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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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