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| 1 // Copyright 2014 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 #include "net/quic/congestion_control/tcp_loss_algorithm.h" | |
| 6 | |
| 7 #include "net/quic/congestion_control/rtt_stats.h" | |
| 8 #include "net/quic/quic_bug_tracker.h" | |
| 9 #include "net/quic/quic_protocol.h" | |
| 10 | |
| 11 namespace net { | |
| 12 | |
| 13 namespace { | |
| 14 | |
| 15 // The minimum delay before a packet will be considered lost, | |
| 16 // regardless of SRTT. Half of the minimum TLP, since the loss algorithm only | |
| 17 // triggers when a nack has been receieved for the packet. | |
| 18 static const size_t kMinLossDelayMs = 5; | |
| 19 | |
| 20 // How many RTTs the algorithm waits before determining a packet is lost due | |
| 21 // to early retransmission. | |
| 22 static const double kEarlyRetransmitLossDelayMultiplier = 1.25; | |
| 23 | |
| 24 } // namespace | |
| 25 | |
| 26 TCPLossAlgorithm::TCPLossAlgorithm() | |
| 27 : loss_detection_timeout_(QuicTime::Zero()) {} | |
| 28 | |
| 29 LossDetectionType TCPLossAlgorithm::GetLossDetectionType() const { | |
| 30 return kNack; | |
| 31 } | |
| 32 | |
| 33 // Uses nack counts to decide when packets are lost. | |
| 34 PacketNumberSet TCPLossAlgorithm::DetectLostPackets( | |
| 35 const QuicUnackedPacketMap& unacked_packets, | |
| 36 const QuicTime& time, | |
| 37 QuicPacketNumber largest_observed, | |
| 38 const RttStats& rtt_stats) { | |
| 39 PacketNumberSet lost_packets; | |
| 40 loss_detection_timeout_ = QuicTime::Zero(); | |
| 41 QuicTime::Delta early_retransmit_delay = QuicTime::Delta::Max( | |
| 42 QuicTime::Delta::FromMilliseconds(kMinLossDelayMs), | |
| 43 rtt_stats.smoothed_rtt().Multiply(kEarlyRetransmitLossDelayMultiplier)); | |
| 44 | |
| 45 QuicPacketNumber packet_number = unacked_packets.GetLeastUnacked(); | |
| 46 for (QuicUnackedPacketMap::const_iterator it = unacked_packets.begin(); | |
| 47 it != unacked_packets.end() && packet_number <= largest_observed; | |
| 48 ++it, ++packet_number) { | |
| 49 if (!it->in_flight) { | |
| 50 continue; | |
| 51 } | |
| 52 | |
| 53 QUIC_BUG_IF(it->nack_count == 0 && it->sent_time.IsInitialized()) | |
| 54 << "All packets less than largest observed should have been nacked." | |
| 55 << " packet_number:" << packet_number | |
| 56 << " largest_observed:" << largest_observed; | |
| 57 if (it->nack_count >= kNumberOfNacksBeforeRetransmission) { | |
| 58 lost_packets.insert(packet_number); | |
| 59 continue; | |
| 60 } | |
| 61 | |
| 62 // Immediately lose the packet if it's been an srtt between the sent time | |
| 63 // of it and the largest observed. This speeds recovery from timer based | |
| 64 // retransmissions, such as TLP and RTO, when there may be fewer than | |
| 65 // kNumberOfNacksBeforeRetransmission nacks. | |
| 66 if (it->sent_time.Add(rtt_stats.smoothed_rtt()) < | |
| 67 unacked_packets.GetTransmissionInfo(largest_observed).sent_time) { | |
| 68 lost_packets.insert(packet_number); | |
| 69 continue; | |
| 70 } | |
| 71 | |
| 72 // Only early retransmit(RFC5827) when the last packet gets acked and | |
| 73 // there are retransmittable packets in flight. | |
| 74 // This also implements a timer-protected variant of FACK. | |
| 75 if (!it->retransmittable_frames.empty() && | |
| 76 unacked_packets.largest_sent_packet() == largest_observed) { | |
| 77 // Early retransmit marks the packet as lost once 1.25RTTs have passed | |
| 78 // since the packet was sent and otherwise sets an alarm. | |
| 79 if (time >= it->sent_time.Add(early_retransmit_delay)) { | |
| 80 lost_packets.insert(packet_number); | |
| 81 } else { | |
| 82 // Set the timeout for the earliest retransmittable packet where early | |
| 83 // retransmit applies. | |
| 84 loss_detection_timeout_ = it->sent_time.Add(early_retransmit_delay); | |
| 85 break; | |
| 86 } | |
| 87 } | |
| 88 } | |
| 89 | |
| 90 return lost_packets; | |
| 91 } | |
| 92 | |
| 93 void TCPLossAlgorithm::DetectLosses( | |
| 94 const QuicUnackedPacketMap& unacked_packets, | |
| 95 const QuicTime& time, | |
| 96 const RttStats& rtt_stats, | |
| 97 SendAlgorithmInterface::CongestionVector* packets_lost) { | |
| 98 QUIC_BUG << "DetectLoss is unsupported by TCPLossAlgorithm."; | |
| 99 } | |
| 100 | |
| 101 QuicTime TCPLossAlgorithm::GetLossTimeout() const { | |
| 102 return loss_detection_timeout_; | |
| 103 } | |
| 104 | |
| 105 } // namespace net | |
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Chromium Code Reviews
Issue 1660593004:
Landing Recent QUIC changes until 01/28/2016 18:41 UTC (Closed)
Base URL: https://chromium.googlesource.com/chromium/src.git@Final_0202