--- ns-2.1b9a/tcl/lib/ns-default.tcl	2002-06-21 00:26:18.000000000 +0200
+++ ns-2.1b9a/tcl/lib/ns-default.tcl	2002-10-21 11:01:29.000000000 +0200
@@ -587,6 +587,10 @@
 Mac/Tdma set slot_packet_len_	1500
 Mac/Tdma set max_node_num_	64
 
+Mac/802_11 set scan_int_        0       ;# added by MT
+Mac/802_11 set scan_len_        0       ;# for MAC load scanning
+Mac/802_11 set smooth_scan_     0       ;# smooth the values (0/1)
+
 LL set mindelay_                50us
 LL set delay_                   25us
 LL set bandwidth_               0       ;# not used
--- ns-2.1b9a/mac/mac-timers.h	1999-01-04 20:45:09.000000000 +0100
+++ ns-2.1b9a/mac/mac-timers.h	2002-10-21 10:56:03.000000000 +0200
@@ -119,5 +119,13 @@
 	void	handle(Event *e);
 };
 
+//! Timer for scanning the medium - MT
+class ScanTimer : public MacTimer {
+public:
+	ScanTimer(Mac802_11 *m) : MacTimer(m) {}
+	
+	void    handle(Event *e);
+};
+
 #endif /* __mac_timers_h__ */
 
--- ns-2.1b9a/mac/mac-timers.cc	1999-09-24 05:50:17.000000000 +0200
+++ ns-2.1b9a/mac/mac-timers.cc	2002-10-21 10:58:45.000000000 +0200
@@ -296,3 +296,16 @@
 }
 
 
+/* ======================================================================
+   Medium scan Timer - MT
+   ====================================================================== */
+void
+ScanTimer::handle(Event *)
+{
+	busy_ = 0;
+	paused_ = 0;
+	stime = 0.0;
+	rtime = 0.0;
+	
+	mac->scanHandler();
+}
--- ns-2.1b9a/mac/mac-802_11.h	2002-03-15 18:26:55.000000000 +0100
+++ ns-2.1b9a/mac/mac-802_11.h	2002-10-21 11:32:52.000000000 +0200
@@ -232,6 +232,7 @@
 	friend class NavTimer;
 	friend class RxTimer;
 	friend class TxTimer;
+	friend class ScanTimer;
 public:
 	Mac802_11(PHY_MIB* p, MAC_MIB *m);
 	void		recv(Packet *p, Handler *h);
@@ -246,6 +247,7 @@
 	void	recvHandler(void);
 	void	sendHandler(void);
 	void	txHandler(void);
+	void    scanHandler(void);      //!< Scan the medium - MT
 
 private:
 	int		command(int argc, const char*const* argv);
@@ -291,6 +293,7 @@
 	 */
 	void		trace_pkt(Packet *p);
 	void		dump(char* fname);
+	void            loadtrace(char* fmt, ...);      //!< trace current MAC load in separate file
 
 	inline int initialized() {
 		return (phymib_ && macmib_ && cache_ && logtarget_ && 
@@ -346,6 +349,8 @@
 	DeferTimer	mhDefer_;	// defer timer
 	BackoffTimer	mhBackoff_;	// backoff timer
 
+	ScanTimer       mhScan_;        //!< continuously scanning the medium - MT
+
 	/* ============================================================
 	   Internal MAC State
 	   ============================================================ */
@@ -374,6 +379,18 @@
 	NsObject*	logtarget_;
 
 	/* ============================================================
+	   Medium scanning state - MT
+	   ============================================================ */
+	double          scan_state_[4]; //!< accumulated medium state - MT
+	int             scan_cnt_;      //!< medium state scan counter - MT
+	double          scan_int_;      //!< parameter for scanning interval - MT
+	int             scan_len_;      //!< parameter for maximum scan count - MT
+	int             smooth_scan_;   //!< if the scanned values should be smoothed - MT
+	int             macLoad_;       //!< current load on MAC layer - MT
+
+	Tcl_Channel     ltr_ch;         //!< used for logging into file opened through TCL - MT
+
+	/* ============================================================
 	   Duplicate Detection state
 	   ============================================================ */
 	u_int16_t	sta_seqno_;	// next seqno that I'll use
--- ns-2.1b9a/mac/mac-802_11.cc	2002-03-15 18:26:55.000000000 +0100
+++ ns-2.1b9a/mac/mac-802_11.cc	2002-10-21 11:45:59.000000000 +0200
@@ -145,8 +145,7 @@
 /* ======================================================================
    Mac Class Functions
    ====================================================================== */
-Mac802_11::Mac802_11(PHY_MIB *p, MAC_MIB *m) : Mac(), mhIF_(this), mhNav_(this), mhRecv_(this), mhSend_(this), mhDefer_(this, p->SlotTime), mhBackoff_(this, p->SlotTime)
-{
+Mac802_11::Mac802_11(PHY_MIB *p, MAC_MIB *m) : Mac(), mhIF_(this), mhNav_(this), mhRecv_(this), mhSend_(this), mhDefer_(this, p->SlotTime), mhBackoff_(this, p->SlotTime) , mhScan_(this) {
 	macmib_ = m;
 	phymib_ = p;
 	
@@ -191,6 +190,14 @@
 		bind_bw("dataRate_", &dataRate_);
 	else
 		dataRate_ = bandwidth_;
+
+	// Initialize medium scanning - MT
+	bind("scan_int_", &scan_int_);
+	bind("scan_len_", &scan_len_);
+	bind("smooth_scan_", &smooth_scan_);
+	scan_cnt_ = 0;
+	if (scan_int_ > 0)
+		mhScan_.start(scan_int_);
 }
 
 
@@ -210,6 +217,13 @@
 			assert(cache_);
 			bzero(cache_, sizeof(Host) * (cache_node_count_+1 ));
 			return TCL_OK;
+		} else if (strcmp(argv[1], "load-trace") == 0) {
+			if (strcmp(argv[2], "") == 0) { return(TCL_OK); }
+			int mode;
+			const char* id = argv[2];
+			Tcl& tcl = Tcl::instance();
+			ltr_ch = Tcl_GetChannel(tcl.interp(), (char*)id, &mode);
+			return(TCL_OK);
 		}
 	}
 	return Mac::command(argc, argv);
@@ -255,6 +269,16 @@
 		mhBackoff_.expire());
 }
 
+void
+Mac802_11::loadtrace(char* fmt, ...)
+{
+	char buffer[256];
+	va_list ap;
+	va_start(ap, fmt);
+	vsprintf(buffer, fmt, ap);
+	(void)Tcl_Write(ltr_ch, buffer, strlen(buffer));
+	va_end(ap);
+}
 
 /* ======================================================================
    Packet Headers Routines
@@ -533,6 +557,35 @@
 	tx_active_ = 0;
 }
 
+// added - MT
+void
+Mac802_11::scanHandler()
+{
+	scan_state_[0] += 1 - is_idle();
+	scan_cnt_++;
+	if (scan_cnt_ == scan_len_) {
+		
+		scan_state_[0] /= scan_len_;
+		if (smooth_scan_) {
+			scan_state_[0] = (scan_state_[0] + 0.8 * scan_state_[1] + 0.5 * scan_state_[2] + 0.2 * scan_state_[3]) / 2.5;
+			for (int i = 0; i < 3; scan_state_[++i] = scan_state_[i - 1]);
+		}
+		macLoad_ = (int) (100 * scan_state_[0]);
+		
+		if (ltr_ch != NULL) {
+			double x, y, z;
+			((MobileNode*) netif_->node())->getLoc(&x, &y, &z);
+			loadtrace("ML %f _%d_ (%.2f/%.2f) %.4f\n",
+				  Scheduler::instance().clock(), addr(), x, y, scan_state_[0]);
+		}
+		
+		scan_cnt_ = 0;
+		scan_state_[0] = 0;
+	}
+	
+	mhScan_.start(scan_int_);
+}
+
 
 /* ======================================================================
    The "real" Timer Handler Routines