1// Copyright (c) 2013 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/available_channel_estimator.h"
6
7static const int kNumberOfSamples = 9;
8
9namespace net {
10
11AvailableChannelEstimator::AvailableChannelEstimator(
12    QuicPacketSequenceNumber sequence_number,
13    QuicTime first_send_time,
14    QuicTime first_receive_time)
15    : first_sequence_number_(sequence_number),
16      first_send_time_(first_send_time),
17      first_receive_time_(first_receive_time),
18      last_incorporated_sequence_number_(sequence_number),
19      last_time_sent_(QuicTime::Zero()),
20      last_receive_time_(QuicTime::Zero()),
21      number_of_sequence_numbers_(0),
22      received_bytes_(0) {
23}
24
25void AvailableChannelEstimator::OnIncomingFeedback(
26    QuicPacketSequenceNumber sequence_number,
27    QuicByteCount packet_size,
28    QuicTime sent_time,
29    QuicTime receive_time) {
30  if (sequence_number <= first_sequence_number_) {
31    // Ignore pre-probe feedback.
32    return;
33  }
34  if (sequence_number <= last_incorporated_sequence_number_) {
35    // Ignore old feedback; will remove duplicates.
36    return;
37  }
38  // Remember the highest received sequence number.
39  last_incorporated_sequence_number_ = sequence_number;
40  if (number_of_sequence_numbers_ < kNumberOfSamples) {
41    // We don't care how many sequence numbers we have after we pass
42    // kNumberOfSamples.
43    number_of_sequence_numbers_++;
44  }
45  last_receive_time_ = receive_time;
46  last_time_sent_ = sent_time;
47  received_bytes_ += packet_size;
48  // TODO(pwestin): the variance here should give us information about accuracy.
49}
50
51AvailableChannelEstimateState
52    AvailableChannelEstimator::GetAvailableChannelEstimate(
53        QuicBandwidth* bandwidth) const {
54  if (number_of_sequence_numbers_ < 2) {
55    return kAvailableChannelEstimateUnknown;
56  }
57  QuicTime::Delta send_delta = last_time_sent_.Subtract(first_send_time_);
58  QuicTime::Delta receive_delta =
59      last_receive_time_.Subtract(first_receive_time_);
60
61  // TODO(pwestin): room for improvement here. Keeping it simple for now.
62  *bandwidth = QuicBandwidth::FromBytesAndTimeDelta(received_bytes_,
63                                                    receive_delta);
64
65  QuicTime::Delta diff = receive_delta.Subtract(send_delta);
66  QuicTime::Delta ten_percent_of_send_time =
67      QuicTime::Delta::FromMicroseconds(send_delta.ToMicroseconds() / 10);
68
69  if (diff < ten_percent_of_send_time) {
70    return kAvailableChannelEstimateSenderLimited;
71  }
72  if (number_of_sequence_numbers_ < kNumberOfSamples) {
73    return kAvailableChannelEstimateUncertain;
74  }
75  return kAvailableChannelEstimateGood;
76}
77
78}  // namespace net
79