tcp-loss-test.cc

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/*
 * Copyright (c) 2020 Tom Henderson
 *
 * SPDX-License-Identifier: GPL-2.0-only
 */
 
#include "tcp-general-test.h"
 
#include "ns3/error-model.h"
#include "ns3/log.h"
 
#include <list>
 
using namespace ns3;
 
NS_LOG_COMPONENT_DEFINE("TcpLossTestSuite");
 
/**
 * \ingroup internet-test
 *
 * \brief Check rollover of sequence number and how that affects loss recovery
 *
 * This test checks that fast recovery is entered correctly even if it has
 * been a long time since the last recovery event.  Merge request !156
 * reported the error and fixed the issue with large transfers.
 *
 * The issue reported is that fast recovery detection relies on comparing
 * the sequence number against the last recovery point, maintained by
 * an 'm_recover' variable.  The sequence number is a 32-bit value that
 * wraps, so the comparison of 'is current sequence number > m_recover'
 * will work for only about half of the 32-bit sequence space.  This
 * test confirms that the above inequality will correctly evaluate even if
 * the current sequence number is greater than half of the sequence space
 * above m_recover.
 *
 * The test configures a large bandwidth, long flow (to wrap the sequence
 * space) and inserts two forced losses.  In the first test case, the two
 * sequence numbers are close in sequence; we expect to see the TCP
 * implementation cycle between CA_OPEN->CA_DISORDER->CA_RECOVERY->CA_OPEN.
 * We also check in the second case when the two sequence numbers are far
 * apart (more than half) in the sequence space.
 */
class TcpLargeTransferLossTest : public TcpGeneralTest
{
  public:
    /**
     * \brief Constructor
     *
     * \param firstLoss First packet number to force loss
     * \param secondLoss Second packet number to force loss
     * \param lastSegment Last packet number to transmit
     * \param desc Description about the test
     */
    TcpLargeTransferLossTest(uint32_t firstLoss,
                             uint32_t secondLoss,
                             uint32_t lastSegment,
                             const std::string& desc);
 
  protected:
    void ConfigureProperties() override;
    void ConfigureEnvironment() override;
    void FinalChecks() override;
    void Tx(const Ptr<const Packet> p, const TcpHeader& h, SocketWho who) override;
    void Rx(const Ptr<const Packet> p, const TcpHeader& h, SocketWho who) override;
    void CongStateTrace(const TcpSocketState::TcpCongState_t oldValue,
                        const TcpSocketState::TcpCongState_t newValue) override;
    Ptr<ErrorModel> CreateReceiverErrorModel() override;
 
  private:
    uint32_t m_firstLoss;            //!< First segment loss
    uint32_t m_secondLoss;           //!< Second segment loss
    uint32_t m_sent{0};              //!< Number of segments sent
    uint32_t m_received{0};          //!< Number of segments received
    uint32_t m_lastSegment{0};       //!< Last received segment
    std::list<int> m_expectedStates; //!< Expected TCP states
};
 
TcpLargeTransferLossTest::TcpLargeTransferLossTest(uint32_t firstLoss,
                                                   uint32_t secondLoss,
                                                   uint32_t lastSegment,
                                                   const std::string& desc)
    : TcpGeneralTest(desc),
      m_firstLoss(firstLoss),
      m_secondLoss(secondLoss),
      m_lastSegment(lastSegment)
{
    NS_TEST_ASSERT_MSG_NE(m_lastSegment, 0, "Last segment should be > 0");
    NS_TEST_ASSERT_MSG_GT(m_secondLoss,
                          m_firstLoss,
                          "Second segment number should be greater than first");
    m_expectedStates.push_back(TcpSocketState::CA_OPEN);
    m_expectedStates.push_back(TcpSocketState::CA_DISORDER);
    m_expectedStates.push_back(TcpSocketState::CA_RECOVERY);
    m_expectedStates.push_back(TcpSocketState::CA_OPEN);
    m_expectedStates.push_back(TcpSocketState::CA_DISORDER);
    m_expectedStates.push_back(TcpSocketState::CA_RECOVERY);
    m_expectedStates.push_back(TcpSocketState::CA_OPEN);
}
 
void
TcpLargeTransferLossTest::CongStateTrace(const TcpSocketState::TcpCongState_t oldValue,
                                         const TcpSocketState::TcpCongState_t newValue)
{
    int expectedOldState = m_expectedStates.front();
    m_expectedStates.pop_front();
    NS_TEST_ASSERT_MSG_EQ(oldValue, expectedOldState, "State transition wrong");
    NS_TEST_ASSERT_MSG_EQ(newValue, m_expectedStates.front(), "State transition wrong");
}
 
void
TcpLargeTransferLossTest::ConfigureEnvironment()
{
    NS_LOG_FUNCTION(this);
    TcpGeneralTest::ConfigureEnvironment();
    SetPropagationDelay(MicroSeconds(1)); // Keep low to avoid window limit
    SetTransmitStart(Seconds(1));
    SetAppPktSize(1000);
    // Note:  4294967295 is the maximum TCP sequence number, so rollover will be
    // on the 4294967th packet with a packet (segment) size of 1000 bytes
    SetAppPktCount(m_lastSegment);
    SetAppPktInterval(MicroSeconds(8)); // 1 Gb/s
}
 
void
TcpLargeTransferLossTest::ConfigureProperties()
{
    NS_LOG_FUNCTION(this);
    TcpGeneralTest::ConfigureProperties();
    SetSegmentSize(SENDER, 1000);
    SetSegmentSize(RECEIVER, 1000);
}
 
Ptr<ErrorModel>
TcpLargeTransferLossTest::CreateReceiverErrorModel()
{
    Ptr<ReceiveListErrorModel> rem = CreateObject<ReceiveListErrorModel>();
    std::list<uint32_t> errorList;
    errorList.push_back(m_firstLoss);
    errorList.push_back(m_secondLoss);
    rem->SetList(errorList);
    return rem;
}
 
void
TcpLargeTransferLossTest::Tx(const Ptr<const Packet> p, const TcpHeader& h, SocketWho who)
{
    m_sent++;
}
 
void
TcpLargeTransferLossTest::Rx(const Ptr<const Packet> p, const TcpHeader& h, SocketWho who)
{
    m_received++;
}
 
void
TcpLargeTransferLossTest::FinalChecks()
{
    // The addition of 2 accounts for the two forcibly lost packets
    NS_TEST_ASSERT_MSG_EQ(m_sent,
                          (m_received + 2),
                          "Did not observe expected number of sent packets");
}
 
/**
 * \ingroup internet-test
 *
 * Test various packet losses
 */
class TcpLossTestSuite : public TestSuite
{
  public:
    TcpLossTestSuite()
        : TestSuite("tcp-loss-test", Type::UNIT)
    {
        // For large transfer tests, the three sequence numbers passed in
        // are the segment (i.e. not byte) number that should be dropped first,
        // then the second drop, and then the last segment number to send
        //
        // If we force a loss at packet 1000 and then shortly after at 2000,
        // the TCP logic should correctly pass this case (no sequence wrapping).
        AddTestCase(
            new TcpLargeTransferLossTest(1000, 2000, 2500, "large-transfer-loss-without-wrap"),
            TestCase::Duration::EXTENSIVE);
        // If we force a loss at packet 1000 and then much later at 3294967, the
        // second sequence number will evaluate to less than 1000 considering
        // the sequence space wrap, so check this case also.
        AddTestCase(
            new TcpLargeTransferLossTest(1000, 3294967, 3295100, "large-transfer-loss-with-wrap"),
            TestCase::Duration::EXTENSIVE);
    }
};
 
static TcpLossTestSuite g_tcpLossTest; //!< static var for test initialization