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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 <stdint.h> | |
12 | |
13 #include "base/macros.h" | |
14 #include "net/base/net_export.h" | |
15 #include "net/quic/quic_bandwidth.h" | |
16 #include "net/quic/quic_clock.h" | |
17 #include "net/quic/quic_connection_stats.h" | |
18 #include "net/quic/quic_time.h" | |
19 | |
20 namespace net { | |
21 | |
22 class NET_EXPORT_PRIVATE CubicBytes { | |
23 public: | |
24 explicit CubicBytes(const QuicClock* clock); | |
25 | |
26 void SetNumConnections(int num_connections); | |
27 | |
28 // Call after a timeout to reset the cubic state. | |
29 void Reset(); | |
30 | |
31 // Compute a new congestion window to use after a loss event. | |
32 // Returns the new congestion window in packets. The new congestion window is | |
33 // a multiplicative decrease of our current window. | |
34 QuicByteCount CongestionWindowAfterPacketLoss(QuicPacketCount current); | |
35 | |
36 // Compute a new congestion window to use after a received ACK. | |
37 // Returns the new congestion window in bytes. The new congestion window | |
38 // follows a cubic function that depends on the time passed since last packet | |
39 // loss. | |
40 QuicByteCount CongestionWindowAfterAck(QuicByteCount acked_bytes, | |
41 QuicByteCount current, | |
42 QuicTime::Delta delay_min); | |
43 | |
44 // Call on ack arrival when sender is unable to use the available congestion | |
45 // window. Resets Cubic state during quiescence. | |
46 void OnApplicationLimited(); | |
47 | |
48 private: | |
49 static const QuicTime::Delta MaxCubicTimeInterval() { | |
50 return QuicTime::Delta::FromMilliseconds(30); | |
51 } | |
52 | |
53 // Compute the TCP Cubic alpha and beta based on the current number of | |
54 // connections. | |
55 float Alpha() const; | |
56 float Beta() const; | |
57 | |
58 const QuicClock* clock_; | |
59 | |
60 // Number of connections to simulate. | |
61 int num_connections_; | |
62 | |
63 // Time when this cycle started, after last loss event. | |
64 QuicTime epoch_; | |
65 | |
66 // Time when we updated last_congestion_window. | |
67 QuicTime last_update_time_; | |
68 | |
69 // Last congestion window used. | |
70 QuicByteCount last_congestion_window_; | |
71 | |
72 // Max congestion window used just before last loss event. | |
73 // Note: to improve fairness to other streams an additional back off is | |
74 // applied to this value if the new value is below our latest value. | |
75 QuicByteCount last_max_congestion_window_; | |
76 | |
77 // Number of acked bytes since the cycle started (epoch). | |
78 QuicByteCount acked_bytes_count_; | |
79 | |
80 // TCP Reno equivalent congestion window in packets. | |
81 QuicByteCount estimated_tcp_congestion_window_; | |
82 | |
83 // Origin point of cubic function. | |
84 QuicByteCount origin_point_congestion_window_; | |
85 | |
86 // Time to origin point of cubic function in 2^10 fractions of a second. | |
87 uint32_t time_to_origin_point_; | |
88 | |
89 // Last congestion window in packets computed by cubic function. | |
90 QuicByteCount last_target_congestion_window_; | |
91 | |
92 DISALLOW_COPY_AND_ASSIGN(CubicBytes); | |
93 }; | |
94 | |
95 } // namespace net | |
96 | |
97 #endif // NET_QUIC_CONGESTION_CONTROL_CUBIC_BYTES_H_ | |
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