Add a time based loss detection algorithm to QUIC that loses packets

net/quic/congestion_control/time_loss_algorithm.h

 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef NET_QUIC_CONGESTION_CONTROL_TCP_LOSS_ALGORITHM_H_
-#define NET_QUIC_CONGESTION_CONTROL_TCP_LOSS_ALGORITHM_H_
+#ifndef NET_QUIC_CONGESTION_CONTROL_TIME_LOSS_ALGORITHM_H_
+#define NET_QUIC_CONGESTION_CONTROL_TIME_LOSS_ALGORITHM_H_
 
 #include <algorithm>
 #include <map>
 
 #include "base/basictypes.h"
 #include "net/quic/congestion_control/loss_detection_interface.h"
 #include "net/quic/quic_protocol.h"
 #include "net/quic/quic_time.h"
 #include "net/quic/quic_unacked_packet_map.h"
 
 namespace net {
 
-// Class which implement's TCP's approach of detecting loss when 3 nacks have
-// been received for a packet.  Also implements TCP's early retransmit(RFC5827).
-class NET_EXPORT_PRIVATE TCPLossAlgorithm : public LossDetectionInterface {
+// A loss detection algorithm which avoids spurious losses and retransmissions
+// by waiting 1.25 RTTs after a packet was sent instead of nack count.
+class NET_EXPORT_PRIVATE TimeLossAlgorithm : public LossDetectionInterface {
  public:
-  TCPLossAlgorithm();
-  virtual ~TCPLossAlgorithm() {}
+  TimeLossAlgorithm();
+  virtual ~TimeLossAlgorithm() {}
 
-  // Uses nack counts to decide when packets are lost.
+  // Declares pending packets less than the largest observed lost when it has
+  // been 1.25 RTT since they were sent.  Packets larger than the largest
+  // observed are retransmitted via TLP.
   virtual SequenceNumberSet DetectLostPackets(
       const QuicUnackedPacketMap& unacked_packets,
       const QuicTime& time,
       QuicPacketSequenceNumber largest_observed,
-      QuicTime::Delta srtt) OVERRIDE;
+      QuicTime::Delta srtt,
+      QuicTime::Delta latest_rtt) OVERRIDE;
 
-  // Return QuicTime::Zero.
+  // Returns the time the next packet will be lost, or zero if there
+  // are no nacked pending packets outstanding.
+  // TODO(ianswett): Ideally the RTT variance and the RTT would be used to
+  // determine the time a packet is considered lost.
+  // TODO(ianswett): Consider using Max(1.25 * srtt, 1.125 * last_rtt).
   virtual QuicTime GetLossTimeout() const OVERRIDE;
+
+ private:
+  QuicTime loss_detection_timeout_;
 };
 
 }  // namespace net
 
-#endif  // NET_QUIC_CONGESTION_CONTROL_TCP_LOSS_ALGORITHM_H_
+#endif  // NET_QUIC_CONGESTION_CONTROL_TIME_LOSS_ALGORITHM_H_