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_clock.h"
  14 #include "net/quic/quic_connection_stats.h"
  15 #include "net/quic/quic_time.h"
  16
  17 namespace net {
  18
  19 // TCP congestion window in QUIC is in packets, not bytes.
  20 typedef uint32 QuicTcpCongestionWindow;
  21
  22 class NET_EXPORT_PRIVATE Cubic {
  23  public:
  24   Cubic(const QuicClock* clock, QuicConnectionStats* stats);
  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   QuicTcpCongestionWindow CongestionWindowAfterPacketLoss(
  33       QuicTcpCongestionWindow current);
  34
  35   // Compute a new congestion window to use after a received ACK.
  36   // Returns the new congestion window in packets. The new congestion window
  37   // follows a cubic function that depends on the time passed since last
  38   // packet loss.
  39   QuicTcpCongestionWindow CongestionWindowAfterAck(
  40       QuicTcpCongestionWindow current,
  41       QuicTime::Delta delay_min);
  42
  43  private:
  44   static const QuicTime::Delta MaxCubicTimeInterval() {
  45     return QuicTime::Delta::FromMilliseconds(30);
  46   }
  47
  48   // Update congestion control variables in QuicConnectionStats.
  49   void UpdateCongestionControlStats(QuicTcpCongestionWindow new_cubic_mode_cwnd,
  50                                     QuicTcpCongestionWindow new_reno_mode_cwnd);
  51   const QuicClock* clock_;
  52
  53   // Time when this cycle started, after last loss event.
  54   QuicTime epoch_;
  55
  56   // Time when we updated last_congestion_window.
  57   QuicTime last_update_time_;
  58
  59   // Last congestion window (in packets) used.
  60   QuicTcpCongestionWindow last_congestion_window_;
  61
  62   // Max congestion window (in packets) used just before last loss event.
  63   // Note: to improve fairness to other streams an additional back off is
  64   // applied to this value if the new value is below our latest value.
  65   QuicTcpCongestionWindow last_max_congestion_window_;
  66
  67   // Number of acked packets since the cycle started (epoch).
  68   uint32 acked_packets_count_;
  69
  70   // TCP Reno equivalent congestion window in packets.
  71   QuicTcpCongestionWindow estimated_tcp_congestion_window_;
  72
  73   // Origin point of cubic function.
  74   QuicTcpCongestionWindow origin_point_congestion_window_;
  75
  76   // Time to origin point of cubic function in 2^10 fractions of a second.
  77   uint32 time_to_origin_point_;
  78
  79   // Last congestion window in packets computed by cubic function.
  80   QuicTcpCongestionWindow last_target_congestion_window_;
  81
  82   // QuicConnectionStats includes congestion control related stats.
  83   QuicConnectionStats* stats_;
  84
  85   DISALLOW_COPY_AND_ASSIGN(Cubic);
  86 };
  87
  88 }  // namespace net
  89
  90 #endif  // NET_QUIC_CONGESTION_CONTROL_CUBIC_H_