diff --git a/library/OSMUX_Types.ttcn b/library/OSMUX_Types.ttcn
new file mode 100644
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+++ b/library/OSMUX_Types.ttcn
@@ -0,0 +1,110 @@
+/*
+ * (C) 2019 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All rights reserved.
+ *
+ * Author: Pau Espin Pedrol <pespin@sysmocom.de>
+ *
+ * Released under the terms of GNU General Public License, Version 2 or
+ * (at your option) any later version.
+ */
+
+module OSMUX_Types {
+
+import from General_Types all;
+
+external function enc_OSMUX_PDU ( in OSMUX_PDU msg ) return octetstring
+        with { extension "prototype(convert) encode(RAW)" };
+external function dec_OSMUX_PDU ( in octetstring msg ) return OSMUX_PDU
+        with { extension "prototype(convert) decode(RAW)" };
+
+type INT1 OsmuxCID	(0 .. 255);
+
+type enumerated OsmuxFT {
+  OSMUX_FT_LAPD,
+  OSMUX_FT_AMR,
+  OSMUX_FT_DUMMY
+};
+
+type record Osmux_AMR_header {
+  BIT1                 marker,
+  INT2b                ft,
+  INT3b                ctr,
+  BIT1                 amr_f,
+  BIT1                 amr_q,
+  INT1                 seq,
+  OsmuxCID             cid,
+  INT4b                amr_ft,
+  INT4b                amr_cmr
+} with {
+  variant "FIELDORDER(msb)"
+}
+
+type record PDU_Osmux_AMR {
+  Osmux_AMR_header     header,
+  octetstring          data
+} with {
+  variant "FIELDORDER(msb)"
+};
+
+type record PDU_Osmux_DUMMY {
+  Osmux_AMR_header     header,
+  octetstring          data
+} with {
+  variant "FIELDORDER(msb)"
+};
+
+type record Osmux_session_par {
+  integer               id optional,
+  charstring            local_address optional,
+  integer               local_port optional,
+  charstring            dest_address optional,
+  integer               dest_port optional
+}
+
+type record ASP_Osmux_Open_session {
+  Osmux_session_par       session_id
+}
+
+type record ASP_Osmux_Open_session_result {
+  Osmux_session_par       session_id
+}
+
+type record ASP_Osmux_Close_session {
+  Osmux_session_par       session_id
+}
+
+type union OSMUX_PDU {
+  PDU_Osmux_AMR               osmux_amr,
+  PDU_Osmux_DUMMY             osmux_dummy
+} with {
+  variant "TAG (
+    osmux_amr, header.ft = 1;
+    osmux_dummy, header.ft = 2;
+  )"
+};
+
+
+/* AMR voice frame type identifiers
+ * See also 3GPP TS 26.101, Table 1a: Interpretation of Frame Type, Mode
+ * Indication and Mode Request fields */
+type enumerated AMRFT {
+  AMR_FT_0,	/* 4.75 */
+  AMR_FT_1,	/* 5.15 */
+  AMR_FT_2,	/* 5.90 */
+  AMR_FT_3,	/* 6.70 */
+  AMR_FT_4,	/* 7.40 */
+  AMR_FT_5,	/* 7.95 */
+  AMR_FT_6,	/* 10.2 */
+  AMR_FT_7,	/* 12.2 */
+  AMR_FT_SID	/* SID */
+};
+
+/* AMR voice frame length (in bytes, rounded),
+ * See also RFC 3267, chapter 3.6 */
+const integer c_AMRFT_len[9] := {12, 13, 15, 17, 19, 20, 26, 31, 5};
+
+function f_amrft_payload_len(INT4b amr_ft) return integer {
+        return c_AMRFT_len[amr_ft];
+}
+
+} with { encode "RAW"}