Prevent BWE rampdowns without new loss reports.

webrtc/modules/bitrate_controller/send_side_bandwidth_estimation_unittest.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.
  */
 
@@ skipping 26 matching lines @@
   EXPECT_EQ(kRembBps, bitrate);
 
   // Second REMB doesn't apply immediately.
   now_ms += 2001;
   bwe.UpdateReceiverEstimate(now_ms, kSecondRembBps);
   bwe.UpdateEstimate(now_ms);
   bitrate = 0;
   bwe.CurrentEstimate(&bitrate, &fraction_loss, &rtt);
   EXPECT_EQ(kRembBps, bitrate);
 }
+
+TEST(SendSideBweTest, DoesntReapplyBitrateDecreaseWithoutFollowingRemb) {
+  SendSideBandwidthEstimation bwe;
+  static const int kMinBitrateBps = 100000;
+  static const int kInitialBitrateBps = 1000000;
+  bwe.SetMinMaxBitrate(kMinBitrateBps, 1500000);
+  bwe.SetSendBitrate(kInitialBitrateBps);
+
+  static const uint8_t kFractionLoss = 128;
+  static const int64_t kRttMs = 50;
+
+  int64_t now_ms = 0;
+  int bitrate_bps;
+  uint8_t fraction_loss;
+  int64_t rtt_ms;
+  bwe.CurrentEstimate(&bitrate_bps, &fraction_loss, &rtt_ms);
+  EXPECT_EQ(kInitialBitrateBps, bitrate_bps);
+  EXPECT_EQ(0, fraction_loss);
+  EXPECT_EQ(0, rtt_ms);
+
+  // Signal heavy loss to go down in bitrate.
+  bwe.UpdateReceiverBlock(kFractionLoss, kRttMs, 100, now_ms);
+  // Trigger an update 2 seconds later to not be rate limited.
+  now_ms += 2000;
+  bwe.UpdateEstimate(now_ms);
+
+  bwe.CurrentEstimate(&bitrate_bps, &fraction_loss, &rtt_ms);
+  EXPECT_LT(bitrate_bps, kInitialBitrateBps);
+  // Verify that the obtained bitrate isn't hitting the min bitrate, or this
+  // test doesn't make sense. If this ever happens, update the thresholds or
+  // loss rates so that it doesn't hit min bitrate after one bitrate update.
+  EXPECT_GT(bitrate_bps, kMinBitrateBps);
+  EXPECT_EQ(kFractionLoss, fraction_loss);
+  EXPECT_EQ(kRttMs, rtt_ms);
+
+  // Triggering an update shouldn't apply further downgrade nor upgrade since
+  // there's no intermediate receiver block received indicating whether this is
+  // currently good or not.
+  int last_bitrate_bps = bitrate_bps;
+  // Trigger an update 2 seconds later to not be rate limited (but it still
+  // shouldn't update).
+  now_ms += 2000;
+  bwe.UpdateEstimate(now_ms);
+  bwe.CurrentEstimate(&bitrate_bps, &fraction_loss, &rtt_ms);
+
+  EXPECT_EQ(last_bitrate_bps, bitrate_bps);
+  // The old loss rate should still be applied though.
+  EXPECT_EQ(kFractionLoss, fraction_loss);
+  EXPECT_EQ(kRttMs, rtt_ms);
+}
+
 }  // namespace webrtc