tcp-bbr.cc

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/*
 * Copyright (c) 2018 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: Vivek Jain <jain.vivek.anand@gmail.com>
 *          Viyom Mittal <viyommittal@gmail.com>
 *          Mohit P. Tahiliani <tahiliani@nitk.edu.in>
 */
 
#include "tcp-bbr.h"
 
#include "ns3/log.h"
#include "ns3/simulator.h"
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("TcpBbr");
NS_OBJECT_ENSURE_REGISTERED(TcpBbr);
 
const double TcpBbr::PACING_GAIN_CYCLE[] = {5.0 / 4, 3.0 / 4, 1, 1, 1, 1, 1, 1};
 
TypeId
TcpBbr::GetTypeId()
{
    static TypeId tid =
        TypeId("ns3::TcpBbr")
            .SetParent<TcpCongestionOps>()
            .AddConstructor<TcpBbr>()
            .SetGroupName("Internet")
            .AddAttribute("Stream",
                          "Random number stream (default is set to 4 to align with Linux results)",
                          UintegerValue(4),
                          MakeUintegerAccessor(&TcpBbr::SetStream),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("HighGain",
                          "Value of high gain",
                          DoubleValue(2.89),
                          MakeDoubleAccessor(&TcpBbr::m_highGain),
                          MakeDoubleChecker<double>())
            .AddAttribute("BwWindowLength",
                          "Length of bandwidth windowed filter",
                          UintegerValue(10),
                          MakeUintegerAccessor(&TcpBbr::m_bandwidthWindowLength),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute("RttWindowLength",
                          "Length of RTT windowed filter",
                          TimeValue(Seconds(10)),
                          MakeTimeAccessor(&TcpBbr::m_rtPropFilterLen),
                          MakeTimeChecker())
            .AddAttribute("ProbeRttDuration",
                          "Time to be spent in PROBE_RTT phase",
                          TimeValue(MilliSeconds(200)),
                          MakeTimeAccessor(&TcpBbr::m_probeRttDuration),
                          MakeTimeChecker())
            .AddAttribute("ExtraAckedRttWindowLength",
                          "Window length of extra acked window",
                          UintegerValue(5),
                          MakeUintegerAccessor(&TcpBbr::m_extraAckedWinRttLength),
                          MakeUintegerChecker<uint32_t>())
            .AddAttribute(
                "AckEpochAckedResetThresh",
                "Max allowed val for m_ackEpochAcked, after which sampling epoch is reset",
                UintegerValue(1 << 12),
                MakeUintegerAccessor(&TcpBbr::m_ackEpochAckedResetThresh),
                MakeUintegerChecker<uint32_t>());
    return tid;
}
 
TcpBbr::TcpBbr()
    : TcpCongestionOps()
{
    NS_LOG_FUNCTION(this);
    m_uv = CreateObject<UniformRandomVariable>();
}
 
TcpBbr::TcpBbr(const TcpBbr& sock)
    : TcpCongestionOps(sock),
      m_bandwidthWindowLength(sock.m_bandwidthWindowLength),
      m_pacingGain(sock.m_pacingGain),
      m_cWndGain(sock.m_cWndGain),
      m_highGain(sock.m_highGain),
      m_isPipeFilled(sock.m_isPipeFilled),
      m_minPipeCwnd(sock.m_minPipeCwnd),
      m_roundCount(sock.m_roundCount),
      m_roundStart(sock.m_roundStart),
      m_nextRoundDelivered(sock.m_nextRoundDelivered),
      m_probeRttDuration(sock.m_probeRttDuration),
      m_probeRtPropStamp(sock.m_probeRtPropStamp),
      m_probeRttDoneStamp(sock.m_probeRttDoneStamp),
      m_probeRttRoundDone(sock.m_probeRttRoundDone),
      m_packetConservation(sock.m_packetConservation),
      m_priorCwnd(sock.m_priorCwnd),
      m_idleRestart(sock.m_idleRestart),
      m_targetCWnd(sock.m_targetCWnd),
      m_fullBandwidth(sock.m_fullBandwidth),
      m_fullBandwidthCount(sock.m_fullBandwidthCount),
      m_rtProp(Time::Max()),
      m_sendQuantum(sock.m_sendQuantum),
      m_cycleStamp(sock.m_cycleStamp),
      m_cycleIndex(sock.m_cycleIndex),
      m_rtPropExpired(sock.m_rtPropExpired),
      m_rtPropFilterLen(sock.m_rtPropFilterLen),
      m_rtPropStamp(sock.m_rtPropStamp),
      m_isInitialized(sock.m_isInitialized),
      m_uv(sock.m_uv),
      m_delivered(sock.m_delivered),
      m_appLimited(sock.m_appLimited),
      m_txItemDelivered(sock.m_txItemDelivered),
      m_extraAckedGain(sock.m_extraAckedGain),
      m_extraAckedWinRtt(sock.m_extraAckedWinRtt),
      m_extraAckedWinRttLength(sock.m_extraAckedWinRttLength),
      m_ackEpochAckedResetThresh(sock.m_ackEpochAckedResetThresh),
      m_extraAckedIdx(sock.m_extraAckedIdx),
      m_ackEpochTime(sock.m_ackEpochTime),
      m_ackEpochAcked(sock.m_ackEpochAcked),
      m_hasSeenRtt(sock.m_hasSeenRtt)
{
    NS_LOG_FUNCTION(this);
}
 
const char* const TcpBbr::BbrModeName[BBR_PROBE_RTT + 1] = {"BBR_STARTUP",
                                                            "BBR_DRAIN",
                                                            "BBR_PROBE_BW",
                                                            "BBR_PROBE_RTT"};
 
void
TcpBbr::SetStream(uint32_t stream)
{
    NS_LOG_FUNCTION(this << stream);
    m_uv->SetStream(stream);
}
 
void
TcpBbr::InitRoundCounting()
{
    NS_LOG_FUNCTION(this);
    m_nextRoundDelivered = 0;
    m_roundStart = false;
    m_roundCount = 0;
}
 
void
TcpBbr::InitFullPipe()
{
    NS_LOG_FUNCTION(this);
    m_isPipeFilled = false;
    m_fullBandwidth = 0;
    m_fullBandwidthCount = 0;
}
 
void
TcpBbr::InitPacingRate(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
 
    if (!tcb->m_pacing)
    {
        NS_LOG_WARN("BBR must use pacing");
        tcb->m_pacing = true;
    }
 
    Time rtt;
    if (tcb->m_minRtt != Time::Max())
    {
        rtt = MilliSeconds(std::max<long int>(tcb->m_minRtt.GetMilliSeconds(), 1));
        m_hasSeenRtt = true;
    }
    else
    {
        rtt = MilliSeconds(1);
    }
 
    DataRate nominalBandwidth(tcb->m_cWnd * 8 / rtt.GetSeconds());
    tcb->m_pacingRate = DataRate(m_pacingGain * nominalBandwidth.GetBitRate());
    m_maxBwFilter = MaxBandwidthFilter_t(m_bandwidthWindowLength,
                                         DataRate(tcb->m_cWnd * 8 / rtt.GetSeconds()),
                                         0);
}
 
void
TcpBbr::EnterStartup()
{
    NS_LOG_FUNCTION(this);
    SetBbrState(BbrMode_t::BBR_STARTUP);
    m_pacingGain = m_highGain;
    m_cWndGain = m_highGain;
}
 
void
TcpBbr::HandleRestartFromIdle(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    if (tcb->m_bytesInFlight.Get() == 0U && rs.m_isAppLimited)
    {
        m_idleRestart = true;
        if (m_state == BbrMode_t::BBR_PROBE_BW)
        {
            SetPacingRate(tcb, 1);
        }
    }
}
 
void
TcpBbr::SetPacingRate(Ptr<TcpSocketState> tcb, double gain)
{
    NS_LOG_FUNCTION(this << tcb << gain);
    DataRate rate(gain * m_maxBwFilter.GetBest().GetBitRate());
    rate = std::min(rate, tcb->m_maxPacingRate);
 
    if (!m_hasSeenRtt && tcb->m_minRtt != Time::Max())
    {
        InitPacingRate(tcb);
    }
 
    if (m_isPipeFilled || rate > tcb->m_pacingRate)
    {
        tcb->m_pacingRate = rate;
    }
}
 
uint32_t
TcpBbr::InFlight(Ptr<TcpSocketState> tcb, double gain)
{
    NS_LOG_FUNCTION(this << tcb << gain);
    if (m_rtProp == Time::Max())
    {
        return tcb->m_initialCWnd * tcb->m_segmentSize;
    }
    double quanta = 3 * m_sendQuantum;
    double estimatedBdp = m_maxBwFilter.GetBest() * m_rtProp / 8.0;
 
    if (m_state == BbrMode_t::BBR_PROBE_BW && m_cycleIndex == 0)
    {
        return (gain * estimatedBdp) + quanta + (2 * tcb->m_segmentSize);
    }
    return (gain * estimatedBdp) + quanta;
}
 
void
TcpBbr::AdvanceCyclePhase()
{
    NS_LOG_FUNCTION(this);
    m_cycleStamp = Simulator::Now();
    m_cycleIndex = (m_cycleIndex + 1) % GAIN_CYCLE_LENGTH;
    m_pacingGain = PACING_GAIN_CYCLE[m_cycleIndex];
}
 
bool
TcpBbr::IsNextCyclePhase(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    bool isFullLength = (Simulator::Now() - m_cycleStamp) > m_rtProp;
    if (m_pacingGain == 1)
    {
        return isFullLength;
    }
    else if (m_pacingGain > 1)
    {
        return isFullLength &&
               (rs.m_bytesLoss > 0 || rs.m_priorInFlight >= InFlight(tcb, m_pacingGain));
    }
    else
    {
        return isFullLength || rs.m_priorInFlight <= InFlight(tcb, 1);
    }
}
 
void
TcpBbr::CheckCyclePhase(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    if (m_state == BbrMode_t::BBR_PROBE_BW && IsNextCyclePhase(tcb, rs))
    {
        AdvanceCyclePhase();
    }
}
 
void
TcpBbr::CheckFullPipe(const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << rs);
    if (m_isPipeFilled || !m_roundStart || rs.m_isAppLimited)
    {
        return;
    }
 
    /* Check if Bottleneck bandwidth is still growing*/
    if (m_maxBwFilter.GetBest().GetBitRate() >= m_fullBandwidth.GetBitRate() * 1.25)
    {
        m_fullBandwidth = m_maxBwFilter.GetBest();
        m_fullBandwidthCount = 0;
        return;
    }
 
    m_fullBandwidthCount++;
    if (m_fullBandwidthCount >= 3)
    {
        NS_LOG_DEBUG("Pipe filled");
        m_isPipeFilled = true;
    }
}
 
void
TcpBbr::EnterDrain()
{
    NS_LOG_FUNCTION(this);
    SetBbrState(BbrMode_t::BBR_DRAIN);
    m_pacingGain = 1.0 / m_highGain;
    m_cWndGain = m_highGain;
}
 
void
TcpBbr::EnterProbeBW()
{
    NS_LOG_FUNCTION(this);
    SetBbrState(BbrMode_t::BBR_PROBE_BW);
    m_pacingGain = 1;
    m_cWndGain = 2;
    m_cycleIndex = GAIN_CYCLE_LENGTH - 1 - (int)m_uv->GetValue(0, 6);
    AdvanceCyclePhase();
}
 
void
TcpBbr::CheckDrain(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    if (m_state == BbrMode_t::BBR_STARTUP && m_isPipeFilled)
    {
        EnterDrain();
        tcb->m_ssThresh = InFlight(tcb, 1);
    }
 
    if (m_state == BbrMode_t::BBR_DRAIN && tcb->m_bytesInFlight <= InFlight(tcb, 1))
    {
        EnterProbeBW();
    }
}
 
void
TcpBbr::UpdateRTprop(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    m_rtPropExpired = Simulator::Now() > (m_rtPropStamp + m_rtPropFilterLen);
    if (tcb->m_lastRtt >= Seconds(0) && (tcb->m_lastRtt <= m_rtProp || m_rtPropExpired))
    {
        m_rtProp = tcb->m_lastRtt;
        m_rtPropStamp = Simulator::Now();
    }
}
 
void
TcpBbr::EnterProbeRTT()
{
    NS_LOG_FUNCTION(this);
    SetBbrState(BbrMode_t::BBR_PROBE_RTT);
    m_pacingGain = 1;
    m_cWndGain = 1;
}
 
void
TcpBbr::SaveCwnd(Ptr<const TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    if (tcb->m_congState != TcpSocketState::CA_RECOVERY && m_state != BbrMode_t::BBR_PROBE_RTT)
    {
        m_priorCwnd = tcb->m_cWnd;
    }
    else
    {
        m_priorCwnd = std::max(m_priorCwnd, tcb->m_cWnd.Get());
    }
}
 
void
TcpBbr::RestoreCwnd(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    tcb->m_cWnd = std::max(m_priorCwnd, tcb->m_cWnd.Get());
}
 
void
TcpBbr::ExitProbeRTT()
{
    NS_LOG_FUNCTION(this);
    if (m_isPipeFilled)
    {
        EnterProbeBW();
    }
    else
    {
        EnterStartup();
    }
}
 
void
TcpBbr::HandleProbeRTT(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    m_appLimited = (m_delivered + tcb->m_bytesInFlight.Get()) ?: 1;
 
    if (m_probeRttDoneStamp == Seconds(0) && tcb->m_bytesInFlight <= m_minPipeCwnd)
    {
        m_probeRttDoneStamp = Simulator::Now() + m_probeRttDuration;
        m_probeRttRoundDone = false;
        m_nextRoundDelivered = m_delivered;
    }
    else if (m_probeRttDoneStamp != Seconds(0))
    {
        if (m_roundStart)
        {
            m_probeRttRoundDone = true;
        }
        if (m_probeRttRoundDone && Simulator::Now() > m_probeRttDoneStamp)
        {
            m_rtPropStamp = Simulator::Now();
            RestoreCwnd(tcb);
            ExitProbeRTT();
        }
    }
}
 
void
TcpBbr::CheckProbeRTT(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb);
    if (m_state != BbrMode_t::BBR_PROBE_RTT && m_rtPropExpired && !m_idleRestart)
    {
        EnterProbeRTT();
        SaveCwnd(tcb);
        m_probeRttDoneStamp = Seconds(0);
    }
 
    if (m_state == BbrMode_t::BBR_PROBE_RTT)
    {
        HandleProbeRTT(tcb);
    }
 
    if (rs.m_delivered)
    {
        m_idleRestart = false;
    }
}
 
void
TcpBbr::SetSendQuantum(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    m_sendQuantum = 1 * tcb->m_segmentSize;
}
 
void
TcpBbr::UpdateTargetCwnd(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    m_targetCWnd = InFlight(tcb, m_cWndGain) + AckAggregationCwnd();
}
 
uint32_t
TcpBbr::AckAggregationCwnd()
{
    uint32_t maxAggrBytes; // MaxBW * 0.1 secs
    uint32_t aggrCwndBytes = 0;
 
    if (m_extraAckedGain && m_isPipeFilled)
    {
        maxAggrBytes = m_maxBwFilter.GetBest().GetBitRate() / (10 * 8);
        aggrCwndBytes = m_extraAckedGain * std::max(m_extraAcked[0], m_extraAcked[1]);
        aggrCwndBytes = std::min(aggrCwndBytes, maxAggrBytes);
    }
    return aggrCwndBytes;
}
 
void
TcpBbr::UpdateAckAggregation(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    uint32_t expectedAcked;
    uint32_t extraAck;
    uint32_t epochProp;
 
    if (!m_extraAckedGain || rs.m_ackedSacked <= 0 || rs.m_delivered < 0)
    {
        return;
    }
 
    if (m_roundStart)
    {
        m_extraAckedWinRtt = std::min<uint32_t>(31, m_extraAckedWinRtt + 1);
        if (m_extraAckedWinRtt >= m_extraAckedWinRttLength)
        {
            m_extraAckedWinRtt = 0;
            m_extraAckedIdx = m_extraAckedIdx ? 0 : 1;
            m_extraAcked[m_extraAckedIdx] = 0;
        }
    }
 
    epochProp = Simulator::Now().GetSeconds() - m_ackEpochTime.GetSeconds();
    expectedAcked = m_maxBwFilter.GetBest().GetBitRate() * epochProp / 8;
 
    if (m_ackEpochAcked <= expectedAcked ||
        (m_ackEpochAcked + rs.m_ackedSacked >= m_ackEpochAckedResetThresh))
    {
        m_ackEpochAcked = 0;
        m_ackEpochTime = Simulator::Now();
        expectedAcked = 0;
    }
 
    m_ackEpochAcked = m_ackEpochAcked + rs.m_ackedSacked;
    extraAck = m_ackEpochAcked - expectedAcked;
    extraAck = std::min(extraAck, tcb->m_cWnd.Get());
 
    if (extraAck > m_extraAcked[m_extraAckedIdx])
    {
        m_extraAcked[m_extraAckedIdx] = extraAck;
    }
}
 
bool
TcpBbr::ModulateCwndForRecovery(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    if (rs.m_bytesLoss > 0)
    {
        tcb->m_cWnd =
            std::max((int)tcb->m_cWnd.Get() - (int)rs.m_bytesLoss, (int)tcb->m_segmentSize);
    }
 
    if (m_packetConservation)
    {
        tcb->m_cWnd = std::max(tcb->m_cWnd.Get(), tcb->m_bytesInFlight.Get() + rs.m_ackedSacked);
        return true;
    }
    return false;
}
 
void
TcpBbr::ModulateCwndForProbeRTT(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
    if (m_state == BbrMode_t::BBR_PROBE_RTT)
    {
        tcb->m_cWnd = std::min(tcb->m_cWnd.Get(), m_minPipeCwnd);
    }
}
 
void
TcpBbr::SetCwnd(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
 
    if (!rs.m_ackedSacked)
    {
        goto done;
    }
 
    if (tcb->m_congState == TcpSocketState::CA_RECOVERY)
    {
        if (ModulateCwndForRecovery(tcb, rs))
        {
            goto done;
        }
    }
 
    UpdateTargetCwnd(tcb);
 
    if (m_isPipeFilled)
    {
        tcb->m_cWnd = std::min(tcb->m_cWnd.Get() + (uint32_t)rs.m_ackedSacked, m_targetCWnd);
    }
    else if (tcb->m_cWnd < m_targetCWnd || m_delivered < tcb->m_initialCWnd * tcb->m_segmentSize)
    {
        tcb->m_cWnd = tcb->m_cWnd.Get() + rs.m_ackedSacked;
    }
    tcb->m_cWnd = std::max(tcb->m_cWnd.Get(), m_minPipeCwnd);
 
done:
    ModulateCwndForProbeRTT(tcb);
}
 
void
TcpBbr::UpdateRound(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    if (rs.m_priorDelivered >= m_nextRoundDelivered)
    {
        m_nextRoundDelivered = m_delivered;
        m_roundCount++;
        m_roundStart = true;
        m_packetConservation = false;
    }
    else
    {
        m_roundStart = false;
    }
}
 
void
TcpBbr::UpdateBtlBw(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
 
    if (rs.m_deliveryRate == 0)
    {
        return;
    }
 
    UpdateRound(tcb, rs);
 
    if (rs.m_deliveryRate >= m_maxBwFilter.GetBest() || !rs.m_isAppLimited)
    {
        m_maxBwFilter.Update(rs.m_deliveryRate, m_roundCount);
    }
}
 
void
TcpBbr::UpdateModelAndState(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    UpdateBtlBw(tcb, rs);
    UpdateAckAggregation(tcb, rs);
    CheckCyclePhase(tcb, rs);
    CheckFullPipe(rs);
    CheckDrain(tcb);
    UpdateRTprop(tcb);
    CheckProbeRTT(tcb, rs);
}
 
void
TcpBbr::UpdateControlParameters(Ptr<TcpSocketState> tcb, const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    SetPacingRate(tcb, m_pacingGain);
    SetSendQuantum(tcb);
    SetCwnd(tcb, rs);
}
 
void
TcpBbr::SetBbrState(BbrMode_t mode)
{
    NS_LOG_FUNCTION(this << mode);
    NS_LOG_DEBUG(Simulator::Now() << " Changing from " << BbrModeName[m_state] << " to "
                                  << BbrModeName[mode]);
    m_state = mode;
}
 
uint32_t
TcpBbr::GetBbrState()
{
    NS_LOG_FUNCTION(this);
    return m_state;
}
 
double
TcpBbr::GetCwndGain()
{
    NS_LOG_FUNCTION(this);
    return m_cWndGain;
}
 
double
TcpBbr::GetPacingGain()
{
    NS_LOG_FUNCTION(this);
    return m_pacingGain;
}
 
std::string
TcpBbr::GetName() const
{
    return "TcpBbr";
}
 
bool
TcpBbr::HasCongControl() const
{
    NS_LOG_FUNCTION(this);
    return true;
}
 
void
TcpBbr::CongControl(Ptr<TcpSocketState> tcb,
                    const TcpRateOps::TcpRateConnection& rc,
                    const TcpRateOps::TcpRateSample& rs)
{
    NS_LOG_FUNCTION(this << tcb << rs);
    m_delivered = rc.m_delivered;
    m_txItemDelivered = rc.m_txItemDelivered;
    UpdateModelAndState(tcb, rs);
    UpdateControlParameters(tcb, rs);
}
 
void
TcpBbr::CongestionStateSet(Ptr<TcpSocketState> tcb, const TcpSocketState::TcpCongState_t newState)
{
    NS_LOG_FUNCTION(this << tcb << newState);
    if (newState == TcpSocketState::CA_OPEN && !m_isInitialized)
    {
        NS_LOG_DEBUG("CongestionStateSet triggered to CA_OPEN :: " << newState);
        m_rtProp = tcb->m_lastRtt.Get() != Time::Max() ? tcb->m_lastRtt.Get() : Time::Max();
        m_rtPropStamp = Simulator::Now();
        m_priorCwnd = tcb->m_cWnd;
        tcb->m_ssThresh = tcb->m_initialSsThresh;
        m_targetCWnd = tcb->m_cWnd;
        m_minPipeCwnd = 4 * tcb->m_segmentSize;
        m_sendQuantum = 1 * tcb->m_segmentSize;
 
        InitRoundCounting();
        InitFullPipe();
        EnterStartup();
        InitPacingRate(tcb);
        m_ackEpochTime = Simulator::Now();
        m_extraAckedWinRtt = 0;
        m_extraAckedIdx = 0;
        m_ackEpochAcked = 0;
        m_extraAcked[0] = 0;
        m_extraAcked[1] = 0;
        m_isInitialized = true;
    }
    else if (newState == TcpSocketState::CA_LOSS)
    {
        NS_LOG_DEBUG("CongestionStateSet triggered to CA_LOSS :: " << newState);
        SaveCwnd(tcb);
        m_roundStart = true;
    }
    else if (newState == TcpSocketState::CA_RECOVERY)
    {
        NS_LOG_DEBUG("CongestionStateSet triggered to CA_RECOVERY :: " << newState);
        SaveCwnd(tcb);
        tcb->m_cWnd =
            tcb->m_bytesInFlight.Get() + std::max(tcb->m_lastAckedSackedBytes, tcb->m_segmentSize);
        m_packetConservation = true;
    }
}
 
void
TcpBbr::CwndEvent(Ptr<TcpSocketState> tcb, const TcpSocketState::TcpCAEvent_t event)
{
    NS_LOG_FUNCTION(this << tcb << event);
    if (event == TcpSocketState::CA_EVENT_COMPLETE_CWR)
    {
        NS_LOG_DEBUG("CwndEvent triggered to CA_EVENT_COMPLETE_CWR :: " << event);
        m_packetConservation = false;
        RestoreCwnd(tcb);
    }
    else if (event == TcpSocketState::CA_EVENT_TX_START && m_appLimited)
    {
        NS_LOG_DEBUG("CwndEvent triggered to CA_EVENT_TX_START :: " << event);
        m_idleRestart = true;
        m_ackEpochTime = Simulator::Now();
        m_ackEpochAcked = 0;
        if (m_state == BbrMode_t::BBR_PROBE_BW)
        {
            SetPacingRate(tcb, 1);
        }
        else if (m_state == BbrMode_t::BBR_PROBE_RTT)
        {
            if (m_probeRttRoundDone && Simulator::Now() > m_probeRttDoneStamp)
            {
                m_rtPropStamp = Simulator::Now();
                RestoreCwnd(tcb);
                ExitProbeRTT();
            }
        }
    }
}
 
uint32_t
TcpBbr::GetSsThresh(Ptr<const TcpSocketState> tcb, uint32_t bytesInFlight)
{
    NS_LOG_FUNCTION(this << tcb << bytesInFlight);
    SaveCwnd(tcb);
    return tcb->m_ssThresh;
}
 
Ptr<TcpCongestionOps>
TcpBbr::Fork()
{
    return CopyObject<TcpBbr>(this);
}
 
} // namespace ns3