diff --git a/include/grgsm/flow_control/burst_sdcch_subslot_filter.h b/include/grgsm/flow_control/burst_sdcch_subslot_filter.h
index 150d76a..5bcf829 100644
--- a/include/grgsm/flow_control/burst_sdcch_subslot_filter.h
+++ b/include/grgsm/flow_control/burst_sdcch_subslot_filter.h
@@ -54,6 +54,13 @@ namespace gr {
        * creating new instances.
        */
       static sptr make(subslot_filter_mode mode, unsigned int subslot);
+
+      /* External API */
+      virtual unsigned int get_ss(void) = 0;
+      virtual unsigned int set_ss(unsigned int ss) = 0;
+
+      virtual subslot_filter_mode get_mode(void) = 0;
+      virtual subslot_filter_mode set_mode(subslot_filter_mode mode) = 0;
     };
   } // namespace gsm
 } // namespace gr
diff --git a/lib/flow_control/burst_sdcch_subslot_filter_impl.cc b/lib/flow_control/burst_sdcch_subslot_filter_impl.cc
index 31e2989..76bf9cd 100644
--- a/lib/flow_control/burst_sdcch_subslot_filter_impl.cc
+++ b/lib/flow_control/burst_sdcch_subslot_filter_impl.cc
@@ -101,5 +101,37 @@ namespace gr {
             message_port_pub(pmt::mp("out"), msg);
         }
     }
+
+    /* External API */
+    unsigned int
+    burst_sdcch_subslot_filter_impl::get_ss(void)
+    {
+      return d_subslot;
+    }
+
+    unsigned int
+    burst_sdcch_subslot_filter_impl::set_ss(unsigned int ss)
+    {
+      if ((d_mode == SS_FILTER_SDCCH8 && ss < 8)
+      || (d_mode == SS_FILTER_SDCCH4 && ss < 4))
+        d_subslot = ss;
+
+      return d_subslot;
+    }
+
+
+    subslot_filter_mode
+    burst_sdcch_subslot_filter_impl::get_mode(void)
+    {
+      return d_mode;
+    }
+
+    subslot_filter_mode
+    burst_sdcch_subslot_filter_impl::set_mode(subslot_filter_mode mode)
+    {
+      d_mode = mode;
+      return d_mode;
+    }
+
   } /* namespace gsm */
 } /* namespace gr */
diff --git a/lib/flow_control/burst_sdcch_subslot_filter_impl.h b/lib/flow_control/burst_sdcch_subslot_filter_impl.h
index 40a603e..9068140 100644
--- a/lib/flow_control/burst_sdcch_subslot_filter_impl.h
+++ b/lib/flow_control/burst_sdcch_subslot_filter_impl.h
@@ -37,6 +37,13 @@ namespace gr {
       burst_sdcch_subslot_filter_impl(subslot_filter_mode mode, unsigned int subslot);
       ~burst_sdcch_subslot_filter_impl();
       void process_burst(pmt::pmt_t msg);
+
+      /* External API */
+      unsigned int get_ss(void);
+      unsigned int set_ss(unsigned int ss);
+
+      subslot_filter_mode get_mode(void);
+      subslot_filter_mode set_mode(subslot_filter_mode mode);
     };
 
   } // namespace gsm