mac-rx-middle.cc

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/*
 * Copyright (c) 2005 INRIA
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 */
 
#include "mac-rx-middle.h"
 
#include "wifi-mpdu.h"
 
#include "ns3/log.h"
#include "ns3/packet.h"
#include "ns3/sequence-number.h"
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("MacRxMiddle");
 
/**
 * A class to keep track of the packet originator status.
 * It recomposes the packet from multiple fragments.
 */
class OriginatorRxStatus
{
  private:
    /**
     * typedef for a list of fragments (i.e. incomplete Packet).
     */
    typedef std::list<Ptr<const Packet>> Fragments;
    /**
     * typedef for a const iterator for Fragments
     */
    typedef std::list<Ptr<const Packet>>::const_iterator FragmentsCI;
 
    bool m_defragmenting;           ///< flag to indicate whether we are defragmenting
    uint16_t m_lastSequenceControl; ///< last sequence control
    Fragments m_fragments;          ///< fragments
 
  public:
    OriginatorRxStatus()
    {
        /* this is a magic value necessary. */
        m_lastSequenceControl = 0xffff;
        m_defragmenting = false;
    }
 
    /**
     * Check if we are de-fragmenting packets.
     *
     * \return true if we are de-fragmenting packets,
     *         false otherwise
     */
    bool IsDeFragmenting() const
    {
        return m_defragmenting;
    }
 
    /**
     * We have received a first fragmented packet.
     * We start the deframentation by saving the first fragment.
     *
     * \param packet the first fragmented packet
     */
    void AccumulateFirstFragment(Ptr<const Packet> packet)
    {
        NS_ASSERT(!m_defragmenting);
        m_defragmenting = true;
        m_fragments.push_back(packet);
    }
 
    /**
     * We have received a last fragment of the fragmented packets
     * (indicated by the no more fragment field).
     * We re-construct the packet from the fragments we saved
     * and return the full packet.
     *
     * \param packet the last fragment
     *
     * \return the fully reconstructed packet
     */
    Ptr<Packet> AccumulateLastFragment(Ptr<const Packet> packet)
    {
        NS_ASSERT(m_defragmenting);
        m_fragments.push_back(packet);
        m_defragmenting = false;
        Ptr<Packet> full = Create<Packet>();
        for (auto i = m_fragments.begin(); i != m_fragments.end(); i++)
        {
            full->AddAtEnd(*i);
        }
        m_fragments.erase(m_fragments.begin(), m_fragments.end());
        return full;
    }
 
    /**
     * We received a fragmented packet (not first and not last).
     * We simply save it into our internal list.
     *
     * \param packet the received fragment
     */
    void AccumulateFragment(Ptr<const Packet> packet)
    {
        NS_ASSERT(m_defragmenting);
        m_fragments.push_back(packet);
    }
 
    /**
     * Check if the sequence control (i.e. fragment number) is
     * in order.
     *
     * \param sequenceControl the raw sequence control
     *
     * \return true if the sequence control is in order,
     *         false otherwise
     */
    bool IsNextFragment(uint16_t sequenceControl) const
    {
        return (sequenceControl >> 4) == (m_lastSequenceControl >> 4) &&
               (sequenceControl & 0x0f) == ((m_lastSequenceControl & 0x0f) + 1);
    }
 
    /**
     * Return the last sequence control we received.
     *
     * \return the last sequence control
     */
    uint16_t GetLastSequenceControl() const
    {
        return m_lastSequenceControl;
    }
 
    /**
     * Set the last sequence control we received.
     *
     * \param sequenceControl the last sequence control we received
     */
    void SetSequenceControl(uint16_t sequenceControl)
    {
        m_lastSequenceControl = sequenceControl;
    }
};
 
MacRxMiddle::MacRxMiddle()
{
    NS_LOG_FUNCTION_NOARGS();
}
 
MacRxMiddle::~MacRxMiddle()
{
    NS_LOG_FUNCTION_NOARGS();
}
 
void
MacRxMiddle::SetForwardCallback(ForwardUpCallback callback)
{
    NS_LOG_FUNCTION_NOARGS();
    m_callback = callback;
}
 
OriginatorRxStatus&
MacRxMiddle::Lookup(const WifiMacHeader& hdr)
{
    NS_LOG_FUNCTION(hdr);
    const auto source = hdr.GetAddr2();
    if (hdr.IsQosData() && !source.IsGroup())
    {
        /* only for QoS data non-broadcast frames */
        const auto key = std::make_pair(source, hdr.GetQosTid());
        auto [it, inserted] = m_qosOriginatorStatus.try_emplace(key);
        return it->second;
    }
    /* - management frames
     * - QoS data broadcast frames
     * - non-QoS data frames
     * see section 7.1.3.4.1
     */
    auto [it, inserted] = m_originatorStatus.try_emplace(source);
    return it->second;
}
 
bool
MacRxMiddle::IsDuplicate(const WifiMacHeader& hdr, const OriginatorRxStatus& originator) const
{
    NS_LOG_FUNCTION(hdr << &originator);
    return hdr.IsRetry() && originator.GetLastSequenceControl() == hdr.GetSequenceControl();
}
 
Ptr<const Packet>
MacRxMiddle::HandleFragments(Ptr<const Packet> packet,
                             const WifiMacHeader& hdr,
                             OriginatorRxStatus& originator)
{
    NS_LOG_FUNCTION(packet << hdr << &originator);
    if (originator.IsDeFragmenting())
    {
        if (hdr.IsMoreFragments())
        {
            if (originator.IsNextFragment(hdr.GetSequenceControl()))
            {
                NS_LOG_DEBUG("accumulate fragment seq=" << hdr.GetSequenceNumber()
                                                        << ", frag=" << +hdr.GetFragmentNumber()
                                                        << ", size=" << packet->GetSize());
                originator.AccumulateFragment(packet);
                originator.SetSequenceControl(hdr.GetSequenceControl());
            }
            else
            {
                NS_LOG_DEBUG("non-ordered fragment");
            }
            return nullptr;
        }
        else
        {
            if (originator.IsNextFragment(hdr.GetSequenceControl()))
            {
                NS_LOG_DEBUG("accumulate last fragment seq=" << hdr.GetSequenceNumber() << ", frag="
                                                             << +hdr.GetFragmentNumber()
                                                             << ", size=" << hdr.GetSize());
                Ptr<Packet> p = originator.AccumulateLastFragment(packet);
                originator.SetSequenceControl(hdr.GetSequenceControl());
                return p;
            }
            else
            {
                NS_LOG_DEBUG("non-ordered fragment");
                return nullptr;
            }
        }
    }
    else
    {
        if (hdr.IsMoreFragments())
        {
            NS_LOG_DEBUG("accumulate first fragment seq=" << hdr.GetSequenceNumber()
                                                          << ", frag=" << +hdr.GetFragmentNumber()
                                                          << ", size=" << packet->GetSize());
            originator.AccumulateFirstFragment(packet);
            originator.SetSequenceControl(hdr.GetSequenceControl());
            return nullptr;
        }
        else
        {
            return packet;
        }
    }
}
 
void
MacRxMiddle::Receive(Ptr<const WifiMpdu> mpdu, uint8_t linkId)
{
    NS_LOG_FUNCTION(*mpdu << +linkId);
    // consider the MAC header of the original MPDU (makes a difference for data frames only)
    const auto& hdr = mpdu->GetOriginal()->GetHeader();
    NS_ASSERT(hdr.IsData() || hdr.IsMgt());
 
    auto& originator = Lookup(hdr);
    /**
     * The check below is really unneeded because it can fail in a lot of
     * normal cases. Specifically, it is possible for sequence numbers to
     * loop back to zero once they reach 0xfff0 and to go up to 0xf7f0 in
     * which case the check below will report the two sequence numbers to
     * not have the correct order relationship.
     * So, this check cannot be used to discard old duplicate frames. It is
     * thus here only for documentation purposes.
     */
    if (!(SequenceNumber16(originator.GetLastSequenceControl()) <
          SequenceNumber16(hdr.GetSequenceControl())))
    {
        NS_LOG_DEBUG("Sequence numbers have looped back. last recorded="
                     << originator.GetLastSequenceControl()
                     << " currently seen=" << hdr.GetSequenceControl());
    }
    // filter duplicates.
    if (IsDuplicate(hdr, originator))
    {
        NS_LOG_DEBUG("duplicate from=" << hdr.GetAddr2() << ", seq=" << hdr.GetSequenceNumber()
                                       << ", frag=" << +hdr.GetFragmentNumber());
        return;
    }
    Ptr<const Packet> aggregate = HandleFragments(mpdu->GetPacket(), hdr, originator);
    if (!aggregate)
    {
        return;
    }
    NS_LOG_DEBUG("forwarding data from=" << hdr.GetAddr2() << ", seq=" << hdr.GetSequenceNumber()
                                         << ", frag=" << +hdr.GetFragmentNumber());
    if (!hdr.GetAddr1().IsGroup())
    {
        originator.SetSequenceControl(hdr.GetSequenceControl());
    }
    if (aggregate == mpdu->GetPacket())
    {
        m_callback(mpdu, linkId);
    }
    else
    {
        // We could do this in all cases, but passing the received mpdu in case of
        // A-MSDUs saves us the time to deaggregate the A-MSDU in MSDUs (which are
        // kept separate in the received mpdu) and allows us to pass the originally
        // transmitted packets (i.e., with the same UID) to the receiver.
        m_callback(Create<WifiMpdu>(aggregate, hdr), linkId);
    }
}
 
} // namespace ns3