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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_protocol.h" | |
| 9 | |
| 10 namespace net { | |
| 11 | |
| 12 namespace { | |
| 13 | |
| 14 // The minimum delay before a packet will be considered lost, | |
| 15 // regardless of SRTT. Half of the minimum TLP, since the loss algorithm only | |
| 16 // triggers when a nack has been receieved for the packet. | |
| 17 static const size_t kMinLossDelayMs = 5; | |
| 18 | |
| 19 // How many RTTs the algorithm waits before determining a packet is lost due | |
| 20 // to early retransmission. | |
| 21 static const double kEarlyRetransmitLossDelayMultiplier = 1.25; | |
| 22 | |
| 23 } // namespace | |
| 24 | |
| 25 TCPLossAlgorithm::TCPLossAlgorithm() | |
| 26 : loss_detection_timeout_(QuicTime::Zero()) { } | |
| 27 | |
| 28 LossDetectionType TCPLossAlgorithm::GetLossDetectionType() const { | |
| 29 return kNack; | |
| 30 } | |
| 31 | |
| 32 // Uses nack counts to decide when packets are lost. | |
| 33 SequenceNumberSet TCPLossAlgorithm::DetectLostPackets( | |
| 34 const QuicUnackedPacketMap& unacked_packets, | |
| 35 const QuicTime& time, | |
| 36 QuicPacketSequenceNumber largest_observed, | |
| 37 const RttStats& rtt_stats) { | |
| 38 SequenceNumberSet lost_packets; | |
| 39 loss_detection_timeout_ = QuicTime::Zero(); | |
| 40 QuicTime::Delta early_retransmit_delay = QuicTime::Delta::Max( | |
| 41 QuicTime::Delta::FromMilliseconds(kMinLossDelayMs), | |
| 42 rtt_stats.smoothed_rtt().Multiply(kEarlyRetransmitLossDelayMultiplier)); | |
| 43 | |
| 44 QuicPacketSequenceNumber sequence_number = unacked_packets.GetLeastUnacked(); | |
| 45 for (QuicUnackedPacketMap::const_iterator it = unacked_packets.begin(); | |
| 46 it != unacked_packets.end() && sequence_number <= largest_observed; | |
| 47 ++it, ++sequence_number) { | |
| 48 if (!it->in_flight) { | |
| 49 continue; | |
| 50 } | |
| 51 | |
| 52 LOG_IF(DFATAL, it->nack_count == 0 && it->sent_time.IsInitialized()) | |
| 53 << "All packets less than largest observed should have been nacked." | |
| 54 << "sequence_number:" << sequence_number | |
| 55 << " largest_observed:" << largest_observed; | |
| 56 if (it->nack_count >= kNumberOfNacksBeforeRetransmission) { | |
| 57 lost_packets.insert(sequence_number); | |
| 58 continue; | |
| 59 } | |
| 60 | |
| 61 // Immediately lose the packet if it's been an srtt between the sent time | |
| 62 // of it and the largest observed. This speeds recovery from timer based | |
| 63 // retransmissions, such as TLP and RTO, when there may be fewer than | |
| 64 // kNumberOfNacksBeforeRetransmission nacks. | |
| 65 if (it->sent_time.Add(rtt_stats.smoothed_rtt()) < | |
| 66 unacked_packets.GetTransmissionInfo(largest_observed).sent_time) { | |
| 67 lost_packets.insert(sequence_number); | |
| 68 continue; | |
| 69 } | |
| 70 | |
| 71 // Only early retransmit(RFC5827) when the last packet gets acked and | |
| 72 // there are retransmittable packets in flight. | |
| 73 // This also implements a timer-protected variant of FACK. | |
| 74 if (it->retransmittable_frames && | |
| 75 unacked_packets.largest_sent_packet() == largest_observed) { | |
| 76 // Early retransmit marks the packet as lost once 1.25RTTs have passed | |
| 77 // since the packet was sent and otherwise sets an alarm. | |
| 78 if (time >= it->sent_time.Add(early_retransmit_delay)) { | |
| 79 lost_packets.insert(sequence_number); | |
| 80 } else { | |
| 81 // Set the timeout for the earliest retransmittable packet where early | |
| 82 // retransmit applies. | |
| 83 loss_detection_timeout_ = it->sent_time.Add(early_retransmit_delay); | |
| 84 break; | |
| 85 } | |
| 86 } | |
| 87 } | |
| 88 | |
| 89 return lost_packets; | |
| 90 } | |
| 91 | |
| 92 QuicTime TCPLossAlgorithm::GetLossTimeout() const { | |
| 93 return loss_detection_timeout_; | |
| 94 } | |
| 95 | |
| 96 } // namespace net | |
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