src/net/quic/congestion_control/inter_arrival_state_machine.cc

   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 #include "net/quic/congestion_control/inter_arrival_state_machine.h"
   6
   7 #include "base/logging.h"
   8
   9 namespace  {
  10 const int kIncreaseEventsBeforeDowngradingState = 5;
  11 const int kDecreaseEventsBeforeUpgradingState = 2;
  12 // Note: Can not be higher than kDecreaseEventsBeforeUpgradingState;
  13 const int kLossEventsBeforeUpgradingState = 2;
  14 // Timeout old loss and delay events after this time.
  15 const int kEventTimeoutMs = 10000;
  16 // A reasonable arbitrary chosen value for initial round trip time.
  17 const int kInitialRttMs = 80;
  18 }
  19
  20 namespace net {
  21
  22 InterArrivalStateMachine::InterArrivalStateMachine(const QuicClock* clock)
  23     : clock_(clock),
  24       current_state_(kInterArrivalStateStable),
  25       smoothed_rtt_(QuicTime::Delta::FromMilliseconds(kInitialRttMs)),
  26       decrease_event_count_(0),
  27       last_decrease_event_(QuicTime::Zero()),
  28       increase_event_count_(0),
  29       last_increase_event_(QuicTime::Zero()),
  30       loss_event_count_(0),
  31       last_loss_event_(QuicTime::Zero()),
  32       delay_event_count_(0),
  33       last_delay_event_(QuicTime::Zero()) {
  34 }
  35
  36 InterArrivalState InterArrivalStateMachine::GetInterArrivalState() {
  37   return current_state_;
  38 }
  39
  40 void InterArrivalStateMachine::IncreaseBitrateDecision() {
  41   // Multiple increase event without packet loss or delay events will drive
  42   // state back to stable.
  43   QuicTime current_time = clock_->ApproximateNow();
  44   if (current_time.Subtract(last_increase_event_) < smoothed_rtt_) {
  45     // Less than one RTT have passed; ignore this event.
  46     return;
  47   }
  48   last_increase_event_ = current_time;
  49   increase_event_count_++;
  50   decrease_event_count_ = 0;  // Reset previous decrease events.
  51
  52   if (increase_event_count_ < kIncreaseEventsBeforeDowngradingState) {
  53     // Not enough increase events to change state.
  54     return;
  55   }
  56   increase_event_count_ = 0;  // Reset increase events.
  57
  58   switch (current_state_) {
  59     case kInterArrivalStateStable:
  60       // Keep this state.
  61       break;
  62     case kInterArrivalStatePacketLoss:
  63       current_state_ = kInterArrivalStateStable;
  64       break;
  65     case kInterArrivalStateDelay:
  66       current_state_ = kInterArrivalStateStable;
  67       break;
  68     case kInterArrivalStateCompetingFlow:
  69       current_state_ = kInterArrivalStateDelay;
  70       break;
  71     case kInterArrivalStateCompetingTcpFLow:
  72       current_state_ = kInterArrivalStateDelay;
  73       break;
  74   }
  75 }
  76
  77 void InterArrivalStateMachine::DecreaseBitrateDecision() {
  78   DCHECK(kDecreaseEventsBeforeUpgradingState >=
  79          kLossEventsBeforeUpgradingState);
  80
  81   QuicTime current_time = clock_->ApproximateNow();
  82   if (current_time.Subtract(last_decrease_event_) < smoothed_rtt_) {
  83     // Less than one RTT have passed; ignore this event.
  84     return;
  85   }
  86   last_decrease_event_ = current_time;
  87   decrease_event_count_++;
  88   increase_event_count_ = 0;  // Reset previous increase events.
  89   if (decrease_event_count_ < kDecreaseEventsBeforeUpgradingState) {
  90     // Not enough decrease events to change state.
  91     return;
  92   }
  93   decrease_event_count_ = 0;  // Reset decrease events.
  94
  95   switch (current_state_) {
  96     case kInterArrivalStateStable:
  97       if (delay_event_count_ == 0 && loss_event_count_ > 0) {
  98         // No recent delay events; only packet loss events.
  99         current_state_ = kInterArrivalStatePacketLoss;
 100       } else {
 101         current_state_ = kInterArrivalStateDelay;
 102       }
 103       break;
 104     case kInterArrivalStatePacketLoss:
 105       // Keep this state.
 106       break;
 107     case kInterArrivalStateDelay:
 108       if (loss_event_count_ >= kLossEventsBeforeUpgradingState) {
 109         // We have packet loss events. Assume fighting with TCP.
 110         current_state_ = kInterArrivalStateCompetingTcpFLow;
 111       } else {
 112         current_state_ = kInterArrivalStateCompetingFlow;
 113       }
 114       break;
 115     case kInterArrivalStateCompetingFlow:
 116       if (loss_event_count_ >= kLossEventsBeforeUpgradingState) {
 117         // We have packet loss events. Assume fighting with TCP.
 118         current_state_ = kInterArrivalStateCompetingTcpFLow;
 119       }
 120       break;
 121     case kInterArrivalStateCompetingTcpFLow:
 122       // Keep this state.
 123       break;
 124   }
 125 }
 126
 127 void InterArrivalStateMachine::set_rtt(QuicTime::Delta rtt) {
 128   smoothed_rtt_ = rtt;
 129 }
 130
 131 bool InterArrivalStateMachine::PacketLossEvent() {
 132   QuicTime current_time = clock_->ApproximateNow();
 133   if (current_time.Subtract(last_loss_event_) < smoothed_rtt_) {
 134     // Less than one RTT have passed; ignore this event.
 135     return false;
 136   }
 137   last_loss_event_ = current_time;
 138   loss_event_count_++;
 139   if (current_time.Subtract(last_delay_event_) >
 140       QuicTime::Delta::FromMilliseconds(kEventTimeoutMs)) {
 141     // Delay event have timed out.
 142     delay_event_count_ = 0;
 143   }
 144   return true;
 145 }
 146
 147 bool InterArrivalStateMachine::IncreasingDelayEvent() {
 148   QuicTime current_time = clock_->ApproximateNow();
 149   if (current_time.Subtract(last_delay_event_) < smoothed_rtt_) {
 150     // Less than one RTT have passed; ignore this event.
 151     return false;
 152   }
 153   last_delay_event_ = current_time;
 154   delay_event_count_++;
 155   if (current_time.Subtract(last_loss_event_) >
 156       QuicTime::Delta::FromMilliseconds(kEventTimeoutMs)) {
 157     // Loss event have timed out.
 158     loss_event_count_ = 0;
 159   }
 160   return true;
 161 }
 162
 163 }  // namespace net