mac-low.cc

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2005,2006 INRIA
 * Copyright (c) 2009 MIRKO BANCHI
 *
 * 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: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 *          Mirko Banchi <mk.banchi@gmail.com>
 *          Stefano Avallone <stavallo@unina.it>
 */

#include "ns3/simulator.h"
#include "ns3/log.h"
#include "mac-low.h"
#include "qos-txop.h"
#include "snr-tag.h"
#include "ampdu-tag.h"
#include "wifi-mac-queue.h"
#include "wifi-psdu.h"
#include "wifi-utils.h"
#include "ctrl-headers.h"
#include "mgt-headers.h"
#include "wifi-remote-station-manager.h"
#include "mpdu-aggregator.h"
#include "msdu-aggregator.h"
#include "ampdu-subframe-header.h"
#include "wifi-phy-listener.h"
#include "wifi-mac-trailer.h"
#include "wifi-phy.h"
#include "wifi-net-device.h"
#include "wifi-mac.h"
#include <algorithm>
#include "wifi-ack-policy-selector.h"

#undef NS_LOG_APPEND_CONTEXT
#define NS_LOG_APPEND_CONTEXT std::clog << "[mac=" << m_self << "] "

// Time (in nanoseconds) to be added to the PSDU duration to yield the duration
// of the timer that is started when the PHY indicates the start of the reception
// of a frame and we are waiting for a response.
#define PSDU_DURATION_SAFEGUARD 400

namespace ns3 {

NS_LOG_COMPONENT_DEFINE ("MacLow");

class PhyMacLowListener : public ns3::WifiPhyListener
{
public:
  PhyMacLowListener (ns3::MacLow *macLow)
    : m_macLow (macLow)
  {
  }
  virtual ~PhyMacLowListener ()
  {
  }
  void NotifyRxStart (Time duration)
  {
  }
  void NotifyRxEndOk (void)
  {
  }
  void NotifyRxEndError (void)
  {
  }
  void NotifyTxStart (Time duration, double txPowerDbm)
  {
  }
  void NotifyMaybeCcaBusyStart (Time duration)
  {
  }
  void NotifySwitchingStart (Time duration)
  {
    m_macLow->NotifySwitchingStartNow (duration);
  }
  void NotifySleep (void)
  {
    m_macLow->NotifySleepNow ();
  }
  void NotifyOff (void)
  {
    m_macLow->NotifyOffNow ();
  }
  void NotifyWakeup (void)
  {
  }
  void NotifyOn (void)
  {
  }

private:
  ns3::MacLow *m_macLow; 
};


MacLow::MacLow ()
  : m_msduAggregator (0),
    m_mpduAggregator (0),
    m_normalAckTimeoutEvent (),
    m_blockAckTimeoutEvent (),
    m_ctsTimeoutEvent (),
    m_sendCtsEvent (),
    m_sendAckEvent (),
    m_sendDataEvent (),
    m_waitIfsEvent (),
    m_endTxNoAckEvent (),
    m_currentPacket (0),
    m_currentTxop (0),
    m_lastNavStart (Seconds (0)),
    m_lastNavDuration (Seconds (0)),
    m_cfpStart (Seconds (0)),
    m_lastBeacon (Seconds (0)),
    m_cfpForeshortening (Seconds (0)),
    m_promisc (false),
    m_phyMacLowListener (0),
    m_ctsToSelfSupported (false),
    m_cfAckInfo ()
{
  NS_LOG_FUNCTION (this);
}

MacLow::~MacLow ()
{
  NS_LOG_FUNCTION (this);
}

/* static */
TypeId
MacLow::GetTypeId (void)
{
  static TypeId tid = TypeId ("ns3::MacLow")
    .SetParent<Object> ()
    .SetGroupName ("Wifi")
    .AddConstructor<MacLow> ()
  ;
  return tid;
}

void
MacLow::SetupPhyMacLowListener (const Ptr<WifiPhy> phy)
{
  m_phyMacLowListener = new PhyMacLowListener (this);
  phy->RegisterListener (m_phyMacLowListener);
}

void
MacLow::RemovePhyMacLowListener (Ptr<WifiPhy> phy)
{
  if (m_phyMacLowListener != 0 )
    {
      phy->UnregisterListener (m_phyMacLowListener);
      delete m_phyMacLowListener;
      m_phyMacLowListener = 0;
    }
}

void
MacLow::DoDispose (void)
{
  NS_LOG_FUNCTION (this);
  m_normalAckTimeoutEvent.Cancel ();
  m_blockAckTimeoutEvent.Cancel ();
  m_ctsTimeoutEvent.Cancel ();
  m_sendCtsEvent.Cancel ();
  m_sendAckEvent.Cancel ();
  m_sendDataEvent.Cancel ();
  m_waitIfsEvent.Cancel ();
  m_endTxNoAckEvent.Cancel ();
  m_msduAggregator = 0;
  m_mpduAggregator = 0;
  m_phy = 0;
  m_stationManager = 0;
  if (m_phyMacLowListener != 0)
    {
      delete m_phyMacLowListener;
      m_phyMacLowListener = 0;
    }
}

void
MacLow::CancelAllEvents (void)
{
  NS_LOG_FUNCTION (this);
  bool oneRunning = false;
  if (m_normalAckTimeoutEvent.IsRunning ())
    {
      m_normalAckTimeoutEvent.Cancel ();
      oneRunning = true;
    }
  if (m_blockAckTimeoutEvent.IsRunning ())
    {
      m_blockAckTimeoutEvent.Cancel ();
      oneRunning = true;
    }
  if (m_ctsTimeoutEvent.IsRunning ())
    {
      m_ctsTimeoutEvent.Cancel ();
      oneRunning = true;
    }
  if (m_sendCtsEvent.IsRunning ())
    {
      m_sendCtsEvent.Cancel ();
      oneRunning = true;
    }
  if (m_sendAckEvent.IsRunning ())
    {
      m_sendAckEvent.Cancel ();
      oneRunning = true;
    }
  if (m_sendDataEvent.IsRunning ())
    {
      m_sendDataEvent.Cancel ();
      oneRunning = true;
    }
  if (m_waitIfsEvent.IsRunning ())
    {
      m_waitIfsEvent.Cancel ();
      oneRunning = true;
    }
  if (m_endTxNoAckEvent.IsRunning ())
    {
      m_endTxNoAckEvent.Cancel ();
      oneRunning = true;
    }
  if (oneRunning && m_currentTxop != 0)
    {
      m_currentTxop->Cancel ();
      m_currentTxop = 0;
    }
}

void
MacLow::SetPhy (const Ptr<WifiPhy> phy)
{
  m_phy = phy;
  m_phy->TraceConnectWithoutContext ("PhyRxPayloadBegin", MakeCallback (&MacLow::RxStartIndication, this));
  m_phy->SetReceiveOkCallback (MakeCallback (&MacLow::DeaggregateAmpduAndReceive, this));
  m_phy->SetReceiveErrorCallback (MakeCallback (&MacLow::ReceiveError, this));
  SetupPhyMacLowListener (phy);
}

Ptr<WifiPhy>
MacLow::GetPhy (void) const
{
  return m_phy;
}

void
MacLow::ResetPhy (void)
{
  m_phy->TraceDisconnectWithoutContext ("PhyRxPayloadBegin", MakeCallback (&MacLow::RxStartIndication, this));
  m_phy->SetReceiveOkCallback (MakeNullCallback<void, Ptr<WifiPsdu>, double, WifiTxVector, std::vector<bool>> ());
  m_phy->SetReceiveErrorCallback (MakeNullCallback<void, Ptr<WifiPsdu>> ());
  RemovePhyMacLowListener (m_phy);
  m_phy = 0;
}

Ptr<QosTxop>
MacLow::GetEdca (uint8_t tid) const
{
  auto it = m_edca.find (QosUtilsMapTidToAc (tid));
  NS_ASSERT (it != m_edca.end ());
  return it->second;
}

void
MacLow::SetMac (const Ptr<WifiMac> mac)
{
  m_mac = mac;
}

void
MacLow::SetWifiRemoteStationManager (const Ptr<WifiRemoteStationManager> manager)
{
  m_stationManager = manager;
}

Ptr<MsduAggregator>
MacLow::GetMsduAggregator (void) const
{
  return m_msduAggregator;
}

Ptr<MpduAggregator>
MacLow::GetMpduAggregator (void) const
{
  return m_mpduAggregator;
}

void
MacLow::SetMsduAggregator (const Ptr<MsduAggregator> aggr)
{
  NS_LOG_FUNCTION (this << aggr);
  m_msduAggregator = aggr;
}

void
MacLow::SetMpduAggregator (const Ptr<MpduAggregator> aggr)
{
  NS_LOG_FUNCTION (this << aggr);
  m_mpduAggregator = aggr;
}

void
MacLow::SetAddress (Mac48Address ad)
{
  m_self = ad;
}

void
MacLow::SetCtsToSelfSupported (bool enable)
{
  m_ctsToSelfSupported = enable;
}

bool
MacLow::GetCtsToSelfSupported (void) const
{
  return m_ctsToSelfSupported;
}

void
MacLow::SetBeaconInterval (Time interval)
{
  m_beaconInterval = interval;
}

void
MacLow::SetCfpMaxDuration (Time cfpMaxDuration)
{
  m_cfpMaxDuration = cfpMaxDuration;
}

void
MacLow::SetBssid (Mac48Address bssid)
{
  m_bssid = bssid;
}

void
MacLow::SetPromisc (void)
{
  m_promisc = true;
}

Mac48Address
MacLow::GetAddress (void) const
{
  return m_self;
}

Time
MacLow::GetSifs (void) const
{
  return m_phy->GetSifs ();
}

Time
MacLow::GetSlotTime (void) const
{
  return m_phy->GetSlot ();
}

Time
MacLow::GetPifs (void) const
{
  return m_phy->GetPifs ();
}

Mac48Address
MacLow::GetBssid (void) const
{
  return m_bssid;
}

Time
MacLow::GetBeaconInterval (void) const
{
  return m_beaconInterval;
}

Time
MacLow::GetCfpMaxDuration (void) const
{
  return m_cfpMaxDuration;
}

bool
MacLow::IsPromisc (void) const
{
  return m_promisc;
}

void
MacLow::SetRxCallback (Callback<void, Ptr<WifiMacQueueItem>> callback)
{
  m_rxCallback = callback;
}

void
MacLow::RegisterChannelAccessManager (Ptr<ChannelAccessManager> channelAccessManager)
{
  m_channelAccessManagers.push_back (channelAccessManager);
}

void
MacLow::StartTransmission (Ptr<WifiMacQueueItem> mpdu,
                           MacLowTransmissionParameters params,
                           Ptr<Txop> txop)
{
  NS_LOG_FUNCTION (this << *mpdu << params << txop);
  NS_ASSERT (!m_cfAckInfo.expectCfAck);
  if (m_phy->IsStateOff ())
    {
      NS_LOG_DEBUG ("Cannot start TX because device is OFF");
      return;
    }
  /* m_currentPacket is not NULL because someone started
   * a transmission and was interrupted before one of:
   *   - ctsTimeout
   *   - sendDataAfterCTS
   * expired. This means that one of these timers is still
   * running. They are all cancelled below anyway by the
   * call to CancelAllEvents (because of at least one
   * of these two timers) which will trigger a call to the
   * previous listener's cancel method.
   *
   * This typically happens because the high-priority
   * QapScheduler has taken access to the channel from
   * one of the EDCA of the QAP.
   */
  m_currentPacket = Create<WifiPsdu> (mpdu, false);
  const WifiMacHeader& hdr = mpdu->GetHeader ();
  CancelAllEvents ();
  m_currentTxop = txop;
  m_txParams = params;
  if (hdr.IsCtl ())
    {
      m_currentTxVector = GetRtsTxVector (mpdu);
    }
  else
    {
      m_currentTxVector = GetDataTxVector (mpdu);
    }

  /* The packet received by this function can be any of the following:
   * (a) a management frame dequeued from the Txop
   * (b) a non-QoS data frame dequeued from the Txop
   * (c) a non-group addressed QoS Data frame peeked or dequeued from a QosTxop
   * (d) a group addressed QoS data or DELBA Request frame dequeued from a QosTxop
   * (e) a BlockAckReq or ADDBA Request frame
   * (f) a fragment of non-QoS/QoS Data frame dequeued from the Txop/QosTxop
   */
  if (hdr.IsQosData () && !hdr.GetAddr1 ().IsGroup ()
      && !hdr.IsMoreFragments () && hdr.GetFragmentNumber () == 0)
    {
      // We get here if the received packet is a non-broadcast QoS data frame
      uint8_t tid = hdr.GetQosTid ();
      Ptr<QosTxop> qosTxop = m_edca.find (QosUtilsMapTidToAc (tid))->second;

      // if a TXOP limit exists, compute the remaining TXOP duration
      Time txopLimit = Time::Min ();
      if (m_currentTxop->GetTxopLimit ().IsStrictlyPositive ())
        {
          txopLimit = m_currentTxop->GetTxopRemaining () - CalculateOverheadTxTime (mpdu, m_txParams);
          NS_ASSERT (txopLimit.IsPositive ());
        }

      // QosTxop may send us a peeked frame
      Ptr<const WifiMacQueueItem> tmp = qosTxop->PeekNextFrame ();
      bool isPeeked = (tmp != 0 && tmp->GetPacket () == mpdu->GetPacket ());

      Ptr<WifiMacQueueItem> newMpdu;
      // If the frame has been peeked, dequeue it if it meets the size and duration constraints
      if (isPeeked)
        {
          newMpdu = qosTxop->DequeuePeekedFrame (mpdu, m_currentTxVector, true, 0, txopLimit);
        }
      else if (IsWithinSizeAndTimeLimits (mpdu, m_currentTxVector, 0, txopLimit))
        {
          newMpdu = mpdu;
        }

      if (newMpdu == 0)
        {
          // if the frame has been dequeued, then there is no BA agreement with the
          // receiver (otherwise the frame would have been peeked). Hence, the frame
          // has been sent under Normal Ack policy, not acknowledged and now retransmitted.
          // If we cannot send it now, let the QosTxop retransmit it again.
          // If the frame has been just peeked, reset the current packet at QosTxop.
          if (isPeeked)
            {
              qosTxop->UpdateCurrentPacket (Create<WifiMacQueueItem> (nullptr, WifiMacHeader ()));
            }
          return;
        }
      // Update the current packet at QosTxop, given that A-MSDU aggregation may have
      // been performed on the peeked frame
      qosTxop->UpdateCurrentPacket (newMpdu);

      //Perform MPDU aggregation if possible
      std::vector<Ptr<WifiMacQueueItem>> mpduList;
      if (m_mpduAggregator != 0)
        {
          mpduList = m_mpduAggregator->GetNextAmpdu (newMpdu, m_currentTxVector, txopLimit);
        }

      if (mpduList.size () > 1)
        {
          m_currentPacket = Create<WifiPsdu> (mpduList);

          NS_LOG_DEBUG ("tx unicast A-MPDU containing " << mpduList.size () << " MPDUs");
          qosTxop->SetAmpduExist (hdr.GetAddr1 (), true);
        }
      else if (m_currentTxVector.GetMode ().GetModulationClass () == WIFI_MOD_CLASS_VHT
               || m_currentTxVector.GetMode ().GetModulationClass () == WIFI_MOD_CLASS_HE)
        {
          // VHT/HE single MPDU
          m_currentPacket = Create<WifiPsdu> (newMpdu, true);

          NS_LOG_DEBUG ("tx unicast S-MPDU with sequence number " << hdr.GetSequenceNumber ());
          qosTxop->SetAmpduExist (hdr.GetAddr1 (), true);
        }
      else  // HT
        {
          m_currentPacket = Create<WifiPsdu> (newMpdu, false);
        }

      // A QoS Txop must have an installed ack policy selector
      NS_ASSERT (qosTxop->GetAckPolicySelector () != 0);
      qosTxop->GetAckPolicySelector ()->UpdateTxParams (m_currentPacket, m_txParams);
      qosTxop->GetAckPolicySelector ()->SetAckPolicy (m_currentPacket, m_txParams);
    }

  NS_LOG_DEBUG ("startTx size=" << m_currentPacket->GetSize () <<
                ", to=" << m_currentPacket->GetAddr1 () << ", txop=" << m_currentTxop);

  if (m_txParams.MustSendRts ())
    {
      SendRtsForPacket ();
    }
  else
    {
      if ((m_ctsToSelfSupported || m_stationManager->GetUseNonErpProtection ()) && NeedCtsToSelf ())
        {
          SendCtsToSelf ();
        }
      else
        {
          SendDataPacket ();
        }
    }

  /* When this method completes, either we have taken ownership of the medium or the device switched off in the meantime. */
  NS_ASSERT (m_phy->IsStateTx () || m_phy->IsStateOff ());
}

bool
MacLow::NeedCtsToSelf (void) const
{
  WifiTxVector dataTxVector = GetDataTxVector (*m_currentPacket->begin ());
  return m_stationManager->NeedCtsToSelf (dataTxVector);
}

bool
MacLow::IsWithinSizeAndTimeLimits (Ptr<const WifiMacQueueItem> mpdu, WifiTxVector txVector,
                                    uint32_t ampduSize, Time ppduDurationLimit)
{
  NS_ASSERT (mpdu != 0 && mpdu->GetHeader ().IsQosData ());

  return IsWithinSizeAndTimeLimits (mpdu->GetSize (), mpdu->GetHeader ().GetAddr1 (),
                                    mpdu->GetHeader ().GetQosTid (), txVector,
                                    ampduSize, ppduDurationLimit);
}

bool
MacLow::IsWithinSizeAndTimeLimits (uint32_t mpduSize, Mac48Address receiver, uint8_t tid,
                                    WifiTxVector txVector, uint32_t ampduSize, Time ppduDurationLimit)
{
  NS_LOG_FUNCTION (this << mpduSize << receiver << +tid << txVector << ampduSize << ppduDurationLimit);

  if (ppduDurationLimit != Time::Min () && ppduDurationLimit.IsNegative ())
    {
      return false;
    }

  WifiModulationClass modulation = txVector.GetMode ().GetModulationClass ();

  uint32_t maxAmpduSize = 0;
  if (GetMpduAggregator ())
    {
      maxAmpduSize = GetMpduAggregator ()->GetMaxAmpduSize (receiver, tid, modulation);
    }

  // If maxAmpduSize is null, then ampduSize must be null as well
  NS_ASSERT (maxAmpduSize || ampduSize == 0);

  uint32_t ppduPayloadSize = mpduSize;

  // compute the correct size for A-MPDUs and S-MPDUs
  if (ampduSize > 0 || modulation >= WIFI_MOD_CLASS_VHT)
    {
      ppduPayloadSize = GetMpduAggregator ()->GetSizeIfAggregated (mpduSize, ampduSize);
    }

  if (maxAmpduSize > 0 && ppduPayloadSize > maxAmpduSize)
    {
      NS_LOG_DEBUG ("the frame does not meet the constraint on max A-MPDU size");
      return false;
    }

  // Get the maximum PPDU Duration based on the preamble type
  Time maxPpduDuration = GetPpduMaxTime (txVector.GetPreambleType ());

  Time txTime = m_phy->CalculateTxDuration (ppduPayloadSize, txVector, m_phy->GetPhyBand ());

  if ((ppduDurationLimit.IsStrictlyPositive () && txTime > ppduDurationLimit)
      || (maxPpduDuration.IsStrictlyPositive () && txTime > maxPpduDuration))
    {
      NS_LOG_DEBUG ("the frame does not meet the constraint on max PPDU duration");
      return false;
    }

  return true;
}

void
MacLow::RxStartIndication (WifiTxVector txVector, Time psduDuration)
{
  NS_LOG_FUNCTION (this);
  NS_LOG_DEBUG ("PSDU reception started for " << psduDuration.ToDouble (Time::US)
                << " us (txVector: " << txVector << ")");
  NS_ASSERT (psduDuration.IsStrictlyPositive ());

  if (m_normalAckTimeoutEvent.IsRunning ())
    {
      // we are waiting for a Normal Ack and something arrived
      NS_LOG_DEBUG ("Rescheduling Normal Ack timeout");
      m_normalAckTimeoutEvent.Cancel ();
      NotifyAckTimeoutResetNow ();
      m_normalAckTimeoutEvent = Simulator::Schedule (psduDuration + NanoSeconds (PSDU_DURATION_SAFEGUARD),
                                                     &MacLow::NormalAckTimeout, this);
    }
  else if (m_blockAckTimeoutEvent.IsRunning ())
    {
      // we are waiting for a BlockAck and something arrived
      NS_LOG_DEBUG ("Rescheduling Block Ack timeout");
      m_blockAckTimeoutEvent.Cancel ();
      NotifyAckTimeoutResetNow ();
      m_blockAckTimeoutEvent = Simulator::Schedule (psduDuration + NanoSeconds (PSDU_DURATION_SAFEGUARD),
                                                    &MacLow::BlockAckTimeout, this);
    }
  else if (m_ctsTimeoutEvent.IsRunning ())
    {
      // we are waiting for a CTS and something arrived
      NS_LOG_DEBUG ("Rescheduling CTS timeout");
      m_ctsTimeoutEvent.Cancel ();
      NotifyCtsTimeoutResetNow ();
      m_ctsTimeoutEvent = Simulator::Schedule (psduDuration + NanoSeconds (PSDU_DURATION_SAFEGUARD),
                                               &MacLow::CtsTimeout, this);
    }
  else if (m_navCounterResetCtsMissed.IsRunning ())
    {
      NS_LOG_DEBUG ("Cannot reset NAV");
      m_navCounterResetCtsMissed.Cancel ();
    }
}

void
MacLow::ReceiveError (Ptr<WifiPsdu> psdu)
{
  NS_LOG_FUNCTION (this << *psdu);
  NS_LOG_DEBUG ("rx failed");
  if (IsCfPeriod () && m_currentPacket->GetHeader (0).IsCfPoll ())
    {
      NS_ASSERT (m_currentTxop != 0);
      m_currentTxop->MissedCfPollResponse (m_cfAckInfo.expectCfAck);
    }
  else if (m_cfAckInfo.expectCfAck)
    {
      NS_ASSERT (m_currentTxop != 0);
      Ptr<Txop> txop = m_currentTxop;
      m_currentTxop = 0;
      txop->MissedAck ();
    }
  m_cfAckInfo.expectCfAck = false;
  return;
}

void
MacLow::NotifySwitchingStartNow (Time duration)
{
  NS_LOG_DEBUG ("switching channel. Cancelling MAC pending events");
  m_stationManager->Reset ();
  CancelAllEvents ();
  if (m_navCounterResetCtsMissed.IsRunning ())
    {
      m_navCounterResetCtsMissed.Cancel ();
    }
  m_lastNavStart = Simulator::Now ();
  m_lastNavDuration = Seconds (0);
  m_currentPacket = 0;
  m_currentTxop = 0;
}

void
MacLow::NotifySleepNow (void)
{
  NS_LOG_DEBUG ("Device in sleep mode. Cancelling MAC pending events");
  CancelAllEvents ();
  if (m_navCounterResetCtsMissed.IsRunning ())
    {
      m_navCounterResetCtsMissed.Cancel ();
    }
  m_lastNavStart = Simulator::Now ();
  m_lastNavDuration = Seconds (0);
  m_currentPacket = 0;
  m_currentTxop = 0;
}

void
MacLow::NotifyOffNow (void)
{
  NS_LOG_DEBUG ("Device is switched off. Cancelling MAC pending events");
  CancelAllEvents ();
  if (m_navCounterResetCtsMissed.IsRunning ())
    {
      m_navCounterResetCtsMissed.Cancel ();
    }
  m_lastNavStart = Simulator::Now ();
  m_lastNavDuration = Seconds (0);
  m_currentPacket = 0;
  m_currentTxop = 0;
}

void
MacLow::ReceiveOk (Ptr<WifiMacQueueItem> mpdu, double rxSnr, WifiTxVector txVector, bool ampduSubframe)
{
  NS_LOG_FUNCTION (this << *mpdu << rxSnr << txVector);
  /* An MPDU is received from the PHY.
   * When we have handled this MPDU,
   * we handle any packet present in the
   * packet queue.
   */
  const WifiMacHeader& hdr = mpdu->GetHeader ();
  Ptr<Packet> packet = mpdu->GetPacket ()->Copy ();

  bool isPrevNavZero = IsNavZero ();
  NS_LOG_DEBUG ("duration/id=" << hdr.GetDuration ());
  NotifyNav (packet, hdr);
  if (hdr.IsRts ())
    {
      /* see section 9.2.5.7 802.11-1999
       * A STA that is addressed by an RTS frame shall transmit a CTS frame after a SIFS
       * period if the NAV at the STA receiving the RTS frame indicates that the medium is
       * idle. If the NAV at the STA receiving the RTS indicates the medium is not idle,
       * that STA shall not respond to the RTS frame.
       */
      if (ampduSubframe)
        {
          NS_FATAL_ERROR ("Received RTS as part of an A-MPDU");
        }
      else
        {
          if (isPrevNavZero
              && hdr.GetAddr1 () == m_self)
            {
              NS_LOG_DEBUG ("rx RTS from=" << hdr.GetAddr2 () << ", schedule CTS");
              NS_ASSERT (m_sendCtsEvent.IsExpired ());
              m_stationManager->ReportRxOk (hdr.GetAddr2 (),
                                            rxSnr, txVector.GetMode ());
              m_sendCtsEvent = Simulator::Schedule (GetSifs (),
                                                    &MacLow::SendCtsAfterRts, this,
                                                    hdr.GetAddr2 (),
                                                    hdr.GetDuration (),
                                                    txVector,
                                                    rxSnr);
            }
          else
            {
              NS_LOG_DEBUG ("rx RTS from=" << hdr.GetAddr2 () << ", cannot schedule CTS");
            }
        }
    }
  else if (hdr.IsCts ()
           && hdr.GetAddr1 () == m_self
           && m_ctsTimeoutEvent.IsRunning ()
           && m_currentPacket != 0)
    {
      if (ampduSubframe)
        {
          NS_FATAL_ERROR ("Received CTS as part of an A-MPDU");
        }

      NS_LOG_DEBUG ("received cts from=" << m_currentPacket->GetAddr1 ());

      SnrTag tag;
      packet->RemovePacketTag (tag);
      m_stationManager->ReportRxOk (m_currentPacket->GetAddr1 (),
                                    rxSnr, txVector.GetMode ());
      m_stationManager->ReportRtsOk (m_currentPacket->GetAddr1 (), &m_currentPacket->GetHeader (0),
                                     rxSnr, txVector.GetMode (), tag.Get ());

      m_ctsTimeoutEvent.Cancel ();
      NotifyCtsTimeoutResetNow ();
      NS_ASSERT (m_sendDataEvent.IsExpired ());
      m_sendDataEvent = Simulator::Schedule (GetSifs (),
                                             &MacLow::SendDataAfterCts, this,
                                             hdr.GetDuration ());
    }
  else if (hdr.IsAck ()
           && hdr.GetAddr1 () == m_self
           && m_normalAckTimeoutEvent.IsRunning ()
           && m_txParams.MustWaitNormalAck ())
    {
      NS_LOG_DEBUG ("receive ack from=" << m_currentPacket->GetAddr1 ());
      SnrTag tag;
      packet->RemovePacketTag (tag);
      //When fragmentation is used, only update manager when the last fragment is acknowledged
      if (!m_txParams.HasNextPacket ())
        {
          m_stationManager->ReportRxOk (m_currentPacket->GetAddr1 (),
                                        rxSnr, txVector.GetMode ());
          m_stationManager->ReportDataOk (m_currentPacket->GetAddr1 (), &m_currentPacket->GetHeader (0),
                                          rxSnr, txVector.GetMode (), tag.Get (),
                                          m_currentTxVector, m_currentPacket->GetSize ());
        }
      // cancel the Normal Ack timer
      m_normalAckTimeoutEvent.Cancel ();
      NotifyAckTimeoutResetNow ();
      m_currentTxop->GotAck ();

      if (m_txParams.HasNextPacket ())
        {
          m_waitIfsEvent = Simulator::Schedule (GetSifs (), &MacLow::WaitIfsAfterEndTxFragment, this);
        }
      else if (m_currentPacket->GetHeader (0).IsQosData () && m_currentTxop->IsQosTxop () &&
               m_currentTxop->GetTxopLimit ().IsStrictlyPositive () && m_currentTxop->GetTxopRemaining () > GetSifs ())
        {
          m_waitIfsEvent = Simulator::Schedule (GetSifs (), &MacLow::WaitIfsAfterEndTxPacket, this);
        }
      else if (m_currentTxop->IsQosTxop ())
        {
          m_currentTxop->TerminateTxop ();
        }
    }
  else if (hdr.IsBlockAck () && hdr.GetAddr1 () == m_self
           && m_txParams.MustWaitBlockAck ()
           && m_blockAckTimeoutEvent.IsRunning ())
    {
      NS_LOG_DEBUG ("got block ack from " << hdr.GetAddr2 ());
      SnrTag tag;
      packet->RemovePacketTag (tag);
      CtrlBAckResponseHeader blockAck;
      packet->RemoveHeader (blockAck);
      m_blockAckTimeoutEvent.Cancel ();
      NotifyAckTimeoutResetNow ();
      m_currentTxop->GotBlockAck (&blockAck, hdr.GetAddr2 (), rxSnr, tag.Get (), m_currentTxVector);
      // start next packet if TXOP remains, otherwise contend for accessing the channel again
      if (m_currentTxop->IsQosTxop () && m_currentTxop->GetTxopLimit ().IsStrictlyPositive ()
          && m_currentTxop->GetTxopRemaining () > GetSifs ())
        {
          m_waitIfsEvent = Simulator::Schedule (GetSifs (), &MacLow::WaitIfsAfterEndTxPacket, this);
        }
      else if (m_currentTxop->IsQosTxop ())
        {
          m_currentTxop->TerminateTxop ();
        }
    }
  else if (hdr.IsBlockAckReq () && hdr.GetAddr1 () == m_self)
    {
      CtrlBAckRequestHeader blockAckReq;
      packet->RemoveHeader (blockAckReq);
      if (!blockAckReq.IsMultiTid ())
        {
          uint8_t tid = blockAckReq.GetTidInfo ();
          AgreementsI it = m_bAckAgreements.find (std::make_pair (hdr.GetAddr2 (), tid));
          if (it != m_bAckAgreements.end ())
            {
              //Update block ack cache
              BlockAckCachesI i = m_bAckCaches.find (std::make_pair (hdr.GetAddr2 (), tid));
              NS_ASSERT (i != m_bAckCaches.end ());
              (*i).second.UpdateWithBlockAckReq (blockAckReq.GetStartingSequence ());

              //NS_ASSERT (m_sendAckEvent.IsExpired ());
              m_sendAckEvent.Cancel ();
              /* See section 11.5.3 in IEEE 802.11 for mean of this timer */
              ResetBlockAckInactivityTimerIfNeeded (it->second.first);
              if ((*it).second.first.IsImmediateBlockAck ())
                {
                  NS_LOG_DEBUG ("rx blockAckRequest/sendImmediateBlockAck from=" << hdr.GetAddr2 ());
                  m_sendAckEvent = Simulator::Schedule (GetSifs (),
                                                        &MacLow::SendBlockAckAfterBlockAckRequest, this,
                                                        blockAckReq,
                                                        hdr.GetAddr2 (),
                                                        hdr.GetDuration (),
                                                        txVector.GetMode (),
                                                        rxSnr);
                }
              else
                {
                  NS_FATAL_ERROR ("Delayed block ack not supported.");
                }
            }
          else
            {
              NS_LOG_DEBUG ("There's not a valid agreement for this block ack request.");
            }
        }
      else
        {
          NS_FATAL_ERROR ("Multi-tid block ack is not supported.");
        }
    }
  else if (hdr.IsCtl ())
    {
      if (hdr.IsCfEnd ())
        {
          NS_LOG_DEBUG ("rx CF-END ");
          m_cfpStart = NanoSeconds (0);
          if (m_cfAckInfo.expectCfAck)
            {
              NS_ASSERT (m_currentTxop != 0);
              if (hdr.IsCfAck ())
                {
                  m_currentTxop->GotAck ();
                }
              else
                {
                  m_currentTxop->MissedAck ();
                }
            }
          if (m_currentTxop != 0)
            {
              m_currentTxop->GotCfEnd ();
            }
          m_cfAckInfo.expectCfAck = false;
        }
      else
        {
          NS_LOG_DEBUG ("rx drop " << hdr.GetTypeString ());
        }
    }
  else if (hdr.GetAddr1 () == m_self)
    {
      if (hdr.IsCfPoll ())
        {
          m_cfpStart = Simulator::Now ();
          if (m_cfAckInfo.expectCfAck && !hdr.IsCfAck ())
            {
              NS_ASSERT (m_currentTxop != 0);
              Ptr<Txop> txop = m_currentTxop;
              m_currentTxop = 0;
              txop->MissedAck ();
              m_cfAckInfo.expectCfAck = false;
            }
        }
      m_stationManager->ReportRxOk (hdr.GetAddr2 (),
                                    rxSnr, txVector.GetMode ());
      if (hdr.IsQosData () && ReceiveMpdu (mpdu))
        {
          /* From section 9.10.4 in IEEE 802.11:
             Upon the receipt of a QoS data frame from the originator for which
             the block ack agreement exists, the recipient shall buffer the MSDU
             regardless of the value of the Ack Policy subfield within the
             QoS Control field of the QoS data frame. */
          if (hdr.IsQosAck () && !ampduSubframe)
            {
              NS_LOG_DEBUG ("rx QoS unicast/sendAck from=" << hdr.GetAddr2 ());
              AgreementsI it = m_bAckAgreements.find (std::make_pair (hdr.GetAddr2 (), hdr.GetQosTid ()));

              RxCompleteBufferedPacketsWithSmallerSequence (it->second.first.GetStartingSequenceControl (),
                                                            hdr.GetAddr2 (), hdr.GetQosTid ());
              RxCompleteBufferedPacketsUntilFirstLost (hdr.GetAddr2 (), hdr.GetQosTid ());
              NS_ASSERT (m_sendAckEvent.IsExpired ());
              m_sendAckEvent = Simulator::Schedule (GetSifs (),
                                                    &MacLow::SendAckAfterData, this,
                                                    hdr.GetAddr2 (),
                                                    hdr.GetDuration (),
                                                    txVector.GetMode (),
                                                    rxSnr);
            }
          else if (hdr.IsQosBlockAck ())
            {
              AgreementsI it = m_bAckAgreements.find (std::make_pair (hdr.GetAddr2 (), hdr.GetQosTid ()));
              /* See section 11.5.3 in IEEE 802.11 for mean of this timer */
              ResetBlockAckInactivityTimerIfNeeded (it->second.first);
            }
          return;
        }
      else if (hdr.IsQosData () && hdr.IsQosBlockAck ())
        {
          /* This happens if a packet with ack policy Block Ack is received and a block ack
             agreement for that packet doesn't exist.

             From section 11.5.3 in IEEE 802.11e:
             When a recipient does not have an active block ack for a TID, but receives
             data MPDUs with the Ack Policy subfield set to Block Ack, it shall discard
             them and shall send a DELBA frame using the normal access
             mechanisms. */
          AcIndex ac = QosUtilsMapTidToAc (hdr.GetQosTid ());
          m_edca[ac]->SendDelbaFrame (hdr.GetAddr2 (), hdr.GetQosTid (), false);
          return;
        }
      else if (hdr.IsQosData () && hdr.IsQosNoAck ())
        {
          if (ampduSubframe)
            {
              NS_LOG_DEBUG ("rx Ampdu with No Ack Policy from=" << hdr.GetAddr2 ());
            }
          else
            {
              NS_LOG_DEBUG ("rx unicast/noAck from=" << hdr.GetAddr2 ());
            }
        }
      else if (hdr.IsData () || hdr.IsMgt ())
        {
          if (hdr.IsProbeResp ())
            {
              // Apply SNR tag for probe response quality measurements
              SnrTag tag;
              tag.Set (rxSnr);
              packet->AddPacketTag (tag);
              mpdu = Create<WifiMacQueueItem> (packet, hdr);
            }
          if (hdr.IsMgt () && ampduSubframe)
            {
              NS_FATAL_ERROR ("Received management packet as part of an A-MPDU");
            }
          else
            {
              if (IsCfPeriod ())
                {
                  if (hdr.HasData ())
                    {
                      m_cfAckInfo.appendCfAck = true;
                      m_cfAckInfo.address = hdr.GetAddr2 ();
                    }
                }
              else
                {
                  NS_LOG_DEBUG ("rx unicast/sendAck from=" << hdr.GetAddr2 ());
                  NS_ASSERT (m_sendAckEvent.IsExpired ());
                  m_sendAckEvent = Simulator::Schedule (GetSifs (),
                                                        &MacLow::SendAckAfterData, this,
                                                        hdr.GetAddr2 (),
                                                        hdr.GetDuration (),
                                                        txVector.GetMode (),
                                                        rxSnr);
                }
            }
        }
      goto rxPacket;
    }
  else if (hdr.GetAddr1 ().IsGroup ())
    {
      if (ampduSubframe)
        {
          NS_FATAL_ERROR ("Received group addressed packet as part of an A-MPDU");
        }
      else
        {
          if (hdr.IsData () || hdr.IsMgt ())
            {
              NS_LOG_DEBUG ("rx group from=" << hdr.GetAddr2 ());
              if (hdr.IsBeacon ())
                {
                  // Apply SNR tag for beacon quality measurements
                  SnrTag tag;
                  tag.Set (rxSnr);
                  packet->AddPacketTag (tag);
                  mpdu = Create<WifiMacQueueItem> (packet, hdr);
                }
              goto rxPacket;
            }
        }
    }
  else if (m_promisc)
    {
      NS_ASSERT (hdr.GetAddr1 () != m_self);
      if (hdr.IsData ())
        {
          goto rxPacket;
        }
    }
  else
    {
      if (m_cfAckInfo.expectCfAck && hdr.IsCfAck ())
        {
          m_cfAckInfo.expectCfAck = false;
          NS_ASSERT (m_currentTxop != 0);
          m_currentTxop->GotAck ();
        }
      NS_LOG_DEBUG ("rx not for me from=" << hdr.GetAddr2 ());
    }
  return;
rxPacket:
  if (m_cfAckInfo.expectCfAck && hdr.IsCfAck ())
    {
      m_cfAckInfo.expectCfAck = false;
      NS_ASSERT (m_currentTxop != 0);
      m_currentTxop->GotAck ();
    }
  m_rxCallback (mpdu);
  return;
}

uint32_t
MacLow::GetCfEndSize (void) const
{
  WifiMacHeader cfEnd;
  if (m_cfAckInfo.expectCfAck || m_cfAckInfo.appendCfAck)
    {
      cfEnd.SetType (WIFI_MAC_CTL_END_ACK);
    }
  else
    {
      cfEnd.SetType (WIFI_MAC_CTL_END);
    }
  return cfEnd.GetSize () + 4;
}

Time
MacLow::GetAckDuration (Mac48Address to, WifiTxVector dataTxVector) const
{
  WifiTxVector ackTxVector = GetAckTxVectorForData (to, dataTxVector.GetMode ());
  return GetAckDuration (ackTxVector);
}

Time
MacLow::GetAckDuration (WifiTxVector ackTxVector) const
{
  NS_ASSERT (ackTxVector.GetMode ().GetModulationClass () != WIFI_MOD_CLASS_HT); //Ack should always use non-HT PPDU (HT PPDU cases not supported yet)
  return m_phy->CalculateTxDuration (GetAckSize (), ackTxVector, m_phy->GetPhyBand ());
}

Time
MacLow::GetBlockAckDuration (WifiTxVector blockAckReqTxVector, BlockAckType type) const
{
  /*
   * For immediate Basic BlockAck we should transmit the frame with the same WifiMode
   * as the BlockAckReq.
   */
  return m_phy->CalculateTxDuration (GetBlockAckSize (type), blockAckReqTxVector, m_phy->GetPhyBand ());
}

Time
MacLow::GetBlockAckRequestDuration (WifiTxVector blockAckReqTxVector, BlockAckType type) const
{
  return m_phy->CalculateTxDuration (GetBlockAckRequestSize (type), blockAckReqTxVector, m_phy->GetPhyBand ());
}

Time
MacLow::GetCtsDuration (Mac48Address to, WifiTxVector rtsTxVector) const
{
  WifiTxVector ctsTxVector = GetCtsTxVectorForRts (to, rtsTxVector.GetMode ());
  return GetCtsDuration (ctsTxVector);
}

Time
MacLow::GetCtsDuration (WifiTxVector ctsTxVector) const
{
  NS_ASSERT (ctsTxVector.GetMode ().GetModulationClass () != WIFI_MOD_CLASS_HT); //CTS should always use non-HT PPDU (HT PPDU cases not supported yet)
  return m_phy->CalculateTxDuration (GetCtsSize (), ctsTxVector, m_phy->GetPhyBand ());
}

WifiTxVector
MacLow::GetRtsTxVector (Ptr<const WifiMacQueueItem> item) const
{
  return m_stationManager->GetRtsTxVector (item->GetHeader ().GetAddr1 ());
}

WifiTxVector
MacLow::GetDataTxVector (Ptr<const WifiMacQueueItem> item) const
{
  return m_stationManager->GetDataTxVector (item->GetHeader ());
}

Time
MacLow::GetResponseDuration (const MacLowTransmissionParameters& params, WifiTxVector dataTxVector,
                             Mac48Address receiver) const
{
  NS_LOG_FUNCTION (this << receiver << dataTxVector << params);

  Time duration = Seconds (0);
  if (params.MustWaitNormalAck ())
    {
      duration += GetSifs ();
      duration += GetAckDuration (receiver, dataTxVector);
    }
  else if (params.MustWaitBlockAck ())
    {
      duration += GetSifs ();
      WifiTxVector blockAckReqTxVector = GetBlockAckTxVector (m_self, dataTxVector.GetMode ());
      duration += GetBlockAckDuration (blockAckReqTxVector, params.GetBlockAckType ());
    }
  else if (params.MustSendBlockAckRequest ())
    {
      duration += 2 * GetSifs ();
      WifiTxVector blockAckReqTxVector = GetBlockAckTxVector (m_self, dataTxVector.GetMode ());
      duration += GetBlockAckRequestDuration (blockAckReqTxVector, params.GetBlockAckRequestType ());
      duration += GetBlockAckDuration (blockAckReqTxVector, params.GetBlockAckRequestType ());
    }
  return duration;
}

WifiMode
MacLow::GetControlAnswerMode (WifiMode reqMode) const
{
  NS_LOG_FUNCTION (this << reqMode);
  WifiMode mode = m_stationManager->GetDefaultMode ();
  bool found = false;
  //First, search the BSS Basic Rate set
  for (uint8_t i = 0; i < m_stationManager->GetNBasicModes (); i++)
    {
      WifiMode testMode = m_stationManager->GetBasicMode (i);
      if ((!found || testMode.IsHigherDataRate (mode))
          && (!testMode.IsHigherDataRate (reqMode))
          && (IsAllowedControlAnswerModulationClass (reqMode.GetModulationClass (), testMode.GetModulationClass ())))
        {
          mode = testMode;
          //We've found a potentially-suitable transmit rate, but we
          //need to continue and consider all the basic rates before
          //we can be sure we've got the right one.
          found = true;
        }
    }
  if (m_stationManager->GetHtSupported ())
    {
      if (!found)
        {
          mode = m_stationManager->GetDefaultMcs ();
          for (uint8_t i = 0; i != m_stationManager->GetNBasicMcs (); i++)
            {
              WifiMode testMode = m_stationManager->GetBasicMcs (i);
              if ((!found || testMode.IsHigherDataRate (mode))
                  && (!testMode.IsHigherDataRate (reqMode))
                  && (testMode.GetModulationClass () == reqMode.GetModulationClass ()))
                {
                  mode = testMode;
                  //We've found a potentially-suitable transmit rate, but we
                  //need to continue and consider all the basic rates before
                  //we can be sure we've got the right one.
                  found = true;
                }
            }
        }
    }
  //If we found a suitable rate in the BSSBasicRateSet, then we are
  //done and can return that mode.
  if (found)
    {
      NS_LOG_DEBUG ("MacLow::GetControlAnswerMode returning " << mode);
      return mode;
    }

  for (uint8_t idx = 0; idx < m_phy->GetNModes (); idx++)
    {
      WifiMode thismode = m_phy->GetMode (idx);
      /* If the rate:
       *
       *  - is a mandatory rate for the PHY, and
       *  - is equal to or faster than our current best choice, and
       *  - is less than or equal to the rate of the received frame, and
       *  - is of the same modulation class as the received frame
       *
       * ...then it's our best choice so far.
       */
      if (thismode.IsMandatory ()
          && (!found || thismode.IsHigherDataRate (mode))
          && (!thismode.IsHigherDataRate (reqMode))
          && (IsAllowedControlAnswerModulationClass (reqMode.GetModulationClass (), thismode.GetModulationClass ())))
        {
          mode = thismode;
          //As above; we've found a potentially-suitable transmit
          //rate, but we need to continue and consider all the
          //mandatory rates before we can be sure we've got the right one.
          found = true;
        }
    }
  if (m_stationManager->GetHtSupported () )
    {
      for (uint8_t idx = 0; idx < m_phy->GetNMcs (); idx++)
        {
          WifiMode thismode = m_phy->GetMcs (idx);
          if (thismode.IsMandatory ()
              && (!found || thismode.IsHigherDataRate (mode))
              && (!thismode.IsHigherCodeRate (reqMode))
              && (thismode.GetModulationClass () == reqMode.GetModulationClass ()))
            {
              mode = thismode;
              //As above; we've found a potentially-suitable transmit
              //rate, but we need to continue and consider all the
              //mandatory rates before we can be sure we've got the right one.
              found = true;
            }
        }
    }

  if (!found)
    {
      NS_FATAL_ERROR ("Can't find response rate for " << reqMode);
    }

  NS_LOG_DEBUG ("MacLow::GetControlAnswerMode returning " << mode);
  return mode;
}

WifiTxVector
MacLow::GetCtsTxVector (Mac48Address to, WifiMode rtsTxMode) const
{
  NS_ASSERT (!to.IsGroup ());
  WifiMode ctsMode = GetControlAnswerMode (rtsTxMode);
  WifiTxVector v;
  v.SetMode (ctsMode);
  v.SetPreambleType (GetPreambleForTransmission (ctsMode.GetModulationClass (), m_stationManager->GetShortPreambleEnabled (), m_stationManager->UseGreenfieldForDestination (to)));
  v.SetTxPowerLevel (m_stationManager->GetDefaultTxPowerLevel ());
  v.SetChannelWidth (GetChannelWidthForTransmission (ctsMode, m_phy->GetChannelWidth ()));
   uint16_t ctsTxGuardInterval = ConvertGuardIntervalToNanoSeconds (ctsMode, DynamicCast<WifiNetDevice> (m_phy->GetDevice ()));
  v.SetGuardInterval (ctsTxGuardInterval);
  v.SetNss (1);
  return v;
}

WifiTxVector
MacLow::GetAckTxVector (Mac48Address to, WifiMode dataTxMode) const
{
  NS_ASSERT (!to.IsGroup ());
  WifiMode ackMode = GetControlAnswerMode (dataTxMode);
  WifiTxVector v;
  v.SetMode (ackMode);
  v.SetPreambleType (GetPreambleForTransmission (ackMode.GetModulationClass (), m_stationManager->GetShortPreambleEnabled (), m_stationManager->UseGreenfieldForDestination (to)));
  v.SetTxPowerLevel (m_stationManager->GetDefaultTxPowerLevel ());
  v.SetChannelWidth (GetChannelWidthForTransmission (ackMode, m_phy->GetChannelWidth ()));
   uint16_t ackTxGuardInterval = ConvertGuardIntervalToNanoSeconds (ackMode, DynamicCast<WifiNetDevice> (m_phy->GetDevice ()));
  v.SetGuardInterval (ackTxGuardInterval);
  v.SetNss (1);
  return v;
}

WifiTxVector
MacLow::GetBlockAckTxVector (Mac48Address to, WifiMode dataTxMode) const
{
  NS_ASSERT (!to.IsGroup ());
  WifiMode blockAckMode = GetControlAnswerMode (dataTxMode);
  WifiTxVector v;
  v.SetMode (blockAckMode);
  v.SetPreambleType (GetPreambleForTransmission (blockAckMode.GetModulationClass (), m_stationManager->GetShortPreambleEnabled (), m_stationManager->UseGreenfieldForDestination (to)));
  v.SetTxPowerLevel (m_stationManager->GetDefaultTxPowerLevel ());
  v.SetChannelWidth (GetChannelWidthForTransmission (blockAckMode, m_phy->GetChannelWidth ()));
uint16_t blockAckTxGuardInterval = ConvertGuardIntervalToNanoSeconds (blockAckMode, DynamicCast<WifiNetDevice> (m_phy->GetDevice ()));
  v.SetGuardInterval (blockAckTxGuardInterval);
  v.SetNss (1);
  return v;
}

WifiTxVector
MacLow::GetCtsTxVectorForRts (Mac48Address to, WifiMode rtsTxMode) const
{
  return GetCtsTxVector (to, rtsTxMode);
}

WifiTxVector
MacLow::GetAckTxVectorForData (Mac48Address to, WifiMode dataTxMode) const
{
  return GetAckTxVector (to, dataTxMode);
}

Time
MacLow::CalculateOverallTxTime (Ptr<const Packet> packet,
                                const WifiMacHeader* hdr,
                                const MacLowTransmissionParameters& params,
                                uint32_t fragmentSize) const
{
  Ptr<const WifiMacQueueItem> item = Create<const WifiMacQueueItem> (packet, *hdr);
  Time txTime = CalculateOverheadTxTime (item, params);
  uint32_t dataSize;
  if (fragmentSize > 0)
    {
      Ptr<const Packet> fragment = Create<Packet> (fragmentSize);
      dataSize = GetSize (fragment, hdr, m_currentPacket && m_currentPacket->IsAggregate ());
    }
  else
    {
      dataSize = GetSize (packet, hdr, m_currentPacket && m_currentPacket->IsAggregate ());
    }
  txTime += m_phy->CalculateTxDuration (dataSize, GetDataTxVector (item), m_phy->GetPhyBand ());
  return txTime;
}

Time
MacLow::CalculateOverheadTxTime (Ptr<const WifiMacQueueItem> item,
                                 const MacLowTransmissionParameters& params) const
{
  Time txTime = Seconds (0);
  if (params.MustSendRts ())
    {
      WifiTxVector rtsTxVector = GetRtsTxVector (item);
      txTime += m_phy->CalculateTxDuration (GetRtsSize (), rtsTxVector, m_phy->GetPhyBand ());
      txTime += GetCtsDuration (item->GetHeader ().GetAddr1 (), rtsTxVector);
      txTime += Time (GetSifs () * 2);
    }
  txTime += GetResponseDuration (params, GetDataTxVector (item), item->GetHeader ().GetAddr1 ());

  return txTime;
}

Time
MacLow::CalculateTransmissionTime (Ptr<const Packet> packet,
                                   const WifiMacHeader* hdr,
                                   const MacLowTransmissionParameters& params) const
{
  Time txTime = CalculateOverallTxTime (packet, hdr, params);
  if (params.HasNextPacket ())
    {
      WifiTxVector dataTxVector = GetDataTxVector (Create<const WifiMacQueueItem> (packet, *hdr));
      txTime += GetSifs ();
      txTime += m_phy->CalculateTxDuration (params.GetNextPacketSize (), dataTxVector, m_phy->GetPhyBand ());
    }
  return txTime;
}

void
MacLow::NotifyNav (Ptr<const Packet> packet, const WifiMacHeader &hdr)
{
  NS_ASSERT (m_lastNavStart <= Simulator::Now ());
  if (hdr.GetRawDuration () > 32767)
    {
      //All stations process Duration field values less than or equal to 32 767 from valid data frames
      //to update their NAV settings as appropriate under the coordination function rules.
      return;
    }
  if (hdr.IsCfEnd () && hdr.GetAddr2 () == m_bssid)
    {
      //see section 9.3.2.2 802.11-1999
      DoNavResetNow (Seconds (0));
      return;
    }
  else if (hdr.GetAddr1 () != m_self)
    {
      // see section 9.2.5.4 802.11-1999
      Time duration = hdr.GetDuration ();
      bool navUpdated = DoNavStartNow (duration);
      if (hdr.IsRts () && navUpdated)
        {
          WifiMacHeader cts;
          cts.SetType (WIFI_MAC_CTL_CTS);
          WifiTxVector txVector = GetRtsTxVector (Create<const WifiMacQueueItem> (packet, hdr));
          Time navCounterResetCtsMissedDelay =
            m_phy->CalculateTxDuration (cts.GetSerializedSize (), txVector, m_phy->GetPhyBand ()) +
            Time (2 * GetSifs ()) + Time (2 * GetSlotTime ()) +
            m_phy->CalculatePhyPreambleAndHeaderDuration (txVector);
          m_navCounterResetCtsMissed = Simulator::Schedule (navCounterResetCtsMissedDelay,
                                                            &MacLow::DoNavResetNow, this,
                                                            Seconds (0));
        }
    }
}

void
MacLow::DoNavResetNow (Time duration)
{
  NS_LOG_FUNCTION (this << duration);
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      (*i)->NotifyNavResetNow (duration);
    }
  m_lastNavStart = Simulator::Now ();
  m_lastNavDuration = duration;
}

bool
MacLow::DoNavStartNow (Time duration)
{
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      (*i)->NotifyNavStartNow (duration);
    }
  Time newNavEnd = Simulator::Now () + duration;
  Time oldNavEnd = m_lastNavStart + m_lastNavDuration;
  if (newNavEnd > oldNavEnd)
    {
      m_lastNavStart = Simulator::Now ();
      m_lastNavDuration = duration;
      return true;
    }
  return false;
}

void
MacLow::NotifyAckTimeoutStartNow (Time duration)
{
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      (*i)->NotifyAckTimeoutStartNow (duration);
    }
}

void
MacLow::NotifyAckTimeoutResetNow (void)
{
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      (*i)->NotifyAckTimeoutResetNow ();
    }
}

void
MacLow::NotifyCtsTimeoutStartNow (Time duration)
{
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      (*i)->NotifyCtsTimeoutStartNow (duration);
    }
}

void
MacLow::NotifyCtsTimeoutResetNow (void)
{
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      (*i)->NotifyCtsTimeoutResetNow ();
    }
}

void
MacLow::ForwardDown (Ptr<const WifiPsdu> psdu, WifiTxVector txVector)
{
  NS_LOG_FUNCTION (this << psdu << txVector);

  NS_ASSERT (psdu->GetNMpdus ());
  const WifiMacHeader& hdr = (*psdu->begin ())->GetHeader ();

  NS_LOG_DEBUG ("send " << hdr.GetTypeString () <<
                ", to=" << hdr.GetAddr1 () <<
                ", size=" << psdu->GetSize () <<
                ", mode=" << txVector.GetMode  () <<
                ", preamble=" << txVector.GetPreambleType () <<
                ", duration=" << hdr.GetDuration () <<
                ", seq=0x" << std::hex << hdr.GetSequenceControl () << std::dec);

  if (hdr.IsCfPoll () && m_stationManager->GetPcfSupported ())
    {
      Simulator::Schedule (GetPifs () + m_phy->CalculateTxDuration (psdu->GetSize (), txVector, m_phy->GetPhyBand ()), &MacLow::CfPollTimeout, this);
    }
  if (hdr.IsBeacon () && m_stationManager->GetPcfSupported ())
    {
      if (Simulator::Now () > m_lastBeacon + m_beaconInterval)
        {
          m_cfpForeshortening = (Simulator::Now () - m_lastBeacon - m_beaconInterval);
        }
      m_lastBeacon = Simulator::Now ();
    }
  else if (hdr.IsCfEnd () && m_stationManager->GetPcfSupported ())
    {
      m_cfpStart = NanoSeconds (0);
      m_cfpForeshortening = NanoSeconds (0);
      m_cfAckInfo.appendCfAck = false;
      m_cfAckInfo.expectCfAck = false;
    }
  else if (IsCfPeriod () && hdr.HasData ())
    {
      m_cfAckInfo.expectCfAck = true;
    }

  if (psdu->IsSingle ())
    {
      txVector.SetAggregation (true);
      NS_LOG_DEBUG ("Sending S-MPDU");
    }
  else if (psdu->IsAggregate ())
    {
      txVector.SetAggregation (true);
      NS_LOG_DEBUG ("Sending A-MPDU");
    }
  else
    {
      NS_LOG_DEBUG ("Sending non aggregate MPDU");
    }

  for (auto& mpdu : *PeekPointer (psdu))
    {
      if (mpdu->GetHeader ().IsQosData ())
        {
          auto edcaIt = m_edca.find (QosUtilsMapTidToAc (mpdu->GetHeader ().GetQosTid ()));
          edcaIt->second->CompleteMpduTx (mpdu);
        }
    }
  m_phy->Send (psdu, txVector);
}

void
MacLow::CfPollTimeout (void)
{
  NS_LOG_FUNCTION (this);
  //to be reworked
  bool busy = false;
  for (ChannelAccessManagersCI i = m_channelAccessManagers.begin (); i != m_channelAccessManagers.end (); i++)
    {
      busy = (*i)->IsBusy ();
    }
  if (!busy)
    {
      NS_ASSERT (m_currentTxop != 0);
      m_currentTxop->MissedCfPollResponse (m_cfAckInfo.expectCfAck);
      m_cfAckInfo.expectCfAck = false;
    }
}

void
MacLow::CtsTimeout (void)
{
  NS_LOG_FUNCTION (this);
  NS_LOG_DEBUG ("cts timeout");
  m_stationManager->ReportRtsFailed (m_currentPacket->GetAddr1 (), &m_currentPacket->GetHeader (0));

  Ptr<QosTxop> qosTxop = DynamicCast<QosTxop> (m_currentTxop);
  if (qosTxop != 0)
    {
      qosTxop->NotifyMissedCts (std::list<Ptr<WifiMacQueueItem>> (m_currentPacket->begin (), m_currentPacket->end ()));
    }
  else
    {
      m_currentTxop->MissedCts ();
    }
  m_currentTxop = 0;
}

void
MacLow::NormalAckTimeout (void)
{
  NS_LOG_FUNCTION (this);
  NS_LOG_DEBUG ("normal ack timeout");
  Ptr<Txop> txop = m_currentTxop;
  m_currentTxop = 0;
  txop->MissedAck ();
}

void
MacLow::BlockAckTimeout (void)
{
  NS_LOG_FUNCTION (this);
  NS_LOG_DEBUG ("block ack timeout");
  Ptr<Txop> txop = m_currentTxop;
  m_currentTxop = 0;
  txop->MissedBlockAck (m_currentPacket->GetNMpdus ());
}

void
MacLow::SendRtsForPacket (void)
{
  NS_LOG_FUNCTION (this);
  /* send an RTS for this packet. */
  WifiMacHeader rts;
  rts.SetType (WIFI_MAC_CTL_RTS);
  rts.SetDsNotFrom ();
  rts.SetDsNotTo ();
  rts.SetNoRetry ();
  rts.SetNoMoreFragments ();
  rts.SetAddr1 (m_currentPacket->GetAddr1 ());
  rts.SetAddr2 (m_self);
  WifiTxVector rtsTxVector = GetRtsTxVector (*m_currentPacket->begin ());
  Time duration = Seconds (0);

  duration += GetSifs ();
  duration += GetCtsDuration (m_currentPacket->GetAddr1 (), rtsTxVector);
  duration += GetSifs ();
  duration += m_phy->CalculateTxDuration (m_currentPacket->GetSize (),
                                          m_currentTxVector, m_phy->GetPhyBand ());
  duration += GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
  if (m_txParams.HasNextPacket ())
    {
      duration += m_phy->CalculateTxDuration (m_txParams.GetNextPacketSize (),
                                              m_currentTxVector, m_phy->GetPhyBand ());
      duration += GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
    }
  rts.SetDuration (duration);

  Time txDuration = m_phy->CalculateTxDuration (GetRtsSize (), rtsTxVector, m_phy->GetPhyBand ());
  // After transmitting an RTS frame, the STA shall wait for a CTSTimeout interval with
  // a value of aSIFSTime + aSlotTime + aRxPHYStartDelay (IEEE 802.11-2016 sec. 10.3.2.7).
  // aRxPHYStartDelay equals the time to transmit the PHY header.
  Time timerDelay = txDuration + GetSifs () + GetSlotTime ()
                    + m_phy->CalculatePhyPreambleAndHeaderDuration (rtsTxVector);
  NS_ASSERT (m_ctsTimeoutEvent.IsExpired ());
  NotifyCtsTimeoutStartNow (timerDelay);
  m_ctsTimeoutEvent = Simulator::Schedule (timerDelay, &MacLow::CtsTimeout, this);

  ForwardDown (Create<const WifiPsdu> (Create<Packet> (), rts), rtsTxVector);
}

void
MacLow::StartDataTxTimers (WifiTxVector dataTxVector)
{
  Time txDuration = m_phy->CalculateTxDuration (m_currentPacket->GetSize (), dataTxVector, m_phy->GetPhyBand ());
  if (m_txParams.MustWaitNormalAck () && !IsCfPeriod ())
    {
      // the timeout duration is "aSIFSTime + aSlotTime + aRxPHYStartDelay, starting
      // at the PHY-TXEND.confirm primitive" (section 10.3.2.9 or 10.22.2.2 of 802.11-2016).
      // aRxPHYStartDelay equals the time to transmit the PHY header.
      WifiTxVector ackTxVector = GetAckTxVector (m_currentPacket->GetAddr1 (),
                                                 dataTxVector.GetMode ());
      Time timerDelay = txDuration + GetSifs () + GetSlotTime ()
                        + m_phy->CalculatePhyPreambleAndHeaderDuration (ackTxVector);
      NS_ASSERT (m_normalAckTimeoutEvent.IsExpired ());
      NotifyAckTimeoutStartNow (timerDelay);
      m_normalAckTimeoutEvent = Simulator::Schedule (timerDelay, &MacLow::NormalAckTimeout, this);
    }
  else if (m_txParams.MustWaitBlockAck ())
    {
      // the timeout duration is "aSIFSTime + aSlotTime + aRxPHYStartDelay, starting
      // at the PHY-TXEND.confirm primitive" (section 10.3.2.9 or 10.22.2.2 of 802.11-2016).
      // aRxPHYStartDelay equals the time to transmit the PHY header.
      WifiTxVector blockAckTxVector = GetBlockAckTxVector (m_currentPacket->GetAddr1 (),
                                                           dataTxVector.GetMode ());
      Time timerDelay = txDuration + GetSifs () + GetSlotTime ()
                        + m_phy->CalculatePhyPreambleAndHeaderDuration (blockAckTxVector);
      NS_ASSERT (m_blockAckTimeoutEvent.IsExpired ());
      NotifyAckTimeoutStartNow (timerDelay);
      m_blockAckTimeoutEvent = Simulator::Schedule (timerDelay, &MacLow::BlockAckTimeout, this);
    }
  else if (m_txParams.HasNextPacket ())
    {
      NS_ASSERT (m_waitIfsEvent.IsExpired ());
      Time delay = txDuration + GetSifs ();
      m_waitIfsEvent = Simulator::Schedule (delay, &MacLow::WaitIfsAfterEndTxFragment, this);
    }
  else if (m_currentPacket->GetHeader (0).IsQosData () && m_currentTxop->IsQosTxop () &&
           m_currentTxop->GetTxopLimit ().IsStrictlyPositive () && m_currentTxop->GetTxopRemaining () > GetSifs ())
   {
      Time delay = txDuration + GetSifs ();
      m_waitIfsEvent = Simulator::Schedule (delay, &MacLow::WaitIfsAfterEndTxPacket, this);
    }
  else
    {
      // since we do not expect any timer to be triggered.
      m_endTxNoAckEvent = Simulator::Schedule (txDuration, &MacLow::EndTxNoAck, this);
    }
}

void
MacLow::SendDataPacket (void)
{
  NS_LOG_FUNCTION (this);
  /* send this packet directly. No RTS is needed. */
  StartDataTxTimers (m_currentTxVector);

  if (!IsCfPeriod ())
    {
      Time duration = GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
      if (m_txParams.HasNextPacket ())
        {
          duration += GetSifs ();
          duration += m_phy->CalculateTxDuration (m_txParams.GetNextPacketSize (),
                                                  m_currentTxVector, m_phy->GetPhyBand ());
          duration += GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
        }
      m_currentPacket->SetDuration (duration);
    }
  else
    {
      if (m_currentPacket->GetHeader (0).IsCfEnd ())
        {
          m_currentPacket->GetHeader (0).SetRawDuration (0);
        }
      else
        {
          m_currentPacket->GetHeader (0).SetRawDuration (32768);
        }
    }

  if (!m_currentPacket->IsAggregate ())
    {
      if (m_cfAckInfo.appendCfAck)
        {
          switch (m_currentPacket->GetHeader (0).GetType ())
            {
            case WIFI_MAC_DATA:
              m_currentPacket->GetHeader (0).SetType (WIFI_MAC_DATA_CFACK, false);
              break;
            case WIFI_MAC_DATA_CFPOLL:
              m_currentPacket->GetHeader (0).SetType (WIFI_MAC_DATA_CFACK_CFPOLL, false);
              break;
            case WIFI_MAC_DATA_NULL:
              m_currentPacket->GetHeader (0).SetType (WIFI_MAC_DATA_NULL_CFACK, false);
              break;
            case WIFI_MAC_DATA_NULL_CFPOLL:
              m_currentPacket->GetHeader (0).SetType (WIFI_MAC_DATA_NULL_CFACK_CFPOLL, false);
              break;
            case WIFI_MAC_CTL_END:
              m_currentPacket->GetHeader (0).SetType (WIFI_MAC_CTL_END_ACK, false);
              break;
            default:
              NS_ASSERT (false);
              break;
            }
          NS_ASSERT (m_cfAckInfo.address != Mac48Address ());
          //Standard says that, for frames of type Data+CF-Ack, Data+CF-Poll+CF-Ack, and CF-Poll+CF-Ack,
          //the rate chosen to transmit the frame must be supported by both the addressed recipient STA and the STA to which the Ack is intended.
          //This ideally requires the rate manager to handle this case, but this requires to update all rate manager classes.
          //Instead, we simply fetch two TxVector and we select the one with the lowest data rate.
          //This should be later changed, at the latest once HCCA is implemented for HT/VHT/HE stations.
          WifiMacHeader tmpHdr = m_currentPacket->GetHeader (0);
          tmpHdr.SetAddr1 (m_cfAckInfo.address);
          WifiTxVector tmpTxVector = GetDataTxVector (Create<const WifiMacQueueItem> (m_currentPacket->GetPayload (0), tmpHdr));
          if (tmpTxVector.GetMode ().GetDataRate (tmpTxVector) < m_currentTxVector.GetMode ().GetDataRate (m_currentTxVector))
            {
              m_currentTxVector = tmpTxVector;
            }
          m_cfAckInfo.appendCfAck = false;
          m_cfAckInfo.address = Mac48Address ();
        }
    }
  if (m_txParams.MustSendBlockAckRequest ())
    {
      Ptr<QosTxop> qosTxop = DynamicCast<QosTxop> (m_currentTxop);
      NS_ASSERT (qosTxop != 0);
      auto bar = qosTxop->PrepareBlockAckRequest (m_currentPacket->GetAddr1 (), *m_currentPacket->GetTids ().begin ());
      qosTxop->ScheduleBar (bar);
    }
  ForwardDown (m_currentPacket, m_currentTxVector);
}

bool
MacLow::IsNavZero (void) const
{
  return (m_lastNavStart + m_lastNavDuration < Simulator::Now ());
}

void
MacLow::SendCtsToSelf (void)
{
  WifiMacHeader cts;
  cts.SetType (WIFI_MAC_CTL_CTS);
  cts.SetDsNotFrom ();
  cts.SetDsNotTo ();
  cts.SetNoMoreFragments ();
  cts.SetNoRetry ();
  cts.SetAddr1 (m_self);

  WifiTxVector ctsTxVector = GetRtsTxVector (*m_currentPacket->begin ());
  Time duration = Seconds (0);

  duration += GetSifs ();
  duration += m_phy->CalculateTxDuration (m_currentPacket->GetSize (),
                                          m_currentTxVector, m_phy->GetPhyBand ());
  duration += GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
  if (m_txParams.HasNextPacket ())
    {
      duration += GetSifs ();
      duration += m_phy->CalculateTxDuration (m_txParams.GetNextPacketSize (),
                                              m_currentTxVector, m_phy->GetPhyBand ());
      duration += GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
    }

  cts.SetDuration (duration);

  ForwardDown (Create<const WifiPsdu> (Create<Packet> (), cts), ctsTxVector);

  Time txDuration = m_phy->CalculateTxDuration (GetCtsSize (), ctsTxVector, m_phy->GetPhyBand ());
  txDuration += GetSifs ();
  NS_ASSERT (m_sendDataEvent.IsExpired ());

  m_sendDataEvent = Simulator::Schedule (txDuration,
                                         &MacLow::SendDataAfterCts, this,
                                         duration);
}

void
MacLow::SendCtsAfterRts (Mac48Address source, Time duration, WifiTxVector rtsTxVector, double rtsSnr)
{
  NS_LOG_FUNCTION (this << source << duration << rtsTxVector.GetMode () << rtsSnr);
  /* send a CTS when you receive a RTS
   * right after SIFS.
   */
  WifiTxVector ctsTxVector = GetCtsTxVector (source, rtsTxVector.GetMode ());
  WifiMacHeader cts;
  cts.SetType (WIFI_MAC_CTL_CTS);
  cts.SetDsNotFrom ();
  cts.SetDsNotTo ();
  cts.SetNoMoreFragments ();
  cts.SetNoRetry ();
  cts.SetAddr1 (source);
  duration -= GetCtsDuration (source, rtsTxVector);
  duration -= GetSifs ();
  NS_ASSERT (duration.IsPositive ());
  cts.SetDuration (duration);

  Ptr<Packet> packet = Create<Packet> ();

  SnrTag tag;
  tag.Set (rtsSnr);
  packet->AddPacketTag (tag);

  //CTS should always use non-HT PPDU (HT PPDU cases not supported yet)
  ForwardDown (Create<const WifiPsdu> (packet, cts), ctsTxVector);
}

void
MacLow::SendDataAfterCts (Time duration)
{
  NS_LOG_FUNCTION (this);
  /* send the third step in a
   * RTS/CTS/Data/Ack handshake
   */
  NS_ASSERT (m_currentPacket != 0);

  StartDataTxTimers (m_currentTxVector);
  Time newDuration = GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
  if (m_txParams.HasNextPacket ())
    {
      newDuration += GetSifs ();
      newDuration += m_phy->CalculateTxDuration (m_txParams.GetNextPacketSize (), m_currentTxVector, m_phy->GetPhyBand ());
      newDuration += GetResponseDuration (m_txParams, m_currentTxVector, m_currentPacket->GetAddr1 ());
    }

  Time txDuration = m_phy->CalculateTxDuration (m_currentPacket->GetSize (), m_currentTxVector, m_phy->GetPhyBand ());
  duration -= txDuration;
  duration -= GetSifs ();

  duration = std::max (duration, newDuration);
  NS_ASSERT (duration.IsPositive ());
  m_currentPacket->SetDuration (duration);
  if (m_txParams.MustSendBlockAckRequest ())
    {
      Ptr<QosTxop> qosTxop = DynamicCast<QosTxop> (m_currentTxop);
      NS_ASSERT (qosTxop != 0);
      auto bar = qosTxop->PrepareBlockAckRequest (m_currentPacket->GetAddr1 (), *m_currentPacket->GetTids ().begin ());
      qosTxop->ScheduleBar (bar);
    }
  ForwardDown (m_currentPacket, m_currentTxVector);
}

void
MacLow::WaitIfsAfterEndTxFragment (void)
{
  NS_LOG_FUNCTION (this);
  m_currentTxop->StartNextFragment ();
}

void
MacLow::WaitIfsAfterEndTxPacket (void)
{
  NS_LOG_FUNCTION (this);
  m_currentTxop->StartNextPacket ();
}

void
MacLow::EndTxNoAck (void)
{
  NS_LOG_FUNCTION (this);
  if (m_currentPacket->GetHeader (0).IsBeacon () && m_stationManager->GetPcfSupported ())
    {
      m_cfpStart = Simulator::Now ();
    }
  if (!m_cfAckInfo.expectCfAck)
    {
      Ptr<Txop> txop = m_currentTxop;
      txop->EndTxNoAck ();
    }
  if (!IsCfPeriod ())
    {
      m_currentTxop = 0;
    }
}

void
MacLow::SendAckAfterData (Mac48Address source, Time duration, WifiMode dataTxMode, double dataSnr)
{
  NS_LOG_FUNCTION (this);
  // send an Ack, after SIFS, when you receive a packet
  WifiTxVector ackTxVector = GetAckTxVector (source, dataTxMode);
  WifiMacHeader ack;
  ack.SetType (WIFI_MAC_CTL_ACK);
  ack.SetDsNotFrom ();
  ack.SetDsNotTo ();
  ack.SetNoRetry ();
  ack.SetNoMoreFragments ();
  ack.SetAddr1 (source);
  // 802.11-2012, Section 8.3.1.4:  Duration/ID is received duration value
  // minus the time to transmit the Ack frame and its SIFS interval
  duration -= GetAckDuration (ackTxVector);
  duration -= GetSifs ();
  NS_ASSERT_MSG (duration.IsPositive (), "Please provide test case to maintainers if this assert is hit.");
  ack.SetDuration (duration);

  Ptr<Packet> packet = Create<Packet> ();

  SnrTag tag;
  tag.Set (dataSnr);
  packet->AddPacketTag (tag);

  //Ack should always use non-HT PPDU (HT PPDU cases not supported yet)
  ForwardDown (Create<const WifiPsdu> (packet, ack), ackTxVector);
}

bool
MacLow::ReceiveMpdu (Ptr<WifiMacQueueItem> mpdu)
{
  const WifiMacHeader& hdr = mpdu->GetHeader ();

  if (m_stationManager->GetHtSupported ()
      || m_stationManager->GetVhtSupported ()
      || m_stationManager->GetHeSupported ())
    {
      Mac48Address originator = hdr.GetAddr2 ();
      uint8_t tid = 0;
      if (hdr.IsQosData ())
        {
          tid = hdr.GetQosTid ();
        }
      uint16_t seqNumber = hdr.GetSequenceNumber ();
      AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
      if (it != m_bAckAgreements.end ())
        {
          //Implement HT immediate BlockAck support for HT Delayed BlockAck is not added yet
          if (!QosUtilsIsOldPacket ((*it).second.first.GetStartingSequence (), seqNumber))
            {
              StoreMpduIfNeeded (mpdu);
              if (!IsInWindow (hdr.GetSequenceNumber (), (*it).second.first.GetStartingSequence (), (*it).second.first.GetBufferSize ()))
                {
                  uint16_t delta = (seqNumber - (*it).second.first.GetWinEnd () + 4096) % 4096;
                  NS_ASSERT (delta > 0);
                  uint16_t bufferSize = (*it).second.first.GetBufferSize ();
                  uint16_t startingSeq = (seqNumber - bufferSize + 1 + 4096) % 4096;
                  (*it).second.first.SetStartingSequence (startingSeq);
                  RxCompleteBufferedPacketsWithSmallerSequence ((*it).second.first.GetStartingSequenceControl (), originator, tid);
                }
              RxCompleteBufferedPacketsUntilFirstLost (originator, tid); //forwards up packets starting from winstart and set winstart to last +1
            }
          return true;
        }
      return false;
    }
  return StoreMpduIfNeeded (mpdu);
}

bool
MacLow::StoreMpduIfNeeded (Ptr<WifiMacQueueItem> mpdu)
{
  const WifiMacHeader& hdr = mpdu->GetHeader ();

  AgreementsI it = m_bAckAgreements.find (std::make_pair (hdr.GetAddr2 (), hdr.GetQosTid ()));
  if (it != m_bAckAgreements.end ())
    {
      uint16_t endSequence = ((*it).second.first.GetStartingSequence () + 2047) % 4096;
      uint32_t mappedSeqControl = QosUtilsMapSeqControlToUniqueInteger (hdr.GetSequenceControl (), endSequence);

      BufferedPacketI i = (*it).second.second.begin ();
      for (; i != (*it).second.second.end ()
           && QosUtilsMapSeqControlToUniqueInteger ((*i)->GetHeader ().GetSequenceControl (), endSequence) < mappedSeqControl; i++)
        {
        }
      (*it).second.second.insert (i, mpdu);

      //Update block ack cache
      BlockAckCachesI j = m_bAckCaches.find (std::make_pair (hdr.GetAddr2 (), hdr.GetQosTid ()));
      NS_ASSERT (j != m_bAckCaches.end ());
      (*j).second.UpdateWithMpdu (&hdr);
      return true;
    }
  return false;
}

void
MacLow::CreateBlockAckAgreement (const MgtAddBaResponseHeader *respHdr, Mac48Address originator,
                                 uint16_t startingSeq)
{
  NS_LOG_FUNCTION (this);
  uint8_t tid = respHdr->GetTid ();
  BlockAckAgreement agreement (originator, tid);
  if (respHdr->IsImmediateBlockAck ())
    {
      agreement.SetImmediateBlockAck ();
    }
  else
    {
      agreement.SetDelayedBlockAck ();
    }
  agreement.SetAmsduSupport (respHdr->IsAmsduSupported ());
  agreement.SetBufferSize (respHdr->GetBufferSize () + 1);
  agreement.SetTimeout (respHdr->GetTimeout ());
  agreement.SetStartingSequence (startingSeq);

  std::list<Ptr<WifiMacQueueItem>> buffer (0);
  AgreementKey key (originator, respHdr->GetTid ());
  AgreementValue value (agreement, buffer);
  m_bAckAgreements.insert (std::make_pair (key, value));

  BlockAckCache cache;
  cache.Init (startingSeq, respHdr->GetBufferSize () + 1);
  m_bAckCaches.insert (std::make_pair (key, cache));

  if (respHdr->GetTimeout () != 0)
    {
      AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, respHdr->GetTid ()));
      Time timeout = MicroSeconds (1024 * agreement.GetTimeout ());

      AcIndex ac = QosUtilsMapTidToAc (agreement.GetTid ());

      it->second.first.m_inactivityEvent = Simulator::Schedule (timeout,
                                                                &QosTxop::SendDelbaFrame,
                                                                m_edca[ac], originator, tid, false);
    }
}

void
MacLow::DestroyBlockAckAgreement (Mac48Address originator, uint8_t tid)
{
  NS_LOG_FUNCTION (this);
  AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
  if (it != m_bAckAgreements.end ())
    {
      RxCompleteBufferedPacketsWithSmallerSequence (it->second.first.GetStartingSequenceControl (), originator, tid);
      RxCompleteBufferedPacketsUntilFirstLost (originator, tid);
      m_bAckAgreements.erase (it);
      BlockAckCachesI i = m_bAckCaches.find (std::make_pair (originator, tid));
      NS_ASSERT (i != m_bAckCaches.end ());
      m_bAckCaches.erase (i);
    }
}

void
MacLow::RxCompleteBufferedPacketsWithSmallerSequence (uint16_t seq, Mac48Address originator, uint8_t tid)
{
  AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
  if (it != m_bAckAgreements.end ())
    {
      uint16_t endSequence = ((*it).second.first.GetStartingSequence () + 2047) % 4096;
      uint32_t mappedStart = QosUtilsMapSeqControlToUniqueInteger (seq, endSequence);
      BufferedPacketI last = (*it).second.second.begin ();
      uint16_t guard = 0;
      if (last != (*it).second.second.end ())
        {
          guard = (*(*it).second.second.begin ())->GetHeader ().GetSequenceControl ();
        }
      BufferedPacketI i = (*it).second.second.begin ();
      for (; i != (*it).second.second.end ()
           && QosUtilsMapSeqControlToUniqueInteger ((*i)->GetHeader ().GetSequenceControl (), endSequence) < mappedStart; )
        {
          if (guard == (*i)->GetHeader ().GetSequenceControl ())
            {
              if (!(*i)->GetHeader ().IsMoreFragments ())
                {
                  while (last != i)
                    {
                      m_rxCallback (*last);
                      last++;
                    }
                  m_rxCallback (*last);
                  last++;
                  /* go to next packet */
                  while (i != (*it).second.second.end () && guard == (*i)->GetHeader ().GetSequenceControl ())
                    {
                      i++;
                    }
                  if (i != (*it).second.second.end ())
                    {
                      guard = (*i)->GetHeader ().GetSequenceControl ();
                      last = i;
                    }
                }
              else
                {
                  guard++;
                }
            }
          else
            {
              /* go to next packet */
              while (i != (*it).second.second.end () && guard == (*i)->GetHeader ().GetSequenceControl ())
                {
                  i++;
                }
              if (i != (*it).second.second.end ())
                {
                  guard = (*i)->GetHeader ().GetSequenceControl ();
                  last = i;
                }
            }
        }
      (*it).second.second.erase ((*it).second.second.begin (), i);
    }
}

void
MacLow::RxCompleteBufferedPacketsUntilFirstLost (Mac48Address originator, uint8_t tid)
{
  AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
  if (it != m_bAckAgreements.end ())
    {
      uint16_t guard = (*it).second.first.GetStartingSequenceControl ();
      BufferedPacketI lastComplete = (*it).second.second.begin ();
      BufferedPacketI i = (*it).second.second.begin ();
      for (; i != (*it).second.second.end () && guard == (*i)->GetHeader ().GetSequenceControl (); i++)
        {
          if (!(*i)->GetHeader ().IsMoreFragments ())
            {
              while (lastComplete != i)
                {
                  m_rxCallback (*lastComplete);
                  lastComplete++;
                }
              m_rxCallback (*lastComplete);
              lastComplete++;
            }
          guard = (*i)->GetHeader ().IsMoreFragments () ? (guard + 1) : ((guard + 16) & 0xfff0);
        }
      (*it).second.first.SetStartingSequenceControl (guard);
      /* All packets already forwarded to WifiMac must be removed from buffer:
      [begin (), lastComplete) */
      (*it).second.second.erase ((*it).second.second.begin (), lastComplete);
    }
}

void
MacLow::SendBlockAckResponse (const CtrlBAckResponseHeader* blockAck, Mac48Address originator, bool immediate,
                              Time duration, WifiMode blockAckReqTxMode, double rxSnr)
{
  NS_LOG_FUNCTION (this);
  Ptr<Packet> packet = Create<Packet> ();
  packet->AddHeader (*blockAck);

  WifiMacHeader hdr;
  hdr.SetType (WIFI_MAC_CTL_BACKRESP);
  hdr.SetAddr1 (originator);
  hdr.SetAddr2 (GetAddress ());
  hdr.SetDsNotFrom ();
  hdr.SetDsNotTo ();
  hdr.SetNoRetry ();
  hdr.SetNoMoreFragments ();

  WifiTxVector blockAckReqTxVector = GetBlockAckTxVector (originator, blockAckReqTxMode);

  if (immediate)
    {
      m_txParams.DisableAck ();
      duration -= GetSifs ();
      duration -= GetBlockAckDuration (blockAckReqTxVector, blockAck->GetType ());
    }
  else
    {
      m_txParams.EnableAck ();
      duration += GetSifs ();
      duration += GetAckDuration (originator, blockAckReqTxVector);
    }
  m_txParams.DisableNextData ();

  if (!immediate)
    {
      StartDataTxTimers (blockAckReqTxVector);
    }

  NS_ASSERT (duration.IsPositive ());
  hdr.SetDuration (duration);
  //here should be present a control about immediate or delayed BlockAck
  //for now we assume immediate
  SnrTag tag;
  tag.Set (rxSnr);
  packet->AddPacketTag (tag);
  ForwardDown (Create<const WifiPsdu> (packet, hdr), blockAckReqTxVector);
}

void
MacLow::SendBlockAckAfterAmpdu (uint8_t tid, Mac48Address originator, Time duration, WifiTxVector blockAckReqTxVector, double rxSnr)
{
  NS_LOG_FUNCTION (this);
  if (!m_phy->IsStateTx () && !m_phy->IsStateRx ())
    {
      NS_LOG_FUNCTION (this << +tid << originator << duration.As (Time::S) << blockAckReqTxVector << rxSnr);
      CtrlBAckResponseHeader blockAck;
      uint16_t seqNumber = 0;
      BlockAckCachesI i = m_bAckCaches.find (std::make_pair (originator, tid));
      NS_ASSERT (i != m_bAckCaches.end ());
      seqNumber = (*i).second.GetWinStart ();

      bool immediate = true;
      AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
      blockAck.SetStartingSequence (seqNumber);
      blockAck.SetTidInfo (tid);
      immediate = (*it).second.first.IsImmediateBlockAck ();
      if ((*it).second.first.GetBufferSize () > 64)
        {
          blockAck.SetType (EXTENDED_COMPRESSED_BLOCK_ACK);
        }
      else
        {
          blockAck.SetType (COMPRESSED_BLOCK_ACK);
        }
      NS_LOG_DEBUG ("Got Implicit block Ack Req with seq " << seqNumber);
      (*i).second.FillBlockAckBitmap (&blockAck);

      WifiTxVector blockAckTxVector = GetBlockAckTxVector (originator, blockAckReqTxVector.GetMode ());

      SendBlockAckResponse (&blockAck, originator, immediate, duration, blockAckTxVector.GetMode (), rxSnr);
    }
  else
    {
      NS_LOG_DEBUG ("Skip block ack response!");
    }
}

void
MacLow::SendBlockAckAfterBlockAckRequest (const CtrlBAckRequestHeader reqHdr, Mac48Address originator,
                                          Time duration, WifiMode blockAckReqTxMode, double rxSnr)
{
  NS_LOG_FUNCTION (this);
  CtrlBAckResponseHeader blockAck;
  uint8_t tid = 0;
  bool immediate = false;
  if (!reqHdr.IsMultiTid ())
    {
      tid = reqHdr.GetTidInfo ();
      AgreementsI it = m_bAckAgreements.find (std::make_pair (originator, tid));
      if (it != m_bAckAgreements.end ())
        {
          blockAck.SetStartingSequence (reqHdr.GetStartingSequence ());
          blockAck.SetTidInfo (tid);
          immediate = (*it).second.first.IsImmediateBlockAck ();
          if (reqHdr.IsBasic ())
            {
              blockAck.SetType (BASIC_BLOCK_ACK);
            }
          else if (reqHdr.IsCompressed ())
            {
              blockAck.SetType (COMPRESSED_BLOCK_ACK);
            }
          else if (reqHdr.IsExtendedCompressed ())
            {
              blockAck.SetType (EXTENDED_COMPRESSED_BLOCK_ACK);
            }
          BlockAckCachesI i = m_bAckCaches.find (std::make_pair (originator, tid));
          NS_ASSERT (i != m_bAckCaches.end ());
          (*i).second.FillBlockAckBitmap (&blockAck);
          NS_LOG_DEBUG ("Got block Ack Req with seq " << reqHdr.GetStartingSequence ());

          if (!m_stationManager->GetHtSupported ()
              && !m_stationManager->GetVhtSupported ()
              && !m_stationManager->GetHeSupported ())
            {
              /* All packets with smaller sequence than starting sequence control must be passed up to WifiMac
               * See 9.10.3 in IEEE 802.11e standard.
               */
              RxCompleteBufferedPacketsWithSmallerSequence (reqHdr.GetStartingSequenceControl (), originator, tid);
              RxCompleteBufferedPacketsUntilFirstLost (originator, tid);
            }
          else
            {
              if (!QosUtilsIsOldPacket ((*it).second.first.GetStartingSequence (), reqHdr.GetStartingSequence ()))
                {
                  (*it).second.first.SetStartingSequence (reqHdr.GetStartingSequence ());
                  RxCompleteBufferedPacketsWithSmallerSequence (reqHdr.GetStartingSequenceControl (), originator, tid);
                  RxCompleteBufferedPacketsUntilFirstLost (originator, tid);
                }
            }
        }
      else
        {
          NS_LOG_DEBUG ("there's not a valid block ack agreement with " << originator);
        }
    }
  else
    {
      NS_FATAL_ERROR ("Multi-tid block ack is not supported.");
    }
  SendBlockAckResponse (&blockAck, originator, immediate, duration, blockAckReqTxMode, rxSnr);
}

void
MacLow::ResetBlockAckInactivityTimerIfNeeded (BlockAckAgreement &agreement)
{
  if (agreement.GetTimeout () != 0)
    {
      NS_ASSERT (agreement.m_inactivityEvent.IsRunning ());
      agreement.m_inactivityEvent.Cancel ();
      Time timeout = MicroSeconds (1024 * agreement.GetTimeout ());
      AcIndex ac = QosUtilsMapTidToAc (agreement.GetTid ());
      agreement.m_inactivityEvent = Simulator::Schedule (timeout,
                                                         &QosTxop::SendDelbaFrame,
                                                         m_edca[ac], agreement.GetPeer (),
                                                         agreement.GetTid (), false);
    }
}

void
MacLow::RegisterEdcaForAc (AcIndex ac, Ptr<QosTxop> edca)
{
  m_edca.insert (std::make_pair (ac, edca));
}

void
MacLow::DeaggregateAmpduAndReceive (Ptr<WifiPsdu> psdu, double rxSnr, WifiTxVector txVector, std::vector<bool> statusPerMpdu)
{
  NS_LOG_FUNCTION (this);
  bool normalAck = false;
  bool ampduSubframe = txVector.IsAggregation (); //flag indicating the packet belongs to an A-MPDU and is not a VHT/HE single MPDU
  //statusPerMpdu is empty for intermediate MPDU forwarding.
  //This function is called also once the PPDU has been fully received by the PHY,
  //in that case statusPerMpdu carries the information about the received MPDUs.
  if (ampduSubframe && !statusPerMpdu.empty ())
    {
      //We are here if a S-MPDU is received or if all MPDUs of an A-MPDU have been
      //received (but have been already forwarded up, so ReceiveOk won't be called)
      NS_ASSERT (psdu->IsAggregate ());
      ampduSubframe = true;
      auto n = psdu->begin ();
      auto status = statusPerMpdu.begin ();
      NS_ABORT_MSG_IF (psdu->GetNMpdus () != statusPerMpdu.size (), "Should have one receive status per MPDU");

      WifiMacHeader firsthdr = (*n)->GetHeader ();
      if (firsthdr.GetAddr1 () == m_self)
        {
          //Iterate over all MPDUs and notify reception only if status OK
          for (; n != psdu->end (); ++n, ++status)
            {
              firsthdr = (*n)->GetHeader ();
              NS_ABORT_MSG_IF (firsthdr.GetAddr1 () != m_self, "All MPDUs of A-MPDU should have the same destination address");
              if (*status) //PER and thus CRC check succeeded
                {
                  if (psdu->IsSingle ())
                    {
                      //If the MPDU is sent as a VHT/HE single MPDU (EOF=1 in A-MPDU subframe header), then the responder sends an Ack.
                      NS_LOG_DEBUG ("Receive S-MPDU");
                      ampduSubframe = false;
                    }
                  else if (!m_sendAckEvent.IsRunning () && firsthdr.IsQosAck ()) // Implicit BAR Ack Policy
                    {
                      m_sendAckEvent = Simulator::Schedule (GetSifs (),
                                                            &MacLow::SendBlockAckAfterAmpdu, this,
                                                            firsthdr.GetQosTid (),
                                                            firsthdr.GetAddr2 (),
                                                            firsthdr.GetDuration (),
                                                            txVector, rxSnr);
                    }

                  if (firsthdr.IsAck () || firsthdr.IsBlockAck () || firsthdr.IsBlockAckReq ())
                    {
                      ReceiveOk ((*n), rxSnr, txVector, ampduSubframe);
                    }
                  else if (firsthdr.IsData () || firsthdr.IsQosData ())
                    {
                      NS_LOG_DEBUG ("Deaggregate packet from " << firsthdr.GetAddr2 () << " with sequence=" << firsthdr.GetSequenceNumber ());
                      if (psdu->IsSingle ())
                        {
                          ReceiveOk ((*n), rxSnr, txVector, ampduSubframe);
                        }
                      if (firsthdr.IsQosAck ())
                        {
                          NS_LOG_DEBUG ("Normal Ack");
                          normalAck = true;
                        }
                    }
                  else
                    {
                      NS_FATAL_ERROR ("Received A-MPDU with invalid first MPDU type");
                    }

                  if (!psdu->IsSingle ())
                    {
                      if (normalAck)
                        {
                          //send BlockAck
                          if (firsthdr.IsBlockAckReq ())
                            {
                              NS_FATAL_ERROR ("Sending a BlockAckReq with QosPolicy equal to Normal Ack");
                            }
                          uint8_t tid = firsthdr.GetQosTid ();
                          AgreementsI it = m_bAckAgreements.find (std::make_pair (firsthdr.GetAddr2 (), tid));
                          if (it != m_bAckAgreements.end ())
                            {
                              /* See section 11.5.3 in IEEE 802.11 for the definition of this timer */
                              ResetBlockAckInactivityTimerIfNeeded (it->second.first);
                              NS_LOG_DEBUG ("rx A-MPDU/sendImmediateBlockAck from=" << firsthdr.GetAddr2 ());
                              NS_ASSERT (m_sendAckEvent.IsRunning ());
                            }
                          else
                            {
                              NS_LOG_DEBUG ("There's not a valid agreement for this block ack request.");
                            }
                        }
                    }
                }
            }
        }
    }
  else
    {
      /* An MPDU has been received */
      NS_ASSERT (!psdu->IsAggregate ());
      ReceiveOk ((*psdu->begin ()), rxSnr, txVector, ampduSubframe);
    }
}

Time
MacLow::GetRemainingCfpDuration (void) const
{
  NS_LOG_FUNCTION (this);
  Time remainingCfpDuration = std::min (m_cfpStart, m_cfpStart + m_cfpMaxDuration - Simulator::Now () - m_cfpForeshortening);
  NS_ASSERT (remainingCfpDuration.IsPositive ());
  return remainingCfpDuration;
}

bool
MacLow::IsCfPeriod (void) const
{
  return (m_stationManager->GetPcfSupported () && m_cfpStart.IsStrictlyPositive ());
}

bool
MacLow::CanTransmitNextCfFrame (void) const
{
  NS_LOG_FUNCTION (this);
  if (!IsCfPeriod ())
    {
      return false;
    }
  NS_ASSERT (GetRemainingCfpDuration ().IsPositive ());
  WifiMacHeader hdr;
  hdr.SetType (WIFI_MAC_DATA);
  WifiMacTrailer fcs;
  uint32_t maxMacFrameSize = MAX_MSDU_SIZE + hdr.GetSerializedSize () + fcs.GetSerializedSize ();
  Time nextTransmission = 2 * m_phy->CalculateTxDuration (maxMacFrameSize, m_currentTxVector, m_phy->GetPhyBand ()) + 3 * GetSifs () + m_phy->CalculateTxDuration (GetCfEndSize (), m_currentTxVector, m_phy->GetPhyBand ());
  return ((GetRemainingCfpDuration () - nextTransmission).IsPositive ());
}

} //namespace ns3