recipient-block-ack-agreement.cc

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/*
 * Copyright (c) 2020 Universita' degli Studi di Napoli Federico II
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Stefano Avallone <stavallo@unina.it>
 */
 
#include "recipient-block-ack-agreement.h"
 
#include "ctrl-headers.h"
#include "mac-rx-middle.h"
#include "wifi-mpdu.h"
#include "wifi-utils.h"
 
#include "ns3/log.h"
#include "ns3/packet.h"
 
#include <algorithm>
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("RecipientBlockAckAgreement");
 
bool
RecipientBlockAckAgreement::Compare::operator()(const Key& a, const Key& b) const
{
    return ((a.first - *a.second + SEQNO_SPACE_SIZE) % SEQNO_SPACE_SIZE) <
           ((b.first - *b.second + SEQNO_SPACE_SIZE) % SEQNO_SPACE_SIZE);
}
 
RecipientBlockAckAgreement::RecipientBlockAckAgreement(Mac48Address originator,
                                                       bool amsduSupported,
                                                       uint8_t tid,
                                                       uint16_t bufferSize,
                                                       uint16_t timeout,
                                                       uint16_t startingSeq,
                                                       bool htSupported)
    : BlockAckAgreement(originator, tid)
{
    NS_LOG_FUNCTION(this << originator << amsduSupported << +tid << bufferSize << timeout
                         << startingSeq << htSupported);
 
    m_amsduSupported = amsduSupported;
    m_bufferSize = bufferSize;
    m_timeout = timeout;
    m_startingSeq = startingSeq;
    m_htSupported = htSupported;
 
    m_scoreboard.Init(startingSeq, bufferSize);
    m_winStartB = startingSeq;
    m_winSizeB = bufferSize;
}
 
RecipientBlockAckAgreement::~RecipientBlockAckAgreement()
{
    NS_LOG_FUNCTION_NOARGS();
    m_bufferedMpdus.clear();
    m_rxMiddle = nullptr;
}
 
void
RecipientBlockAckAgreement::SetMacRxMiddle(const Ptr<MacRxMiddle> rxMiddle)
{
    NS_LOG_FUNCTION(this << rxMiddle);
    m_rxMiddle = rxMiddle;
}
 
void
RecipientBlockAckAgreement::PassBufferedMpdusUntilFirstLost()
{
    NS_LOG_FUNCTION(this);
 
    // There cannot be old MPDUs in the buffer (we just check the MPDU with the
    // highest sequence number)
    NS_ASSERT(m_bufferedMpdus.empty() || GetDistance(m_bufferedMpdus.rbegin()->first.first,
                                                     m_winStartB) < SEQNO_SPACE_HALF_SIZE);
 
    auto it = m_bufferedMpdus.begin();
 
    while (it != m_bufferedMpdus.end() && it->first.first == m_winStartB)
    {
        NS_LOG_DEBUG("Forwarding up: " << *it->second);
        m_rxMiddle->Receive(it->second, WIFI_LINKID_UNDEFINED);
        it = m_bufferedMpdus.erase(it);
        m_winStartB = (m_winStartB + 1) % SEQNO_SPACE_SIZE;
    }
}
 
void
RecipientBlockAckAgreement::PassBufferedMpdusWithSeqNumberLessThan(uint16_t newWinStartB)
{
    NS_LOG_FUNCTION(this << newWinStartB);
 
    // There cannot be old MPDUs in the buffer (we just check the MPDU with the
    // highest sequence number)
    NS_ASSERT(m_bufferedMpdus.empty() || GetDistance(m_bufferedMpdus.rbegin()->first.first,
                                                     m_winStartB) < SEQNO_SPACE_HALF_SIZE);
 
    auto it = m_bufferedMpdus.begin();
 
    while (it != m_bufferedMpdus.end() &&
           GetDistance(it->first.first, m_winStartB) < GetDistance(newWinStartB, m_winStartB))
    {
        NS_LOG_DEBUG("Forwarding up: " << *it->second);
        m_rxMiddle->Receive(it->second, WIFI_LINKID_UNDEFINED);
        it = m_bufferedMpdus.erase(it);
    }
    m_winStartB = newWinStartB;
}
 
void
RecipientBlockAckAgreement::NotifyReceivedMpdu(Ptr<const WifiMpdu> mpdu)
{
    NS_LOG_FUNCTION(this << *mpdu);
 
    uint16_t mpduSeqNumber = mpdu->GetHeader().GetSequenceNumber();
    uint16_t distance = GetDistance(mpduSeqNumber, m_scoreboard.GetWinStart());
 
    /* Update the scoreboard (see Section 10.24.7.3 of 802.11-2016) */
    if (distance < m_scoreboard.GetWinSize())
    {
        // set to 1 the bit in position SN within the bitmap
        m_scoreboard.At(distance) = true;
    }
    else if (distance < SEQNO_SPACE_HALF_SIZE)
    {
        m_scoreboard.Advance(distance - m_scoreboard.GetWinSize() + 1);
        m_scoreboard.At(m_scoreboard.GetWinSize() - 1) = true;
    }
 
    distance = GetDistance(mpduSeqNumber, m_winStartB);
 
    /* Update the receive reordering buffer (see Section 10.24.7.6.2 of 802.11-2016) */
    if (distance < m_winSizeB)
    {
        // 1. Store the received MPDU in the buffer, if no MSDU with the same sequence
        // number is already present
        m_bufferedMpdus.insert({{mpdu->GetHeader().GetSequenceNumber(), &m_winStartB}, mpdu});
 
        // 2. Pass MSDUs or A-MSDUs up to the next MAC process if they are stored in
        // the buffer in order of increasing value of the Sequence Number subfield
        // starting with the MSDU or A-MSDU that has SN=WinStartB
        // 3. Set WinStartB to the value of the Sequence Number subfield of the last
        // MSDU or A-MSDU that was passed up to the next MAC process plus one.
        PassBufferedMpdusUntilFirstLost();
    }
    else if (distance < SEQNO_SPACE_HALF_SIZE)
    {
        // 1. Store the received MPDU in the buffer, if no MSDU with the same sequence
        // number is already present
        m_bufferedMpdus.insert({{mpdu->GetHeader().GetSequenceNumber(), &m_winStartB}, mpdu});
 
        // 2. Set WinEndB = SN
        // 3. Set WinStartB = WinEndB – WinSizeB + 1
        // 4. Pass any complete MSDUs or A-MSDUs stored in the buffer with Sequence Number
        // subfield values that are lower than the new value of WinStartB up to the next
        // MAC process in order of increasing Sequence Number subfield value. Gaps may
        // exist in the Sequence Number subfield values of the MSDUs or A-MSDUs that are
        // passed up to the next MAC process.
        const uint16_t newWinStartB =
            (mpdu->GetHeader().GetSequenceNumber() - m_winSizeB + 1 + SEQNO_SPACE_SIZE) %
            SEQNO_SPACE_SIZE;
        PassBufferedMpdusWithSeqNumberLessThan(newWinStartB);
 
        // 5. Pass MSDUs or A-MSDUs stored in the buffer up to the next MAC process in
        // order of increasing value of the Sequence Number subfield starting with
        // WinStartB and proceeding sequentially until there is no buffered MSDU or
        // A-MSDU for the next sequential Sequence Number subfield value
        PassBufferedMpdusUntilFirstLost();
    }
}
 
void
RecipientBlockAckAgreement::Flush()
{
    NS_LOG_FUNCTION(this);
    PassBufferedMpdusWithSeqNumberLessThan(m_scoreboard.GetWinStart());
    PassBufferedMpdusUntilFirstLost();
}
 
void
RecipientBlockAckAgreement::NotifyReceivedBar(uint16_t startingSequenceNumber)
{
    NS_LOG_FUNCTION(this << startingSequenceNumber);
 
    uint16_t distance = GetDistance(startingSequenceNumber, m_scoreboard.GetWinStart());
 
    /* Update the scoreboard (see Section 10.24.7.3 of 802.11-2016) */
    if (distance > 0 && distance < m_scoreboard.GetWinSize())
    {
        // advance by SSN - WinStartR, so that WinStartR becomes equal to SSN
        m_scoreboard.Advance(distance);
        NS_ASSERT(m_scoreboard.GetWinStart() == startingSequenceNumber);
    }
    else if (distance > 0 && distance < SEQNO_SPACE_HALF_SIZE)
    {
        // reset the window and set WinStartR to SSN
        m_scoreboard.Reset(startingSequenceNumber);
    }
 
    distance = GetDistance(startingSequenceNumber, m_winStartB);
 
    /* Update the receive reordering buffer (see Section 10.24.7.6.2 of 802.11-2016) */
    if (distance > 0 && distance < SEQNO_SPACE_HALF_SIZE)
    {
        // 1. set WinStartB = SSN
        // 3. Pass any complete MSDUs or A-MSDUs stored in the buffer with Sequence
        // Number subfield values that are lower than the new value of WinStartB up to
        // the next MAC process in order of increasing Sequence Number subfield value
        PassBufferedMpdusWithSeqNumberLessThan(startingSequenceNumber);
 
        // 4. Pass MSDUs or A-MSDUs stored in the buffer up to the next MAC process
        // in order of increasing Sequence Number subfield value starting with
        // SN=WinStartB and proceeding sequentially until there is no buffered MSDU
        // or A-MSDU for the next sequential Sequence Number subfield value
        PassBufferedMpdusUntilFirstLost();
    }
}
 
void
RecipientBlockAckAgreement::FillBlockAckBitmap(CtrlBAckResponseHeader& blockAckHeader,
                                               std::size_t index) const
{
    NS_LOG_FUNCTION(this << blockAckHeader << index);
    if (blockAckHeader.IsBasic())
    {
        NS_FATAL_ERROR("Basic block ack is not supported.");
    }
    else if (blockAckHeader.IsMultiTid())
    {
        NS_FATAL_ERROR("Multi-tid block ack is not supported.");
    }
    else if (blockAckHeader.IsCompressed() || blockAckHeader.IsExtendedCompressed() ||
             blockAckHeader.IsMultiSta() || blockAckHeader.IsGcr())
    {
        // The Starting Sequence Number subfield of the Block Ack Starting Sequence
        // Control subfield of the BlockAck frame shall be set to any value in the
        // range (WinEndR – 63) to WinStartR (Sec. 10.24.7.5 of 802.11-2016).
        // We set it to WinStartR
        uint16_t ssn = m_scoreboard.GetWinStart();
        NS_LOG_DEBUG("SSN=" << ssn);
        blockAckHeader.SetStartingSequence(ssn, index);
        blockAckHeader.ResetBitmap(index);
 
        for (std::size_t i = 0; i < m_scoreboard.GetWinSize(); i++)
        {
            if (m_scoreboard.At(i))
            {
                blockAckHeader.SetReceivedPacket((ssn + i) % SEQNO_SPACE_SIZE, index);
            }
        }
    }
}
 
} // namespace ns3