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: MaxCubicTimeInterval()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_ 91