Bug 2138 - SimpleNetDevice could send overlapped packets.

RELEASE_NOTES

@@ -29,6 +29,7 @@ Bugs fixed
 - Bug 2126 - LrWpanNetDevice silently accepts no mobility on the node
 - Bug 2135 - TCP doesn't honor the socket's output interface
 - Bug 2136 - The usage of tid in wifi and wave module shall be "if (tid > 7)" rather than "if (tid >= 7)"
+- Bug 2138 - SimpleNetDevice could send overlapped packets.
 
 Known issues
 ------------

src/network/utils/simple-net-device.cc

@@ -446,7 +446,7 @@ SimpleNetDevice::SendFrom (Ptr<Packet> p, const Address& source, const Address&
 
   if (m_queue->Enqueue (p))
     {
-      if (m_queue->GetNPackets () == 1)
+      if (m_queue->GetNPackets () == 1 && !TransmitCompleteEvent.IsRunning ())
         {
           p = m_queue->Dequeue ();
           p->RemovePacketTag (tag);