qos-txop.cc

Go to the documentation of this file.

/*
 * Copyright (c) 2006, 2009 INRIA
 * Copyright (c) 2009 MIRKO BANCHI
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Authors: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 *          Mirko Banchi <mk.banchi@gmail.com>
 *          Stefano Avallone <stavalli@unina.it>
 */
 
#include "qos-txop.h"
 
#include "ap-wifi-mac.h"
#include "channel-access-manager.h"
#include "ctrl-headers.h"
#include "gcr-manager.h"
#include "mac-tx-middle.h"
#include "mgt-action-headers.h"
#include "mpdu-aggregator.h"
#include "msdu-aggregator.h"
#include "wifi-mac-queue-scheduler.h"
#include "wifi-mac-queue.h"
#include "wifi-mac-trailer.h"
#include "wifi-phy.h"
#include "wifi-psdu.h"
#include "wifi-tx-parameters.h"
 
#include "ns3/ht-configuration.h"
#include "ns3/ht-frame-exchange-manager.h"
#include "ns3/log.h"
#include "ns3/pointer.h"
#include "ns3/random-variable-stream.h"
#include "ns3/simulator.h"
 
#undef NS_LOG_APPEND_CONTEXT
#define NS_LOG_APPEND_CONTEXT WIFI_TXOP_NS_LOG_APPEND_CONTEXT
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("QosTxop");
 
NS_OBJECT_ENSURE_REGISTERED(QosTxop);
 
TypeId
QosTxop::GetTypeId()
{
    static TypeId tid =
        TypeId("ns3::QosTxop")
            .SetParent<ns3::Txop>()
            .SetGroupName("Wifi")
            .AddConstructor<QosTxop>()
            .AddAttribute("UseExplicitBarAfterMissedBlockAck",
                          "Specify whether explicit BlockAckRequest should be sent upon missed "
                          "BlockAck Response.",
                          BooleanValue(true),
                          MakeBooleanAccessor(&QosTxop::m_useExplicitBarAfterMissedBlockAck),
                          MakeBooleanChecker())
            .AddAttribute("AddBaResponseTimeout",
                          "The timeout to wait for ADDBA response after the Ack to "
                          "ADDBA request is received.",
                          TimeValue(MilliSeconds(5)),
                          MakeTimeAccessor(&QosTxop::SetAddBaResponseTimeout,
                                           &QosTxop::GetAddBaResponseTimeout),
                          MakeTimeChecker())
            .AddAttribute(
                "FailedAddBaTimeout",
                "The timeout after a failed BA agreement. During this "
                "timeout, the originator resumes sending packets using normal "
                "MPDU. After that, BA agreement is reset and the originator "
                "will retry BA negotiation.",
                TimeValue(MilliSeconds(200)),
                MakeTimeAccessor(&QosTxop::SetFailedAddBaTimeout, &QosTxop::GetFailedAddBaTimeout),
                MakeTimeChecker())
            .AddAttribute("BlockAckManager",
                          "The BlockAckManager object.",
                          PointerValue(),
                          MakePointerAccessor(&QosTxop::m_baManager),
                          MakePointerChecker<BlockAckManager>())
            .AddAttribute("NMaxInflights",
                          "The maximum number of links (in the range 1-15) on which an MPDU can be "
                          "simultaneously in-flight.",
                          UintegerValue(1),
                          MakeUintegerAccessor(&QosTxop::m_nMaxInflights),
                          MakeUintegerChecker<uint8_t>(1, 15))
            .AddTraceSource("TxopTrace",
                            "Trace source for TXOP start and duration times",
                            MakeTraceSourceAccessor(&QosTxop::m_txopTrace),
                            "ns3::QosTxop::TxopTracedCallback")
            .AddTraceSource("BaEstablished",
                            "A block ack agreement is established with the given recipient for "
                            "the given TID (and the given GCR group address, if any).",
                            MakeTraceSourceAccessor(&QosTxop::m_baEstablishedCallback),
                            "ns3::QosTxop::BaEstablishedCallback");
    return tid;
}
 
QosTxop::QosTxop()
{
    NS_LOG_FUNCTION(this);
    m_baManager = CreateObject<BlockAckManager>();
}
 
void
QosTxop::CreateQueue(AcIndex aci)
{
    NS_LOG_FUNCTION(this << aci);
    Txop::CreateQueue(aci);
    m_ac = aci;
    m_baManager->SetQueue(m_queue);
    m_baManager->SetBlockDestinationCallback(
        Callback<void, Mac48Address, uint8_t>([this](Mac48Address recipient, uint8_t tid) {
            m_mac->GetMacQueueScheduler()->BlockQueues(WifiQueueBlockedReason::WAITING_ADDBA_RESP,
                                                       m_ac,
                                                       {WIFI_QOSDATA_QUEUE},
                                                       recipient,
                                                       m_mac->GetLocalAddress(recipient),
                                                       {tid});
        }));
    m_baManager->SetUnblockDestinationCallback(
        Callback<void, Mac48Address, uint8_t>([this](Mac48Address recipient, uint8_t tid) {
            // save the status of AC queues before unblocking the transmissions to the recipient
            std::map<uint8_t, bool> hasFramesToTransmit;
            for (const auto& [id, link] : GetLinks())
            {
                hasFramesToTransmit[id] = HasFramesToTransmit(id);
            }
 
            m_mac->GetMacQueueScheduler()->UnblockQueues(WifiQueueBlockedReason::WAITING_ADDBA_RESP,
                                                         m_ac,
                                                         {WIFI_QOSDATA_QUEUE},
                                                         recipient,
                                                         m_mac->GetLocalAddress(recipient),
                                                         {tid});
 
            // start access (if needed) on all the links
            for (const auto& [id, link] : GetLinks())
            {
                StartAccessAfterEvent(id, hasFramesToTransmit.at(id), CHECK_MEDIUM_BUSY);
            }
        }));
    m_queue->TraceConnectWithoutContext(
        "Expired",
        MakeCallback(&BlockAckManager::NotifyDiscardedMpdu, m_baManager));
}
 
QosTxop::~QosTxop()
{
    NS_LOG_FUNCTION(this);
}
 
void
QosTxop::DoDispose()
{
    NS_LOG_FUNCTION(this);
    if (m_baManager)
    {
        m_baManager->Dispose();
    }
    m_baManager = nullptr;
    Txop::DoDispose();
}
 
std::unique_ptr<Txop::LinkEntity>
QosTxop::CreateLinkEntity() const
{
    return std::make_unique<QosLinkEntity>();
}
 
QosTxop::QosLinkEntity&
QosTxop::GetLink(uint8_t linkId) const
{
    return static_cast<QosLinkEntity&>(Txop::GetLink(linkId));
}
 
uint8_t
QosTxop::GetQosQueueSize(uint8_t tid, Mac48Address receiver) const
{
    const auto queueId = MakeWifiUnicastQueueId(WIFI_QOSDATA_QUEUE, receiver, tid);
    uint32_t bufferSize = m_queue->GetNBytes(queueId);
    // A queue size value of 254 is used for all sizes greater than 64 768 octets.
    uint8_t queueSize = static_cast<uint8_t>(std::ceil(std::min(bufferSize, 64769U) / 256.0));
    NS_LOG_DEBUG("Buffer size=" << bufferSize << " Queue Size=" << +queueSize);
    return queueSize;
}
 
void
QosTxop::SetDroppedMpduCallback(DroppedMpdu callback)
{
    NS_LOG_FUNCTION(this << &callback);
    Txop::SetDroppedMpduCallback(callback);
    m_baManager->SetDroppedOldMpduCallback(callback.Bind(WIFI_MAC_DROP_QOS_OLD_PACKET));
}
 
void
QosTxop::SetMuCwMin(uint16_t cwMin, uint8_t linkId)
{
    NS_LOG_FUNCTION(this << cwMin << +linkId);
    GetLink(linkId).muCwMin = cwMin;
}
 
void
QosTxop::SetMuCwMax(uint16_t cwMax, uint8_t linkId)
{
    NS_LOG_FUNCTION(this << cwMax << +linkId);
    GetLink(linkId).muCwMax = cwMax;
}
 
void
QosTxop::SetMuAifsn(uint8_t aifsn, uint8_t linkId)
{
    NS_LOG_FUNCTION(this << +aifsn << +linkId);
    GetLink(linkId).muAifsn = aifsn;
}
 
void
QosTxop::SetMuEdcaTimer(Time timer, uint8_t linkId)
{
    NS_LOG_FUNCTION(this << timer << +linkId);
    GetLink(linkId).muEdcaTimer = timer;
}
 
void
QosTxop::StartMuEdcaTimerNow(uint8_t linkId)
{
    NS_LOG_FUNCTION(this << +linkId);
    auto& link = GetLink(linkId);
    link.muEdcaTimerStartTime = Simulator::Now();
    if (EdcaDisabled(linkId))
    {
        NS_LOG_DEBUG("Disable EDCA for " << link.muEdcaTimer.As(Time::MS));
        m_mac->GetChannelAccessManager(linkId)->DisableEdcaFor(this, link.muEdcaTimer);
    }
}
 
bool
QosTxop::MuEdcaTimerRunning(uint8_t linkId) const
{
    auto& link = GetLink(linkId);
    return (link.muEdcaTimerStartTime.IsStrictlyPositive() &&
            link.muEdcaTimer.IsStrictlyPositive() &&
            link.muEdcaTimerStartTime + link.muEdcaTimer > Simulator::Now());
}
 
bool
QosTxop::EdcaDisabled(uint8_t linkId) const
{
    return (MuEdcaTimerRunning(linkId) && GetLink(linkId).muAifsn == 0);
}
 
uint32_t
QosTxop::GetMinCw(uint8_t linkId) const
{
    if (!MuEdcaTimerRunning(linkId))
    {
        return GetLink(linkId).cwMin;
    }
    NS_ASSERT(!EdcaDisabled(linkId));
    return GetLink(linkId).muCwMin;
}
 
uint32_t
QosTxop::GetMaxCw(uint8_t linkId) const
{
    if (!MuEdcaTimerRunning(linkId))
    {
        return GetLink(linkId).cwMax;
    }
    NS_ASSERT(!EdcaDisabled(linkId));
    return GetLink(linkId).muCwMax;
}
 
uint8_t
QosTxop::GetAifsn(uint8_t linkId) const
{
    if (!MuEdcaTimerRunning(linkId))
    {
        return GetLink(linkId).aifsn;
    }
    return GetLink(linkId).muAifsn;
}
 
Ptr<BlockAckManager>
QosTxop::GetBaManager()
{
    return m_baManager;
}
 
uint16_t
QosTxop::GetBaBufferSize(Mac48Address address, uint8_t tid, bool isGcr) const
{
    return isGcr ? m_baManager->GetGcrBufferSize(address, tid)
                 : m_baManager->GetRecipientBufferSize(address, tid);
}
 
uint16_t
QosTxop::GetBaStartingSequence(Mac48Address address, uint8_t tid, bool isGcr) const
{
    return isGcr ? m_baManager->GetGcrStartingSequence(address, tid)
                 : m_baManager->GetOriginatorStartingSequence(address, tid);
}
 
std::pair<CtrlBAckRequestHeader, WifiMacHeader>
QosTxop::PrepareBlockAckRequest(Mac48Address recipient,
                                uint8_t tid,
                                std::optional<Mac48Address> gcrGroupAddr) const
{
    NS_LOG_FUNCTION(this << recipient << +tid << gcrGroupAddr.has_value());
    NS_ASSERT(QosUtilsMapTidToAc(tid) == m_ac);
 
    auto recipientMld = m_mac->GetMldAddress(recipient);
 
    auto reqHdr =
        m_baManager->GetBlockAckReqHeader(recipientMld.value_or(recipient), tid, gcrGroupAddr);
 
    WifiMacHeader hdr;
    hdr.SetType(WIFI_MAC_CTL_BACKREQ);
    hdr.SetAddr1(recipient);
    hdr.SetAddr2(m_mac->GetLocalAddress(recipient));
    hdr.SetDsNotTo();
    hdr.SetDsNotFrom();
    hdr.SetNoRetry();
    hdr.SetNoMoreFragments();
 
    return {reqHdr, hdr};
}
 
bool
QosTxop::UseExplicitBarAfterMissedBlockAck() const
{
    return m_useExplicitBarAfterMissedBlockAck;
}
 
bool
QosTxop::HasFramesToTransmit(uint8_t linkId)
{
    // remove MSDUs with expired lifetime starting from the head of the queue
    m_queue->WipeAllExpiredMpdus();
    auto hasFramesToTransmit = static_cast<bool>(m_queue->PeekFirstAvailable(linkId));
 
    // Print the number of packets that are actually in the queue (which might not be
    // eligible for transmission for some reason, e.g., TID not mapped to the link, etc.)
    NS_LOG_DEBUG(m_ac << " on link " << +linkId << (hasFramesToTransmit ? " has" : " has not")
                      << " frames to transmit with " << m_queue->GetNPackets()
                      << " packets in the queue");
    return hasFramesToTransmit;
}
 
uint16_t
QosTxop::GetNextSequenceNumberFor(const WifiMacHeader* hdr)
{
    return m_txMiddle->GetNextSequenceNumberFor(hdr);
}
 
uint16_t
QosTxop::PeekNextSequenceNumberFor(const WifiMacHeader* hdr)
{
    return m_txMiddle->PeekNextSequenceNumberFor(hdr);
}
 
bool
QosTxop::IsQosOldPacket(Ptr<const WifiMpdu> mpdu)
{
    NS_LOG_FUNCTION(this << *mpdu);
 
    if (!mpdu->GetHeader().IsQosData())
    {
        return false;
    }
 
    Mac48Address recipient = mpdu->GetHeader().GetAddr1();
    uint8_t tid = mpdu->GetHeader().GetQosTid();
 
    if (!m_mac->GetBaAgreementEstablishedAsOriginator(recipient, tid))
    {
        return false;
    }
 
    return QosUtilsIsOldPacket(GetBaStartingSequence(recipient, tid),
                               mpdu->GetHeader().GetSequenceNumber());
}
 
Ptr<WifiMpdu>
QosTxop::PeekNextMpdu(uint8_t linkId, uint8_t tid, Mac48Address recipient, Ptr<const WifiMpdu> mpdu)
{
    NS_LOG_FUNCTION(this << +linkId << +tid << recipient << mpdu);
 
    // lambda to peek the next frame
    auto peek = [this, &linkId, &tid, &recipient, &mpdu]() -> Ptr<WifiMpdu> {
        if (tid == 8 && recipient.IsBroadcast()) // undefined TID and recipient
        {
            return m_queue->PeekFirstAvailable(linkId, mpdu);
        }
        const auto queueId =
            recipient.IsGroup()
                ? MakeWifiGroupcastQueueId(WIFI_QOSDATA_QUEUE,
                                           recipient,
                                           m_mac->GetFrameExchangeManager(linkId)->GetAddress(),
                                           tid)
                : MakeWifiUnicastQueueId(WIFI_QOSDATA_QUEUE, recipient, tid);
        if (auto mask = m_mac->GetMacQueueScheduler()->GetQueueLinkMask(m_ac, queueId, linkId);
            mask && mask->none())
        {
            return m_queue->PeekByQueueId(queueId, mpdu);
        }
        return nullptr;
    };
 
    auto item = peek();
    // remove old packets (must be retransmissions or in flight, otherwise they did
    // not get a sequence number assigned)
    while (item && !item->IsFragment())
    {
        if (item->GetHeader().IsCtl() && !item->GetHeader().IsPsPoll())
        {
            NS_LOG_DEBUG("Skipping control frame: " << *item);
            mpdu = item;
            item = peek();
            continue;
        }
 
        if (item->HasSeqNoAssigned() && IsQosOldPacket(item))
        {
            NS_LOG_DEBUG("Removing an old packet from EDCA queue: " << *item);
            if (!m_droppedMpduCallback.IsNull())
            {
                m_droppedMpduCallback(WIFI_MAC_DROP_QOS_OLD_PACKET, item);
            }
            mpdu = item;
            item = peek();
            m_queue->Remove(mpdu);
            continue;
        }
 
        if (auto linkIds = item->GetInFlightLinkIds(); !linkIds.empty()) // MPDU is in-flight
        {
            // if the MPDU is not already in-flight on the link for which we are requesting an
            // MPDU and the number of links on which the MPDU is in-flight is less than the
            // maximum number, then we can transmit this MPDU
            if (!linkIds.contains(linkId) && (linkIds.size() < m_nMaxInflights))
            {
                break;
            }
 
            if (item->GetHeader().IsQosData())
            {
                auto apMac = DynamicCast<ApWifiMac>(m_mac);
                const auto isGcr = IsGcr(m_mac, item->GetHeader());
                const auto agreementEstablished =
                    isGcr
                        ? apMac->IsGcrBaAgreementEstablishedWithAllMembers(
                              item->GetHeader().GetAddr1(),
                              item->GetHeader().GetQosTid())
                        : m_mac
                              ->GetBaAgreementEstablishedAsOriginator(item->GetHeader().GetAddr1(),
                                                                      item->GetHeader().GetQosTid())
                              .has_value();
                // if no BA agreement, we cannot have multiple MPDUs in-flight
                if (!agreementEstablished)
                {
                    NS_LOG_DEBUG("No BA agreement and an MPDU is already in-flight");
                    return nullptr;
                }
            }
 
            NS_LOG_DEBUG("Skipping in flight MPDU: " << *item);
            mpdu = item;
            item = peek();
            continue;
        }
 
        if (item->GetHeader().HasData() &&
            !m_mac->CanForwardPacketsTo(item->GetHeader().GetAddr1()))
        {
            NS_LOG_DEBUG("Skipping frame that cannot be forwarded: " << *item);
            mpdu = item;
            item = peek();
            continue;
        }
        break;
    }
 
    if (!item)
    {
        return nullptr;
    }
 
    auto& hdr = item->GetHeader();
 
    // peek the next sequence number and check if it is within the transmit window
    // in case of QoS data frame
    const auto sequence = item->HasSeqNoAssigned() ? hdr.GetSequenceNumber()
                                                   : m_txMiddle->PeekNextSequenceNumberFor(&hdr);
    if (hdr.IsQosData())
    {
        const auto recipient = hdr.GetAddr1();
        const auto tid = hdr.GetQosTid();
        const auto isGcr = IsGcr(m_mac, hdr);
        const auto bufferSize = GetBaBufferSize(recipient, tid, isGcr);
        const auto startSeq = GetBaStartingSequence(recipient, tid, isGcr);
        auto apMac = DynamicCast<ApWifiMac>(m_mac);
        const auto agreementEstablished =
            isGcr ? apMac->IsGcrBaAgreementEstablishedWithAllMembers(recipient, tid)
                  : m_mac->GetBaAgreementEstablishedAsOriginator(recipient, tid).has_value();
        if (agreementEstablished && !IsInWindow(sequence, startSeq, bufferSize))
        {
            NS_LOG_DEBUG("Packet beyond the end of the current transmit window");
            return nullptr;
        }
    }
 
    // Assign a sequence number if this is not a fragment nor it already has one assigned
    if (!item->IsFragment() && !item->HasSeqNoAssigned())
    {
        hdr.SetSequenceNumber(sequence);
    }
    NS_LOG_DEBUG("Packet peeked from EDCA queue: " << *item);
    return item;
}
 
Ptr<WifiMpdu>
QosTxop::GetNextMpdu(uint8_t linkId,
                     Ptr<WifiMpdu> peekedItem,
                     WifiTxParameters& txParams,
                     Time availableTime,
                     bool initialFrame)
{
    NS_ASSERT(peekedItem);
    NS_LOG_FUNCTION(this << +linkId << *peekedItem << &txParams << availableTime << initialFrame);
 
    Mac48Address recipient = peekedItem->GetHeader().GetAddr1();
 
    // The TXOP limit can be exceeded by the TXOP holder if it does not transmit more
    // than one Data or Management frame in the TXOP and the frame is not in an A-MPDU
    // consisting of more than one MPDU (Sec. 10.22.2.8 of 802.11-2016)
    Time actualAvailableTime =
        (initialFrame && txParams.GetSize(recipient) == 0 ? Time::Min() : availableTime);
 
    auto qosFem = StaticCast<QosFrameExchangeManager>(m_mac->GetFrameExchangeManager(linkId));
    if (!qosFem->TryAddMpdu(peekedItem, txParams, actualAvailableTime))
    {
        return nullptr;
    }
 
    NS_ASSERT(peekedItem->IsQueued());
    Ptr<WifiMpdu> mpdu;
 
    // If it is a non-broadcast QoS Data frame and it is not a retransmission nor a fragment,
    // attempt A-MSDU aggregation
    if (peekedItem->GetHeader().IsQosData())
    {
        uint8_t tid = peekedItem->GetHeader().GetQosTid();
 
        // we should not be asked to dequeue an MPDU that is beyond the transmit window.
        // Note that PeekNextMpdu() temporarily assigns the next available sequence number
        // to the peeked frame
        NS_ASSERT(!m_mac->GetBaAgreementEstablishedAsOriginator(recipient, tid) ||
                  IsInWindow(
                      peekedItem->GetHeader().GetSequenceNumber(),
                      GetBaStartingSequence(peekedItem->GetOriginal()->GetHeader().GetAddr1(), tid),
                      GetBaBufferSize(peekedItem->GetOriginal()->GetHeader().GetAddr1(), tid)));
 
        // try A-MSDU aggregation if the MPDU does not contain an A-MSDU and does not already
        // have a sequence number assigned (may be a retransmission) unless it is a concealed GCR
        // MPDU:
        if (auto apMac = DynamicCast<ApWifiMac>(m_mac);
            m_mac->GetHtConfiguration() && !recipient.IsBroadcast() &&
            !peekedItem->GetHeader().IsQosAmsdu() && !peekedItem->IsFragment() &&
            (!peekedItem->HasSeqNoAssigned() ||
             (IsGcr(m_mac, peekedItem->GetHeader()) &&
              (apMac->GetGcrManager()->UseConcealment(peekedItem->GetHeader())))))
        {
            auto htFem = StaticCast<HtFrameExchangeManager>(qosFem);
            mpdu = htFem->GetMsduAggregator()->GetNextAmsdu(peekedItem, txParams, availableTime);
        }
 
        if (mpdu)
        {
            NS_LOG_DEBUG("Prepared an MPDU containing an A-MSDU");
        }
        // else aggregation was not attempted or failed
    }
 
    if (!mpdu)
    {
        mpdu = peekedItem;
    }
 
    // Assign a sequence number if this is not a fragment nor a retransmission
    AssignSequenceNumber(mpdu);
    NS_LOG_DEBUG("Got MPDU from EDCA queue: " << *mpdu);
 
    return mpdu;
}
 
void
QosTxop::AssignSequenceNumber(Ptr<WifiMpdu> mpdu) const
{
    NS_LOG_FUNCTION(this << *mpdu);
 
    if (!mpdu->IsFragment() && !mpdu->HasSeqNoAssigned())
    {
        // in case of 11be MLDs, sequence numbers refer to the MLD address
        auto origMpdu = m_queue->GetOriginal(mpdu);
        uint16_t sequence = m_txMiddle->GetNextSequenceNumberFor(&origMpdu->GetHeader());
        mpdu->AssignSeqNo(sequence);
    }
}
 
void
QosTxop::NotifyChannelAccessed(uint8_t linkId, Time txopDuration)
{
    NS_LOG_FUNCTION(this << +linkId << txopDuration);
 
    NS_ASSERT(txopDuration != Time::Min());
    GetLink(linkId).startTxop = Simulator::Now();
    GetLink(linkId).txopDuration = txopDuration;
    Txop::NotifyChannelAccessed(linkId);
}
 
std::optional<Time>
QosTxop::GetTxopStartTime(uint8_t linkId) const
{
    auto& link = GetLink(linkId);
    NS_LOG_FUNCTION(this << link.startTxop.has_value());
    return link.startTxop;
}
 
void
QosTxop::NotifyChannelReleased(uint8_t linkId)
{
    NS_LOG_FUNCTION(this << +linkId);
    auto& link = GetLink(linkId);
 
    if (link.startTxop)
    {
        NS_LOG_DEBUG("Terminating TXOP. Duration = " << Simulator::Now() - *link.startTxop);
        m_txopTrace(*link.startTxop, Simulator::Now() - *link.startTxop, linkId);
    }
 
    // generate a new backoff value if either the TXOP duration is not null (i.e., some frames
    // were transmitted) or no frame was transmitted but the queue actually contains frame to
    // transmit and the user indicated that a backoff value should be generated in this situation.
    // This behavior reflects the following specs text (Sec. 35.3.16.4 of 802.11be D4.0):
    // An AP or non-AP STA affiliated with an MLD that has gained the right to initiate the
    // transmission of a frame as described in 10.23.2.4 (Obtaining an EDCA TXOP) for an AC but
    // does not transmit any frame corresponding to that AC for the reasons stated above may:
    // - invoke a backoff for the EDCAF associated with that AC as allowed per h) of 10.23.2.2
    //   (EDCA backoff procedure).
    auto hasTransmitted = link.startTxop.has_value() && Simulator::Now() > *link.startTxop;
 
    m_queue->WipeAllExpiredMpdus();
    if ((hasTransmitted) ||
        (!m_queue->IsEmpty() && m_mac->GetChannelAccessManager(linkId)->GetGenerateBackoffOnNoTx()))
    {
        GenerateBackoff(linkId);
        if (!m_queue->IsEmpty())
        {
            // if the channel released notification (below) leads the power save manager to put the
            // PHY in sleep state, do not request channel access (which would wake up the PHY)
            Simulator::ScheduleNow([=, this]() {
                if (auto phy = m_mac->GetWifiPhy(linkId); phy && !phy->IsStateSleep())
                {
                    NS_LOG_DEBUG("Request channel access again after releasing the channel");
                    RequestAccess(linkId);
                }
            });
        }
    }
    link.startTxop.reset();
    GetLink(linkId).access = NOT_REQUESTED;
    m_mac->NotifyChannelReleased(this, linkId);
}
 
Time
QosTxop::GetRemainingTxop(uint8_t linkId) const
{
    auto& link = GetLink(linkId);
    NS_ASSERT(link.startTxop.has_value());
 
    Time remainingTxop = link.txopDuration;
    remainingTxop -= (Simulator::Now() - *link.startTxop);
    if (remainingTxop.IsStrictlyNegative())
    {
        remainingTxop = Seconds(0);
    }
    NS_LOG_FUNCTION(this << remainingTxop);
    return remainingTxop;
}
 
void
QosTxop::GotAddBaResponse(const MgtAddBaResponseHeader& respHdr, Mac48Address recipient)
{
    NS_LOG_FUNCTION(this << respHdr << recipient);
    uint8_t tid = respHdr.GetTid();
 
    if (respHdr.GetStatusCode().IsSuccess())
    {
        const auto gcrGroup = respHdr.GetGcrGroupAddress();
        NS_LOG_DEBUG("block ack agreement established with "
                     << recipient << " tid " << +tid << (gcrGroup ? " group " : "")
                     << (gcrGroup ? gcrGroup->ConvertTo() : Address()));
        m_baEstablishedCallback(recipient, tid, gcrGroup);
        // A (destination, TID) pair is "blocked" (i.e., no more packets are sent) when an
        // Add BA Request is sent to the destination. However, when the Add BA Request timer
        // expires, the (destination, TID) pair is "unblocked" and packets to the destination are
        // sent again (under normal ack policy). Thus, there may be a packet with a sequence number
        // already assigned waiting to be retransmitted (or being transmitted on another link)
        // when the Add BA Response is received. In this case, the starting sequence number shall
        // be set equal to the sequence number of such packet.
        const auto queueRecipient = respHdr.GetGcrGroupAddress().value_or(recipient);
        auto startingSeq = m_txMiddle->GetNextSeqNumberByTidAndAddress(tid, queueRecipient);
        for (const auto linkId : m_mac->GetLinkIds())
        {
            const auto src = m_mac->GetFrameExchangeManager(linkId)->GetAddress();
            auto peekedItem = m_queue->PeekByTidAndAddress(tid, queueRecipient, src);
            if (peekedItem && peekedItem->HasSeqNoAssigned())
            {
                startingSeq = peekedItem->GetHeader().GetSequenceNumber();
                break;
            }
        }
        m_baManager->UpdateOriginatorAgreement(respHdr, recipient, startingSeq);
    }
    else
    {
        NS_LOG_DEBUG("discard ADDBA response" << recipient);
        m_baManager->NotifyOriginatorAgreementRejected(recipient,
                                                       tid,
                                                       respHdr.GetGcrGroupAddress());
    }
}
 
void
QosTxop::GotDelBaFrame(const MgtDelBaHeader* delBaHdr, Mac48Address recipient)
{
    NS_LOG_FUNCTION(this << delBaHdr << recipient);
    NS_LOG_DEBUG("received DELBA frame from=" << recipient);
    m_baManager->DestroyOriginatorAgreement(recipient,
                                            delBaHdr->GetTid(),
                                            delBaHdr->GetGcrGroupAddress());
}
 
void
QosTxop::NotifyOriginatorAgreementNoReply(const Mac48Address& recipient,
                                          uint8_t tid,
                                          std::optional<Mac48Address> gcrGroupAddr)
{
    NS_LOG_FUNCTION(this << recipient << tid << gcrGroupAddr.has_value());
    m_baManager->NotifyOriginatorAgreementNoReply(recipient, tid, gcrGroupAddr);
}
 
void
QosTxop::CompleteMpduTx(Ptr<WifiMpdu> mpdu)
{
    NS_LOG_FUNCTION(this << *mpdu);
    NS_ASSERT(mpdu->GetHeader().IsQosData());
    // If there is an established BA agreement, store the packet in the queue of outstanding packets
 
    if (auto apMac = DynamicCast<ApWifiMac>(m_mac);
        IsGcr(m_mac, mpdu->GetHeader()) &&
        (apMac->GetGcrManager()->GetRetransmissionPolicyFor(mpdu->GetHeader()) ==
         GroupAddressRetransmissionPolicy::GCR_BLOCK_ACK))
    {
        NS_ASSERT(mpdu->IsQueued());
        NS_ASSERT(m_queue->GetAc() == mpdu->GetQueueAc());
        const auto recipient = mpdu->begin()->second.GetDestinationAddr();
        m_baManager->StoreGcrPacket(
            m_queue->GetOriginal(mpdu),
            apMac->GetGcrManager()->GetMemberStasForGroupAddress(recipient));
        return;
    }
 
    if (const auto recipient = mpdu->GetHeader().GetAddr1();
        m_mac->GetBaAgreementEstablishedAsOriginator(recipient, mpdu->GetHeader().GetQosTid()))
    {
        NS_ASSERT(mpdu->IsQueued());
        NS_ASSERT(m_queue->GetAc() == mpdu->GetQueueAc());
        m_baManager->StorePacket(m_queue->GetOriginal(mpdu));
    }
}
 
void
QosTxop::SetBlockAckThreshold(uint8_t threshold)
{
    NS_LOG_FUNCTION(this << +threshold);
    m_blockAckThreshold = threshold;
    m_baManager->SetBlockAckThreshold(threshold);
}
 
void
QosTxop::SetBlockAckInactivityTimeout(uint16_t timeout)
{
    NS_LOG_FUNCTION(this << timeout);
    m_blockAckInactivityTimeout = timeout;
}
 
uint8_t
QosTxop::GetBlockAckThreshold() const
{
    NS_LOG_FUNCTION(this);
    return m_blockAckThreshold;
}
 
uint16_t
QosTxop::GetBlockAckInactivityTimeout() const
{
    return m_blockAckInactivityTimeout;
}
 
void
QosTxop::AddBaResponseTimeout(Mac48Address recipient,
                              uint8_t tid,
                              std::optional<Mac48Address> gcrGroupAddr)
{
    NS_LOG_FUNCTION(this << recipient << +tid << gcrGroupAddr.has_value());
    // If agreement is still pending, ADDBA response is not received
    auto agreement = m_baManager->GetAgreementAsOriginator(recipient, tid, gcrGroupAddr);
    if (agreement && agreement->get().IsPending())
    {
        NotifyOriginatorAgreementNoReply(recipient, tid, gcrGroupAddr);
        Simulator::Schedule(m_failedAddBaTimeout,
                            &QosTxop::ResetBa,
                            this,
                            recipient,
                            tid,
                            gcrGroupAddr);
    }
}
 
void
QosTxop::ResetBa(Mac48Address recipient, uint8_t tid, std::optional<Mac48Address> gcrGroupAddr)
{
    NS_LOG_FUNCTION(this << recipient << +tid << gcrGroupAddr.has_value());
    // This function is scheduled when waiting for an ADDBA response. However,
    // before this function is called, a DELBA request may arrive, which causes
    // the agreement to be deleted. Hence, check if an agreement exists before
    // notifying that the agreement has to be reset.
    auto agreement = m_baManager->GetAgreementAsOriginator(recipient, tid, gcrGroupAddr);
    if (agreement && !agreement->get().IsEstablished())
    {
        m_baManager->NotifyOriginatorAgreementReset(recipient, tid, gcrGroupAddr);
    }
}
 
void
QosTxop::SetAddBaResponseTimeout(Time addBaResponseTimeout)
{
    NS_LOG_FUNCTION(this << addBaResponseTimeout);
    m_addBaResponseTimeout = addBaResponseTimeout;
}
 
Time
QosTxop::GetAddBaResponseTimeout() const
{
    return m_addBaResponseTimeout;
}
 
void
QosTxop::SetFailedAddBaTimeout(Time failedAddBaTimeout)
{
    NS_LOG_FUNCTION(this << failedAddBaTimeout);
    m_failedAddBaTimeout = failedAddBaTimeout;
}
 
Time
QosTxop::GetFailedAddBaTimeout() const
{
    return m_failedAddBaTimeout;
}
 
bool
QosTxop::IsQosTxop() const
{
    return true;
}
 
AcIndex
QosTxop::GetAccessCategory() const
{
    return m_ac;
}
 
} // namespace ns3