--- a/CHANGES.html	Sun Dec 11 13:25:42 2016 +0100
+++ b/CHANGES.html	Sun Dec 11 16:23:26 2016 +0100
@@ -58,6 +58,7 @@
     parameter to specify the time units used on the report.  The new parameter is
     optional and if not specified defaults to the previous behavior (Time::S).
 </li>
+<li><b>TxopTrace</b>: new trace source exported by EdcaTxopN.</li>
 </ul>
 <h2>Changes to existing API:</h2>
 <ul>

--- a/RELEASE_NOTES	Sun Dec 11 13:25:42 2016 +0100
+++ b/RELEASE_NOTES	Sun Dec 11 16:23:26 2016 +0100
@@ -27,6 +27,7 @@
 - Bug 2007 - uan: Remove deprecation on SetRxThresholdDb
 - Bug 2221 - network: Remove constraint on size of ns3::Packet Tag objects
 - Bug 2450 - LogDistancePropagationLossModel is not continuous
+- Bug 2463 - create trace source to trace the TXOP time that is actually used
 - Bug 2477 - DCF manager assert
 - Bug 2492 - uan: Make use of RxGain attribute in UanPhyGen class
 - Bug 2511 - HT Greenfield is not working

--- a/src/wifi/model/edca-txop-n.cc	Sun Dec 11 13:25:42 2016 +0100
+++ b/src/wifi/model/edca-txop-n.cc	Sun Dec 11 16:23:26 2016 +0100
@@ -248,6 +248,10 @@
                      "Trace source for contention window values",
                      MakeTraceSourceAccessor (&EdcaTxopN::m_cwTrace),
                      "ns3::TracedValue::Uint32Callback")
+    .AddTraceSource ("TxopTrace",
+                     "Trace source for txop start and duration times",
+                     MakeTraceSourceAccessor (&EdcaTxopN::m_txopTrace),
+                     "ns3::TracedValueCallback::Time")
   ;
   return tid;
 }
@@ -1184,9 +1188,10 @@
 EdcaTxopN::StartNext (void)
 {
   NS_LOG_FUNCTION (this);
+  NS_ASSERT (GetTxopLimit () == NanoSeconds (0) || Simulator::Now () - m_startTxop <= GetTxopLimit ());
+
   WifiMacHeader hdr;
   Time tstamp;
-
   Ptr<const Packet> peekedPacket = m_queue->PeekByTidAndAddress (&hdr,
                                                                  m_currentHdr.GetQosTid (),
                                                                  WifiMacHeader::ADDR1,
@@ -1194,6 +1199,11 @@
                                                                  &tstamp);
   if (peekedPacket == 0)
     {
+      if (GetTxopLimit () > NanoSeconds (0))
+        {
+          NS_ASSERT (Simulator::Now () - m_startTxop <= GetTxopLimit ());
+          m_txopTrace (m_startTxop, Simulator::Now () - m_startTxop);
+        }
       return;
     }
     
@@ -1227,6 +1237,11 @@
                                                          m_currentHdr.GetAddr1 ());
       GetLow ()->StartTransmission (m_currentPacket, &m_currentHdr, params, m_transmissionListener);
     }
+  else if (GetTxopLimit () > NanoSeconds (0))
+    {
+      NS_ASSERT (Simulator::Now () - m_startTxop <= GetTxopLimit ());
+      m_txopTrace (m_startTxop, Simulator::Now () - m_startTxop);
+    }
 }
 
 Time

--- a/src/wifi/model/edca-txop-n.h	Sun Dec 11 13:25:42 2016 +0100
+++ b/src/wifi/model/edca-txop-n.h	Sun Dec 11 16:23:26 2016 +0100
@@ -579,6 +579,7 @@
   bool m_isAccessRequestedForRts;
   TracedValue<uint32_t> m_backoffTrace;
   TracedValue<uint32_t> m_cwTrace;
+  TracedCallback<Time, Time> m_txopTrace;
 };
 
 } //namespace ns3

--- a/src/wifi/test/wifi-test.cc	Sun Dec 11 13:25:42 2016 +0100
+++ b/src/wifi/test/wifi-test.cc	Sun Dec 11 16:23:26 2016 +0100
@@ -1023,6 +1023,9 @@
   phy.SetChannel (channel.Create ());
 
   WifiHelper wifi;
+  wifi.SetRemoteStationManager ("ns3::ConstantRateWifiManager",
+                                "DataMode", StringValue ("OfdmRate54Mbps"),
+                                "ControlMode", StringValue ("OfdmRate24Mbps"));
   WifiMacHelper mac;
   Ssid ssid = Ssid ("ns-3-ssid");
   mac.SetType ("ns3::AdhocWifiMac",