diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index 6dc7e16..8cbdd91 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -28,7 +28,7 @@
 			sgsn_ctrl.c sgsn_auth.c gprs_subscriber.c \
 			gprs_utils.c gprs_gsup_client.c \
 			sgsn_cdr.c sgsn_ares.c \
-			oap.c oap_messages.c
+			oap.c oap_messages.c gprs_llc_xid.c
 osmo_sgsn_LDADD = 	\
 			$(top_builddir)/src/libcommon/libcommon.a \
 			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) \
diff --git a/openbsc/src/gprs/gprs_llc_xid.c b/openbsc/src/gprs/gprs_llc_xid.c
new file mode 100644
index 0000000..4b1685e
--- /dev/null
+++ b/openbsc/src/gprs/gprs_llc_xid.c
@@ -0,0 +1,262 @@
+/* GPRS LLC XID field encoding/decoding as per 3GPP TS 44.064 */
+
+/* (C) 2016 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Philipp Maier
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/talloc.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/sgsn.h>
+#include <openbsc/gprs_llc_xid.h>
+
+/* Parse XID parameter field */
+static int decode_xid_field(struct gprs_llc_xid_field *xid_field,
+			    const uint8_t *src, uint8_t src_len)
+{
+	uint8_t xl;
+	uint8_t type;
+	uint8_t len;
+	int src_counter = 0;
+
+	/* Exit immediately if it is clear that no
+	 * parseable data is present */
+	if (src_len < 1 || !src)
+		return -EINVAL;
+
+	/* Extract header info */
+	xl = (*src >> 7) & 1;
+	type = (*src >> 2) & 0x1F;
+
+	/* Extract length field */
+	len = (*src) & 0x3;
+	src++;
+	src_counter++;
+	if (xl) {
+		if (src_len < 2)
+			return -EINVAL;
+		len = (len << 6) & 0xC0;
+		len |= ((*src) >> 2) & 0x3F;
+		src++;
+		src_counter++;
+	}
+
+	/* Fill out struct */
+	xid_field->type = type;
+	xid_field->data_len = len;
+	if (len > 0) {
+		if (src_len < src_counter + len)
+			return -EINVAL;
+		xid_field->data =
+			talloc_memdup(xid_field,src,xid_field->data_len);
+	} else
+		xid_field->data = NULL;
+
+	/* Return consumed length */
+	return src_counter + len;
+}
+
+/* Encode XID parameter field */
+static int encode_xid_field(uint8_t *dst, int dst_maxlen,
+			    const struct gprs_llc_xid_field *xid_field)
+{
+	int xl = 0;
+
+	/* When the length does not fit into 2 bits,
+	 * we need extended length fields */
+	if (xid_field->data_len > 3)
+		xl = 1;
+
+	/* Exit immediately if it is clear that no
+	 * encoding result can be stored */
+	if (dst_maxlen < xid_field->data_len + 1 + xl)
+		return -EINVAL;
+
+	/* There are only 5 bits reserved for the type, exit on exceed */
+	if (xid_field->type > 31)
+		return -EINVAL;
+
+	/* Encode header */
+	memset(dst, 0, dst_maxlen);
+	if (xl)
+		dst[0] |= 0x80;
+	dst[0] |= (((xid_field->type) & 0x1F) << 2);
+
+	if (xl) {
+		dst[0] |= (((xid_field->data_len) >> 6) & 0x03);
+		dst[1] = ((xid_field->data_len) << 2) & 0xFC;
+	} else
+		dst[0] |= ((xid_field->data_len) & 0x03);
+
+	/* Append payload data */
+	if (xid_field->data && xid_field->data_len)
+		memcpy(dst + 1 + xl, xid_field->data, xid_field->data_len);
+
+	/* Return generated length */
+	return xid_field->data_len + 1 + xl;
+}
+
+/* Transform a list with XID fields into a XID message (dst) */
+int gprs_llc_compile_xid(uint8_t *dst, int dst_maxlen,
+			 const struct llist_head *xid_fields)
+{
+	struct gprs_llc_xid_field *xid_field;
+	int rc;
+	int byte_counter = 0;
+
+	OSMO_ASSERT(xid_fields);
+	OSMO_ASSERT(dst);
+
+	llist_for_each_entry_reverse(xid_field, xid_fields, list) {
+		/* Encode XID-Field */
+		rc = encode_xid_field(dst, dst_maxlen, xid_field);
+		if (rc < 0)
+			return -EINVAL;
+
+		/* Advance pointer and lower maxlen for the
+		 * next encoding round */
+		dst += rc;
+		byte_counter += rc;
+		dst_maxlen -= rc;
+	}
+
+	/* Return generated length */
+	return byte_counter;
+}
+
+/* Transform a XID message (dst) into a list of XID fields */
+struct llist_head *gprs_llc_parse_xid(const void *ctx, const uint8_t *src,
+				      int src_len)
+{
+	struct gprs_llc_xid_field *xid_field;
+	struct llist_head *xid_fields;
+
+	int rc;
+	int max_loops = src_len;
+
+	OSMO_ASSERT(src);
+
+	xid_fields = talloc_zero(ctx, struct llist_head);
+	INIT_LLIST_HEAD(xid_fields);
+
+	while (1) {
+		/* Bail in case decode_xid_field() constantly returns zero */
+		if (max_loops <= 0) {
+			talloc_free(xid_fields);
+			return NULL;
+		}
+
+		/* Decode XID field */
+		xid_field = talloc_zero(xid_fields, struct gprs_llc_xid_field);
+		rc = decode_xid_field(xid_field, src, src_len);
+
+		/* Immediately stop on error */
+		if (rc < 0) {
+			talloc_free(xid_fields);
+			return NULL;
+		}
+
+		/* Add parsed XID field to list */
+		llist_add(&xid_field->list, xid_fields);
+
+		/* Advance pointer and lower dst_len for the next
+		 * decoding round */
+		src += rc;
+		src_len -= rc;
+
+		/* We are (scuccessfully) done when no further byes are left */
+		if (src_len == 0)
+			return xid_fields;
+
+		max_loops--;
+	}
+}
+
+/* Create a duplicate of an XID-Field */
+struct gprs_llc_xid_field *gprs_llc_dup_xid_field(const void *ctx, const struct
+						  gprs_llc_xid_field
+						  *xid_field)
+{
+	struct gprs_llc_xid_field *dup;
+
+	OSMO_ASSERT(xid_field);
+
+	/* Create a copy of the XID field in memory */
+	dup = talloc_memdup(ctx, xid_field, sizeof(*xid_field));
+	dup->data = talloc_memdup(ctx, xid_field->data, xid_field->data_len);
+
+	/* Unlink duplicate from source list */
+	INIT_LLIST_HEAD(&dup->list);
+
+	return dup;
+}
+
+/* Copy an llist with xid fields */
+struct llist_head *gprs_llc_copy_xid(const void *ctx,
+				     const struct llist_head *xid_fields)
+{
+	struct gprs_llc_xid_field *xid_field;
+	struct llist_head *xid_fields_copy;
+
+	OSMO_ASSERT(xid_fields);
+
+	xid_fields_copy = talloc_zero(ctx, struct llist_head);
+	INIT_LLIST_HEAD(xid_fields_copy);
+
+	/* Create duplicates and add them to the target list */
+	llist_for_each_entry(xid_field, xid_fields, list) {
+		llist_add(&gprs_llc_dup_xid_field(ctx, xid_field)->list,
+			  xid_fields_copy);
+	}
+
+	return xid_fields_copy;
+}
+
+/* Dump a list with XID fields (Debug) */
+void gprs_llc_dump_xid_fields(const struct llist_head *xid_fields,
+			      unsigned int logl)
+{
+	struct gprs_llc_xid_field *xid_field;
+
+	OSMO_ASSERT(xid_fields);
+
+	llist_for_each_entry(xid_field, xid_fields, list) {
+		if (xid_field->data_len) {
+			OSMO_ASSERT(xid_field->data);
+			LOGP(DLLC, logl,
+			     "XID: type=%d, data_len=%d, data=%s\n",
+			     xid_field->type, xid_field->data_len,
+			     osmo_hexdump_nospc(xid_field->data,
+						xid_field->data_len));
+		} else {
+			LOGP(DLLC, logl,
+			     "XID: type=%d, data_len=%d, data=NULL\n",
+			     xid_field->type, xid_field->data_len);
+		}
+	}
+}