move openbsc/* to repos root

This is the first step in creating this repository from the legacy openbsc.git.

Like all other Osmocom repositories, keep the autoconf and automake files in
the repository root. openbsc.git has been the sole exception, which ends now.

Change-Id: I9c6f2a448d9cb1cc088cf1cf6918b69d7e69b4e7

1 files changed, 1258 insertions, 0 deletions

diff --git a/src/gprs/gprs_sndcp.c b/src/gprs/gprs_sndcp.c
new file mode 100644
index 000000000..a18998f9e
--- /dev/null
+++ b/src/gprs/gprs_sndcp.c
@@ -0,0 +1,1258 @@
+/* GPRS SNDCP protocol implementation as per 3GPP TS 04.65 */
+
+/* (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010 by On-Waves
+ *
+ * All Rights Reserved
+ *
+ * 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 <errno.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/timer.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/gprs/gprs_bssgp.h>
+
+#include <openbsc/gsm_data.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/sgsn.h>
+#include <openbsc/gprs_sndcp.h>
+#include <openbsc/gprs_llc_xid.h>
+#include <openbsc/gprs_sndcp_xid.h>
+#include <openbsc/gprs_sndcp_pcomp.h>
+#include <openbsc/gprs_sndcp_dcomp.h>
+#include <openbsc/gprs_sndcp_comp.h>
+
+#define DEBUG_IP_PACKETS 0	/* 0=Disabled, 1=Enabled */
+
+#if DEBUG_IP_PACKETS == 1
+/* Calculate TCP/IP checksum */
+static uint16_t calc_ip_csum(uint8_t *data, int len)
+{
+	int i;
+	uint32_t accumulator = 0;
+	uint16_t *pointer = (uint16_t *) data;
+
+	for (i = len; i > 1; i -= 2) {
+		accumulator += *pointer;
+		pointer++;
+	}
+
+	if (len % 2)
+		accumulator += *pointer;
+
+	accumulator = (accumulator & 0xffff) + ((accumulator >> 16) & 0xffff);
+	accumulator += (accumulator >> 16) & 0xffff;
+	return (~accumulator);
+}
+
+/* Calculate TCP/IP checksum */
+static uint16_t calc_tcpip_csum(const void *ctx, uint8_t *packet, int len)
+{
+	uint8_t *buf;
+	uint16_t csum;
+
+	buf = talloc_zero_size(ctx, len);
+	memset(buf, 0, len);
+	memcpy(buf, packet + 12, 8);
+	buf[9] = packet[9];
+	buf[11] = (len - 20) & 0xFF;
+	buf[10] = (len - 20) >> 8 & 0xFF;
+	memcpy(buf + 12, packet + 20, len - 20);
+	csum = calc_ip_csum(buf, len - 20 + 12);
+	talloc_free(buf);
+	return csum;
+}
+
+/* Show some ip packet details */
+static void debug_ip_packet(uint8_t *data, int len, int dir, char *info)
+{
+	uint8_t tcp_flags;
+	char flags_debugmsg[256];
+	int len_short;
+	static unsigned int packet_count = 0;
+	static unsigned int tcp_csum_err_count = 0;
+	static unsigned int ip_csum_err_count = 0;
+
+	packet_count++;
+
+	if (len > 80)
+		len_short = 80;
+	else
+		len_short = len;
+
+	if (dir)
+		DEBUGP(DSNDCP, "%s: MS => SGSN: %s\n", info,
+		       osmo_hexdump_nospc(data, len_short));
+	else
+		DEBUGP(DSNDCP, "%s: MS <= SGSN: %s\n", info,
+		       osmo_hexdump_nospc(data, len_short));
+
+	DEBUGP(DSNDCP, "%s: Length.: %d\n", info, len);
+	DEBUGP(DSNDCP, "%s: NO.: %d\n", info, packet_count);
+
+	if (len < 20) {
+		DEBUGP(DSNDCP, "%s: Error: Short IP packet!\n", info);
+		return;
+	}
+
+	if (calc_ip_csum(data, 20) != 0) {
+		DEBUGP(DSNDCP, "%s: Bad IP-Header checksum!\n", info);
+		ip_csum_err_count++;
+	} else
+		DEBUGP(DSNDCP, "%s: IP-Header checksum ok.\n", info);
+
+	if (data[9] == 0x06) {
+		if (len < 40) {
+			DEBUGP(DSNDCP, "%s: Error: Short TCP packet!\n", info);
+			return;
+		}
+
+		DEBUGP(DSNDCP, "%s: Protocol type: TCP\n", info);
+		tcp_flags = data[33];
+
+		if (calc_tcpip_csum(NULL, data, len) != 0) {
+			DEBUGP(DSNDCP, "%s: Bad TCP checksum!\n", info);
+			tcp_csum_err_count++;
+		} else
+			DEBUGP(DSNDCP, "%s: TCP checksum ok.\n", info);
+
+		memset(flags_debugmsg, 0, sizeof(flags_debugmsg));
+		if (tcp_flags & 1)
+			strcat(flags_debugmsg, "FIN ");
+		if (tcp_flags & 2)
+			strcat(flags_debugmsg, "SYN ");
+		if (tcp_flags & 4)
+			strcat(flags_debugmsg, "RST ");
+		if (tcp_flags & 8)
+			strcat(flags_debugmsg, "PSH ");
+		if (tcp_flags & 16)
+			strcat(flags_debugmsg, "ACK ");
+		if (tcp_flags & 32)
+			strcat(flags_debugmsg, "URG ");
+		DEBUGP(DSNDCP, "%s: FLAGS: %s\n", info, flags_debugmsg);
+	} else if (data[9] == 0x11) {
+		DEBUGP(DSNDCP, "%s: Protocol type: UDP\n", info);
+	} else {
+		DEBUGP(DSNDCP, "%s: Protocol type: (%02x)\n", info, data[9]);
+	}
+
+	DEBUGP(DSNDCP, "%s: IP-Header checksum errors: %d\n", info,
+	       ip_csum_err_count);
+	DEBUGP(DSNDCP, "%s: TCP-Checksum errors: %d\n", info,
+	       tcp_csum_err_count);
+}
+#endif
+
+/* Chapter 7.2: SN-PDU Formats */
+struct sndcp_common_hdr {
+	/* octet 1 */
+	uint8_t nsapi:4;
+	uint8_t more:1;
+	uint8_t type:1;
+	uint8_t first:1;
+	uint8_t spare:1;
+} __attribute__((packed));
+
+/* PCOMP / DCOMP only exist in first fragment */
+struct sndcp_comp_hdr {
+	/* octet 2 */
+	uint8_t pcomp:4;
+	uint8_t dcomp:4;
+} __attribute__((packed));
+
+struct sndcp_udata_hdr {
+	/* octet 3 */
+	uint8_t npdu_high:4;
+	uint8_t seg_nr:4;
+	/* octet 4 */
+	uint8_t npdu_low;
+} __attribute__((packed));
+
+
+static void *tall_sndcp_ctx;
+
+/* A fragment queue entry, containing one framgent of a N-PDU */
+struct defrag_queue_entry {
+	struct llist_head list;
+	/* segment number of this fragment */
+	uint32_t seg_nr;
+	/* length of the data area of this fragment */
+	uint32_t data_len;
+	/* pointer to the data of this fragment */
+	uint8_t *data;
+};
+
+LLIST_HEAD(gprs_sndcp_entities);
+
+/* Check if any compression parameters are set in the sgsn configuration */
+static inline int any_pcomp_or_dcomp_active(struct sgsn_instance *sgsn) {
+	if (sgsn->cfg.pcomp_rfc1144.active || sgsn->cfg.pcomp_rfc1144.passive ||
+	    sgsn->cfg.dcomp_v42bis.active || sgsn->cfg.dcomp_v42bis.passive)
+		return true;
+	else
+		return false;
+}
+
+/* Enqueue a fragment into the defragment queue */
+static int defrag_enqueue(struct gprs_sndcp_entity *sne, uint8_t seg_nr,
+			  uint8_t *data, uint32_t data_len)
+{
+	struct defrag_queue_entry *dqe;
+
+	dqe = talloc_zero(tall_sndcp_ctx, struct defrag_queue_entry);
+	if (!dqe)
+		return -ENOMEM;
+	dqe->data = talloc_zero_size(dqe, data_len);
+	if (!dqe->data) {
+		talloc_free(dqe);
+		return -ENOMEM;
+	}
+	dqe->seg_nr = seg_nr;
+	dqe->data_len = data_len;
+
+	llist_add(&dqe->list, &sne->defrag.frag_list);
+
+	if (seg_nr > sne->defrag.highest_seg)
+		sne->defrag.highest_seg = seg_nr;
+
+	sne->defrag.seg_have |= (1 << seg_nr);
+	sne->defrag.tot_len += data_len;
+
+	memcpy(dqe->data, data, data_len);
+
+	return 0;
+}
+
+/* return if we have all segments of this N-PDU */
+static int defrag_have_all_segments(struct gprs_sndcp_entity *sne)
+{
+	uint32_t seg_needed = 0;
+	unsigned int i;
+
+	/* create a bitmask of needed segments */
+	for (i = 0; i <= sne->defrag.highest_seg; i++)
+		seg_needed |= (1 << i);
+
+	if (seg_needed == sne->defrag.seg_have)
+		return 1;
+
+	return 0;
+}
+
+static struct defrag_queue_entry *defrag_get_seg(struct gprs_sndcp_entity *sne,
+						 uint32_t seg_nr)
+{
+	struct defrag_queue_entry *dqe;
+
+	llist_for_each_entry(dqe, &sne->defrag.frag_list, list) {
+		if (dqe->seg_nr == seg_nr) {
+			llist_del(&dqe->list);
+			return dqe;
+		}
+	}
+	return NULL;
+}
+
+/* Perform actual defragmentation and create an output packet */
+static int defrag_segments(struct gprs_sndcp_entity *sne)
+{
+	struct msgb *msg;
+	unsigned int seg_nr;
+	uint8_t *npdu;
+	int npdu_len;
+	int rc;
+	uint8_t *expnd = NULL;
+
+	LOGP(DSNDCP, LOGL_DEBUG, "TLLI=0x%08x NSAPI=%u: Defragment output PDU %u "
+		"num_seg=%u tot_len=%u\n", sne->lle->llme->tlli, sne->nsapi,
+		sne->defrag.npdu, sne->defrag.highest_seg, sne->defrag.tot_len);
+	msg = msgb_alloc_headroom(sne->defrag.tot_len+256, 128, "SNDCP Defrag");
+	if (!msg)
+		return -ENOMEM;
+
+	/* FIXME: message headers + identifiers */
+
+	npdu = msg->data;
+
+	for (seg_nr = 0; seg_nr <= sne->defrag.highest_seg; seg_nr++) {
+		struct defrag_queue_entry *dqe;
+		uint8_t *data;
+
+		dqe = defrag_get_seg(sne, seg_nr);
+		if (!dqe) {
+			LOGP(DSNDCP, LOGL_ERROR, "Segment %u missing\n", seg_nr);
+			msgb_free(msg);
+			return -EIO;
+		}
+		/* actually append the segment to the N-PDU */
+		data = msgb_put(msg, dqe->data_len);
+		memcpy(data, dqe->data, dqe->data_len);
+
+		/* release memory for the fragment queue entry */
+		talloc_free(dqe);
+	}
+
+	npdu_len = sne->defrag.tot_len;
+
+	/* FIXME: cancel timer */
+
+	/* actually send the N-PDU to the SGSN core code, which then
+	 * hands it off to the correct GTP tunnel + GGSN via gtp_data_req() */
+
+	/* Decompress packet */
+#if DEBUG_IP_PACKETS == 1
+	DEBUGP(DSNDCP, "                                                   \n");
+	DEBUGP(DSNDCP, ":::::::::::::::::::::::::::::::::::::::::::::::::::\n");
+	DEBUGP(DSNDCP, "===================================================\n");
+#endif
+	if (any_pcomp_or_dcomp_active(sgsn)) {
+
+		expnd = talloc_zero_size(msg, npdu_len * MAX_DATADECOMPR_FAC +
+					 MAX_HDRDECOMPR_INCR);
+		memcpy(expnd, npdu, npdu_len);
+
+		/* Apply data decompression */
+		rc = gprs_sndcp_dcomp_expand(expnd, npdu_len, sne->defrag.dcomp,
+					     sne->defrag.data);
+		if (rc < 0) {
+			LOGP(DSNDCP, LOGL_ERROR,
+			     "Data decompression failed!\n");
+			talloc_free(expnd);
+			return -EIO;
+		}
+
+		/* Apply header decompression */
+		rc = gprs_sndcp_pcomp_expand(expnd, rc, sne->defrag.pcomp,
+					     sne->defrag.proto);
+		if (rc < 0) {
+			LOGP(DSNDCP, LOGL_ERROR,
+			     "TCP/IP Header decompression failed!\n");
+			talloc_free(expnd);
+			return -EIO;
+		}
+
+		/* Modify npu length, expnd is handed directly handed
+		 * over to gsn_rx_sndcp_ud_ind(), see below */
+		npdu_len = rc;
+	} else
+		expnd = npdu;
+#if DEBUG_IP_PACKETS == 1
+	debug_ip_packet(expnd, npdu_len, 1, "defrag_segments()");
+	DEBUGP(DSNDCP, "===================================================\n");
+	DEBUGP(DSNDCP, ":::::::::::::::::::::::::::::::::::::::::::::::::::\n");
+	DEBUGP(DSNDCP, "                                                   \n");
+#endif
+
+	/* Hand off packet to gtp */
+	rc = sgsn_rx_sndcp_ud_ind(&sne->ra_id, sne->lle->llme->tlli,
+				  sne->nsapi, msg, npdu_len, expnd);
+
+	if (any_pcomp_or_dcomp_active(sgsn))
+		talloc_free(expnd);
+
+	return rc;
+}
+
+static int defrag_input(struct gprs_sndcp_entity *sne, struct msgb *msg,
+			uint8_t *hdr, unsigned int len)
+{
+	struct sndcp_common_hdr *sch;
+	struct sndcp_udata_hdr *suh;
+	uint16_t npdu_num;
+	uint8_t *data;
+	int rc;
+
+	sch = (struct sndcp_common_hdr *) hdr;
+	if (sch->first) {
+		suh = (struct sndcp_udata_hdr *) (hdr + 1 + sizeof(struct sndcp_common_hdr));
+	} else
+		suh = (struct sndcp_udata_hdr *) (hdr + sizeof(struct sndcp_common_hdr));
+
+	data = (uint8_t *)suh + sizeof(struct sndcp_udata_hdr);
+
+	npdu_num = (suh->npdu_high << 8) | suh->npdu_low;
+
+	LOGP(DSNDCP, LOGL_DEBUG, "TLLI=0x%08x NSAPI=%u: Input PDU %u Segment %u "
+		"Length %u %s %s\n", sne->lle->llme->tlli, sne->nsapi, npdu_num,
+		suh->seg_nr, len, sch->first ? "F " : "", sch->more ? "M" : "");
+
+	if (sch->first) {
+		/* first segment of a new packet.  Discard all leftover fragments of
+		 * previous packet */
+		if (!llist_empty(&sne->defrag.frag_list)) {
+			struct defrag_queue_entry *dqe, *dqe2;
+			LOGP(DSNDCP, LOGL_INFO, "TLLI=0x%08x NSAPI=%u: Dropping "
+			     "SN-PDU %u due to insufficient segments (%04x)\n",
+			     sne->lle->llme->tlli, sne->nsapi, sne->defrag.npdu,
+			     sne->defrag.seg_have);
+			llist_for_each_entry_safe(dqe, dqe2, &sne->defrag.frag_list, list) {
+				llist_del(&dqe->list);
+				talloc_free(dqe);
+			}
+		}
+		/* store the currently de-fragmented PDU number */
+		sne->defrag.npdu = npdu_num;
+
+		/* Re-set fragmentation state */
+		sne->defrag.no_more = sne->defrag.highest_seg = sne->defrag.seg_have = 0;
+		sne->defrag.tot_len = 0;
+		/* FIXME: (re)start timer */
+	}
+
+	if (sne->defrag.npdu != npdu_num) {
+		LOGP(DSNDCP, LOGL_INFO, "Segment for different SN-PDU "
+			"(%u != %u)\n", npdu_num, sne->defrag.npdu);
+		/* FIXME */
+	}
+
+	/* FIXME: check if seg_nr already exists */
+	/* make sure to subtract length of SNDCP header from 'len' */
+	rc = defrag_enqueue(sne, suh->seg_nr, data, len - (data - hdr));
+	if (rc < 0)
+		return rc;
+
+	if (!sch->more) {
+		/* this is suppsed to be the last segment of the N-PDU, but it
+		 * might well be not the last to arrive */
+		sne->defrag.no_more = 1;
+	}
+
+	if (sne->defrag.no_more) {
+		/* we have already received the last segment before, let's check
+		 * if all the previous segments exist */
+		if (defrag_have_all_segments(sne))
+			return defrag_segments(sne);
+	}
+
+	return 0;
+}
+
+static struct gprs_sndcp_entity *gprs_sndcp_entity_by_lle(const struct gprs_llc_lle *lle,
+						uint8_t nsapi)
+{
+	struct gprs_sndcp_entity *sne;
+
+	llist_for_each_entry(sne, &gprs_sndcp_entities, list) {
+		if (sne->lle == lle && sne->nsapi == nsapi)
+			return sne;
+	}
+	return NULL;
+}
+
+static struct gprs_sndcp_entity *gprs_sndcp_entity_alloc(struct gprs_llc_lle *lle,
+						uint8_t nsapi)
+{
+	struct gprs_sndcp_entity *sne;
+
+	sne = talloc_zero(tall_sndcp_ctx, struct gprs_sndcp_entity);
+	if (!sne)
+		return NULL;
+
+	sne->lle = lle;
+	sne->nsapi = nsapi;
+	sne->defrag.timer.data = sne;
+	//sne->fqueue.timer.cb = FIXME;
+	sne->rx_state = SNDCP_RX_S_FIRST;
+	INIT_LLIST_HEAD(&sne->defrag.frag_list);
+
+	llist_add(&sne->list, &gprs_sndcp_entities);
+
+	return sne;
+}
+
+/* Entry point for the SNSM-ACTIVATE.indication */
+int sndcp_sm_activate_ind(struct gprs_llc_lle *lle, uint8_t nsapi)
+{
+	LOGP(DSNDCP, LOGL_INFO, "SNSM-ACTIVATE.ind (lle=%p TLLI=%08x, "
+	     "SAPI=%u, NSAPI=%u)\n", lle, lle->llme->tlli, lle->sapi, nsapi);
+
+	if (gprs_sndcp_entity_by_lle(lle, nsapi)) {
+		LOGP(DSNDCP, LOGL_ERROR, "Trying to ACTIVATE "
+			"already-existing entity (TLLI=%08x, NSAPI=%u)\n",
+			lle->llme->tlli, nsapi);
+		return -EEXIST;
+	}
+
+	if (!gprs_sndcp_entity_alloc(lle, nsapi)) {
+		LOGP(DSNDCP, LOGL_ERROR, "Out of memory during ACTIVATE\n");
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+/* Entry point for the SNSM-DEACTIVATE.indication */
+int sndcp_sm_deactivate_ind(struct gprs_llc_lle *lle, uint8_t nsapi)
+{
+	struct gprs_sndcp_entity *sne;
+
+	LOGP(DSNDCP, LOGL_INFO, "SNSM-DEACTIVATE.ind (lle=%p, TLLI=%08x, "
+	     "SAPI=%u, NSAPI=%u)\n", lle, lle->llme->tlli, lle->sapi, nsapi);
+
+	sne = gprs_sndcp_entity_by_lle(lle, nsapi);
+	if (!sne) {
+		LOGP(DSNDCP, LOGL_ERROR, "SNSM-DEACTIVATE.ind for non-"
+		     "existing TLLI=%08x SAPI=%u NSAPI=%u\n", lle->llme->tlli,
+		     lle->sapi, nsapi);
+		return -ENOENT;
+	}
+	llist_del(&sne->list);
+	/* frag queue entries are hierarchically allocated, so no need to
+	 * free them explicitly here */
+	talloc_free(sne);
+
+	return 0;
+}
+
+/* Fragmenter state */
+struct sndcp_frag_state {
+	uint8_t frag_nr;
+	struct msgb *msg;	/* original message */
+	uint8_t *next_byte;	/* first byte of next fragment */
+
+	struct gprs_sndcp_entity *sne;
+	void *mmcontext;
+};
+
+/* returns '1' if there are more fragments to send, '0' if none */
+static int sndcp_send_ud_frag(struct sndcp_frag_state *fs,
+			      uint8_t pcomp, uint8_t dcomp)
+{
+	struct gprs_sndcp_entity *sne = fs->sne;
+	struct gprs_llc_lle *lle = sne->lle;
+	struct sndcp_common_hdr *sch;
+	struct sndcp_comp_hdr *scomph;
+	struct sndcp_udata_hdr *suh;
+	struct msgb *fmsg;
+	unsigned int max_payload_len;
+	unsigned int len;
+	uint8_t *data;
+	int rc, more;
+
+	fmsg = msgb_alloc_headroom(fs->sne->lle->params.n201_u+256, 128,
+				   "SNDCP Frag");
+	if (!fmsg) {
+		msgb_free(fs->msg);
+		return -ENOMEM;
+	}
+
+	/* make sure lower layers route the fragment like the original */
+	msgb_tlli(fmsg) = msgb_tlli(fs->msg);
+	msgb_bvci(fmsg) = msgb_bvci(fs->msg);
+	msgb_nsei(fmsg) = msgb_nsei(fs->msg);
+
+	/* prepend common SNDCP header */
+	sch = (struct sndcp_common_hdr *) msgb_put(fmsg, sizeof(*sch));
+	sch->nsapi = sne->nsapi;
+	/* Set FIRST bit if we are the first fragment in a series */
+	if (fs->frag_nr == 0)
+		sch->first = 1;
+	sch->type = 1;
+
+	/* append the compression header for first fragment */
+	if (sch->first) {
+		scomph = (struct sndcp_comp_hdr *)
+				msgb_put(fmsg, sizeof(*scomph));
+		scomph->pcomp = pcomp;
+		scomph->dcomp = dcomp;
+	}
+
+	/* append the user-data header */
+	suh = (struct sndcp_udata_hdr *) msgb_put(fmsg, sizeof(*suh));
+	suh->npdu_low = sne->tx_npdu_nr & 0xff;
+	suh->npdu_high = (sne->tx_npdu_nr >> 8) & 0xf;
+	suh->seg_nr = fs->frag_nr % 0xf;
+
+	/* calculate remaining length to be sent */
+	len = (fs->msg->data + fs->msg->len) - fs->next_byte;
+	/* how much payload can we actually send via LLC? */
+	max_payload_len = lle->params.n201_u - (sizeof(*sch) + sizeof(*suh));
+	if (sch->first)
+		max_payload_len -= sizeof(*scomph);
+	/* check if we're exceeding the max */
+	if (len > max_payload_len)
+		len = max_payload_len;
+
+	/* copy the actual fragment data into our fmsg */
+	data = msgb_put(fmsg, len);
+	memcpy(data, fs->next_byte, len);
+
+	/* Increment fragment number and data pointer to next fragment */
+	fs->frag_nr++;
+	fs->next_byte += len;
+
+	/* determine if we have more fragemnts to send */
+	if ((fs->msg->data + fs->msg->len) <= fs->next_byte)
+		more = 0;
+	else
+		more = 1;
+
+	/* set the MORE bit of the SNDCP header accordingly */
+	sch->more = more;
+
+	rc = gprs_llc_tx_ui(fmsg, lle->sapi, 0, fs->mmcontext, true);
+	/* abort in case of error, do not advance frag_nr / next_byte */
+	if (rc < 0) {
+		msgb_free(fs->msg);
+		return rc;
+	}
+
+	if (!more) {
+		/* we've sent all fragments */
+		msgb_free(fs->msg);
+		memset(fs, 0, sizeof(*fs));
+		/* increment NPDU number for next frame */
+		sne->tx_npdu_nr = (sne->tx_npdu_nr + 1) % 0xfff;
+		return 0;
+	}
+
+	/* default: more fragments to send */
+	return 1;
+}
+
+/* Request transmission of a SN-PDU over specified LLC Entity + SAPI */
+int sndcp_unitdata_req(struct msgb *msg, struct gprs_llc_lle *lle, uint8_t nsapi,
+			void *mmcontext)
+{
+	struct gprs_sndcp_entity *sne;
+	struct sndcp_common_hdr *sch;
+	struct sndcp_comp_hdr *scomph;
+	struct sndcp_udata_hdr *suh;
+	struct sndcp_frag_state fs;
+	uint8_t pcomp = 0;
+	uint8_t dcomp = 0;
+	int rc;
+
+	/* Identifiers from UP: (TLLI, SAPI) + (BVCI, NSEI) */
+
+	/* Compress packet */
+#if DEBUG_IP_PACKETS == 1
+	DEBUGP(DSNDCP, "                                                   \n");
+	DEBUGP(DSNDCP, ":::::::::::::::::::::::::::::::::::::::::::::::::::\n");
+	DEBUGP(DSNDCP, "===================================================\n");
+	debug_ip_packet(msg->data, msg->len, 0, "sndcp_initdata_req()");
+#endif
+	if (any_pcomp_or_dcomp_active(sgsn)) {
+
+		/* Apply header compression */
+		rc = gprs_sndcp_pcomp_compress(msg->data, msg->len, &pcomp,
+					       lle->llme->comp.proto, nsapi);
+		if (rc < 0) {
+			LOGP(DSNDCP, LOGL_ERROR,
+			     "TCP/IP Header compression failed!\n");
+			return -EIO;
+		}
+
+		/* Fixup pointer locations and sizes in message buffer to match
+		 * the new, compressed buffer size */
+		msgb_get(msg, msg->len);
+		msgb_put(msg, rc);
+
+		/* Apply data compression */
+		rc = gprs_sndcp_dcomp_compress(msg->data, msg->len, &dcomp,
+					       lle->llme->comp.data, nsapi);
+		if (rc < 0) {
+			LOGP(DSNDCP, LOGL_ERROR, "Data compression failed!\n");
+			return -EIO;
+		}
+
+		/* Fixup pointer locations and sizes in message buffer to match
+		 * the new, compressed buffer size */
+		msgb_get(msg, msg->len);
+		msgb_put(msg, rc);
+	}
+#if DEBUG_IP_PACKETS == 1
+	DEBUGP(DSNDCP, "===================================================\n");
+	DEBUGP(DSNDCP, ":::::::::::::::::::::::::::::::::::::::::::::::::::\n");
+	DEBUGP(DSNDCP, "                                                   \n");
+#endif
+
+	sne = gprs_sndcp_entity_by_lle(lle, nsapi);
+	if (!sne) {
+		LOGP(DSNDCP, LOGL_ERROR, "Cannot find SNDCP Entity\n");
+		msgb_free(msg);
+		return -EIO;
+	}
+
+	/* Check if we need to fragment this N-PDU into multiple SN-PDUs */
+	if (msg->len > lle->params.n201_u - 
+			(sizeof(*sch) + sizeof(*suh) + sizeof(*scomph))) {
+		/* initialize the fragmenter state */
+		fs.msg = msg;
+		fs.frag_nr = 0;
+		fs.next_byte = msg->data;
+		fs.sne = sne;
+		fs.mmcontext = mmcontext;
+
+		/* call function to generate and send fragments until all
+		 * of the N-PDU has been sent */
+		while (1) {
+			int rc = sndcp_send_ud_frag(&fs,pcomp,dcomp);
+			if (rc == 0)
+				return 0;
+			if (rc < 0)
+				return rc;
+		}
+		/* not reached */
+		return 0;
+	}
+
+	/* this is the non-fragmenting case where we only build 1 SN-PDU */
+
+	/* prepend the user-data header */
+	suh = (struct sndcp_udata_hdr *) msgb_push(msg, sizeof(*suh));
+	suh->npdu_low = sne->tx_npdu_nr & 0xff;
+	suh->npdu_high = (sne->tx_npdu_nr >> 8) & 0xf;
+	suh->seg_nr = 0;
+	sne->tx_npdu_nr = (sne->tx_npdu_nr + 1) % 0xfff;
+
+	scomph = (struct sndcp_comp_hdr *) msgb_push(msg, sizeof(*scomph));
+	scomph->pcomp = pcomp;
+	scomph->dcomp = dcomp;
+
+	/* prepend common SNDCP header */
+	sch = (struct sndcp_common_hdr *) msgb_push(msg, sizeof(*sch));
+	sch->first = 1;
+	sch->type = 1;
+	sch->nsapi = nsapi;
+
+	return gprs_llc_tx_ui(msg, lle->sapi, 0, mmcontext, true);
+}
+
+/* Section 5.1.2.17 LL-UNITDATA.ind */
+int sndcp_llunitdata_ind(struct msgb *msg, struct gprs_llc_lle *lle,
+			 uint8_t *hdr, uint16_t len)
+{
+	struct gprs_sndcp_entity *sne;
+	struct sndcp_common_hdr *sch = (struct sndcp_common_hdr *)hdr;
+	struct sndcp_comp_hdr *scomph = NULL;
+	struct sndcp_udata_hdr *suh;
+	uint8_t *npdu;
+	uint16_t npdu_num __attribute__((unused));
+	int npdu_len;
+	int rc;
+	uint8_t *expnd = NULL;
+
+	sch = (struct sndcp_common_hdr *) hdr;
+	if (sch->first) {
+		scomph = (struct sndcp_comp_hdr *) (hdr + 1);
+		suh = (struct sndcp_udata_hdr *) (hdr + 1 + sizeof(struct sndcp_common_hdr));
+	} else
+		suh = (struct sndcp_udata_hdr *) (hdr + sizeof(struct sndcp_common_hdr));
+
+	if (sch->type == 0) {
+		LOGP(DSNDCP, LOGL_ERROR, "SN-DATA PDU at unitdata_ind() function\n");
+		return -EINVAL;
+	}
+
+	if (len < sizeof(*sch) + sizeof(*suh)) {
+		LOGP(DSNDCP, LOGL_ERROR, "SN-UNITDATA PDU too short (%u)\n", len);
+		return -EIO;
+	}
+
+	sne = gprs_sndcp_entity_by_lle(lle, sch->nsapi);
+	if (!sne) {
+		LOGP(DSNDCP, LOGL_ERROR, "Message for non-existing SNDCP Entity "
+			"(lle=%p, TLLI=%08x, SAPI=%u, NSAPI=%u)\n", lle,
+			lle->llme->tlli, lle->sapi, sch->nsapi);
+		return -EIO;
+	}
+	/* FIXME: move this RA_ID up to the LLME or even higher */
+	bssgp_parse_cell_id(&sne->ra_id, msgb_bcid(msg));
+
+	if (scomph) {
+		sne->defrag.pcomp = scomph->pcomp;
+		sne->defrag.dcomp = scomph->dcomp;
+		sne->defrag.proto = lle->llme->comp.proto;
+		sne->defrag.data = lle->llme->comp.data;
+	}
+
+	/* any non-first segment is by definition something to defragment
+	 * as is any segment that tells us there are more segments */
+	if (!sch->first || sch->more)
+		return defrag_input(sne, msg, hdr, len);
+
+	npdu_num = (suh->npdu_high << 8) | suh->npdu_low;
+	npdu = (uint8_t *)suh + sizeof(*suh);
+	npdu_len = (msg->data + msg->len) - npdu - 3;	/* -3 'removes' the FCS */
+
+	if (npdu_len <= 0) {
+		LOGP(DSNDCP, LOGL_ERROR, "Short SNDCP N-PDU: %d\n", npdu_len);
+		return -EIO;
+	}
+	/* actually send the N-PDU to the SGSN core code, which then
+	 * hands it off to the correct GTP tunnel + GGSN via gtp_data_req() */
+
+	/* Decompress packet */
+#if DEBUG_IP_PACKETS == 1
+	DEBUGP(DSNDCP, "                                                   \n");
+	DEBUGP(DSNDCP, ":::::::::::::::::::::::::::::::::::::::::::::::::::\n");
+	DEBUGP(DSNDCP, "===================================================\n");
+#endif
+	if (any_pcomp_or_dcomp_active(sgsn)) {
+
+		expnd = talloc_zero_size(msg, npdu_len * MAX_DATADECOMPR_FAC +
+					 MAX_HDRDECOMPR_INCR);
+		memcpy(expnd, npdu, npdu_len);
+
+		/* Apply data decompression */
+		rc = gprs_sndcp_dcomp_expand(expnd, npdu_len, sne->defrag.dcomp,
+					     sne->defrag.data);
+		if (rc < 0) {
+			LOGP(DSNDCP, LOGL_ERROR,
+			     "Data decompression failed!\n");
+			talloc_free(expnd);
+			return -EIO;
+		}
+
+		/* Apply header decompression */
+		rc = gprs_sndcp_pcomp_expand(expnd, rc, sne->defrag.pcomp,
+					     sne->defrag.proto);
+		if (rc < 0) {
+			LOGP(DSNDCP, LOGL_ERROR,
+			     "TCP/IP Header decompression failed!\n");
+			talloc_free(expnd);
+			return -EIO;
+		}
+
+		/* Modify npu length, expnd is handed directly handed
+		 * over to gsn_rx_sndcp_ud_ind(), see below */
+		npdu_len = rc;
+	} else
+		expnd = npdu;
+#if DEBUG_IP_PACKETS == 1
+	debug_ip_packet(expnd, npdu_len, 1, "sndcp_llunitdata_ind()");
+	DEBUGP(DSNDCP, "===================================================\n");
+	DEBUGP(DSNDCP, ":::::::::::::::::::::::::::::::::::::::::::::::::::\n");
+	DEBUGP(DSNDCP, "                                                   \n");
+#endif
+
+	/* Hand off packet to gtp */
+	rc = sgsn_rx_sndcp_ud_ind(&sne->ra_id, lle->llme->tlli,
+				  sne->nsapi, msg, npdu_len, expnd);
+
+	if (any_pcomp_or_dcomp_active(sgsn))
+		talloc_free(expnd);
+
+	return rc;
+}
+
+#if 0
+/* Section 5.1.2.1 LL-RESET.ind */
+static int sndcp_ll_reset_ind(struct gprs_sndcp_entity *se)
+{
+	/* treat all outstanding SNDCP-LLC request type primitives as not sent */
+	/* reset all SNDCP XID parameters to default values */
+	LOGP(DSNDCP, LOGL_NOTICE, "not implemented.\n");
+	return 0;
+}
+
+static int sndcp_ll_status_ind()
+{
+	/* inform the SM sub-layer by means of SNSM-STATUS.req */
+	LOGP(DSNDCP, LOGL_NOTICE, "not implemented.\n");
+	return 0;
+}
+
+static struct sndcp_state_list {{
+	uint32_t	states;
+	unsigned int	type;
+	int		(*rout)(struct gprs_sndcp_entity *se, struct msgb *msg);
+} sndcp_state_list[] = {
+	{ ALL_STATES,
+	  LL_RESET_IND, sndcp_ll_reset_ind },
+	{ ALL_STATES,
+	  LL_ESTABLISH_IND, sndcp_ll_est_ind },
+	{ SBIT(SNDCP_S_EST_RQD),
+	  LL_ESTABLISH_RESP, sndcp_ll_est_ind },
+	{ SBIT(SNDCP_S_EST_RQD),
+	  LL_ESTABLISH_CONF, sndcp_ll_est_conf },
+	{ SBIT(SNDCP_S_
+};
+
+static int sndcp_rx_llc_prim()
+{
+	case LL_ESTABLISH_REQ:
+	case LL_RELEASE_REQ:
+	case LL_XID_REQ:
+	case LL_DATA_REQ:
+	LL_UNITDATA_REQ,	/* TLLI, SN-PDU, Ref, QoS, Radio Prio, Ciph */
+
+	switch (prim) {
+	case LL_RESET_IND:
+	case LL_ESTABLISH_IND:
+	case LL_ESTABLISH_RESP:
+	case LL_ESTABLISH_CONF:
+	case LL_RELEASE_IND:
+	case LL_RELEASE_CONF:
+	case LL_XID_IND:
+	case LL_XID_RESP:
+	case LL_XID_CONF:
+	case LL_DATA_IND:
+	case LL_DATA_CONF:
+	case LL_UNITDATA_IND:
+	case LL_STATUS_IND:
+	}
+}
+#endif
+
+/* Generate SNDCP-XID message */
+static int gprs_llc_gen_sndcp_xid(uint8_t *bytes, int bytes_len, uint8_t nsapi)
+{
+	int entity = 0;
+	LLIST_HEAD(comp_fields);
+	struct gprs_sndcp_pcomp_rfc1144_params rfc1144_params;
+	struct gprs_sndcp_comp_field rfc1144_comp_field;
+	struct gprs_sndcp_dcomp_v42bis_params v42bis_params;
+	struct gprs_sndcp_comp_field v42bis_comp_field;
+
+	memset(&rfc1144_comp_field, 0, sizeof(struct gprs_sndcp_comp_field));
+	memset(&v42bis_comp_field, 0, sizeof(struct gprs_sndcp_comp_field));
+
+	/* Setup rfc1144 */
+	if (sgsn->cfg.pcomp_rfc1144.active) {
+		rfc1144_params.nsapi[0] = nsapi;
+		rfc1144_params.nsapi_len = 1;
+		rfc1144_params.s01 = sgsn->cfg.pcomp_rfc1144.s01;
+		rfc1144_comp_field.p = 1;
+		rfc1144_comp_field.entity = entity;
+		rfc1144_comp_field.algo = RFC_1144;
+		rfc1144_comp_field.comp[RFC1144_PCOMP1] = 1;
+		rfc1144_comp_field.comp[RFC1144_PCOMP2] = 2;
+		rfc1144_comp_field.comp_len = RFC1144_PCOMP_NUM;
+		rfc1144_comp_field.rfc1144_params = &rfc1144_params;
+		entity++;
+		llist_add(&rfc1144_comp_field.list, &comp_fields);
+	}
+
+	/* Setup V.42bis */
+	if (sgsn->cfg.dcomp_v42bis.active) {
+		v42bis_params.nsapi[0] = nsapi;
+		v42bis_params.nsapi_len = 1;
+		v42bis_params.p0 = sgsn->cfg.dcomp_v42bis.p0;
+		v42bis_params.p1 = sgsn->cfg.dcomp_v42bis.p1;
+		v42bis_params.p2 = sgsn->cfg.dcomp_v42bis.p2;
+		v42bis_comp_field.p = 1;
+		v42bis_comp_field.entity = entity;
+		v42bis_comp_field.algo = V42BIS;
+		v42bis_comp_field.comp[V42BIS_DCOMP1] = 1;
+		v42bis_comp_field.comp_len = V42BIS_DCOMP_NUM;
+		v42bis_comp_field.v42bis_params = &v42bis_params;
+		entity++;
+		llist_add(&v42bis_comp_field.list, &comp_fields);
+	}
+
+	/* Do not attempt to compile anything if there is no data in the list */
+	if (llist_empty(&comp_fields))
+		return 0;
+
+	/* Compile bytestream */
+	return gprs_sndcp_compile_xid(bytes, bytes_len, &comp_fields,
+				      DEFAULT_SNDCP_VERSION);
+}
+
+/* Set of SNDCP-XID bnegotiation (See also: TS 144 065,
+ * Section 6.8 XID parameter negotiation) */
+int sndcp_sn_xid_req(struct gprs_llc_lle *lle, uint8_t nsapi)
+{
+	/* Note: The specification requires the SNDCP-User to set of an
+	 * SNDCP xid request. See also 3GPP TS 44.065, 6.8 XID parameter
+	 * negotiation, Figure 11: SNDCP XID negotiation procedure. In
+	 * our case the SNDCP-User is sgsn_libgtp.c, which calls
+	 * sndcp_sn_xid_req directly. */
+
+	uint8_t l3params[1024];
+	int xid_len;
+	struct gprs_llc_xid_field xid_field_request;
+
+	/* Wipe off all compression entities and their states to
+	 * get rid of possible leftovers from a previous session */
+	gprs_sndcp_comp_free(lle->llme->comp.proto);
+	gprs_sndcp_comp_free(lle->llme->comp.data);
+	lle->llme->comp.proto = gprs_sndcp_comp_alloc(lle->llme);
+	lle->llme->comp.data = gprs_sndcp_comp_alloc(lle->llme);
+	talloc_free(lle->llme->xid);
+	lle->llme->xid = NULL;
+
+	/* Generate compression parameter bytestream */
+	xid_len = gprs_llc_gen_sndcp_xid(l3params, sizeof(l3params), nsapi);
+
+	/* Send XID with the SNDCP-XID bytetsream included */
+	if (xid_len > 0) {
+		xid_field_request.type = GPRS_LLC_XID_T_L3_PAR;
+		xid_field_request.data = l3params;
+		xid_field_request.data_len = xid_len;
+		return gprs_ll_xid_req(lle, &xid_field_request);
+	}
+
+	/* When bytestream can not be generated, proceed without SNDCP-XID */
+	return gprs_ll_xid_req(lle, NULL);
+
+}
+
+/* Handle header compression entites */
+static int handle_pcomp_entities(struct gprs_sndcp_comp_field *comp_field,
+				 struct gprs_llc_lle *lle)
+{
+	/* Note: This functions also transforms the comp_field into its
+	 * echo form (strips comp values, resets propose bit etc...)
+	 * the processed comp_fields can then be sent back as XID-
+	 * Response without further modification. */
+
+	/* Delete propose bit */
+	comp_field->p = 0;
+
+	/* Process proposed parameters */
+	switch (comp_field->algo) {
+	case RFC_1144:
+		if (sgsn->cfg.pcomp_rfc1144.passive
+		    && comp_field->rfc1144_params->nsapi_len > 0) {
+			DEBUGP(DSNDCP,
+			       "Accepting RFC1144 header compression...\n");
+			gprs_sndcp_comp_add(lle->llme, lle->llme->comp.proto,
+					    comp_field);
+		} else {
+			DEBUGP(DSNDCP,
+			       "Rejecting RFC1144 header compression...\n");
+			gprs_sndcp_comp_delete(lle->llme->comp.proto,
+					       comp_field->entity);
+			comp_field->rfc1144_params->nsapi_len = 0;
+		}
+		break;
+	case RFC_2507:
+		/* RFC 2507 is not yet supported,
+		 * so we set applicable nsapis to zero */
+		DEBUGP(DSNDCP, "Rejecting RFC2507 header compression...\n");
+		comp_field->rfc2507_params->nsapi_len = 0;
+		gprs_sndcp_comp_delete(lle->llme->comp.proto,
+				       comp_field->entity);
+		break;
+	case ROHC:
+		/* ROHC is not yet supported,
+		 * so we set applicable nsapis to zero */
+		DEBUGP(DSNDCP, "Rejecting ROHC header compression...\n");
+		comp_field->rohc_params->nsapi_len = 0;
+		gprs_sndcp_comp_delete(lle->llme->comp.proto,
+				       comp_field->entity);
+		break;
+	}
+
+	return 0;
+}
+
+/* Hanle data compression entites */
+static int handle_dcomp_entities(struct gprs_sndcp_comp_field *comp_field,
+				 struct gprs_llc_lle *lle)
+{
+	/* See note in handle_pcomp_entities() */
+
+	/* Delete propose bit */
+	comp_field->p = 0;
+
+	/* Process proposed parameters */
+	switch (comp_field->algo) {
+	case V42BIS:
+		if (sgsn->cfg.dcomp_v42bis.passive &&
+		    comp_field->v42bis_params->nsapi_len > 0) {
+			DEBUGP(DSNDCP,
+			       "Accepting V.42bis data compression...\n");
+			gprs_sndcp_comp_add(lle->llme, lle->llme->comp.data,
+					    comp_field);
+		} else {
+			LOGP(DSNDCP, LOGL_DEBUG,
+			     "Rejecting V.42bis data compression...\n");
+			gprs_sndcp_comp_delete(lle->llme->comp.data,
+					       comp_field->entity);
+			comp_field->v42bis_params->nsapi_len = 0;
+		}
+		break;
+	case V44:
+		/* V44 is not yet supported,
+		 * so we set applicable nsapis to zero */
+		DEBUGP(DSNDCP, "Rejecting V.44 data compression...\n");
+		comp_field->v44_params->nsapi_len = 0;
+		gprs_sndcp_comp_delete(lle->llme->comp.data,
+				       comp_field->entity);
+		break;
+	}
+
+	return 0;
+
+}
+
+/* Process SNDCP-XID indication
+ * (See also: TS 144 065, Section 6.8 XID parameter negotiation) */
+int sndcp_sn_xid_ind(struct gprs_llc_xid_field *xid_field_indication,
+		     struct gprs_llc_xid_field *xid_field_response,
+		     struct gprs_llc_lle *lle)
+{
+	/* Note: This function computes the SNDCP-XID response that is sent
+	 * back to the ms when a ms originated XID is received. The
+	 * Input XID fields are directly processed and the result is directly
+	 * handed back. */
+
+	int rc;
+	int compclass;
+	int version;
+
+	struct llist_head *comp_fields;
+	struct gprs_sndcp_comp_field *comp_field;
+
+	OSMO_ASSERT(xid_field_indication);
+	OSMO_ASSERT(xid_field_response);
+	OSMO_ASSERT(lle);
+
+	/* Parse SNDCP-CID XID-Field */
+	comp_fields = gprs_sndcp_parse_xid(&version, lle->llme,
+					   xid_field_indication->data,
+					   xid_field_indication->data_len,
+					   NULL);
+	if (!comp_fields)
+		return -EINVAL;
+
+	/* Handle compression entites */
+	DEBUGP(DSNDCP, "SNDCP-XID-IND (ms):\n");
+	gprs_sndcp_dump_comp_fields(comp_fields, LOGL_DEBUG);
+
+	llist_for_each_entry(comp_field, comp_fields, list) {
+		compclass = gprs_sndcp_get_compression_class(comp_field);
+		if (compclass == SNDCP_XID_PROTOCOL_COMPRESSION)
+			rc = handle_pcomp_entities(comp_field, lle);
+		else if (compclass == SNDCP_XID_DATA_COMPRESSION)
+			rc = handle_dcomp_entities(comp_field, lle);
+		else {
+			gprs_sndcp_comp_delete(lle->llme->comp.proto,
+					       comp_field->entity);
+			gprs_sndcp_comp_delete(lle->llme->comp.data,
+					       comp_field->entity);
+			rc = 0;
+		}
+
+		if (rc < 0) {
+			talloc_free(comp_fields);
+			return -EINVAL;
+		}
+	}
+
+	DEBUGP(DSNDCP, "SNDCP-XID-RES (sgsn):\n");
+	gprs_sndcp_dump_comp_fields(comp_fields, LOGL_DEBUG);
+
+	/* Reserve some memory to store the modified SNDCP-XID bytes */
+	xid_field_response->data =
+	    talloc_zero_size(lle->llme, xid_field_indication->data_len);
+
+	/* Set Type flag for response */
+	xid_field_response->type = GPRS_LLC_XID_T_L3_PAR;
+
+	/* Compile modified SNDCP-XID bytes */
+	rc = gprs_sndcp_compile_xid(xid_field_response->data,
+				    xid_field_indication->data_len,
+				    comp_fields, 0);
+
+	if (rc > 0)
+		xid_field_response->data_len = rc;
+	else {
+		talloc_free(xid_field_response->data);
+		xid_field_response->data = NULL;
+		xid_field_response->data_len = 0;
+		return -EINVAL;
+	}
+
+	talloc_free(comp_fields);
+
+	return 0;
+}
+
+/* Process SNDCP-XID indication
+ * (See also: TS 144 065, Section 6.8 XID parameter negotiation) */
+int sndcp_sn_xid_conf(struct gprs_llc_xid_field *xid_field_conf,
+		      struct gprs_llc_xid_field *xid_field_request,
+		      struct gprs_llc_lle *lle)
+{
+	/* Note: This function handles an incomming SNDCP-XID confirmiation.
+	 * Since the confirmation fields may lack important parameters we
+	 * will reconstruct these missing fields using the original request
+	 * we have sent. After that we will create (or delete) the
+	 * compression entites */
+
+	struct llist_head *comp_fields_req;
+	struct llist_head *comp_fields_conf;
+	struct gprs_sndcp_comp_field *comp_field;
+	int rc;
+	int compclass;
+
+	/* We need both, the confirmation that is sent back by the ms,
+	 * and the original request we have sent. If one of this is missing
+	 * we can not process the confirmation, the caller must check if
+	 * request and confirmation fields are available. */
+	OSMO_ASSERT(xid_field_conf);
+	OSMO_ASSERT(xid_field_request);
+
+	/* Parse SNDCP-CID XID-Field */
+	comp_fields_req = gprs_sndcp_parse_xid(NULL, lle->llme,
+					       xid_field_request->data,
+					       xid_field_request->data_len,
+					       NULL);
+	if (!comp_fields_req)
+		return -EINVAL;
+
+	DEBUGP(DSNDCP, "SNDCP-XID-REQ (sgsn):\n");
+	gprs_sndcp_dump_comp_fields(comp_fields_req, LOGL_DEBUG);
+
+	/* Parse SNDCP-CID XID-Field */
+	comp_fields_conf = gprs_sndcp_parse_xid(NULL, lle->llme,
+						xid_field_conf->data,
+						xid_field_conf->data_len,
+						comp_fields_req);
+	if (!comp_fields_conf)
+		return -EINVAL;
+
+	DEBUGP(DSNDCP, "SNDCP-XID-CONF (ms):\n");
+	gprs_sndcp_dump_comp_fields(comp_fields_conf, LOGL_DEBUG);
+
+	/* Handle compression entites */
+	llist_for_each_entry(comp_field, comp_fields_conf, list) {
+		compclass = gprs_sndcp_get_compression_class(comp_field);
+		if (compclass == SNDCP_XID_PROTOCOL_COMPRESSION)
+			rc = handle_pcomp_entities(comp_field, lle);
+		else if (compclass == SNDCP_XID_DATA_COMPRESSION)
+			rc = handle_dcomp_entities(comp_field, lle);
+		else {
+			gprs_sndcp_comp_delete(lle->llme->comp.proto,
+					       comp_field->entity);
+			gprs_sndcp_comp_delete(lle->llme->comp.data,
+					       comp_field->entity);
+			rc = 0;
+		}
+
+		if (rc < 0) {
+			talloc_free(comp_fields_req);
+			talloc_free(comp_fields_conf);
+			return -EINVAL;
+		}
+	}
+
+	talloc_free(comp_fields_req);
+	talloc_free(comp_fields_conf);
+
+	return 0;
+}