Ignore allocated bitrate during initial exponential BWE.

The reason why we want to do this is  because audio can allocate a needed bitrate before video when starting a call, which may lead to a race between the first probe result and updating the allocated bitrate.
That is the, initial probe will try to probe up to the max configured bitrate.

ProbeController::SetFirstProbeToMaxBitrate will allow the first probe to
continue up to the max configured bitrate, regardless of of the max
allocated bitrate.

Bug: webrtc:14928
Change-Id: I6e0ae90e21a78466527f3464951e6033dc846470
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/346760
Reviewed-by: Diep Bui <diepbp@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42049}

api/transport/network_types.h

@@ -46,6 +46,10 @@ struct StreamsConfig {
   ~StreamsConfig();
   Timestamp at_time = Timestamp::PlusInfinity();
   absl::optional<bool> requests_alr_probing;
+  // If `initial_probe_to_max_bitrate` is set to true, the first probe
+  // may probe up to the max configured bitrate and can ignore
+  // max_total_allocated_bitrate.
+  absl::optional<bool> initial_probe_to_max_bitrate;
   absl::optional<double> pacing_factor;
 
   // TODO(srte): Use BitrateAllocationLimits here.

call/rtp_transport_controller_send.cc

@@ -262,6 +262,11 @@ void RtpTransportControllerSend::ReconfigureBandwidthEstimation(
   RTC_DCHECK_RUN_ON(&sequence_checker_);
   bwe_settings_ = settings;
 
+  bool allow_probe_without_media = bwe_settings_.allow_probe_without_media &&
+                                   packet_router_.SupportsRtxPayloadPadding();
+  streams_config_.initial_probe_to_max_bitrate = allow_probe_without_media;
+  pacer_.SetAllowProbeWithoutMediaPacket(allow_probe_without_media);
+
   if (controller_) {
     // Recreate the controller and handler.
     control_handler_ = nullptr;
@@ -275,9 +280,6 @@ void RtpTransportControllerSend::ReconfigureBandwidthEstimation(
       UpdateNetworkAvailability();
     }
   }
-  pacer_.SetAllowProbeWithoutMediaPacket(
-      bwe_settings_.allow_probe_without_media &&
-      packet_router_.SupportsRtxPayloadPadding());
 }
 
 void RtpTransportControllerSend::RegisterTargetTransferRateObserver(

modules/congestion_controller/goog_cc/goog_cc_network_control.cc

@@ -218,6 +218,10 @@ NetworkControlUpdate GoogCcNetworkController::OnProcessInterval(
       probe_controller_->EnablePeriodicAlrProbing(
           *initial_config_->stream_based_config.requests_alr_probing);
     }
+    if (initial_config_->stream_based_config.initial_probe_to_max_bitrate) {
+      probe_controller_->SetFirstProbeToMaxBitrate(
+          *initial_config_->stream_based_config.initial_probe_to_max_bitrate);
+    }
     absl::optional<DataRate> total_bitrate =
         initial_config_->stream_based_config.max_total_allocated_bitrate;
     if (total_bitrate) {

modules/congestion_controller/goog_cc/probe_controller.cc

@@ -272,6 +272,22 @@ std::vector<ProbeClusterConfig> ProbeController::OnNetworkAvailability(
   return std::vector<ProbeClusterConfig>();
 }
 
+void ProbeController::UpdateState(State new_state) {
+  switch (new_state) {
+    case State::kInit:
+      state_ = State::kInit;
+      break;
+    case State::kWaitingForProbingResult:
+      state_ = State::kWaitingForProbingResult;
+      break;
+    case State::kProbingComplete:
+      state_ = State::kProbingComplete;
+      waiting_for_initial_probe_result_ = false;
+      min_bitrate_to_probe_further_ = DataRate::PlusInfinity();
+      break;
+  }
+}
+
 std::vector<ProbeClusterConfig> ProbeController::InitiateExponentialProbing(
     Timestamp at_time) {
   RTC_DCHECK(network_available_);
@@ -287,6 +303,8 @@ std::vector<ProbeClusterConfig> ProbeController::InitiateExponentialProbing(
     probes.push_back(config_.second_exponential_probe_scale.Value() *
                      start_bitrate_);
   }
+  waiting_for_initial_probe_result_ = true;
+
   return InitiateProbing(at_time, probes, true);
 }
 
@@ -307,6 +325,7 @@ std::vector<ProbeClusterConfig> ProbeController::SetEstimatedBitrate(
     if (config_.abort_further_probe_if_max_lower_than_current &&
         (bitrate > max_bitrate_ ||
          (!max_total_allocated_bitrate_.IsZero() &&
+          !(waiting_for_initial_probe_result_ && first_probe_to_max_bitrate_) &&
           bitrate > 2 * max_total_allocated_bitrate_))) {
       // No need to continue probing.
       min_bitrate_to_probe_further_ = DataRate::PlusInfinity();
@@ -335,6 +354,11 @@ void ProbeController::EnablePeriodicAlrProbing(bool enable) {
   enable_periodic_alr_probing_ = enable;
 }
 
+void ProbeController::SetFirstProbeToMaxBitrate(
+    bool first_probe_to_max_bitrate) {
+  first_probe_to_max_bitrate_ = first_probe_to_max_bitrate;
+}
+
 void ProbeController::SetAlrStartTimeMs(
     absl::optional<int64_t> alr_start_time_ms) {
   if (alr_start_time_ms) {
@@ -391,6 +415,7 @@ void ProbeController::SetNetworkStateEstimate(
 void ProbeController::Reset(Timestamp at_time) {
   bandwidth_limited_cause_ = BandwidthLimitedCause::kDelayBasedLimited;
   state_ = State::kInit;
+  waiting_for_initial_probe_result_ = false;
   min_bitrate_to_probe_further_ = DataRate::PlusInfinity();
   time_last_probing_initiated_ = Timestamp::Zero();
   estimated_bitrate_ = DataRate::Zero();
@@ -452,8 +477,7 @@ std::vector<ProbeClusterConfig> ProbeController::Process(Timestamp at_time) {
       kMaxWaitingTimeForProbingResult) {
     if (state_ == State::kWaitingForProbingResult) {
       RTC_LOG(LS_INFO) << "kWaitingForProbingResult: timeout";
-      state_ = State::kProbingComplete;
-      min_bitrate_to_probe_further_ = DataRate::PlusInfinity();
+      UpdateState(State::kProbingComplete);
     }
   }
   if (estimated_bitrate_.IsZero() || state_ != State::kProbingComplete) {
@@ -480,14 +504,14 @@ std::vector<ProbeClusterConfig> ProbeController::InitiateProbing(
             : std::min(max_total_allocated_bitrate_, max_bitrate_);
     if (std::min(network_estimate, estimated_bitrate_) >
         config_.skip_if_estimate_larger_than_fraction_of_max * max_probe_rate) {
-      state_ = State::kProbingComplete;
-      min_bitrate_to_probe_further_ = DataRate::PlusInfinity();
+      UpdateState(State::kProbingComplete);
       return {};
     }
   }
 
   DataRate max_probe_bitrate = max_bitrate_;
-  if (max_total_allocated_bitrate_ > DataRate::Zero()) {
+  if (max_total_allocated_bitrate_ > DataRate::Zero() &&
+      !waiting_for_initial_probe_result_) {
     // If a max allocated bitrate has been configured, allow probing up to 2x
     // that rate. This allows some overhead to account for bursty streams,
     // which otherwise would have to ramp up when the overshoot is already in
@@ -555,15 +579,14 @@ std::vector<ProbeClusterConfig> ProbeController::InitiateProbing(
   }
   time_last_probing_initiated_ = now;
   if (probe_further) {
-    state_ = State::kWaitingForProbingResult;
+    UpdateState(State::kWaitingForProbingResult);
     // Dont expect probe results to be larger than a fraction of the actual
     // probe rate.
     min_bitrate_to_probe_further_ =
         std::min(estimate_capped_bitrate, (*(bitrates_to_probe.end() - 1))) *
         config_.further_probe_threshold;
   } else {
-    state_ = State::kProbingComplete;
-    min_bitrate_to_probe_further_ = DataRate::PlusInfinity();
+    UpdateState(State::kProbingComplete);
   }
   return pending_probes;
 }

modules/congestion_controller/goog_cc/probe_controller.h

@@ -121,6 +121,9 @@ class ProbeController {
       Timestamp at_time);
 
   void EnablePeriodicAlrProbing(bool enable);
+  // The first initial probe ignores allocated bitrate constraints and probe up
+  // to max configured bitrate configured via SetBitrates.
+  void SetFirstProbeToMaxBitrate(bool first_probe_to_max_bitrate);
 
   void SetAlrStartTimeMs(absl::optional<int64_t> alr_start_time);
   void SetAlrEndedTimeMs(int64_t alr_end_time);
@@ -148,6 +151,7 @@ class ProbeController {
     kProbingComplete,
   };
 
+  void UpdateState(State new_state);
   ABSL_MUST_USE_RESULT std::vector<ProbeClusterConfig>
   InitiateExponentialProbing(Timestamp at_time);
   ABSL_MUST_USE_RESULT std::vector<ProbeClusterConfig> InitiateProbing(
@@ -158,6 +162,8 @@ class ProbeController {
   bool TimeForNetworkStateProbe(Timestamp at_time) const;
 
   bool network_available_;
+  bool waiting_for_initial_probe_result_ = false;
+  bool first_probe_to_max_bitrate_ = false;
   BandwidthLimitedCause bandwidth_limited_cause_ =
       BandwidthLimitedCause::kDelayBasedLimited;
   State state_;

modules/congestion_controller/goog_cc/probe_controller_unittest.cc

@@ -327,6 +327,32 @@ TEST(ProbeControllerTest, TestExponentialProbing) {
   EXPECT_EQ(probes[0].target_data_rate.bps(), 2 * 1800);
 }
 
+TEST(ProbeControllerTest, ExponentialProbingStopIfMaxBitrateLow) {
+  ProbeControllerFixture fixture(
+      "WebRTC-Bwe-ProbingConfiguration/abort_further:true/");
+  std::unique_ptr<ProbeController> probe_controller =
+      fixture.CreateController();
+  ASSERT_THAT(
+      probe_controller->OnNetworkAvailability({.network_available = true}),
+      IsEmpty());
+  auto probes = probe_controller->SetBitrates(
+      kMinBitrate, kStartBitrate, kMaxBitrate, fixture.CurrentTime());
+  ASSERT_THAT(probes, SizeIs(Gt(0)));
+
+  // Repeated probe normally is sent when estimated bitrate climbs above
+  // 0.7 * 6 * kStartBitrate = 1260. But since max bitrate is low, expect
+  // exponential probing to stop.
+  probes = probe_controller->SetBitrates(kMinBitrate, kStartBitrate,
+                                         /*max_bitrate=*/kStartBitrate,
+                                         fixture.CurrentTime());
+  EXPECT_THAT(probes, IsEmpty());
+
+  probes = probe_controller->SetEstimatedBitrate(
+      DataRate::BitsPerSec(1800), BandwidthLimitedCause::kDelayBasedLimited,
+      fixture.CurrentTime());
+  EXPECT_THAT(probes, IsEmpty());
+}
+
 TEST(ProbeControllerTest, ExponentialProbingStopIfMaxAllocatedBitrateLow) {
   ProbeControllerFixture fixture(
       "WebRTC-Bwe-ProbingConfiguration/abort_further:true/");
@@ -352,6 +378,39 @@ TEST(ProbeControllerTest, ExponentialProbingStopIfMaxAllocatedBitrateLow) {
   EXPECT_THAT(probes, IsEmpty());
 }
 
+TEST(ProbeControllerTest,
+     InitialProbingIgnoreLowMaxAllocatedbitrateIfSetFirstProbeToMaxBitrate) {
+  ProbeControllerFixture fixture(
+      "WebRTC-Bwe-ProbingConfiguration/abort_further:true/");
+  std::unique_ptr<ProbeController> probe_controller =
+      fixture.CreateController();
+  ASSERT_THAT(
+      probe_controller->OnNetworkAvailability({.network_available = true}),
+      IsEmpty());
+  auto probes = probe_controller->SetBitrates(
+      kMinBitrate, kStartBitrate, kMaxBitrate, fixture.CurrentTime());
+  ASSERT_THAT(probes, SizeIs(Gt(0)));
+  probe_controller->SetFirstProbeToMaxBitrate(true);
+
+  // Repeated probe is sent when estimated bitrate climbs above
+  // 0.7 * 6 * kStartBitrate = 1260. During the initial probe, we ignore the
+  // allocation limit and probe up to the max.
+  probes = probe_controller->OnMaxTotalAllocatedBitrate(kStartBitrate,
+                                                        fixture.CurrentTime());
+  EXPECT_THAT(probes, IsEmpty());
+
+  probes = probe_controller->SetEstimatedBitrate(
+      DataRate::BitsPerSec(1800), BandwidthLimitedCause::kDelayBasedLimited,
+      fixture.CurrentTime());
+  EXPECT_EQ(probes.size(), 1u);
+  EXPECT_EQ(probes[0].target_data_rate.bps(), 2 * 1800);
+
+  probes = probe_controller->SetEstimatedBitrate(
+      probes[0].target_data_rate, BandwidthLimitedCause::kDelayBasedLimited,
+      fixture.CurrentTime());
+  EXPECT_EQ(probes.size(), 1u);
+}
+
 TEST(ProbeControllerTest, TestExponentialProbingTimeout) {
   ProbeControllerFixture fixture;
   std::unique_ptr<ProbeController> probe_controller =