From 0a5e12b07d920cc57cba9e1555ea295cece0ab5d Mon Sep 17 00:00:00 2001
From: Per Kjellander <perkj@webrtc.org>
Date: Fri, 18 Mar 2022 15:13:52 +0100
Subject: [PATCH] Reland "Apply lower bound of delay based estimate in
 AimdRateControl::ClampBitrate"

This reverts commit 865d94e45258c9c8876ea4cbdd5dade510cb7d93.

First patch is the same as original cl. Second patch includes a fix to ensure the clamped bitrate does not increase to 85% of the last network estimate.

Bug: none
Change-Id: Idf1b2af3fb60c0d392c48c1b6c0d8526f900f9d6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/256016
Reviewed-by: Diep Bui <diepbp@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36270}
---
 .../aimd_rate_control.cc                      | 12 +++++----
 .../aimd_rate_control_unittest.cc             | 27 ++++++++++++++++++-
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/modules/remote_bitrate_estimator/aimd_rate_control.cc b/modules/remote_bitrate_estimator/aimd_rate_control.cc
index 1714dd115a..3297df9c83 100644
--- a/modules/remote_bitrate_estimator/aimd_rate_control.cc
+++ b/modules/remote_bitrate_estimator/aimd_rate_control.cc
@@ -338,11 +338,6 @@ void AimdRateControl::ChangeBitrate(const RateControlInput& input,
           decreased_bitrate = beta_ * link_capacity_.estimate();
         }
       }
-      if (estimate_bounded_backoff_ && network_estimate_) {
-        decreased_bitrate = std::max(
-            decreased_bitrate, network_estimate_->link_capacity_lower * beta_);
-      }
-
       // Avoid increasing the rate when over-using.
       if (decreased_bitrate < current_bitrate_) {
         new_bitrate = decreased_bitrate;
@@ -386,6 +381,13 @@ DataRate AimdRateControl::ClampBitrate(DataRate new_bitrate) const {
     }
     new_bitrate = std::min(upper_bound, new_bitrate);
   }
+  if (estimate_bounded_backoff_ && network_estimate_ &&
+      network_estimate_->link_capacity_lower.IsFinite() &&
+      new_bitrate < current_bitrate_) {
+    new_bitrate = std::min(
+        current_bitrate_,
+        std::max(new_bitrate, network_estimate_->link_capacity_lower * beta_));
+  }
   new_bitrate = std::max(new_bitrate, min_configured_bitrate_);
   return new_bitrate;
 }
diff --git a/modules/remote_bitrate_estimator/aimd_rate_control_unittest.cc b/modules/remote_bitrate_estimator/aimd_rate_control_unittest.cc
index 5d9c328e06..1fe5799545 100644
--- a/modules/remote_bitrate_estimator/aimd_rate_control_unittest.cc
+++ b/modules/remote_bitrate_estimator/aimd_rate_control_unittest.cc
@@ -255,7 +255,7 @@ TEST(AimdRateControlTest, SetEstimateIncreaseBweInAlr) {
             2 * kInitialBitrateBps);
 }
 
-TEST(AimdRateControlTest, SetEstimateClampedByNetworkEstimate) {
+TEST(AimdRateControlTest, SetEstimateUpperLimitedByNetworkEstimate) {
   auto states = CreateAimdRateControlStates(/*send_side=*/true);
   NetworkStateEstimate network_estimate;
   network_estimate.link_capacity_upper = DataRate::KilobitsPerSec(400);
@@ -265,6 +265,31 @@ TEST(AimdRateControlTest, SetEstimateClampedByNetworkEstimate) {
             network_estimate.link_capacity_upper);
 }
 
+TEST(AimdRateControlTest, SetEstimateLowerLimitedByNetworkEstimate) {
+  auto states = CreateAimdRateControlStates(/*send_side=*/true);
+  NetworkStateEstimate network_estimate;
+  network_estimate.link_capacity_lower = DataRate::KilobitsPerSec(400);
+  states.aimd_rate_control->SetNetworkStateEstimate(network_estimate);
+  SetEstimate(states, 100'000);
+  // 0.85 is default backoff factor. (`beta_`)
+  EXPECT_EQ(states.aimd_rate_control->LatestEstimate(),
+            network_estimate.link_capacity_lower * 0.85);
+}
+
+TEST(AimdRateControlTest,
+     SetEstimateIgnoredIfLowerThanNetworkEstimateAndCurrent) {
+  auto states = CreateAimdRateControlStates(/*send_side=*/true);
+  SetEstimate(states, 200'000);
+  ASSERT_EQ(states.aimd_rate_control->LatestEstimate().kbps(), 200);
+  NetworkStateEstimate network_estimate;
+  network_estimate.link_capacity_lower = DataRate::KilobitsPerSec(400);
+  states.aimd_rate_control->SetNetworkStateEstimate(network_estimate);
+  // Ignore the next SetEstimate, since the estimate is lower than 85% of
+  // the network estimate.
+  SetEstimate(states, 100'000);
+  EXPECT_EQ(states.aimd_rate_control->LatestEstimate().kbps(), 200);
+}
+
 TEST(AimdRateControlTest, SetEstimateIgnoresNetworkEstimatesLowerThanCurrent) {
   test::ScopedFieldTrials override_field_trials(
       "WebRTC-Bwe-EstimateBoundedIncrease/"