diff --git a/gprs_gb/BSSGP_Helper.cc b/gprs_gb/BSSGP_Helper.cc
new file mode 100644
index 0000000..8cf97d2
--- /dev/null
+++ b/gprs_gb/BSSGP_Helper.cc
@@ -0,0 +1,96 @@
+
+#include "Octetstring.hh"
+#include "Error.hh"
+#include "Logger.hh"
+
+#include <stdint.h>
+
+namespace BSSGP__Helper__Functions {
+
+/* convert a buffer filled with TLVs that have variable-length "length" fields (Osmocom TvLV) into a
+ * buffer filled with TLVs that have fixed 16-bit length values (TL16V format) */
+static OCTETSTRING transcode_tlv_part(OCTETSTRING const &in)
+{
+	const unsigned char *in_ptr = (const unsigned char *)in;
+	int in_len = in.lengthof();
+	int ofs = 0;
+	uint16_t data_len;
+	OCTETSTRING out(0, (const unsigned char *)"");
+
+	while (ofs < in_len) {
+		int remain_len = in_len - ofs;
+		int tl_length;
+
+		if (remain_len < 2) {
+			TTCN_error("Remaining input length (%d) insufficient for Tag+Length", remain_len);
+			break;
+		}
+
+		/* copy over tag */
+		if (in_ptr[ofs+1] & 0x80) {
+			/* E bit is set, 7-bit length field */
+			data_len = in_ptr[ofs+1] & 0x7F;
+			tl_length = 2;
+		} else {
+			/* E bit is not set, 15 bit length field */
+			if (in_len < 3) {
+				TTCN_error("Remaining input length insufficient for 2-octet length");
+				break;
+			}
+			data_len = in_ptr[ofs+1] << 8 | in_ptr[ofs+2];
+			tl_length = 3;
+		}
+		if (in_len < tl_length + data_len) {
+			TTCN_error("Remaining input length insufficient for TLV value length");
+			break;
+		}
+
+		/* Tag + 16bit length */
+		uint8_t hdr_buf[3];
+		hdr_buf[0] = in_ptr[ofs+0];
+		hdr_buf[1] = data_len >> 8;
+		hdr_buf[2] = data_len & 0xff;
+
+		OCTETSTRING tlv_hdr(3, hdr_buf);
+		out += tlv_hdr;
+
+		if (data_len) {
+			/* append octet string of current TLV to output octetstring */
+			OCTETSTRING tlv_val(data_len, in_ptr + ofs + tl_length);
+			out += tlv_val;
+		}
+
+		/* advance input offset*/
+		ofs += data_len + tl_length;
+	}
+
+	return out;
+}
+
+#define BSSGP_PDUT_DL_UNITDATA	0x00
+#define BSSGP_PDUT_UL_UNITDATA	0x01
+
+/* expand all the variable-length "length" fields of a BSSGP message (Osmocom TvLV) into 
+ * statlc TL16V format */
+OCTETSTRING f__BSSGP__preprocess__pdu(OCTETSTRING const &in)
+{
+	const unsigned char *in_ptr = (const unsigned char *)in;
+	int in_len = in.lengthof();
+	uint8_t pdu_type = in_ptr[0];
+	uint8_t static_hdr_len = 1;
+
+	if (pdu_type == BSSGP_PDUT_DL_UNITDATA || pdu_type == BSSGP_PDUT_UL_UNITDATA)
+		static_hdr_len = 8;
+
+	if (in_len < static_hdr_len)
+		TTCN_error("BSSGP message is shorter (%u bytes) than minimum header length (%u bytes) for msg_type 0x%02x",
+				in_len, static_hdr_len, pdu_type);
+
+	/* prefix = non-TLV section of header */
+	OCTETSTRING prefix(static_hdr_len, in_ptr);
+	OCTETSTRING tlv_part_in(in_len - static_hdr_len, in_ptr + static_hdr_len);
+
+	return prefix + transcode_tlv_part(tlv_part_in);
+}
+
+}