wifi: Flush recipient window upon reception of groupcast A-MPDUs

src/wifi/model/ht/ht-frame-exchange-manager.cc

@@ -64,6 +64,10 @@ void
 HtFrameExchangeManager::DoDispose()
 {
     NS_LOG_FUNCTION(this);
+    if (m_flushGroupcastMpdusEvent.IsPending())
+    {
+        m_flushGroupcastMpdusEvent.Cancel();
+    }
     m_pendingAddBaResp.clear();
     m_msduAggregator = nullptr;
     m_mpduAggregator = nullptr;
@@ -1938,7 +1942,56 @@ HtFrameExchangeManager::EndReceiveAmpdu(Ptr<const WifiPsdu> psdu,
                 GetWifiRemoteStationManager()->GetBlockAckTxVector(psdu->GetAddr2(), txVector),
                 rxSignalInfo.snr);
         }
+        else if (psdu->GetAddr1().IsGroup() && (ackPolicy == WifiMacHeader::NO_ACK))
+        {
+            // groupcast A-MPDU received
+            m_flushGroupcastMpdusEvent.Cancel();
+
+            /*
+             * There might be pending MPDUs from a previous groupcast transmission
+             * that have not been forwarded up yet (e.g. all transmission attempts
+             * of a given MPDU have failed). For groupcast transmissions using GCR-UR service,
+             * transmitter keeps advancing its window since there is no feedback from the
+             * recipients. In order to forward up previously received groupcast MPDUs and avoid
+             * following MPDUs not to be forwarded up, we flush the recipient window. The sequence
+             * number to use can easily be deduced since sequence number of groupcast MPDUs are
+             * consecutive.
+             */
+            const auto startSeq = psdu->GetHeader(0).GetSequenceNumber();
+            const auto groupAddress = psdu->GetHeader(0).IsQosAmsdu()
+                                          ? (*psdu->begin())->begin()->second.GetDestinationAddr()
+                                          : psdu->GetAddr1();
+            FlushGroupcastMpdus(groupAddress, psdu->GetAddr2(), tid, startSeq);
+
+            /*
+             * In case all MPDUs of all following transmissions are corrupted or
+             * if no following groupcast transmission happens, some groupcast MPDUs
+             * of the currently received A-MPDU would never be forwarded up. To prevent this,
+             * we schedule a flush of the recipient window once the MSDU lifetime limit elapsed.
+             */
+            const auto stopSeq = (startSeq + perMpduStatus.size()) % 4096;
+            const auto maxDelay = m_mac->GetQosTxop(tid)->GetWifiMacQueue()->GetMaxDelay();
+            m_flushGroupcastMpdusEvent =
+                Simulator::Schedule(maxDelay,
+                                    &HtFrameExchangeManager::FlushGroupcastMpdus,
+                                    this,
+                                    groupAddress,
+                                    psdu->GetAddr2(),
+                                    tid,
+                                    stopSeq);
+        }
     }
 }
 
+void
+HtFrameExchangeManager::FlushGroupcastMpdus(const Mac48Address& groupAddress,
+                                            const Mac48Address& originator,
+                                            uint8_t tid,
+                                            uint16_t seq)
+{
+    NS_LOG_FUNCTION(this << groupAddress << originator << tid << seq);
+    // We can flush the recipient window by indicating the reception of an implicit GCR BAR
+    GetBaManager(tid)->NotifyGotBlockAckRequest(originator, tid, seq, groupAddress);
+}
+
 } // namespace ns3

src/wifi/model/ht/ht-frame-exchange-manager.h

@@ -372,6 +372,22 @@ class HtFrameExchangeManager : public QosFrameExchangeManager
      */
     virtual void MissedBlockAck(Ptr<WifiPsdu> psdu, const WifiTxVector& txVector);
 
+    /**
+     * Perform required actions to ensure the receiver window is flushed when a groupcast A-MPDU is
+     * received via the GCR service. If there are pending groupcast MPDUs from that recipient and
+     * that traffic ID, these MPDUs are forwarded up, by assuming an implicit BAR from the
+     * originator.
+     *
+     * @param groupAddress the destination group address of the MPDUs
+     * @param originator MAC address of the sender of the groupcast MPDUs
+     * @param tid Traffic ID
+     * @param seq the starting sequence number of the recipient window
+     */
+    void FlushGroupcastMpdus(const Mac48Address& groupAddress,
+                             const Mac48Address& originator,
+                             uint8_t tid,
+                             uint16_t seq);
+
     /// agreement key typedef (MAC address and TID)
     typedef std::pair<Mac48Address, uint8_t> AgreementKey;
 
@@ -390,6 +406,9 @@ class HtFrameExchangeManager : public QosFrameExchangeManager
 
     Ptr<WifiPsdu> m_psdu;        //!< the A-MPDU being transmitted
     WifiTxParameters m_txParams; //!< the TX parameters for the current frame
+
+    EventId m_flushGroupcastMpdusEvent; //!< the event to flush pending groupcast MPDUs from
+                                        //!< previously received A-MPDU
 };
 
 } // namespace ns3