net/quic/congestion_control/cubic_bytes.h

   1 // Copyright (c) 2015 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_BYTES_H_
   9 #define NET_QUIC_CONGESTION_CONTROL_CUBIC_BYTES_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 CubicBytes {
  21  public:
  22   explicit CubicBytes(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   QuicByteCount CongestionWindowAfterPacketLoss(QuicPacketCount current);
  33
  34   // Compute a new congestion window to use after a received ACK.
  35   // Returns the new congestion window in bytes. The new congestion window
  36   // follows a cubic function that depends on the time passed since last packet
  37   // loss.
  38   QuicByteCount CongestionWindowAfterAck(QuicByteCount acked_bytes,
  39                                          QuicByteCount current,
  40                                          QuicTime::Delta delay_min);
  41
  42   // Call on ack arrival when sender is unable to use the available congestion
  43   // window. Resets Cubic state during quiescence.
  44   void OnApplicationLimited();
  45
  46  private:
  47   static const QuicTime::Delta MaxCubicTimeInterval() {
  48     return QuicTime::Delta::FromMilliseconds(30);
  49   }
  50
  51   // Compute the TCP Cubic alpha and beta based on the current number of
  52   // connections.
  53   float Alpha() const;
  54   float Beta() const;
  55
  56   const QuicClock* clock_;
  57
  58   // Number of connections to simulate.
  59   int num_connections_;
  60
  61   // Time when this cycle started, after last loss event.
  62   QuicTime epoch_;
  63
  64   // Time when we updated last_congestion_window.
  65   QuicTime last_update_time_;
  66
  67   // Last congestion window used.
  68   QuicByteCount last_congestion_window_;
  69
  70   // Max congestion window used just before last loss event.
  71   // Note: to improve fairness to other streams an additional back off is
  72   // applied to this value if the new value is below our latest value.
  73   QuicByteCount last_max_congestion_window_;
  74
  75   // Number of acked bytes since the cycle started (epoch).
  76   QuicByteCount acked_bytes_count_;
  77
  78   // TCP Reno equivalent congestion window in packets.
  79   QuicByteCount estimated_tcp_congestion_window_;
  80
  81   // Origin point of cubic function.
  82   QuicByteCount origin_point_congestion_window_;
  83
  84   // Time to origin point of cubic function in 2^10 fractions of a second.
  85   uint32 time_to_origin_point_;
  86
  87   // Last congestion window in packets computed by cubic function.
  88   QuicByteCount last_target_congestion_window_;
  89
  90   DISALLOW_COPY_AND_ASSIGN(CubicBytes);
  91 };
  92
  93 }  // namespace net
  94
  95 #endif  // NET_QUIC_CONGESTION_CONTROL_CUBIC_BYTES_H_