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_2008.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 // Start a new slow start phase. 30 void Restart(); 31 32 // Returns true if this ack the last sequence number of our current slow start 33 // round. 34 // Call Reset if this returns true. 35 bool EndOfRound(QuicPacketSequenceNumber ack); 36 37 // Call for each round (burst) in the slow start phase. 38 void Reset(QuicPacketSequenceNumber end_sequence_number); 39 40 // rtt: it the RTT for this ack packet. 41 // delay_min: is the lowest delay (RTT) we have seen during the session. 42 void Update(QuicTime::Delta rtt, QuicTime::Delta delay_min); 43 44 // Returns true when we should exit slow start. 45 bool Exit(); 46 47 bool started() { return started_; } 48 49 QuicTime::Delta SmoothedRtt(); 50 51 private: 52 const QuicClock* clock_; 53 bool started_; 54 bool found_ack_train_; 55 bool found_delay_; 56 QuicTime round_start_; // Beginning of each slow start round. 57 QuicPacketSequenceNumber end_sequence_number_; // End of slow start round. 58 QuicTime last_time_; // Last time when the ACK spacing was close. 59 uint8 sample_count_; // Number of samples to decide current RTT. 60 QuicTime::Delta current_rtt_; // The minimum rtt of current round. 61 62 DISALLOW_COPY_AND_ASSIGN(HybridSlowStart); 63 }; 64 65 } // namespace net 66 67 #endif // NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ 68
