qos-frame-exchange-manager.cc

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/*
 * Copyright (c) 2020 Universita' degli Studi di Napoli Federico II
 *
 * 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
 *
 * Author: Stefano Avallone <stavallo@unina.it>
 */
 
#include "qos-frame-exchange-manager.h"
 
#include "ap-wifi-mac.h"
#include "wifi-mac-queue.h"
#include "wifi-mac-trailer.h"
 
#include "ns3/abort.h"
#include "ns3/log.h"
 
#undef NS_LOG_APPEND_CONTEXT
#define NS_LOG_APPEND_CONTEXT std::clog << "[link=" << +m_linkId << "][mac=" << m_self << "] "
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("QosFrameExchangeManager");
 
NS_OBJECT_ENSURE_REGISTERED(QosFrameExchangeManager);
 
TypeId
QosFrameExchangeManager::GetTypeId()
{
    static TypeId tid =
        TypeId("ns3::QosFrameExchangeManager")
            .SetParent<FrameExchangeManager>()
            .AddConstructor<QosFrameExchangeManager>()
            .SetGroupName("Wifi")
            .AddAttribute("PifsRecovery",
                          "Perform a PIFS recovery as a response to transmission failure "
                          "within a TXOP",
                          BooleanValue(true),
                          MakeBooleanAccessor(&QosFrameExchangeManager::m_pifsRecovery),
                          MakeBooleanChecker())
            .AddAttribute("SetQueueSize",
                          "Whether to set the Queue Size subfield of the QoS Control field "
                          "of QoS data frames sent by non-AP stations",
                          BooleanValue(false),
                          MakeBooleanAccessor(&QosFrameExchangeManager::m_setQosQueueSize),
                          MakeBooleanChecker());
    return tid;
}
 
QosFrameExchangeManager::QosFrameExchangeManager()
    : m_initialFrame(false)
{
    NS_LOG_FUNCTION(this);
}
 
QosFrameExchangeManager::~QosFrameExchangeManager()
{
    NS_LOG_FUNCTION_NOARGS();
}
 
void
QosFrameExchangeManager::DoDispose()
{
    NS_LOG_FUNCTION(this);
    m_edca = nullptr;
    m_edcaBackingOff = nullptr;
    m_pifsRecoveryEvent.Cancel();
    FrameExchangeManager::DoDispose();
}
 
bool
QosFrameExchangeManager::SendCfEndIfNeeded()
{
    NS_LOG_FUNCTION(this);
    NS_ASSERT(m_edca);
    NS_ASSERT(m_edca->GetTxopLimit(m_linkId).IsStrictlyPositive());
 
    WifiMacHeader cfEnd;
    cfEnd.SetType(WIFI_MAC_CTL_END);
    cfEnd.SetDsNotFrom();
    cfEnd.SetDsNotTo();
    cfEnd.SetNoRetry();
    cfEnd.SetNoMoreFragments();
    cfEnd.SetDuration(Seconds(0));
    cfEnd.SetAddr1(Mac48Address::GetBroadcast());
    cfEnd.SetAddr2(m_self);
 
    WifiTxVector cfEndTxVector = GetWifiRemoteStationManager()->GetRtsTxVector(cfEnd.GetAddr1());
 
    Time txDuration = m_phy->CalculateTxDuration(cfEnd.GetSize() + WIFI_MAC_FCS_LENGTH,
                                                 cfEndTxVector,
                                                 m_phy->GetPhyBand());
 
    // Send the CF-End frame if the remaining duration is long enough to transmit this frame
    if (m_edca->GetRemainingTxop(m_linkId) > txDuration)
    {
        NS_LOG_DEBUG("Send CF-End frame");
        m_phy->Send(Create<WifiPsdu>(Create<Packet>(), cfEnd), cfEndTxVector);
        Simulator::Schedule(txDuration, &Txop::NotifyChannelReleased, m_edca, m_linkId);
        return true;
    }
 
    m_edca->NotifyChannelReleased(m_linkId);
    m_edca = nullptr;
    return false;
}
 
void
QosFrameExchangeManager::PifsRecovery()
{
    NS_LOG_FUNCTION(this);
    NS_ASSERT(m_edca);
    NS_ASSERT(m_edca->IsTxopStarted(m_linkId));
 
    // Release the channel if it has not been idle for the last PIFS interval
    if (m_channelAccessManager->GetAccessGrantStart() - m_phy->GetSifs() >
        Simulator::Now() - m_phy->GetPifs())
    {
        m_edca->NotifyChannelReleased(m_linkId);
        m_edca = nullptr;
    }
    else
    {
        // the txopDuration parameter is unused because we are not starting a new TXOP
        StartTransmission(m_edca, Seconds(0));
    }
}
 
void
QosFrameExchangeManager::CancelPifsRecovery()
{
    NS_LOG_FUNCTION(this);
    NS_ASSERT(m_pifsRecoveryEvent.IsRunning());
    NS_ASSERT(m_edca);
 
    NS_LOG_DEBUG("Cancel PIFS recovery being attempted by EDCAF " << m_edca);
    m_pifsRecoveryEvent.Cancel();
    m_edca->NotifyChannelReleased(m_linkId);
}
 
bool
QosFrameExchangeManager::StartTransmission(Ptr<Txop> edca, uint16_t allowedWidth)
{
    NS_LOG_FUNCTION(this << edca << allowedWidth);
 
    if (m_pifsRecoveryEvent.IsRunning())
    {
        // Another AC (having AIFS=1 or lower, if the user changed the default settings)
        // gained channel access while performing PIFS recovery. Abort PIFS recovery
        CancelPifsRecovery();
    }
 
    // TODO This will become an assert once no Txop is installed on a QoS station
    if (!edca->IsQosTxop())
    {
        m_edca = nullptr;
        return FrameExchangeManager::StartTransmission(edca, allowedWidth);
    }
 
    m_allowedWidth = allowedWidth;
    auto qosTxop = StaticCast<QosTxop>(edca);
    return StartTransmission(qosTxop, qosTxop->GetTxopLimit(m_linkId));
}
 
bool
QosFrameExchangeManager::StartTransmission(Ptr<QosTxop> edca, Time txopDuration)
{
    NS_LOG_FUNCTION(this << edca << txopDuration);
 
    if (m_pifsRecoveryEvent.IsRunning())
    {
        // Another AC (having AIFS=1 or lower, if the user changed the default settings)
        // gained channel access while performing PIFS recovery. Abort PIFS recovery
        CancelPifsRecovery();
    }
 
    if (m_txTimer.IsRunning())
    {
        m_txTimer.Cancel();
    }
    m_dcf = edca;
    m_edca = edca;
 
    // We check if this EDCAF invoked the backoff procedure (without terminating
    // the TXOP) because the transmission of a non-initial frame of a TXOP failed
    bool backingOff = (m_edcaBackingOff == m_edca);
 
    if (backingOff)
    {
        NS_ASSERT(m_edca->GetTxopLimit(m_linkId).IsStrictlyPositive());
        NS_ASSERT(m_edca->IsTxopStarted(m_linkId));
        NS_ASSERT(!m_pifsRecovery);
        NS_ASSERT(!m_initialFrame);
 
        // clear the member variable
        m_edcaBackingOff = nullptr;
    }
 
    if (m_edca->GetTxopLimit(m_linkId).IsStrictlyPositive())
    {
        // TXOP limit is not null. We have to check if this EDCAF is starting a
        // new TXOP. This includes the case when the transmission of a non-initial
        // frame of a TXOP failed and backoff was invoked without terminating the
        // TXOP. In such a case, we assume that a new TXOP is being started if it
        // elapsed more than TXOPlimit since the start of the paused TXOP. Note
        // that GetRemainingTxop returns 0 iff Now - TXOPstart >= TXOPlimit
        if (!m_edca->IsTxopStarted(m_linkId) ||
            (backingOff && m_edca->GetRemainingTxop(m_linkId).IsZero()))
        {
            // starting a new TXOP
            m_edca->NotifyChannelAccessed(m_linkId, txopDuration);
 
            if (StartFrameExchange(m_edca, txopDuration, true))
            {
                m_initialFrame = true;
                return true;
            }
 
            // TXOP not even started, return false
            NS_LOG_DEBUG("No frame transmitted");
            m_edca->NotifyChannelReleased(m_linkId);
            m_edca = nullptr;
            return false;
        }
 
        // We are continuing a TXOP, check if we can transmit another frame
        NS_ASSERT(!m_initialFrame);
 
        if (!StartFrameExchange(m_edca, m_edca->GetRemainingTxop(m_linkId), false))
        {
            NS_LOG_DEBUG("Not enough remaining TXOP time");
            return SendCfEndIfNeeded();
        }
 
        return true;
    }
 
    // we get here if TXOP limit is null
    m_initialFrame = true;
 
    if (StartFrameExchange(m_edca, Time::Min(), true))
    {
        m_edca->NotifyChannelAccessed(m_linkId, Seconds(0));
        return true;
    }
 
    NS_LOG_DEBUG("No frame transmitted");
    m_edca->NotifyChannelReleased(m_linkId);
    m_edca = nullptr;
    return false;
}
 
bool
QosFrameExchangeManager::StartFrameExchange(Ptr<QosTxop> edca,
                                            Time availableTime,
                                            bool initialFrame)
{
    NS_LOG_FUNCTION(this << edca << availableTime << initialFrame);
 
    Ptr<WifiMpdu> mpdu = edca->PeekNextMpdu(m_linkId);
 
    // Even though channel access is requested when the queue is not empty, at
    // the time channel access is granted the lifetime of the packet might be
    // expired and the queue might be empty.
    if (!mpdu)
    {
        NS_LOG_DEBUG("Queue empty");
        return false;
    }
 
    mpdu = CreateAliasIfNeeded(mpdu);
    WifiTxParameters txParams;
    txParams.m_txVector =
        GetWifiRemoteStationManager()->GetDataTxVector(mpdu->GetHeader(), m_allowedWidth);
 
    Ptr<WifiMpdu> item = edca->GetNextMpdu(m_linkId, mpdu, txParams, availableTime, initialFrame);
 
    if (!item)
    {
        NS_LOG_DEBUG("Not enough time to transmit a frame");
        return false;
    }
 
    NS_ASSERT_MSG(!item->GetHeader().IsQosData() || !item->GetHeader().IsQosAmsdu(),
                  "We should not get an A-MSDU here");
 
    // check if the MSDU needs to be fragmented
    item = GetFirstFragmentIfNeeded(item);
 
    // update the protection method if the frame was fragmented
    if (item->IsFragment() && item->GetSize() != mpdu->GetSize())
    {
        WifiTxParameters fragmentTxParams;
        fragmentTxParams.m_txVector = txParams.m_txVector;
        txParams.m_protection = GetProtectionManager()->TryAddMpdu(item, fragmentTxParams);
        NS_ASSERT(txParams.m_protection);
    }
 
    SendMpduWithProtection(item, txParams);
 
    return true;
}
 
Ptr<WifiMpdu>
QosFrameExchangeManager::CreateAliasIfNeeded(Ptr<WifiMpdu> mpdu) const
{
    return mpdu;
}
 
bool
QosFrameExchangeManager::TryAddMpdu(Ptr<const WifiMpdu> mpdu,
                                    WifiTxParameters& txParams,
                                    Time availableTime) const
{
    NS_ASSERT(mpdu);
    NS_LOG_FUNCTION(this << *mpdu << &txParams << availableTime);
 
    // check if adding the given MPDU requires a different protection method
    Time protectionTime = Time::Min(); // uninitialized
    if (txParams.m_protection)
    {
        protectionTime = txParams.m_protection->protectionTime;
    }
 
    std::unique_ptr<WifiProtection> protection;
    protection = GetProtectionManager()->TryAddMpdu(mpdu, txParams);
    bool protectionSwapped = false;
 
    if (protection)
    {
        // the protection method has changed, calculate the new protection time
        CalculateProtectionTime(protection.get());
        protectionTime = protection->protectionTime;
        // swap unique pointers, so that the txParams that is passed to the next
        // call to IsWithinLimitsIfAddMpdu is the most updated one
        txParams.m_protection.swap(protection);
        protectionSwapped = true;
    }
    NS_ASSERT(protectionTime != Time::Min());
    NS_LOG_DEBUG("protection time=" << protectionTime);
 
    // check if adding the given MPDU requires a different acknowledgment method
    Time acknowledgmentTime = Time::Min(); // uninitialized
    if (txParams.m_acknowledgment)
    {
        acknowledgmentTime = txParams.m_acknowledgment->acknowledgmentTime;
    }
 
    std::unique_ptr<WifiAcknowledgment> acknowledgment;
    acknowledgment = GetAckManager()->TryAddMpdu(mpdu, txParams);
    bool acknowledgmentSwapped = false;
 
    if (acknowledgment)
    {
        // the acknowledgment method has changed, calculate the new acknowledgment time
        CalculateAcknowledgmentTime(acknowledgment.get());
        acknowledgmentTime = acknowledgment->acknowledgmentTime;
        // swap unique pointers, so that the txParams that is passed to the next
        // call to IsWithinLimitsIfAddMpdu is the most updated one
        txParams.m_acknowledgment.swap(acknowledgment);
        acknowledgmentSwapped = true;
    }
    NS_ASSERT(acknowledgmentTime != Time::Min());
    NS_LOG_DEBUG("acknowledgment time=" << acknowledgmentTime);
 
    Time ppduDurationLimit = Time::Min();
    if (availableTime != Time::Min())
    {
        ppduDurationLimit = availableTime - protectionTime - acknowledgmentTime;
    }
 
    if (!IsWithinLimitsIfAddMpdu(mpdu, txParams, ppduDurationLimit))
    {
        // adding MPDU failed, restore protection and acknowledgment methods
        // if they were swapped
        if (protectionSwapped)
        {
            txParams.m_protection.swap(protection);
        }
        if (acknowledgmentSwapped)
        {
            txParams.m_acknowledgment.swap(acknowledgment);
        }
        return false;
    }
 
    // the given MPDU can be added, hence update the txParams
    txParams.AddMpdu(mpdu);
    UpdateTxDuration(mpdu->GetHeader().GetAddr1(), txParams);
 
    return true;
}
 
bool
QosFrameExchangeManager::IsWithinLimitsIfAddMpdu(Ptr<const WifiMpdu> mpdu,
                                                 const WifiTxParameters& txParams,
                                                 Time ppduDurationLimit) const
{
    NS_ASSERT(mpdu);
    NS_LOG_FUNCTION(this << *mpdu << &txParams << ppduDurationLimit);
 
    // A QoS station only has to check that the MPDU transmission time does not
    // exceed the given limit
    return IsWithinSizeAndTimeLimits(mpdu->GetSize(),
                                     mpdu->GetHeader().GetAddr1(),
                                     txParams,
                                     ppduDurationLimit);
}
 
bool
QosFrameExchangeManager::IsWithinSizeAndTimeLimits(uint32_t ppduPayloadSize,
                                                   Mac48Address receiver,
                                                   const WifiTxParameters& txParams,
                                                   Time ppduDurationLimit) const
{
    NS_LOG_FUNCTION(this << ppduPayloadSize << receiver << &txParams << ppduDurationLimit);
 
    if (ppduDurationLimit != Time::Min() && ppduDurationLimit.IsNegative())
    {
        NS_LOG_DEBUG("ppduDurationLimit is null or negative, time limit is trivially exceeded");
        return false;
    }
 
    if (ppduPayloadSize > WifiPhy::GetMaxPsduSize(txParams.m_txVector.GetModulationClass()))
    {
        NS_LOG_DEBUG("the frame exceeds the max PSDU size");
        return false;
    }
 
    // Get the maximum PPDU Duration based on the preamble type
    Time maxPpduDuration = GetPpduMaxTime(txParams.m_txVector.GetPreambleType());
 
    Time txTime = GetTxDuration(ppduPayloadSize, receiver, txParams);
    NS_LOG_DEBUG("PPDU duration: " << txTime.As(Time::MS));
 
    if ((ppduDurationLimit.IsStrictlyPositive() && txTime > ppduDurationLimit) ||
        (maxPpduDuration.IsStrictlyPositive() && txTime > maxPpduDuration))
    {
        NS_LOG_DEBUG(
            "the frame does not meet the constraint on max PPDU duration or PPDU duration limit");
        return false;
    }
 
    return true;
}
 
Time
QosFrameExchangeManager::GetFrameDurationId(const WifiMacHeader& header,
                                            uint32_t size,
                                            const WifiTxParameters& txParams,
                                            Ptr<Packet> fragmentedPacket) const
{
    NS_LOG_FUNCTION(this << header << size << &txParams << fragmentedPacket);
 
    // TODO This will be removed once no Txop is installed on a QoS station
    if (!m_edca)
    {
        return FrameExchangeManager::GetFrameDurationId(header, size, txParams, fragmentedPacket);
    }
 
    if (m_edca->GetTxopLimit(m_linkId).IsZero())
    {
        return FrameExchangeManager::GetFrameDurationId(header, size, txParams, fragmentedPacket);
    }
 
    NS_ASSERT(txParams.m_acknowledgment &&
              txParams.m_acknowledgment->acknowledgmentTime != Time::Min());
 
    // under multiple protection settings, if the TXOP limit is not null, Duration/ID
    // is set to cover the remaining TXOP time (Sec. 9.2.5.2 of 802.11-2016).
    // The TXOP holder may exceed the TXOP limit in some situations (Sec. 10.22.2.8
    // of 802.11-2016)
    return std::max(m_edca->GetRemainingTxop(m_linkId) -
                        m_phy->CalculateTxDuration(size, txParams.m_txVector, m_phy->GetPhyBand()),
                    txParams.m_acknowledgment->acknowledgmentTime);
}
 
Time
QosFrameExchangeManager::GetRtsDurationId(const WifiTxVector& rtsTxVector,
                                          Time txDuration,
                                          Time response) const
{
    NS_LOG_FUNCTION(this << rtsTxVector << txDuration << response);
 
    // TODO This will be removed once no Txop is installed on a QoS station
    if (!m_edca)
    {
        return FrameExchangeManager::GetRtsDurationId(rtsTxVector, txDuration, response);
    }
 
    if (m_edca->GetTxopLimit(m_linkId).IsZero())
    {
        return FrameExchangeManager::GetRtsDurationId(rtsTxVector, txDuration, response);
    }
 
    // under multiple protection settings, if the TXOP limit is not null, Duration/ID
    // is set to cover the remaining TXOP time (Sec. 9.2.5.2 of 802.11-2016).
    // The TXOP holder may exceed the TXOP limit in some situations (Sec. 10.22.2.8
    // of 802.11-2016)
    return std::max(m_edca->GetRemainingTxop(m_linkId) -
                        m_phy->CalculateTxDuration(GetRtsSize(), rtsTxVector, m_phy->GetPhyBand()),
                    Seconds(0));
}
 
Time
QosFrameExchangeManager::GetCtsToSelfDurationId(const WifiTxVector& ctsTxVector,
                                                Time txDuration,
                                                Time response) const
{
    NS_LOG_FUNCTION(this << ctsTxVector << txDuration << response);
 
    // TODO This will be removed once no Txop is installed on a QoS station
    if (!m_edca)
    {
        return FrameExchangeManager::GetCtsToSelfDurationId(ctsTxVector, txDuration, response);
    }
 
    if (m_edca->GetTxopLimit(m_linkId).IsZero())
    {
        return FrameExchangeManager::GetCtsToSelfDurationId(ctsTxVector, txDuration, response);
    }
 
    // under multiple protection settings, if the TXOP limit is not null, Duration/ID
    // is set to cover the remaining TXOP time (Sec. 9.2.5.2 of 802.11-2016).
    // The TXOP holder may exceed the TXOP limit in some situations (Sec. 10.22.2.8
    // of 802.11-2016)
    return std::max(m_edca->GetRemainingTxop(m_linkId) -
                        m_phy->CalculateTxDuration(GetCtsSize(), ctsTxVector, m_phy->GetPhyBand()),
                    Seconds(0));
}
 
void
QosFrameExchangeManager::ForwardMpduDown(Ptr<WifiMpdu> mpdu, WifiTxVector& txVector)
{
    NS_LOG_FUNCTION(this << *mpdu << txVector);
 
    WifiMacHeader& hdr = mpdu->GetHeader();
 
    if (hdr.IsQosData() && m_mac->GetTypeOfStation() == STA &&
        (m_setQosQueueSize || hdr.IsQosEosp()))
    {
        uint8_t tid = hdr.GetQosTid();
        hdr.SetQosEosp();
        hdr.SetQosQueueSize(m_mac->GetQosTxop(tid)->GetQosQueueSize(tid, hdr.GetAddr1()));
    }
    FrameExchangeManager::ForwardMpduDown(mpdu, txVector);
}
 
void
QosFrameExchangeManager::TransmissionSucceeded()
{
    NS_LOG_DEBUG(this);
 
    // TODO This will be removed once no Txop is installed on a QoS station
    if (!m_edca)
    {
        FrameExchangeManager::TransmissionSucceeded();
        return;
    }
 
    if (m_edca->GetTxopLimit(m_linkId).IsStrictlyPositive() &&
        m_edca->GetRemainingTxop(m_linkId) > m_phy->GetSifs())
    {
        NS_LOG_DEBUG("Schedule another transmission in a SIFS");
        bool (QosFrameExchangeManager::*fp)(Ptr<QosTxop>, Time) =
            &QosFrameExchangeManager::StartTransmission;
 
        // we are continuing a TXOP, hence the txopDuration parameter is unused
        Simulator::Schedule(m_phy->GetSifs(), fp, this, m_edca, Seconds(0));
    }
    else
    {
        m_edca->NotifyChannelReleased(m_linkId);
        m_edca = nullptr;
    }
    m_initialFrame = false;
}
 
void
QosFrameExchangeManager::TransmissionFailed()
{
    NS_LOG_FUNCTION(this);
 
    // TODO This will be removed once no Txop is installed on a QoS station
    if (!m_edca)
    {
        FrameExchangeManager::TransmissionFailed();
        return;
    }
 
    if (m_initialFrame)
    {
        // The backoff procedure shall be invoked by an EDCAF when the transmission
        // of an MPDU in the initial PPDU of a TXOP fails (Sec. 10.22.2.2 of 802.11-2016)
        NS_LOG_DEBUG("TX of the initial frame of a TXOP failed: terminate TXOP");
        m_edca->NotifyChannelReleased(m_linkId);
        m_edca = nullptr;
    }
    else
    {
        NS_ASSERT_MSG(m_edca->GetTxopLimit(m_linkId).IsStrictlyPositive(),
                      "Cannot transmit more than one frame if TXOP Limit is zero");
 
        // A STA can perform a PIFS recovery or perform a backoff as a response to
        // transmission failure within a TXOP. How it chooses between these two is
        // implementation dependent. (Sec. 10.22.2.2 of 802.11-2016)
        if (m_pifsRecovery)
        {
            // we can continue the TXOP if the carrier sense mechanism indicates that
            // the medium is idle in a PIFS
            NS_LOG_DEBUG("TX of a non-initial frame of a TXOP failed: perform PIFS recovery");
            NS_ASSERT(!m_pifsRecoveryEvent.IsRunning());
            m_pifsRecoveryEvent =
                Simulator::Schedule(m_phy->GetPifs(), &QosFrameExchangeManager::PifsRecovery, this);
        }
        else
        {
            // In order not to terminate (yet) the TXOP, we call the NotifyChannelReleased
            // method of the Txop class, which only generates a new backoff value and
            // requests channel access if needed,
            NS_LOG_DEBUG("TX of a non-initial frame of a TXOP failed: invoke backoff");
            m_edca->Txop::NotifyChannelReleased(m_linkId);
            m_edcaBackingOff = m_edca;
            m_edca = nullptr;
        }
    }
    m_initialFrame = false;
}
 
void
QosFrameExchangeManager::PreProcessFrame(Ptr<const WifiPsdu> psdu, const WifiTxVector& txVector)
{
    NS_LOG_FUNCTION(this << psdu << txVector);
 
    // APs store buffer size report of associated stations
    if (m_mac->GetTypeOfStation() == AP && psdu->GetAddr1() == m_self)
    {
        for (const auto& mpdu : *PeekPointer(psdu))
        {
            const WifiMacHeader& hdr = mpdu->GetHeader();
 
            if (hdr.IsQosData() && hdr.IsQosEosp())
            {
                NS_LOG_DEBUG("Station " << hdr.GetAddr2() << " reported a buffer status of "
                                        << +hdr.GetQosQueueSize()
                                        << " for tid=" << +hdr.GetQosTid());
                StaticCast<ApWifiMac>(m_mac)->SetBufferStatus(
                    hdr.GetQosTid(),
                    mpdu->GetOriginal()->GetHeader().GetAddr2(),
                    hdr.GetQosQueueSize());
            }
        }
    }
 
    // before updating the NAV, check if the NAV counted down to zero. In such a
    // case, clear the saved TXOP holder address.
    ClearTxopHolderIfNeeded();
 
    FrameExchangeManager::PreProcessFrame(psdu, txVector);
}
 
void
QosFrameExchangeManager::PostProcessFrame(Ptr<const WifiPsdu> psdu, const WifiTxVector& txVector)
{
    NS_LOG_FUNCTION(this << psdu << txVector);
 
    SetTxopHolder(psdu, txVector);
    FrameExchangeManager::PostProcessFrame(psdu, txVector);
}
 
void
QosFrameExchangeManager::SetTxopHolder(Ptr<const WifiPsdu> psdu, const WifiTxVector& txVector)
{
    NS_LOG_FUNCTION(this << psdu << txVector);
 
    const WifiMacHeader& hdr = psdu->GetHeader(0);
 
    // A STA shall save the TXOP holder address for the BSS in which it is associated.
    // The TXOP holder address is the MAC address from the Address 2 field of the frame
    // that initiated a frame exchange sequence, except if this is a CTS frame, in which
    // case the TXOP holder address is the Address 1 field. (Sec. 10.23.2.4 of 802.11-2020)
    if ((hdr.IsQosData() || hdr.IsMgt() || hdr.IsRts()) &&
        (hdr.GetAddr1() == m_bssid || hdr.GetAddr2() == m_bssid))
    {
        m_txopHolder = psdu->GetAddr2();
    }
    else if (hdr.IsCts() && hdr.GetAddr1() == m_bssid)
    {
        m_txopHolder = psdu->GetAddr1();
    }
}
 
void
QosFrameExchangeManager::ClearTxopHolderIfNeeded()
{
    NS_LOG_FUNCTION(this);
    if (m_navEnd <= Simulator::Now())
    {
        m_txopHolder.reset();
    }
}
 
void
QosFrameExchangeManager::NavResetTimeout()
{
    NS_LOG_FUNCTION(this);
    FrameExchangeManager::NavResetTimeout();
    ClearTxopHolderIfNeeded();
}
 
void
QosFrameExchangeManager::ReceiveMpdu(Ptr<const WifiMpdu> mpdu,
                                     RxSignalInfo rxSignalInfo,
                                     const WifiTxVector& txVector,
                                     bool inAmpdu)
{
    // The received MPDU is either broadcast or addressed to this station
    NS_ASSERT(mpdu->GetHeader().GetAddr1().IsGroup() || mpdu->GetHeader().GetAddr1() == m_self);
 
    double rxSnr = rxSignalInfo.snr;
    const WifiMacHeader& hdr = mpdu->GetHeader();
 
    if (hdr.IsCfEnd())
    {
        // reset NAV
        NavResetTimeout();
        return;
    }
 
    if (hdr.IsRts())
    {
        NS_ABORT_MSG_IF(inAmpdu, "Received RTS as part of an A-MPDU");
 
        // If a non-VHT STA receives an RTS frame with the RA address matching the
        // MAC address of the STA and the MAC address in the TA field in the RTS
        // frame matches the saved TXOP holder address, then the STA shall send the
        // CTS frame after SIFS, without regard for, and without resetting, its NAV.
        // (sec. 10.22.2.4 of 802.11-2016)
        if (hdr.GetAddr2() == m_txopHolder || VirtualCsMediumIdle())
        {
            NS_LOG_DEBUG("Received RTS from=" << hdr.GetAddr2() << ", schedule CTS");
            Simulator::Schedule(m_phy->GetSifs(),
                                &QosFrameExchangeManager::SendCtsAfterRts,
                                this,
                                hdr,
                                txVector.GetMode(),
                                rxSnr);
        }
        else
        {
            NS_LOG_DEBUG("Received RTS from=" << hdr.GetAddr2() << ", cannot schedule CTS");
        }
        return;
    }
 
    if (hdr.IsQosData())
    {
        if (hdr.GetAddr1() == m_self && hdr.GetQosAckPolicy() == WifiMacHeader::NORMAL_ACK)
        {
            NS_LOG_DEBUG("Received " << hdr.GetTypeString() << " from=" << hdr.GetAddr2()
                                     << ", schedule ACK");
            Simulator::Schedule(m_phy->GetSifs(),
                                &QosFrameExchangeManager::SendNormalAck,
                                this,
                                hdr,
                                txVector,
                                rxSnr);
        }
 
        // Forward up the frame if it is not a QoS Null frame
        if (hdr.HasData())
        {
            m_rxMiddle->Receive(mpdu, m_linkId);
        }
 
        // the received data frame has been processed
        return;
    }
 
    return FrameExchangeManager::ReceiveMpdu(mpdu, rxSignalInfo, txVector, inAmpdu);
}
 
} // namespace ns3