1 files changed, 129 insertions, 0 deletions
diff --git a/webrtc/modules/pacing/bitrate_prober.cc b/webrtc/modules/pacing/bitrate_prober.cc
new file mode 100644
index 0000000000..bbbe54f54e
--- /dev/null
+++ b/webrtc/modules/pacing/bitrate_prober.cc
@@ -0,0 +1,129 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/pacing/bitrate_prober.h"
+
+#include <assert.h>
+#include <algorithm>
+#include <limits>
+#include <sstream>
+
+#include "webrtc/modules/pacing/include/paced_sender.h"
+#include "webrtc/system_wrappers/include/logging.h"
+
+namespace webrtc {
+
+namespace {
+int ComputeDeltaFromBitrate(size_t packet_size, int bitrate_bps) {
+  assert(bitrate_bps > 0);
+  // Compute the time delta needed to send packet_size bytes at bitrate_bps
+  // bps. Result is in milliseconds.
+  return static_cast<int>(1000ll * static_cast<int64_t>(packet_size) * 8ll /
+      bitrate_bps);
+}
+}  // namespace
+
+BitrateProber::BitrateProber()
+    : probing_state_(kDisabled),
+      packet_size_last_send_(0),
+      time_last_send_ms_(-1) {
+}
+
+void BitrateProber::SetEnabled(bool enable) {
+  if (enable) {
+    if (probing_state_ == kDisabled) {
+      probing_state_ = kAllowedToProbe;
+      LOG(LS_INFO) << "Initial bandwidth probing enabled";
+    }
+  } else {
+    probing_state_ = kDisabled;
+    LOG(LS_INFO) << "Initial bandwidth probing disabled";
+  }
+}
+
+bool BitrateProber::IsProbing() const {
+  return probing_state_ == kProbing;
+}
+
+void BitrateProber::MaybeInitializeProbe(int bitrate_bps) {
+  if (probing_state_ != kAllowedToProbe)
+    return;
+  probe_bitrates_.clear();
+  // Max number of packets used for probing.
+  const int kMaxNumProbes = 2;
+  const int kPacketsPerProbe = 5;
+  const float kProbeBitrateMultipliers[kMaxNumProbes] = {3, 6};
+  int bitrates_bps[kMaxNumProbes];
+  std::stringstream bitrate_log;
+  bitrate_log << "Start probing for bandwidth, bitrates:";
+  for (int i = 0; i < kMaxNumProbes; ++i) {
+    bitrates_bps[i] = kProbeBitrateMultipliers[i] * bitrate_bps;
+    bitrate_log << " " << bitrates_bps[i];
+    // We need one extra to get 5 deltas for the first probe.
+    if (i == 0)
+      probe_bitrates_.push_back(bitrates_bps[i]);
+    for (int j = 0; j < kPacketsPerProbe; ++j)
+      probe_bitrates_.push_back(bitrates_bps[i]);
+  }
+  bitrate_log << ", num packets: " << probe_bitrates_.size();
+  LOG(LS_INFO) << bitrate_log.str().c_str();
+  probing_state_ = kProbing;
+}
+
+int BitrateProber::TimeUntilNextProbe(int64_t now_ms) {
+  if (probing_state_ != kDisabled && probe_bitrates_.empty()) {
+    probing_state_ = kWait;
+  }
+  if (probe_bitrates_.empty()) {
+    // No probe started, or waiting for next probe.
+    return -1;
+  }
+  int64_t elapsed_time_ms = now_ms - time_last_send_ms_;
+  // We will send the first probe packet immediately if no packet has been
+  // sent before.
+  int time_until_probe_ms = 0;
+  if (packet_size_last_send_ > PacedSender::kMinProbePacketSize &&
+      probing_state_ == kProbing) {
+    int next_delta_ms = ComputeDeltaFromBitrate(packet_size_last_send_,
+                                                probe_bitrates_.front());
+    time_until_probe_ms = next_delta_ms - elapsed_time_ms;
+    // There is no point in trying to probe with less than 1 ms between packets
+    // as it essentially means trying to probe at infinite bandwidth.
+    const int kMinProbeDeltaMs = 1;
+    // If we have waited more than 3 ms for a new packet to probe with we will
+    // consider this probing session over.
+    const int kMaxProbeDelayMs = 3;
+    if (next_delta_ms < kMinProbeDeltaMs ||
+        time_until_probe_ms < -kMaxProbeDelayMs) {
+      // We currently disable probing after the first probe, as we only want
+      // to probe at the beginning of a connection. We should set this to
+      // kWait if we later want to probe periodically.
+      probing_state_ = kWait;
+      LOG(LS_INFO) << "Next delta too small, stop probing.";
+      time_until_probe_ms = 0;
+    }
+  }
+  return std::max(time_until_probe_ms, 0);
+}
+
+size_t BitrateProber::RecommendedPacketSize() const {
+  return packet_size_last_send_;
+}
+
+void BitrateProber::PacketSent(int64_t now_ms, size_t packet_size) {
+  assert(packet_size > 0);
+  packet_size_last_send_ = packet_size;
+  time_last_send_ms_ = now_ms;
+  if (probing_state_ != kProbing)
+    return;
+  if (!probe_bitrates_.empty())
+    probe_bitrates_.pop_front();
+}
+}  // namespace webrtc