diff --git a/openbsc/.gitignore b/openbsc/.gitignore
index 0a2965d..518a960 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -81,6 +81,7 @@
 tests/oap/oap_test
 tests/gtphub/gtphub_test
 tests/mm_auth/mm_auth_test
+tests/xid/xid_test
 
 tests/atconfig
 tests/atlocal
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 0980413..fbf2930 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -229,6 +229,7 @@
     tests/oap/Makefile
     tests/gtphub/Makefile
     tests/mm_auth/Makefile
+    tests/xid/Makefile
     doc/Makefile
     doc/examples/Makefile
     Makefile)
diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index c272b14..11f650d 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -18,7 +18,7 @@
 		 gprs_gb_parse.h smpp.h meas_feed.h \
 		 gprs_gsup_client.h bsc_msg_filter.h \
 		 oap.h oap_messages.h \
-		 gtphub.h
+		 gtphub.h gprs_llc_xid.h
 
 openbsc_HEADERS = gsm_04_08.h meas_rep.h bsc_api.h
 openbscdir = $(includedir)/openbsc
diff --git a/openbsc/include/openbsc/gprs_llc_xid.h b/openbsc/include/openbsc/gprs_llc_xid.h
new file mode 100644
index 0000000..d340d40
--- /dev/null
+++ b/openbsc/include/openbsc/gprs_llc_xid.h
@@ -0,0 +1,57 @@
+/* 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/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <osmocom/core/linuxlist.h>
+
+/* 3GPP TS 44.064 6.4.1.6 Exchange Identification (XID)
+   command/response parameter field */
+struct gprs_llc_xid_field {
+	struct llist_head list;
+	uint8_t type;		/* See also Table 6: LLC layer parameter
+				   negotiation */
+	uint8_t *data;		/* Payload data (memory is owned by the
+				 * creator of the struct) */
+	unsigned int data_len;	/* Payload length */
+};
+
+/* 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);
+
+/* 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);
+
+/* 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);
+
+/* Copy an llist with xid fields */
+struct llist_head *gprs_llc_copy_xid(const void *ctx,
+				     const struct llist_head *xid_fields);
+
+/* Dump a list with XID fields (Debug) */
+void gprs_llc_dump_xid_fields(const struct llist_head *xid_fields,
+			      unsigned int logl);
+
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);
+		}
+	}
+}
diff --git a/openbsc/tests/Makefile.am b/openbsc/tests/Makefile.am
index 09298a3..ba5ca28 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -1,4 +1,4 @@
-SUBDIRS = gsm0408 db channel mgcp gprs abis gbproxy trau subscr mm_auth
+SUBDIRS = gsm0408 db channel mgcp gprs abis gbproxy trau subscr mm_auth xid
 
 if BUILD_NAT
 SUBDIRS += bsc-nat bsc-nat-trie
diff --git a/openbsc/tests/testsuite.at b/openbsc/tests/testsuite.at
index dab9568..6470ab9 100644
--- a/openbsc/tests/testsuite.at
+++ b/openbsc/tests/testsuite.at
@@ -124,3 +124,8 @@
 AT_CHECK([$abs_top_builddir/tests/mm_auth/mm_auth_test], [], [expout], [ignore])
 AT_CLEANUP
 
+AT_SETUP([xid])
+AT_KEYWORDS([xid])
+cat $abs_srcdir/xid/xid_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/xid/xid_test], [], [expout], [ignore])
+AT_CLEANUP
diff --git a/openbsc/tests/xid/Makefile.am b/openbsc/tests/xid/Makefile.am
new file mode 100644
index 0000000..9b64965
--- /dev/null
+++ b/openbsc/tests/xid/Makefile.am
@@ -0,0 +1,21 @@
+AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include
+AM_CFLAGS=-Wall -ggdb3 $(LIBOSMOCORE_CFLAGS) $(LIBOSMOGSM_CFLAGS) $(LIBCARES_CFLAGS)
+
+EXTRA_DIST = xid_test.ok
+
+noinst_PROGRAMS = xid_test
+
+xid_test_SOURCES = xid_test.c
+
+xid_test_LDADD = \
+	$(top_builddir)/src/gprs/gprs_llc_xid.o \
+	$(top_builddir)/src/libcommon/libcommon.a \
+	$(LIBOSMOABIS_LIBS) \
+	$(LIBOSMOCORE_LIBS) \
+	$(LIBOSMOGSM_LIBS) \
+	$(LIBOSMOGB_LIBS) \
+	$(LIBCARES_LIBS) \
+	$(LIBCRYPTO_LIBS) \
+	-lgtp -lrt -lm
+
+
diff --git a/openbsc/tests/xid/xid_test.c b/openbsc/tests/xid/xid_test.c
new file mode 100644
index 0000000..b77a4ae
--- /dev/null
+++ b/openbsc/tests/xid/xid_test.c
@@ -0,0 +1,164 @@
+/* Test LLC-XID Encoding/Decoding */
+
+/* (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 <openbsc/gprs_llc_xid.h>
+#include <openbsc/debug.h>
+
+#include <osmocom/core/talloc.h>
+#include <osmocom/core/utils.h>
+
+#include <osmocom/core/application.h>
+
+#include <stdio.h>
+#include <string.h>
+
+/* Test XID encoding */
+static void test_xid_encode(const void *ctx)
+{
+	struct gprs_llc_xid_field xid_field_1;
+	struct gprs_llc_xid_field xid_field_2;
+	struct gprs_llc_xid_field xid_field_3;
+	struct gprs_llc_xid_field xid_field_4;
+	LLIST_HEAD(xid_fields);
+	uint8_t xid[255];
+	uint8_t xid_expected[] =
+	    { 0x10, 0x8c, 0x14, 0x43, 0x43, 0x43, 0x43, 0x43, 0x0b, 0x42, 0x42,
+	0x42, 0x05, 0x41 };
+	int rc;
+
+	printf("Testing LLC XID-Encoder\n");
+
+	/* Setup some simple XID data */
+	xid_field_1.type = 1;
+	xid_field_2.type = 2;
+	xid_field_3.type = 3;
+	xid_field_4.type = 4;
+
+	xid_field_1.data = (uint8_t *) "A";
+	xid_field_2.data = (uint8_t *) "BBB";
+	xid_field_3.data = (uint8_t *) "CCCCC";
+	xid_field_4.data = NULL;
+
+	xid_field_1.data_len = 1;
+	xid_field_2.data_len = 3;
+	xid_field_3.data_len = 5;
+	xid_field_4.data_len = 0;
+
+	llist_add(&xid_field_4.list, &xid_fields);
+	llist_add(&xid_field_3.list, &xid_fields);
+	llist_add(&xid_field_2.list, &xid_fields);
+	llist_add(&xid_field_1.list, &xid_fields);
+
+	printf("Data to encode:\n");
+	gprs_llc_dump_xid_fields(&xid_fields, DSNDCP);
+
+	/* Encode data */
+	rc = gprs_llc_compile_xid(xid, sizeof(xid), &xid_fields);
+	OSMO_ASSERT(rc == 14);
+	printf("Encoded:  %s (%i bytes)\n", osmo_hexdump_nospc(xid, rc), rc);
+	printf("Expected: %s (%i bytes)\n",
+	       osmo_hexdump_nospc(xid_expected, sizeof(xid_expected)),
+	       (int)sizeof(xid_expected));
+
+	OSMO_ASSERT(memcmp(xid_expected, xid, sizeof(xid_expected)) == 0);
+
+	printf("\n");
+}
+
+/* Test XID decoding */
+static void test_xid_decode(const void *ctx)
+{
+	struct llist_head *xid_fields;
+	int rc;
+
+	printf("Testing LLC XID-Decoder/Encoder\n");
+
+	/* Example of a real world LLC-XID message */
+	uint8_t xid[] =
+	    { 0x01, 0x00, 0x16, 0x05, 0xf0, 0x1a, 0x05, 0xf0, 0xac, 0xd8, 0x00,
+	0x01, 0x00, 0x02, 0x31, 0x82, 0x02, 0x27, 0x89, 0xff, 0xe0, 0x00, 0x0f,
+	0x00, 0xa8, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x00, 0x02, 0x01, 0x02,
+	0x00, 0x03, 0x01, 0x03, 0x00, 0x04, 0x01, 0x04, 0x00, 0x05, 0x01, 0x05,
+	0x00, 0x06, 0x00, 0x07, 0x01, 0x07, 0x00, 0x08, 0x01, 0x08, 0x80, 0x00,
+	0x04, 0x12, 0x00, 0x40, 0x07 };
+
+	uint8_t xid_r[512];
+
+	/* Decode and display XID fields */
+	xid_fields = gprs_llc_parse_xid(ctx, xid, sizeof(xid));
+	OSMO_ASSERT(xid_fields);
+
+	printf("Decoded:\n");
+	gprs_llc_dump_xid_fields(xid_fields, DSNDCP);
+
+
+	/* Encode xid-fields again */
+	rc = gprs_llc_compile_xid(xid_r, sizeof(xid_r), xid_fields);
+	printf("Result length=%i\n",rc);
+	printf("Encoded:  %s\n", osmo_hexdump_nospc(xid, sizeof(xid)));
+	printf("Rencoded: %s\n", osmo_hexdump_nospc(xid_r, rc));
+
+	OSMO_ASSERT(rc == 64);
+	OSMO_ASSERT(memcmp(xid, xid_r, sizeof(xid)) == 0);
+
+	/* Free xid fields */
+	talloc_free(xid_fields);
+
+	printf("\n");
+}
+
+static struct log_info_cat gprs_categories[] = {
+	[DSNDCP] = {
+		    .name = "DSNDCP",
+		    .description =
+		    "GPRS Sub-Network Dependent Control Protocol (SNDCP)",
+		    .enabled = 1,.loglevel = LOGL_DEBUG,
+		    }
+};
+
+static struct log_info info = {
+	.cat = gprs_categories,
+	.num_cat = ARRAY_SIZE(gprs_categories),
+};
+
+int main(int argc, char **argv)
+{
+	void *xid_ctx;
+
+	osmo_init_logging(&info);
+
+	xid_ctx = talloc_named_const(NULL, 0, "xid_ctx");
+
+	test_xid_decode(xid_ctx);
+	test_xid_encode(xid_ctx);
+	printf("Done\n");
+
+	talloc_report_full(xid_ctx, stderr);
+	OSMO_ASSERT(talloc_total_blocks(xid_ctx) == 1);
+	return 0;
+}
+
+/* stubs */
+struct osmo_prim_hdr;
+int bssgp_prim_cb(struct osmo_prim_hdr *oph, void *ctx)
+{
+        abort();
+}
diff --git a/openbsc/tests/xid/xid_test.ok b/openbsc/tests/xid/xid_test.ok
new file mode 100644
index 0000000..4cf825c
--- /dev/null
+++ b/openbsc/tests/xid/xid_test.ok
@@ -0,0 +1,12 @@
+Testing LLC XID-Decoder/Encoder
+Decoded:
+Result length=64
+Encoded:  01001605f01a05f0acd8000100023182022789ffe0000f00a8000000010101000201020003010300040104000501050006000701070008010880000412004007
+Rencoded: 01001605f01a05f0acd8000100023182022789ffe0000f00a8000000010101000201020003010300040104000501050006000701070008010880000412004007
+
+Testing LLC XID-Encoder
+Data to encode:
+Encoded:  108c1443434343430b4242420541 (14 bytes)
+Expected: 108c1443434343430b4242420541 (14 bytes)
+
+Done