| // 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. |
| // This does not implement ack train detection because it interacts poorly with |
| // pacing. |
| // http://netsrv.csc.ncsu.edu/export/hybridstart_pfldnet08.pdf |
| // http://research.csc.ncsu.edu/netsrv/sites/default/files/hystart_techreport_2008.pdf |
| |
| #ifndef QUICHE_QUIC_CORE_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ |
| #define QUICHE_QUIC_CORE_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ |
| |
| #include <cstdint> |
| |
| #include "quiche/quic/core/quic_packets.h" |
| #include "quiche/quic/core/quic_time.h" |
| #include "quiche/quic/platform/api/quic_export.h" |
| |
| namespace quic { |
| |
| class QUIC_EXPORT_PRIVATE HybridSlowStart { |
| public: |
| HybridSlowStart(); |
| HybridSlowStart(const HybridSlowStart&) = delete; |
| HybridSlowStart& operator=(const HybridSlowStart&) = delete; |
| |
| void OnPacketAcked(QuicPacketNumber acked_packet_number); |
| |
| void OnPacketSent(QuicPacketNumber packet_number); |
| |
| // ShouldExitSlowStart should be called on every new ack frame, since a new |
| // RTT measurement can be made then. |
| // rtt: the RTT for this ack packet. |
| // min_rtt: is the lowest delay (RTT) we have seen during the session. |
| // congestion_window: the congestion window in packets. |
| bool ShouldExitSlowStart(QuicTime::Delta rtt, QuicTime::Delta min_rtt, |
| QuicPacketCount congestion_window); |
| |
| // Start a new slow start phase. |
| void Restart(); |
| |
| // TODO(ianswett): The following methods should be private, but that requires |
| // a follow up CL to update the unit test. |
| // Returns true if this ack the last packet number of our current slow start |
| // round. |
| // Call Reset if this returns true. |
| bool IsEndOfRound(QuicPacketNumber ack) const; |
| |
| // Call for the start of each receive round (burst) in the slow start phase. |
| void StartReceiveRound(QuicPacketNumber last_sent); |
| |
| // Whether slow start has started. |
| bool started() const { return started_; } |
| |
| private: |
| // Whether a condition for exiting slow start has been found. |
| enum HystartState { |
| NOT_FOUND, |
| DELAY, // Too much increase in the round's min_rtt was observed. |
| }; |
| |
| // Whether the hybrid slow start has been started. |
| bool started_; |
| HystartState hystart_found_; |
| // Last packet number sent which was CWND limited. |
| QuicPacketNumber last_sent_packet_number_; |
| |
| // Variables for tracking acks received during a slow start round. |
| QuicPacketNumber end_packet_number_; // End of the receive round. |
| uint32_t rtt_sample_count_; // Number of rtt samples in the current round. |
| QuicTime::Delta current_min_rtt_; // The minimum rtt of current round. |
| }; |
| |
| } // namespace quic |
| |
| #endif // QUICHE_QUIC_CORE_CONGESTION_CONTROL_HYBRID_SLOW_START_H_ |