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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 // This class is a helper class to TcpCubicSender. | |
6 // Slow start is the initial startup phase of TCP, it lasts until first packet | |
7 // loss. This class implements hybrid slow start of the TCP cubic send side | |
8 // congestion algorithm. The key feaure of hybrid slow start is that it tries to | |
9 // avoid running into the wall too hard during the slow start phase, which | |
10 // the traditional TCP implementation does. | |
11 // http://netsrv.csc.ncsu.edu/export/hybridstart_pfldnet08.pdf | |
12 // http://research.csc.ncsu.edu/netsrv/sites/default/files/hystart_techreport_20
08.pdf | |
13 | |
14 #ifndef NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ | |
15 #define NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ | |
16 | |
17 #include "base/basictypes.h" | |
18 #include "net/base/net_export.h" | |
19 #include "net/quic/quic_clock.h" | |
20 #include "net/quic/quic_protocol.h" | |
21 #include "net/quic/quic_time.h" | |
22 | |
23 namespace net { | |
24 | |
25 class NET_EXPORT_PRIVATE HybridSlowStart { | |
26 public: | |
27 explicit HybridSlowStart(const QuicClock* clock); | |
28 | |
29 void OnPacketAcked(QuicPacketSequenceNumber acked_sequence_number, | |
30 bool in_slow_start); | |
31 | |
32 void OnPacketSent(QuicPacketSequenceNumber sequence_number); | |
33 | |
34 // ShouldExitSlowStart should be called on every new ack frame, since a new | |
35 // RTT measurement can be made then. | |
36 // rtt: the RTT for this ack packet. | |
37 // min_rtt: is the lowest delay (RTT) we have seen during the session. | |
38 // congestion_window: the congestion window in packets. | |
39 bool ShouldExitSlowStart(QuicTime::Delta rtt, | |
40 QuicTime::Delta min_rtt, | |
41 int64 congestion_window); | |
42 | |
43 // Start a new slow start phase. | |
44 void Restart(); | |
45 | |
46 // TODO(ianswett): The following methods should be private, but that requires | |
47 // a follow up CL to update the unit test. | |
48 // Returns true if this ack the last sequence number of our current slow start | |
49 // round. | |
50 // Call Reset if this returns true. | |
51 bool IsEndOfRound(QuicPacketSequenceNumber ack) const; | |
52 | |
53 // Call for the start of each receive round (burst) in the slow start phase. | |
54 void StartReceiveRound(QuicPacketSequenceNumber last_sent); | |
55 | |
56 void set_ack_train_detection(bool ack_train_detection) { | |
57 ack_train_detection_ = ack_train_detection; | |
58 } | |
59 | |
60 bool ack_train_detection() const { | |
61 return ack_train_detection_; | |
62 } | |
63 | |
64 // Whether slow start has started. | |
65 bool started() const { | |
66 return started_; | |
67 } | |
68 | |
69 private: | |
70 // Whether a condition for exiting slow start has been found. | |
71 enum HystartState { | |
72 NOT_FOUND, | |
73 ACK_TRAIN, // A closely spaced ack train is too long. | |
74 DELAY, // Too much increase in the round's min_rtt was observed. | |
75 }; | |
76 | |
77 const QuicClock* clock_; | |
78 bool ack_train_detection_; | |
79 // Whether the hybrid slow start has been started. | |
80 bool started_; | |
81 HystartState hystart_found_; | |
82 // Last sequence number sent which was CWND limited. | |
83 QuicPacketSequenceNumber last_sent_sequence_number_; | |
84 | |
85 // Variables for tracking acks received during a slow start round. | |
86 QuicTime round_start_; // Beginning of each slow start receive round. | |
87 QuicPacketSequenceNumber end_sequence_number_; // End of the receive round. | |
88 // Last time when the spacing between ack arrivals was less than 2 ms. | |
89 // Defaults to the beginning of the round. | |
90 QuicTime last_close_ack_pair_time_; | |
91 uint32 rtt_sample_count_; // Number of rtt samples in the current round. | |
92 QuicTime::Delta current_min_rtt_; // The minimum rtt of current round. | |
93 | |
94 DISALLOW_COPY_AND_ASSIGN(HybridSlowStart); | |
95 }; | |
96 | |
97 } // namespace net | |
98 | |
99 #endif // NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ | |
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