msdu-aggregator.cc

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * 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
 *
 * Author: Mirko Banchi <mk.banchi@gmail.com>
 *         Stefano Avallone <stavallo@unina.it>
 */
 
#include "ns3/log.h"
#include "ns3/packet.h"
#include "msdu-aggregator.h"
#include "qos-txop.h"
#include "wifi-remote-station-manager.h"
#include "ns3/ht-capabilities.h"
#include "wifi-mac.h"
#include "wifi-mac-queue.h"
#include "wifi-mac-trailer.h"
#include "ns3/ht-frame-exchange-manager.h"
#include "wifi-tx-parameters.h"
#include <algorithm>
 
namespace ns3 {
 
NS_LOG_COMPONENT_DEFINE ("MsduAggregator");
 
NS_OBJECT_ENSURE_REGISTERED (MsduAggregator);
 
TypeId
MsduAggregator::GetTypeId (void)
{
  static TypeId tid = TypeId ("ns3::MsduAggregator")
    .SetParent<Object> ()
    .SetGroupName ("Wifi")
    .AddConstructor<MsduAggregator> ()
  ;
  return tid;
}
 
MsduAggregator::MsduAggregator ()
{
}
 
MsduAggregator::~MsduAggregator ()
{
}
 
void
MsduAggregator::DoDispose ()
{
  m_mac = 0;
  m_htFem = 0;
  Object::DoDispose ();
}
 
void
MsduAggregator::SetWifiMac (const Ptr<WifiMac> mac)
{
  NS_LOG_FUNCTION (this << mac);
  m_mac = mac;
  m_htFem = DynamicCast<HtFrameExchangeManager> (m_mac->GetFrameExchangeManager ());
}
 
uint16_t
MsduAggregator::GetSizeIfAggregated (uint16_t msduSize, uint16_t amsduSize)
{
  NS_LOG_FUNCTION (msduSize << amsduSize);
 
  // the size of the A-MSDU subframe header is 14 bytes: DA (6), SA (6) and Length (2)
  return amsduSize + CalculatePadding (amsduSize) + 14 + msduSize;
}
 
Ptr<WifiMacQueueItem>
MsduAggregator::GetNextAmsdu (Ptr<const WifiMacQueueItem> peekedItem, WifiTxParameters& txParams,
                              Time availableTime) const
{
  NS_LOG_FUNCTION (this << *peekedItem << &txParams << availableTime);
 
  Ptr<WifiMacQueue> queue = m_mac->GetTxopQueue (peekedItem->GetQueueAc ());
 
  uint8_t tid = peekedItem->GetHeader ().GetQosTid ();
  Mac48Address recipient = peekedItem->GetHeader ().GetAddr1 ();
 
  /* "The Address 1 field of an MPDU carrying an A-MSDU shall be set to an
   * individual address or to the GCR concealment address" (Section 10.12
   * of 802.11-2016)
   */
  NS_ABORT_MSG_IF (recipient.IsBroadcast (), "Recipient address is broadcast");
 
  /* "A STA shall not transmit an A-MSDU within a QoS Data frame under a block
   * ack agreement unless the recipient indicates support for A-MSDU by setting
   * the A-MSDU Supported field to 1 in its BlockAck Parameter Set field of the
   * ADDBA Response frame" (Section 10.12 of 802.11-2016)
   */
  // No check required for now, as we always set the A-MSDU Supported field to 1
 
  // TODO Add support for the Max Number Of MSDUs In A-MSDU field in the Extended
  // Capabilities element sent by the recipient
 
  NS_ASSERT (m_htFem != 0);
 
  if (GetMaxAmsduSize (recipient, tid, txParams.m_txVector.GetModulationClass ()) == 0)
    {
      NS_LOG_DEBUG ("A-MSDU aggregation disabled");
      return nullptr;
    }
 
  Ptr<WifiMacQueueItem> amsdu = peekedItem->GetItem ();  // amsdu points to the peeked MPDU, but it's non-const
  uint8_t nMsdu = 1;
  peekedItem = queue->PeekByTidAndAddress (tid, recipient, peekedItem);
 
  while (peekedItem != nullptr
         && m_htFem->TryAggregateMsdu (peekedItem, txParams, availableTime))
    {
      // find the next MPDU before dequeuing the current one
      Ptr<const WifiMacQueueItem> msdu = peekedItem;
      peekedItem = queue->PeekByTidAndAddress (tid, recipient, peekedItem);
      queue->DequeueIfQueued (msdu);
 
      // perform A-MSDU aggregation
      queue->Transform (amsdu, [&msdu](Ptr<WifiMacQueueItem> amsdu)
                               {
                                 amsdu->Aggregate (msdu);
                               });
 
      nMsdu++;
    }
 
  if (nMsdu == 1)
    {
      NS_LOG_DEBUG ("Aggregation failed (could not aggregate at least two MSDUs)");
      return nullptr;
    }
 
  // Aggregation succeeded
  return amsdu;
}
 
uint8_t
MsduAggregator::CalculatePadding (uint16_t amsduSize)
{
  return (4 - (amsduSize % 4 )) % 4;
}
 
uint16_t
MsduAggregator::GetMaxAmsduSize (Mac48Address recipient, uint8_t tid,
                                 WifiModulationClass modulation) const
{
  NS_LOG_FUNCTION (this << recipient << +tid << modulation);
 
  AcIndex ac = QosUtilsMapTidToAc (tid);
 
  // Find the A-MSDU max size configured on this device
  uint16_t maxAmsduSize = m_mac->GetMaxAmsduSize (ac);
 
  if (maxAmsduSize == 0)
    {
      NS_LOG_DEBUG ("A-MSDU Aggregation is disabled on this station for AC " << ac);
      return 0;
    }
 
  Ptr<WifiRemoteStationManager> stationManager = m_mac->GetWifiRemoteStationManager ();
  NS_ASSERT (stationManager);
 
  // Retrieve the Capabilities elements advertised by the recipient
  Ptr<const VhtCapabilities> vhtCapabilities = stationManager->GetStationVhtCapabilities (recipient);
  Ptr<const HtCapabilities> htCapabilities = stationManager->GetStationHtCapabilities (recipient);
 
  if (!htCapabilities)
    {
      /* "A non-DMG STA shall not transmit an A-MSDU to a STA from which it has
       * not received a frame containing an HT Capabilities element" (Section
       * 10.12 of 802.11-2016)
       */
      NS_LOG_DEBUG ("A-MSDU Aggregation disabled because the recipient did not"
                    " send an HT Capabilities element");
      return 0;
    }
 
  // Determine the constraint imposed by the recipient based on the PPDU
  // format used to transmit the A-MSDU
  if (modulation >= WIFI_MOD_CLASS_VHT)
    {
      // the maximum A-MSDU size is indirectly constrained by the maximum MPDU
      // size supported by the recipient and advertised in the VHT Capabilities
      // element (see Table 9-19 of 802.11-2016 as amended by 802.11ax)
      NS_ABORT_MSG_IF (!vhtCapabilities, "VHT Capabilities element not received");
 
      maxAmsduSize = std::min (maxAmsduSize, static_cast<uint16_t>(vhtCapabilities->GetMaxMpduLength () - 56));
    }
  else if (modulation == WIFI_MOD_CLASS_HT)
    {
      // the maximum A-MSDU size is constrained by the maximum A-MSDU size
      // supported by the recipient and advertised in the HT Capabilities
      // element (see Table 9-19 of 802.11-2016)
 
      maxAmsduSize = std::min (maxAmsduSize, htCapabilities->GetMaxAmsduLength ());
    }
  else  // non-HT PPDU
    {
      // the maximum A-MSDU size is indirectly constrained by the maximum PSDU size
      // supported by the recipient (see Table 9-19 of 802.11-2016)
 
      maxAmsduSize = std::min (maxAmsduSize, static_cast<uint16_t>(3839));
    }
 
  return maxAmsduSize;
}
 
WifiMacQueueItem::DeaggregatedMsdus
MsduAggregator::Deaggregate (Ptr<Packet> aggregatedPacket)
{
  NS_LOG_FUNCTION_NOARGS ();
  WifiMacQueueItem::DeaggregatedMsdus set;
 
  AmsduSubframeHeader hdr;
  Ptr<Packet> extractedMsdu = Create<Packet> ();
  uint32_t maxSize = aggregatedPacket->GetSize ();
  uint16_t extractedLength;
  uint8_t padding;
  uint32_t deserialized = 0;
 
  while (deserialized < maxSize)
    {
      deserialized += aggregatedPacket->RemoveHeader (hdr);
      extractedLength = hdr.GetLength ();
      extractedMsdu = aggregatedPacket->CreateFragment (0, static_cast<uint32_t> (extractedLength));
      aggregatedPacket->RemoveAtStart (extractedLength);
      deserialized += extractedLength;
 
      padding = (4 - ((extractedLength + 14) % 4 )) % 4;
 
      if (padding > 0 && deserialized < maxSize)
        {
          aggregatedPacket->RemoveAtStart (padding);
          deserialized += padding;
        }
 
      std::pair<Ptr<const Packet>, AmsduSubframeHeader> packetHdr (extractedMsdu, hdr);
      set.push_back (packetHdr);
    }
  NS_LOG_INFO ("Deaggreated A-MSDU: extracted " << set.size () << " MSDUs");
  return set;
}
 
} //namespace ns3