net/quic/congestion_control/rtt_stats.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4 //
   5 // A convenience class to store rtt samples and calculate smoothed rtt.
   6
   7 #ifndef NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
   8 #define NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
   9
  10 #include <algorithm>
  11
  12 #include "base/basictypes.h"
  13 #include "net/quic/quic_protocol.h"
  14 #include "net/quic/quic_time.h"
  15
  16 namespace net {
  17
  18 class NET_EXPORT_PRIVATE RttStats {
  19  public:
  20   RttStats();
  21
  22   // Returns true if any RTT measurements have been made.
  23   bool HasUpdates() const;
  24
  25   // Updates the RTT from an incoming ack which is received |send_delta| after
  26   // the packet is sent and the peer reports the ack being delayed |ack_delay|.
  27   void UpdateRtt(QuicTime::Delta send_delta, QuicTime::Delta ack_delay);
  28
  29   QuicTime::Delta SmoothedRtt() const;
  30
  31   // Sets an initial RTT to be used for SmoothedRtt before any RTT updates.
  32   void set_initial_rtt_us(int64 initial_rtt_us) {
  33     initial_rtt_us_ = initial_rtt_us;
  34   }
  35
  36   QuicTime::Delta latest_rtt() const {
  37     return latest_rtt_;
  38   }
  39
  40   QuicTime::Delta min_rtt() const {
  41     return min_rtt_;
  42   }
  43
  44   QuicTime::Delta mean_deviation() const {
  45     return mean_deviation_;
  46   }
  47
  48  private:
  49   QuicTime::Delta latest_rtt_;
  50   QuicTime::Delta min_rtt_;
  51   QuicTime::Delta smoothed_rtt_;
  52   // Mean RTT deviation during this session.
  53   // Approximation of standard deviation, the error is roughly 1.25 times
  54   // larger than the standard deviation, for a normally distributed signal.
  55   QuicTime::Delta mean_deviation_;
  56   int64 initial_rtt_us_;
  57 };
  58
  59 }  // namespace net
  60
  61 #endif  // NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_