diff -r b1df486516a4 -r 0b54480c4fd1 src/devices/wifi/dca-txop.h
--- a/src/devices/wifi/dca-txop.h	Fri Feb 22 23:28:01 2008 +0100
+++ b/src/devices/wifi/dca-txop.h	Fri Feb 22 23:34:53 2008 +0100
@@ -26,6 +26,7 @@
 #include "ns3/packet.h"
 #include "ns3/callback-trace-source.h"
 #include "ns3/nstime.h"
+#include "ns3/object.h"
 #include "wifi-mac-header.h"
 #include "wifi-mode.h"
 
@@ -61,7 +62,7 @@
  * The rts/cts policy is similar to the fragmentation policy: when
  * a packet is bigger than a threshold, the rts/cts protocol is used.
  */
-class DcaTxop 
+class DcaTxop : public Object
 {
 public:
   typedef Callback <void, WifiMacHeader const&> TxOk;
@@ -80,7 +81,7 @@
   DcaTxop (uint32_t cwMin, uint32_t cwMax, uint32_t aifsn, DcfManager *manager);
   ~DcaTxop ();
 
-  void SetLow (MacLow *low);
+  void SetLow (Ptr<MacLow> low);
   void SetParameters (MacParameters *parameters);
   void SetStations (MacStations *stations);
   void SetTxMiddle (MacTxMiddle *txMiddle);
@@ -115,7 +116,9 @@
   friend class Dcf;
   friend class TransmissionListener;
 
-  MacLow *Low (void);
+  // Inherited from ns3::Object
+  virtual Ptr<TraceResolver> GetTraceResolver (void) const;  
+  Ptr<MacLow> Low (void);
   MacParameters *Parameters (void);
 
   /* dcf notifications forwarded here */
@@ -151,7 +154,7 @@
   TxFailed m_txFailedCallback;
   WifiMacQueue *m_queue;
   MacTxMiddle *m_txMiddle;
-  MacLow *m_low;
+  Ptr <MacLow> m_low;
   MacStations *m_stations;
   MacParameters *m_parameters;
   TransmissionListener *m_transmissionListener;