quiche/quic/core/congestion_control/send_algorithm_test.cc

// Copyright 2013 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 <cstddef>
#include <cstdint>
#include <memory>
#include <ostream>
#include <string>
#include <utility>
#include <vector>

#include "absl/strings/str_cat.h"
#include "quiche/quic/core/congestion_control/rtt_stats.h"
#include "quiche/quic/core/congestion_control/send_algorithm_interface.h"
#include "quiche/quic/core/crypto/quic_random.h"
#include "quiche/quic/core/quic_bandwidth.h"
#include "quiche/quic/core/quic_clock.h"
#include "quiche/quic/core/quic_connection_stats.h"
#include "quiche/quic/core/quic_constants.h"
#include "quiche/quic/core/quic_time.h"
#include "quiche/quic/core/quic_types.h"
#include "quiche/quic/platform/api/quic_logging.h"
#include "quiche/quic/platform/api/quic_test.h"
#include "quiche/quic/test_tools/quic_connection_peer.h"
#include "quiche/quic/test_tools/quic_sent_packet_manager_peer.h"
#include "quiche/quic/test_tools/quic_test_utils.h"
#include "quiche/quic/test_tools/simulator/actor.h"
#include "quiche/quic/test_tools/simulator/link.h"
#include "quiche/quic/test_tools/simulator/quic_endpoint.h"
#include "quiche/quic/test_tools/simulator/simulator.h"
#include "quiche/quic/test_tools/simulator/switch.h"

namespace quic {
namespace test {
namespace {

// Use the initial CWND of 10, as 32 is too much for the test network.
const uint32_t kInitialCongestionWindowPackets = 10;

// Test network parameters.  Here, the topology of the network is:
//
//           QUIC Sender
//               |
//               |  <-- local link
//               |
//        Network switch
//               *  <-- the bottleneck queue in the direction
//               |          of the receiver
//               |
//               |  <-- test link
//               |
//               |
//           Receiver
//
// When setting the bandwidth of the local link and test link, choose
// a bandwidth lower than 20Mbps, as the clock-granularity of the
// simulator can only handle a granularity of 1us.

// Default settings between the switch and the sender.
const QuicBandwidth kLocalLinkBandwidth =
    QuicBandwidth::FromKBitsPerSecond(10000);
const QuicTime::Delta kLocalPropagationDelay =
    QuicTime::Delta::FromMilliseconds(2);

// Wired network settings.  A typical desktop network setup, a
// high-bandwidth, 30ms test link to the receiver.
const QuicBandwidth kTestLinkWiredBandwidth =
    QuicBandwidth::FromKBitsPerSecond(4000);
const QuicTime::Delta kTestLinkWiredPropagationDelay =
    QuicTime::Delta::FromMilliseconds(50);
const QuicTime::Delta kTestWiredTransferTime =
    kTestLinkWiredBandwidth.TransferTime(kMaxOutgoingPacketSize) +
    kLocalLinkBandwidth.TransferTime(kMaxOutgoingPacketSize);
const QuicTime::Delta kTestWiredRtt =
    (kTestLinkWiredPropagationDelay + kLocalPropagationDelay +
     kTestWiredTransferTime) *
    2;
const QuicByteCount kTestWiredBdp = kTestWiredRtt * kTestLinkWiredBandwidth;

// Small BDP, Bandwidth-policed network settings.  In this scenario,
// the receiver has a low-bandwidth, short propagation-delay link,
// resulting in a small BDP.  We model the policer by setting the
// queue size to only one packet.
const QuicBandwidth kTestLinkLowBdpBandwidth =
    QuicBandwidth::FromKBitsPerSecond(200);
const QuicTime::Delta kTestLinkLowBdpPropagationDelay =
    QuicTime::Delta::FromMilliseconds(50);
const QuicByteCount kTestPolicerQueue = kMaxOutgoingPacketSize;

// Satellite network settings.  In a satellite network, the bottleneck
// buffer is typically sized for non-satellite links , but the
// propagation delay of the test link to the receiver is as much as a
// quarter second.
const QuicTime::Delta kTestSatellitePropagationDelay =
    QuicTime::Delta::FromMilliseconds(250);

// Cellular scenarios.  In a cellular network, the bottleneck queue at
// the edge of the network can be as great as 3MB.
const QuicBandwidth kTestLink2GBandwidth =
    QuicBandwidth::FromKBitsPerSecond(100);
const QuicBandwidth kTestLink3GBandwidth =
    QuicBandwidth::FromKBitsPerSecond(1500);
const QuicByteCount kCellularQueue = 3 * 1024 * 1024;
const QuicTime::Delta kTestCellularPropagationDelay =
    QuicTime::Delta::FromMilliseconds(40);

// Small RTT scenario, below the per-ack-update threshold of 30ms.
const QuicTime::Delta kTestLinkSmallRTTDelay =
    QuicTime::Delta::FromMilliseconds(10);

struct TestParams {
  explicit TestParams(CongestionControlType congestion_control_type)
      : congestion_control_type(congestion_control_type) {}

  friend std::ostream& operator<<(std::ostream& os, const TestParams& p) {
    os << "{ congestion_control_type: "
       << CongestionControlTypeToString(p.congestion_control_type);
    os << " }";
    return os;
  }

  const CongestionControlType congestion_control_type;
};

std::string TestParamToString(
    const testing::TestParamInfo<TestParams>& params) {
  return CongestionControlTypeToString(params.param.congestion_control_type);
}

// Constructs various test permutations.
std::vector<TestParams> GetTestParams() {
  std::vector<TestParams> params;
  for (const CongestionControlType congestion_control_type :
       {kBBR, kBBRv2, kCubicBytes, kRenoBytes}) {
    params.push_back(TestParams(congestion_control_type));
  }
  return params;
}

// Adds a fixed amount of data to the simulated QUIC sender at a fixed time
// interval.
class ConstantRateDataSender : public simulator::Actor {
 public:
  ConstantRateDataSender(simulator::Simulator* simulator, std::string name,
                         simulator::QuicEndpoint* endpoint, QuicBandwidth rate,
                         QuicTimeDelta interval)
      : Actor(simulator, std::move(name)),
        endpoint_(endpoint),
        interval_(interval),
        chunk_size_(interval * rate) {
    Schedule(clock_->Now());
  }

  void Act() override {
    endpoint_->AddBytesToTransfer(chunk_size_);
    Schedule(clock_->Now() + interval_);
  }

 private:
  simulator::QuicEndpoint* endpoint_;
  QuicTimeDelta interval_;
  QuicByteCount chunk_size_;
};

class SendAlgorithmTest : public QuicTestWithParam<TestParams> {
 protected:
  SendAlgorithmTest()
      : simulator_(),
        quic_sender_(&simulator_, "QUIC sender", "Receiver",
                     Perspective::IS_CLIENT, TestConnectionId()),
        receiver_(&simulator_, "Receiver", "QUIC sender",
                  Perspective::IS_SERVER, TestConnectionId()) {
    rtt_stats_ = quic_sender_.connection()->sent_packet_manager().GetRttStats();
    sender_ = SendAlgorithmInterface::Create(
        simulator_.GetClock(), rtt_stats_,
        QuicSentPacketManagerPeer::GetUnackedPacketMap(
            QuicConnectionPeer::GetSentPacketManager(
                quic_sender_.connection())),
        GetParam().congestion_control_type, &random_, &stats_,
        kInitialCongestionWindowPackets, nullptr);
    quic_sender_.RecordTrace();

    QuicConnectionPeer::SetSendAlgorithm(quic_sender_.connection(), sender_);
    const int kTestMaxPacketSize = 1350;
    quic_sender_.connection()->SetMaxPacketLength(kTestMaxPacketSize);
    clock_ = simulator_.GetClock();
    simulator_.set_random_generator(&random_);

    uint64_t seed = QuicRandom::GetInstance()->RandUint64();
    random_.set_seed(seed);
    QUIC_LOG(INFO) << "SendAlgorithmTest simulator set up.  Seed: " << seed;
  }

  // Creates a simulated network, with default settings between the
  // sender and the switch and the given settings from the switch to
  // the receiver.
  void CreateSetup(const QuicBandwidth& test_bandwidth,
                   const QuicTime::Delta& test_link_delay,
                   QuicByteCount bottleneck_queue_length) {
    switch_ = std::make_unique<simulator::Switch>(&simulator_, "Switch", 8,
                                                  bottleneck_queue_length);
    quic_sender_link_ = std::make_unique<simulator::SymmetricLink>(
        &quic_sender_, switch_->port(1), kLocalLinkBandwidth,
        kLocalPropagationDelay);
    receiver_link_ = std::make_unique<simulator::SymmetricLink>(
        &receiver_, switch_->port(2), test_bandwidth, test_link_delay);
  }

  void DoSimpleTransfer(QuicByteCount transfer_size, QuicTime::Delta deadline) {
    quic_sender_.AddBytesToTransfer(transfer_size);
    bool simulator_result = simulator_.RunUntilOrTimeout(
        [this]() { return quic_sender_.bytes_to_transfer() == 0; }, deadline);
    EXPECT_TRUE(simulator_result)
        << "Simple transfer failed.  Bytes remaining: "
        << quic_sender_.bytes_to_transfer();
  }

  void SendBursts(size_t number_of_bursts, QuicByteCount bytes,
                  QuicTime::Delta rtt, QuicTime::Delta wait_time) {
    ASSERT_EQ(0u, quic_sender_.bytes_to_transfer());
    for (size_t i = 0; i < number_of_bursts; i++) {
      quic_sender_.AddBytesToTransfer(bytes);

      // Transfer data and wait for three seconds between each transfer.
      simulator_.RunFor(wait_time);

      // Ensure the connection did not time out.
      ASSERT_TRUE(quic_sender_.connection()->connected());
      ASSERT_TRUE(receiver_.connection()->connected());
    }

    simulator_.RunFor(wait_time + rtt);
    EXPECT_EQ(0u, quic_sender_.bytes_to_transfer());
  }

  // Estimates the elapsed time for a given transfer size, given the
  // bottleneck bandwidth and link propagation delay.
  QuicTime::Delta EstimatedElapsedTime(
      QuicByteCount transfer_size_bytes, QuicBandwidth test_link_bandwidth,
      const QuicTime::Delta& test_link_delay) const {
    return test_link_bandwidth.TransferTime(transfer_size_bytes) +
           2 * test_link_delay;
  }

  QuicTime QuicSenderStartTime() {
    return quic_sender_.connection()->GetStats().connection_creation_time;
  }

  void PrintTransferStats() {
    const QuicConnectionStats& stats = quic_sender_.connection()->GetStats();
    QUIC_LOG(INFO) << "Summary for scenario " << GetParam();
    QUIC_LOG(INFO) << "Sender stats is " << stats;
    const double rtx_rate =
        static_cast<double>(stats.bytes_retransmitted) / stats.bytes_sent;
    QUIC_LOG(INFO) << "Retransmit rate (num_rtx/num_total_sent): " << rtx_rate;
    QUIC_LOG(INFO) << "Connection elapsed time: "
                   << (clock_->Now() - QuicSenderStartTime()).ToMilliseconds()
                   << " (ms)";
  }

  simulator::Simulator simulator_;
  simulator::QuicEndpoint quic_sender_;
  simulator::QuicEndpoint receiver_;
  std::unique_ptr<simulator::Switch> switch_;
  std::unique_ptr<simulator::SymmetricLink> quic_sender_link_;
  std::unique_ptr<simulator::SymmetricLink> receiver_link_;
  QuicConnectionStats stats_;

  SimpleRandom random_;

  // Owned by different components of the connection.
  const QuicClock* clock_;
  const RttStats* rtt_stats_;
  SendAlgorithmInterface* sender_;
};

INSTANTIATE_TEST_SUITE_P(SendAlgorithmTests, SendAlgorithmTest,
                         ::testing::ValuesIn(GetTestParams()),
                         TestParamToString);

// Test a simple long data transfer in the default setup.
TEST_P(SendAlgorithmTest, SimpleWiredNetworkTransfer) {
  CreateSetup(kTestLinkWiredBandwidth, kTestLinkWiredPropagationDelay,
              kTestWiredBdp);
  const QuicByteCount kTransferSizeBytes = 12 * 1024 * 1024;
  const QuicTime::Delta maximum_elapsed_time =
      EstimatedElapsedTime(kTransferSizeBytes, kTestLinkWiredBandwidth,
                           kTestLinkWiredPropagationDelay) *
      1.2;
  DoSimpleTransfer(kTransferSizeBytes, maximum_elapsed_time);
  PrintTransferStats();
}

TEST_P(SendAlgorithmTest, LowBdpPolicedNetworkTransfer) {
  CreateSetup(kTestLinkLowBdpBandwidth, kTestLinkLowBdpPropagationDelay,
              kTestPolicerQueue);
  const QuicByteCount kTransferSizeBytes = 5 * 1024 * 1024;
  const QuicTime::Delta maximum_elapsed_time =
      EstimatedElapsedTime(kTransferSizeBytes, kTestLinkLowBdpBandwidth,
                           kTestLinkLowBdpPropagationDelay) *
      1.2;
  DoSimpleTransfer(kTransferSizeBytes, maximum_elapsed_time);
  PrintTransferStats();
}

TEST_P(SendAlgorithmTest, AppLimitedBurstsOverWiredNetwork) {
  CreateSetup(kTestLinkWiredBandwidth, kTestLinkWiredPropagationDelay,
              kTestWiredBdp);
  const QuicByteCount kBurstSizeBytes = 512;
  const int kNumBursts = 20;
  const QuicTime::Delta kWaitTime = QuicTime::Delta::FromSeconds(3);
  SendBursts(kNumBursts, kBurstSizeBytes, kTestWiredRtt, kWaitTime);
  PrintTransferStats();

  const QuicTime::Delta estimated_burst_time =
      EstimatedElapsedTime(kBurstSizeBytes, kTestLinkWiredBandwidth,
                           kTestLinkWiredPropagationDelay) +
      kWaitTime;
  const QuicTime::Delta max_elapsed_time =
      kNumBursts * estimated_burst_time + kWaitTime;
  const QuicTime::Delta actual_elapsed_time =
      clock_->Now() - QuicSenderStartTime();
  EXPECT_GE(max_elapsed_time, actual_elapsed_time);
}

TEST_P(SendAlgorithmTest, SatelliteNetworkTransfer) {
  CreateSetup(kTestLinkWiredBandwidth, kTestSatellitePropagationDelay,
              kTestWiredBdp);
  const QuicByteCount kTransferSizeBytes = 12 * 1024 * 1024;
  const QuicTime::Delta maximum_elapsed_time =
      EstimatedElapsedTime(kTransferSizeBytes, kTestLinkWiredBandwidth,
                           kTestSatellitePropagationDelay) *
      1.25;
  DoSimpleTransfer(kTransferSizeBytes, maximum_elapsed_time);
  PrintTransferStats();
}

TEST_P(SendAlgorithmTest, 2GNetworkTransfer) {
  CreateSetup(kTestLink2GBandwidth, kTestCellularPropagationDelay,
              kCellularQueue);
  const QuicByteCount kTransferSizeBytes = 1024 * 1024;
  const QuicTime::Delta maximum_elapsed_time =
      EstimatedElapsedTime(kTransferSizeBytes, kTestLink2GBandwidth,
                           kTestCellularPropagationDelay) *
      1.2;
  DoSimpleTransfer(kTransferSizeBytes, maximum_elapsed_time);
  PrintTransferStats();
}

TEST_P(SendAlgorithmTest, 3GNetworkTransfer) {
  CreateSetup(kTestLink3GBandwidth, kTestCellularPropagationDelay,
              kCellularQueue);
  const QuicByteCount kTransferSizeBytes = 5 * 1024 * 1024;
  const QuicTime::Delta maximum_elapsed_time =
      EstimatedElapsedTime(kTransferSizeBytes, kTestLink3GBandwidth,
                           kTestCellularPropagationDelay) *
      1.2;
  DoSimpleTransfer(kTransferSizeBytes, maximum_elapsed_time);
  PrintTransferStats();
}

TEST_P(SendAlgorithmTest, LowRTTTransfer) {
  CreateSetup(kTestLinkWiredBandwidth, kTestLinkSmallRTTDelay, kCellularQueue);

  const QuicByteCount kTransferSizeBytes = 12 * 1024 * 1024;
  const QuicTime::Delta maximum_elapsed_time =
      EstimatedElapsedTime(kTransferSizeBytes, kTestLinkWiredBandwidth,
                           kTestLinkSmallRTTDelay) *
      1.2;
  DoSimpleTransfer(kTransferSizeBytes, maximum_elapsed_time);
  PrintTransferStats();
}

// In the scenario below, the IW/RTT implies a bandwidth that is much larger
// than what the link can sustain, while the sender hits the app-limited state
// often during the startup phase.
TEST_P(SendAlgorithmTest, AppLimitedStart) {
  constexpr QuicBandwidth kBandwidth = QuicBandwidth::FromKBitsPerSecond(900);
  constexpr QuicTimeDelta kRtt = QuicTimeDelta::FromMilliseconds(20);
  CreateSetup(kBandwidth, kRtt, 2 * kBandwidth * kRtt);

  constexpr QuicBandwidth kDataRate = QuicBandwidth::FromKBitsPerSecond(1000);
  constexpr QuicTimeDelta kInterval = QuicTimeDelta::FromMicroseconds(1e6 / 60);
  ConstantRateDataSender sender(&simulator_, "Data Sender", &quic_sender_,
                                kDataRate, kInterval);

  simulator_.RunFor(QuicTimeDelta::FromSeconds(15));
  PrintTransferStats();
}

TEST(NetworkParamsStringifyTest, Stringifies) {
  SendAlgorithmInterface::NetworkParams params(
      /*bandwidth=*/QuicBandwidth::FromKBitsPerSecond(1000),
      /*rtt=*/QuicTime::Delta::FromSeconds(2),
      /*allow_cwnd_to_decrease=*/true);

  params.max_initial_congestion_window = 42;
  params.is_rtt_trusted = true;

  EXPECT_EQ(testing::PrintToString(params),
            "NetworkParams { bandwidth: 1000.00 kbits/s (125.00 kbytes/s), "
            "rtt: 2s, "
            "max_initial_congestion_window: 42, "
            "allow_cwnd_to_decrease: true, "
            "is_rtt_trusted: true, "
            "clamp_cwnd_and_rtt_before_send_algorithm: false}");
}

}  // namespace
}  // namespace test
}  // namespace quic