//this may be caused only if PHY has started to receive a packet

      if (Simulator::Now () - m_lastRxStart <= m_sifs)

      //inside SIFS, so, we check that lastRxStart was maximum a SIFS ago

        {

      NS_ASSERT (Simulator::Now () - m_lastRxStart <= m_sifs);

          //this may be caused if PHY has started to receive a packet

      m_lastRxEnd = Simulator::Now ();

          //inside SIFS, so, we check that lastRxStart was within a SIFS ago

      m_lastRxDuration = m_lastRxEnd - m_lastRxStart;

          m_lastRxEnd = Simulator::Now ();

      m_lastRxReceivedOk = true;

          m_lastRxDuration = m_lastRxEnd - m_lastRxStart;

      m_rxing = false;

          m_lastRxReceivedOk = true;

          m_rxing = false;

        }

      else

        {

          // Bug 2477:  It is possible for the DCF to fall out of 

          //            sync with the PHY state if there are problems

          //            receiving A-MPDUs.  PHY will cancel the reception

          //            and start to transmit

          NS_LOG_DEBUG ("Phy is transmitting despite DCF being in receive state");

          m_lastRxEnd = Simulator::Now ();

          m_lastRxDuration = m_lastRxEnd - m_lastRxStart;

          m_lastRxReceivedOk = false;

          m_rxing = false;

        }