Tweaked version of BBR for WebRTC.

webrtc/modules/remote_bitrate_estimator/test/estimators/congestion_window.cc

 /*
  *  Copyright (c) 2017 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 19 matching lines @@
 const int CongestionWindow::kMinimumCongestionWindowBytes;
 
 CongestionWindow::CongestionWindow() : data_inflight_bytes_(0) {}
 
 CongestionWindow::~CongestionWindow() {}
 
 int CongestionWindow::GetCongestionWindow(BbrBweSender::Mode mode,
                                           int64_t bandwidth_estimate_bps,
                                           rtc::Optional<int64_t> min_rtt_ms,
                                           float gain) {
-  if (mode == BbrBweSender::PROBE_RTT)
-    return CongestionWindow::kMinimumCongestionWindowBytes;

[philipel, 2017/08/17 12:52:27]

Why don't we have a min congestion window any more?

[gnish1, 2017/08/17 15:37:49]

This implementation of BBR doesn't use minimum congestion window, but congestion
window gain of 0.65 instead.

   return GetTargetCongestionWindow(bandwidth_estimate_bps, min_rtt_ms, gain);
 }
 
 void CongestionWindow::PacketSent(size_t sent_packet_size_bytes) {
   data_inflight_bytes_ += sent_packet_size_bytes;
 }
 
 void CongestionWindow::AckReceived(size_t received_packet_size_bytes) {
   data_inflight_bytes_ -= received_packet_size_bytes;
 }
 
 int CongestionWindow::GetTargetCongestionWindow(
     int64_t bandwidth_estimate_bps,
     rtc::Optional<int64_t> min_rtt_ms,
     float gain) {
   // If we have no rtt sample yet, return the starting congestion window size.
   if (!min_rtt_ms)
     return gain * kStartingCongestionWindowBytes;
-  int bdp = *min_rtt_ms * bandwidth_estimate_bps;
+  int bdp = *min_rtt_ms * bandwidth_estimate_bps / 8000;

[philipel, 2017/08/17 12:52:27]

Why do we suddenly measure bandwidth delay product in kB?

[gnish1, 2017/08/17 15:37:49]

Because packet's are measured in bytes, so data_inflight is measured in bytes,
which means congestion window should be measured in bytes as well.

   int congestion_window = bdp * gain;
   // Congestion window could be zero in rare cases, when either no bandwidth
   // estimate is available, or path's min_rtt value is zero.
   if (!congestion_window)
     congestion_window = gain * kStartingCongestionWindowBytes;
-  return std::max(congestion_window,
-                  CongestionWindow::kMinimumCongestionWindowBytes);
+  return congestion_window;
 }
 }  // namespace bwe
 }  // namespace testing
 }  // namespace webrtc