diff -r b92ee3137f95 src/devices/wifi/dca-txop.cc
--- a/src/devices/wifi/dca-txop.cc	Wed Oct 27 21:19:12 2010 -0700
+++ b/src/devices/wifi/dca-txop.cc	Fri Nov 05 20:34:35 2010 +0100
@@ -89,6 +89,9 @@
   virtual void Cancel (void) {
     m_txop->Cancel ();
   }
+  virtual void EndTxNoAck (void) {
+    m_txop->EndTxNoAck ();
+  }
 
 private:
   DcaTxop *m_txop;
@@ -387,9 +390,6 @@
                                  params,
                                  m_transmissionListener);
       m_currentPacket = 0;
-      m_dcf->ResetCw ();
-      m_dcf->StartBackoffNow (m_rng->GetNext (0, m_dcf->GetCw ()));
-      StartAccessIfNeeded ();
       NS_LOG_DEBUG ("tx broadcast");
     } 
   else 
@@ -600,4 +600,15 @@
    */
 }
 
+void
+DcaTxop::EndTxNoAck (void)
+{
+  NS_LOG_FUNCTION (this);
+  NS_LOG_DEBUG ("a transmission that did not require an ACK just finished");
+  NS_ASSERT (m_currentPacket == 0);
+  m_dcf->ResetCw ();
+  m_dcf->StartBackoffNow (m_rng->GetNext (0, m_dcf->GetCw ()));
+  StartAccessIfNeeded ();
+}
+
 } // namespace ns3
diff -r b92ee3137f95 src/devices/wifi/dca-txop.h
--- a/src/devices/wifi/dca-txop.h	Wed Oct 27 21:19:12 2010 -0700
+++ b/src/devices/wifi/dca-txop.h	Fri Nov 05 20:34:35 2010 +0100
@@ -137,6 +137,7 @@
   void MissedAck (void);
   void StartNext (void);
   void Cancel (void);
+  void EndTxNoAck (void);
 
   void RestartAccessIfNeeded (void);
   void StartAccessIfNeeded (void);
diff -r b92ee3137f95 src/devices/wifi/edca-txop-n.cc
--- a/src/devices/wifi/edca-txop-n.cc	Wed Oct 27 21:19:12 2010 -0700
+++ b/src/devices/wifi/edca-txop-n.cc	Fri Nov 05 20:34:35 2010 +0100
@@ -96,6 +96,9 @@
   virtual void Cancel (void) {
     m_txop->Cancel ();
   }
+  virtual void EndTxNoAck (void) {
+    m_txop->EndTxNoAck ();
+  }
 
 private:
   EdcaTxopN *m_txop;
@@ -371,9 +374,6 @@
                                 m_transmissionListener);
       
       m_currentPacket = 0;
-      m_dcf->ResetCw ();
-      m_dcf->StartBackoffNow (m_rng->GetNext (0, m_dcf->GetCw ()));
-      StartAccessIfNeeded ();
       NS_LOG_DEBUG ("tx broadcast");
     }
   else if (m_currentHdr.GetType() == WIFI_MAC_CTL_BACKREQ)
@@ -716,6 +716,19 @@
   NS_LOG_DEBUG ("transmission cancelled");
 }
 
+
+void
+EdcaTxopN::EndTxNoAck (void)
+{
+  NS_LOG_FUNCTION (this);
+  NS_LOG_DEBUG ("a transmission that did not require an ACK just finished");
+  NS_ASSERT (m_currentPacket == 0);
+  m_dcf->ResetCw ();
+  m_dcf->StartBackoffNow (m_rng->GetNext (0, m_dcf->GetCw ()));
+  StartAccessIfNeeded ();
+}
+
+
 bool
 EdcaTxopN::NeedFragmentation (void) const
 {
diff -r b92ee3137f95 src/devices/wifi/edca-txop-n.h
--- a/src/devices/wifi/edca-txop-n.h	Wed Oct 27 21:19:12 2010 -0700
+++ b/src/devices/wifi/edca-txop-n.h	Fri Nov 05 20:34:35 2010 +0100
@@ -124,6 +124,7 @@
   void MissedAck (void);
   void StartNext (void);
   void Cancel (void);
+  void EndTxNoAck (void);
 
   void RestartAccessIfNeeded (void);
   void StartAccessIfNeeded (void);
diff -r b92ee3137f95 src/devices/wifi/mac-low.cc
--- a/src/devices/wifi/mac-low.cc	Wed Oct 27 21:19:12 2010 -0700
+++ b/src/devices/wifi/mac-low.cc	Fri Nov 05 20:34:35 2010 +0100
@@ -344,6 +344,7 @@
     m_sendAckEvent (),
     m_sendDataEvent (),
     m_waitSifsEvent (),
+    m_endTxNoAckEvent (),
     m_currentPacket (0),
     m_listener (0)
 {
@@ -379,6 +380,7 @@
   m_sendAckEvent.Cancel ();
   m_sendDataEvent.Cancel ();
   m_waitSifsEvent.Cancel ();
+  m_endTxNoAckEvent.Cancel ();
   m_phy = 0;
   m_stationManager = 0;
   delete m_phyMacLowListener;
@@ -440,6 +442,11 @@
       m_waitSifsEvent.Cancel ();
       oneRunning = true;
     }
+  if (m_endTxNoAckEvent.IsRunning ()) 
+    {
+      m_endTxNoAckEvent.Cancel ();
+      oneRunning = true;
+    }
   if (oneRunning && m_listener != 0) 
     {
       m_listener->Cancel ();
diff -r b92ee3137f95 src/devices/wifi/mac-low.h
--- a/src/devices/wifi/mac-low.h	Wed Oct 27 21:19:12 2010 -0700
+++ b/src/devices/wifi/mac-low.h	Fri Nov 05 20:34:35 2010 +0100
@@ -122,6 +122,14 @@
    * down the stack to the PHY.
    */
   virtual void Cancel (void) = 0;
+
+  /** 
+   * Invoked upon the end of the transmission of a frame that does not
+   * require an ACK (e.g., broadcast and multicast frames).
+   * 
+   */
+  virtual void EndTxNoAck (void) = 0;
+
 };
 
 
@@ -596,6 +604,7 @@
   EventId m_sendAckEvent;
   EventId m_sendDataEvent;
   EventId m_waitSifsEvent;
+  EventId m_endTxNoAckEvent;
   EventId m_navCounterResetCtsMissed;
 
   Ptr<Packet> m_currentPacket;