() const;
+  void CalculateInstantLowerBound();
+
+  void CalculateTemporalWeights();
+  void NewtonsMethodUpdate(ChannelParameters& channel_parameters) const;
+
+  // Returns false if no observation was created.
+  bool PushBackObservation(rtc::ArrayView<const PacketResult> packet_results);
+  void UpdateResult();
+  bool IsEstimateIncreasingWhenLossLimited(DataRate old_estimate,
+                                           DataRate new_estimate);
+  bool IsInLossLimitedState() const;
+  bool CanKeepIncreasingState(DataRate estimate) const;
+
+  absl::optional<DataRate> acknowledged_bitrate_;
+  absl::optional<Config> config_;
+  ChannelParameters current_best_estimate_;
+  int num_observations_ = 0;
+  std::vector<Observation> observations_;
+  PartialObservation partial_observation_;
+  Timestamp last_send_time_most_recent_observation_ = Timestamp::PlusInfinity();
+  Timestamp last_time_estimate_reduced_ = Timestamp::MinusInfinity();
+  absl::optional<DataRate> cached_instant_upper_bound_;
+  absl::optional<DataRate> cached_instant_lower_bound_;
+  std::vector<double> instant_upper_bound_temporal_weights_;
+  std::vector<double> temporal_weights_;
+  Timestamp recovering_after_loss_timestamp_ = Timestamp::MinusInfinity();
+  DataRate bandwidth_limit_in_current_window_ = DataRate::PlusInfinity();
+  DataRate min_bitrate_ = DataRate::KilobitsPerSec(1);
+  DataRate max_bitrate_ = DataRate::PlusInfinity();
+  DataRate delay_based_estimate_ = DataRate::PlusInfinity();
+  LossBasedBweV2::Result loss_based_result_ = LossBasedBweV2::Result();
+  Timestamp last_hold_timestamp_ = Timestamp::MinusInfinity();
+  TimeDelta hold_duration_ = TimeDelta::Zero();
+  PaddingInfo last_padding_info_ = PaddingInfo();
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_CONGESTION_CONTROLLER_GOOG_CC_LOSS_BASED_BWE_V2_H_