New ProbingCalculator class.

webrtc/modules/congestion_controller/probing_calculator.cc

Index: webrtc/modules/congestion_controller/probing_calculator.cc
diff --git a/webrtc/modules/congestion_controller/probing_calculator.cc b/webrtc/modules/congestion_controller/probing_calculator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e30fc96cf2ada2d3d1542f639c06604cbe11e228
--- /dev/null
+++ b/webrtc/modules/congestion_controller/probing_calculator.cc
@@ -0,0 +1,99 @@
+/*
+ *  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;

[brandtr, 2016/07/07 14:58:30]

Is there a motivation for this number?

[For the future: would it be relevant to adapt this number depending on the
network the user is on?]

[philipel, 2016/07/08 09:27:48]

Kind of, we don't want the receive rate to be that much higher since that would
indicate that packets have been sent in a burst, which does not give us
information about the available bandwidth.

If someone were to ask me if 1.15 or 1.25 is a better ratio, I would say "I
don't know".
I don't think so, what would be interesting is to increase the number of packets
in the probing attempt in order to avoid having them all delivered in a single
burst.

[brandtr, 2016/07/08 09:39:20]

Right, this is what I wondered :)

+}
+
+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 probing packet or if this probing packet

[brandtr, 2016/07/07 14:58:30]

Minor: "If this is not _a_ probing..."

[philipel, 2016/07/08 09:27:48]

Done.

+  // 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)
+    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;
+  }
+
+  int send_bps = cluster->size / send_interval_ms * 1000;
+  int receive_bps = cluster->size / receive_interval_ms * 1000;

[brandtr, 2016/07/07 14:58:30]

Integer division may not be desirable when the cluster size and
|receive_interval_ms| have different orders of magnitude.

[philipel, 2016/07/08 09:27:48]

Switched to float.

+  float ratio = receive_bps / static_cast<float>(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);
+}
+}  // namespace webrtc