diff --git a/lib/flow_control/burst_timeslot_filter_impl.cc b/lib/flow_control/burst_timeslot_filter_impl.cc
index ccf4d4c..20306d1 100644
--- a/lib/flow_control/burst_timeslot_filter_impl.cc
+++ b/lib/flow_control/burst_timeslot_filter_impl.cc
@@ -73,5 +73,24 @@
             message_port_pub(pmt::mp("out"), msg);
         }
     }
+
+    /*
+     * External API
+     */
+    unsigned int
+    burst_timeslot_filter_impl::get_tn(void)
+    {
+      return d_timeslot;
+    }
+
+    unsigned int
+    burst_timeslot_filter_impl::set_tn(unsigned int tn)
+    {
+      if (tn < 8)
+        d_timeslot = tn;
+
+      return d_timeslot;
+    }
+
   } /* namespace gsm */
 } /* namespace gr */