Adds stable bandwidth estimate to GoogCC.

The intention is to provide a bandwidth estimate that only updates if
the actual available bandwidth is known to have changed. This will be
used in media streams to avoid changing the configuration (such as
frame size, audio frame length etc), just because the control target
rate changed.

Bug: webrtc:9718
Change-Id: I17ba5a2f9e5bd408a71f89c690d45541655a68e2
Reviewed-on: https://webrtc-review.googlesource.com/c/107726
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25772}

modules/bitrate_controller/send_side_bandwidth_estimation.cc

@@ -104,6 +104,48 @@ bool ReadBweLossExperimentParameters(float* low_loss_threshold,
 }
 }  // namespace
 
+LinkCapacityTracker::LinkCapacityTracker()
+    : tracking_rate("rate", TimeDelta::seconds(10)) {
+  ParseFieldTrial({&tracking_rate},
+                  field_trial::FindFullName("WebRTC-Bwe-LinkCapacity"));
+}
+
+LinkCapacityTracker::~LinkCapacityTracker() {}
+
+void LinkCapacityTracker::OnOveruse(DataRate acknowledged_rate,
+                                    Timestamp at_time) {
+  capacity_estimate_bps_ =
+      std::min(capacity_estimate_bps_, acknowledged_rate.bps<double>());
+  last_link_capacity_update_ = at_time;
+}
+
+void LinkCapacityTracker::OnStartingRate(DataRate start_rate) {
+  if (last_link_capacity_update_.IsInfinite())
+    capacity_estimate_bps_ = start_rate.bps<double>();
+}
+
+void LinkCapacityTracker::OnRateUpdate(DataRate acknowledged,
+                                       Timestamp at_time) {
+  if (acknowledged.bps() > capacity_estimate_bps_) {
+    TimeDelta delta = at_time - last_link_capacity_update_;
+    double alpha = delta.IsFinite() ? exp(-(delta / tracking_rate.Get())) : 0;
+    capacity_estimate_bps_ = alpha * capacity_estimate_bps_ +
+                             (1 - alpha) * acknowledged.bps<double>();
+  }
+  last_link_capacity_update_ = at_time;
+}
+
+void LinkCapacityTracker::OnRttBackoff(DataRate backoff_rate,
+                                       Timestamp at_time) {
+  capacity_estimate_bps_ =
+      std::min(capacity_estimate_bps_, backoff_rate.bps<double>());
+  last_link_capacity_update_ = at_time;
+}
+
+DataRate LinkCapacityTracker::estimate() const {
+  return DataRate::bps(capacity_estimate_bps_);
+}
+
 RttBasedBackoff::RttBasedBackoff()
     : rtt_limit_("limit", TimeDelta::PlusInfinity()),
       drop_fraction_("fraction", 0.5),
@@ -220,8 +262,10 @@ void SendSideBandwidthEstimation::SetBitrates(
     DataRate max_bitrate,
     Timestamp at_time) {
   SetMinMaxBitrate(min_bitrate, max_bitrate);
-  if (send_bitrate)
+  if (send_bitrate) {
+    link_capacity_.OnStartingRate(*send_bitrate);
     SetSendBitrate(*send_bitrate, at_time);
+  }
 }
 
 void SendSideBandwidthEstimation::SetSendBitrate(DataRate bitrate,
@@ -261,6 +305,10 @@ void SendSideBandwidthEstimation::CurrentEstimate(int* bitrate,
   *rtt = last_round_trip_time_.ms<int64_t>();
 }
 
+DataRate SendSideBandwidthEstimation::GetEstimatedLinkCapacity() const {
+  return link_capacity_.estimate();
+}
+
 void SendSideBandwidthEstimation::UpdateReceiverEstimate(Timestamp at_time,
                                                          DataRate bandwidth) {
   bwe_incoming_ = bandwidth;
@@ -269,21 +317,31 @@ void SendSideBandwidthEstimation::UpdateReceiverEstimate(Timestamp at_time,
 
 void SendSideBandwidthEstimation::UpdateDelayBasedEstimate(Timestamp at_time,
                                                            DataRate bitrate) {
+  if (acknowledged_rate_) {
+    if (bitrate < delay_based_bitrate_) {
+      link_capacity_.OnOveruse(*acknowledged_rate_, at_time);
+    }
+  }
   delay_based_bitrate_ = bitrate;
   CapBitrateToThresholds(at_time, current_bitrate_);
 }
 
-void SendSideBandwidthEstimation::IncomingPacketFeedbackVector(
+void SendSideBandwidthEstimation::SetAcknowledgedRate(
-    const TransportPacketsFeedback& report,
+    absl::optional<DataRate> acknowledged_rate,
-    absl::optional<DataRate> acked_bitrate) {
+    Timestamp at_time) {
-  if (!loss_based_bandwidth_estimation_.Enabled())
+  acknowledged_rate_ = acknowledged_rate;
-    return;
+  if (acknowledged_rate && loss_based_bandwidth_estimation_.Enabled()) {
-  if (acked_bitrate) {
     loss_based_bandwidth_estimation_.UpdateAcknowledgedBitrate(
-        *acked_bitrate, report.feedback_time);
+        *acknowledged_rate, at_time);
+  }
+}
+
+void SendSideBandwidthEstimation::IncomingPacketFeedbackVector(
+    const TransportPacketsFeedback& report) {
+  if (loss_based_bandwidth_estimation_.Enabled()) {
+    loss_based_bandwidth_estimation_.UpdateLossStatistics(
+        report.packet_feedbacks, report.feedback_time);
   }
-  loss_based_bandwidth_estimation_.UpdateLossStatistics(report.packet_feedbacks,
-                                                        report.feedback_time);
 }
 
 void SendSideBandwidthEstimation::UpdateReceiverBlock(uint8_t fraction_loss,
@@ -378,6 +436,7 @@ void SendSideBandwidthEstimation::UpdateEstimate(Timestamp at_time) {
     if (at_time - time_last_decrease_ >= rtt_backoff_.drop_interval_) {
       time_last_decrease_ = at_time;
       new_bitrate = current_bitrate_ * rtt_backoff_.drop_fraction_;
+      link_capacity_.OnRttBackoff(new_bitrate, at_time);
     }
     CapBitrateToThresholds(at_time, new_bitrate);
     return;
@@ -580,5 +639,10 @@ void SendSideBandwidthEstimation::CapBitrateToThresholds(Timestamp at_time,
     last_rtc_event_log_ = at_time;
   }
   current_bitrate_ = bitrate;
+
+  if (acknowledged_rate_) {
+    link_capacity_.OnRateUpdate(std::min(current_bitrate_, *acknowledged_rate_),
+                                at_time);
+  }
 }
 }  // namespace webrtc

modules/bitrate_controller/send_side_bandwidth_estimation.h

@@ -31,6 +31,22 @@ namespace webrtc {
 
 class RtcEventLog;
 
+class LinkCapacityTracker {
+ public:
+  LinkCapacityTracker();
+  ~LinkCapacityTracker();
+  void OnOveruse(DataRate acknowledged_rate, Timestamp at_time);
+  void OnStartingRate(DataRate start_rate);
+  void OnRateUpdate(DataRate acknowledged, Timestamp at_time);
+  void OnRttBackoff(DataRate backoff_rate, Timestamp at_time);
+  DataRate estimate() const;
+
+ private:
+  FieldTrialParameter<TimeDelta> tracking_rate;
+  double capacity_estimate_bps_ = 0;
+  Timestamp last_link_capacity_update_ = Timestamp::MinusInfinity();
+};
+
 class RttBasedBackoff {
  public:
   RttBasedBackoff();
@@ -57,7 +73,7 @@ class SendSideBandwidthEstimation {
 
   void OnRouteChange();
   void CurrentEstimate(int* bitrate, uint8_t* loss, int64_t* rtt) const;
-
+  DataRate GetEstimatedLinkCapacity() const;
   // Call periodically to update estimate.
   void UpdateEstimate(Timestamp at_time);
   void OnSentPacket(SentPacket sent_packet);
@@ -90,8 +106,9 @@ class SendSideBandwidthEstimation {
   void SetSendBitrate(DataRate bitrate, Timestamp at_time);
   void SetMinMaxBitrate(DataRate min_bitrate, DataRate max_bitrate);
   int GetMinBitrate() const;
-  void IncomingPacketFeedbackVector(const TransportPacketsFeedback& report,
+  void SetAcknowledgedRate(absl::optional<DataRate> acknowledged_rate,
-                                    absl::optional<DataRate> acked_bitrate);
+                           Timestamp at_time);
+  void IncomingPacketFeedbackVector(const TransportPacketsFeedback& report);
 
  private:
   enum UmaState { kNoUpdate, kFirstDone, kDone };
@@ -112,6 +129,7 @@ class SendSideBandwidthEstimation {
   void CapBitrateToThresholds(Timestamp at_time, DataRate bitrate);
 
   RttBasedBackoff rtt_backoff_;
+  LinkCapacityTracker link_capacity_;
 
   std::deque<std::pair<Timestamp, DataRate> > min_bitrate_history_;
 
@@ -119,6 +137,7 @@ class SendSideBandwidthEstimation {
   int lost_packets_since_last_loss_update_;
   int expected_packets_since_last_loss_update_;
 
+  absl::optional<DataRate> acknowledged_rate_;
   DataRate current_bitrate_;
   DataRate min_bitrate_configured_;
   DataRate max_bitrate_configured_;

modules/congestion_controller/goog_cc/goog_cc_network_control.cc

@@ -134,6 +134,8 @@ GoogCcNetworkController::GoogCcNetworkController(RtcEventLog* event_log,
       packet_feedback_only_(feedback_only),
       safe_reset_on_route_change_("Enabled"),
       safe_reset_acknowledged_rate_("ack"),
+      use_stable_bandwidth_estimate_(
+          field_trial::IsEnabled("WebRTC-Bwe-StableBandwidthEstimate")),
       probe_controller_(new ProbeController()),
       congestion_window_pushback_controller_(
           MaybeInitalizeCongestionWindowPushbackController()),
@@ -145,7 +147,7 @@ GoogCcNetworkController::GoogCcNetworkController(RtcEventLog* event_log,
       acknowledged_bitrate_estimator_(
           absl::make_unique<AcknowledgedBitrateEstimator>()),
       initial_config_(config),
-      last_bandwidth_(*config.constraints.starting_rate),
+      last_target_rate_(*config.constraints.starting_rate),
       pacing_factor_(config.stream_based_config.pacing_factor.value_or(
           kDefaultPaceMultiplier)),
       min_pacing_rate_(config.stream_based_config.min_pacing_rate.value_or(
@@ -484,8 +486,9 @@ NetworkControlUpdate GoogCcNetworkController::OnTransportPacketsFeedback(
   acknowledged_bitrate_estimator_->IncomingPacketFeedbackVector(
       received_feedback_vector);
   auto acknowledged_bitrate = acknowledged_bitrate_estimator_->bitrate();
-  bandwidth_estimation_->IncomingPacketFeedbackVector(report,
+  bandwidth_estimation_->SetAcknowledgedRate(acknowledged_bitrate,
-                                                      acknowledged_bitrate);
+                                             report.feedback_time);
+  bandwidth_estimation_->IncomingPacketFeedbackVector(report);
   for (const auto& feedback : received_feedback_vector) {
     if (feedback.pacing_info.probe_cluster_id != PacedPacketInfo::kNotAProbe) {
       probe_bitrate_estimator_->HandleProbeAndEstimateBitrate(feedback);
@@ -528,7 +531,7 @@ NetworkControlUpdate GoogCcNetworkController::OnTransportPacketsFeedback(
     const DataSize kMinCwnd = DataSize::bytes(2 * 1500);
     TimeDelta time_window =
         TimeDelta::ms(min_feedback_max_rtt_ms + accepted_queue_ms_);
-    DataSize data_window = last_bandwidth_ * time_window;
+    DataSize data_window = last_target_rate_ * time_window;
     if (current_data_window_) {
       data_window =
           std::max(kMinCwnd, (data_window + current_data_window_.value()) / 2);
@@ -595,14 +598,16 @@ void GoogCcNetworkController::MaybeTriggerOnNetworkChanged(
 
     alr_detector_->SetEstimatedBitrate(estimated_bitrate_bps);
 
-    DataRate bandwidth = DataRate::bps(estimated_bitrate_bps);
+    last_target_rate_ = DataRate::bps(estimated_bitrate_bps);
-    last_bandwidth_ = bandwidth;
+    DataRate bandwidth = use_stable_bandwidth_estimate_
+                             ? bandwidth_estimation_->GetEstimatedLinkCapacity()
+                             : last_target_rate_;
 
     TimeDelta bwe_period = delay_based_bwe_->GetExpectedBwePeriod();
 
     // Set the target rate to the full estimated bandwidth since the estimation
     // for legacy reasons includes target rate constraints.
-    DataRate target_rate = bandwidth;
+    DataRate target_rate = last_target_rate_;
     if (congestion_window_pushback_controller_) {
       int64_t pushback_rate =
           congestion_window_pushback_controller_->UpdateTargetBitrate(
@@ -623,8 +628,8 @@ void GoogCcNetworkController::MaybeTriggerOnNetworkChanged(
 
     update->target_rate = target_rate_msg;
 
-    auto probes =
+    auto probes = probe_controller_->SetEstimatedBitrate(
-        probe_controller_->SetEstimatedBitrate(bandwidth.bps(), at_time.ms());
+        last_target_rate_.bps(), at_time.ms());
     update->probe_cluster_configs.insert(update->probe_cluster_configs.end(),
                                          probes.begin(), probes.end());
     update->pacer_config = GetPacingRates(at_time);
@@ -633,8 +638,8 @@ void GoogCcNetworkController::MaybeTriggerOnNetworkChanged(
 
 PacerConfig GoogCcNetworkController::GetPacingRates(Timestamp at_time) const {
   DataRate pacing_rate =
-      std::max(min_pacing_rate_, last_bandwidth_) * pacing_factor_;
+      std::max(min_pacing_rate_, last_target_rate_) * pacing_factor_;
-  DataRate padding_rate = std::min(max_padding_rate_, last_bandwidth_);
+  DataRate padding_rate = std::min(max_padding_rate_, last_target_rate_);
   PacerConfig msg;
   msg.at_time = at_time;
   msg.time_window = TimeDelta::seconds(1);

modules/congestion_controller/goog_cc/goog_cc_network_control.h

@@ -66,6 +66,7 @@ class GoogCcNetworkController : public NetworkControllerInterface {
   const bool packet_feedback_only_;
   FieldTrialFlag safe_reset_on_route_change_;
   FieldTrialFlag safe_reset_acknowledged_rate_;
+  const bool use_stable_bandwidth_estimate_;
 
   const std::unique_ptr<ProbeController> probe_controller_;
   const std::unique_ptr<CongestionWindowPushbackController>
@@ -87,8 +88,7 @@ class GoogCcNetworkController : public NetworkControllerInterface {
 
   std::deque<int64_t> feedback_max_rtts_;
 
-  DataRate last_bandwidth_;
+  DataRate last_target_rate_;
-  absl::optional<TargetTransferRate> last_target_rate_;
 
   int32_t last_estimated_bitrate_bps_ = 0;
   uint8_t last_estimated_fraction_loss_ = 0;

modules/congestion_controller/goog_cc/goog_cc_network_control_unittest.cc

@@ -399,5 +399,61 @@ TEST_F(GoogCcNetworkControllerTest, UpdatesTargetRateBasedOnLinkCapacity) {
   EXPECT_NEAR(client->target_rate_kbps(), 90, 20);
 }
 
+TEST_F(GoogCcNetworkControllerTest, DefaultEstimateVariesInSteadyState) {
+  ScopedFieldTrials trial("WebRTC-Bwe-StableBandwidthEstimate/Disabled/");
+  Scenario s("googcc_unit/no_stable_varies", false);
+  SimulatedTimeClientConfig config;
+  config.transport.cc =
+      TransportControllerConfig::CongestionController::kGoogCcFeedback;
+  NetworkNodeConfig net_conf;
+  net_conf.simulation.bandwidth = DataRate::kbps(500);
+  net_conf.simulation.delay = TimeDelta::ms(100);
+  net_conf.update_frequency = TimeDelta::ms(5);
+  auto send_net = s.CreateSimulationNode(net_conf);
+  auto ret_net = s.CreateSimulationNode(net_conf);
+  SimulatedTimeClient* client = s.CreateSimulatedTimeClient(
+      "send", config, {PacketStreamConfig()}, {send_net}, {ret_net});
+  // Run for a while to allow the estimate to stabilize.
+  s.RunFor(TimeDelta::seconds(20));
+  DataRate min_estimate = DataRate::PlusInfinity();
+  DataRate max_estimate = DataRate::MinusInfinity();
+  // Measure variation in steady state.
+  for (int i = 0; i < 20; ++i) {
+    min_estimate = std::min(min_estimate, client->link_capacity());
+    max_estimate = std::max(max_estimate, client->link_capacity());
+    s.RunFor(TimeDelta::seconds(1));
+  }
+  // We should expect drops by at least 15% (default backoff.)
+  EXPECT_LT(min_estimate / max_estimate, 0.85);
+}
+
+TEST_F(GoogCcNetworkControllerTest, StableEstimateDoesNotVaryInSteadyState) {
+  ScopedFieldTrials trial("WebRTC-Bwe-StableBandwidthEstimate/Enabled/");
+  Scenario s("googcc_unit/stable_is_stable", false);
+  SimulatedTimeClientConfig config;
+  config.transport.cc =
+      TransportControllerConfig::CongestionController::kGoogCcFeedback;
+  NetworkNodeConfig net_conf;
+  net_conf.simulation.bandwidth = DataRate::kbps(500);
+  net_conf.simulation.delay = TimeDelta::ms(100);
+  net_conf.update_frequency = TimeDelta::ms(5);
+  auto send_net = s.CreateSimulationNode(net_conf);
+  auto ret_net = s.CreateSimulationNode(net_conf);
+  SimulatedTimeClient* client = s.CreateSimulatedTimeClient(
+      "send", config, {PacketStreamConfig()}, {send_net}, {ret_net});
+  // Run for a while to allow the estimate to stabilize.
+  s.RunFor(TimeDelta::seconds(20));
+  DataRate min_estimate = DataRate::PlusInfinity();
+  DataRate max_estimate = DataRate::MinusInfinity();
+  // Measure variation in steady state.
+  for (int i = 0; i < 20; ++i) {
+    min_estimate = std::min(min_estimate, client->link_capacity());
+    max_estimate = std::max(max_estimate, client->link_capacity());
+    s.RunFor(TimeDelta::seconds(1));
+  }
+  // We expect no variation under the trial in steady state.
+  EXPECT_GT(min_estimate / max_estimate, 0.95);
+}
+
 }  // namespace test
 }  // namespace webrtc

test/scenario/simulated_time.cc

@@ -308,6 +308,7 @@ void SimulatedTimeClient::Update(NetworkControlUpdate update) {
     DataRate rate_per_stream =
         update.target_rate->target_rate * ratio_per_stream;
     target_rate_ = update.target_rate->target_rate;
+    link_capacity_ = update.target_rate->network_estimate.bandwidth;
     for (auto& stream : packet_streams_)
       stream->OnTargetRateUpdate(rate_per_stream);
   }
@@ -349,6 +350,10 @@ TimeDelta SimulatedTimeClient::GetNetworkControllerProcessInterval() const {
   return network_controller_factory_.GetProcessInterval();
 }
 
+DataRate SimulatedTimeClient::link_capacity() const {
+  return link_capacity_;
+}
+
 double SimulatedTimeClient::target_rate_kbps() const {
   return target_rate_.kbps<double>();
 }

test/scenario/simulated_time.h

@@ -132,6 +132,7 @@ class SimulatedTimeClient : NetworkReceiverInterface {
   void TriggerFakeReroute(Timestamp at_time);
   TimeDelta GetNetworkControllerProcessInterval() const;
   double target_rate_kbps() const;
+  DataRate link_capacity() const;
 
   bool TryDeliverPacket(rtc::CopyOnWriteBuffer packet,
                         uint64_t receiver,
@@ -147,6 +148,7 @@ class SimulatedTimeClient : NetworkReceiverInterface {
   SimulatedFeedback feedback_;
   TargetRateConstraints current_contraints_;
   DataRate target_rate_ = DataRate::Infinity();
+  DataRate link_capacity_ = DataRate::Infinity();
   FILE* packet_log_ = nullptr;
 
   std::vector<std::unique_ptr<PacketStream>> packet_streams_;