frame-exchange-manager.cc

Go to the documentation of this file.

/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2020 Universita' degli Studi di Napoli Federico II
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Author: Stefano Avallone <stavallo@unina.it>
 */

#include "ns3/log.h"
#include "ns3/abort.h"
#include "frame-exchange-manager.h"
#include "channel-access-manager.h"
#include "wifi-utils.h"
#include "snr-tag.h"
#include "wifi-mac-queue.h"
#include "wifi-default-protection-manager.h"
#include "wifi-default-ack-manager.h"
#include "wifi-mac-trailer.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 ("FrameExchangeManager");

NS_OBJECT_ENSURE_REGISTERED (FrameExchangeManager);

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

FrameExchangeManager::FrameExchangeManager ()
  : m_navEnd (Seconds (0)),
    m_promisc (false),
    m_moreFragments (false)
{
  NS_LOG_FUNCTION (this);
}

FrameExchangeManager::~FrameExchangeManager ()
{
  NS_LOG_FUNCTION_NOARGS ();
}

void
FrameExchangeManager::Reset (void)
{
  NS_LOG_FUNCTION (this);
  m_txTimer.Cancel ();
  if (m_navResetEvent.IsRunning ())
    {
      m_navResetEvent.Cancel ();
    }
  m_navEnd = Simulator::Now ();
  m_mpdu = 0;
  m_txParams.Clear ();
  m_dcf = 0;
}

void
FrameExchangeManager::DoDispose (void)
{
  NS_LOG_FUNCTION (this);
  Reset ();
  m_fragmentedPacket = 0;
  m_mac = 0;
  m_txMiddle = 0;
  m_rxMiddle = 0;
  m_channelAccessManager = 0;
  m_protectionManager = 0;
  m_ackManager = 0;
  if (m_phy != 0)
    {
      m_phy->TraceDisconnectWithoutContext ("PhyRxPayloadBegin",
                                            MakeCallback (&FrameExchangeManager::RxStartIndication, this));
    }
  m_phy = 0;
  Object::DoDispose ();
}

void
FrameExchangeManager::SetProtectionManager (Ptr<WifiProtectionManager> protectionManager)
{
  NS_LOG_FUNCTION (this << protectionManager);
  m_protectionManager = protectionManager;
}

Ptr<WifiProtectionManager>
FrameExchangeManager::GetProtectionManager (void) const
{
  return m_protectionManager;
}

void
FrameExchangeManager::SetAckManager (Ptr<WifiAckManager> ackManager)
{
  NS_LOG_FUNCTION (this << ackManager);
  m_ackManager = ackManager;
}

Ptr<WifiAckManager>
FrameExchangeManager::GetAckManager (void) const
{
  return m_ackManager;
}

void
FrameExchangeManager::SetWifiMac (Ptr<RegularWifiMac> mac)
{
  NS_LOG_FUNCTION (this << mac);
  m_mac = mac;
}

void
FrameExchangeManager::SetMacTxMiddle (const Ptr<MacTxMiddle> txMiddle)
{
  NS_LOG_FUNCTION (this << txMiddle);
  m_txMiddle = txMiddle;
}

void
FrameExchangeManager::SetMacRxMiddle (const Ptr<MacRxMiddle> rxMiddle)
{
  NS_LOG_FUNCTION (this << rxMiddle);
  m_rxMiddle = rxMiddle;
}

void
FrameExchangeManager::SetChannelAccessManager (const Ptr<ChannelAccessManager> channelAccessManager)
{
  NS_LOG_FUNCTION (this << channelAccessManager);
  m_channelAccessManager = channelAccessManager;
}

void
FrameExchangeManager::SetWifiPhy (Ptr<WifiPhy> phy)
{
  NS_LOG_FUNCTION (this << phy);
  m_phy = phy;
  m_phy->TraceConnectWithoutContext ("PhyRxPayloadBegin",
                                     MakeCallback (&FrameExchangeManager::RxStartIndication, this));
  m_phy->SetReceiveOkCallback (MakeCallback (&FrameExchangeManager::Receive, this));
}

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

void
FrameExchangeManager::SetAddress (Mac48Address address)
{
  NS_LOG_FUNCTION (this << address);
  m_self = address;
}

void
FrameExchangeManager::SetBssid (Mac48Address bssid)
{
  NS_LOG_FUNCTION (this << bssid);
  m_bssid = bssid;
}

void
FrameExchangeManager::SetDroppedMpduCallback (DroppedMpdu callback)
{
  NS_LOG_FUNCTION (this << &callback);
  m_droppedMpduCallback = callback;
}

void
FrameExchangeManager::SetAckedMpduCallback (AckedMpdu callback)
{
  NS_LOG_FUNCTION (this << &callback);
  m_ackedMpduCallback = callback;
}

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

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

const WifiTxTimer&
FrameExchangeManager::GetWifiTxTimer (void) const
{
  return m_txTimer;
}

void
FrameExchangeManager::NotifyPacketDiscarded (Ptr<const WifiMacQueueItem> mpdu)
{
  if (!m_droppedMpduCallback.IsNull ())
    {
      m_droppedMpduCallback (WIFI_MAC_DROP_REACHED_RETRY_LIMIT, mpdu);
    }
}

void
FrameExchangeManager::RxStartIndication (WifiTxVector txVector, Time psduDuration)
{
  NS_LOG_FUNCTION (this << "PSDU reception started for " << psduDuration.As (Time::US)
                   << " (txVector: " << txVector << ")");

  if (psduDuration.IsZero ())
    {
      // PHY-RXEND immediately follows PHY-RXSTART (e.g. when PPDU has been filtered),
      // no need to reschedule timeouts (CCA will take over)
      return;
    }

  NS_ASSERT (psduDuration.IsStrictlyPositive ());
  NS_ASSERT_MSG (!m_txTimer.IsRunning () || !m_navResetEvent.IsRunning (),
                 "The TX timer and the NAV reset event cannot be both running");

  if (m_txTimer.IsRunning ())
    {
      // we are waiting for a response and something arrived
      NS_LOG_DEBUG ("Rescheduling timeout event");
      m_txTimer.Reschedule (psduDuration + NanoSeconds (PSDU_DURATION_SAFEGUARD));
      // PHY has switched to RX, so we can reset the ack timeout
      m_channelAccessManager->NotifyAckTimeoutResetNow ();
    }
  else if (m_navResetEvent.IsRunning ())
    {
      m_navResetEvent.Cancel ();
    }
}

bool
FrameExchangeManager::StartTransmission (Ptr<Txop> dcf)
{
  NS_LOG_FUNCTION (this << dcf);

  NS_ASSERT (m_mpdu == 0);
  if (m_txTimer.IsRunning ())
    {
      m_txTimer.Cancel ();
    }
  m_dcf = dcf;

  Ptr<WifiMacQueue> queue = dcf->GetWifiMacQueue ();

  // Even though channel access is requested when the queue is not empty, at
  // the time channel access is granted the lifetime of the packet might be
  // expired and the queue might be empty.
  if (queue->IsEmpty ())
    {
      NS_LOG_DEBUG ("Queue empty");
      m_dcf->NotifyChannelReleased ();
      m_dcf = 0;
      return false;
    }

  m_dcf->NotifyChannelAccessed ();
  Ptr<WifiMacQueueItem> mpdu = *queue->Peek ()->GetQueueIteratorPairs ().front ().it;
  NS_ASSERT (mpdu != 0);
  NS_ASSERT (mpdu->GetHeader ().IsData () || mpdu->GetHeader ().IsMgt ());

  // assign a sequence number if this is not a fragment nor a retransmission
  if (!mpdu->IsFragment () && !mpdu->GetHeader ().IsRetry ())
    {
      uint16_t sequence = m_txMiddle->GetNextSequenceNumberFor (&mpdu->GetHeader ());
      mpdu->GetHeader ().SetSequenceNumber (sequence);
    }

  NS_LOG_DEBUG ("MPDU payload size=" << mpdu->GetPacketSize () <<
                ", to=" << mpdu->GetHeader ().GetAddr1 () <<
                ", seq=" << mpdu->GetHeader ().GetSequenceControl ());

  // check if the MSDU needs to be fragmented
  mpdu = GetFirstFragmentIfNeeded (mpdu);

  NS_ASSERT (m_protectionManager != 0);
  NS_ASSERT (m_ackManager != 0);
  WifiTxParameters txParams;
  txParams.m_txVector = m_mac->GetWifiRemoteStationManager ()->GetDataTxVector (mpdu->GetHeader ());
  txParams.m_protection = m_protectionManager->TryAddMpdu (mpdu, txParams);
  txParams.m_acknowledgment = m_ackManager->TryAddMpdu (mpdu, txParams);
  txParams.AddMpdu (mpdu);
  UpdateTxDuration (mpdu->GetHeader ().GetAddr1 (), txParams);

  SendMpduWithProtection (mpdu, txParams);

  return true;
}

Ptr<WifiMacQueueItem>
FrameExchangeManager::GetFirstFragmentIfNeeded (Ptr<WifiMacQueueItem> mpdu)
{
  NS_LOG_FUNCTION (this << *mpdu);

  if (mpdu->IsFragment ())
    {
      // a fragment cannot be further fragmented
      NS_ASSERT (m_fragmentedPacket != 0);
    }
  else if (m_mac->GetWifiRemoteStationManager ()->NeedFragmentation (mpdu))
    {
      NS_LOG_DEBUG ("Fragmenting the MSDU");
      m_fragmentedPacket = mpdu->GetPacket ()->Copy ();
      // dequeue the MSDU
      WifiMacQueueItem::QueueIteratorPair queueIt = mpdu->GetQueueIteratorPairs ().front ();
      queueIt.queue->Dequeue (queueIt.it);
      // create the first fragment
      mpdu->GetHeader ().SetMoreFragments ();
      Ptr<Packet> fragment = m_fragmentedPacket->CreateFragment (0, m_mac->GetWifiRemoteStationManager ()->GetFragmentSize (mpdu, 0));
      // enqueue the first fragment
      Ptr<WifiMacQueueItem> item = Create<WifiMacQueueItem> (fragment, mpdu->GetHeader (), mpdu->GetTimeStamp ());
      queueIt.queue->PushFront (item);
      return item;
    }
  return mpdu;
}

void
FrameExchangeManager::SendMpduWithProtection (Ptr<WifiMacQueueItem> mpdu, WifiTxParameters& txParams)
{
  NS_LOG_FUNCTION (this << *mpdu << &txParams);

  m_mpdu = mpdu;
  m_txParams = std::move (txParams);

  // If protection is required, the MPDU must be stored in some queue because
  // it is not put back in a queue if the RTS/CTS exchange fails
  NS_ASSERT (m_txParams.m_protection->method == WifiProtection::NONE
             || m_mpdu->GetHeader ().IsCtl ()
             || m_mpdu->IsQueued ());

  // Make sure that the acknowledgment time has been computed, so that SendRts()
  // and SendCtsToSelf() can reuse this value.
  NS_ASSERT (m_txParams.m_acknowledgment);

  if (m_txParams.m_acknowledgment->acknowledgmentTime == Time::Min ())
    {
      CalculateAcknowledgmentTime (m_txParams.m_acknowledgment.get ());
    }

  // Set QoS Ack policy if this is a QoS data frame
  WifiAckManager::SetQosAckPolicy (m_mpdu, m_txParams.m_acknowledgment.get ());

  switch (m_txParams.m_protection->method)
    {
    case WifiProtection::RTS_CTS:
      SendRts (m_txParams);
      break;
    case WifiProtection::CTS_TO_SELF:
      SendCtsToSelf (m_txParams);
      break;
    case WifiProtection::NONE:
      SendMpdu ();
      break;
    default:
      NS_ABORT_MSG ("Unknown protection type");
    }
}

void
FrameExchangeManager::SendMpdu (void)
{
  NS_LOG_FUNCTION (this);

  Time txDuration = m_phy->CalculateTxDuration (m_mpdu->GetSize (), m_txParams.m_txVector, m_phy->GetPhyBand ());

  NS_ASSERT (m_txParams.m_acknowledgment);

  if (m_txParams.m_acknowledgment->method == WifiAcknowledgment::NONE)
    {
      Simulator::Schedule (txDuration, &FrameExchangeManager::TransmissionSucceeded, this);
    }
  else if (m_txParams.m_acknowledgment->method == WifiAcknowledgment::NORMAL_ACK)
    {
      m_mpdu->GetHeader ().SetDuration (GetFrameDurationId (m_mpdu->GetHeader (), m_mpdu->GetSize (),
                                                            m_txParams, m_fragmentedPacket));

      // 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.
      WifiNormalAck* normalAcknowledgment = static_cast<WifiNormalAck*> (m_txParams.m_acknowledgment.get ());

      Time timeout = txDuration
                    + m_phy->GetSifs ()
                    + m_phy->GetSlot ()
                    + m_phy->CalculatePhyPreambleAndHeaderDuration (normalAcknowledgment->ackTxVector);
      NS_ASSERT (!m_txTimer.IsRunning ());
      m_txTimer.Set (WifiTxTimer::WAIT_NORMAL_ACK, timeout, &FrameExchangeManager::NormalAckTimeout,
                     this, m_mpdu, m_txParams.m_txVector);
      m_channelAccessManager->NotifyAckTimeoutStartNow (timeout);
    }
  else
    {
      NS_ABORT_MSG ("Unable to handle the selected acknowledgment method ("
                    << m_txParams.m_acknowledgment.get () << ")");
    }

  // transmit the MPDU
  ForwardMpduDown (m_mpdu, m_txParams.m_txVector);

  if (m_txParams.m_acknowledgment->method == WifiAcknowledgment::NONE)
    {
      // we are done with frames that do not require acknowledgment
      m_mpdu = 0;
    }
}

void
FrameExchangeManager::ForwardMpduDown (Ptr<WifiMacQueueItem> mpdu, WifiTxVector& txVector)
{
  NS_LOG_FUNCTION (this << *mpdu << txVector);

  // The MPDU is about to be transmitted, we can now dequeue it if it is stored in a queue
  DequeueMpdu (mpdu);

  m_phy->Send (Create<WifiPsdu> (mpdu, false), txVector);
}

void
FrameExchangeManager::DequeueMpdu (Ptr<WifiMacQueueItem> mpdu)
{
  NS_LOG_DEBUG (this << *mpdu);

  if (mpdu->IsQueued ())
    {
      WifiMacQueueItem::QueueIteratorPair queueIt = mpdu->GetQueueIteratorPairs ().front ();
      NS_ASSERT (*queueIt.it == mpdu);
      queueIt.queue->Dequeue (queueIt.it);
    }
}

void
FrameExchangeManager::CalculateProtectionTime (WifiProtection* protection) const
{
  NS_LOG_FUNCTION (this << protection);
  NS_ASSERT (protection != nullptr);

  if (protection->method == WifiProtection::NONE)
    {
      protection->protectionTime = Seconds (0);
    }
  else if (protection->method == WifiProtection::RTS_CTS)
    {
      WifiRtsCtsProtection* rtsCtsProtection = static_cast<WifiRtsCtsProtection*> (protection);
      rtsCtsProtection->protectionTime = m_phy->CalculateTxDuration (GetRtsSize (), rtsCtsProtection->rtsTxVector,
                                                                     m_phy->GetPhyBand ())
                                         + m_phy->CalculateTxDuration (GetCtsSize (), rtsCtsProtection->ctsTxVector,
                                                                       m_phy->GetPhyBand ())
                                         + 2 * m_phy->GetSifs ();
    }
  else if (protection->method == WifiProtection::CTS_TO_SELF)
    {
      WifiCtsToSelfProtection* ctsToSelfProtection = static_cast<WifiCtsToSelfProtection*> (protection);
      ctsToSelfProtection->protectionTime = m_phy->CalculateTxDuration (GetCtsSize (),
                                                                        ctsToSelfProtection->ctsTxVector,
                                                                        m_phy->GetPhyBand ())
                                            + m_phy->GetSifs ();
    }
}

void
FrameExchangeManager::CalculateAcknowledgmentTime (WifiAcknowledgment* acknowledgment) const
{
  NS_LOG_FUNCTION (this << acknowledgment);
  NS_ASSERT (acknowledgment != nullptr);

  if (acknowledgment->method == WifiAcknowledgment::NONE)
    {
      acknowledgment->acknowledgmentTime = Seconds (0);
    }
  else if (acknowledgment->method == WifiAcknowledgment::NORMAL_ACK)
    {
      WifiNormalAck* normalAcknowledgment = static_cast<WifiNormalAck*> (acknowledgment);
      normalAcknowledgment->acknowledgmentTime = m_phy->GetSifs ()
                                                 + m_phy->CalculateTxDuration (GetAckSize (),
                                                                               normalAcknowledgment->ackTxVector,
                                                                               m_phy->GetPhyBand ());
    }
}

Time
FrameExchangeManager::GetTxDuration (uint32_t ppduPayloadSize, Mac48Address receiver,
                                     const WifiTxParameters& txParams) const
{
  return m_phy->CalculateTxDuration (ppduPayloadSize, txParams.m_txVector, m_phy->GetPhyBand ());
}

void
FrameExchangeManager::UpdateTxDuration (Mac48Address receiver, WifiTxParameters& txParams) const
{
  txParams.m_txDuration = GetTxDuration (txParams.GetSize (receiver), receiver, txParams);
}

Time
FrameExchangeManager::GetFrameDurationId (const WifiMacHeader& header, uint32_t size,
                                          const WifiTxParameters& txParams,
                                          Ptr<Packet> fragmentedPacket) const
{
  NS_LOG_FUNCTION (this << header << size << &txParams << fragmentedPacket);

  NS_ASSERT (txParams.m_acknowledgment && txParams.m_acknowledgment->acknowledgmentTime != Time::Min ());
  Time durationId = txParams.m_acknowledgment->acknowledgmentTime;

  // if the current frame is a fragment followed by another fragment, we have to
  // update the Duration/ID to cover the next fragment and the corresponding Ack
  if (header.IsMoreFragments ())
    {
      uint32_t payloadSize = size - header.GetSize () - WIFI_MAC_FCS_LENGTH;
      uint32_t nextFragmentOffset = (header.GetFragmentNumber () + 1) * payloadSize;
      uint32_t nextFragmentSize = std::min (fragmentedPacket->GetSize () - nextFragmentOffset,
                                            payloadSize);
      WifiTxVector ackTxVector = m_mac->GetWifiRemoteStationManager ()->GetAckTxVector (header.GetAddr1 (),
                                                                                        txParams.m_txVector);

      durationId += 2 * m_phy->GetSifs ()
                    + m_phy->CalculateTxDuration (GetAckSize (), ackTxVector, m_phy->GetPhyBand ())
                    + m_phy->CalculateTxDuration (nextFragmentSize, txParams.m_txVector, m_phy->GetPhyBand ());
    }
  return durationId;
}

Time
FrameExchangeManager::GetRtsDurationId (const WifiTxVector& rtsTxVector, Time txDuration, Time response) const
{
  NS_LOG_FUNCTION (this << rtsTxVector << txDuration << response);

  WifiTxVector ctsTxVector;
  ctsTxVector = m_mac->GetWifiRemoteStationManager ()->GetCtsTxVector (m_self, rtsTxVector.GetMode ());

  return m_phy->GetSifs ()
         + m_phy->CalculateTxDuration (GetCtsSize (), ctsTxVector, m_phy->GetPhyBand ()) /* CTS */
         + m_phy->GetSifs () + txDuration + response;
}

void
FrameExchangeManager::SendRts (const WifiTxParameters& txParams)
{
  NS_LOG_FUNCTION (this << &txParams);

  NS_ASSERT (txParams.GetPsduInfoMap ().size () == 1);
  Mac48Address receiver = txParams.GetPsduInfoMap ().begin ()->first;

  WifiMacHeader rts;
  rts.SetType (WIFI_MAC_CTL_RTS);
  rts.SetDsNotFrom ();
  rts.SetDsNotTo ();
  rts.SetNoRetry ();
  rts.SetNoMoreFragments ();
  rts.SetAddr1 (receiver);
  rts.SetAddr2 (m_self);

  NS_ASSERT (txParams.m_protection && txParams.m_protection->method == WifiProtection::RTS_CTS);
  WifiRtsCtsProtection* rtsCtsProtection = static_cast<WifiRtsCtsProtection*> (txParams.m_protection.get ());

  NS_ASSERT (txParams.m_txDuration != Time::Min ());
  rts.SetDuration (GetRtsDurationId (rtsCtsProtection->rtsTxVector, txParams.m_txDuration,
                                      txParams.m_acknowledgment->acknowledgmentTime));
  Ptr<WifiMacQueueItem> mpdu = Create<WifiMacQueueItem> (Create<Packet> (), rts);

  // 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 timeout = m_phy->CalculateTxDuration (GetRtsSize (), rtsCtsProtection->rtsTxVector, m_phy->GetPhyBand ())
                 + m_phy->GetSifs ()
                 + m_phy->GetSlot ()
                 + m_phy->CalculatePhyPreambleAndHeaderDuration (rtsCtsProtection->ctsTxVector);
  NS_ASSERT (!m_txTimer.IsRunning ());
  m_txTimer.Set (WifiTxTimer::WAIT_CTS, timeout, &FrameExchangeManager::CtsTimeout, this,
                 mpdu, rtsCtsProtection->rtsTxVector);
  m_channelAccessManager->NotifyCtsTimeoutStartNow (timeout);

  ForwardMpduDown (mpdu, rtsCtsProtection->rtsTxVector);
}

void
FrameExchangeManager::DoSendCtsAfterRts (const WifiMacHeader& rtsHdr, WifiTxVector& ctsTxVector,
                                         double rtsSnr)
{
  NS_LOG_FUNCTION (this << rtsHdr << ctsTxVector << rtsSnr);

  WifiMacHeader cts;
  cts.SetType (WIFI_MAC_CTL_CTS);
  cts.SetDsNotFrom ();
  cts.SetDsNotTo ();
  cts.SetNoMoreFragments ();
  cts.SetNoRetry ();
  cts.SetAddr1 (rtsHdr.GetAddr2 ());
  Time duration = rtsHdr.GetDuration () - m_phy->GetSifs ()
                  - m_phy->CalculateTxDuration (GetCtsSize (), ctsTxVector, m_phy->GetPhyBand ());
  // The TXOP holder may exceed the TXOP limit in some situations (Sec. 10.22.2.8 of 802.11-2016)
  if (duration.IsStrictlyNegative ())
    {
      duration = Seconds (0);
    }
  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)
  ForwardMpduDown (Create<WifiMacQueueItem> (packet, cts), ctsTxVector);
}

void
FrameExchangeManager::SendCtsAfterRts (const WifiMacHeader& rtsHdr, WifiMode rtsTxMode, double rtsSnr)
{
  NS_LOG_FUNCTION (this << rtsHdr << rtsTxMode << rtsSnr);

  WifiTxVector ctsTxVector = m_mac->GetWifiRemoteStationManager ()->GetCtsTxVector (rtsHdr.GetAddr2 (), rtsTxMode);
  DoSendCtsAfterRts (rtsHdr, ctsTxVector, rtsSnr);
}

Time
FrameExchangeManager::GetCtsToSelfDurationId (const WifiTxVector& ctsTxVector,
                                               Time txDuration, Time response) const
{
  NS_LOG_FUNCTION (this << ctsTxVector << txDuration << response);

  return m_phy->GetSifs () + txDuration + response;
}

void
FrameExchangeManager::SendCtsToSelf (const WifiTxParameters& txParams)
{
  NS_LOG_FUNCTION (this << &txParams);

  WifiMacHeader cts;
  cts.SetType (WIFI_MAC_CTL_CTS);
  cts.SetDsNotFrom ();
  cts.SetDsNotTo ();
  cts.SetNoMoreFragments ();
  cts.SetNoRetry ();
  cts.SetAddr1 (m_self);

  NS_ASSERT (txParams.m_protection && txParams.m_protection->method == WifiProtection::CTS_TO_SELF);
  WifiCtsToSelfProtection* ctsToSelfProtection = static_cast<WifiCtsToSelfProtection*> (txParams.m_protection.get ());

  NS_ASSERT (txParams.m_txDuration != Time::Min ());
  cts.SetDuration (GetCtsToSelfDurationId (ctsToSelfProtection->ctsTxVector, txParams.m_txDuration,
                                            txParams.m_acknowledgment->acknowledgmentTime));

  ForwardMpduDown (Create<WifiMacQueueItem> (Create<Packet> (), cts), ctsToSelfProtection->ctsTxVector);

  Time ctsDuration = m_phy->CalculateTxDuration (GetCtsSize (), ctsToSelfProtection->ctsTxVector,
                                                 m_phy->GetPhyBand ());
  Simulator::Schedule (ctsDuration + m_phy->GetSifs (), &FrameExchangeManager::SendMpdu, this);
}

void
FrameExchangeManager::SendNormalAck (const WifiMacHeader& hdr, const WifiTxVector& dataTxVector,
                                     double dataSnr)
{
  NS_LOG_FUNCTION (this << hdr << dataTxVector << dataSnr);

  WifiTxVector ackTxVector = m_mac->GetWifiRemoteStationManager ()->GetAckTxVector (hdr.GetAddr2 (), dataTxVector);
  WifiMacHeader ack;
  ack.SetType (WIFI_MAC_CTL_ACK);
  ack.SetDsNotFrom ();
  ack.SetDsNotTo ();
  ack.SetNoRetry ();
  ack.SetNoMoreFragments ();
  ack.SetAddr1 (hdr.GetAddr2 ());
  // 802.11-2016, Section 9.2.5.7: Duration/ID is received duration value
  // minus the time to transmit the Ack frame and its SIFS interval
  Time duration = hdr.GetDuration () - m_phy->GetSifs ()
                  - m_phy->CalculateTxDuration (GetAckSize (), ackTxVector, m_phy->GetPhyBand ());
  // The TXOP holder may exceed the TXOP limit in some situations (Sec. 10.22.2.8 of 802.11-2016)
  if (duration.IsStrictlyNegative ())
    {
      duration = Seconds (0);
    }
  ack.SetDuration (duration);

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

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

  ForwardMpduDown (Create<WifiMacQueueItem> (packet, ack), ackTxVector);
}

Ptr<WifiMacQueueItem>
FrameExchangeManager::GetNextFragment (void)
{
  NS_LOG_FUNCTION (this);
  NS_ASSERT (m_mpdu->GetHeader ().IsMoreFragments ());

  WifiMacHeader& hdr = m_mpdu->GetHeader ();
  hdr.SetFragmentNumber (hdr.GetFragmentNumber () + 1);

  uint32_t startOffset = hdr.GetFragmentNumber () * m_mpdu->GetPacketSize ();
  uint32_t size = m_fragmentedPacket->GetSize () - startOffset;

  if (size > m_mpdu->GetPacketSize ())
    {
      // this is not the last fragment
      size = m_mpdu->GetPacketSize ();
      hdr.SetMoreFragments ();
    }
  else
    {
      hdr.SetNoMoreFragments ();
    }

  return Create<WifiMacQueueItem> (m_fragmentedPacket->CreateFragment (startOffset, size), hdr);
}

void
FrameExchangeManager::TransmissionSucceeded (void)
{
  NS_LOG_FUNCTION (this);

  // Upon a transmission success, a non-QoS station transmits the next fragment,
  // if any, or releases the channel, otherwise
  if (m_moreFragments)
    {
      NS_LOG_DEBUG ("Schedule transmission of next fragment in a SIFS");
      Simulator::Schedule (m_phy->GetSifs (), &FrameExchangeManager::StartTransmission, this, m_dcf);
      m_moreFragments = false;
    }
  else
    {
      m_dcf->NotifyChannelReleased ();
      m_dcf = 0;
    }
}

void
FrameExchangeManager::TransmissionFailed (void)
{
  NS_LOG_FUNCTION (this);
  // A non-QoS station always releases the channel upon a transmission failure
  m_dcf->NotifyChannelReleased ();
  m_dcf = 0;
}

void
FrameExchangeManager::NormalAckTimeout (Ptr<WifiMacQueueItem> mpdu, const WifiTxVector& txVector)
{
  NS_LOG_FUNCTION (this << *mpdu << txVector);

  m_mac->GetWifiRemoteStationManager ()->ReportDataFailed (mpdu);

  if (!m_mac->GetWifiRemoteStationManager ()->NeedRetransmission (mpdu))
    {
      NS_LOG_DEBUG ("Missed Ack, discard MPDU");
      NotifyPacketDiscarded (mpdu);
      m_mac->GetWifiRemoteStationManager ()->ReportFinalDataFailed (mpdu);
      m_dcf->ResetCw ();
    }
  else
    {
      NS_LOG_DEBUG ("Missed Ack, retransmit MPDU");
      mpdu->GetHeader ().SetRetry ();
      RetransmitMpduAfterMissedAck (mpdu);
      m_dcf->UpdateFailedCw ();
    }

  m_mpdu = 0;
  TransmissionFailed ();
}

void
FrameExchangeManager::RetransmitMpduAfterMissedAck (Ptr<WifiMacQueueItem> mpdu) const
{
  NS_LOG_FUNCTION (this << *mpdu);

  // insert the MPDU in the DCF queue again
  m_dcf->GetWifiMacQueue ()->PushFront (mpdu);
}

void
FrameExchangeManager::CtsTimeout (Ptr<WifiMacQueueItem> rts, const WifiTxVector& txVector)
{
  NS_LOG_FUNCTION (this << *rts << txVector);

  m_mac->GetWifiRemoteStationManager ()->ReportRtsFailed (m_mpdu->GetHeader ());

  if (!m_mac->GetWifiRemoteStationManager ()->NeedRetransmission (m_mpdu))
    {
      NS_LOG_DEBUG ("Missed CTS, discard MPDU");
      // Dequeue the MPDU if it is stored in a queue
      DequeueMpdu (m_mpdu);
      NotifyPacketDiscarded (m_mpdu);
      m_mac->GetWifiRemoteStationManager ()->ReportFinalRtsFailed (m_mpdu->GetHeader ());
      m_dcf->ResetCw ();
    }
  else
    {
      NS_LOG_DEBUG ("Missed CTS, retransmit RTS");
      RetransmitMpduAfterMissedCts (m_mpdu);
      m_dcf->UpdateFailedCw ();
    }
  m_mpdu = 0;
  TransmissionFailed ();
}

void
FrameExchangeManager::RetransmitMpduAfterMissedCts (Ptr<WifiMacQueueItem> mpdu) const
{
  NS_LOG_FUNCTION (this << *mpdu);

  // the MPDU should be still in the DCF queue, unless it expired.
  // If the MPDU has never been transmitted, it will be assigned a sequence
  // number again the next time we try to transmit it. Therefore, we need to
  // make its sequence number available again
  if (!mpdu->GetHeader ().IsRetry ())
    {
      m_txMiddle->SetSequenceNumberFor (&mpdu->GetHeader ());
    }
}

void
FrameExchangeManager::NotifySwitchingStartNow (Time duration)
{
  NS_LOG_DEBUG ("Switching channel. Cancelling MAC pending events");
  m_mac->GetWifiRemoteStationManager ()->Reset ();
  Reset ();
}

void
FrameExchangeManager::NotifySleepNow (void)
{
  NS_LOG_DEBUG ("Device in sleep mode. Cancelling MAC pending events");
  Reset ();
}

void
FrameExchangeManager::NotifyOffNow (void)
{
  NS_LOG_DEBUG ("Device is switched off. Cancelling MAC pending events");
  Reset ();
}

void
FrameExchangeManager::Receive (Ptr<WifiPsdu> psdu, RxSignalInfo rxSignalInfo,
                               WifiTxVector txVector, std::vector<bool> perMpduStatus)
{
  NS_LOG_FUNCTION (this << psdu << rxSignalInfo << txVector << perMpduStatus.size ()
                   << std::all_of (perMpduStatus.begin(), perMpduStatus.end(), [](bool v) { return v; }));

  if (!perMpduStatus.empty ())
    {
      // for A-MPDUs, we get here only once
      PreProcessFrame (psdu, txVector);
    }

  // ignore unicast frames that are not addressed to us
  Mac48Address addr1 = psdu->GetAddr1 ();
  if (!addr1.IsGroup () && addr1 != m_self)
    {
      if (m_promisc && psdu->GetNMpdus () == 1 && psdu->GetHeader (0).IsData ())
        {
          m_rxMiddle->Receive (*psdu->begin ());
        }
      return;
    }

  if (psdu->GetNMpdus () == 1)
    {
      // if perMpduStatus is not empty (i.e., this MPDU is not included in an A-MPDU)
      // then it must contain a single value which must be true (i.e., the MPDU
      // has been correctly received)
      NS_ASSERT (perMpduStatus.empty () || (perMpduStatus.size () == 1 && perMpduStatus[0]));
      // Ack and CTS do not carry Addr2
      if (!psdu->GetHeader (0).IsAck () && !psdu->GetHeader (0).IsCts ())
        {
          m_mac->GetWifiRemoteStationManager ()->ReportRxOk (psdu->GetHeader (0).GetAddr2 (),
                                                             rxSignalInfo, txVector);
        }
      ReceiveMpdu (*(psdu->begin ()), rxSignalInfo, txVector, perMpduStatus.empty ());
    }
  else
    {
      EndReceiveAmpdu (psdu, rxSignalInfo, txVector, perMpduStatus);
    }
}

void
FrameExchangeManager::PreProcessFrame (Ptr<const WifiPsdu> psdu, const WifiTxVector& txVector)
{
  NS_LOG_FUNCTION (this << psdu << txVector);

  UpdateNav (psdu, txVector);
}

void
FrameExchangeManager::UpdateNav (Ptr<const WifiPsdu> psdu, const WifiTxVector& txVector)
{
  NS_LOG_FUNCTION (this << psdu << txVector);

  if (psdu->GetHeader (0).GetRawDuration () > 32767)
    {
      // When the contents of a received Duration/ID field, treated as an unsigned
      // integer, are greater than 32 768, the contents are interpreted as appropriate
      // for the frame type and subtype or ignored if the receiving MAC entity does
      // not have a defined interpretation for that type and subtype (IEEE 802.11-2016
      // sec. 10.27.3)
      return;
    }

  Time duration = psdu->GetDuration ();
  NS_LOG_DEBUG ("Duration/ID=" << duration);

  if (psdu->GetAddr1 () == m_self)
    {
      // When the received frame’s RA is equal to the STA’s own MAC address, the STA
      // shall not update its NAV (IEEE 802.11-2016, sec. 10.3.2.4)
      return;
    }

  // For all other received frames the STA shall update its NAV when the received
  // Duration is greater than the STA’s current NAV value (IEEE 802.11-2016 sec. 10.3.2.4)
  Time navEnd = Simulator::Now () + duration;
  if (navEnd > m_navEnd)
    {
      m_navEnd = navEnd;
      NS_LOG_DEBUG ("Updated NAV=" << m_navEnd);

      // A STA that used information from an RTS frame as the most recent basis to update
      // its NAV setting is permitted to reset its NAV if no PHY-RXSTART.indication
      // primitive is received from the PHY during a NAVTimeout period starting when the
      // MAC receives a PHY-RXEND.indication primitive corresponding to the detection of
      // the RTS frame. NAVTimeout period is equal to:
      // (2 x aSIFSTime) + (CTS_Time) + aRxPHYStartDelay + (2 x aSlotTime)
      // The “CTS_Time” shall be calculated using the length of the CTS frame and the data
      // rate at which the RTS frame used for the most recent NAV update was received
      // (IEEE 802.11-2016 sec. 10.3.2.4)
      if (psdu->GetHeader (0).IsRts ())
        {
          Time navResetDelay = 2 * m_phy->GetSifs ()
                               + WifiPhy::CalculateTxDuration (GetCtsSize (), txVector,
                                                               m_phy->GetPhyBand ())
                               + m_phy->CalculatePhyPreambleAndHeaderDuration (txVector)
                               + 2 * m_phy->GetSlot ();
          m_navResetEvent = Simulator::Schedule (navResetDelay, &FrameExchangeManager::NavResetTimeout, this);
        }
    }

  m_channelAccessManager->NotifyNavStartNow (duration);
}

void
FrameExchangeManager::NavResetTimeout (void)
{
  m_navEnd = Simulator::Now ();
  m_channelAccessManager->NotifyNavResetNow (Seconds (0));
}

void
FrameExchangeManager::ReceiveMpdu (Ptr<WifiMacQueueItem> mpdu, RxSignalInfo rxSignalInfo,
                                   const WifiTxVector& txVector, bool inAmpdu)
{
  NS_LOG_FUNCTION (this << *mpdu << rxSignalInfo << txVector << inAmpdu);
  // The received MPDU is either broadcast or addressed to this station
  NS_ASSERT (mpdu->GetHeader ().GetAddr1 ().IsGroup ()
             || mpdu->GetHeader ().GetAddr1 () == m_self);

  double rxSnr = rxSignalInfo.snr;
  const WifiMacHeader& hdr = mpdu->GetHeader ();

  if (hdr.IsCtl ())
    {
      if (hdr.IsRts ())
        {
          NS_ABORT_MSG_IF (inAmpdu, "Received RTS as part of an A-MPDU");

          // A non-VHT STA that is addressed by an RTS frame behaves as follows:
          // - If the NAV indicates idle, the STA shall respond with a CTS frame after a SIFS
          // - Otherwise, the STA shall not respond with a CTS frame
          // (IEEE 802.11-2016 sec. 10.3.2.7)
          if (m_navEnd <= Simulator::Now ())
            {
              NS_LOG_DEBUG ("Received RTS from=" << hdr.GetAddr2 () << ", schedule CTS");
              Simulator::Schedule (m_phy->GetSifs (), &FrameExchangeManager::SendCtsAfterRts,
                                   this, hdr, txVector.GetMode (), rxSnr);
            }
          else
            {
              NS_LOG_DEBUG ("Received RTS from=" << hdr.GetAddr2 () << ", cannot schedule CTS");
            }
        }
      else if (hdr.IsCts () && m_txTimer.IsRunning () && m_txTimer.GetReason () == WifiTxTimer::WAIT_CTS
               && m_mpdu != 0)
        {
          NS_ABORT_MSG_IF (inAmpdu, "Received CTS as part of an A-MPDU");
          NS_ASSERT (hdr.GetAddr1 () == m_self);

          Mac48Address sender = m_mpdu->GetHeader ().GetAddr1 ();
          NS_LOG_DEBUG ("Received CTS from=" << sender);

          SnrTag tag;
          mpdu->GetPacket ()->PeekPacketTag (tag);
          m_mac->GetWifiRemoteStationManager ()->ReportRxOk (sender, rxSignalInfo, txVector);
          m_mac->GetWifiRemoteStationManager ()->ReportRtsOk (m_mpdu->GetHeader (),
                                                              rxSnr, txVector.GetMode (), tag.Get ());

          m_txTimer.Cancel ();
          m_channelAccessManager->NotifyCtsTimeoutResetNow ();
          Simulator::Schedule (m_phy->GetSifs (), &FrameExchangeManager::SendMpdu, this);
        }
      else if (hdr.IsAck () && m_mpdu != 0 && m_txTimer.IsRunning ()
               && m_txTimer.GetReason () == WifiTxTimer::WAIT_NORMAL_ACK)
        {
          NS_ASSERT (hdr.GetAddr1 () == m_self);
          SnrTag tag;
          mpdu->GetPacket ()->PeekPacketTag (tag);
          ReceivedNormalAck (m_mpdu, m_txParams.m_txVector, txVector, rxSignalInfo, tag.Get ());
          m_mpdu = 0;
        }
    }
  else if (hdr.IsMgt ())
    {
      NS_ABORT_MSG_IF (inAmpdu, "Received management frame as part of an A-MPDU");

      if (hdr.IsBeacon () || hdr.IsProbeResp ())
        {
          // Apply SNR tag for beacon quality measurements
          SnrTag tag;
          tag.Set (rxSnr);
          Ptr<Packet> packet = mpdu->GetPacket ()->Copy ();
          packet->AddPacketTag (tag);
          mpdu = Create<WifiMacQueueItem> (packet, hdr);
        }

      if (hdr.GetAddr1 () == m_self)
        {
          NS_LOG_DEBUG ("Received " << hdr.GetTypeString () << " from=" << hdr.GetAddr2 () << ", schedule ACK");
          Simulator::Schedule (m_phy->GetSifs (), &FrameExchangeManager::SendNormalAck,
                               this, hdr, txVector, rxSnr);
        }

      m_rxMiddle->Receive (mpdu);
    }
  else if (hdr.IsData () && !hdr.IsQosData ())
    {
      if (hdr.GetAddr1 () == m_self)
        {
          NS_LOG_DEBUG ("Received " << hdr.GetTypeString () << " from=" << hdr.GetAddr2 () << ", schedule ACK");
          Simulator::Schedule (m_phy->GetSifs (), &FrameExchangeManager::SendNormalAck,
                               this, hdr, txVector, rxSnr);
        }

      m_rxMiddle->Receive (mpdu);
    }
}

void
FrameExchangeManager::ReceivedNormalAck (Ptr<WifiMacQueueItem> mpdu, const WifiTxVector& txVector,
                                         const WifiTxVector& ackTxVector, const RxSignalInfo& rxInfo,
                                         double snr)
{
  Mac48Address sender = mpdu->GetHeader ().GetAddr1 ();
  NS_LOG_DEBUG ("Received ACK from=" << sender);

  NotifyReceivedNormalAck (mpdu);

  // When fragmentation is used, only update manager when the last fragment is acknowledged
  if (!mpdu->GetHeader ().IsMoreFragments ())
    {
      m_mac->GetWifiRemoteStationManager ()->ReportRxOk (sender, rxInfo, ackTxVector);
      m_mac->GetWifiRemoteStationManager ()->ReportDataOk (mpdu, rxInfo.snr, ackTxVector.GetMode (),
                                                           snr, txVector);
    }
  // cancel the timer
  m_txTimer.Cancel ();
  m_channelAccessManager->NotifyAckTimeoutResetNow ();

  // The CW shall be reset to aCWmin after every successful attempt to transmit
  // a frame containing all or part of an MSDU or MMPDU (sec. 10.3.3 of 802.11-2016)
  m_dcf->ResetCw ();

  if (mpdu->GetHeader ().IsMoreFragments ())
    {
      // enqueue the next fragment
      Ptr<WifiMacQueueItem> next = GetNextFragment ();
      m_dcf->GetWifiMacQueue ()->PushFront (next);
      m_moreFragments = true;
    }

  TransmissionSucceeded ();
}

void
FrameExchangeManager::NotifyReceivedNormalAck (Ptr<WifiMacQueueItem> mpdu)
{
  NS_LOG_FUNCTION (this << *mpdu);

  // inform the MAC that the transmission was successful
  if (!m_ackedMpduCallback.IsNull ())
    {
      m_ackedMpduCallback (mpdu);
    }
}

void
FrameExchangeManager::EndReceiveAmpdu (Ptr<const WifiPsdu> psdu, const RxSignalInfo& rxSignalInfo,
                                       const WifiTxVector& txVector, const std::vector<bool>& perMpduStatus)
{
  NS_ASSERT_MSG (false, "A non-QoS station should not receive an A-MPDU");
}

} //namespace ns3