New ProbingCalculator class.

webrtc/modules/congestion_controller/probing_calculator.cc

+/*
+ *  Copyright (c) 2016 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/congestion_controller/probing_calculator.h"
+
+#include <algorithm>
+
+#include "webrtc/base/logging.h"
+
+namespace {
+// The minumum number of probes we need for a valid cluster.
+constexpr int kMinNumProbesValidCluster = 4;
+
+// The maximum (receive rate)/(send rate) ratio for a valid estimate.
+constexpr float kValidRatio = 1.2f;
+}
+
+namespace webrtc {
+
+ProbingCalculator::ProbingCalculator(ProbingResultCallback* result_callback)
+    : result_callback_(result_callback), last_valid_cluster_id_(0) {}
+
+void ProbingCalculator::PacketFeedback(const PacketInfo& packet_info) {
+  // If this is not a probing packet or if this probing packet
+  // belongs to an old cluster, do nothing.
+  if (packet_info.probe_cluster_id == PacketInfo::kNotAProbe ||
+      packet_info.probe_cluster_id < last_valid_cluster_id_) {
+    return;
+  }
+
+  AggregatedCluster* cluster = &clusters_[packet_info.probe_cluster_id];
+  cluster->first_send_ms =
+      std::min(cluster->first_send_ms, packet_info.send_time_ms);
+  cluster->last_send_ms =
+      std::max(cluster->last_send_ms, packet_info.send_time_ms);
+  cluster->first_receive_ms =
+      std::min(cluster->first_receive_ms, packet_info.arrival_time_ms);
+  cluster->last_receive_ms =
+      std::max(cluster->last_receive_ms, packet_info.arrival_time_ms);
+  cluster->size += packet_info.payload_size;
+  cluster->num_probes += 1;
+
+  if (cluster->num_probes < kMinNumProbesValidCluster)

[terelius, 2016/07/11 10:07:48]

Question about future follow up: Do we have any plans to take packet loss into
account in the probe? If the probe cluster is supposed to contain 8 packets and
we lose 4 but receive the other 4 in rapid succession, we still consider the
probe a success and set a high bitrate.

[philipel, 2016/07/11 11:18:55]

Might be something that's interesting in the future, but for now we know that a
probing cluster contains 5-6 packets. This threshold/logic might have to be
revised as we tune/update the probing.

[terelius, 2016/07/11 11:34:51]

Acknowledged.

+    return;
+
+  int send_interval_ms = cluster->last_send_ms - cluster->first_send_ms;
+  int receive_interval_ms =
+      cluster->last_receive_ms - cluster->first_receive_ms;
+
+  if (send_interval_ms == 0 || receive_interval_ms == 0) {
+    LOG(LS_INFO) << "Probing unsuccessful, invalid send/receive interval!"
+                 << " [cluster id: " << packet_info.probe_cluster_id
+                 << "] [send interval: " << send_interval_ms << " ms]"
+                 << " [receive interval: " << receive_interval_ms << " ms]";
+    return;
+  }
+
+  float send_bps =
+      static_cast<float>(cluster->size) / send_interval_ms * 1000;
+  float receive_bps =
+      static_cast<float>(cluster->size) / receive_interval_ms * 1000;
+  float ratio = receive_bps / send_bps;
+  if (ratio > kValidRatio) {
+    LOG(LS_INFO) << "Probing unsuccessful, receive/send ratio to high!"
+                 << " [cluster id: " << packet_info.probe_cluster_id
+                 << "] [send: " << cluster->size << " bytes / "
+                 << send_interval_ms << " ms = " << send_bps / 1000 << " kB/s]"
+                 << " [receive: " << cluster->size << " bytes / "
+                 << receive_interval_ms << " ms = " << receive_bps / 1000
+                 << " kB/s]"
+                 << " [ratio: " << receive_bps / 1000 << " / "
+                 << send_bps / 1000 << " = " << ratio << " > kValidRatio ("
+                 << kValidRatio << ")]";
+    return;
+  }
+  // We have a valid estimate.
+  int result_bps = std::min(send_bps, receive_bps);
+  result_callback_->ProbingResult(result_bps, packet_info.arrival_time_ms);
+  last_valid_cluster_id_ = packet_info.probe_cluster_id;
+  LOG(LS_INFO) << "Probing successful!"
+               << " [cluster id: " << packet_info.probe_cluster_id
+               << "] [send: " << cluster->size << " bytes / "
+               << send_interval_ms << " ms = " << send_bps / 1000 << " kB/s]"
+               << " [receive: " << cluster->size << " bytes / "
+               << receive_interval_ms << " ms = " << receive_bps / 1000
+               << " kB/s]";
+
+  // Clean up old clusters.
+  auto erase_to = clusters_.lower_bound(packet_info.probe_cluster_id);
+  clusters_.erase(clusters_.begin(), erase_to);

[terelius, 2016/07/11 10:07:48]

We only clear the map after a successful probe? What happens if a bug causes
(almost) all probes to fail and the map grows without bounds?

[philipel, 2016/07/11 11:18:55]

fixed.

+}
+}  // namespace webrtc