/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */

/*

 * Copyright (c) 2005,2006 INRIA

 *

 * 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: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>

 */

#include "yans-wifi-phy.h"

#include "yans-wifi-channel.h"

#include "wifi-mode.h"

#include "wifi-preamble.h"

#include "wifi-phy-state-helper.h"

#include "error-rate-model.h"

#include "ns3/simulator.h"

#include "ns3/packet.h"

#include "ns3/random-variable.h"

#include "ns3/assert.h"

#include "ns3/log.h"

#include "ns3/double.h"

#include "ns3/uinteger.h"

#include "ns3/enum.h"

#include "ns3/pointer.h"

#include "ns3/net-device.h"

#include "ns3/trace-source-accessor.h"

#include <math.h>

NS_LOG_COMPONENT_DEFINE ("YansWifiPhy");

namespace ns3 {

NS_OBJECT_ENSURE_REGISTERED (YansWifiPhy);

TypeId 

YansWifiPhy::GetTypeId (void)

{

  static TypeId tid = TypeId ("ns3::YansWifiPhy")

    .SetParent<WifiPhy> ()

    .AddConstructor<YansWifiPhy> ()

    .AddAttribute ("EnergyDetectionThreshold",

                   "The energy of a received signal should be higher than "

                   "this threshold (dbm) to allow the PHY layer to detect the signal.",

                   DoubleValue (-96.0),

                   MakeDoubleAccessor (&YansWifiPhy::SetEdThreshold,

                                       &YansWifiPhy::GetEdThreshold),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("CcaMode1Threshold",

                   "The energy of a received signal should be higher than "

                   "this threshold (dbm) to allow the PHY layer to declare CCA BUSY state",

                   DoubleValue (-99.0),

                   MakeDoubleAccessor (&YansWifiPhy::SetCcaMode1Threshold,

                                       &YansWifiPhy::GetCcaMode1Threshold),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("TxGain",

                   "Transmission gain (dB).",

                   DoubleValue (1.0),

                   MakeDoubleAccessor (&YansWifiPhy::SetTxGain,

                                       &YansWifiPhy::GetTxGain),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("RxGain",

                   "Reception gain (dB).",

                   DoubleValue (1.0),

                   MakeDoubleAccessor (&YansWifiPhy::SetRxGain,

                                       &YansWifiPhy::GetRxGain),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("TxPowerLevels",

                   "Number of transmission power levels available between "

                   "TxPowerBase and TxPowerEnd included.",

                   UintegerValue (1),

                   MakeUintegerAccessor (&YansWifiPhy::m_nTxPower),

                   MakeUintegerChecker<uint32_t> ())

    .AddAttribute ("TxPowerEnd",

                   "Maximum available transmission level (dbm).",

                   DoubleValue (16.0206),

                   MakeDoubleAccessor (&YansWifiPhy::SetTxPowerEnd, 

                                       &YansWifiPhy::GetTxPowerEnd),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("TxPowerStart",

                   "Minimum available transmission level (dbm).",

                   DoubleValue (16.0206),

                   MakeDoubleAccessor (&YansWifiPhy::SetTxPowerStart, 

                                       &YansWifiPhy::GetTxPowerStart),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("RxNoiseFigure",

                   "Loss (dB) in the Signal-to-Noise-Ratio due to non-idealities in the receiver."

                   " According to Wikipedia (http://en.wikipedia.org/wiki/Noise_figure), this is "

                   "\"the difference in decibels (dB) between"

                   " the noise output of the actual receiver to the noise output of an "

                   " ideal receiver with the same overall gain and bandwidth when the receivers "

                   " are connected to sources at the standard noise temperature T0 (usually 290 K)\"."

                   " For",

                   DoubleValue (7),

                   MakeDoubleAccessor (&YansWifiPhy::SetRxNoiseFigure,

                                       &YansWifiPhy::GetRxNoiseFigure),

                   MakeDoubleChecker<double> ())

    .AddAttribute ("State", "The state of the PHY layer",

                   PointerValue (),

                   MakePointerAccessor (&YansWifiPhy::m_state),

                   MakePointerChecker<WifiPhyStateHelper> ())

    .AddAttribute ("ChannelSwitchDelay",

                   "Delay between two short frames transmitted on different frequencies. NOTE: Unused now.",

                   TimeValue (MicroSeconds (250)),

                   MakeTimeAccessor (&YansWifiPhy::m_channelSwitchDelay), 

                   MakeTimeChecker ())

    .AddAttribute ("ChannelNumber",

                   "Channel center frequency = Channel starting frequency + 5 MHz * (nch - 1)",

                   UintegerValue (1),

                   MakeUintegerAccessor (&YansWifiPhy::SetChannelNumber, 

                                         &YansWifiPhy::GetChannelNumber),

                   MakeUintegerChecker<uint16_t> ())

    ;

  return tid;

}

YansWifiPhy::YansWifiPhy ()

  :  m_channelNumber (1),

     m_endSyncEvent (),

     m_random (0.0, 1.0),

     m_channelStartingFrequency (0)

{

  NS_LOG_FUNCTION (this);

  m_state = CreateObject<WifiPhyStateHelper> ();

}

YansWifiPhy::~YansWifiPhy ()

{

  NS_LOG_FUNCTION (this);

}

void

YansWifiPhy::DoDispose (void)

{

  NS_LOG_FUNCTION (this);

  m_channel = 0;

  m_modes.clear ();

  m_device = 0;

  m_mobility = 0;

  m_state = 0;

}

void

YansWifiPhy::ConfigureStandard (enum WifiPhyStandard standard)

{

  NS_LOG_FUNCTION (this << standard);

  switch (standard) {

  case WIFI_PHY_STANDARD_80211a:

    Configure80211a ();

    break;

  case WIFI_PHY_STANDARD_80211b:

    Configure80211b ();

    break;

  case WIFI_PHY_STANDARD_80211_10Mhz: 

    Configure80211_10Mhz ();

    break;

  case WIFI_PHY_STANDARD_80211_5Mhz:

    Configure80211_5Mhz ();

    break; 

  case WIFI_PHY_STANDARD_holland:

    ConfigureHolland ();

    break;

  default:

    NS_ASSERT (false);

    break;

  }

}

void 

YansWifiPhy::SetRxNoiseFigure (double noiseFigureDb)

{

  NS_LOG_FUNCTION (this << noiseFigureDb);

  m_interference.SetNoiseFigure (DbToRatio (noiseFigureDb));

}

void 

YansWifiPhy::SetTxPowerStart (double start)

{

  NS_LOG_FUNCTION (this << start);

  m_txPowerBaseDbm = start;

}

void 

YansWifiPhy::SetTxPowerEnd (double end)

{

  NS_LOG_FUNCTION (this << end);

  m_txPowerEndDbm = end;

}

void 

YansWifiPhy::SetNTxPower (uint32_t n)

{

  NS_LOG_FUNCTION (this << n);

  m_nTxPower = n;

}

void 

YansWifiPhy::SetTxGain (double gain)

{

  NS_LOG_FUNCTION (this << gain);

  m_txGainDb = gain;

}

void 

YansWifiPhy::SetRxGain (double gain)

{

  NS_LOG_FUNCTION (this << gain);

  m_rxGainDb = gain;

}

void 

YansWifiPhy::SetEdThreshold (double threshold)

{

  NS_LOG_FUNCTION (this << threshold);

  m_edThresholdW = DbmToW (threshold);

}

void 

YansWifiPhy::SetCcaMode1Threshold (double threshold)

{

  NS_LOG_FUNCTION (this << threshold);

  m_ccaMode1ThresholdW = DbmToW (threshold);

}

void 

YansWifiPhy::SetErrorRateModel (Ptr<ErrorRateModel> rate)

{

  m_interference.SetErrorRateModel (rate);

}

void 

YansWifiPhy::SetDevice (Ptr<Object> device)

{

  m_device = device;

}

void 

YansWifiPhy::SetMobility (Ptr<Object> mobility)

{

  m_mobility = mobility;

}

double 

YansWifiPhy::GetRxNoiseFigure (void) const

{

  return RatioToDb (m_interference.GetNoiseFigure ());

}

double 

YansWifiPhy::GetTxPowerStart (void) const

{

  return m_txPowerBaseDbm;

}

double 

YansWifiPhy::GetTxPowerEnd (void) const

{

  return m_txPowerEndDbm;

}

double 

YansWifiPhy::GetTxGain (void) const

{

  return m_txGainDb;

}

double 

YansWifiPhy::GetRxGain (void) const

{

  return m_rxGainDb;

}

double 

YansWifiPhy::GetEdThreshold (void) const

{

  return WToDbm (m_edThresholdW);

}

double 

YansWifiPhy::GetCcaMode1Threshold (void) const

{

  return WToDbm (m_ccaMode1ThresholdW);

}

Ptr<ErrorRateModel> 

YansWifiPhy::GetErrorRateModel (void) const

{

  return m_interference.GetErrorRateModel ();

}

Ptr<Object> 

YansWifiPhy::GetDevice (void) const

{

  return m_device;

}

Ptr<Object> 

YansWifiPhy::GetMobility (void)

{

  return m_mobility;

}

double 

YansWifiPhy::CalculateSnr (WifiMode txMode, double ber) const

{

  return m_interference.GetErrorRateModel ()->CalculateSnr (txMode, ber);

}

Ptr<WifiChannel> 

YansWifiPhy::GetChannel (void) const

{

  return m_channel;

}

void 

YansWifiPhy::SetChannel (Ptr<YansWifiChannel> channel)

{

  m_channel = channel;

  m_channel->Add (this);

}

void 

YansWifiPhy::SetChannelNumber (uint16_t nch)

{

  NS_ASSERT(!IsStateSwitching()); 

  switch (m_state->GetState ()) {

  case YansWifiPhy::SYNC:

    NS_LOG_DEBUG ("drop packet because of channel switching while reception");

    m_endSyncEvent.Cancel();

    goto switchChannel;

    break;

  case YansWifiPhy::TX:

      NS_LOG_DEBUG ("channel switching postponed until end of current transmission");

      Simulator::Schedule (GetDelayUntilIdle(), &YansWifiPhy::SetChannelNumber, this, nch);

    break;

  case YansWifiPhy::CCA_BUSY:

  case YansWifiPhy::IDLE:

    goto switchChannel;

    break;

  default:

    NS_ASSERT (false);

    break;

  }

  return;

  switchChannel: 

  NS_LOG_DEBUG("switching channel " << m_channelNumber << " -> " << nch);

  m_state->SwitchToChannelSwitching(m_channelSwitchDelay); 

  m_interference.EraseEvents(); 

  /*

   * Needed here to be able to correctly sensed the medium for the first

   * time after the switching. The actual switching is not performed until

   * after m_channelSwitchDelay. Packets received during the switching

   * state are added to the event list and are employed later to figure

   * out the state of the medium after the switching.

   */

  m_channelNumber = nch;

}

uint16_t 

YansWifiPhy::GetChannelNumber() const

{

  return m_channelNumber;

}

double

YansWifiPhy::GetChannelFrequencyMhz() const

{

  return m_channelStartingFrequency + 5 * (GetChannelNumber() - 1);

}

void 

YansWifiPhy::SetReceiveOkCallback (SyncOkCallback callback)

{

  m_state->SetReceiveOkCallback (callback);

}

void 

YansWifiPhy::SetReceiveErrorCallback (SyncErrorCallback callback)

{

  m_state->SetReceiveErrorCallback (callback);

}

void 

YansWifiPhy::StartReceivePacket (Ptr<Packet> packet, 

                                 double rxPowerDbm,

                                 WifiMode txMode,

                                 enum WifiPreamble preamble)

{

  NS_LOG_FUNCTION (this << packet << rxPowerDbm << txMode << preamble);

  rxPowerDbm += m_rxGainDb;

  double rxPowerW = DbmToW (rxPowerDbm);

  Time rxDuration = CalculateTxDuration (packet->GetSize (), txMode, preamble);

  Time endRx = Simulator::Now () + rxDuration;

  Ptr<InterferenceHelper::Event> event;

  event = m_interference.Add (packet->GetSize (), 

                              txMode,

                              preamble,

                              rxDuration,

                              rxPowerW);

  switch (m_state->GetState ()) {

  case YansWifiPhy::SWITCHING: 

    NS_LOG_DEBUG ("drop packet because of channel switching");

    NotifyRxDrop (packet);

    /*

     * Packets received on the upcoming channel are added to the event list

     * during the switching state. This way the medium can be correctly sensed

     * when the device listens to the channel for the first time after the

     * switching e.g. after channel switching, the channel may be sensed as

     * busy due to other devices' tramissions started before the end of

     * the switching.

     */

    if (endRx > Simulator::Now () + m_state->GetDelayUntilIdle ()) 

      {

        // that packet will be noise _after_ the completion of the

        // channel switching.

        goto maybeCcaBusy;

      }

    break;

  case YansWifiPhy::SYNC:

    NS_LOG_DEBUG ("drop packet because already in Sync (power="<<

                  rxPowerW<<"W)");

    NotifyRxDrop (packet);

    if (endRx > Simulator::Now () + m_state->GetDelayUntilIdle ()) 

      {

        // that packet will be noise _after_ the reception of the

        // currently-received packet.

        goto maybeCcaBusy;

      }

    break;

  case YansWifiPhy::TX:

    NS_LOG_DEBUG ("drop packet because already in Tx (power="<<

                  rxPowerW<<"W)");

    NotifyRxDrop (packet);

    if (endRx > Simulator::Now () + m_state->GetDelayUntilIdle ()) 

      {

        // that packet will be noise _after_ the transmission of the

        // currently-transmitted packet.

        goto maybeCcaBusy;

      }

    break;

  case YansWifiPhy::CCA_BUSY:

  case YansWifiPhy::IDLE:

    if (rxPowerW > m_edThresholdW) 

      {

        NS_LOG_DEBUG ("sync (power="<<rxPowerW<<"W)");

        // sync to signal

        m_state->SwitchToSync (rxDuration);

        NS_ASSERT (m_endSyncEvent.IsExpired ());

        NotifyRxBegin (packet);

        m_endSyncEvent = Simulator::Schedule (rxDuration, &YansWifiPhy::EndSync, this, 

                                              packet,

                                              event);

      }

    else 

      {

        NS_LOG_DEBUG ("drop packet because signal power too Small ("<<

                      rxPowerW<<"<"<<m_edThresholdW<<")");

        NotifyRxDrop (packet);

        goto maybeCcaBusy;

      }

    break;

  }

  return;

 maybeCcaBusy:

  // We are here because we have received the first bit of a packet and we are

  // not going to be able to synchronize on it

  // In this model, CCA becomes busy when the aggregation of all signals as

  // tracked by the InterferenceHelper class is higher than the CcaBusyThreshold

  Time delayUntilCcaEnd = m_interference.GetEnergyDuration (m_ccaMode1ThresholdW);

  if (!delayUntilCcaEnd.IsZero ())

    {

      m_state->SwitchMaybeToCcaBusy (delayUntilCcaEnd);

    }

}

void 

YansWifiPhy::SendPacket (Ptr<const Packet> packet, WifiMode txMode, WifiPreamble preamble, uint8_t txPower)

{

  NS_LOG_FUNCTION (this << packet << txMode << preamble << (uint32_t)txPower);

  /* Transmission can happen if:

   *  - we are syncing on a packet. It is the responsability of the

   *    MAC layer to avoid doing this but the PHY does nothing to 

   *    prevent it.

   *  - we are idle

   */

  NS_ASSERT (!m_state->IsStateTx () && !m_state->IsStateSwitching ());

  Time txDuration = CalculateTxDuration (packet->GetSize (), txMode, preamble);

  if (m_state->IsStateSync ())

    {

      m_endSyncEvent.Cancel ();

    }

  NotifyTxBegin (packet);

  uint32_t dataRate500KbpsUnits = txMode.GetDataRate () / 500000;   

  bool isShortPreamble = (WIFI_PREAMBLE_SHORT == preamble);

  NotifyPromiscSniffTx (packet, (uint16_t)GetChannelFrequencyMhz (), GetChannelNumber (), dataRate500KbpsUnits, isShortPreamble);

  m_state->SwitchToTx (txDuration, packet, txMode, preamble, txPower);

  m_channel->Send (this, packet, GetPowerDbm (txPower) + m_txGainDb, txMode, preamble);

}

uint32_t 

YansWifiPhy::GetNModes (void) const

{

  return m_modes.size ();

}

WifiMode 

YansWifiPhy::GetMode (uint32_t mode) const

{

  return m_modes[mode];

}

uint32_t 

YansWifiPhy::GetNTxPower (void) const

{

  return m_nTxPower;

}

void

YansWifiPhy::Configure80211a (void)

{

  NS_LOG_FUNCTION (this);

  m_channelStartingFrequency = 5e3; // 5.000 GHz 

  m_modes.push_back (WifiPhy::Get6mba ());

  m_modes.push_back (WifiPhy::Get9mba ());

  m_modes.push_back (WifiPhy::Get12mba ());

  m_modes.push_back (WifiPhy::Get18mba ());

  m_modes.push_back (WifiPhy::Get24mba ());

  m_modes.push_back (WifiPhy::Get36mba ());

  m_modes.push_back (WifiPhy::Get48mba ());

  m_modes.push_back (WifiPhy::Get54mba ());

}

void

YansWifiPhy::Configure80211b (void)

{

  NS_LOG_FUNCTION (this);

  m_channelStartingFrequency = 2412; // 2.412 GHz 

  m_modes.push_back (WifiPhy::Get1mbb ());

  m_modes.push_back (WifiPhy::Get2mbb ());

  m_modes.push_back (WifiPhy::Get5_5mbb ());

  m_modes.push_back (WifiPhy::Get11mbb ());

}

void

YansWifiPhy::Configure80211_10Mhz (void)

{

  NS_LOG_FUNCTION (this);

  m_channelStartingFrequency = 5e3; // 5.000 GHz, suppose 802.11a 

  m_modes.push_back (WifiPhy::Get3mb10Mhz ());

  m_modes.push_back (WifiPhy::Get4_5mb10Mhz ());

  m_modes.push_back (WifiPhy::Get6mb10Mhz ());

  m_modes.push_back (WifiPhy::Get9mb10Mhz ());

  m_modes.push_back (WifiPhy::Get12mb10Mhz ());

  m_modes.push_back (WifiPhy::Get18mb10Mhz ());

  m_modes.push_back (WifiPhy::Get24mb10Mhz ());

  m_modes.push_back (WifiPhy::Get27mb10Mhz  ());

}

void

YansWifiPhy::Configure80211_5Mhz (void)

{

  NS_LOG_FUNCTION (this); 

  m_channelStartingFrequency = 5e3; // 5.000 GHz, suppose 802.11a

  m_modes.push_back (WifiPhy::Get1_5mb5Mhz ());

  m_modes.push_back (WifiPhy::Get2_25mb5Mhz ());

  m_modes.push_back (WifiPhy::Get3mb5Mhz ());

  m_modes.push_back (WifiPhy::Get4_5mb5Mhz ());

  m_modes.push_back (WifiPhy::Get6mb5Mhz ());

  m_modes.push_back (WifiPhy::Get9mb5Mhz ());

  m_modes.push_back (WifiPhy::Get12mb5Mhz ());

  m_modes.push_back (WifiPhy::Get13_5mb5Mhz  ());

}

void

YansWifiPhy::ConfigureHolland (void)

{

  NS_LOG_FUNCTION (this);

  m_channelStartingFrequency = 5e3; // 5.000 GHz 

  m_modes.push_back (WifiPhy::Get6mba ());

  m_modes.push_back (WifiPhy::Get12mba ());

  m_modes.push_back (WifiPhy::Get18mba ());

  m_modes.push_back (WifiPhy::Get36mba ());

  m_modes.push_back (WifiPhy::Get54mba ());

}

void 

YansWifiPhy::RegisterListener (WifiPhyListener *listener)

{

  m_state->RegisterListener (listener);

}

bool 

YansWifiPhy::IsStateCcaBusy (void)

{

  return m_state->IsStateCcaBusy ();

}

bool 

YansWifiPhy::IsStateIdle (void)

{

  return m_state->IsStateIdle ();

}

bool 

YansWifiPhy::IsStateBusy (void)

{

  return m_state->IsStateBusy ();

}

bool 

YansWifiPhy::IsStateSync (void)

{

  return m_state->IsStateSync ();

}

bool 

YansWifiPhy::IsStateTx (void)

{

  return m_state->IsStateTx ();

}

bool 

YansWifiPhy::IsStateSwitching (void)

{

  return m_state->IsStateSwitching ();

}

Time

YansWifiPhy::GetStateDuration (void)

{

  return m_state->GetStateDuration ();

}

Time

YansWifiPhy::GetDelayUntilIdle (void)

{

  return m_state->GetDelayUntilIdle ();

}

Time 

YansWifiPhy::GetLastRxStartTime (void) const

{

  return m_state->GetLastRxStartTime ();

}

Time 

YansWifiPhy::CalculateTxDuration (uint32_t size, WifiMode payloadMode, enum WifiPreamble preamble) const

{

  return m_interference.CalculateTxDuration (size, payloadMode, preamble);

}

double 

YansWifiPhy::DbToRatio (double dB) const

{

  double ratio = pow(10.0,dB/10.0);

  return ratio;

}

double 

YansWifiPhy::DbmToW (double dBm) const

{

  double mW = pow(10.0,dBm/10.0);

  return mW / 1000.0;

}

double

YansWifiPhy::WToDbm (double w) const

{

  return 10.0 * log10(w * 1000.0);

}

double

YansWifiPhy::RatioToDb (double ratio) const

{

  return 10.0 * log10(ratio);

}

double

YansWifiPhy::GetEdThresholdW (void) const

{

  return m_edThresholdW;

}

double 

YansWifiPhy::GetPowerDbm (uint8_t power) const

{

  NS_ASSERT (m_txPowerBaseDbm <= m_txPowerEndDbm);

  NS_ASSERT (m_nTxPower > 0);

  double dbm = m_txPowerBaseDbm + power * (m_txPowerEndDbm - m_txPowerBaseDbm) / m_nTxPower;

  return dbm;

}

void

YansWifiPhy::EndSync (Ptr<Packet> packet, Ptr<InterferenceHelper::Event> event)

{

  NS_LOG_FUNCTION (this << packet << event);

  NS_ASSERT (IsStateSync ());

  NS_ASSERT (event->GetEndTime () == Simulator::Now ());

  struct InterferenceHelper::SnrPer snrPer;

  snrPer = m_interference.CalculateSnrPer (event);

  NS_LOG_DEBUG ("mode="<<(event->GetPayloadMode ().GetDataRate ())<<

                ", snr="<<snrPer.snr<<", per="<<snrPer.per<<", size="<<packet->GetSize ());

  if (m_random.GetValue () > snrPer.per) 

    {

      NotifyRxEnd (packet); 

      uint32_t dataRate500KbpsUnits = event->GetPayloadMode ().GetDataRate () / 500000;   

      bool isShortPreamble = (WIFI_PREAMBLE_SHORT == event->GetPreambleType ());  

      double signalDbm = RatioToDb (event->GetRxPowerW ()) + 30;

      double noiseDbm = RatioToDb(event->GetRxPowerW() / snrPer.snr) - GetRxNoiseFigure() + 30 ;

      NotifyPromiscSniffRx (packet, (uint16_t)GetChannelFrequencyMhz (), GetChannelNumber (), dataRate500KbpsUnits, isShortPreamble, signalDbm, noiseDbm);

      m_state->SwitchFromSyncEndOk (packet, snrPer.snr, event->GetPayloadMode (), event->GetPreambleType ());

    } 

  else 

    {

      /* failure. */

      NotifyRxDrop (packet);

      m_state->SwitchFromSyncEndError (packet, snrPer.snr);

    }

}

} // namespace ns3