First-order-FEC recoverability calculation

webrtc/voice_engine/transport_feedback_packet_loss_tracker.h

 /*
  *  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.
  */
 
 #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 {
  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);
+  // * Up to |max_window_size| latest packet statuses will be used for
+  //   calculating the packet loss metrics.
+  // * PLR (packet-loss-rate) is reliably computable once the statuses of
+  //   |plr_min_num_packets| packets are known.
+  // * RPLR (recoverable-packet-loss-rate) is reliably computable once the
+  //   statuses of |rplr_min_num_pairs| pairs are known.
+  TransportFeedbackPacketLossTracker(size_t max_window_size,
+                                     size_t plr_min_num_packets,
+                                     size_t rplr_min_num_pairs);
 
   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;
+  // Returns the packet loss rate, if the window has enough packet statuses to
+  // reliably compute it. Otherwise, returns empty.
+  rtc::Optional<float> GetPacketLossRate() const;
+
+  // Returns the first-order-FEC recoverable packet loss rate, if the window has
+  // enough status pairs to reliably compute it. Otherwise, returns empty.
+  rtc::Optional<float> GetRecoverablePacketLossRate() const;
 
   // Verifies that the internal states are correct. Only used for tests.
   void Validate() const;
 
  private:
   // PacketStatus is a map from sequence number to its reception status. The
   // status is true if the corresponding packet is received, and false if it is
   // lost. Unknown statuses are not present in the map.
   typedef std::map<uint16_t, bool> PacketStatus;
   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);
+
+  void UpdateMetrics(PacketStatusIterator it, bool apply /* false = undo */);
+  void UpdatePlr(PacketStatusIterator it, bool apply /* false = undo */);
+  void UpdateRplr(PacketStatusIterator it, bool apply /* false = undo */);
+
   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_;
+  // Packet-loss-rate calculation (lost / all-known-packets).
+  struct PlrState {
+    explicit PlrState(size_t min_num_packets)
+        : min_num_packets_(min_num_packets) {
+      Reset();
+    }
+    void Reset() {
+      num_received_packets_ = 0;
+      num_lost_packets_ = 0;
+    }
+    rtc::Optional<float> GetMetric() const;
+    const size_t min_num_packets_;
+    size_t num_received_packets_;
+    size_t num_lost_packets_;
+  } plr_state_;
+
+  // Recoverable packet loss calculation (first-order-FEC recoverable).
+  struct RplrState {
+    explicit RplrState(size_t min_num_pairs)
+        : min_num_pairs_(min_num_pairs) {
+      Reset();
+    }
+    void Reset() {
+      num_known_pairs_ = 0;
+      num_recoverable_losses_ = 0;
+    }
+    rtc::Optional<float> GetMetric() const;
+    // Recoverable packets are those which were lost, but immediately followed
+    // by a properly received packet. If that second packet carried FEC,
+    // the data from the former (lost) packet could be recovered.
+    // The RPLR is calculated as the fraction of such pairs (lost-received) out
+    // of all pairs of consecutive acked packets.
+    const size_t min_num_pairs_;
+    size_t num_known_pairs_;
+    size_t num_recoverable_losses_;
+  } rplr_state_;
+
+  size_t num_consecutive_old_reports_;  // TODO(elad.alon): Upcoming CL removes.
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_