diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index 59136bd..3b58399 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -72,6 +72,7 @@
 	gprs_sgsn.c \
 	gprs_sndcp.c \
 	gprs_sndcp_vty.c \
+	gprs_sndcp_xid.c \
 	sgsn_main.c \
 	sgsn_vty.c \
 	sgsn_libgtp.c \
@@ -98,6 +99,7 @@
 	$(LIBCRYPTO_LIBS) \
 	-lrt \
 	-lgtp \
+	-lm \
 	$(NULL)
 if BUILD_IU
 osmo_sgsn_LDADD += \
diff --git a/openbsc/src/gprs/gprs_sndcp_xid.c b/openbsc/src/gprs/gprs_sndcp_xid.c
new file mode 100644
index 0000000..270bdee
--- /dev/null
+++ b/openbsc/src/gprs/gprs_sndcp_xid.c
@@ -0,0 +1,1803 @@
+/* GPRS SNDCP XID field encoding/decoding as per 3GPP TS 44.065 */
+
+/* (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 <math.h>
+#include <errno.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/gsm/tlv.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/sgsn.h>
+#include <openbsc/gprs_sndcp_xid.h>
+
+/* When the propose bit in an SNDCP-XID compression field is set to zero,
+ * the algorithm identifier is stripped. The algoritm parameters are specific
+ * for each algorithms. The following struct is used to pass the information
+ * about the referenced algorithm to the parser. */
+struct entity_algo_table {
+	unsigned int entity;	/* see also: 6.5.1.1.3 and 6.6.1.1.3 */
+	unsigned int algo;	/* see also: 6.5.1.1.4 and 6.6.1.1.4 */
+	unsigned int compclass;	/* Can be either SNDCP_XID_DATA_COMPRESSION or
+				   SNDCP_XID_PROTOCOL_COMPRESSION */
+};
+
+/* FUNCTIONS RELATED TO SNDCP-XID ENCODING */
+
+/* Encode applicable sapis (works the same in all three compression schemes) */
+static int encode_pcomp_applicable_sapis(uint8_t *dst,
+					 const uint8_t *nsapis,
+					 uint8_t nsapis_len)
+{
+	/* NOTE: Buffer *dst needs offer at 2 bytes
+	 * of space to store the generation results */
+
+	uint16_t blob;
+	uint8_t nsapi;
+	int i;
+
+	/* Bail if number of possible nsapis exceeds valid range
+	 * (Only 11 nsapis possible for PDP-Contexts) */
+	OSMO_ASSERT(nsapis_len <= 11);
+
+	/* Encode applicable SAPIs */
+	blob = 0;
+	for (i = 0; i < nsapis_len; i++) {
+		nsapi = nsapis[i];
+		/* Only NSAPI 5 to 15 are applicable for user traffic (PDP-
+		 * contexts). Only for these NSAPIs SNDCP-XID parameters
+		 * can apply. See also 3GPP TS 44.065, 5.1 Service primitives */
+		OSMO_ASSERT(nsapi >= 5 && nsapi <= 15);
+		blob |= (1 << nsapi);
+	}
+
+	/* Store result */
+	*dst = (blob >> 8) & 0xFF;
+	dst++;
+	*dst = blob & 0xFF;
+
+	return 2;
+}
+
+/* Encode rfc1144 parameter field
+ * (see also: 3GPP TS 44.065, 6.5.2.1, Table 5) */
+static int encode_pcomp_rfc1144_params(uint8_t *dst, unsigned int dst_maxlen,
+				       const struct
+				       gprs_sndcp_pcomp_rfc1144_params *params)
+{
+	/* NOTE: Buffer *dst should offer at least 3 bytes
+	 * of space to store the generation results */
+
+	int dst_counter = 0;
+	int rc;
+
+	OSMO_ASSERT(dst_maxlen >= 3);
+
+	/* Zero out buffer */
+	memset(dst, 0, dst_maxlen);
+
+	/* Encode applicable SAPIs */
+	rc = encode_pcomp_applicable_sapis(dst, params->nsapi,
+					   params->nsapi_len);
+	dst += rc;
+	dst_counter += rc;
+
+	/* Encode s01 (see also: 3GPP TS 44.065, 6.5.2.1, Table 5) */
+	OSMO_ASSERT(params->s01 >= 0);
+	OSMO_ASSERT(params->s01 <= 255);
+	*dst = params->s01;
+	dst++;
+	dst_counter++;
+
+	/* Return generated length */
+	return dst_counter;
+}
+
+/*
+ * Encode rfc2507 parameter field
+ * (see also: 3GPP TS 44.065, 6.5.3.1, Table 6)
+ */
+static int encode_pcomp_rfc2507_params(uint8_t *dst, unsigned int dst_maxlen,
+				       const struct
+				       gprs_sndcp_pcomp_rfc2507_params *params)
+{
+	/* NOTE: Buffer *dst should offer at least 3 bytes
+	 * of space to store the generation results */
+
+	int dst_counter = 0;
+	int rc;
+
+	OSMO_ASSERT(dst_maxlen >= 9);
+
+	/* Zero out buffer */
+	memset(dst, 0, dst_maxlen);
+
+	/* Encode applicable SAPIs */
+	rc = encode_pcomp_applicable_sapis(dst, params->nsapi,
+					   params->nsapi_len);
+	dst += rc;
+	dst_counter += rc;
+
+	/* Encode F_MAX_PERIOD (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	OSMO_ASSERT(params->f_max_period >= 1);
+	OSMO_ASSERT(params->f_max_period <= 65535);
+	*dst = (params->f_max_period >> 8) & 0xFF;
+	dst++;
+	dst_counter++;
+	*dst = (params->f_max_period) & 0xFF;
+	dst++;
+	dst_counter++;
+
+	/* Encode F_MAX_TIME (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	OSMO_ASSERT(params->f_max_time >= 1);
+	OSMO_ASSERT(params->f_max_time <= 255);
+	*dst = params->f_max_time;
+	dst++;
+	dst_counter++;
+
+	/* Encode MAX_HEADER (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	OSMO_ASSERT(params->max_header >= 60);
+	OSMO_ASSERT(params->max_header <= 255);
+	*dst = params->max_header;
+	dst++;
+	dst_counter++;
+
+	/* Encode TCP_SPACE (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	OSMO_ASSERT(params->tcp_space >= 3);
+	OSMO_ASSERT(params->tcp_space <= 255);
+	*dst = params->tcp_space;
+	dst++;
+	dst_counter++;
+
+	/* Encode NON_TCP_SPACE (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	OSMO_ASSERT(params->non_tcp_space >= 3);
+	OSMO_ASSERT(params->non_tcp_space <= 65535);
+	*dst = (params->non_tcp_space >> 8) & 0xFF;
+	dst++;
+	dst_counter++;
+	*dst = (params->non_tcp_space) & 0xFF;
+	dst++;
+	dst_counter++;
+
+	/* Return generated length */
+	return dst_counter;
+}
+
+/* Encode ROHC parameter field
+ * (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+static int encode_pcomp_rohc_params(uint8_t *dst, unsigned int dst_maxlen,
+				    const struct gprs_sndcp_pcomp_rohc_params
+				    *params)
+{
+	/* NOTE: Buffer *dst should offer at least 36
+	 * (2 * 16 Profiles + 2 * 3 Parameter) bytes
+	 * of memory space to store generation results */
+
+	int i;
+	int dst_counter = 0;
+	int rc;
+
+	OSMO_ASSERT(dst_maxlen >= 38);
+
+	/* Bail if number of ROHC profiles exceeds limit
+	 * (ROHC supports only a maximum of 16 different profiles) */
+	OSMO_ASSERT(params->profile_len >= 0);
+	OSMO_ASSERT(params->profile_len <= 16);
+
+	/* Zero out buffer */
+	memset(dst, 0, dst_maxlen);
+
+	/* Encode applicable SAPIs */
+	rc = encode_pcomp_applicable_sapis(dst, params->nsapi,
+					   params->nsapi_len);
+	dst += rc;
+	dst_counter += rc;
+
+	/* Encode MAX_CID (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+	OSMO_ASSERT(params->max_cid >= 0);
+	OSMO_ASSERT(params->max_cid <= 16383);
+	*dst = (params->max_cid >> 8) & 0xFF;
+	dst++;
+	*dst = params->max_cid & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Encode MAX_HEADER (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+	OSMO_ASSERT(params->max_header >= 60);
+	OSMO_ASSERT(params->max_header <= 255);
+	*dst = (params->max_header >> 8) & 0xFF;
+	dst++;
+	*dst = params->max_header & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Encode ROHC Profiles (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+	for (i = 0; i < params->profile_len; i++) {
+		*dst = (params->profile[i] >> 8) & 0xFF;
+		dst++;
+		*dst = params->profile[i] & 0xFF;
+		dst++;
+		dst_counter += 2;
+	}
+
+	/* Return generated length */
+	return dst_counter;
+}
+
+/* Encode V.42bis parameter field
+ * (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+static int encode_dcomp_v42bis_params(uint8_t *dst, unsigned int dst_maxlen,
+				      const struct
+				      gprs_sndcp_dcomp_v42bis_params *params)
+{
+	/* NOTE: Buffer *dst should offer at least 6 bytes
+	 * of space to store the generation results */
+
+	int dst_counter = 0;
+	int rc;
+
+	OSMO_ASSERT(dst_maxlen >= 6);
+
+	/* Zero out buffer */
+	memset(dst, 0, dst_maxlen);
+
+	/* Encode applicable SAPIs */
+	rc = encode_pcomp_applicable_sapis(dst, params->nsapi,
+					   params->nsapi_len);
+	dst += rc;
+	dst_counter += rc;
+
+	/* Encode P0 (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+	OSMO_ASSERT(params->p0 >= 0);
+	OSMO_ASSERT(params->p0 <= 3);
+	*dst = params->p0 & 0x03;
+	dst++;
+	dst_counter++;
+
+	/* Encode P1 (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+	OSMO_ASSERT(params->p1 >= 512);
+	OSMO_ASSERT(params->p1 <= 65535);
+	*dst = (params->p1 >> 8) & 0xFF;
+	dst++;
+	*dst = params->p1 & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Encode P2 (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+	OSMO_ASSERT(params->p2 >= 6);
+	OSMO_ASSERT(params->p2 <= 250);
+	*dst = params->p2;
+	dst++;
+	dst_counter++;
+
+	/* Return generated length */
+	return dst_counter;
+}
+
+/* Encode V44 parameter field
+ * (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+static int encode_dcomp_v44_params(uint8_t *dst, unsigned int dst_maxlen,
+				   const struct gprs_sndcp_dcomp_v44_params
+				   *params)
+{
+	/* NOTE: Buffer *dst should offer at least 12 bytes
+	 * of space to store the generation results */
+
+	int dst_counter = 0;
+	int rc;
+
+	OSMO_ASSERT(dst_maxlen >= 12);
+
+	/* Zero out buffer */
+	memset(dst, 0, dst_maxlen);
+
+	/* Encode applicable SAPIs */
+	rc = encode_pcomp_applicable_sapis(dst, params->nsapi,
+					   params->nsapi_len);
+	dst += rc;
+	dst_counter += rc;
+
+	/* Encode C0 (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	OSMO_ASSERT(params->c0 == 0x80 || params->c0 == 0xC0);
+	*dst = params->c0 & 0xC0;
+	dst++;
+	dst_counter++;
+
+	/* Encode P0 (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	OSMO_ASSERT(params->p0 >= 0);
+	OSMO_ASSERT(params->p0 <= 3);
+	*dst = params->p0 & 0x03;
+	dst++;
+	dst_counter++;
+
+	/* Encode P1T (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	OSMO_ASSERT(params->p1t >= 256);
+	OSMO_ASSERT(params->p1t <= 65535);
+	*dst = (params->p1t >> 8) & 0xFF;
+	dst++;
+	*dst = params->p1t & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Encode P1R (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	OSMO_ASSERT(params->p1r >= 256);
+	OSMO_ASSERT(params->p1r <= 65535);
+	*dst = (params->p1r >> 8) & 0xFF;
+	dst++;
+	*dst = params->p1r & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Encode P3T (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	OSMO_ASSERT(params->p3t >= 0);
+	OSMO_ASSERT(params->p3t <= 65535);
+	OSMO_ASSERT(params->p3t >= 2 * params->p1t);
+	*dst = (params->p3t >> 8) & 0xFF;
+	dst++;
+	*dst = params->p3t & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Encode P3R (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	OSMO_ASSERT(params->p3r >= 0);
+	OSMO_ASSERT(params->p3r <= 65535);
+	OSMO_ASSERT(params->p3r >= 2 * params->p1r);
+	*dst = (params->p3r >> 8) & 0xFF;
+	dst++;
+	*dst = params->p3r & 0xFF;
+	dst++;
+	dst_counter += 2;
+
+	/* Return generated length */
+	return dst_counter;
+}
+
+/* Encode data or protocol control information compression field
+ * (see also: 3GPP TS 44.065, 6.6.1.1, Figure 9 and
+ *            3GPP TS 44.065, 6.5.1.1, Figure 7) */
+static int encode_comp_field(uint8_t *dst, unsigned int dst_maxlen,
+			     const struct gprs_sndcp_comp_field *comp_field)
+{
+	int dst_counter = 0;
+	int len;
+	int expected_length;
+	int i;
+
+	uint8_t payload_bytes[256];
+	int payload_bytes_len = -1;
+
+	/* If possible, try do encode payload bytes first */
+	if (comp_field->rfc1144_params) {
+		payload_bytes_len =
+		    encode_pcomp_rfc1144_params(payload_bytes,
+						sizeof(payload_bytes),
+						comp_field->rfc1144_params);
+	} else if (comp_field->rfc2507_params) {
+		payload_bytes_len =
+		    encode_pcomp_rfc2507_params(payload_bytes,
+						sizeof(payload_bytes),
+						comp_field->rfc2507_params);
+	} else if (comp_field->rohc_params) {
+		payload_bytes_len =
+		    encode_pcomp_rohc_params(payload_bytes,
+					     sizeof(payload_bytes),
+					     comp_field->rohc_params);
+	} else if (comp_field->v42bis_params) {
+		payload_bytes_len =
+		    encode_dcomp_v42bis_params(payload_bytes,
+					       sizeof(payload_bytes),
+					       comp_field->v42bis_params);
+	} else if (comp_field->v44_params) {
+		payload_bytes_len =
+		    encode_dcomp_v44_params(payload_bytes,
+					    sizeof(payload_bytes),
+					    comp_field->v44_params);
+	} else
+		OSMO_ASSERT(false);
+
+	/* Bail immediately if payload byte generation failed */
+	OSMO_ASSERT(payload_bytes_len >= 0);
+
+	/* Bail if comp_len is out of bounds */
+	OSMO_ASSERT(comp_field->comp_len <= sizeof(comp_field->comp));
+
+	/* Calculate length field of the data block */
+	if (comp_field->p) {
+		len =
+		    payload_bytes_len +
+		    ceil((double)(comp_field->comp_len) / 2.0);
+		expected_length = len + 3;
+	} else {
+		len = payload_bytes_len;
+		expected_length = len + 2;
+	}
+
+	/* Bail immediately if no sufficient memory space is supplied */
+	OSMO_ASSERT(dst_maxlen >= expected_length);
+
+	/* Check if the entity number is within bounds */
+	OSMO_ASSERT(comp_field->entity <= 0x1f);
+
+	/* Check if the algorithm number is within bounds */
+	OSMO_ASSERT(comp_field->algo >= 0 || comp_field->algo <= 0x1f);
+
+	/* Zero out buffer */
+	memset(dst, 0, dst_maxlen);
+
+	/* Encode Propose bit */
+	if (comp_field->p)
+		*dst |= (1 << 7);
+
+	/* Encode entity number */
+	*dst |= comp_field->entity & 0x1F;
+	dst++;
+	dst_counter++;
+
+	/* Encode algorithm number */
+	if (comp_field->p) {
+		*dst |= comp_field->algo & 0x1F;
+		dst++;
+		dst_counter++;
+	}
+
+	/* Encode length field */
+	*dst |= len & 0xFF;
+	dst++;
+	dst_counter++;
+
+	/* Encode PCOMP/DCOMP values */
+	if (comp_field->p) {
+		for (i = 0; i < comp_field->comp_len; i++) {
+			/* Check if submitted PCOMP/DCOMP
+			   values are within bounds */
+			if ((comp_field->comp[i] < 0)
+			    || (comp_field->comp[i] > 0x0F))
+				return -EINVAL;
+
+			if (i & 1) {
+				*dst |= comp_field->comp[i] & 0x0F;
+				dst++;
+				dst_counter++;
+			} else
+				*dst |= (comp_field->comp[i] << 4) & 0xF0;
+		}
+
+		if (i & 1) {
+			dst++;
+			dst_counter++;
+		}
+	}
+
+	/* Append payload bytes */
+	memcpy(dst, payload_bytes, payload_bytes_len);
+	dst_counter += payload_bytes_len;
+
+	/* Return generated length */
+	return dst_counter;
+}
+
+/* Find out to which compression class the specified comp-field belongs
+ * (header compression or data compression?) */
+int gprs_sndcp_get_compression_class(const struct gprs_sndcp_comp_field
+				     *comp_field)
+{
+	OSMO_ASSERT(comp_field);
+
+	if (comp_field->rfc1144_params)
+		return SNDCP_XID_PROTOCOL_COMPRESSION;
+	else if (comp_field->rfc2507_params)
+		return SNDCP_XID_PROTOCOL_COMPRESSION;
+	else if (comp_field->rohc_params)
+		return SNDCP_XID_PROTOCOL_COMPRESSION;
+	else if (comp_field->v42bis_params)
+		return SNDCP_XID_DATA_COMPRESSION;
+	else if (comp_field->v44_params)
+		return SNDCP_XID_DATA_COMPRESSION;
+	else
+		return -EINVAL;
+}
+
+/* Convert all compression fields to bytstreams */
+static int gprs_sndcp_pack_fields(const struct llist_head *comp_fields,
+				  uint8_t *dst,
+				  unsigned int dst_maxlen, int class)
+{
+	struct gprs_sndcp_comp_field *comp_field;
+	int byte_counter = 0;
+	int rc;
+
+	llist_for_each_entry_reverse(comp_field, comp_fields, list) {
+		if (class == gprs_sndcp_get_compression_class(comp_field)) {
+			rc = encode_comp_field(dst + byte_counter,
+					       dst_maxlen - byte_counter,
+					       comp_field);
+
+			/* When input data is correct, there is
+			 * no reason for the encoder to fail! */
+			OSMO_ASSERT(rc >= 0);
+
+			byte_counter += rc;
+		}
+	}
+
+	/* Return generated length */
+	return byte_counter;
+}
+
+/* Transform a list with compression fields into an SNDCP-XID message (dst) */
+int gprs_sndcp_compile_xid(uint8_t *dst, unsigned int dst_maxlen,
+			   const struct llist_head *comp_fields)
+{
+	int rc;
+	int byte_counter = 0;
+	uint8_t comp_bytes[512];
+	uint8_t xid_version_number[1] = { CURRENT_SNDCP_VERSION };
+
+	OSMO_ASSERT(comp_fields);
+	OSMO_ASSERT(dst);
+	OSMO_ASSERT(dst_maxlen >= 2 + sizeof(xid_version_number));
+
+	/* Bail if there is no input */
+	if (llist_empty(comp_fields))
+		return -EINVAL;
+
+	/* Prepend header */
+	dst =
+	    tlv_put(dst, SNDCP_XID_VERSION_NUMBER,
+		    sizeof(xid_version_number), xid_version_number);
+	byte_counter += (sizeof(xid_version_number) + 2);
+
+	/* Add data compression fields */
+	rc = gprs_sndcp_pack_fields(comp_fields, comp_bytes,
+				    sizeof(comp_bytes),
+				    SNDCP_XID_DATA_COMPRESSION);
+	OSMO_ASSERT(rc >= 0);
+
+	if (rc > 0) {
+		dst = tlv_put(dst, SNDCP_XID_DATA_COMPRESSION, rc, comp_bytes);
+		byte_counter += rc + 2;
+	}
+
+	/* Add header compression fields */
+	rc = gprs_sndcp_pack_fields(comp_fields, comp_bytes,
+				    sizeof(comp_bytes),
+				    SNDCP_XID_PROTOCOL_COMPRESSION);
+	OSMO_ASSERT(rc >= 0);
+
+	if (rc > 0) {
+		dst = tlv_put(dst, SNDCP_XID_PROTOCOL_COMPRESSION, rc,
+			      comp_bytes);
+		byte_counter += rc + 2;
+	}
+
+	/* Return generated length */
+	return byte_counter;
+}
+
+/* FUNCTIONS RELATED TO SNDCP-XID DECODING */
+
+/* Decode applicable sapis (works the same in all three compression schemes) */
+static int decode_pcomp_applicable_sapis(uint8_t *nsapis,
+					 uint8_t *nsapis_len,
+					 const uint8_t *src,
+					 unsigned int src_len)
+{
+	uint16_t blob;
+	int i;
+	int nsapi_len = 0;
+
+	/* Exit immediately if no result can be stored */
+	if (!nsapis)
+		return -EINVAL;
+
+	/* Exit immediately if not enough input data is available */
+	if (src_len < 2)
+		return -EINVAL;
+
+	/* Read bitmask */
+	blob = *src;
+	blob = (blob << 8) & 0xFF00;
+	src++;
+	blob |= (*src) & 0xFF;
+	blob = (blob >> 5);
+
+	/* Decode applicable SAPIs */
+	for (i = 0; i < 15; i++) {
+		if ((blob >> i) & 1) {
+			nsapis[nsapi_len] = i + 5;
+			nsapi_len++;
+		}
+	}
+
+	/* Return consumed length */
+	*nsapis_len = nsapi_len;
+	return 2;
+}
+
+/* Decode 16 bit field */
+static int decode_pcomp_16_bit_field(int *value_int, uint16_t * value_uint16,
+				     const uint8_t *src,
+				     unsigned int src_len,
+				     int value_min, int value_max)
+{
+	uint16_t blob;
+
+	/* Reset values to zero (just to be sure) */
+	if (value_int)
+		*value_int = -1;
+	if (value_uint16)
+		*value_uint16 = 0;
+
+	/* Exit if not enough src are available */
+	if (src_len < 2)
+		return -EINVAL;
+
+	/* Decode bit value */
+	blob = *src;
+	blob = (blob << 8) & 0xFF00;
+	src++;
+	blob |= *src;
+
+	/* Check if parsed value is within bounds */
+	if (blob < value_min)
+		return -EINVAL;
+	if (blob > value_max)
+		return -EINVAL;
+
+	/* Hand back results to the caller */
+	if (value_int)
+		*value_int = blob;
+	if (value_uint16)
+		*value_uint16 = blob;
+
+	/* Return consumed length */
+	return 2;
+}
+
+/* Decode 8 bit field */
+static int decode_pcomp_8_bit_field(int *value_int, uint8_t *value_uint8,
+				    const uint8_t *src,
+				    unsigned int src_len,
+				    int value_min, int value_max)
+{
+	uint8_t blob;
+
+	/* Reset values to invalid (just to be sure) */
+	if (value_int)
+		*value_int = -1;
+	if (value_uint8)
+		*value_uint8 = 0;
+
+	/* Exit if not enough src are available */
+	if (src_len < 1)
+		return -EINVAL;
+
+	/* Decode bit value */
+	blob = *src;
+
+	/* Check if parsed value is within bounds */
+	if (blob < value_min)
+		return -EINVAL;
+	if (blob > value_max)
+		return -EINVAL;
+
+	/* Hand back results to the caller */
+	if (value_int)
+		*value_int = blob;
+	if (value_uint8)
+		*value_uint8 = blob;
+
+	/* Return consumed length */
+	return 1;
+}
+
+/* Decode rfc1144 parameter field see also: 3GPP TS 44.065, 6.5.2.1, Table 5) */
+static int decode_pcomp_rfc1144_params(struct gprs_sndcp_pcomp_rfc1144_params
+				       *params, const uint8_t *src,
+				       unsigned int src_len)
+{
+	int rc;
+	int byte_counter = 0;
+
+	/* Mark all optional parameters invalid by default */
+	params->s01 = -1;
+
+	/* Decode applicable SAPIs */
+	rc = decode_pcomp_applicable_sapis(params->nsapi, &params->nsapi_len,
+					   src, src_len);
+	if (rc > 0) {
+		byte_counter += rc;
+		src += rc;
+	} else
+		return byte_counter;
+
+	/* Decode parameter S0 -1
+	 * (see also: 3GPP TS 44.065, 6.5.2.1, Table 5) */
+	rc = decode_pcomp_8_bit_field(&params->s01, NULL, src,
+				      src_len - byte_counter, 0, 255);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Return consumed length */
+	return byte_counter;
+}
+
+/* Decode rfc2507 parameter field
+ * (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+static int decode_pcomp_rfc2507_params(struct gprs_sndcp_pcomp_rfc2507_params
+				       *params, const uint8_t *src,
+				       unsigned int src_len)
+{
+	int rc;
+	int byte_counter = 0;
+
+	/* Mark all optional parameters invalid by default */
+	params->f_max_period = -1;
+	params->f_max_time = -1;
+	params->max_header = -1;
+	params->tcp_space = -1;
+	params->non_tcp_space = -1;
+
+	/* Decode applicable SAPIs */
+	rc = decode_pcomp_applicable_sapis(params->nsapi, &params->nsapi_len,
+					   src, src_len);
+	if (rc > 0) {
+		byte_counter += rc;
+		src += rc;
+	} else
+		return byte_counter;
+
+	/* Decode F_MAX_PERIOD (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	rc = decode_pcomp_16_bit_field(&params->f_max_period, NULL, src,
+				       src_len - byte_counter, 1, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode F_MAX_TIME (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	rc = decode_pcomp_8_bit_field(&params->f_max_time, NULL, src,
+				      src_len - byte_counter, 1, 255);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode MAX_HEADER (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	rc = decode_pcomp_8_bit_field(&params->max_header, NULL, src,
+				      src_len - byte_counter, 60, 255);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode TCP_SPACE (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	rc = decode_pcomp_8_bit_field(&params->tcp_space, NULL, src,
+				      src_len - byte_counter, 3, 255);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode NON_TCP_SPACE (see also: 3GPP TS 44.065, 6.5.3.1, Table 6) */
+	rc = decode_pcomp_16_bit_field(&params->non_tcp_space, NULL, src,
+				       src_len - byte_counter, 3, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Return consumed length */
+	return byte_counter;
+}
+
+/* Decode ROHC parameter field (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+static int decode_pcomp_rohc_params(struct gprs_sndcp_pcomp_rohc_params *params,
+				    const uint8_t *src, unsigned int src_len)
+{
+	int rc;
+	int byte_counter = 0;
+	int i;
+
+	/* Mark all optional parameters invalid by default */
+	params->max_cid = -1;
+	params->max_header = -1;
+
+	/* Decode applicable SAPIs */
+	rc = decode_pcomp_applicable_sapis(params->nsapi, &params->nsapi_len,
+					   src, src_len);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode MAX_CID (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+	rc = decode_pcomp_16_bit_field(&params->max_cid, NULL, src,
+				       src_len - byte_counter, 0, 16383);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode MAX_HEADER (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+	rc = decode_pcomp_16_bit_field(&params->max_header, NULL, src,
+				       src_len - byte_counter, 60, 255);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode Profiles (see also: 3GPP TS 44.065, 6.5.4.1, Table 10) */
+	for (i = 0; i < 16; i++) {
+		params->profile_len = 0;
+		rc = decode_pcomp_16_bit_field(NULL, &params->profile[i], src,
+					       src_len - byte_counter, 0,
+					       65535);
+		if (rc <= 0)
+			return byte_counter;
+		byte_counter += rc;
+		src += rc;
+		params->profile_len = i + 1;
+	}
+
+	/* Return consumed length */
+	return byte_counter;
+}
+
+/* Decode V.42bis parameter field
+ * (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+static int decode_dcomp_v42bis_params(struct gprs_sndcp_dcomp_v42bis_params
+				      *params, const uint8_t *src,
+				      unsigned int src_len)
+{
+	int rc;
+	int byte_counter = 0;
+
+	/* Mark all optional parameters invalid by default */
+	params->p0 = -1;
+	params->p1 = -1;
+	params->p2 = -1;
+
+	/* Decode applicable SAPIs */
+	rc = decode_pcomp_applicable_sapis(params->nsapi, &params->nsapi_len,
+					   src, src_len);
+	if (rc > 0) {
+		byte_counter += rc;
+		src += rc;
+	} else
+		return byte_counter;
+
+	/* Decode P0 (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+	rc = decode_pcomp_8_bit_field(&params->p0, NULL, src,
+				      src_len - byte_counter, 0, 3);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P1 (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+	rc = decode_pcomp_16_bit_field(&params->p1, NULL, src,
+				       src_len - byte_counter, 512, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P2 (see also: 3GPP TS 44.065, 6.6.2.1, Table 7a) */
+	rc = decode_pcomp_8_bit_field(&params->p2, NULL, src,
+				      src_len - byte_counter, 6, 250);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Return consumed length */
+	return byte_counter;
+}
+
+/* Decode V44 parameter field (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+static int decode_dcomp_v44_params(struct gprs_sndcp_dcomp_v44_params *params,
+				   const uint8_t *src, unsigned int src_len)
+{
+	int rc;
+	int byte_counter = 0;
+
+	/* Mark all optional parameters invalid by default */
+	params->c0 = -1;
+	params->p0 = -1;
+	params->p1t = -1;
+	params->p1r = -1;
+	params->p3t = -1;
+	params->p3r = -1;
+
+	/* Decode applicable SAPIs */
+	rc = decode_pcomp_applicable_sapis(params->nsapi, &params->nsapi_len,
+					   src, src_len);
+	if (rc > 0) {
+		byte_counter += rc;
+		src += rc;
+	} else
+		return byte_counter;
+
+	/* Decode C0 (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	rc = decode_pcomp_8_bit_field(&params->c0, NULL, src,
+				      src_len - byte_counter, 0, 255);
+	if (rc <= 0)
+		return byte_counter;
+	if ((params->c0 != 0x80) && (params->c0 != 0xC0))
+		return -EINVAL;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P0 (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	rc = decode_pcomp_8_bit_field(&params->p0, NULL, src,
+				      src_len - byte_counter, 0, 3);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P1T (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	rc = decode_pcomp_16_bit_field(&params->p1t, NULL, src,
+				       src_len - byte_counter, 265, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P1R (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	rc = decode_pcomp_16_bit_field(&params->p1r, NULL, src,
+				       src_len - byte_counter, 265, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P3T (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	rc = decode_pcomp_16_bit_field(&params->p3t, NULL, src,
+				       src_len - byte_counter, 265, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	if (params->p3t < 2 * params->p1t)
+		return -EINVAL;
+	byte_counter += rc;
+	src += rc;
+
+	/* Decode P3R (see also: 3GPP TS 44.065, 6.6.3.1, Table 7c) */
+	rc = decode_pcomp_16_bit_field(&params->p3r, NULL, src,
+				       src_len - byte_counter, 265, 65535);
+	if (rc <= 0)
+		return byte_counter;
+	if (params->p3r < 2 * params->p1r)
+		return -EINVAL;
+	byte_counter += rc;
+	src += rc;
+
+	/* Return consumed length */
+	return byte_counter;
+}
+
+/* Lookup algorithm identfier by entity ID */
+static int lookup_algorithm_identifier(int entity, const struct
+				       entity_algo_table
+				       *lt, unsigned int lt_len, int compclass)
+{
+	int i;
+
+	if (!lt)
+		return -1;
+
+	for (i = 0; i < lt_len; i++) {
+		if ((lt[i].entity == entity)
+		    && (lt[i].compclass == compclass))
+			return lt[i].algo;
+	}
+
+	return -1;
+}
+
+/* Helper function for decode_comp_field(), decodes
+ * numeric pcomp/dcomp values */
+static int decode_comp_values(struct gprs_sndcp_comp_field *comp_field,
+			      const uint8_t *src, int compclass)
+{
+	int src_counter = 0;
+	int i;
+
+	if (comp_field->p) {
+		/* Determine the number of expected PCOMP/DCOMP values */
+		if (compclass == SNDCP_XID_PROTOCOL_COMPRESSION) {
+			/* For protocol compression */
+			switch (comp_field->algo) {
+			case RFC_1144:
+				comp_field->comp_len = RFC1144_PCOMP_NUM;
+				break;
+			case RFC_2507:
+				comp_field->comp_len = RFC2507_PCOMP_NUM;
+				break;
+			case ROHC:
+				comp_field->comp_len = ROHC_PCOMP_NUM;
+				break;
+
+				/* Exit if the algorithem type encodes
+				   something unknown / unspecified */
+			default:
+				return -EINVAL;
+			}
+		} else {
+			/* For data compression */
+			switch (comp_field->algo) {
+			case V42BIS:
+				comp_field->comp_len = V42BIS_DCOMP_NUM;
+				break;
+			case V44:
+				comp_field->comp_len = V44_DCOMP_NUM;
+				break;
+
+				/* Exit if the algorithem type encodes
+				   something unknown / unspecified */
+			default:
+				return -EINVAL;
+			}
+		}
+
+		for (i = 0; i < comp_field->comp_len; i++) {
+			if (i & 1) {
+				comp_field->comp[i] = (*src) & 0x0F;
+				src++;
+				src_counter++;
+			} else
+				comp_field->comp[i] = ((*src) >> 4) & 0x0F;
+		}
+
+		if (i & 1) {
+			src++;
+			src_counter++;
+		}
+	}
+
+	return src_counter;
+}
+
+/* Helper function for decode_comp_field(), decodes the parameters
+ * which are protocol compression specific */
+static int decode_pcomp_params(struct gprs_sndcp_comp_field *comp_field,
+			       const uint8_t *src, int src_len)
+{
+	int rc;
+
+	switch (comp_field->algo) {
+	case RFC_1144:
+		comp_field->rfc1144_params = talloc_zero(comp_field, struct
+					gprs_sndcp_pcomp_rfc1144_params);
+		rc = decode_pcomp_rfc1144_params(comp_field->rfc1144_params,
+						 src, src_len);
+		if (rc < 0)
+			talloc_free(comp_field->rfc1144_params);
+		break;
+	case RFC_2507:
+		comp_field->rfc2507_params = talloc_zero(comp_field, struct
+					gprs_sndcp_pcomp_rfc2507_params);
+		rc = decode_pcomp_rfc2507_params(comp_field->rfc2507_params,
+						 src, src_len);
+		if (rc < 0)
+			talloc_free(comp_field->rfc1144_params);
+		break;
+	case ROHC:
+		comp_field->rohc_params = talloc_zero(comp_field, struct
+					gprs_sndcp_pcomp_rohc_params);
+		rc = decode_pcomp_rohc_params(comp_field->rohc_params, src,
+					      src_len);
+		if (rc < 0)
+			talloc_free(comp_field->rohc_params);
+		break;
+
+		/* If no suitable decoder is detected,
+		   leave the remaining bytes undecoded */
+	default:
+		rc = src_len;
+	}
+
+	if (rc < 0) {
+		comp_field->rfc1144_params = NULL;
+		comp_field->rfc2507_params = NULL;
+		comp_field->rohc_params = NULL;
+	}
+
+	return rc;
+}
+
+/* Helper function for decode_comp_field(), decodes the parameters
+ * which are data compression specific */
+static int decode_dcomp_params(struct gprs_sndcp_comp_field *comp_field,
+			       const uint8_t *src, int src_len)
+{
+	int rc;
+
+	switch (comp_field->algo) {
+	case V42BIS:
+		comp_field->v42bis_params = talloc_zero(comp_field, struct
+					gprs_sndcp_dcomp_v42bis_params);
+		rc = decode_dcomp_v42bis_params(comp_field->v42bis_params, src,
+						src_len);
+		if (rc < 0)
+			talloc_free(comp_field->v42bis_params);
+		break;
+	case V44:
+		comp_field->v44_params = talloc_zero(comp_field, struct
+					gprs_sndcp_dcomp_v44_params);
+		rc = decode_dcomp_v44_params(comp_field->v44_params, src,
+					     src_len);
+		if (rc < 0)
+			talloc_free(comp_field->v44_params);
+		break;
+
+		/* If no suitable decoder is detected,
+		 * leave the remaining bytes undecoded */
+	default:
+		rc = src_len;
+	}
+
+	if (rc < 0) {
+		comp_field->v42bis_params = NULL;
+		comp_field->v44_params = NULL;
+	}
+
+	return rc;
+}
+
+/* Decode data or protocol control information compression field
+ * (see also: 3GPP TS 44.065, 6.6.1.1, Figure 9 and
+ *            3GPP TS 44.065, 6.5.1.1, Figure 7) */
+static int decode_comp_field(struct gprs_sndcp_comp_field *comp_field,
+			     const uint8_t *src, unsigned int src_len,
+			     const struct entity_algo_table *lt,
+			     unsigned int lt_len, int compclass)
+{
+	int src_counter = 0;
+	unsigned int len;
+	int rc;
+
+	OSMO_ASSERT(comp_field);
+
+	/* Exit immediately if it is clear that no
+	   parseable data is present */
+	if (src_len < 1 || !src)
+		return -EINVAL;
+
+	/* Zero out target struct */
+	memset(comp_field, 0, sizeof(struct gprs_sndcp_comp_field));
+
+	/* Decode Propose bit and Entity number */
+	if ((*src) & 0x80)
+		comp_field->p = 1;
+	comp_field->entity = (*src) & 0x1F;
+	src_counter++;
+	src++;
+
+	/* Decode algorithm number (if present) */
+	if (comp_field->p) {
+		comp_field->algo = (*src) & 0x1F;
+		src_counter++;
+		src++;
+	}
+	/* Alternatively take the information from the lookup table */
+	else
+		comp_field->algo =
+		    lookup_algorithm_identifier(comp_field->entity, lt,
+						lt_len, compclass);
+
+	/* Decode length field */
+	len = *src;
+	src_counter++;
+	src++;
+
+	/* Decode PCOMP/DCOMP values */
+	rc = decode_comp_values(comp_field, src, compclass);
+	if (rc < 0)
+		return -EINVAL;
+	src_counter += rc;
+	src += rc;
+	len -= rc;
+
+	/* Decode algorithm specific payload data */
+	if (compclass == SNDCP_XID_PROTOCOL_COMPRESSION)
+		rc = decode_pcomp_params(comp_field, src, len);
+	else if (compclass == SNDCP_XID_DATA_COMPRESSION)
+		rc = decode_dcomp_params(comp_field, src, len);
+	else
+		return -EINVAL;
+
+	if (rc >= 0)
+		src_counter += rc;
+	else
+		return -EINVAL;
+
+	/* Return consumed length */
+	return src_counter;
+}
+
+/* Helper function for gprs_sndcp_decode_xid() to decode XID blocks */
+static int decode_xid_block(struct llist_head *comp_fields, uint8_t tag,
+			    uint16_t tag_len, const uint8_t *val,
+			    const struct entity_algo_table *lt,
+			    unsigned int lt_len)
+{
+	struct gprs_sndcp_comp_field *comp_field;
+	int byte_counter = 0;
+	int comp_field_count = 0;
+	int rc;
+
+	byte_counter = 0;
+	do {
+		/* Bail if more than the maximum number of
+		   comp_fields is generated */
+		if (comp_field_count > MAX_ENTITIES * 2) {
+			return -EINVAL;
+		}
+
+		/* Parse and add comp_field */
+		comp_field =
+		    talloc_zero(comp_fields, struct gprs_sndcp_comp_field);
+
+		rc = decode_comp_field(comp_field, val + byte_counter,
+				       tag_len - byte_counter, lt, lt_len, tag);
+
+		if (rc < 0) {
+			talloc_free(comp_field);
+			return -EINVAL;
+		}
+
+		byte_counter += rc;
+		llist_add(&comp_field->list, comp_fields);
+		comp_field_count++;
+	}
+	while (tag_len - byte_counter > 0);
+
+	return byte_counter;
+}
+
+/* Transform an SNDCP-XID message (src) into a list of SNDCP-XID fields */
+static int gprs_sndcp_decode_xid(struct llist_head *comp_fields,
+				 const uint8_t *src, unsigned int src_len,
+				 const struct
+				 entity_algo_table
+				 *lt, unsigned int lt_len)
+{
+	int src_pos = 0;
+	uint8_t tag;
+	uint16_t tag_len;
+	const uint8_t *val;
+	int byte_counter = 0;
+	int rc;
+	int tlv_count = 0;
+
+	/* Valid TLV-Tag and types */
+	static const struct tlv_definition sndcp_xid_def = {
+		.def = {
+			[SNDCP_XID_VERSION_NUMBER] = {TLV_TYPE_TLV,},
+			[SNDCP_XID_DATA_COMPRESSION] = {TLV_TYPE_TLV,},
+			[SNDCP_XID_PROTOCOL_COMPRESSION] = {TLV_TYPE_TLV,},
+			},
+	};
+
+	/* Parse TLV-Encoded SNDCP-XID message and defer payload
+	   to the apporpiate sub-parser functions */
+	while (1) {
+
+		/* Bail if an the maximum number of TLV fields
+		 * have been parsed */
+		if (tlv_count >= 3) {
+			talloc_free(comp_fields);
+			return -EINVAL;
+		}
+
+		/* Parse TLV field */
+		rc = tlv_parse_one(&tag, &tag_len, &val, &sndcp_xid_def,
+				   src + src_pos, src_len - src_pos);
+		if (rc > 0)
+			src_pos += rc;
+		else {
+			talloc_free(comp_fields);
+			return -EINVAL;
+		}
+
+		/* Decode compression parameters */
+		if ((tag == SNDCP_XID_PROTOCOL_COMPRESSION)
+		    || (tag == SNDCP_XID_DATA_COMPRESSION)) {
+			rc = decode_xid_block(comp_fields, tag, tag_len, val,
+					      lt, lt_len);
+
+			if (rc < 0) {
+				talloc_free(comp_fields);
+				return -EINVAL;
+			} else
+				byte_counter += rc;
+		}
+
+		/* Stop when no further TLV elements can be expected */
+		if (src_len - src_pos <= 2)
+			break;
+
+		tlv_count++;
+	}
+
+	return 0;
+}
+
+/* Fill up lookutable from a list with comression entitiy fields */
+static int gprs_sndcp_fill_table(struct
+				 entity_algo_table *lt,
+				 unsigned int lt_len,
+				 const struct llist_head *comp_fields)
+{
+	struct gprs_sndcp_comp_field *comp_field;
+	int i = 0;
+
+	if (!comp_fields)
+		return -EINVAL;
+	if (!lt)
+		return -EINVAL;
+
+	memset(lt, 0, lt_len * sizeof(lt));
+
+	llist_for_each_entry(comp_field, comp_fields, list) {
+
+		lt[i].entity = comp_field->entity;
+		lt[i].algo = comp_field->algo;
+		lt[i].compclass = gprs_sndcp_get_compression_class(comp_field);
+
+		if (lt[i].compclass < 0) {
+			memset(lt, 0, lt_len * sizeof(lt));
+			return -EINVAL;
+		}
+
+		i++;
+	}
+
+	return i;
+}
+
+/* Complete comp field params
+ * (if a param (dst) is not valid, it will be copied from source (src) */
+static int complete_comp_field_params(struct gprs_sndcp_comp_field
+				      *comp_field_dst, const struct
+				      gprs_sndcp_comp_field *comp_field_src)
+{
+	if (comp_field_dst->algo < 0)
+		return -EINVAL;
+
+	if (comp_field_dst->rfc1144_params && comp_field_src->rfc1144_params) {
+		if (comp_field_dst->rfc1144_params->s01 < 0) {
+			comp_field_dst->rfc1144_params->s01 =
+			    comp_field_src->rfc1144_params->s01;
+		}
+		return 0;
+	}
+
+	if (comp_field_dst->rfc2507_params && comp_field_src->rfc2507_params) {
+
+		if (comp_field_dst->rfc2507_params->f_max_period < 0) {
+			comp_field_dst->rfc2507_params->f_max_period =
+			    comp_field_src->rfc2507_params->f_max_period;
+		}
+		if (comp_field_dst->rfc2507_params->f_max_time < 0) {
+			comp_field_dst->rfc2507_params->f_max_time =
+			    comp_field_src->rfc2507_params->f_max_time;
+		}
+		if (comp_field_dst->rfc2507_params->max_header < 0) {
+			comp_field_dst->rfc2507_params->max_header =
+			    comp_field_src->rfc2507_params->max_header;
+		}
+		if (comp_field_dst->rfc2507_params->tcp_space < 0) {
+			comp_field_dst->rfc2507_params->tcp_space =
+			    comp_field_src->rfc2507_params->tcp_space;
+		}
+		if (comp_field_dst->rfc2507_params->non_tcp_space < 0) {
+			comp_field_dst->rfc2507_params->non_tcp_space =
+			    comp_field_src->rfc2507_params->non_tcp_space;
+		}
+		return 0;
+	}
+
+	if (comp_field_dst->rohc_params && comp_field_src->rohc_params) {
+		if (comp_field_dst->rohc_params->max_cid < 0) {
+			comp_field_dst->rohc_params->max_cid =
+			    comp_field_src->rohc_params->max_cid;
+		}
+		if (comp_field_dst->rohc_params->max_header < 0) {
+			comp_field_dst->rohc_params->max_header =
+			    comp_field_src->rohc_params->max_header;
+		}
+		if (comp_field_dst->rohc_params->profile_len > 0) {
+			memcpy(comp_field_dst->rohc_params->profile,
+			       comp_field_src->rohc_params->profile,
+			       sizeof(comp_field_dst->rohc_params->profile));
+			comp_field_dst->rohc_params->profile_len =
+			    comp_field_src->rohc_params->profile_len;
+		}
+
+		return 0;
+	}
+
+	if (comp_field_dst->v42bis_params && comp_field_src->v42bis_params) {
+		if (comp_field_dst->v42bis_params->p0 < 0) {
+			comp_field_dst->v42bis_params->p0 =
+			    comp_field_src->v42bis_params->p0;
+		}
+		if (comp_field_dst->v42bis_params->p1 < 0) {
+			comp_field_dst->v42bis_params->p1 =
+			    comp_field_src->v42bis_params->p1;
+		}
+		if (comp_field_dst->v42bis_params->p2 < 0) {
+			comp_field_dst->v42bis_params->p2 =
+			    comp_field_src->v42bis_params->p2;
+		}
+		return 0;
+	}
+
+	if (comp_field_dst->v44_params && comp_field_src->v44_params) {
+		if (comp_field_dst->v44_params->c0 < 0) {
+			comp_field_dst->v44_params->c0 =
+			    comp_field_src->v44_params->c0;
+		}
+		if (comp_field_dst->v44_params->p0 < 0) {
+			comp_field_dst->v44_params->p0 =
+			    comp_field_src->v44_params->p0;
+		}
+		if (comp_field_dst->v44_params->p1t < 0) {
+			comp_field_dst->v44_params->p1t =
+			    comp_field_src->v44_params->p1t;
+		}
+		if (comp_field_dst->v44_params->p1r < 0) {
+			comp_field_dst->v44_params->p1r =
+			    comp_field_src->v44_params->p1r;
+		}
+		if (comp_field_dst->v44_params->p3t < 0) {
+			comp_field_dst->v44_params->p3t =
+			    comp_field_src->v44_params->p3t;
+		}
+		if (comp_field_dst->v44_params->p3r < 0) {
+			comp_field_dst->v44_params->p3r =
+			    comp_field_src->v44_params->p3r;
+		}
+		return 0;
+	}
+
+	/* There should be at least exist one param set
+	 * in the destination struct, otherwise something
+	 * must be wrong! */
+	return -EINVAL;
+}
+
+/* Complete missing parameters in a comp_field */
+static int gprs_sndcp_complete_comp_field(struct gprs_sndcp_comp_field
+					  *comp_field, const struct llist_head
+					  *comp_fields)
+{
+	struct gprs_sndcp_comp_field *comp_field_src;
+	int rc = 0;
+
+	llist_for_each_entry(comp_field_src, comp_fields, list) {
+		if (comp_field_src->entity == comp_field->entity) {
+
+			/* Complete header fields */
+			if (comp_field_src->comp_len > 0) {
+				memcpy(comp_field->comp,
+				       comp_field_src->comp,
+				       sizeof(comp_field_src->comp));
+				comp_field->comp_len = comp_field_src->comp_len;
+			}
+
+			/* Complete parameter fields */
+			rc = complete_comp_field_params(comp_field,
+							comp_field_src);
+		}
+	}
+
+	return rc;
+}
+
+/* Complete missing parameters of all comp_field in a list */
+static int gprs_sndcp_complete_comp_fields(struct llist_head
+					   *comp_fields_incomplete,
+					   const struct llist_head *comp_fields)
+{
+	struct gprs_sndcp_comp_field *comp_field_incomplete;
+	int rc;
+
+	llist_for_each_entry(comp_field_incomplete, comp_fields_incomplete,
+			     list) {
+
+		rc = gprs_sndcp_complete_comp_field(comp_field_incomplete,
+						    comp_fields);
+		if (rc < 0)
+			return -EINVAL;
+
+	}
+
+	return 0;
+}
+
+/* Transform an SNDCP-XID message (src) into a list of SNDCP-XID fields */
+struct llist_head *gprs_sndcp_parse_xid(const void *ctx,
+					const uint8_t *src,
+					unsigned int src_len,
+					const struct llist_head
+					*comp_fields_req)
+{
+	int rc;
+	int lt_len;
+	struct llist_head *comp_fields;
+	struct entity_algo_table lt[MAX_ENTITIES * 2];
+
+	OSMO_ASSERT(src);
+
+	comp_fields = talloc_zero(ctx, struct llist_head);
+	INIT_LLIST_HEAD(comp_fields);
+
+	if (comp_fields_req) {
+		/* Generate lookup table */
+		lt_len =
+		    gprs_sndcp_fill_table(lt, MAX_ENTITIES * 2,
+					  comp_fields_req);
+		if (lt_len < 0) {
+			talloc_free(comp_fields);
+			return NULL;
+		}
+
+		/* Parse SNDCP-CID XID-Field */
+		rc = gprs_sndcp_decode_xid(comp_fields, src, src_len, lt,
+					   lt_len);
+		if (rc < 0) {
+			talloc_free(comp_fields);
+			return NULL;
+		}
+
+		rc = gprs_sndcp_complete_comp_fields(comp_fields,
+						     comp_fields_req);
+		if (rc < 0) {
+			talloc_free(comp_fields);
+			return NULL;
+		}
+
+	} else {
+		/* Parse SNDCP-CID XID-Field */
+		rc = gprs_sndcp_decode_xid(comp_fields, src, src_len, NULL, 0);
+		if (rc < 0) {
+			talloc_free(comp_fields);
+			return NULL;
+		}
+	}
+
+	return comp_fields;
+}
+
+/* Helper for gprs_sndcp_dump_comp_fields(),
+ * dumps protocol compression parameters */
+static void dump_pcomp_params(const struct gprs_sndcp_comp_field
+			      *comp_field, unsigned int logl)
+{
+	int i;
+
+	switch (comp_field->algo) {
+	case RFC_1144:
+		if (comp_field->rfc1144_params == NULL) {
+			LOGP(DSNDCP, logl,
+			     "   gprs_sndcp_pcomp_rfc1144_params=NULL\n");
+			break;
+		}
+		LOGP(DSNDCP, logl, "   gprs_sndcp_pcomp_rfc1144_params {\n");
+		LOGP(DSNDCP, logl,
+		     "      nsapi_len=%d;\n",
+		     comp_field->rfc1144_params->nsapi_len);
+		if (comp_field->rfc1144_params->nsapi_len == 0)
+			LOGP(DSNDCP, logl, "      nsapi[] = NULL;\n");
+		for (i = 0; i < comp_field->rfc1144_params->nsapi_len; i++) {
+			LOGP(DSNDCP, logl,
+			     "      nsapi[%d]=%d;\n", i,
+			     comp_field->rfc1144_params->nsapi[i]);
+		}
+		LOGP(DSNDCP, logl, "      s01=%d;\n",
+		     comp_field->rfc1144_params->s01);
+		LOGP(DSNDCP, logl, "   }\n");
+		break;
+	case RFC_2507:
+		if (comp_field->rfc2507_params == NULL) {
+			LOGP(DSNDCP, logl,
+			     "   gprs_sndcp_pcomp_rfc2507_params=NULL\n");
+			break;
+		}
+		LOGP(DSNDCP, logl, "   gprs_sndcp_pcomp_rfc2507_params {\n");
+		LOGP(DSNDCP, logl,
+		     "      nsapi_len=%d;\n",
+		     comp_field->rfc2507_params->nsapi_len);
+		if (comp_field->rfc2507_params->nsapi_len == 0)
+			LOGP(DSNDCP, logl, "      nsapi[] = NULL;\n");
+		for (i = 0; i < comp_field->rfc2507_params->nsapi_len; i++) {
+			LOGP(DSNDCP, logl,
+			     "      nsapi[%d]=%d;\n", i,
+			     comp_field->rfc2507_params->nsapi[i]);
+		}
+		LOGP(DSNDCP, logl,
+		     "      f_max_period=%d;\n",
+		     comp_field->rfc2507_params->f_max_period);
+		LOGP(DSNDCP, logl,
+		     "      f_max_time=%d;\n",
+		     comp_field->rfc2507_params->f_max_time);
+		LOGP(DSNDCP, logl,
+		     "      max_header=%d;\n",
+		     comp_field->rfc2507_params->max_header);
+		LOGP(DSNDCP, logl,
+		     "      tcp_space=%d;\n",
+		     comp_field->rfc2507_params->tcp_space);
+		LOGP(DSNDCP, logl,
+		     "      non_tcp_space=%d;\n",
+		     comp_field->rfc2507_params->non_tcp_space);
+		LOGP(DSNDCP, logl, "   }\n");
+		break;
+	case ROHC:
+		if (comp_field->rohc_params == NULL) {
+			LOGP(DSNDCP, logl,
+			     "   gprs_sndcp_pcomp_rohc_params=NULL\n");
+			break;
+		}
+		LOGP(DSNDCP, logl, "   gprs_sndcp_pcomp_rohc_params {\n");
+		LOGP(DSNDCP, logl,
+		     "      nsapi_len=%d;\n",
+		     comp_field->rohc_params->nsapi_len);
+		if (comp_field->rohc_params->nsapi_len == 0)
+			LOGP(DSNDCP, logl, "      nsapi[] = NULL;\n");
+		for (i = 0; i < comp_field->rohc_params->nsapi_len; i++) {
+			LOGP(DSNDCP, logl,
+			     "      nsapi[%d]=%d;\n", i,
+			     comp_field->rohc_params->nsapi[i]);
+		}
+		LOGP(DSNDCP, logl,
+		     "      max_cid=%d;\n", comp_field->rohc_params->max_cid);
+		LOGP(DSNDCP, logl,
+		     "      max_header=%d;\n",
+		     comp_field->rohc_params->max_header);
+		LOGP(DSNDCP, logl,
+		     "      profile_len=%d;\n",
+		     comp_field->rohc_params->profile_len);
+		if (comp_field->rohc_params->profile_len == 0)
+			LOGP(DSNDCP, logl, "      profile[] = NULL;\n");
+		for (i = 0; i < comp_field->rohc_params->profile_len; i++)
+			LOGP(DSNDCP, logl,
+			     "      profile[%d]=%04x;\n",
+			     i, comp_field->rohc_params->profile[i]);
+		LOGP(DSNDCP, logl, "   }\n");
+		break;
+	}
+
+}
+
+/* Helper for gprs_sndcp_dump_comp_fields(),
+ * data protocol compression parameters */
+static void dump_dcomp_params(const struct gprs_sndcp_comp_field
+			      *comp_field, unsigned int logl)
+{
+	int i;
+
+	switch (comp_field->algo) {
+	case V42BIS:
+		if (comp_field->v42bis_params == NULL) {
+			LOGP(DSNDCP, logl,
+			     "   gprs_sndcp_dcomp_v42bis_params=NULL\n");
+			break;
+		}
+		LOGP(DSNDCP, logl, "   gprs_sndcp_dcomp_v42bis_params {\n");
+		LOGP(DSNDCP, logl,
+		     "      nsapi_len=%d;\n",
+		     comp_field->v42bis_params->nsapi_len);
+		if (comp_field->v42bis_params->nsapi_len == 0)
+			LOGP(DSNDCP, logl, "      nsapi[] = NULL;\n");
+		for (i = 0; i < comp_field->v42bis_params->nsapi_len; i++)
+			LOGP(DSNDCP, logl,
+			     "      nsapi[%d]=%d;\n", i,
+			     comp_field->v42bis_params->nsapi[i]);
+		LOGP(DSNDCP, logl, "      p0=%d;\n",
+		     comp_field->v42bis_params->p0);
+		LOGP(DSNDCP, logl, "      p1=%d;\n",
+		     comp_field->v42bis_params->p1);
+		LOGP(DSNDCP, logl, "      p2=%d;\n",
+		     comp_field->v42bis_params->p2);
+		LOGP(DSNDCP, logl, "   }\n");
+		break;
+	case V44:
+		if (comp_field->v44_params == NULL) {
+			LOGP(DSNDCP, logl,
+			     "   gprs_sndcp_dcomp_v44_params=NULL\n");
+			break;
+		}
+		LOGP(DSNDCP, logl, "   gprs_sndcp_dcomp_v44_params {\n");
+		LOGP(DSNDCP, logl,
+		     "      nsapi_len=%d;\n",
+		     comp_field->v44_params->nsapi_len);
+		if (comp_field->v44_params->nsapi_len == 0)
+			LOGP(DSNDCP, logl, "      nsapi[] = NULL;\n");
+		for (i = 0; i < comp_field->v44_params->nsapi_len; i++) {
+			LOGP(DSNDCP, logl,
+			     "      nsapi[%d]=%d;\n", i,
+			     comp_field->v44_params->nsapi[i]);
+		}
+		LOGP(DSNDCP, logl, "      c0=%d;\n",
+		     comp_field->v44_params->c0);
+		LOGP(DSNDCP, logl, "      p0=%d;\n",
+		     comp_field->v44_params->p0);
+		LOGP(DSNDCP, logl, "      p1t=%d;\n",
+		     comp_field->v44_params->p1t);
+		LOGP(DSNDCP, logl, "      p1r=%d;\n",
+		     comp_field->v44_params->p1r);
+		LOGP(DSNDCP, logl, "      p3t=%d;\n",
+		     comp_field->v44_params->p3t);
+		LOGP(DSNDCP, logl, "      p3r=%d;\n",
+		     comp_field->v44_params->p3r);
+		LOGP(DSNDCP, logl, "   }\n");
+		break;
+	}
+}
+
+/* Dump a list with SNDCP-XID fields (Debug) */
+void gprs_sndcp_dump_comp_fields(const struct llist_head *comp_fields,
+				 unsigned int logl)
+{
+	struct gprs_sndcp_comp_field *comp_field;
+	int i;
+	int compclass;
+
+	OSMO_ASSERT(comp_fields);
+
+	llist_for_each_entry(comp_field, comp_fields, list) {
+		LOGP(DSNDCP, logl, "SNDCP-XID:\n");
+		LOGP(DSNDCP, logl, "struct gprs_sndcp_comp_field {\n");
+		LOGP(DSNDCP, logl, "   entity=%d;\n", comp_field->entity);
+		LOGP(DSNDCP, logl, "   algo=%d;\n", comp_field->algo);
+		LOGP(DSNDCP, logl, "   comp_len=%d;\n", comp_field->comp_len);
+		if (comp_field->comp_len == 0)
+			LOGP(DSNDCP, logl, "   comp[] = NULL;\n");
+		for (i = 0; i < comp_field->comp_len; i++) {
+			LOGP(DSNDCP, logl, "   comp[%d]=%d;\n", i,
+			     comp_field->comp[i]);
+		}
+
+		compclass = gprs_sndcp_get_compression_class(comp_field);
+
+		if (compclass == SNDCP_XID_PROTOCOL_COMPRESSION) {
+			dump_pcomp_params(comp_field, logl);
+		} else if (compclass == SNDCP_XID_DATA_COMPRESSION) {
+			dump_dcomp_params(comp_field, logl);
+		}
+
+		LOGP(DSNDCP, logl, "}\n");
+	}
+
+}