diff --git a/library/GTPv2_CodecPort.ttcn b/library/GTPv2_CodecPort.ttcn
new file mode 100644
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--- /dev/null
+++ b/library/GTPv2_CodecPort.ttcn
@@ -0,0 +1,57 @@
+/* dual-faced port sitting on top of IPL4_asp UDP to encode/decode GTPv2C
+ * (C) 2019 Harald Welte <laforge@gnumonks.org>
+ * All rights reserved.
+ *
+ * Released under the terms of GNU General Public License, Version 2 or
+ * (at your option) any later version.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+
+module GTPv2_CodecPort {
+	import from IPL4asp_PortType all;
+	import from IPL4asp_Types all;
+	import from GTPv2C_Types all;
+
+	/* identifies a remote peer (sender or receiver) */
+	type record GtpPeer {
+		ConnectionId	connId,
+		HostName	remName,
+		PortNumber	remPort
+	}
+
+	/* Decoded GTP2C (Control Plane), used in send and receive direction */
+	type record Gtp2cUnitdata {
+		GtpPeer		peer,
+		PDU_GTPCv2	gtpc
+	}
+
+ 	/* Translation port on top of IPL4asp; ASP_Event passed through transparently */
+	type port GTPv2C_PT message {
+		out	Gtp2cUnitdata;
+		in	Gtp2cUnitdata,
+			ASP_ConnId_ReadyToRelease,
+			ASP_Event;
+	} with { extension "user IPL4asp_PT
+		out(Gtp2cUnitdata -> ASP_SendTo: function(f_enc_Gtp2cUD))
+		in(ASP_RecvFrom -> Gtp2cUnitdata: function(f_dec_Gtp2cUD);
+		   ASP_ConnId_ReadyToRelease -> ASP_ConnId_ReadyToRelease: simple;
+		   ASP_Event -> ASP_Event: simple)" }
+
+	private function f_enc_Gtp2cUD(in Gtp2cUnitdata in_ud, out ASP_SendTo out_ud) {
+		out_ud.connId := in_ud.peer.connId;
+		out_ud.remName := in_ud.peer.remName;
+		out_ud.remPort := in_ud.peer.remPort;
+		out_ud.proto := { udp := {} };
+		out_ud.msg := enc_PDU_GTPCv2(in_ud.gtpc);
+	} with { extension "prototype(fast)" };
+
+	private function f_dec_Gtp2cUD(in ASP_RecvFrom in_ud, out Gtp2cUnitdata out_ud) {
+		out_ud.peer.connId := in_ud.connId;
+		out_ud.peer.remName := in_ud.remName;
+		out_ud.peer.remPort := in_ud.remPort;
+		out_ud.gtpc := dec_PDU_GTPCv2(in_ud.msg);
+	} with { extension "prototype(fast)" };
+
+}