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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// This class is a helper class to TcpCubicSender.
// Slow start is the initial startup phase of TCP, it lasts until first packet
// loss. This class implements hybrid slow start of the TCP cubic send side
// congestion algorithm. The key feaure of hybrid slow start is that it tries to
// avoid running into the wall too hard during the slow start phase, which
// the traditional TCP implementation does.
// http://netsrv.csc.ncsu.edu/export/hybridstart_pfldnet08.pdf
// http://research.csc.ncsu.edu/netsrv/sites/default/files/hystart_techreport_2008.pdf
#ifndef NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_
#define NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_
#include "base/basictypes.h"
#include "net/base/net_export.h"
#include "net/quic/quic_clock.h"
#include "net/quic/quic_protocol.h"
#include "net/quic/quic_time.h"
namespace net {
class NET_EXPORT_PRIVATE HybridSlowStart {
public:
explicit HybridSlowStart(const QuicClock* clock);
// Start a new slow start phase.
void Restart();
// Returns true if this ack the last sequence number of our current slow start
// round.
// Call Reset if this returns true.
bool EndOfRound(QuicPacketSequenceNumber ack);
// Call for each round (burst) in the slow start phase.
void Reset(QuicPacketSequenceNumber end_sequence_number);
// rtt: it the RTT for this ack packet.
// delay_min: is the lowest delay (RTT) we have seen during the session.
void Update(QuicTime::Delta rtt, QuicTime::Delta delay_min);
// Returns true when we should exit slow start.
bool Exit();
bool started() { return started_; }
QuicTime::Delta SmoothedRtt();
private:
const QuicClock* clock_;
bool started_;
bool found_ack_train_;
bool found_delay_;
QuicTime round_start_; // Beginning of each slow start round.
QuicPacketSequenceNumber end_sequence_number_; // End of slow start round.
QuicTime last_time_; // Last time when the ACK spacing was close.
uint8 sample_count_; // Number of samples to decide current RTT.
QuicTime::Delta current_rtt_; // The minimum rtt of current round.
DISALLOW_COPY_AND_ASSIGN(HybridSlowStart);
};
} // namespace net
#endif // NET_QUIC_CONGESTION_CONTROL_HYBRID_SLOW_START_H_
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