Add TransportFeedbackPacketLossTracker.

webrtc/voice_engine/transport_feedback_packet_loss_tracker.h

+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_
+#define WEBRTC_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_
+
+#include <map>
+
+#include "webrtc/base/optional.h"
+#include "webrtc/modules/include/module_common_types.h"
+
+namespace webrtc {
+
+namespace rtcp {
+class TransportFeedback;
+}
+
+class TransportFeedbackPacketLossTracker final {

[kwiberg-webrtc, 2016/12/22 02:31:41]

Bonus points for using "final"!

[minyue-webrtc, 2016/12/28 14:48:33]

Acknowledged.

+ public:
+  // Up to |max_window_size| latest packet statuses wil be used for calculating
+  // the packet loss metrics. When less than |min_window_size| samples are
+  // available for making a reliable estimation, GetPacketLossRates() will
+  // return false to indicate packet loss metrics are not ready.
+  TransportFeedbackPacketLossTracker(size_t min_window_size,
+                                     size_t max_window_size);
+
+  void OnReceivedTransportFeedback(const rtcp::TransportFeedback& feedback);
+
+  // Returns true if packet loss rate and packet loss episode duration are ready
+  // and assigns respective values to |*packet_loss_rate| and
+  // |*consecutive_packet_loss_rate|. Continuous packet loss rate is defined as
+  // the probability of losing two adjacent packets.
+  bool GetPacketLossRates(float* packet_loss_rate,
+                          float* consecutive_packet_loss_rate) const;

[kwiberg-webrtc, 2016/12/22 02:31:41]

Consider returning Optional<PacketLossRates>, where

  struct PacketLossRates {
    float single_rate;
    float two_in_a_row_rate;
  };

[minyue-webrtc, 2016/12/28 14:48:33]

Actually, the return API is subject to a change. We do not really need
packet_loss_rate for the moment. So I would like to change it to

Optional<float> GetConsecutivePacketLossRate(), or something like that.

To make this CL slightly more focused, I would do it as a follow up, or a later
patch set.

[kwiberg-webrtc, 2017/01/05 02:51:11]

Acknowledged.

+
+  // Verifies that the internal states are correct. Only used for tests.
+  void Validate() const;

[kwiberg-webrtc, 2016/12/22 02:31:41]

Make this private, and DCHECK it at the beginning and/or end of methods? See
webrtc/base/buffer.h for an example of this. Or is it too expensive?

[minyue-webrtc, 2016/12/28 14:48:33]

We think it is too expensive. We currently keep this here to allow fuzzer test.
Once it is good enough, we'd remove it (move it to unittest)

[kwiberg-webrtc, 2017/01/05 02:51:11]

Acknowledged.

+
+ private:
+  // PacketStatus is a map from sequence number to a boolean. The boolean is
+  // true if it is received.
+  typedef std::map<uint16_t, bool> PacketStatus;

[kwiberg-webrtc, 2016/12/22 02:31:41]

Is there a difference between false and a missing entry? If so, document. If
not, use std::set instead?

[minyue-webrtc, 2016/12/28 14:48:33]

yes, missing entries are not taken into account

say 1???01??1

we count 4 statuses, out of which 1 is lost. This way, we try to minimize the
effect of feedback-losses on the downlink.

[kwiberg-webrtc, 2017/01/05 02:51:11]

Please document this.

+  typedef PacketStatus::const_iterator PacketStatusIterator;
+
+  void Reset();
+  // ReferenceSequenceNumber() provides a sequence number that defines the
+  // order of packet reception info stored in |packet_status_window_|. In
+  // particular, given any sequence number |x|,
+  // (2^16 + x - ref_seq_num_) % 2^16 defines its actual position in
+  // |packet_status_window_|.
+  uint16_t ReferenceSequenceNumber() const;
+  bool IsOldSequenceNumber(uint16_t seq_num) const;
+  void InsertPacketStatus(uint16_t seq_num, bool received);
+  void RemoveOldestPacketStatus();
+  void ApplyPacketStatus(PacketStatusIterator it);
+  void UndoPacketStatus(PacketStatusIterator it);
+  PacketStatusIterator PreviousPacketStatus(PacketStatusIterator it);
+  PacketStatusIterator NextPacketStatus(PacketStatusIterator it);
+
+  const size_t min_window_size_;
+  const size_t max_window_size_;
+
+  PacketStatus packet_status_window_;
+  // |ref_packet_status_| points to the oldest item in |packet_status_window_|.
+  PacketStatusIterator ref_packet_status_;
+
+  size_t num_received_packets_;
+  size_t num_lost_packets_;
+  size_t num_consecutive_losses_;
+  size_t num_consecutive_old_reports_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_