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| 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 Cubic(const QuicClock* clock, QuicConnectionStats* stats); | |
| 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 private: | |
| 42 static const QuicTime::Delta MaxCubicTimeInterval() { | |
| 43 return QuicTime::Delta::FromMilliseconds(30); | |
| 44 } | |
| 45 | |
| 46 // Compute the TCP Cubic alpha and beta based on the current number of | |
| 47 // connections. | |
| 48 float Alpha() const; | |
| 49 float Beta() const; | |
| 50 | |
| 51 // Update congestion control variables in QuicConnectionStats. | |
| 52 void UpdateCongestionControlStats(QuicPacketCount new_cubic_mode_cwnd, | |
| 53 QuicPacketCount new_reno_mode_cwnd); | |
| 54 const QuicClock* clock_; | |
| 55 | |
| 56 // Number of connections to simulate. | |
| 57 int num_connections_; | |
| 58 | |
| 59 // Time when this cycle started, after last loss event. | |
| 60 QuicTime epoch_; | |
| 61 | |
| 62 // Time when we updated last_congestion_window. | |
| 63 QuicTime last_update_time_; | |
| 64 | |
| 65 // Last congestion window (in packets) used. | |
| 66 QuicPacketCount last_congestion_window_; | |
| 67 | |
| 68 // Max congestion window (in packets) used just before last loss event. | |
| 69 // Note: to improve fairness to other streams an additional back off is | |
| 70 // applied to this value if the new value is below our latest value. | |
| 71 QuicPacketCount last_max_congestion_window_; | |
| 72 | |
| 73 // Number of acked packets since the cycle started (epoch). | |
| 74 QuicPacketCount acked_packets_count_; | |
| 75 | |
| 76 // TCP Reno equivalent congestion window in packets. | |
| 77 QuicPacketCount estimated_tcp_congestion_window_; | |
| 78 | |
| 79 // Origin point of cubic function. | |
| 80 QuicPacketCount origin_point_congestion_window_; | |
| 81 | |
| 82 // Time to origin point of cubic function in 2^10 fractions of a second. | |
| 83 uint32 time_to_origin_point_; | |
| 84 | |
| 85 // Last congestion window in packets computed by cubic function. | |
| 86 QuicPacketCount last_target_congestion_window_; | |
| 87 | |
| 88 // QuicConnectionStats includes congestion control related stats. | |
| 89 QuicConnectionStats* stats_; | |
| 90 | |
| 91 DISALLOW_COPY_AND_ASSIGN(Cubic); | |
| 92 }; | |
| 93 | |
| 94 } // namespace net | |
| 95 | |
| 96 #endif // NET_QUIC_CONGESTION_CONTROL_CUBIC_H_ | |
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