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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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