diff --git a/ggsn_tests/GTP_CodecPort.ttcn b/ggsn_tests/GTP_CodecPort.ttcn
new file mode 100644
index 0000000..44c71e2
--- /dev/null
+++ b/ggsn_tests/GTP_CodecPort.ttcn
@@ -0,0 +1,84 @@
+/* Translation Port sitting on top of IPL4_asp UDP to encode/decode GTP */
+/* (C) 2017 by Harald Welte <laforge@gnumonks.org */
+module GTP_CodecPort {
+	import from IPL4asp_PortType all;
+	import from IPL4asp_Types all;
+	import from GTPC_Types all;
+	import from GTPU_Types all;
+
+	/* identifies a remote peer (sender or receiver) */
+	type record GtpPeer {
+		ConnectionId	connId,
+		HostName	remName,
+		PortNumber	remPort
+	}
+
+	/* Decoded GTP1C (Control Plane), used in send and receive direction */
+	type record Gtp1cUnitdata {
+		GtpPeer		peer,
+		PDU_GTPC	gtpc
+	}
+
+	/* Decoded GTP1U (User Plane), used in send and receive direction */
+	type record Gtp1uUnitdata {
+		GtpPeer		peer,
+		PDU_GTPU	gtpu
+	}
+
+ 	/* Translation port on top of IPL4asp; ASP_Event passed through transparently */
+	type port GTPC_PT message map to IPL4asp_PT {
+		out	Gtp1cUnitdata to ASP_SendTo with f_enc_Gtp1cUD();
+		in	Gtp1cUnitdata from ASP_RecvFrom with f_dec_Gtp1cUD(),
+			ASP_Event;
+		/* we can declare variables here and use them from all functions with "port" label */
+	}
+
+	function f_enc_Gtp1cUD(in Gtp1cUnitdata in_ud, out ASP_SendTo out_ud) port GTPC_PT {
+		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_GTPC(in_ud.gtpc);
+		port.setstate(0);
+	} with { extension "prototype(fast)" };
+
+	function f_dec_Gtp1cUD(in ASP_RecvFrom in_ud, out Gtp1cUnitdata out_ud) port GTPC_PT {
+		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_GTPC(in_ud.msg);
+		port.setstate(0);
+	} with { extension "prototype(fast)" };
+
+
+	/* Translation port on top of IPL4asp; ASP_Event passed through transparently */
+	type port GTPU_PT message map to IPL4asp_PT {
+		out	Gtp1uUnitdata to ASP_SendTo with f_enc_Gtp1uUD();
+		in	Gtp1uUnitdata from ASP_RecvFrom with f_dec_Gtp1uUD(),
+			ASP_Event;
+		/* we can declare variables here and use them from all functions with "port" label */
+	}
+
+	function f_enc_Gtp1uUD(in Gtp1uUnitdata in_ud, out ASP_SendTo out_ud) port GTPU_PT {
+		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_GTPU(in_ud.gtpu);
+		port.setstate(0);
+	} with { extension "prototype(fast)" };
+
+	function f_dec_Gtp1uUD(in ASP_RecvFrom in_ud, out Gtp1uUnitdata out_ud) port GTPU_PT {
+		out_ud.peer.connId := in_ud.connId;
+		out_ud.peer.remName := in_ud.remName;
+		out_ud.peer.remPort := in_ud.remPort;
+		out_ud.gtpu := dec_PDU_GTPU(in_ud.msg);
+		port.setstate(0);
+	} with { extension "prototype(fast)" };
+/*
+	function f_GTPC_listen(inout GTPC_PT portRef, in HostName locName,
+				in PortNumber locPort) return Result { 
+		return f_IPL4_listen(portRef, locName, locPort, { udp := {} });
+	}
+*/
+}