net/quic/congestion_control/cubic.h

   1 // Copyright (c) 2012 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 // Cubic algorithm, helper class to TCP cubic.
   6 // For details see http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf.
   7
   8 #ifndef NET_QUIC_CONGESTION_CONTROL_CUBIC_H_
   9 #define NET_QUIC_CONGESTION_CONTROL_CUBIC_H_
  10
  11 #include "base/basictypes.h"
  12 #include "net/base/net_export.h"
  13 #include "net/quic/quic_bandwidth.h"
  14 #include "net/quic/quic_clock.h"
  15 #include "net/quic/quic_connection_stats.h"
  16 #include "net/quic/quic_time.h"
  17
  18 namespace net {
  19
  20 class NET_EXPORT_PRIVATE Cubic {
  21  public:
  22   explicit Cubic(const QuicClock* clock);
  23
  24   void SetNumConnections(int num_connections);
  25
  26   // Call after a timeout to reset the cubic state.
  27   void Reset();
  28
  29   // Compute a new congestion window to use after a loss event.
  30   // Returns the new congestion window in packets. The new congestion window is
  31   // a multiplicative decrease of our current window.
  32   QuicPacketCount CongestionWindowAfterPacketLoss(QuicPacketCount current);
  33
  34   // Compute a new congestion window to use after a received ACK.
  35   // Returns the new congestion window in packets. The new congestion window
  36   // follows a cubic function that depends on the time passed since last
  37   // packet loss.
  38   QuicPacketCount CongestionWindowAfterAck(QuicPacketCount current,
  39                                            QuicTime::Delta delay_min);
  40
  41   // Call on ack arrival when sender is unable to use the available congestion
  42   // window. Resets Cubic state during quiescence.
  43   void OnApplicationLimited();
  44
  45  private:
  46   static const QuicTime::Delta MaxCubicTimeInterval() {
  47     return QuicTime::Delta::FromMilliseconds(30);
  48   }
  49
  50   // Compute the TCP Cubic alpha and beta based on the current number of
  51   // connections.
  52   float Alpha() const;
  53   float Beta() const;
  54
  55   const QuicClock* clock_;
  56
  57   // Number of connections to simulate.
  58   int num_connections_;
  59
  60   // Time when this cycle started, after last loss event.
  61   QuicTime epoch_;
  62
  63   // Time when we updated last_congestion_window.
  64   QuicTime last_update_time_;
  65
  66   // Last congestion window (in packets) used.
  67   QuicPacketCount last_congestion_window_;
  68
  69   // Max congestion window (in packets) used just before last loss event.
  70   // Note: to improve fairness to other streams an additional back off is
  71   // applied to this value if the new value is below our latest value.
  72   QuicPacketCount last_max_congestion_window_;
  73
  74   // Number of acked packets since the cycle started (epoch).
  75   QuicPacketCount acked_packets_count_;
  76
  77   // TCP Reno equivalent congestion window in packets.
  78   QuicPacketCount estimated_tcp_congestion_window_;
  79
  80   // Origin point of cubic function.
  81   QuicPacketCount origin_point_congestion_window_;
  82
  83   // Time to origin point of cubic function in 2^10 fractions of a second.
  84   uint32 time_to_origin_point_;
  85
  86   // Last congestion window in packets computed by cubic function.
  87   QuicPacketCount last_target_congestion_window_;
  88
  89   DISALLOW_COPY_AND_ASSIGN(Cubic);
  90 };
  91
  92 }  // namespace net
  93
  94 #endif  // NET_QUIC_CONGESTION_CONTROL_CUBIC_H_