--- a/src/devices/point-to-point/point-to-point-net-device.cc	Tue Sep 23 16:38:51 2008 -0700
+++ a/src/devices/point-to-point/point-to-point-net-device.cc	Wed Sep 24 14:10:04 2008 -0700
@@ -200,6 +200,10 @@ 
 //
 // Got another packet off of the queue, so start the transmit process agin.
 //
+  if (!m_sendReadyCallback.IsNull()) // signal callback when we pop.
+    {
+      m_sendReadyCallback();
+    }
   TransmitStart(p);
 }
 
@@ -481,6 +485,13 @@ 
   m_promiscCallback = cb;
 }
 
+void
+PointToPointNetDevice::SetSendReadyCallback(NetDevice::SendReadyCallback cb)
+{
+  NS_LOG_FUNCTION_NOARGS();
+  m_sendReadyCallback = cb;
+}
+
   bool
 PointToPointNetDevice::SupportsSendFrom (void) const
 {
--- a/src/devices/point-to-point/point-to-point-net-device.h	Tue Sep 23 16:38:51 2008 -0700
+++ a/src/devices/point-to-point/point-to-point-net-device.h	Wed Sep 24 14:10:04 2008 -0700
@@ -265,6 +265,7 @@ 
   virtual void SetReceiveCallback (NetDevice::ReceiveCallback cb);
 
   virtual void SetPromiscReceiveCallback (PromiscReceiveCallback cb);
+  virtual void SetSendReadyCallback(NetDevice::SendReadyCallback cb);
   virtual bool SupportsSendFrom (void) const;
 
 private:
@@ -410,6 +411,7 @@ 
   Mac48Address m_address;
   NetDevice::ReceiveCallback m_rxCallback;
   NetDevice::PromiscReceiveCallback m_promiscCallback;
+  NetDevice::SendReadyCallback m_sendReadyCallback;
   uint32_t m_ifIndex;
   std::string m_name;
   bool m_linkUp;
--- a/src/node/net-device.h	Tue Sep 23 16:38:51 2008 -0700
+++ a/src/node/net-device.h	Wed Sep 24 14:10:04 2008 -0700
@@ -122,6 +122,17 @@ 
    * whenever the link goes up.
    */
   virtual void SetLinkChangeCallback (Callback<void> callback) = 0;
+
+  /**
+   * Signal that the NetDevice has removed a packet from the Queue.
+   * params are TBD. return is TBD.
+   */
+  typedef Callback< void > SendReadyCallback;
+  /**
+   * Register a callback to be invoked whenever a packet is removed
+   * from the Tx Queue.
+   */
+  virtual void SetSendReadyCallback(SendReadyCallback cb) {};
   /**
    * \return true if this interface supports a broadcast address,
    *         false otherwise.