net/quic/congestion_control/inter_arrival_state_machine.h

   1 // Copyright (c) 2013 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 // State machine for congestion control. The state is updated by calls from
   6 // other modules as they detect events, or decide on taking specific actions.
   7 // Events include things like packet loss, or growing delay, while decisions
   8 // include decisions to increase or decrease bitrates.
   9 // This class should be called for every event and decision made by the
  10 // congestion control, this class will coalesce all calls relative to the
  11 // smoothed RTT.
  12
  13 #ifndef NET_QUIC_CONGESTION_CONTROL_INTER_ARRIVAL_STATE_MACHINE_H_
  14 #define NET_QUIC_CONGESTION_CONTROL_INTER_ARRIVAL_STATE_MACHINE_H_
  15
  16 #include "net/base/net_export.h"
  17 #include "net/quic/quic_clock.h"
  18 #include "net/quic/quic_time.h"
  19
  20 namespace net {
  21
  22 //  State transition diagram.
  23 //
  24 //                     kInterArrivalStatePacketLoss
  25 //                                   |
  26 //                       kInterArrivalStateStable
  27 //                                   |
  28 //                       kInterArrivalStateDelay
  29 //                           |              |
  30 //  kInterArrivalStateCompetingFlow -> kInterArrivalStateCompetingTcpFLow
  31
  32 enum NET_EXPORT_PRIVATE InterArrivalState {
  33   // We are on a network with a delay that is too small to be reliably detected,
  34   // such as a local ethernet.
  35   kInterArrivalStatePacketLoss = 1,
  36   // We are on an underutilized network operating with low delay and low loss.
  37   kInterArrivalStateStable = 2,
  38   // We are on a network where we can detect delay changes and suffer only
  39   // low loss. Nothing indicates that we are competing with another flow.
  40   kInterArrivalStateDelay = 3,
  41   // We are on a network where we can detect delay changes and suffer only
  42   // low loss. We have indications that we are compete with another flow.
  43   kInterArrivalStateCompetingFlow = 4,
  44   // We are on a network where we can detect delay changes, however we suffer
  45   // packet loss due to sharing the bottleneck link with another flow, which is
  46   // most likely a TCP flow.
  47   kInterArrivalStateCompetingTcpFLow = 5,
  48 };
  49
  50 class NET_EXPORT_PRIVATE InterArrivalStateMachine {
  51  public:
  52   explicit InterArrivalStateMachine(const QuicClock* clock);
  53
  54   InterArrivalState GetInterArrivalState();
  55
  56   // Inter arrival congestion control decided to increase bitrate.
  57   void IncreaseBitrateDecision();
  58
  59   // Inter arrival congestion control decided to decrease bitrate.
  60   void DecreaseBitrateDecision();
  61
  62   // Estimated smoothed round trip time.
  63   // This should be called whenever the smoothed RTT estimate is updated.
  64   void set_rtt(QuicTime::Delta rtt);
  65
  66   // This method is called when a packet loss was reported.
  67   bool PacketLossEvent();
  68
  69   // This method is called when we believe that packet transit delay is
  70   // increasing, presumably due to a growing queue along the path.
  71   bool IncreasingDelayEvent();
  72
  73  private:
  74   const QuicClock* clock_;
  75   InterArrivalState current_state_;
  76   QuicTime::Delta smoothed_rtt_;
  77
  78   int decrease_event_count_;
  79   QuicTime last_decrease_event_;
  80
  81   int increase_event_count_;
  82   QuicTime last_increase_event_;
  83
  84   int loss_event_count_;
  85   QuicTime last_loss_event_;
  86
  87   int delay_event_count_;
  88   QuicTime last_delay_event_;
  89
  90   DISALLOW_COPY_AND_ASSIGN(InterArrivalStateMachine);
  91 };
  92
  93 }  // namespace net
  94 #endif  // NET_QUIC_CONGESTION_CONTROL_INTER_ARRIVAL_STATE_MACHINE_H_