modules/congestion_controller/goog_cc/delay_based_bwe_unittest.cc - src - Git at Google

 /*
  *  Copyright (c) 2016 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 "modules/congestion_controller/goog_cc/delay_based_bwe.h"

 #include <string>

 #include "api/transport/network_types.h"
 #include "modules/congestion_controller/goog_cc/acknowledged_bitrate_estimator.h"
 #include "modules/congestion_controller/goog_cc/delay_based_bwe_unittest_helper.h"
 #include "system_wrappers/include/clock.h"
 #include "test/gtest.h"

 namespace webrtc {

 namespace {
 constexpr int kNumProbesCluster0 = 5;
 constexpr int kNumProbesCluster1 = 8;
 const PacedPacketInfo kPacingInfo0(0, kNumProbesCluster0, 2000);
 const PacedPacketInfo kPacingInfo1(1, kNumProbesCluster1, 4000);
 constexpr float kTargetUtilizationFraction = 0.95f;
 }  // namespace

 TEST_F(DelayBasedBweTest, ProbeDetection) {
   int64_t now_ms = clock_.TimeInMilliseconds();

   // First burst sent at 8 * 1000 / 10 = 800 kbps.
   for (int i = 0; i < kNumProbesCluster0; ++i) {
     clock_.AdvanceTimeMilliseconds(10);
     now_ms = clock_.TimeInMilliseconds();
     IncomingFeedback(now_ms, now_ms, 1000, kPacingInfo0);
   }
   EXPECT_TRUE(bitrate_observer_.updated());

   // Second burst sent at 8 * 1000 / 5 = 1600 kbps.
   for (int i = 0; i < kNumProbesCluster1; ++i) {
     clock_.AdvanceTimeMilliseconds(5);
     now_ms = clock_.TimeInMilliseconds();
     IncomingFeedback(now_ms, now_ms, 1000, kPacingInfo1);
   }

   EXPECT_TRUE(bitrate_observer_.updated());
   EXPECT_GT(bitrate_observer_.latest_bitrate(), 1500000u);
 }

 TEST_F(DelayBasedBweTest, ProbeDetectionNonPacedPackets) {
   int64_t now_ms = clock_.TimeInMilliseconds();
   // First burst sent at 8 * 1000 / 10 = 800 kbps, but with every other packet
   // not being paced which could mess things up.
   for (int i = 0; i < kNumProbesCluster0; ++i) {
     clock_.AdvanceTimeMilliseconds(5);
     now_ms = clock_.TimeInMilliseconds();
     IncomingFeedback(now_ms, now_ms, 1000, kPacingInfo0);
     // Non-paced packet, arriving 5 ms after.
     clock_.AdvanceTimeMilliseconds(5);
     IncomingFeedback(now_ms, now_ms, 100, PacedPacketInfo());
   }

   EXPECT_TRUE(bitrate_observer_.updated());
   EXPECT_GT(bitrate_observer_.latest_bitrate(), 800000u);
 }

 TEST_F(DelayBasedBweTest, ProbeDetectionFasterArrival) {
   int64_t now_ms = clock_.TimeInMilliseconds();
   // First burst sent at 8 * 1000 / 10 = 800 kbps.
   // Arriving at 8 * 1000 / 5 = 1600 kbps.
   int64_t send_time_ms = 0;
   for (int i = 0; i < kNumProbesCluster0; ++i) {
     clock_.AdvanceTimeMilliseconds(1);
     send_time_ms += 10;
     now_ms = clock_.TimeInMilliseconds();
     IncomingFeedback(now_ms, send_time_ms, 1000, kPacingInfo0);
   }

   EXPECT_FALSE(bitrate_observer_.updated());
 }

 TEST_F(DelayBasedBweTest, ProbeDetectionSlowerArrival) {
   int64_t now_ms = clock_.TimeInMilliseconds();
   // First burst sent at 8 * 1000 / 5 = 1600 kbps.
   // Arriving at 8 * 1000 / 7 = 1142 kbps.
   // Since the receive rate is significantly below the send rate, we expect to
   // use 95% of the estimated capacity.
   int64_t send_time_ms = 0;
   for (int i = 0; i < kNumProbesCluster1; ++i) {
     clock_.AdvanceTimeMilliseconds(7);
     send_time_ms += 5;
     now_ms = clock_.TimeInMilliseconds();
     IncomingFeedback(now_ms, send_time_ms, 1000, kPacingInfo1);
   }

   EXPECT_TRUE(bitrate_observer_.updated());
   EXPECT_NEAR(bitrate_observer_.latest_bitrate(),
               kTargetUtilizationFraction * 1140000u, 10000u);
 }

 TEST_F(DelayBasedBweTest, ProbeDetectionSlowerArrivalHighBitrate) {
   int64_t now_ms = clock_.TimeInMilliseconds();
   // Burst sent at 8 * 1000 / 1 = 8000 kbps.
   // Arriving at 8 * 1000 / 2 = 4000 kbps.
   // Since the receive rate is significantly below the send rate, we expect to
   // use 95% of the estimated capacity.
   int64_t send_time_ms = 0;
   for (int i = 0; i < kNumProbesCluster1; ++i) {
     clock_.AdvanceTimeMilliseconds(2);
     send_time_ms += 1;
     now_ms = clock_.TimeInMilliseconds();
     IncomingFeedback(now_ms, send_time_ms, 1000, kPacingInfo1);
   }

   EXPECT_TRUE(bitrate_observer_.updated());
   EXPECT_NEAR(bitrate_observer_.latest_bitrate(),
               kTargetUtilizationFraction * 4000000u, 10000u);
 }

 TEST_F(DelayBasedBweTest, GetExpectedBwePeriodMs) {
   auto default_interval = bitrate_estimator_->GetExpectedBwePeriod();
   EXPECT_GT(default_interval.ms(), 0);
   CapacityDropTestHelper(1, true, 333, 0);
   auto interval = bitrate_estimator_->GetExpectedBwePeriod();
   EXPECT_GT(interval.ms(), 0);
   EXPECT_NE(interval.ms(), default_interval.ms());
 }

 TEST_F(DelayBasedBweTest, InitialBehavior) {
   InitialBehaviorTestHelper(730000);
 }

 TEST_F(DelayBasedBweTest, InitializeResult) {
   DelayBasedBwe::Result result;
   EXPECT_EQ(result.delay_detector_state, BandwidthUsage::kBwNormal);
 }

 TEST_F(DelayBasedBweTest, RateIncreaseReordering) {
   RateIncreaseReorderingTestHelper(730000);
 }
 TEST_F(DelayBasedBweTest, RateIncreaseRtpTimestamps) {
   RateIncreaseRtpTimestampsTestHelper(622);
 }

 TEST_F(DelayBasedBweTest, CapacityDropOneStream) {
   CapacityDropTestHelper(1, false, 300, 0);
 }

 TEST_F(DelayBasedBweTest, CapacityDropPosOffsetChange) {
   CapacityDropTestHelper(1, false, 867, 30000);
 }

 TEST_F(DelayBasedBweTest, CapacityDropNegOffsetChange) {
   CapacityDropTestHelper(1, false, 933, -30000);
 }

 TEST_F(DelayBasedBweTest, CapacityDropOneStreamWrap) {
   CapacityDropTestHelper(1, true, 333, 0);
 }

 TEST_F(DelayBasedBweTest, TestTimestampGrouping) {
   TestTimestampGroupingTestHelper();
 }

 TEST_F(DelayBasedBweTest, TestShortTimeoutAndWrap) {
   // Simulate a client leaving and rejoining the call after 35 seconds. This
   // will make abs send time wrap, so if streams aren't timed out properly
   // the next 30 seconds of packets will be out of order.
   TestWrappingHelper(35);
 }

 TEST_F(DelayBasedBweTest, TestLongTimeoutAndWrap) {
   // Simulate a client leaving and rejoining the call after some multiple of
   // 64 seconds later. This will cause a zero difference in abs send times due
   // to the wrap, but a big difference in arrival time, if streams aren't
   // properly timed out.
   TestWrappingHelper(10 * 64);
 }

 TEST_F(DelayBasedBweTest, TestInitialOveruse) {
   const DataRate kStartBitrate = DataRate::KilobitsPerSec(300);
   const DataRate kInitialCapacity = DataRate::KilobitsPerSec(200);
   const uint32_t kDummySsrc = 0;
   // High FPS to ensure that we send a lot of packets in a short time.
   const int kFps = 90;

   stream_generator_->AddStream(new test::RtpStream(kFps, kStartBitrate.bps()));
   stream_generator_->set_capacity_bps(kInitialCapacity.bps());

   // Needed to initialize the AimdRateControl.
   bitrate_estimator_->SetStartBitrate(kStartBitrate);

   // Produce 30 frames (in 1/3 second) and give them to the estimator.
   int64_t bitrate_bps = kStartBitrate.bps();
   bool seen_overuse = false;
   for (int i = 0; i < 30; ++i) {
     bool overuse = GenerateAndProcessFrame(kDummySsrc, bitrate_bps);
     // The purpose of this test is to ensure that we back down even if we don't
     // have any acknowledged bitrate estimate yet. Hence, if the test works
     // as expected, we should not have a measured bitrate yet.
     EXPECT_FALSE(acknowledged_bitrate_estimator_->bitrate().has_value());
     if (overuse) {
       EXPECT_TRUE(bitrate_observer_.updated());
       EXPECT_NEAR(bitrate_observer_.latest_bitrate(), kStartBitrate.bps() / 2,
                   15000);
       bitrate_bps = bitrate_observer_.latest_bitrate();
       seen_overuse = true;
       break;
     } else if (bitrate_observer_.updated()) {
       bitrate_bps = bitrate_observer_.latest_bitrate();
       bitrate_observer_.Reset();
     }
   }
   EXPECT_TRUE(seen_overuse);
   EXPECT_NEAR(bitrate_observer_.latest_bitrate(), kStartBitrate.bps() / 2,
               15000);
 }

 TEST_F(DelayBasedBweTest, TestTimestampPrecisionHandling) {
   // This test does some basic checks to make sure that timestamps with higher
   // than millisecond precision are handled properly and do not cause any
   // problems in the estimator. Specifically, previously reported in
   // webrtc:14023 and described in more details there, the rounding to the
   // nearest milliseconds caused discrepancy in the accumulated delay. This lead
   // to false-positive overuse detection.
   // Technical details of the test:
   // Send times(ms): 0.000,  9.725, 20.000, 29.725, 40.000, 49.725, ...
   // Recv times(ms): 0.500, 10.000, 20.500, 30.000, 40.500, 50.000, ...
   // Send deltas(ms):   9.750,  10.250,  9.750, 10.250,  9.750, ...
   // Recv deltas(ms):   9.500,  10.500,  9.500, 10.500,  9.500, ...
   // There is no delay building up between the send times and the receive times,
   // therefore this case should never lead to an overuse detection. However, if
   // the time deltas were accidentally rounded to the nearest milliseconds, then
   // all the send deltas would be equal to 10ms while some recv deltas would
   // round up to 11ms which would lead in a false illusion of delay build up.
   uint32_t last_bitrate = bitrate_observer_.latest_bitrate();
   for (int i = 0; i < 1000; ++i) {
     clock_.AdvanceTimeMicroseconds(500);
     IncomingFeedback(clock_.CurrentTime(),
                      clock_.CurrentTime() - TimeDelta::Micros(500), 1000,
                      PacedPacketInfo());
     clock_.AdvanceTimeMicroseconds(9500);
     IncomingFeedback(clock_.CurrentTime(),
                      clock_.CurrentTime() - TimeDelta::Micros(250), 1000,
                      PacedPacketInfo());
     clock_.AdvanceTimeMicroseconds(10000);

     // The bitrate should never decrease in this test.
     EXPECT_LE(last_bitrate, bitrate_observer_.latest_bitrate());
     last_bitrate = bitrate_observer_.latest_bitrate();
   }
 }

 class DelayBasedBweTestWithBackoffTimeoutExperiment : public DelayBasedBweTest {
  public:
   DelayBasedBweTestWithBackoffTimeoutExperiment()
       : DelayBasedBweTest(
             "WebRTC-BweAimdRateControlConfig/initial_backoff_interval:200ms/") {
   }
 };

 // This test subsumes and improves DelayBasedBweTest.TestInitialOveruse above.
 TEST_F(DelayBasedBweTestWithBackoffTimeoutExperiment, TestInitialOveruse) {
   const DataRate kStartBitrate = DataRate::KilobitsPerSec(300);
   const DataRate kInitialCapacity = DataRate::KilobitsPerSec(200);
   const uint32_t kDummySsrc = 0;
   // High FPS to ensure that we send a lot of packets in a short time.
   const int kFps = 90;

   stream_generator_->AddStream(new test::RtpStream(kFps, kStartBitrate.bps()));
   stream_generator_->set_capacity_bps(kInitialCapacity.bps());

   // Needed to initialize the AimdRateControl.
   bitrate_estimator_->SetStartBitrate(kStartBitrate);

   // Produce 30 frames (in 1/3 second) and give them to the estimator.
   int64_t bitrate_bps = kStartBitrate.bps();
   bool seen_overuse = false;
   for (int frames = 0; frames < 30 && !seen_overuse; ++frames) {
     bool overuse = GenerateAndProcessFrame(kDummySsrc, bitrate_bps);
     // The purpose of this test is to ensure that we back down even if we don't
     // have any acknowledged bitrate estimate yet. Hence, if the test works
     // as expected, we should not have a measured bitrate yet.
     EXPECT_FALSE(acknowledged_bitrate_estimator_->bitrate().has_value());
     if (overuse) {
       EXPECT_TRUE(bitrate_observer_.updated());
       EXPECT_NEAR(bitrate_observer_.latest_bitrate(), kStartBitrate.bps() / 2,
                   15000);
       bitrate_bps = bitrate_observer_.latest_bitrate();
       seen_overuse = true;
     } else if (bitrate_observer_.updated()) {
       bitrate_bps = bitrate_observer_.latest_bitrate();
       bitrate_observer_.Reset();
     }
   }
   EXPECT_TRUE(seen_overuse);
   // Continue generating an additional 15 frames (equivalent to 167 ms) and
   // verify that we don't back down further.
   for (int frames = 0; frames < 15 && seen_overuse; ++frames) {
     bool overuse = GenerateAndProcessFrame(kDummySsrc, bitrate_bps);
     EXPECT_FALSE(overuse);
     if (bitrate_observer_.updated()) {
       bitrate_bps = bitrate_observer_.latest_bitrate();
       EXPECT_GE(bitrate_bps, kStartBitrate.bps() / 2 - 15000);
       EXPECT_LE(bitrate_bps, kInitialCapacity.bps() + 15000);
       bitrate_observer_.Reset();
     }
   }
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2016 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 "modules/congestion_controller/goog_cc/delay_based_bwe.h"

	#include <string>

	#include "api/transport/network_types.h"
	#include "modules/congestion_controller/goog_cc/acknowledged_bitrate_estimator.h"
	#include "modules/congestion_controller/goog_cc/delay_based_bwe_unittest_helper.h"
	#include "system_wrappers/include/clock.h"
	#include "test/gtest.h"

	namespace webrtc {

	namespace {
	constexpr int kNumProbesCluster0 = 5;
	constexpr int kNumProbesCluster1 = 8;
	const PacedPacketInfo kPacingInfo0(0, kNumProbesCluster0, 2000);
	const PacedPacketInfo kPacingInfo1(1, kNumProbesCluster1, 4000);
	constexpr float kTargetUtilizationFraction = 0.95f;
	} // namespace

	TEST_F(DelayBasedBweTest, ProbeDetection) {
	int64_t now_ms = clock_.TimeInMilliseconds();

	// First burst sent at 8 * 1000 / 10 = 800 kbps.
	for (int i = 0; i < kNumProbesCluster0; ++i) {
	clock_.AdvanceTimeMilliseconds(10);
	now_ms = clock_.TimeInMilliseconds();
	IncomingFeedback(now_ms, now_ms, 1000, kPacingInfo0);
	}
	EXPECT_TRUE(bitrate_observer_.updated());

	// Second burst sent at 8 * 1000 / 5 = 1600 kbps.
	for (int i = 0; i < kNumProbesCluster1; ++i) {
	clock_.AdvanceTimeMilliseconds(5);
	now_ms = clock_.TimeInMilliseconds();
	IncomingFeedback(now_ms, now_ms, 1000, kPacingInfo1);
	}

	EXPECT_TRUE(bitrate_observer_.updated());
	EXPECT_GT(bitrate_observer_.latest_bitrate(), 1500000u);
	}

	TEST_F(DelayBasedBweTest, ProbeDetectionNonPacedPackets) {
	int64_t now_ms = clock_.TimeInMilliseconds();
	// First burst sent at 8 * 1000 / 10 = 800 kbps, but with every other packet
	// not being paced which could mess things up.
	for (int i = 0; i < kNumProbesCluster0; ++i) {
	clock_.AdvanceTimeMilliseconds(5);
	now_ms = clock_.TimeInMilliseconds();
	IncomingFeedback(now_ms, now_ms, 1000, kPacingInfo0);
	// Non-paced packet, arriving 5 ms after.
	clock_.AdvanceTimeMilliseconds(5);
	IncomingFeedback(now_ms, now_ms, 100, PacedPacketInfo());
	}

	EXPECT_TRUE(bitrate_observer_.updated());
	EXPECT_GT(bitrate_observer_.latest_bitrate(), 800000u);
	}

	TEST_F(DelayBasedBweTest, ProbeDetectionFasterArrival) {
	int64_t now_ms = clock_.TimeInMilliseconds();
	// First burst sent at 8 * 1000 / 10 = 800 kbps.
	// Arriving at 8 * 1000 / 5 = 1600 kbps.
	int64_t send_time_ms = 0;
	for (int i = 0; i < kNumProbesCluster0; ++i) {
	clock_.AdvanceTimeMilliseconds(1);
	send_time_ms += 10;
	now_ms = clock_.TimeInMilliseconds();
	IncomingFeedback(now_ms, send_time_ms, 1000, kPacingInfo0);
	}

	EXPECT_FALSE(bitrate_observer_.updated());
	}

	TEST_F(DelayBasedBweTest, ProbeDetectionSlowerArrival) {
	int64_t now_ms = clock_.TimeInMilliseconds();
	// First burst sent at 8 * 1000 / 5 = 1600 kbps.
	// Arriving at 8 * 1000 / 7 = 1142 kbps.
	// Since the receive rate is significantly below the send rate, we expect to
	// use 95% of the estimated capacity.
	int64_t send_time_ms = 0;
	for (int i = 0; i < kNumProbesCluster1; ++i) {
	clock_.AdvanceTimeMilliseconds(7);
	send_time_ms += 5;
	now_ms = clock_.TimeInMilliseconds();
	IncomingFeedback(now_ms, send_time_ms, 1000, kPacingInfo1);
	}

	EXPECT_TRUE(bitrate_observer_.updated());
	EXPECT_NEAR(bitrate_observer_.latest_bitrate(),
	kTargetUtilizationFraction * 1140000u, 10000u);
	}

	TEST_F(DelayBasedBweTest, ProbeDetectionSlowerArrivalHighBitrate) {
	int64_t now_ms = clock_.TimeInMilliseconds();
	// Burst sent at 8 * 1000 / 1 = 8000 kbps.
	// Arriving at 8 * 1000 / 2 = 4000 kbps.
	// Since the receive rate is significantly below the send rate, we expect to
	// use 95% of the estimated capacity.
	int64_t send_time_ms = 0;
	for (int i = 0; i < kNumProbesCluster1; ++i) {
	clock_.AdvanceTimeMilliseconds(2);
	send_time_ms += 1;
	now_ms = clock_.TimeInMilliseconds();
	IncomingFeedback(now_ms, send_time_ms, 1000, kPacingInfo1);
	}

	EXPECT_TRUE(bitrate_observer_.updated());
	EXPECT_NEAR(bitrate_observer_.latest_bitrate(),
	kTargetUtilizationFraction * 4000000u, 10000u);
	}

	TEST_F(DelayBasedBweTest, GetExpectedBwePeriodMs) {
	auto default_interval = bitrate_estimator_->GetExpectedBwePeriod();
	EXPECT_GT(default_interval.ms(), 0);
	CapacityDropTestHelper(1, true, 333, 0);
	auto interval = bitrate_estimator_->GetExpectedBwePeriod();
	EXPECT_GT(interval.ms(), 0);
	EXPECT_NE(interval.ms(), default_interval.ms());
	}

	TEST_F(DelayBasedBweTest, InitialBehavior) {
	InitialBehaviorTestHelper(730000);
	}

	TEST_F(DelayBasedBweTest, InitializeResult) {
	DelayBasedBwe::Result result;
	EXPECT_EQ(result.delay_detector_state, BandwidthUsage::kBwNormal);
	}

	TEST_F(DelayBasedBweTest, RateIncreaseReordering) {
	RateIncreaseReorderingTestHelper(730000);
	}
	TEST_F(DelayBasedBweTest, RateIncreaseRtpTimestamps) {
	RateIncreaseRtpTimestampsTestHelper(622);
	}

	TEST_F(DelayBasedBweTest, CapacityDropOneStream) {
	CapacityDropTestHelper(1, false, 300, 0);
	}

	TEST_F(DelayBasedBweTest, CapacityDropPosOffsetChange) {
	CapacityDropTestHelper(1, false, 867, 30000);
	}

	TEST_F(DelayBasedBweTest, CapacityDropNegOffsetChange) {
	CapacityDropTestHelper(1, false, 933, -30000);
	}

	TEST_F(DelayBasedBweTest, CapacityDropOneStreamWrap) {
	CapacityDropTestHelper(1, true, 333, 0);
	}

	TEST_F(DelayBasedBweTest, TestTimestampGrouping) {
	TestTimestampGroupingTestHelper();
	}

	TEST_F(DelayBasedBweTest, TestShortTimeoutAndWrap) {
	// Simulate a client leaving and rejoining the call after 35 seconds. This
	// will make abs send time wrap, so if streams aren't timed out properly
	// the next 30 seconds of packets will be out of order.
	TestWrappingHelper(35);
	}

	TEST_F(DelayBasedBweTest, TestLongTimeoutAndWrap) {
	// Simulate a client leaving and rejoining the call after some multiple of
	// 64 seconds later. This will cause a zero difference in abs send times due
	// to the wrap, but a big difference in arrival time, if streams aren't
	// properly timed out.
	TestWrappingHelper(10 * 64);
	}

	TEST_F(DelayBasedBweTest, TestInitialOveruse) {
	const DataRate kStartBitrate = DataRate::KilobitsPerSec(300);
	const DataRate kInitialCapacity = DataRate::KilobitsPerSec(200);
	const uint32_t kDummySsrc = 0;
	// High FPS to ensure that we send a lot of packets in a short time.
	const int kFps = 90;

	stream_generator_->AddStream(new test::RtpStream(kFps, kStartBitrate.bps()));
	stream_generator_->set_capacity_bps(kInitialCapacity.bps());

	// Needed to initialize the AimdRateControl.
	bitrate_estimator_->SetStartBitrate(kStartBitrate);

	// Produce 30 frames (in 1/3 second) and give them to the estimator.
	int64_t bitrate_bps = kStartBitrate.bps();
	bool seen_overuse = false;
	for (int i = 0; i < 30; ++i) {
	bool overuse = GenerateAndProcessFrame(kDummySsrc, bitrate_bps);
	// The purpose of this test is to ensure that we back down even if we don't
	// have any acknowledged bitrate estimate yet. Hence, if the test works
	// as expected, we should not have a measured bitrate yet.
	EXPECT_FALSE(acknowledged_bitrate_estimator_->bitrate().has_value());
	if (overuse) {
	EXPECT_TRUE(bitrate_observer_.updated());
	EXPECT_NEAR(bitrate_observer_.latest_bitrate(), kStartBitrate.bps() / 2,
	15000);
	bitrate_bps = bitrate_observer_.latest_bitrate();
	seen_overuse = true;
	break;
	} else if (bitrate_observer_.updated()) {
	bitrate_bps = bitrate_observer_.latest_bitrate();
	bitrate_observer_.Reset();
	}
	}
	EXPECT_TRUE(seen_overuse);
	EXPECT_NEAR(bitrate_observer_.latest_bitrate(), kStartBitrate.bps() / 2,
	15000);
	}

	TEST_F(DelayBasedBweTest, TestTimestampPrecisionHandling) {
	// This test does some basic checks to make sure that timestamps with higher
	// than millisecond precision are handled properly and do not cause any
	// problems in the estimator. Specifically, previously reported in
	// webrtc:14023 and described in more details there, the rounding to the
	// nearest milliseconds caused discrepancy in the accumulated delay. This lead
	// to false-positive overuse detection.
	// Technical details of the test:
	// Send times(ms): 0.000, 9.725, 20.000, 29.725, 40.000, 49.725, ...
	// Recv times(ms): 0.500, 10.000, 20.500, 30.000, 40.500, 50.000, ...
	// Send deltas(ms): 9.750, 10.250, 9.750, 10.250, 9.750, ...
	// Recv deltas(ms): 9.500, 10.500, 9.500, 10.500, 9.500, ...
	// There is no delay building up between the send times and the receive times,
	// therefore this case should never lead to an overuse detection. However, if
	// the time deltas were accidentally rounded to the nearest milliseconds, then
	// all the send deltas would be equal to 10ms while some recv deltas would
	// round up to 11ms which would lead in a false illusion of delay build up.
	uint32_t last_bitrate = bitrate_observer_.latest_bitrate();
	for (int i = 0; i < 1000; ++i) {
	clock_.AdvanceTimeMicroseconds(500);
	IncomingFeedback(clock_.CurrentTime(),
	clock_.CurrentTime() - TimeDelta::Micros(500), 1000,
	PacedPacketInfo());
	clock_.AdvanceTimeMicroseconds(9500);
	IncomingFeedback(clock_.CurrentTime(),
	clock_.CurrentTime() - TimeDelta::Micros(250), 1000,
	PacedPacketInfo());
	clock_.AdvanceTimeMicroseconds(10000);

	// The bitrate should never decrease in this test.
	EXPECT_LE(last_bitrate, bitrate_observer_.latest_bitrate());
	last_bitrate = bitrate_observer_.latest_bitrate();
	}
	}

	class DelayBasedBweTestWithBackoffTimeoutExperiment : public DelayBasedBweTest {
	public:
	DelayBasedBweTestWithBackoffTimeoutExperiment()
	: DelayBasedBweTest(
	"WebRTC-BweAimdRateControlConfig/initial_backoff_interval:200ms/") {
	}
	};

	// This test subsumes and improves DelayBasedBweTest.TestInitialOveruse above.
	TEST_F(DelayBasedBweTestWithBackoffTimeoutExperiment, TestInitialOveruse) {
	const DataRate kStartBitrate = DataRate::KilobitsPerSec(300);
	const DataRate kInitialCapacity = DataRate::KilobitsPerSec(200);
	const uint32_t kDummySsrc = 0;
	// High FPS to ensure that we send a lot of packets in a short time.
	const int kFps = 90;

	stream_generator_->AddStream(new test::RtpStream(kFps, kStartBitrate.bps()));
	stream_generator_->set_capacity_bps(kInitialCapacity.bps());

	// Needed to initialize the AimdRateControl.
	bitrate_estimator_->SetStartBitrate(kStartBitrate);

	// Produce 30 frames (in 1/3 second) and give them to the estimator.
	int64_t bitrate_bps = kStartBitrate.bps();
	bool seen_overuse = false;
	for (int frames = 0; frames < 30 && !seen_overuse; ++frames) {
	bool overuse = GenerateAndProcessFrame(kDummySsrc, bitrate_bps);
	// The purpose of this test is to ensure that we back down even if we don't
	// have any acknowledged bitrate estimate yet. Hence, if the test works
	// as expected, we should not have a measured bitrate yet.
	EXPECT_FALSE(acknowledged_bitrate_estimator_->bitrate().has_value());
	if (overuse) {
	EXPECT_TRUE(bitrate_observer_.updated());
	EXPECT_NEAR(bitrate_observer_.latest_bitrate(), kStartBitrate.bps() / 2,
	15000);
	bitrate_bps = bitrate_observer_.latest_bitrate();
	seen_overuse = true;
	} else if (bitrate_observer_.updated()) {
	bitrate_bps = bitrate_observer_.latest_bitrate();
	bitrate_observer_.Reset();
	}
	}
	EXPECT_TRUE(seen_overuse);
	// Continue generating an additional 15 frames (equivalent to 167 ms) and
	// verify that we don't back down further.
	for (int frames = 0; frames < 15 && seen_overuse; ++frames) {
	bool overuse = GenerateAndProcessFrame(kDummySsrc, bitrate_bps);
	EXPECT_FALSE(overuse);
	if (bitrate_observer_.updated()) {
	bitrate_bps = bitrate_observer_.latest_bitrate();
	EXPECT_GE(bitrate_bps, kStartBitrate.bps() / 2 - 15000);
	EXPECT_LE(bitrate_bps, kInitialCapacity.bps() + 15000);
	bitrate_observer_.Reset();
	}
	}
	}

	} // namespace webrtc