Tweaked version of BBR for WebRTC.

webrtc/modules/pacing/bbr_paced_sender.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.
+ */
+
+#include "webrtc/modules/pacing/bbr_paced_sender.h"
+
+#include <algorithm>
+#include <queue>
+#include <set>
+#include <vector>
+
+#include "webrtc/modules/pacing/paced_sender.h"
+#include "webrtc/system_wrappers/include/clock.h"
+
+namespace webrtc {
+namespace bbr_paced_sender {
+struct Packet {

[philipel, 2017/08/17 12:52:26]

I think you should move this struct into BbrPacedSender and remove the
bbr_paced_sender namespace. Also you can define it in the .h file

[gnish1, 2017/08/17 15:37:48]

Done.

+  Packet(RtpPacketSender::Priority priority,
+         uint32_t ssrc,
+         uint16_t seq_number,
+         int64_t capture_time_ms,
+         int64_t enqueue_time_ms,
+         size_t size_in_bytes,
+         bool retransmission)
+      : priority(priority),
+        ssrc(ssrc),
+        sequence_number(seq_number),
+        capture_time_ms(capture_time_ms),
+        enqueue_time_ms(enqueue_time_ms),
+        size_in_bytes(size_in_bytes),
+        retransmission(retransmission) {}
+  RtpPacketSender::Priority priority;
+  uint32_t ssrc;
+  uint16_t sequence_number;
+  int64_t capture_time_ms;
+  int64_t enqueue_time_ms;
+  size_t size_in_bytes;
+  bool retransmission;
+};
+}  // namespace bbr_paced_sender
+BbrPacedSender::BbrPacedSender(const Clock* clock,
+                               PacedSender::PacketSender* packet_sender,
+                               RtcEventLog* event_log)
+    : clock_(clock),
+      packet_sender_(packet_sender),
+      estimated_bitrate_bps_(100000),
+      min_send_bitrate_kbps_(0),
+      pacing_bitrate_kbps_(0),
+      time_last_update_us_(clock->TimeInMicroseconds()),
+      time_last_update_ms_(clock->TimeInMilliseconds()),
+      next_packet_send_time_(clock_->TimeInMilliseconds()),
+      extra_time_(0.0f),
+      packets_(),
+      data_inflight_(0),
+      // pacing_budget_(0),

[philipel, 2017/08/17 12:52:26]

remove commented code

[gnish1, 2017/08/17 15:37:48]

Done.

+      congestion_window_(6000),
+      in_probe_rtt_(false) {}
+BbrPacedSender::~BbrPacedSender() {}
+
+void BbrPacedSender::SetEstimatedBitrateAndCongestionWindow(
+    uint32_t bitrate_bps,
+    bool in_probe_rtt,
+    uint64_t congestion_window) {
+  estimated_bitrate_bps_ = bitrate_bps;
+  congestion_window_ = congestion_window;
+  in_probe_rtt_ = in_probe_rtt;
+}
+
+void BbrPacedSender::SetMinBitrate(int min_send_bitrate_bps) {
+  min_send_bitrate_kbps_ = min_send_bitrate_bps / 1000;
+  pacing_bitrate_kbps_ =
+      std::max(min_send_bitrate_kbps_, estimated_bitrate_bps_ / 1000);
+}
+
+void BbrPacedSender::InsertPacket(RtpPacketSender::Priority priority,
+                                  uint32_t ssrc,
+                                  uint16_t sequence_number,
+                                  int64_t capture_time_ms,
+                                  size_t bytes,
+                                  bool retransmission) {
+  int64_t now_ms = clock_->TimeInMilliseconds();
+  if (capture_time_ms < 0)
+    capture_time_ms = now_ms;
+  packets_.push_back(new bbr_paced_sender::Packet(
+      priority, ssrc, sequence_number, capture_time_ms, now_ms, bytes,
+      retransmission));
+}
+
+int64_t BbrPacedSender::TimeUntilNextProcess() {
+  // Once errors absolute value hits 2 milliseconds, add compensating term to
+  // the |next_packet_send_time_|, so that we can send packet earlier or later,
+  // depending on the error.
+  extra_time_ = std::min(extra_time_, 2.0f);

[philipel, 2017/08/17 12:52:26]

Why don't we try to compensate the |next_packet_send_time_| with the accumulated
error every time we calculate it?

[gnish1, 2017/08/17 15:37:48]

Done.

+  if (extra_time_ < -1.9f)
+    extra_time_ = -2.0f;
+  int64_t result =
+      std::max<int64_t>(next_packet_send_time_ + time_last_update_ms_ -
+                            clock_->TimeInMilliseconds(),
+                        0);
+  if (extra_time_ == 2.0f || extra_time_ == -2.0f) {
+    next_packet_send_time_ -= extra_time_;
+    result = std::max<int64_t>(next_packet_send_time_ + time_last_update_ms_ -
+                                   clock_->TimeInMilliseconds(),
+                               0);
+    extra_time_ = 0;
+  }
+  return result;
+}
+
+void BbrPacedSender::OnBytesAcked(size_t bytes) {
+  assert(data_inflight_ >= bytes);

[philipel, 2017/08/17 12:52:26]

RTC_DCHECK_GE

[gnish1, 2017/08/17 15:37:48]

Done.

+  data_inflight_ -= bytes;
+}
+
+void BbrPacedSender::Process() {
+  pacing_bitrate_kbps_ =
+      std::max(min_send_bitrate_kbps_, estimated_bitrate_bps_ / 1000);
+  // If we have nothing to send, try sending again in 1 millisecond.
+  if (packets_.empty()) {
+    next_packet_send_time_ = 1;
+    return;
+  }
+  // If congestion window doesn't allow sending, try again in 1 millisecond.
+  if (packets_.front()->size_in_bytes + data_inflight_ > congestion_window_) {
+    next_packet_send_time_ = 1;
+    return;
+  }
+  bool sent = TryToSendPacket(packets_.front());
+  if (sent) {
+    data_inflight_ += packets_.front()->size_in_bytes;
+    delete packets_.front();
+    packets_.pop_front();
+    time_last_update_ms_ = clock_->TimeInMilliseconds();
+    if (!packets_.empty()) {
+      // Calculate in what time we should send current packet.
+      next_packet_send_time_ = (packets_.front()->size_in_bytes * 8000 +
+                                estimated_bitrate_bps_ / 2) /
+                               estimated_bitrate_bps_;
+      // As rounding errors may happen, |extra_time_| could be positive or
+      // negative depending on packet was sent earlier or later, after it hits
+      // certain threshold we will send a packet earlier or later depending on
+      // error we had so far.
+      extra_time_ +=
+          (next_packet_send_time_ - packets_.front()->size_in_bytes * 8000.0f /
+                                        estimated_bitrate_bps_ * 1.0f);
+    } else {
+      // If sending was unsuccessful try again in 1 millisecond.
+      next_packet_send_time_ = 1;
+    }
+  }
+}
+
+bool BbrPacedSender::TryToSendPacket(bbr_paced_sender::Packet* packet) {
+  PacedPacketInfo pacing_info;
+  return packet_sender_->TimeToSendPacket(packet->ssrc, packet->sequence_number,
+                                          packet->capture_time_ms,
+                                          packet->retransmission, pacing_info);
+}
+
+}  // namespace webrtc