Make the BWE threshold adaptive.

webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc

 /*
  *  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 int64_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),
+      beta_(0.85f),
       rtt_(kDefaultRttMs),
-      time_of_last_log_(-1) {}
+      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 {
@@ skipping 38 matching lines @@
   if (now_ms - time_of_last_log_ > kLogIntervalMs) {
     time_of_last_log_ = now_ms;
   }
   return current_bitrate_bps_;
 }
 
 void AimdRateControl::SetRtt(int64_t rtt) {
   rtt_ = rtt;
 }
 
-RateControlRegion AimdRateControl::Update(const RateControlInput* input,
-                                          int64_t now_ms) {
+void 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) {
   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);
+    case kRcHold:
       break;
-    }
-    case kRcIncrease: {
-      if (avg_max_bitrate_kbps_ >= 0) {
-        if (incoming_bitrate_kbps > avg_max_bitrate_kbps_ +
+
+    case kRcIncrease:
+      if (avg_max_bitrate_kbps_ >= 0 &&
+          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);
-        }
+        ChangeRegion(kRcMaxUnknown);
+        avg_max_bitrate_kbps_ = -1.0;
       }

[mflodman, 2015/07/03 08:29:55]

Why was the kRcAboveMax removed?

[Gaetano Carlucci, 2015/07/03 10:54:28]

kRcNearMax, kRcAboveMax and kRcMaxUnknown were introduced as a simple strategy
to adapt the threshold based on a debatable statistic approach.
The plan is to remove all of them (kRcNearMax, kRcAboveMax and kRcMaxUnknown)
and improve the increase phase of the algorithm (possibly when we move all the
algorithm logic at the sender).
We have left for now only kRcNearMax and kRcMaxUnknown just to switch between
multiplicative/additive increase in order to tune the algorithm speed in
increase phase.

[stefan-webrtc, 2015/07/03 13:45:10]

We decided to simplify back-off and have the back-off factor be constant (0.85)
to improve fairness. We may want to try to improve it later in a more controlled
way, to ensure we still have good fairness and low delay.

       if (rate_control_region_ == kRcNearMax) {
         // Approximate the over-use estimator delay to 100 ms.
         const int64_t response_time = rtt_ + 100;
         uint32_t additive_increase_bps = AdditiveRateIncrease(
             now_ms, time_last_bitrate_change_, response_time);
         current_bitrate_bps += additive_increase_bps;
 
       } else {
         uint32_t multiplicative_increase_bps = MultiplicativeRateIncrease(
             now_ms, time_last_bitrate_change_, current_bitrate_bps);
         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: {
+
+    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) &&
+  if ((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, int64_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);
+    beta = 0.5 *
+           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) {
@@ skipping 37 matching lines @@
     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