Add TransportFeedbackPacketLossTracker.

webrtc/voice_engine/transport_feedback_packet_loss_tracker_unittest.cc

Index: webrtc/voice_engine/transport_feedback_packet_loss_tracker_unittest.cc
diff --git a/webrtc/voice_engine/transport_feedback_packet_loss_tracker_unittest.cc b/webrtc/voice_engine/transport_feedback_packet_loss_tracker_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3706fca748f3d0a40ef1097db02b97e64e497293
--- /dev/null
+++ b/webrtc/voice_engine/transport_feedback_packet_loss_tracker_unittest.cc
@@ -0,0 +1,719 @@
+/*
+ *  Copyright (c) 2015 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 <limits>
+#include <memory>
+#include <vector>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/mod_ops.h"
+#include "webrtc/modules/rtp_rtcp/mocks/mock_transport_feedback.h"
+#include "webrtc/test/gmock.h"
+#include "webrtc/test/gtest.h"
+#include "webrtc/voice_engine/transport_feedback_packet_loss_tracker.h"
+
+using webrtc::rtcp::MockTransportFeedback;
+using webrtc::rtcp::TransportFeedback;
+using testing::Return;
+using testing::StrictMock;
+
+namespace webrtc {
+
+namespace {
+
+constexpr size_t kMaxConsecutiveOldReports = 4;
+
+// All tests are run multiple times with various baseline sequence number,
+// to weed out potential bugs with wrap-around handling.
+constexpr uint16_t kBases[] = {0x0000, 0x3456, 0xc032, 0xfffe};
+
+void AddTransportFeedbackAndValidate(
+    TransportFeedbackPacketLossTracker* tracker,
+    uint16_t base_sequence_num,
+    const std::vector<bool>& reception_status_vec) {
+  std::vector<TransportFeedback::StatusSymbol> statuses;
+  for (bool status : reception_status_vec) {
+    if (!status) {
+      statuses.push_back(TransportFeedback::StatusSymbol::kNotReceived);
+    } else {
+      // |kReceivedSmallDelta| and |kReceivedLargeDelta| make no difference to
+      // TransportFeedbackPacketLossTracker. So we test only one case.
+      statuses.push_back(TransportFeedback::StatusSymbol::kReceivedSmallDelta);
+    }
+  }
+  StrictMock<MockTransportFeedback> mock_feedback;
+  EXPECT_CALL(mock_feedback, GetBaseSequence())
+      .WillOnce(Return(base_sequence_num));
+  EXPECT_CALL(mock_feedback, GetStatusVector()).WillOnce(Return(statuses));
+  tracker->OnReceivedTransportFeedback(mock_feedback);
+  tracker->Validate();
+}
+
+}  // namespace
+
+// Sanity check on an empty window.
+TEST(TransportFeedbackPacketLossTrackerTest, EmptyWindow) {
+  std::unique_ptr<TransportFeedback> feedback;
+  float plr = 0.0f;   // Packet-loss-rate
+  float cplr = 0.0f;  // Consecutive-packet-loss-rate
+
+  TransportFeedbackPacketLossTracker tracker(5, 10);
+
+  // PLR and CPLR reported as unknown before reception of first feedback.
+  EXPECT_FALSE(tracker.GetPacketLossRates(&plr, &cplr));
+}
+
+// Sanity check on partially filled window.
+TEST(TransportFeedbackPacketLossTrackerTest, PartiallyFilledWindow) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // PLR and CPLR reported as unknown before minimum window size reached.
+    // Expected window contents: [] -> [1001].
+    AddTransportFeedbackAndValidate(&tracker, base, {true, false, false, true});
+    EXPECT_FALSE(tracker.GetPacketLossRates(&plr, &cplr));
+  }
+}
+
+// Sanity check on minimum filled window.
+TEST(TransportFeedbackPacketLossTrackerTest, MinimumFilledWindow) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // PLR and CPLR correctly calculated after minimum window size reached.
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 5.0f);
+    EXPECT_EQ(cplr, 1.0f / 5.0f);
+  }
+}
+
+// Additional reports update PLR and CPLR.
+TEST(TransportFeedbackPacketLossTrackerTest, ExtendWindow) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Expected window contents: [10011] -> [10011-10101].
+    AddTransportFeedbackAndValidate(&tracker, base + 5,
+                                    {true, false, true, false, true});
+
+    // Expected window contents: [10011-10101] -> [10011-10101-10001].
+    AddTransportFeedbackAndValidate(&tracker, base + 10,
+                                    {true, false, false, false, true});
+
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 7.0f / 15.0f);
+    EXPECT_EQ(cplr, 3.0f / 15.0f);
+  }
+}
+
+TEST(TransportFeedbackPacketLossTrackerTest, AllReceived) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // PLR and CPLR correctly calculated after minimum window size reached.
+    // Expected window contents: [] -> [11111].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, true, true, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 0.0f);
+    EXPECT_EQ(cplr, 0.0f);
+  }
+}
+
+TEST(TransportFeedbackPacketLossTrackerTest, AllLost) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // PLR and CPLR correctly calculated after minimum window size reached.
+    // Expected window contents: [] -> [00000].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {false, false, false, false, false});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 5.0f / 5.0f);
+    EXPECT_EQ(cplr, 4.0f / 5.0f);
+  }
+}
+
+// Repeated reports are ignored.
+TEST(TransportFeedbackPacketLossTrackerTest, ReportRepetition) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Repeat entire previous feedback
+    // Expected window contents: [10011] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 5.0f);
+    EXPECT_EQ(cplr, 1.0f / 5.0f);
+  }
+}
+
+// Report overlap.
+TEST(TransportFeedbackPacketLossTrackerTest, ReportOverlap) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Expected window contents: [10011] -> [10011-01].
+    AddTransportFeedbackAndValidate(&tracker, base + 3,
+                                    {true, true, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 3.0f / 7.0f);
+    EXPECT_EQ(cplr, 1.0f / 7.0f);
+  }
+}
+
+// Report conflict.
+TEST(TransportFeedbackPacketLossTrackerTest, ReportConflict) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // Expected window contents: [] -> [01001].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {false, true, false, false, true});
+
+    // Expected window contents: [01001] -> [11101].
+    // While false->true will be applied, true -> false will be ignored.
+    AddTransportFeedbackAndValidate(&tracker, base, {true, false, true});
+
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 1.0f / 5.0f);
+    EXPECT_EQ(cplr, 0.0f / 5.0f);
+  }
+}
+
+// Skipped packets treated as unknown (not lost).
+TEST(TransportFeedbackPacketLossTrackerTest, SkippedPackets) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 10);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Expected window contents: [10011] -> [10011-101].
+    AddTransportFeedbackAndValidate(&tracker, base + 100, {true, false, true});
+
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 3.0f / 8.0f);
+    EXPECT_EQ(cplr, 1.0f / 8.0f);
+  }
+}
+
+// The window retain information up to the configured max-window-size, but
+// starts discarding after that.
+TEST(TransportFeedbackPacketLossTrackerTest, MaxWindowSize) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(10, 10);
+
+    // Expected window contents: [] -> [10101-00001].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, true, false, true, false, false, false, false, true});
+
+    // Up to max-window-size retained.
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 6.0f / 10.0f);
+    EXPECT_EQ(cplr, 3.0f / 10.0f);
+
+    // Expected window contents: [10101-00001] -> [00001-10111].
+    AddTransportFeedbackAndValidate(&tracker, base + 10,
+                                    {true, false, true, true, true});
+
+    // After max-window-size, older entries discarded to accommodate newer ones.
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 5.0f / 10.0f);
+    EXPECT_EQ(cplr, 3.0f / 10.0f);
+  }
+}
+
+// Inserting into the middle of a full window works correctly.
+TEST(TransportFeedbackPacketLossTrackerTest, InsertIntoMiddle) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(10, 10);
+
+    // Expected window contents: [] -> [10101].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, true, false, true});
+
+    // Expected window contents: [10101] -> [10101-10001].
+    AddTransportFeedbackAndValidate(&tracker, base + 100,
+                                    {true, false, false, false, true});
+
+    // Setup sanity
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 5.0f / 10.0f);
+    EXPECT_EQ(cplr, 2.0f / 10.0f);
+
+    // Insert into the middle of this full window - it discards the older data.
+    // Expected window contents: [10101-10001] -> [11111-10001].
+    AddTransportFeedbackAndValidate(&tracker, base + 50,
+                                    {true, true, true, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 3.0f / 10.0f);
+    EXPECT_EQ(cplr, 2.0f / 10.0f);
+  }
+}
+
+// Entries in the second quadrant treated like those in the first.
+// The sequence number is used in a looped manner. 0xFFFF is followed by 0x0000.

[kwiberg-webrtc, 2017/01/05 02:51:12]

I think the usual term is "wrapped", as in "after 0xffff, the sequence number
wraps back to 0x0000".

[minyue-webrtc, 2017/01/19 10:57:55]

the word was chosen to explain why "quadrant", as a name, makes sense. I now
change "looped" to "circular", and see if that reads easier.

+// In many tests, we divide the circle of sequence number into 4 quadrants, and
+// verify the behavior of TransportFeedbackPacketLossTracker over them.

[kwiberg-webrtc, 2017/01/05 02:51:12]

So each quadrant is 14 bits' worth of sequence numbers? With no fixed position
(i.e. the first quadrant being 0x0000-0x3ffff, etc.) because the absolute offset
doesn't matter? Probably worth spelling out (especially if I still got it
wrong!).

[minyue-webrtc, 2017/01/19 10:57:55]

I updated the wording here. See if that helps.

+TEST(TransportFeedbackPacketLossTrackerTest, SecondQuadrant) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Window *does* get updated with inputs from quadrant #2.
+    // Expected window contents: [10011] -> [10011-1].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x4321, {true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 6.0f);
+    EXPECT_EQ(cplr, 1.0f / 6.0f);
+
+    // Correct recognition of quadrant #2: up to, but not including, base +
+    // 0x8000
+    // Expected window contents: [10011-1] -> [10011-11].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x7fff, {true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 7.0f);
+    EXPECT_EQ(cplr, 1.0f / 7.0f);
+  }
+}
+
+// Insertion into the third quadrant moves the base of the window.
+TEST(TransportFeedbackPacketLossTrackerTest, ThirdQuadrantMovesBase) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Seed the test.
+    // Expected window contents: [] -> [10011-01].
+    AddTransportFeedbackAndValidate(
+        &tracker, base, {true, false, false, true, true, false, true});
+
+    // Quadrant #3 begins at base + 0x8000. It triggers moving the window so
+    // that
+    // at least one (oldest) report shifts out of window.
+    // Expected window contents: [10011-01] -> [10110-01].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8000,
+                                    {true, false, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 3.0f / 7.0f);
+    EXPECT_EQ(cplr, 1.0f / 7.0f);
+
+    // The base can move more than once, because the minimum quadrant-1 packets
+    // were dropped out of the window, and some remain.
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8000 + 4, {true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 7.0f);
+    EXPECT_EQ(cplr, 1.0f / 7.0f);
+  }
+}
+
+// After the base has moved due to insertion into the third quadrant, it is
+// still possible to insert into the middle of the window and obtain the correct
+// PLR and CPLR. Insertion into the middle before the max window size has been
+// achieved does not cause older packets to be dropped.
+TEST(TransportFeedbackPacketLossTrackerTest, InsertIntoMiddleAfterBaseMove) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Seed the test.
+    // Expected window contents: [] -> [10011-01].
+    AddTransportFeedbackAndValidate(
+        &tracker, base, {true, false, false, true, true, false, true});
+
+    // Expected window contents: [10011-01] -> [10110-01].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8000,
+                                    {true, false, false, true});
+
+    // Inserting into the middle still works after the base has shifted.
+    // Expected window contents: [10110-01] -> [10110-01011-001].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x5000,
+                                    {true, false, false, true, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 6.0f / 13.0f);
+    EXPECT_EQ(cplr, 2.0f / 13.0f);
+
+    // The base can keep moving after inserting into the middle.
+    // Expected window contents: [10110-01011-001] -> [11001-01100-111].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8000 + 4, {true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 5.0f / 13.0f);
+    EXPECT_EQ(cplr, 2.0f / 13.0f);
+  }
+}
+
+// After moving the base of the window, the max window size is still observed.
+TEST(TransportFeedbackPacketLossTrackerTest, ThirdQuadrantObservesMaxWindow) {

[kwiberg-webrtc, 2017/01/05 02:51:12]

Aha, who's the eagle eye, I wonder...

+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(10, 15);
+
+    // Expected window contents: [] -> [10011-10101].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, false, true, true, true, false, true, false, true});
+
+    // Expected window contents: [10011-10101] -> [11101-01101].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8000,
+                                    {true, false, true});
+
+    // Push into middle until max window is reached.
+    // Expected window contents: [11101-01101] -> [11101-01100-01101].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x4000,
+                                    {true, false, false, false, true});
+
+    // Setup sanity
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 6.0f / 15.0f);
+    EXPECT_EQ(cplr, 2.0f / 15.0f);
+
+    // Pushing new packets into the middle would discard older packets.
+    // Expected window contents: [11101-01100-01101] -> [01011-00011-01101].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x4000 + 5,
+                                    {true, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 7.0f / 15.0f);
+    EXPECT_EQ(cplr, 2.0f / 15.0f);
+  }
+}
+
+// A new feedback in quadrant #3 might shift enough old feedbacks out of window,
+// that we'd go back to an unknown PLR and CPLR.
+TEST(TransportFeedbackPacketLossTrackerTest, QuadrantThreeMovedBaseMinWindow) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011-10101].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, false, true, true, true, false, true, false, true});
+    EXPECT_TRUE(
+        tracker.GetPacketLossRates(&plr, &cplr));  // Min window reached.
+
+    // A new feedback in quadrant #3 might shift enough old feedbacks out of
+    // window, that we'd go back to an unknown PLR and CPLR. This *doesn't*
+    // necessarily mean all of the old ones were discarded, though.
+    // Expected window contents: [10011-10101] -> [0111].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8006, {true, true});
+    EXPECT_FALSE(tracker.GetPacketLossRates(&plr, &cplr));
+
+    // Inserting in the middle shows that though some of the elements were
+    // ejected, some were retained.
+    // Expected window contents: [] -> [01101-11].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x4000,
+                                    {true, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 7.0f);
+    EXPECT_EQ(cplr, 0.0f / 7.0f);
+  }
+}
+
+// Quadrant four reports ignored for up to kMaxConsecutiveOldReports times.
+TEST(TransportFeedbackPacketLossTrackerTest, QuadrantFourInitiallyIgnored) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Feedbacks in quadrant #4 are discarded (up to kMaxConsecutiveOldReports
+    // consecutive reports).
+    // Expected window contents: [10011] -> [10011].
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000, {true, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 2.0f / 5.0f);
+      EXPECT_EQ(cplr, 1.0f / 5.0f);
+    }
+  }
+}
+
+// Receiving a packet from quadrant #1 resets the counter for quadrant #4.
+TEST(TransportFeedbackPacketLossTrackerTest, QuadrantFourCounterResetByQ1) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Feedbacks in quadrant #4 are discarded (up to kMaxConsecutiveOldReports
+    // consecutive reports).
+    // Expected window contents: [10011] -> [10011].
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000, {true, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 2.0f / 5.0f);
+      EXPECT_EQ(cplr, 1.0f / 5.0f);
+    }
+
+    // If we receive a feedback in quadrant #1, the above counter is reset.
+    // Expected window contents: [10011] -> [10011-1].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x000f, {true});
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      // Note: though the feedback message reports three packets, it only gets
+      // counted once.
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000,
+                                      {true, false, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 2.0f / 6.0f);
+      EXPECT_EQ(cplr, 1.0f / 6.0f);
+    }
+  }
+}
+
+// Receiving a packet from quadrant #2 resets the counter for quadrant #4.
+TEST(TransportFeedbackPacketLossTrackerTest, QuadrantFourCounterResetByQ2) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+
+    // Feedbacks in quadrant #4 are discarded (up to kMaxConsecutiveOldReports
+    // consecutive reports).
+    // Expected window contents: [10011] -> [10011].
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000, {true, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 2.0f / 5.0f);
+      EXPECT_EQ(cplr, 1.0f / 5.0f);
+    }
+
+    // If we receive a feedback in quadrant #1, the above counter is reset.
+    // Expected window contents: [10011] -> [10011-1].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x400f, {true});
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      // Note: though the feedback message reports three packets, it only gets
+      // counted once.
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000,
+                                      {true, false, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 2.0f / 6.0f);
+      EXPECT_EQ(cplr, 1.0f / 6.0f);
+    }
+  }
+}
+
+// Receiving a packet from quadrant #3 resets the counter for quadrant #4.
+TEST(TransportFeedbackPacketLossTrackerTest, QuadrantFourCounterResetByQ3) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011-10001].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, false, true, true, true, false, false, false, true});
+
+    // Feedbacks in quadrant #4 are discarded (up to kMaxConsecutiveOldReports
+    // consecutive reports).
+    // Expected window contents: [10011-10001] -> [10011-10001].
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000, {true, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 5.0f / 10.0f);
+      EXPECT_EQ(cplr, 3.0f / 10.0f);
+    }
+
+    // If we receive a feedback in quadrant #1, the above counter is reset.
+    // Expected window contents: [10011-10001] -> [11100-01111].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x8000,
+                                    {true, true, true});
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      // Note: though the feedback message reports three packets, it only gets
+      // counted once.
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000 + 10,
+                                      {true, false, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 3.0f / 10.0f);
+      EXPECT_EQ(cplr, 2.0f / 10.0f);
+    }
+  }
+}
+
+// Quadrant four reports ignored for up to kMaxConsecutiveOldReports times.
+// After that, the window is reset.
+TEST(TransportFeedbackPacketLossTrackerTest, QuadrantFourReset) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011-10001].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, false, true, true, true, false, false, false, true});
+
+    // The first kMaxConsecutiveOldReports quadrant #4 reports are ignored.
+    // It doesn't matter that they consist of multiple packets - each report
+    // is only counted once.
+    for (size_t i = 0; i < kMaxConsecutiveOldReports; i++) {
+      // Expected window contents: [10011-10001] -> [10011-10001].
+      AddTransportFeedbackAndValidate(&tracker, base + 0xc000,
+                                      {true, true, false, true});
+      EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+      EXPECT_EQ(plr, 5.0f / 10.0f);
+      EXPECT_EQ(cplr, 3.0f / 10.0f);
+    }
+
+    // One additional feedback in quadrant #4 brings us over
+    // kMaxConsecutiveOldReports consecutive "old" reports, resetting the
+    // window.
+    // Note: The report doesn't have to be the same as the previous ones.
+    // Expected window contents: [10011-10001] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base + 0xc000,
+                                    {true, false, false, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+
+    // The new window is not completely empty - it's been seeded with the
+    // packets reported in the feedback that has triggered the reset.
+    EXPECT_EQ(plr, 2.0f / 5.0f);
+    EXPECT_EQ(cplr, 1.0f / 5.0f);
+  }
+}
+
+// Feedbacks spanning multiple quadrant are treated correctly (Q1-Q2).
+TEST(TransportFeedbackPacketLossTrackerTest, MultiQuadrantQ1Q2) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base,
+                                    {true, false, false, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+
+    // A feedback with entries in both quadrant #1 and #2 gets both counted:
+    // Expected window contents: [10011] -> [10011-11].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x3fff, {true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 7.0f);
+    EXPECT_EQ(cplr, 1.0f / 7.0f);
+  }
+}
+
+// Feedbacks spanning multiple quadrant are treated correctly (Q2-Q3).
+TEST(TransportFeedbackPacketLossTrackerTest, MultiQuadrantQ2Q3) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011-00001].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, false, true, true, false, false, false, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 6.0f / 10.0f);
+    EXPECT_EQ(cplr, 4.0f / 10.0f);
+
+    // A feedback with entries in both quadrant #2 and #3 gets both counted,
+    // but only those from #3 trigger throwing out old entries from quadrant #1:
+    // Expected window contents: [10011-00001] -> [01100-00110-01].
+    AddTransportFeedbackAndValidate(&tracker, base + 0x7ffe,
+                                    {true, false, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 7.0f / 12.0f);
+    EXPECT_EQ(cplr, 4.0f / 12.0f);
+  }
+}
+
+// Feedbacks spanning multiple quadrant are treated correctly (Q2-Q3).
+TEST(TransportFeedbackPacketLossTrackerTest, MultiQuadrantQ3Q4) {
+  for (uint16_t base : kBases) {
+    float plr = 0.0f;   // Packet-loss-rate
+    float cplr = 0.0f;  // Consecutive-packet-loss-rate
+
+    TransportFeedbackPacketLossTracker tracker(5, 20);
+
+    // Expected window contents: [] -> [10011-00001].
+    AddTransportFeedbackAndValidate(
+        &tracker, base,
+        {true, false, false, true, true, false, false, false, false, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 6.0f / 10.0f);
+    EXPECT_EQ(cplr, 4.0f / 10.0f);
+
+    // A feedback with entries in both quadrant #3 and #4 would have the entries
+    // from quadrant #3 shift enough quadrant #1 entries out of window, that
+    // by the time the #4 packets are examined, the moving baseline has made
+    // them into quadrant #3 packets.
+    // Expected window contents: [10011-00001] -> [10011].
+    AddTransportFeedbackAndValidate(&tracker, base + 0xbfff,
+                                    {true, false, false, true, true});
+    EXPECT_TRUE(tracker.GetPacketLossRates(&plr, &cplr));
+    EXPECT_EQ(plr, 2.0f / 5.0f);
+    EXPECT_EQ(cplr, 1.0f / 5.0f);
+  }
+}
+
+}  // namespace webrtc