net/quic/congestion_control/tcp_cubic_sender_test.cc

// 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.

#include <algorithm>

#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "net/quic/congestion_control/rtt_stats.h"
#include "net/quic/congestion_control/tcp_cubic_sender.h"
#include "net/quic/congestion_control/tcp_receiver.h"
#include "net/quic/crypto/crypto_protocol.h"
#include "net/quic/quic_utils.h"
#include "net/quic/test_tools/mock_clock.h"
#include "net/quic/test_tools/quic_config_peer.h"
#include "testing/gtest/include/gtest/gtest.h"

using std::make_pair;
using std::min;

namespace net {
namespace test {

const int64 kInitialCongestionWindow = 10;
const uint32 kDefaultWindowTCP = kInitialCongestionWindow * kDefaultTCPMSS;
const float kRenoBeta = 0.7f;  // Reno backoff factor.

// TODO(ianswett): Remove 10000 once b/10075719 is fixed.
const QuicPacketCount kDefaultMaxCongestionWindowTCP = 10000;

class TcpCubicSenderPeer : public TcpCubicSender {
 public:
  TcpCubicSenderPeer(const QuicClock* clock,
                     bool reno,
                     QuicPacketCount max_tcp_congestion_window)
      : TcpCubicSender(
            clock, &rtt_stats_, reno, max_tcp_congestion_window, &stats_) {
  }

  QuicPacketCount congestion_window() {
    return congestion_window_;
  }

  QuicPacketCount slowstart_threshold() {
    return slowstart_threshold_;
  }

  const HybridSlowStart& hybrid_slow_start() const {
    return hybrid_slow_start_;
  }

  float GetRenoBeta() const {
    return RenoBeta();
  }

  RttStats rtt_stats_;
  QuicConnectionStats stats_;
};

class TcpCubicSenderTest : public ::testing::Test {
 protected:
  TcpCubicSenderTest()
      : one_ms_(QuicTime::Delta::FromMilliseconds(1)),
        sender_(new TcpCubicSenderPeer(&clock_, true,
                                       kDefaultMaxCongestionWindowTCP)),
        receiver_(new TcpReceiver()),
        sequence_number_(1),
        acked_sequence_number_(0),
        bytes_in_flight_(0) {
    standard_packet_.bytes_sent = kDefaultTCPMSS;
  }

  int SendAvailableSendWindow() {
    // Send as long as TimeUntilSend returns Zero.
    int packets_sent = 0;
    bool can_send = sender_->TimeUntilSend(
        clock_.Now(), bytes_in_flight_, HAS_RETRANSMITTABLE_DATA).IsZero();
    while (can_send) {
      sender_->OnPacketSent(clock_.Now(), bytes_in_flight_, sequence_number_++,
                            kDefaultTCPMSS, HAS_RETRANSMITTABLE_DATA);
      ++packets_sent;
      bytes_in_flight_ += kDefaultTCPMSS;
      can_send = sender_->TimeUntilSend(
          clock_.Now(), bytes_in_flight_, HAS_RETRANSMITTABLE_DATA).IsZero();
    }
    return packets_sent;
  }

  // Normal is that TCP acks every other segment.
  void AckNPackets(int n) {
    sender_->rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(60),
                                  QuicTime::Delta::Zero(),
                                  clock_.Now());
    SendAlgorithmInterface::CongestionVector acked_packets;
    SendAlgorithmInterface::CongestionVector lost_packets;
    for (int i = 0; i < n; ++i) {
      ++acked_sequence_number_;
      acked_packets.push_back(
          make_pair(acked_sequence_number_, standard_packet_));
    }
    sender_->OnCongestionEvent(
        true, bytes_in_flight_, acked_packets, lost_packets);
    bytes_in_flight_ -= n * kDefaultTCPMSS;
    clock_.AdvanceTime(one_ms_);
  }

  void LoseNPackets(int n) {
    SendAlgorithmInterface::CongestionVector acked_packets;
    SendAlgorithmInterface::CongestionVector lost_packets;
    for (int i = 0; i < n; ++i) {
      ++acked_sequence_number_;
      lost_packets.push_back(
          make_pair(acked_sequence_number_, standard_packet_));
    }
    sender_->OnCongestionEvent(
        false, bytes_in_flight_, acked_packets, lost_packets);
    bytes_in_flight_ -= n * kDefaultTCPMSS;
  }

  // Does not increment acked_sequence_number_.
  void LosePacket(QuicPacketSequenceNumber sequence_number) {
    SendAlgorithmInterface::CongestionVector acked_packets;
    SendAlgorithmInterface::CongestionVector lost_packets;
    lost_packets.push_back(
        make_pair(sequence_number, standard_packet_));
    sender_->OnCongestionEvent(
        false, bytes_in_flight_, acked_packets, lost_packets);
    bytes_in_flight_ -= kDefaultTCPMSS;
  }

  const QuicTime::Delta one_ms_;
  MockClock clock_;
  scoped_ptr<TcpCubicSenderPeer> sender_;
  scoped_ptr<TcpReceiver> receiver_;
  QuicPacketSequenceNumber sequence_number_;
  QuicPacketSequenceNumber acked_sequence_number_;
  QuicByteCount bytes_in_flight_;
  TransmissionInfo standard_packet_;
};

TEST_F(TcpCubicSenderTest, SimpleSender) {
  // At startup make sure we are at the default.
  EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
  // At startup make sure we can send.
  EXPECT_TRUE(sender_->TimeUntilSend(clock_.Now(),
                                     0,
                                     HAS_RETRANSMITTABLE_DATA).IsZero());
  // Make sure we can send.
  EXPECT_TRUE(sender_->TimeUntilSend(clock_.Now(),
                                     0,
                                     HAS_RETRANSMITTABLE_DATA).IsZero());
  // And that window is un-affected.
  EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());

  // Fill the send window with data, then verify that we can't send.
  SendAvailableSendWindow();
  EXPECT_FALSE(sender_->TimeUntilSend(clock_.Now(),
                                      sender_->GetCongestionWindow(),
                                      HAS_RETRANSMITTABLE_DATA).IsZero());
}

TEST_F(TcpCubicSenderTest, ApplicationLimitedSlowStart) {
  // Send exactly 10 packets and ensure the CWND ends at 14 packets.
  const int kNumberOfAcks = 5;
  // At startup make sure we can send.
  EXPECT_TRUE(sender_->TimeUntilSend(clock_.Now(),
      0,
      HAS_RETRANSMITTABLE_DATA).IsZero());
  // Make sure we can send.
  EXPECT_TRUE(sender_->TimeUntilSend(clock_.Now(),
                                     0,
                                     HAS_RETRANSMITTABLE_DATA).IsZero());

  SendAvailableSendWindow();
  for (int i = 0; i < kNumberOfAcks; ++i) {
    AckNPackets(2);
  }
  QuicByteCount bytes_to_send = sender_->GetCongestionWindow();
  // It's expected 2 acks will arrive when the bytes_in_flight are greater than
  // half the CWND.
  EXPECT_EQ(kDefaultWindowTCP + kDefaultTCPMSS * 2 * 2,
            bytes_to_send);
}

TEST_F(TcpCubicSenderTest, ExponentialSlowStart) {
  const int kNumberOfAcks = 20;
  // At startup make sure we can send.
  EXPECT_TRUE(sender_->TimeUntilSend(clock_.Now(),
      0,
      HAS_RETRANSMITTABLE_DATA).IsZero());
  // Make sure we can send.
  EXPECT_TRUE(sender_->TimeUntilSend(clock_.Now(),
                                     0,
                                     HAS_RETRANSMITTABLE_DATA).IsZero());

  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  QuicByteCount bytes_to_send = sender_->GetCongestionWindow();
  EXPECT_EQ(kDefaultWindowTCP + kDefaultTCPMSS * 2 * kNumberOfAcks,
            bytes_to_send);
}

TEST_F(TcpCubicSenderTest, SlowStartAckTrain) {
  sender_->SetNumEmulatedConnections(1);
  EXPECT_EQ(kDefaultMaxCongestionWindowTCP * kDefaultTCPMSS,
            sender_->GetSlowStartThreshold());

  // Make sure that we fall out of slow start when we send ACK train longer
  // than half the RTT, in this test case 30ms, which is more than 30 calls to
  // Ack2Packets in one round.
  // Since we start at 10 packet first round will be 5 second round 10 etc
  // Hence we should pass 30 at 65 = 5 + 10 + 20 + 30
  const int kNumberOfAcks = 65;
  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  QuicByteCount expected_send_window =
      kDefaultWindowTCP + (kDefaultTCPMSS * 2 * kNumberOfAcks);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // We should now have fallen out of slow start.
  // Testing Reno phase.
  // We should need 140(65*2+10) ACK:ed packets before increasing window by
  // one.
  for (int i = 0; i < 69; ++i) {
    SendAvailableSendWindow();
    AckNPackets(2);
    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  }
  SendAvailableSendWindow();
  AckNPackets(2);
  QuicByteCount expected_ss_tresh = expected_send_window;
  expected_send_window += kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  EXPECT_EQ(expected_ss_tresh, sender_->GetSlowStartThreshold());
  EXPECT_EQ(140u, sender_->slowstart_threshold());

  // Now RTO and ensure slow start gets reset.
  EXPECT_TRUE(sender_->hybrid_slow_start().started());
  sender_->OnRetransmissionTimeout(true);
  EXPECT_FALSE(sender_->hybrid_slow_start().started());
  EXPECT_EQ(2 * kDefaultTCPMSS, sender_->GetCongestionWindow());
  EXPECT_EQ(expected_send_window / 2 / kDefaultTCPMSS,
            sender_->slowstart_threshold());

  // Now revert the RTO and ensure the CWND and slowstart threshold revert.
  sender_->RevertRetransmissionTimeout();
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  EXPECT_EQ(140u, sender_->slowstart_threshold());
}

TEST_F(TcpCubicSenderTest, SlowStartPacketLoss) {
  sender_->SetNumEmulatedConnections(1);
  const int kNumberOfAcks = 10;
  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  SendAvailableSendWindow();
  QuicByteCount expected_send_window = kDefaultWindowTCP +
      (kDefaultTCPMSS * 2 * kNumberOfAcks);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Lose a packet to exit slow start.
  LoseNPackets(1);
  size_t packets_in_recovery_window = expected_send_window / kDefaultTCPMSS;

  // We should now have fallen out of slow start with a reduced window.
  expected_send_window *= kRenoBeta;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Recovery phase. We need to ack every packet in the recovery window before
  // we exit recovery.
  size_t number_of_packets_in_window = expected_send_window / kDefaultTCPMSS;
  DVLOG(1) << "number_packets: " << number_of_packets_in_window;
  AckNPackets(packets_in_recovery_window);
  SendAvailableSendWindow();
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // We need to ack an entire window before we increase CWND by 1.
  AckNPackets(number_of_packets_in_window - 2);
  SendAvailableSendWindow();
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Next ack should increase cwnd by 1.
  AckNPackets(1);
  expected_send_window += kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Now RTO and ensure slow start gets reset.
  EXPECT_TRUE(sender_->hybrid_slow_start().started());
  sender_->OnRetransmissionTimeout(true);
  EXPECT_FALSE(sender_->hybrid_slow_start().started());
}

TEST_F(TcpCubicSenderTest, NoPRRWhenLessThanOnePacketInFlight) {
  SendAvailableSendWindow();
  LoseNPackets(kInitialCongestionWindow - 1);
  AckNPackets(1);
  // PRR will allow 2 packets for every ack during recovery.
  EXPECT_EQ(2, SendAvailableSendWindow());
  // Simulate abandoning all packets by supplying a bytes_in_flight of 0.
  // PRR should now allow a packet to be sent, even though prr's state
  // variables believe it has sent enough packets.
  EXPECT_EQ(QuicTime::Delta::Zero(),
            sender_->TimeUntilSend(clock_.Now(), 0, HAS_RETRANSMITTABLE_DATA));
}

TEST_F(TcpCubicSenderTest, SlowStartPacketLossPRR) {
  sender_->SetNumEmulatedConnections(1);
  // Test based on the first example in RFC6937.
  // Ack 10 packets in 5 acks to raise the CWND to 20, as in the example.
  const int kNumberOfAcks = 5;
  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  SendAvailableSendWindow();
  QuicByteCount expected_send_window = kDefaultWindowTCP +
      (kDefaultTCPMSS * 2 * kNumberOfAcks);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  LoseNPackets(1);

  // We should now have fallen out of slow start with a reduced window.
  size_t send_window_before_loss = expected_send_window;
  expected_send_window *= kRenoBeta;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Testing TCP proportional rate reduction.
  // We should send packets paced over the received acks for the remaining
  // outstanding packets. The number of packets before we exit recovery is the
  // original CWND minus the packet that has been lost and the one which
  // triggered the loss.
  size_t remaining_packets_in_recovery =
      send_window_before_loss / kDefaultTCPMSS - 2;

  for (size_t i = 0; i < remaining_packets_in_recovery; ++i) {
    AckNPackets(1);
    SendAvailableSendWindow();
    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  }

  // We need to ack another window before we increase CWND by 1.
  size_t number_of_packets_in_window = expected_send_window / kDefaultTCPMSS;
  for (size_t i = 0; i < number_of_packets_in_window; ++i) {
    AckNPackets(1);
    EXPECT_EQ(1, SendAvailableSendWindow());
    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  }

  AckNPackets(1);
  expected_send_window += kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, SlowStartBurstPacketLossPRR) {
  sender_->SetNumEmulatedConnections(1);
  // Test based on the second example in RFC6937, though we also implement
  // forward acknowledgements, so the first two incoming acks will trigger
  // PRR immediately.
  // Ack 20 packets in 10 acks to raise the CWND to 30.
  const int kNumberOfAcks = 10;
  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  SendAvailableSendWindow();
  QuicByteCount expected_send_window = kDefaultWindowTCP +
      (kDefaultTCPMSS * 2 * kNumberOfAcks);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Lose one more than the congestion window reduction, so that after loss,
  // bytes_in_flight is lesser than the congestion window.
  size_t send_window_after_loss = kRenoBeta * expected_send_window;
  size_t num_packets_to_lose =
      (expected_send_window - send_window_after_loss) / kDefaultTCPMSS + 1;
  LoseNPackets(num_packets_to_lose);
  // Immediately after the loss, ensure at least one packet can be sent.
  // Losses without subsequent acks can occur with timer based loss detection.
  EXPECT_TRUE(sender_->TimeUntilSend(
      clock_.Now(), bytes_in_flight_, HAS_RETRANSMITTABLE_DATA).IsZero());
  AckNPackets(1);

  // We should now have fallen out of slow start with a reduced window.
  expected_send_window *= kRenoBeta;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Only 2 packets should be allowed to be sent, per PRR-SSRB
  EXPECT_EQ(2, SendAvailableSendWindow());

  // Ack the next packet, which triggers another loss.
  LoseNPackets(1);
  AckNPackets(1);

  // Send 2 packets to simulate PRR-SSRB.
  EXPECT_EQ(2, SendAvailableSendWindow());

  // Ack the next packet, which triggers another loss.
  LoseNPackets(1);
  AckNPackets(1);

  // Send 2 packets to simulate PRR-SSRB.
  EXPECT_EQ(2, SendAvailableSendWindow());

  // Exit recovery and return to sending at the new rate.
  for (int i = 0; i < kNumberOfAcks; ++i) {
    AckNPackets(1);
    EXPECT_EQ(1, SendAvailableSendWindow());
  }
}

TEST_F(TcpCubicSenderTest, RTOCongestionWindowAndRevert) {
  EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
  EXPECT_EQ(10000u, sender_->slowstart_threshold());

  // Expect the window to decrease to the minimum once the RTO fires
  // and slow start threshold to be set to 1/2 of the CWND.
  sender_->OnRetransmissionTimeout(true);
  EXPECT_EQ(2 * kDefaultTCPMSS, sender_->GetCongestionWindow());
  EXPECT_EQ(5u, sender_->slowstart_threshold());

  // Now repair the RTO and ensure the slowstart threshold reverts.
  sender_->RevertRetransmissionTimeout();
  EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
  EXPECT_EQ(10000u, sender_->slowstart_threshold());
}

TEST_F(TcpCubicSenderTest, RTOCongestionWindowNoRetransmission) {
  EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());

  // Expect the window to remain unchanged if the RTO fires but no
  // packets are retransmitted.
  sender_->OnRetransmissionTimeout(false);
  EXPECT_EQ(kDefaultWindowTCP, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, RetransmissionDelay) {
  const int64 kRttMs = 10;
  const int64 kDeviationMs = 3;
  EXPECT_EQ(QuicTime::Delta::Zero(), sender_->RetransmissionDelay());

  sender_->rtt_stats_.UpdateRtt(QuicTime::Delta::FromMilliseconds(kRttMs),
                                QuicTime::Delta::Zero(), clock_.Now());

  // Initial value is to set the median deviation to half of the initial
  // rtt, the median in then multiplied by a factor of 4 and finally the
  // smoothed rtt is added which is the initial rtt.
  QuicTime::Delta expected_delay =
      QuicTime::Delta::FromMilliseconds(kRttMs + kRttMs / 2 * 4);
  EXPECT_EQ(expected_delay, sender_->RetransmissionDelay());

  for (int i = 0; i < 100; ++i) {
    // Run to make sure that we converge.
    sender_->rtt_stats_.UpdateRtt(
        QuicTime::Delta::FromMilliseconds(kRttMs + kDeviationMs),
        QuicTime::Delta::Zero(), clock_.Now());
    sender_->rtt_stats_.UpdateRtt(
        QuicTime::Delta::FromMilliseconds(kRttMs - kDeviationMs),
        QuicTime::Delta::Zero(), clock_.Now());
  }
  expected_delay = QuicTime::Delta::FromMilliseconds(kRttMs + kDeviationMs * 4);

  EXPECT_NEAR(kRttMs, sender_->rtt_stats_.SmoothedRtt().ToMilliseconds(), 1);
  EXPECT_NEAR(expected_delay.ToMilliseconds(),
              sender_->RetransmissionDelay().ToMilliseconds(),
              1);
  EXPECT_EQ(static_cast<int64>(
                sender_->GetCongestionWindow() * kNumMicrosPerSecond /
                sender_->rtt_stats_.SmoothedRtt().ToMicroseconds()),
            sender_->BandwidthEstimate().ToBytesPerSecond());
}

TEST_F(TcpCubicSenderTest, SlowStartMaxSendWindow) {
  const QuicPacketCount kMaxCongestionWindowTCP = 50;
  const int kNumberOfAcks = 100;
  sender_.reset(
      new TcpCubicSenderPeer(&clock_, false, kMaxCongestionWindowTCP));

  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  QuicByteCount expected_send_window =
      kMaxCongestionWindowTCP * kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, TcpRenoMaxCongestionWindow) {
  const QuicPacketCount kMaxCongestionWindowTCP = 50;
  const int kNumberOfAcks = 1000;
  sender_.reset(
      new TcpCubicSenderPeer(&clock_, true, kMaxCongestionWindowTCP));

  SendAvailableSendWindow();
  AckNPackets(2);
  // Make sure we fall out of slow start.
  LoseNPackets(1);

  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }

  QuicByteCount expected_send_window =
      kMaxCongestionWindowTCP * kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, TcpCubicMaxCongestionWindow) {
  const QuicPacketCount kMaxCongestionWindowTCP = 50;
  // Set to 10000 to compensate for small cubic alpha.
  const int kNumberOfAcks = 10000;

  sender_.reset(
      new TcpCubicSenderPeer(&clock_, false, kMaxCongestionWindowTCP));

  SendAvailableSendWindow();
  AckNPackets(2);
  // Make sure we fall out of slow start.
  LoseNPackets(1);

  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }

  QuicByteCount expected_send_window =
      kMaxCongestionWindowTCP * kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, MultipleLossesInOneWindow) {
  SendAvailableSendWindow();
  const QuicByteCount initial_window = sender_->GetCongestionWindow();
  LosePacket(acked_sequence_number_ + 1);
  const QuicByteCount post_loss_window = sender_->GetCongestionWindow();
  EXPECT_GT(initial_window, post_loss_window);
  LosePacket(acked_sequence_number_ + 3);
  EXPECT_EQ(post_loss_window, sender_->GetCongestionWindow());
  LosePacket(sequence_number_ - 1);
  EXPECT_EQ(post_loss_window, sender_->GetCongestionWindow());

  // Lose a later packet and ensure the window decreases.
  LosePacket(sequence_number_);
  EXPECT_GT(post_loss_window, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, DontTrackAckPackets) {
  // Send a packet with no retransmittable data, and ensure it's not tracked.
  EXPECT_FALSE(sender_->OnPacketSent(clock_.Now(), bytes_in_flight_,
                                     sequence_number_++, kDefaultTCPMSS,
                                     NO_RETRANSMITTABLE_DATA));

  // Send a data packet with retransmittable data, and ensure it is tracked.
  EXPECT_TRUE(sender_->OnPacketSent(clock_.Now(), bytes_in_flight_,
                                    sequence_number_++, kDefaultTCPMSS,
                                    HAS_RETRANSMITTABLE_DATA));
}

TEST_F(TcpCubicSenderTest, ConfigureMaxInitialWindow) {
  QuicPacketCount congestion_window = sender_->congestion_window();
  QuicConfig config;
  QuicConfigPeer::SetReceivedInitialWindow(&config, 2 * congestion_window);

  sender_->SetFromConfig(config, true);
  EXPECT_EQ(2 * congestion_window, sender_->congestion_window());

  // Verify that kCOPT: kIW10 forces the congestion window to the
  // default of 10 regardless of ReceivedInitialWindow.
  QuicTagVector options;
  options.push_back(kIW10);
  QuicConfigPeer::SetReceivedConnectionOptions(&config, options);
  sender_->SetFromConfig(config, true);
  EXPECT_EQ(congestion_window, sender_->congestion_window());
}

TEST_F(TcpCubicSenderTest, 2ConnectionCongestionAvoidanceAtEndOfRecovery) {
  sender_->SetNumEmulatedConnections(2);
  // Ack 10 packets in 5 acks to raise the CWND to 20.
  const int kNumberOfAcks = 5;
  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  SendAvailableSendWindow();
  QuicByteCount expected_send_window = kDefaultWindowTCP +
      (kDefaultTCPMSS * 2 * kNumberOfAcks);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  LoseNPackets(1);

  // We should now have fallen out of slow start with a reduced window.
  expected_send_window = expected_send_window * sender_->GetRenoBeta();
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // No congestion window growth should occur in recovery phase, i.e., until the
  // currently outstanding 20 packets are acked.
  for (int i = 0; i < 10; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    EXPECT_TRUE(sender_->InRecovery());
    AckNPackets(2);
    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  }
  EXPECT_FALSE(sender_->InRecovery());

  // Out of recovery now. Congestion window should not grow for half an RTT.
  size_t packets_in_send_window = expected_send_window / kDefaultTCPMSS;
  SendAvailableSendWindow();
  AckNPackets(packets_in_send_window / 2 - 2);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Next ack should increase congestion window by 1MSS.
  SendAvailableSendWindow();
  AckNPackets(2);
  expected_send_window += kDefaultTCPMSS;
  packets_in_send_window += 1;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Congestion window should remain steady again for half an RTT.
  SendAvailableSendWindow();
  AckNPackets(packets_in_send_window / 2 - 1);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // Next ack should cause congestion window to grow by 1MSS.
  SendAvailableSendWindow();
  AckNPackets(2);
  expected_send_window += kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
}

TEST_F(TcpCubicSenderTest, 1ConnectionCongestionAvoidanceAtEndOfRecovery) {
  sender_->SetNumEmulatedConnections(1);
  // Ack 10 packets in 5 acks to raise the CWND to 20.
  const int kNumberOfAcks = 5;
  for (int i = 0; i < kNumberOfAcks; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
  }
  SendAvailableSendWindow();
  QuicByteCount expected_send_window = kDefaultWindowTCP +
      (kDefaultTCPMSS * 2 * kNumberOfAcks);
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  LoseNPackets(1);

  // We should now have fallen out of slow start with a reduced window.
  expected_send_window *= kRenoBeta;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());

  // No congestion window growth should occur in recovery phase, i.e., until the
  // currently outstanding 20 packets are acked.
  for (int i = 0; i < 10; ++i) {
    // Send our full send window.
    SendAvailableSendWindow();
    EXPECT_TRUE(sender_->InRecovery());
    AckNPackets(2);
    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  }
  EXPECT_FALSE(sender_->InRecovery());

  // Out of recovery now. Congestion window should not grow during RTT.
  for (uint64 i = 0; i < expected_send_window / kDefaultTCPMSS - 2; i += 2) {
    // Send our full send window.
    SendAvailableSendWindow();
    AckNPackets(2);
    EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
  }

  // Next ack should cause congestion window to grow by 1MSS.
  SendAvailableSendWindow();
  AckNPackets(2);
  expected_send_window += kDefaultTCPMSS;
  EXPECT_EQ(expected_send_window, sender_->GetCongestionWindow());
}

}  // namespace test
}  // namespace net