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/time_loss_algorithm.h"
6
7#include "net/quic/congestion_control/rtt_stats.h"
8#include "net/quic/quic_protocol.h"
9
10namespace net {
11namespace {
12
13// The minimum delay before a packet will be considered lost,
14// regardless of SRTT.  Half of the minimum TLP, since the loss algorithm only
15// triggers when a nack has been receieved for the packet.
16static const size_t kMinLossDelayMs = 5;
17
18// How many RTTs the algorithm waits before determining a packet is lost.
19static const double kLossDelayMultiplier = 1.25;
20
21}  // namespace
22
23TimeLossAlgorithm::TimeLossAlgorithm()
24    : loss_detection_timeout_(QuicTime::Zero()) { }
25
26LossDetectionType TimeLossAlgorithm::GetLossDetectionType() const {
27  return kTime;
28}
29
30SequenceNumberSet TimeLossAlgorithm::DetectLostPackets(
31    const QuicUnackedPacketMap& unacked_packets,
32    const QuicTime& time,
33    QuicPacketSequenceNumber largest_observed,
34    const RttStats& rtt_stats) {
35  SequenceNumberSet lost_packets;
36  loss_detection_timeout_ = QuicTime::Zero();
37  QuicTime::Delta loss_delay = QuicTime::Delta::Max(
38      QuicTime::Delta::FromMilliseconds(kMinLossDelayMs),
39      QuicTime::Delta::Max(rtt_stats.SmoothedRtt(), rtt_stats.latest_rtt())
40          .Multiply(kLossDelayMultiplier));
41
42  QuicPacketSequenceNumber sequence_number = unacked_packets.GetLeastUnacked();
43  for (QuicUnackedPacketMap::const_iterator it = unacked_packets.begin();
44       it != unacked_packets.end() && sequence_number <= largest_observed;
45       ++it, ++sequence_number) {
46    if (!it->in_flight) {
47      continue;
48    }
49    LOG_IF(DFATAL, it->nack_count == 0)
50        << "All packets less than largest observed should have been nacked.";
51
52    // Packets are sent in order, so break when we haven't waited long enough
53    // to lose any more packets and leave the loss_time_ set for the timeout.
54    QuicTime when_lost = it->sent_time.Add(loss_delay);
55    if (time < when_lost) {
56      loss_detection_timeout_ = when_lost;
57      break;
58    }
59    lost_packets.insert(sequence_number);
60  }
61
62  return lost_packets;
63}
64
65// loss_time_ is updated in DetectLostPackets, which must be called every time
66// an ack is received or the timeout expires.
67QuicTime TimeLossAlgorithm::GetLossTimeout() const {
68  return loss_detection_timeout_;
69}
70
71}  // namespace net
72