tcp-pacing-test.cc

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/*
 * Copyright (c) 2020 NITK Surathkal
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Authors: Deepak Kumaraswamy <deepakkavoor99@gmail.com>
 *
 */
#include "tcp-general-test.h"
 
#include "ns3/config.h"
#include "ns3/log.h"
#include "ns3/simple-channel.h"
#include "ns3/test.h"
 
using namespace ns3;
 
NS_LOG_COMPONENT_DEFINE("TcpPacingTestSuite");
 
class TcpPacingTest : public TcpGeneralTest
{
  public:
    TcpPacingTest(uint32_t segmentSize,
                  uint32_t packetSize,
                  uint32_t packets,
                  uint16_t pacingSsRatio,
                  uint16_t pacingCaRatio,
                  uint32_t ssThresh,
                  bool paceInitialWindow,
                  uint32_t delAckMaxCount,
                  const TypeId& congControl,
                  const std::string& desc);
 
  protected:
    void CWndTrace(uint32_t oldValue, uint32_t newValue) override;
    void RttTrace(Time oldTime, Time newTime) override;
    void BytesInFlightTrace(uint32_t oldValue, uint32_t newValue) 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 QueueDrop(SocketWho who) override;
    void PhyDrop(SocketWho who) override;
    void NormalClose(SocketWho who) override;
 
    virtual void UpdateExpectedInterval();
 
    void ConfigureEnvironment() override;
    void ConfigureProperties() override;
 
  private:
    uint32_t m_segmentSize; 
    uint32_t m_packetSize;  
    uint32_t m_packets;     
    EventId m_event;        
    bool m_initial;         
    uint32_t m_initialCwnd; 
    uint32_t m_curCwnd;     
    bool m_isFullCwndSent; 
    uint32_t m_bytesInFlight;     
    Time m_prevTxTime;            
    uint16_t m_pacingSsRatio;     
    uint16_t m_pacingCaRatio;     
    uint32_t m_ssThresh;          
    bool m_paceInitialWindow;     
    uint32_t m_delAckMaxCount;    
    bool m_isConnAboutToEnd;      
    Time m_transmissionStartTime; 
    Time m_expectedInterval; 
    uint32_t m_packetsSent;  
    Time m_nextPacketInterval; 
    Time m_tracedRtt; 
};
 
TcpPacingTest::TcpPacingTest(uint32_t segmentSize,
                             uint32_t packetSize,
                             uint32_t packets,
                             uint16_t pacingSsRatio,
                             uint16_t pacingCaRatio,
                             uint32_t ssThresh,
                             bool paceInitialWindow,
                             uint32_t delAckMaxCount,
                             const TypeId& typeId,
                             const std::string& desc)
    : TcpGeneralTest(desc),
      m_segmentSize(segmentSize),
      m_packetSize(packetSize),
      m_packets(packets),
      m_initial(true),
      m_initialCwnd(10),
      m_curCwnd(0),
      m_isFullCwndSent(true),
      m_bytesInFlight(0),
      m_prevTxTime(0),
      m_pacingSsRatio(pacingSsRatio),
      m_pacingCaRatio(pacingCaRatio),
      m_ssThresh(ssThresh),
      m_paceInitialWindow(paceInitialWindow),
      m_delAckMaxCount(delAckMaxCount),
      m_isConnAboutToEnd(false),
      m_transmissionStartTime(Seconds(0)),
      m_expectedInterval(Seconds(0)),
      m_packetsSent(0),
      m_nextPacketInterval(Seconds(0)),
      m_tracedRtt(Seconds(0))
{
    m_congControlTypeId = typeId;
}
 
void
TcpPacingTest::ConfigureEnvironment()
{
    TcpGeneralTest::ConfigureEnvironment();
    SetAppPktSize(m_packetSize);
    SetAppPktCount(m_packets);
    SetAppPktInterval(NanoSeconds(10));
    SetMTU(1500);
    SetTransmitStart(Seconds(0));
    SetPropagationDelay(MilliSeconds(50));
}
 
void
TcpPacingTest::ConfigureProperties()
{
    TcpGeneralTest::ConfigureProperties();
    SetSegmentSize(SENDER, m_segmentSize);
    SetInitialSsThresh(SENDER, m_ssThresh);
    SetInitialCwnd(SENDER, m_initialCwnd);
    SetPacingStatus(SENDER, true);
    SetPaceInitialWindow(SENDER, m_paceInitialWindow);
    SetDelAckMaxCount(RECEIVER, m_delAckMaxCount);
    NS_LOG_DEBUG("segSize: " << m_segmentSize << " ssthresh: " << m_ssThresh
                             << " paceInitialWindow: " << m_paceInitialWindow << " delAckMaxCount "
                             << m_delAckMaxCount);
}
 
void
TcpPacingTest::RttTrace(Time oldTime, Time newTime)
{
    NS_LOG_FUNCTION(this << oldTime << newTime);
    m_tracedRtt = newTime;
    UpdateExpectedInterval();
}
 
void
TcpPacingTest::CWndTrace(uint32_t oldValue, uint32_t newValue)
{
    NS_LOG_FUNCTION(this << oldValue << newValue);
    m_curCwnd = newValue;
    if (m_initial)
    {
        m_initial = false;
    }
    // CWndTrace () is called after Rx ()
    // Therefore, call UpdateExpectedInterval () here instead of in Rx ()
    UpdateExpectedInterval();
}
 
void
TcpPacingTest::BytesInFlightTrace(uint32_t oldValue, uint32_t newValue)
{
    m_bytesInFlight = newValue;
}
 
void
TcpPacingTest::UpdateExpectedInterval()
{
    double_t factor;
    Time rtt = 2 * GetPropagationDelay();
    if (m_curCwnd < m_ssThresh / 2)
    {
        factor = static_cast<double>(m_pacingSsRatio) / 100;
    }
    else
    {
        factor = static_cast<double>(m_pacingCaRatio) / 100;
    }
 
    if (!m_paceInitialWindow && (m_curCwnd == m_initialCwnd * m_segmentSize))
    {
        // If initial cwnd is not paced, we expect packet pacing interval to be zero
        m_expectedInterval = Seconds(0);
    }
    else
    {
        // Use the estimate according to update equation
        m_expectedInterval =
            Seconds((m_segmentSize * m_tracedRtt.GetSeconds()) / (factor * m_curCwnd));
    }
}
 
void
TcpPacingTest::Rx(const Ptr<const Packet> p, const TcpHeader& h, SocketWho who)
{
    if (who == SENDER)
    {
        uint8_t flags = h.GetFlags();
        uint8_t hasFin = flags & TcpHeader::FIN;
        uint8_t hasAck = flags & TcpHeader::ACK;
        if (hasFin && hasAck)
        {
            m_isConnAboutToEnd = true;
            NS_LOG_DEBUG("Sender received a FIN/ACK packet");
        }
        else
        {
            m_isConnAboutToEnd = false;
            NS_LOG_DEBUG("Sender received an ACK packet");
        }
    }
}
 
void
TcpPacingTest::Tx(const Ptr<const Packet> p, const TcpHeader& h, SocketWho who)
{
    NS_LOG_FUNCTION(this << p << h << who);
 
    if (who == SENDER)
    {
        m_packetsSent++;
        // Start pacing checks from the second data packet onwards because
        // an interval to check does not exist for the first data packet.
        // The first two (non-data) packets correspond to SYN and an
        // empty ACK, respectively, so start checking after three packets are sent
        bool beyondInitialDataSegment = (m_packetsSent > 3);
        Time actualInterval = Simulator::Now() - m_prevTxTime;
        NS_LOG_DEBUG("TX sent: packetsSent: " << m_packetsSent << " fullCwnd: " << m_isFullCwndSent
                                              << " nearEnd: " << m_isConnAboutToEnd
                                              << " beyondInitialDataSegment "
                                              << beyondInitialDataSegment);
        if (!m_isFullCwndSent && !m_isConnAboutToEnd && beyondInitialDataSegment)
        {
            // Consider a small error margin, and ensure that the actual and expected intervals lie
            // within this error
            Time errorMargin = NanoSeconds(10);
            NS_TEST_ASSERT_MSG_LT_OR_EQ(
                std::abs((actualInterval - m_nextPacketInterval).GetSeconds()),
                errorMargin.GetSeconds(),
                "Packet delivery in slow start didn't match pacing rate");
            NS_LOG_DEBUG("Pacing Check: interval (s): "
                         << actualInterval.GetSeconds() << " expected interval (s): "
                         << m_nextPacketInterval.GetSeconds() << " difference (s): "
                         << std::abs((actualInterval - m_nextPacketInterval).GetSeconds())
                         << " errorMargin (s): " << errorMargin.GetSeconds());
        }
 
        m_prevTxTime = Simulator::Now();
        // bytesInFlight isn't updated yet. Its trace is called after Tx
        // so add an additional m_segmentSize to bytesInFlight
        uint32_t soonBytesInFlight = m_bytesInFlight + m_segmentSize;
        bool canPacketBeSent = ((m_curCwnd - soonBytesInFlight) >= m_segmentSize);
        if (!canPacketBeSent || (m_curCwnd == 0))
        {
            m_isFullCwndSent = true;
        }
        else
        {
            m_isFullCwndSent = false;
        }
        m_nextPacketInterval = m_expectedInterval;
        NS_LOG_DEBUG("Next expected interval (s): " << m_nextPacketInterval.GetSeconds());
    }
}
 
void
TcpPacingTest::QueueDrop(SocketWho who)
{
    NS_FATAL_ERROR("Drop on the queue; cannot validate congestion avoidance");
}
 
void
TcpPacingTest::PhyDrop(SocketWho who)
{
    NS_FATAL_ERROR("Drop on the phy: cannot validate congestion avoidance");
}
 
void
TcpPacingTest::NormalClose(SocketWho who)
{
    if (who == SENDER)
    {
        m_event.Cancel();
    }
}
 
class TcpPacingTestSuite : public TestSuite
{
  public:
    TcpPacingTestSuite()
        : TestSuite("tcp-pacing-test", UNIT)
    {
        uint16_t pacingSsRatio = 200;
        uint16_t pacingCaRatio = 120;
        uint32_t segmentSize = 1000;
        uint32_t packetSize = 1000;
        uint32_t numPackets = 40;
        uint32_t delAckMaxCount = 1;
        TypeId tid = TcpNewReno::GetTypeId();
        uint32_t ssThresh = 1e9; // default large value
        bool paceInitialWindow = false;
        std::string description;
 
        description = std::string("Pacing case 1: Slow start only, no initial pacing");
        AddTestCase(new TcpPacingTest(segmentSize,
                                      packetSize,
                                      numPackets,
                                      pacingSsRatio,
                                      pacingCaRatio,
                                      ssThresh,
                                      paceInitialWindow,
                                      delAckMaxCount,
                                      tid,
                                      description),
                    TestCase::QUICK);
 
        paceInitialWindow = true;
        description = std::string("Pacing case 2: Slow start only, initial pacing");
        AddTestCase(new TcpPacingTest(segmentSize,
                                      packetSize,
                                      numPackets,
                                      pacingSsRatio,
                                      pacingCaRatio,
                                      ssThresh,
                                      paceInitialWindow,
                                      delAckMaxCount,
                                      tid,
                                      description),
                    TestCase::QUICK);
 
        // set ssThresh to some smaller value to check that pacing
        // slows down in second half of slow start, then transitions to CA
        description = std::string("Pacing case 3: Slow start, followed by transition to Congestion "
                                  "avoidance, no initial pacing");
        paceInitialWindow = false;
        ssThresh = 40;
        numPackets = 60;
        AddTestCase(new TcpPacingTest(segmentSize,
                                      packetSize,
                                      numPackets,
                                      pacingSsRatio,
                                      pacingCaRatio,
                                      ssThresh,
                                      paceInitialWindow,
                                      delAckMaxCount,
                                      tid,
                                      description),
                    TestCase::QUICK);
 
        // Repeat tests, but with more typical delAckMaxCount == 2
        delAckMaxCount = 2;
        paceInitialWindow = false;
        ssThresh = 1e9;
        numPackets = 40;
        description =
            std::string("Pacing case 4: Slow start only, no initial pacing, delayed ACKs");
        AddTestCase(new TcpPacingTest(segmentSize,
                                      packetSize,
                                      numPackets,
                                      pacingSsRatio,
                                      pacingCaRatio,
                                      ssThresh,
                                      paceInitialWindow,
                                      delAckMaxCount,
                                      tid,
                                      description),
                    TestCase::QUICK);
 
        paceInitialWindow = true;
        description = std::string("Pacing case 5: Slow start only, initial pacing, delayed ACKs");
        AddTestCase(new TcpPacingTest(segmentSize,
                                      packetSize,
                                      numPackets,
                                      pacingSsRatio,
                                      pacingCaRatio,
                                      ssThresh,
                                      paceInitialWindow,
                                      delAckMaxCount,
                                      tid,
                                      description),
                    TestCase::QUICK);
 
        description = std::string("Pacing case 6: Slow start, followed by transition to Congestion "
                                  "avoidance, no initial pacing, delayed ACKs");
        paceInitialWindow = false;
        ssThresh = 40;
        numPackets = 60;
        AddTestCase(new TcpPacingTest(segmentSize,
                                      packetSize,
                                      numPackets,
                                      pacingSsRatio,
                                      pacingCaRatio,
                                      ssThresh,
                                      paceInitialWindow,
                                      delAckMaxCount,
                                      tid,
                                      description),
                    TestCase::QUICK);
    }
};
 
static TcpPacingTestSuite g_tcpPacingTest;