diff --git a/utils/ndn-limits-rate.cc b/utils/ndn-limits-rate.cc
index 27e2f0d..f323cdb 100644
--- a/utils/ndn-limits-rate.cc
+++ b/utils/ndn-limits-rate.cc
@@ -57,7 +57,7 @@
           NS_ASSERT_MSG (GetObject<Face> ()->GetNode () != 0, "Node object should exist on the face");
           
           m_isLeakScheduled = true;
-          UniformVariable r (0,1);
+          UniformVariable r (0.0, 1.0);
           Simulator::ScheduleWithContext (GetObject<Face> ()->GetNode ()->GetId (),
                                           Seconds (r.GetValue ()), &LimitsRate::LeakBucket, this, 0.0);
         }
@@ -120,6 +120,8 @@
       NS_LOG_DEBUG ("Leak from " << m_bucket << " to " << std::max (0.0, m_bucket - leak));
     }
 #endif
+
+  double bucketOld = m_bucket;
   
   m_bucket = std::max (0.0, m_bucket - leak);
 
@@ -129,6 +131,12 @@
     {
       newInterval = 1.001 / m_bucketLeak;
     }
+
+  if (m_bucketMax - bucketOld < 1.0 &&
+      m_bucketMax - m_bucket >= 1.0) // limit number of times this stuff is called
+    {
+      this->FireAvailableSlotCallback ();
+    }
   
   Simulator::Schedule (Seconds (newInterval), &LimitsRate::LeakBucket, this, newInterval);
 }
diff --git a/utils/ndn-limits-window.cc b/utils/ndn-limits-window.cc
index 95c221b..a859be5 100644
--- a/utils/ndn-limits-window.cc
+++ b/utils/ndn-limits-window.cc
@@ -80,6 +80,8 @@
 
   NS_ASSERT_MSG (m_outstanding >= (uint32_t)1, "Should not be possible, unless we decreasing this number twice somewhere");
   m_outstanding -= 1;
+
+  FireAvailableSlotCallback ();
 }
 
 } // namespace ndn
diff --git a/utils/ndn-limits.cc b/utils/ndn-limits.cc
index 338d195..ee4160e 100644
--- a/utils/ndn-limits.cc
+++ b/utils/ndn-limits.cc
@@ -40,5 +40,27 @@
   return tid;
 }
 
+Limits::Limits ()
+  : m_maxRate (-1)
+  , m_maxDelay (1.0)
+  , m_handler (MakeNullCallback<void> ())
+{
+}
+
+
+void
+Limits::RegisterAvailableSlotCallback (CallbackHandler handler)
+{
+  m_handler = handler;
+}
+
+void
+Limits::FireAvailableSlotCallback ()
+{
+  if (!m_handler.IsNull ())
+    m_handler ();
+}
+
+
 } // namespace ndn
 } // namespace ns3
diff --git a/utils/ndn-limits.h b/utils/ndn-limits.h
index cf5c039..5fdad53 100644
--- a/utils/ndn-limits.h
+++ b/utils/ndn-limits.h
@@ -36,16 +36,15 @@
     public Object
 {
 public:
+  typedef Callback<void> CallbackHandler;
+
   static TypeId
   GetTypeId ();
 
   /**
    * @brief Default constructor
    */
-  Limits ()
-  : m_maxRate (-1)
-  , m_maxDelay (1.0)
-  { }
+  Limits ();
 
   /**
    * @brief Virtual destructor
@@ -135,10 +134,26 @@
    */
   virtual void
   ReturnLimit () = 0;
+
+  ////////////////////////////////////////////////////////////////////////////
+  ////////////////////////////////////////////////////////////////////////////
+  ////////////////////////////////////////////////////////////////////////////
+
+  /**
+   * @brief Set callback which will be called when exhausted limit gets a new slot
+   */
+  void
+  RegisterAvailableSlotCallback (CallbackHandler handler);
+
+protected:
+  void
+  FireAvailableSlotCallback ();
   
 private:
   double m_maxRate;
   double m_maxDelay;
+
+  CallbackHandler m_handler;
 };