modules/remote_bitrate_estimator/aimd_rate_control.cc - src/webrtc - Git at Google

 /*
  *  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 "webrtc/modules/remote_bitrate_estimator/aimd_rate_control.h"

 #include <algorithm>
 #include <cassert>
 #include <cmath>

 #include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_logging.h"

 namespace webrtc {

 static const uint32_t kDefaultRttMs = 200;
 static const int64_t kLogIntervalMs = 1000;
 static const double kWithinIncomingBitrateHysteresis = 1.05;

 AimdRateControl::AimdRateControl(uint32_t min_bitrate_bps)
     : min_configured_bitrate_bps_(min_bitrate_bps),
       max_configured_bitrate_bps_(30000000),
       current_bitrate_bps_(max_configured_bitrate_bps_),
       max_hold_rate_bps_(0),
       avg_max_bitrate_kbps_(-1.0f),
       var_max_bitrate_kbps_(0.4f),
       rate_control_state_(kRcHold),
       came_from_state_(kRcDecrease),
       rate_control_region_(kRcMaxUnknown),
       time_last_bitrate_change_(-1),
       current_input_(kBwNormal, 0, 1.0),
       updated_(false),
       time_first_incoming_estimate_(-1),
       bitrate_is_initialized_(false),
       beta_(0.9f),
       rtt_(kDefaultRttMs),
       time_of_last_log_(-1) {}

 RateControlType AimdRateControl::GetControlType() const {
   return kAimdControl;
 }

 uint32_t AimdRateControl::GetMinBitrate() const {
   return min_configured_bitrate_bps_;
 }

 bool AimdRateControl::ValidEstimate() const {
   return bitrate_is_initialized_;
 }

 int64_t AimdRateControl::GetFeedbackInterval() const {
   // Estimate how often we can send RTCP if we allocate up to 5% of bandwidth
   // to feedback.
   static const int kRtcpSize = 80;
   int64_t interval = static_cast<int64_t>(
       kRtcpSize * 8.0 * 1000.0 / (0.05 * current_bitrate_bps_) + 0.5);
   const int64_t kMinFeedbackIntervalMs = 200;
   return std::min(std::max(interval, kMinFeedbackIntervalMs),
                   kMaxFeedbackIntervalMs);
 }

 bool AimdRateControl::TimeToReduceFurther(int64_t time_now,
                                           uint32_t incoming_bitrate_bps) const {
   const int bitrate_reduction_interval = std::max(std::min(rtt_, 200u), 10u);
   if (time_now - time_last_bitrate_change_ >= bitrate_reduction_interval) {
     return true;
   }
   if (ValidEstimate()) {
     const int threshold = static_cast<int>(kWithinIncomingBitrateHysteresis *
                                            incoming_bitrate_bps);
     const int bitrate_difference = LatestEstimate() - incoming_bitrate_bps;
     return bitrate_difference > threshold;
   }
   return false;
 }

 uint32_t AimdRateControl::LatestEstimate() const {
   return current_bitrate_bps_;
 }

 uint32_t AimdRateControl::UpdateBandwidthEstimate(int64_t now_ms) {
   current_bitrate_bps_ = ChangeBitrate(current_bitrate_bps_,
                                        current_input_._incomingBitRate,
                                        now_ms);
   if (now_ms - time_of_last_log_ > kLogIntervalMs) {
     time_of_last_log_ = now_ms;
   }
   return current_bitrate_bps_;
 }

 void AimdRateControl::SetRtt(uint32_t rtt) {
   rtt_ = rtt;
 }

 RateControlRegion AimdRateControl::Update(const RateControlInput* input,
                                           int64_t now_ms) {
   assert(input);

   // Set the initial bit rate value to what we're receiving the first half
   // second.
   if (!bitrate_is_initialized_) {
     if (time_first_incoming_estimate_ < 0) {
       if (input->_incomingBitRate > 0) {
         time_first_incoming_estimate_ = now_ms;
       }
     } else if (now_ms - time_first_incoming_estimate_ > 500 &&
                input->_incomingBitRate > 0) {
       current_bitrate_bps_ = input->_incomingBitRate;
       bitrate_is_initialized_ = true;
     }
   }

   if (updated_ && current_input_._bwState == kBwOverusing) {
     // Only update delay factor and incoming bit rate. We always want to react
     // on an over-use.
     current_input_._noiseVar = input->_noiseVar;
     current_input_._incomingBitRate = input->_incomingBitRate;
   } else {
     updated_ = true;
     current_input_ = *input;
   }
   return rate_control_region_;
 }

 void AimdRateControl::SetEstimate(int bitrate_bps, int64_t now_ms) {
   updated_ = true;
   bitrate_is_initialized_ = true;
   current_bitrate_bps_ = ChangeBitrate(bitrate_bps, bitrate_bps, now_ms);
 }

 uint32_t AimdRateControl::ChangeBitrate(uint32_t current_bitrate_bps,
                                         uint32_t incoming_bitrate_bps,
                                         int64_t now_ms) {
   BWE_TEST_LOGGING_PLOT("estimated_incoming#1", -1,
                         incoming_bitrate_bps / 1000);
   if (!updated_) {
     return current_bitrate_bps_;
   }
   updated_ = false;
   ChangeState(current_input_, now_ms);
   // Calculated here because it's used in multiple places.
   const float incoming_bitrate_kbps = incoming_bitrate_bps / 1000.0f;
   // Calculate the max bit rate std dev given the normalized
   // variance and the current incoming bit rate.
   const float std_max_bit_rate = sqrt(var_max_bitrate_kbps_ *
                                       avg_max_bitrate_kbps_);
   bool fast_recovery_after_hold = false;
   switch (rate_control_state_) {
     case kRcHold: {
       max_hold_rate_bps_ = std::max(max_hold_rate_bps_, incoming_bitrate_bps);
       break;
     }
     case kRcIncrease: {
       if (avg_max_bitrate_kbps_ >= 0) {
         if (incoming_bitrate_kbps > avg_max_bitrate_kbps_ +
             3 * std_max_bit_rate) {
           ChangeRegion(kRcMaxUnknown);
           avg_max_bitrate_kbps_ = -1.0;
         } else if (incoming_bitrate_kbps > avg_max_bitrate_kbps_ +
             2.5 * std_max_bit_rate) {
           ChangeRegion(kRcAboveMax);
         }
       }
       if (rate_control_region_ == kRcNearMax) {
         // Approximate the over-use estimator delay to 100 ms.
         const uint32_t response_time = rtt_ + 100;
         uint32_t additive_increase_bps = AdditiveRateIncrease(
             now_ms, time_last_bitrate_change_, response_time);
         BWE_TEST_LOGGING_PLOT("add_increase#1", -1,
                               additive_increase_bps / 1000);
         current_bitrate_bps += additive_increase_bps;

       } else {
         uint32_t multiplicative_increase_bps = MultiplicativeRateIncrease(
             now_ms, time_last_bitrate_change_, current_bitrate_bps);
         BWE_TEST_LOGGING_PLOT("mult_increase#1", -1,
                               multiplicative_increase_bps / 1000);
         current_bitrate_bps += multiplicative_increase_bps;
       }

       if (max_hold_rate_bps_ > 0 &&
           beta_ * max_hold_rate_bps_ > current_bitrate_bps) {
         current_bitrate_bps = static_cast<uint32_t>(beta_ * max_hold_rate_bps_);
         avg_max_bitrate_kbps_ = beta_ * max_hold_rate_bps_ / 1000.0f;
         ChangeRegion(kRcNearMax);
         fast_recovery_after_hold = true;
       }
       max_hold_rate_bps_ = 0;
       time_last_bitrate_change_ = now_ms;
       break;
     }
     case kRcDecrease: {
       if (incoming_bitrate_bps < min_configured_bitrate_bps_) {
         current_bitrate_bps = min_configured_bitrate_bps_;
       } else {
         // Set bit rate to something slightly lower than max
         // to get rid of any self-induced delay.
         current_bitrate_bps = static_cast<uint32_t>(beta_ *
                                                     incoming_bitrate_bps + 0.5);
         if (current_bitrate_bps > current_bitrate_bps_) {
           // Avoid increasing the rate when over-using.
           if (rate_control_region_ != kRcMaxUnknown) {
             current_bitrate_bps = static_cast<uint32_t>(
                 beta_ * avg_max_bitrate_kbps_ * 1000 + 0.5f);
           }
           current_bitrate_bps = std::min(current_bitrate_bps,
                                          current_bitrate_bps_);
         }
         ChangeRegion(kRcNearMax);

         if (incoming_bitrate_kbps < avg_max_bitrate_kbps_ -
             3 * std_max_bit_rate) {
           avg_max_bitrate_kbps_ = -1.0f;
         }

         UpdateMaxBitRateEstimate(incoming_bitrate_kbps);
       }
       // Stay on hold until the pipes are cleared.
       ChangeState(kRcHold);
       time_last_bitrate_change_ = now_ms;
       break;
     }
     default:
       assert(false);
   }
   if (!fast_recovery_after_hold && (incoming_bitrate_bps > 100000 ||
       current_bitrate_bps > 150000) &&
       current_bitrate_bps > 1.5 * incoming_bitrate_bps) {
     // Allow changing the bit rate if we are operating at very low rates
     // Don't change the bit rate if the send side is too far off
     current_bitrate_bps = current_bitrate_bps_;
     time_last_bitrate_change_ = now_ms;
   }
   return current_bitrate_bps;
 }

 uint32_t AimdRateControl::MultiplicativeRateIncrease(
     int64_t now_ms, int64_t last_ms, uint32_t current_bitrate_bps) const {
   double alpha = 1.08;
   if (last_ms > -1) {
     int time_since_last_update_ms = std::min(static_cast<int>(now_ms - last_ms),
                                              1000);
     alpha = pow(alpha,  time_since_last_update_ms / 1000.0);
   }
   uint32_t multiplicative_increase_bps = std::max(
       current_bitrate_bps * (alpha - 1.0), 1000.0);
   return multiplicative_increase_bps;
 }

 uint32_t AimdRateControl::AdditiveRateIncrease(
     int64_t now_ms, int64_t last_ms, uint32_t response_time_ms) const {
   assert(response_time_ms > 0);
   double beta = 0.0;
   if (last_ms > 0) {
     beta = std::min((now_ms - last_ms) /
                     static_cast<double>(response_time_ms), 1.0);
   }
   double bits_per_frame = static_cast<double>(current_bitrate_bps_) / 30.0;
   double packets_per_frame = std::ceil(bits_per_frame / (8.0 * 1200.0));
   double avg_packet_size_bits = bits_per_frame / packets_per_frame;
   uint32_t additive_increase_bps = std::max(
       1000.0, beta * avg_packet_size_bits);
   return additive_increase_bps;
 }

 void AimdRateControl::UpdateMaxBitRateEstimate(float incoming_bitrate_kbps) {
   const float alpha = 0.05f;
   if (avg_max_bitrate_kbps_ == -1.0f) {
     avg_max_bitrate_kbps_ = incoming_bitrate_kbps;
   } else {
     avg_max_bitrate_kbps_ = (1 - alpha) * avg_max_bitrate_kbps_ +
         alpha * incoming_bitrate_kbps;
   }
   // Estimate the max bit rate variance and normalize the variance
   // with the average max bit rate.
   const float norm = std::max(avg_max_bitrate_kbps_, 1.0f);
   var_max_bitrate_kbps_ = (1 - alpha) * var_max_bitrate_kbps_ +
       alpha * (avg_max_bitrate_kbps_ - incoming_bitrate_kbps) *
           (avg_max_bitrate_kbps_ - incoming_bitrate_kbps) / norm;
   // 0.4 ~= 14 kbit/s at 500 kbit/s
   if (var_max_bitrate_kbps_ < 0.4f) {
     var_max_bitrate_kbps_ = 0.4f;
   }
   // 2.5f ~= 35 kbit/s at 500 kbit/s
   if (var_max_bitrate_kbps_ > 2.5f) {
     var_max_bitrate_kbps_ = 2.5f;
   }
 }

 void AimdRateControl::ChangeState(const RateControlInput& input,
                                   int64_t now_ms) {
   switch (current_input_._bwState) {
     case kBwNormal:
       if (rate_control_state_ == kRcHold) {
         time_last_bitrate_change_ = now_ms;
         ChangeState(kRcIncrease);
       }
       break;
     case kBwOverusing:
       if (rate_control_state_ != kRcDecrease) {
         ChangeState(kRcDecrease);
       }
       break;
     case kBwUnderusing:
       ChangeState(kRcHold);
       break;
     default:
       assert(false);
   }
 }

 void AimdRateControl::ChangeRegion(RateControlRegion region) {
   rate_control_region_ = region;
   switch (rate_control_region_) {
     case kRcAboveMax:
     case kRcMaxUnknown:
       beta_ = 0.9f;
       break;
     case kRcNearMax:
       beta_ = 0.95f;
       break;
     default:
       assert(false);
   }
 }

 void AimdRateControl::ChangeState(RateControlState new_state) {
   came_from_state_ = rate_control_state_;
   rate_control_state_ = new_state;
 }
 }  // namespace webrtc
	/*
	* 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 "webrtc/modules/remote_bitrate_estimator/aimd_rate_control.h"

	#include <algorithm>
	#include <cassert>
	#include <cmath>

	#include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_logging.h"

	namespace webrtc {

	static const uint32_t kDefaultRttMs = 200;
	static const int64_t kLogIntervalMs = 1000;
	static const double kWithinIncomingBitrateHysteresis = 1.05;

	AimdRateControl::AimdRateControl(uint32_t min_bitrate_bps)
	: min_configured_bitrate_bps_(min_bitrate_bps),
	max_configured_bitrate_bps_(30000000),
	current_bitrate_bps_(max_configured_bitrate_bps_),
	max_hold_rate_bps_(0),
	avg_max_bitrate_kbps_(-1.0f),
	var_max_bitrate_kbps_(0.4f),
	rate_control_state_(kRcHold),
	came_from_state_(kRcDecrease),
	rate_control_region_(kRcMaxUnknown),
	time_last_bitrate_change_(-1),
	current_input_(kBwNormal, 0, 1.0),
	updated_(false),
	time_first_incoming_estimate_(-1),
	bitrate_is_initialized_(false),
	beta_(0.9f),
	rtt_(kDefaultRttMs),
	time_of_last_log_(-1) {}

	RateControlType AimdRateControl::GetControlType() const {
	return kAimdControl;
	}

	uint32_t AimdRateControl::GetMinBitrate() const {
	return min_configured_bitrate_bps_;
	}

	bool AimdRateControl::ValidEstimate() const {
	return bitrate_is_initialized_;
	}

	int64_t AimdRateControl::GetFeedbackInterval() const {
	// Estimate how often we can send RTCP if we allocate up to 5% of bandwidth
	// to feedback.
	static const int kRtcpSize = 80;
	int64_t interval = static_cast<int64_t>(
	kRtcpSize * 8.0 * 1000.0 / (0.05 * current_bitrate_bps_) + 0.5);
	const int64_t kMinFeedbackIntervalMs = 200;
	return std::min(std::max(interval, kMinFeedbackIntervalMs),
	kMaxFeedbackIntervalMs);
	}

	bool AimdRateControl::TimeToReduceFurther(int64_t time_now,
	uint32_t incoming_bitrate_bps) const {
	const int bitrate_reduction_interval = std::max(std::min(rtt_, 200u), 10u);
	if (time_now - time_last_bitrate_change_ >= bitrate_reduction_interval) {
	return true;
	}
	if (ValidEstimate()) {
	const int threshold = static_cast<int>(kWithinIncomingBitrateHysteresis *
	incoming_bitrate_bps);
	const int bitrate_difference = LatestEstimate() - incoming_bitrate_bps;
	return bitrate_difference > threshold;
	}
	return false;
	}

	uint32_t AimdRateControl::LatestEstimate() const {
	return current_bitrate_bps_;
	}

	uint32_t AimdRateControl::UpdateBandwidthEstimate(int64_t now_ms) {
	current_bitrate_bps_ = ChangeBitrate(current_bitrate_bps_,
	current_input_._incomingBitRate,
	now_ms);
	if (now_ms - time_of_last_log_ > kLogIntervalMs) {
	time_of_last_log_ = now_ms;
	}
	return current_bitrate_bps_;
	}

	void AimdRateControl::SetRtt(uint32_t rtt) {
	rtt_ = rtt;
	}

	RateControlRegion AimdRateControl::Update(const RateControlInput* input,
	int64_t now_ms) {
	assert(input);

	// Set the initial bit rate value to what we're receiving the first half
	// second.
	if (!bitrate_is_initialized_) {
	if (time_first_incoming_estimate_ < 0) {
	if (input->_incomingBitRate > 0) {
	time_first_incoming_estimate_ = now_ms;
	}
	} else if (now_ms - time_first_incoming_estimate_ > 500 &&
	input->_incomingBitRate > 0) {
	current_bitrate_bps_ = input->_incomingBitRate;
	bitrate_is_initialized_ = true;
	}
	}

	if (updated_ && current_input_._bwState == kBwOverusing) {
	// Only update delay factor and incoming bit rate. We always want to react
	// on an over-use.
	current_input_._noiseVar = input->_noiseVar;
	current_input_._incomingBitRate = input->_incomingBitRate;
	} else {
	updated_ = true;
	current_input_ = *input;
	}
	return rate_control_region_;
	}

	void AimdRateControl::SetEstimate(int bitrate_bps, int64_t now_ms) {
	updated_ = true;
	bitrate_is_initialized_ = true;
	current_bitrate_bps_ = ChangeBitrate(bitrate_bps, bitrate_bps, now_ms);
	}

	uint32_t AimdRateControl::ChangeBitrate(uint32_t current_bitrate_bps,
	uint32_t incoming_bitrate_bps,
	int64_t now_ms) {
	BWE_TEST_LOGGING_PLOT("estimated_incoming#1", -1,
	incoming_bitrate_bps / 1000);
	if (!updated_) {
	return current_bitrate_bps_;
	}
	updated_ = false;
	ChangeState(current_input_, now_ms);
	// Calculated here because it's used in multiple places.
	const float incoming_bitrate_kbps = incoming_bitrate_bps / 1000.0f;
	// Calculate the max bit rate std dev given the normalized
	// variance and the current incoming bit rate.
	const float std_max_bit_rate = sqrt(var_max_bitrate_kbps_ *
	avg_max_bitrate_kbps_);
	bool fast_recovery_after_hold = false;
	switch (rate_control_state_) {
	case kRcHold: {
	max_hold_rate_bps_ = std::max(max_hold_rate_bps_, incoming_bitrate_bps);
	break;
	}
	case kRcIncrease: {
	if (avg_max_bitrate_kbps_ >= 0) {
	if (incoming_bitrate_kbps > avg_max_bitrate_kbps_ +
	3 * std_max_bit_rate) {
	ChangeRegion(kRcMaxUnknown);
	avg_max_bitrate_kbps_ = -1.0;
	} else if (incoming_bitrate_kbps > avg_max_bitrate_kbps_ +
	2.5 * std_max_bit_rate) {
	ChangeRegion(kRcAboveMax);
	}
	}
	if (rate_control_region_ == kRcNearMax) {
	// Approximate the over-use estimator delay to 100 ms.
	const uint32_t response_time = rtt_ + 100;
	uint32_t additive_increase_bps = AdditiveRateIncrease(
	now_ms, time_last_bitrate_change_, response_time);
	BWE_TEST_LOGGING_PLOT("add_increase#1", -1,
	additive_increase_bps / 1000);
	current_bitrate_bps += additive_increase_bps;

	} else {
	uint32_t multiplicative_increase_bps = MultiplicativeRateIncrease(
	now_ms, time_last_bitrate_change_, current_bitrate_bps);
	BWE_TEST_LOGGING_PLOT("mult_increase#1", -1,
	multiplicative_increase_bps / 1000);
	current_bitrate_bps += multiplicative_increase_bps;
	}

	if (max_hold_rate_bps_ > 0 &&
	beta_ * max_hold_rate_bps_ > current_bitrate_bps) {
	current_bitrate_bps = static_cast<uint32_t>(beta_ * max_hold_rate_bps_);
	avg_max_bitrate_kbps_ = beta_ * max_hold_rate_bps_ / 1000.0f;
	ChangeRegion(kRcNearMax);
	fast_recovery_after_hold = true;
	}
	max_hold_rate_bps_ = 0;
	time_last_bitrate_change_ = now_ms;
	break;
	}
	case kRcDecrease: {
	if (incoming_bitrate_bps < min_configured_bitrate_bps_) {
	current_bitrate_bps = min_configured_bitrate_bps_;
	} else {
	// Set bit rate to something slightly lower than max
	// to get rid of any self-induced delay.
	current_bitrate_bps = static_cast<uint32_t>(beta_ *
	incoming_bitrate_bps + 0.5);
	if (current_bitrate_bps > current_bitrate_bps_) {
	// Avoid increasing the rate when over-using.
	if (rate_control_region_ != kRcMaxUnknown) {
	current_bitrate_bps = static_cast<uint32_t>(
	beta_ * avg_max_bitrate_kbps_ * 1000 + 0.5f);
	}
	current_bitrate_bps = std::min(current_bitrate_bps,
	current_bitrate_bps_);
	}
	ChangeRegion(kRcNearMax);

	if (incoming_bitrate_kbps < avg_max_bitrate_kbps_ -
	3 * std_max_bit_rate) {
	avg_max_bitrate_kbps_ = -1.0f;
	}

	UpdateMaxBitRateEstimate(incoming_bitrate_kbps);
	}
	// Stay on hold until the pipes are cleared.
	ChangeState(kRcHold);
	time_last_bitrate_change_ = now_ms;
	break;
	}
	default:
	assert(false);
	}
	if (!fast_recovery_after_hold && (incoming_bitrate_bps > 100000 \|\|
	current_bitrate_bps > 150000) &&
	current_bitrate_bps > 1.5 * incoming_bitrate_bps) {
	// Allow changing the bit rate if we are operating at very low rates
	// Don't change the bit rate if the send side is too far off
	current_bitrate_bps = current_bitrate_bps_;
	time_last_bitrate_change_ = now_ms;
	}
	return current_bitrate_bps;
	}

	uint32_t AimdRateControl::MultiplicativeRateIncrease(
	int64_t now_ms, int64_t last_ms, uint32_t current_bitrate_bps) const {
	double alpha = 1.08;
	if (last_ms > -1) {
	int time_since_last_update_ms = std::min(static_cast<int>(now_ms - last_ms),
	1000);
	alpha = pow(alpha, time_since_last_update_ms / 1000.0);
	}
	uint32_t multiplicative_increase_bps = std::max(
	current_bitrate_bps * (alpha - 1.0), 1000.0);
	return multiplicative_increase_bps;
	}

	uint32_t AimdRateControl::AdditiveRateIncrease(
	int64_t now_ms, int64_t last_ms, uint32_t response_time_ms) const {
	assert(response_time_ms > 0);
	double beta = 0.0;
	if (last_ms > 0) {
	beta = std::min((now_ms - last_ms) /
	static_cast<double>(response_time_ms), 1.0);
	}
	double bits_per_frame = static_cast<double>(current_bitrate_bps_) / 30.0;
	double packets_per_frame = std::ceil(bits_per_frame / (8.0 * 1200.0));
	double avg_packet_size_bits = bits_per_frame / packets_per_frame;
	uint32_t additive_increase_bps = std::max(
	1000.0, beta * avg_packet_size_bits);
	return additive_increase_bps;
	}

	void AimdRateControl::UpdateMaxBitRateEstimate(float incoming_bitrate_kbps) {
	const float alpha = 0.05f;
	if (avg_max_bitrate_kbps_ == -1.0f) {
	avg_max_bitrate_kbps_ = incoming_bitrate_kbps;
	} else {
	avg_max_bitrate_kbps_ = (1 - alpha) * avg_max_bitrate_kbps_ +
	alpha * incoming_bitrate_kbps;
	}
	// Estimate the max bit rate variance and normalize the variance
	// with the average max bit rate.
	const float norm = std::max(avg_max_bitrate_kbps_, 1.0f);
	var_max_bitrate_kbps_ = (1 - alpha) * var_max_bitrate_kbps_ +
	alpha * (avg_max_bitrate_kbps_ - incoming_bitrate_kbps) *
	(avg_max_bitrate_kbps_ - incoming_bitrate_kbps) / norm;
	// 0.4 ~= 14 kbit/s at 500 kbit/s
	if (var_max_bitrate_kbps_ < 0.4f) {
	var_max_bitrate_kbps_ = 0.4f;
	}
	// 2.5f ~= 35 kbit/s at 500 kbit/s
	if (var_max_bitrate_kbps_ > 2.5f) {
	var_max_bitrate_kbps_ = 2.5f;
	}
	}

	void AimdRateControl::ChangeState(const RateControlInput& input,
	int64_t now_ms) {
	switch (current_input_._bwState) {
	case kBwNormal:
	if (rate_control_state_ == kRcHold) {
	time_last_bitrate_change_ = now_ms;
	ChangeState(kRcIncrease);
	}
	break;
	case kBwOverusing:
	if (rate_control_state_ != kRcDecrease) {
	ChangeState(kRcDecrease);
	}
	break;
	case kBwUnderusing:
	ChangeState(kRcHold);
	break;
	default:
	assert(false);
	}
	}

	void AimdRateControl::ChangeRegion(RateControlRegion region) {
	rate_control_region_ = region;
	switch (rate_control_region_) {
	case kRcAboveMax:
	case kRcMaxUnknown:
	beta_ = 0.9f;
	break;
	case kRcNearMax:
	beta_ = 0.95f;
	break;
	default:
	assert(false);
	}
	}

	void AimdRateControl::ChangeState(RateControlState new_state) {
	came_from_state_ = rate_control_state_;
	rate_control_state_ = new_state;
	}
	} // namespace webrtc