diff --git a/include/openbsc/trau_mux.h b/include/openbsc/trau_mux.h
new file mode 100644
index 0000000..43836db
--- /dev/null
+++ b/include/openbsc/trau_mux.h
@@ -0,0 +1,41 @@
+/* Simple TRAU frame reflector to route voice calls */
+
+/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+/* The "TRAU mux map" defines which particular 16kbit sub-slot (in which E1
+ * timeslot on which E1 interface) should be directly muxed to which other 
+ * sub-slot.  Entries in the mux map are always bi-directional. 
+ *
+ * The idea of all this is to directly switch voice channels in the BSC
+ * from one phone to another.  We do this right now since we don't support
+ * any external interface for voice channels, and in the future as an
+ * optimization to routing them externally.
+ */
+
+/* map a TRAU mux map entry */
+int trau_mux_map(const struct gsm_e1_subslot *src,
+		 const struct gsm_e1_subslot *dst);
+
+/* unmap a TRAU mux map entry */
+int trau_mux_unmap(const struct gsm_e1_subslot *ss);
+
+/* we get called by subchan_demux */
+int trau_mux_input(struct gsm_e1_subslot *src_e1_ss,
+		   const u_int8_t *trau_bits, int num_bits);