diff --git a/openbsc/include/openbsc/sgsn.h b/openbsc/include/openbsc/sgsn.h
index 1ce608a..b782568 100644
--- a/openbsc/include/openbsc/sgsn.h
+++ b/openbsc/include/openbsc/sgsn.h
@@ -50,4 +50,12 @@
 					 struct tlv_parsed *tp);
 int sgsn_delete_pdp_ctx(struct sgsn_pdp_ctx *pctx);
 
+/* gprs_sndcp.c */
+
+/* Entry point for the SNSM-ACTIVATE.indication */
+int sndcp_sm_activate_ind(struct gprs_llc_lle *lle, uint8_t nsapi);
+/* Called by SNDCP when it has received/re-assembled a N-PDU */
+int sgsn_rx_sndcp_ud_ind(uint32_t tlli, uint8_t nsapi, struct msgb *msg,
+			 uint32_t npdu_len, uint8_t *npdu);
+
 #endif
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index 11b2ac9..30b45f6 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -19,7 +19,7 @@
 			$(top_srcdir)/src/socket.c $(top_srcdir)/src/debug.c
 osmo_gbproxy_LDADD = libgb.a $(top_builddir)/src/libvty.a
 
-osmo_sgsn_SOURCES =	gprs_gmm.c gprs_sgsn.c \
+osmo_sgsn_SOURCES =	gprs_gmm.c gprs_sgsn.c gprs_sndcp.c \
 			sgsn_main.c sgsn_vty.c sgsn_libgtp.c \
 			$(top_srcdir)/src/socket.c $(top_srcdir)/src/debug.c
 osmo_sgsn_LDADD = libgb.a $(top_builddir)/src/libvty.a -lgtp
diff --git a/openbsc/src/gprs/gprs_llc.c b/openbsc/src/gprs/gprs_llc.c
index 26730d4..cb581f1 100644
--- a/openbsc/src/gprs/gprs_llc.c
+++ b/openbsc/src/gprs/gprs_llc.c
@@ -340,6 +340,15 @@
 			gprs_llc_tx_xid(lle, resp);
 		}
 		break;
+	case GPRS_LLC_UI:
+		if (gph->seq_tx < lle->vu_recv) {
+			LOGP(DLLC, "TLLI=%08x dropping UI, vurecv %u <= %u\n",
+				gph->seq_tx, lle->vu_recv);
+			return -EIO;
+		}
+		/* Increment the sequence number that we expect in the next frame */
+		lle->vu_recv = (gph->seq_tx + 1) % 512;
+		break;
 	}
 
 	return 0;
@@ -583,16 +592,18 @@
 			/* send LL_UNITDATA_IND to GMM */
 			rc = gsm0408_gprs_rcvmsg(msg, lle->llme);
 			break;
-		case GPRS_SAPI_TOM2:
-		case GPRS_SAPI_TOM8:
-			/* FIXME: send LL_DATA_IND/LL_UNITDATA_IND to TOM */
 		case GPRS_SAPI_SNDCP3:
 		case GPRS_SAPI_SNDCP5:
 		case GPRS_SAPI_SNDCP9:
 		case GPRS_SAPI_SNDCP11:
-			/* FIXME: send LL_DATA_IND/LL_UNITDATA_IND to SNDCP */
+			/* send LL_DATA_IND/LL_UNITDATA_IND to SNDCP */
+			rc = sndcp_llunitdata_ind(msg, lle, llhp.data, llhp.data_len);
+			break;
 		case GPRS_SAPI_SMS:
 			/* FIXME */
+		case GPRS_SAPI_TOM2:
+		case GPRS_SAPI_TOM8:
+			/* FIXME: send LL_DATA_IND/LL_UNITDATA_IND to TOM */
 		default:
 			LOGP(DLLC, LOGL_NOTICE, "Unsupported SAPI %u\n", llhp.sapi);
 			rc = -EINVAL;
diff --git a/openbsc/src/gprs/gprs_sndcp.c b/openbsc/src/gprs/gprs_sndcp.c
index 99a7638..ec704e0 100644
--- a/openbsc/src/gprs/gprs_sndcp.c
+++ b/openbsc/src/gprs/gprs_sndcp.c
@@ -32,6 +32,7 @@
 #include <openbsc/debug.h>
 #include <openbsc/gprs_bssgp.h>
 #include <openbsc/gprs_llc.h>
+#include <openbsc/sgsn.h>
 
 /* Chapter 7.2: SN-PDU Formats */
 struct sndcp_common_hdr {
@@ -44,7 +45,7 @@
 	/* octet 2 */
 	uint8_t pcomp;
 	uint8_t dcomp;
-};
+} __attribute__((packed));
 
 struct sndcp_udata_hdr {
 	/* octet 3 */
@@ -52,42 +53,172 @@
 	uint8_t seg_nr:4;
 	/* octet 4 */
 	uint8_t npdu_low;
+} __attribute__((packed));
+
+/* See 6.7.1.2 Reassembly */
+enum sndcp_rx_state {
+	SNDCP_RX_S_FIRST,
+	SNDCP_RX_S_SUBSEQ,
+	SNDCP_RX_S_DISCARD,
+};
+
+
+static void *tall_sndcp_ctx;
+
+/* A fragment queue entry, containing one framgent of a N-PDU */
+struct frag_queue_entry {
+	struct llist_head list;
+	uint8_t seg_nr;
+	uint32_t data_len;
+	uint8_t data[0];
+};
+
+/* A fragment queue header, maintaining list of fragments for one N-PDU */
+struct frag_queue_head {
+	uint16_t npdu;
+
+	/* linked list of frag_queue_entry: one for each fragment  */
+	struct llist_head frag_list;
+
+	struct timer_list timer;
 };
 
 struct sndcp_entity {
+	struct llist_head list;
+
+	struct gprs_llc_lle *lle;
+	uint8_t nsapi;
+
+	enum sndcp_rx_state rx_state;
+	struct frag_queue_head fqueue;
 };
 
-/* Entry point for the LL-UNITDATA.indication */
-int sndcp_unitdata_ind(struct msgb *msg, uint8_t sapi, uint8_t *hdr, uint8_t len)
-{
-	struct sndcp_udata_hdr *suh;
-	uint16_t npdu;
+LLIST_HEAD(sndcp_entities);
 
-	if (suh->type == 0) {
+#if 0
+static struct frag_queue_entry _find_fqe(struct freg_queue_head *fqh, uint8_t seg_nr)
+{
+
+}
+
+static struct frag_queue_head _find_fqh(struct sndcp_entity *sne, uint16_t npdu)
+{
+
+}
+
+static int ul_enqueue_fragment(struct sndcp_entity *sne, uint16_t npdu,
+			       uint8_t seg_nr, uint32_t data_len, uint8_t *data)
+{
+	
+}
+#endif
+
+static struct sndcp_entity *sndcp_entity_by_lle(const struct gprs_llc_lle *lle,
+						uint8_t nsapi)
+{
+	struct sndcp_entity *sne;
+
+	llist_for_each_entry(sne, &sndcp_entities, list) {
+		if (sne->lle == lle && sne->nsapi == nsapi)
+			return sne;
+	}
+	return NULL;
+}
+
+static struct sndcp_entity *sndcp_entity_alloc(struct gprs_llc_lle *lle,
+						uint8_t nsapi)
+{
+	struct sndcp_entity *sne;
+
+	sne = talloc_zero(tall_sndcp_ctx, struct sndcp_entity);
+	if (!sne)
+		return NULL;
+
+	sne->lle = lle;
+	sne->nsapi = nsapi;
+	sne->fqueue.timer.data = sne;
+	//sne->fqueue.timer.cb = FIXME;
+	sne->rx_state = SNDCP_RX_S_FIRST;
+
+	return sne;
+}
+
+/* Entry point for the SNSM-ACTIVATE.indication */
+int sndcp_sm_activate_ind(struct gprs_llc_lle *lle, uint8_t nsapi)
+{
+	if (sndcp_entity_by_lle(lle, nsapi))
+		return -EEXIST;
+
+	if (!sndcp_entity_alloc(lle, nsapi))
+		return -ENOMEM;
+
+	return 0;
+}
+
+/* Section 5.1.2.17 LL-UNITDATA.ind */
+int sndcp_llunitdata_ind(struct msgb *msg, struct gprs_llc_lle *lle, uint8_t *hdr, uint8_t len)
+{
+	struct sndcp_entity *sne;
+	struct sndcp_common_hdr *sch = (struct sndcp_common_hdr *)hdr;
+	struct sndcp_udata_hdr *suh;
+	uint8_t *comp, *npdu;
+	uint16_t npdu_num;
+	int npdu_len;
+
+	if (sch->type == 0) {
 		LOGP(DGPRS, LOGL_ERROR, "SN-DATA PDU at unitdata_ind() function\n");
 		return -EINVAL;
 	}
 
-	npdu = (suh->npdu_high << 8) | suh->npdu_low;
+	if (len < sizeof(*sch) + sizeof(*comp) + sizeof(*suh)) {
+		LOGP(DGPRS, LOGL_ERROR, "SN-UNITDATA PDU too short (%u)\n", len);
+		return -EIO;
+	}
+
+	sne = sndcp_entity_by_lle(lle, sch->nsapi);
+	if (!sne) {
+		LOGP(DGPRS, LOGL_ERROR, "Message for non-existing SNDCP Entity\n");
+		return -EIO;
+	}
+
+	if (!sch->first || sch->more) {
+		/* FIXME: implement fragment re-assembly */
+		LOGP(DGPRS, LOGL_ERROR, "We don't support reassembly yet\n");
+		return -EIO;
+	}
+
+	comp = (hdr + sizeof(struct sndcp_common_hdr));
+	if (comp) {
+		LOGP(DGPRS, LOGL_ERROR, "We don't support compression yet\n");
+		return -EIO;
+	}
+	suh = (struct sndcp_udata_hdr *) (comp + sizeof(*comp));
+	npdu_num = (suh->npdu_high << 8) | suh->npdu_low;
+
+	npdu = (uint8_t *)suh + sizeof(*suh);
+	npdu_len = (msg->data + msg->len) - npdu;
+	if (npdu_len) {
+		LOGP(DGPRS, 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() */
+	return sgsn_rx_sndcp_ud_ind(lle->llme->tlli, sne->nsapi, msg, npdu_len, npdu);
 }
 
 /* Section 5.1.2.1 LL-RESET.ind */
-static int sndcp_ll_reset_ind(struct sndcp_entity *se,)
+static int sndcp_ll_reset_ind(struct sndcp_entity *se)
 {
 	/* treat all outstanding SNDCP-LLC request type primitives as not sent */
 	/* reset all SNDCP XID parameters to default values */
 }
 
-/* Section 5.1.2.17 LL-UNITDATA.ind */
-static int sndcp_ll_unitdata_ind()
-{
-}
-
 static int sndcp_ll_status_ind()
 {
 	/* inform the SM sub-layer by means of SNSM-STATUS.req */
 }
 
+#if 0
 static struct sndcp_state_list {{
 	uint32_t	states;
 	unsigned int	type;
@@ -127,3 +258,4 @@
 	case LL_UNITDATA_IND:
 	case LL_STATUS_IND:
 }
+#endif
diff --git a/openbsc/src/gprs/sgsn_libgtp.c b/openbsc/src/gprs/sgsn_libgtp.c
index 7df9325..03de8cc 100644
--- a/openbsc/src/gprs/sgsn_libgtp.c
+++ b/openbsc/src/gprs/sgsn_libgtp.c
@@ -42,6 +42,8 @@
 #include <openbsc/signal.h>
 #include <openbsc/debug.h>
 #include <openbsc/sgsn.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/gprs_bssgp.h>
 #include <openbsc/gprs_sgsn.h>
 #include <openbsc/gprs_gmm.h>
 
@@ -255,6 +257,9 @@
 		goto reject;
 	}
 
+	/* Activate the SNDCP layer */
+	sndcp_sm_activate_ind(&pctx->mm->llme->lle[pctx->sapi], pctx->nsapi);
+
 	/* Send PDP CTX ACT to MS */
 	return gsm48_tx_gsm_act_pdp_acc(pctx);
 
@@ -356,6 +361,36 @@
 	return 0;
 }
 
+/* Called by SNDCP when it has received/re-assembled a N-PDU */
+int sgsn_rx_sndcp_ud_ind(uint32_t tlli, uint8_t nsapi, struct msgb *msg,
+			 uint32_t npdu_len, uint8_t *npdu)
+{
+	struct sgsn_mm_ctx *mmctx;
+	struct sgsn_pdp_ctx *pdp;
+	struct gprs_ra_id ra_id;
+
+	/* look-up the MM context for this message */
+	bssgp_parse_cell_id(&ra_id, msgb_bcid(msg));
+	mmctx = sgsn_mm_ctx_by_tlli(tlli, &ra_id);
+	if (!mmctx) {
+		LOGP(DGPRS, LOGL_ERROR,
+			"Cannot find MM CTX for TLLI %08x\n", tlli);
+		return -EIO;
+	}
+	/* look-up the PDP context for this message */
+	pdp = sgsn_pdp_ctx_by_nsapi(mmctx, nsapi);
+	if (!pdp) {
+		LOGP(DGPRS, LOGL_ERROR, "Cannot find PDP CTX for "
+			"TLLI=%08x, NSAPI=%u\n", tlli, nsapi);
+		return -EIO;
+	}
+	if (!pdp->lib) {
+		LOGP(DGPRS, LOGL_ERROR, "PDP CTX without libgtp\n");
+		return -EIO;
+	}
+	return gtp_data_req(pdp->ggsn->gsn, pdp->lib, npdu, npdu_len);
+}
+
 /* libgtp select loop integration */
 static int sgsn_gtp_fd_cb(struct bsc_fd *fd, unsigned int what)
 {