diff --git a/src/iu_client.c b/src/iu_client.c
new file mode 100644
index 0000000..83ed276
--- /dev/null
+++ b/src/iu_client.c
@@ -0,0 +1,783 @@
+/* Common parts of IuCS and IuPS interfaces implementation */
+
+/* (C) 2016-2017 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * 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 <stdint.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include <osmocom/ranap/iu_client.h>
+
+#include <osmocom/core/logging.h>
+#include <osmocom/crypt/auth.h>
+#include <osmocom/gprs/gprs_msgb.h>
+#include <osmocom/sigtran/sccp_sap.h>
+#include <osmocom/ranap/ranap_ies_defs.h>
+#include <osmocom/ranap/ranap_msg_factory.h>
+
+/* Parsed global RNC id. See also struct RANAP_GlobalRNC_ID, and note that the
+ * PLMN identity is a BCD representation of the MCC and MNC.
+ * See iu_grnc_id_parse(). */
+struct iu_grnc_id {
+	uint16_t mcc;
+	uint16_t mnc;
+	uint16_t rnc_id;
+};
+
+/* A remote RNC (Radio Network Controller, like BSC but for UMTS) that has
+ * called us and is currently reachable at the given osmo_sccp_addr. So, when we
+ * know a LAC for a subscriber, we can page it at the RNC matching that LAC or
+ * RAC. An HNB-GW typically presents itself as if it were a single RNC, even
+ * though it may have several RNCs in hNodeBs connected to it. Those will then
+ * share the same RNC id, which they actually receive and adopt from the HNB-GW
+ * in the HNBAP HNB REGISTER ACCEPT message. */
+struct ranap_iu_rnc {
+	struct llist_head entry;
+
+	uint16_t rnc_id;
+	uint16_t lac; /* Location Area Code (used for CS and PS) */
+	uint8_t rac; /* Routing Area Code (used for PS only) */
+	struct osmo_sccp_addr sccp_addr;
+};
+
+void *talloc_iu_ctx;
+void *talloc_asn1_ctx;
+
+/* Implement the extern asn_debug from libasn1c to indicate whether to print
+ * asn.1 debug messages (see libasn1c). */
+int asn_debug = 0;
+
+/* Implement the extern asn1_xer_print to indicate whether the ASN.1 binary
+ * code decoded and encoded during Iu communication should be logged to stderr
+ * (see asn.1 generated code in osmo-iuh). */
+int asn1_xer_print = 0;
+
+ranap_iu_recv_cb_t global_iu_recv_cb = NULL;
+ranap_iu_event_cb_t global_iu_event_cb = NULL;
+int iu_log_subsystem = 0;
+
+#define LOGPIU(level, fmt, args...) \
+	LOGP(iu_log_subsystem, level, fmt, ## args)
+
+static LLIST_HEAD(ue_conn_ctx_list);
+static LLIST_HEAD(rnc_list);
+
+static struct osmo_sccp_instance *g_sccp;
+static struct osmo_sccp_user *g_scu;
+
+const struct value_string ranap_iu_event_type_names[] = {
+	OSMO_VALUE_STRING(RANAP_IU_EVENT_RAB_ASSIGN),
+	OSMO_VALUE_STRING(RANAP_IU_EVENT_SECURITY_MODE_COMPLETE),
+	OSMO_VALUE_STRING(RANAP_IU_EVENT_IU_RELEASE),
+	OSMO_VALUE_STRING(RANAP_IU_EVENT_LINK_INVALIDATED),
+	{ 0, NULL }
+};
+
+static struct ranap_ue_conn_ctx *ue_conn_ctx_alloc(struct ranap_iu_rnc *rnc, uint32_t conn_id)
+{
+	struct ranap_ue_conn_ctx *ctx = talloc_zero(talloc_iu_ctx, struct ranap_ue_conn_ctx);
+
+	ctx->rnc = rnc;
+	ctx->conn_id = conn_id;
+	llist_add(&ctx->list, &ue_conn_ctx_list);
+
+	return ctx;
+}
+
+static struct ranap_ue_conn_ctx *ue_conn_ctx_find(uint32_t conn_id)
+{
+	struct ranap_ue_conn_ctx *ctx;
+
+	llist_for_each_entry(ctx, &ue_conn_ctx_list, list) {
+		if (ctx->conn_id == conn_id)
+			return ctx;
+	}
+	return NULL;
+}
+
+static struct ranap_iu_rnc *iu_rnc_alloc(uint16_t rnc_id, uint16_t lac, uint8_t rac,
+					 struct osmo_sccp_addr *addr)
+{
+	struct ranap_iu_rnc *rnc = talloc_zero(talloc_iu_ctx, struct ranap_iu_rnc);
+
+	rnc->rnc_id = rnc_id;
+	rnc->lac = lac;
+	rnc->rac = rac;
+	rnc->sccp_addr = *addr;
+	llist_add(&rnc->entry, &rnc_list);
+
+	LOGPIU(LOGL_NOTICE, "New RNC %d (LAC=%d RAC=%d)\n",
+	       rnc->rnc_id, rnc->lac, rnc->rac);
+
+	return rnc;
+}
+
+static struct ranap_iu_rnc *iu_rnc_register(uint16_t rnc_id, uint16_t lac,
+					    uint8_t rac, struct osmo_sccp_addr *addr)
+{
+	struct ranap_iu_rnc *rnc;
+	llist_for_each_entry(rnc, &rnc_list, entry) {
+		if (rnc->rnc_id != rnc_id)
+			continue;
+
+		/* We have this RNC Id registered already. Make sure that the
+		 * details match. */
+
+		/* TODO should a mismatch be an error? */
+		if (rnc->lac != lac || rnc->rac != rac)
+			LOGPIU(LOGL_NOTICE, "RNC %d changes its details:"
+			       " LAC=%d RAC=%d --> LAC=%d RAC=%d\n",
+			       rnc->rnc_id, rnc->lac, rnc->rac,
+			       lac, rac);
+		rnc->lac = lac;
+		rnc->rac = rac;
+
+		if (addr && memcmp(&rnc->sccp_addr, addr, sizeof(*addr)))
+			LOGPIU(LOGL_NOTICE, "RNC %d on New SCCP Addr %s"
+			       " (LAC=%d RAC=%d)\n",
+			       rnc->rnc_id, osmo_sccp_addr_dump(addr), rnc->lac, rnc->rac);
+		rnc->sccp_addr = *addr;
+		return rnc;
+	}
+
+	/* Not found, make a new one. */
+	return iu_rnc_alloc(rnc_id, lac, rac, addr);
+}
+
+/***********************************************************************
+ * RANAP handling
+ ***********************************************************************/
+
+int ranap_iu_rab_act(struct ranap_ue_conn_ctx *ue_ctx, struct msgb *msg)
+{
+	struct osmo_scu_prim *prim;
+
+	/* wrap RANAP message in SCCP N-DATA.req */
+	prim = (struct osmo_scu_prim *) msgb_push(msg, sizeof(*prim));
+	prim->u.data.conn_id = ue_ctx->conn_id;
+	osmo_prim_init(&prim->oph,
+		       SCCP_SAP_USER,
+		       OSMO_SCU_PRIM_N_DATA,
+		       PRIM_OP_REQUEST,
+		       msg);
+	return osmo_sccp_user_sap_down(g_scu, &prim->oph);
+}
+
+int ranap_iu_rab_deact(struct ranap_ue_conn_ctx *ue_ctx, uint8_t rab_id)
+{
+	/* FIXME */
+	return -1;
+}
+
+int ranap_iu_tx_sec_mode_cmd(struct ranap_ue_conn_ctx *uectx, struct osmo_auth_vector *vec,
+			     int send_ck, int new_key)
+{
+	struct osmo_scu_prim *prim;
+	struct msgb *msg;
+
+	/* create RANAP message */
+	msg = ranap_new_msg_sec_mod_cmd(vec->ik, send_ck? vec->ck : NULL,
+			new_key ? RANAP_KeyStatus_new : RANAP_KeyStatus_old);
+	msg->l2h = msg->data;
+	/* wrap RANAP message in SCCP N-DATA.req */
+	prim = (struct osmo_scu_prim *) msgb_push(msg, sizeof(*prim));
+	prim->u.data.conn_id = uectx->conn_id;
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_DATA,
+			PRIM_OP_REQUEST, msg);
+	osmo_sccp_user_sap_down(g_scu, &prim->oph);
+
+	return 0;
+}
+
+int ranap_iu_tx_common_id(struct ranap_ue_conn_ctx *uectx, const char *imsi)
+{
+	struct msgb *msg;
+	struct osmo_scu_prim *prim;
+
+	LOGPIU(LOGL_INFO, "Transmitting RANAP CommonID (SCCP conn_id %u)\n",
+	       uectx->conn_id);
+
+	msg = ranap_new_msg_common_id(imsi);
+	msg->l2h = msg->data;
+	prim = (struct osmo_scu_prim *) msgb_push(msg, sizeof(*prim));
+	prim->u.data.conn_id = uectx->conn_id;
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_DATA,
+			PRIM_OP_REQUEST, msg);
+	osmo_sccp_user_sap_down(g_scu, &prim->oph);
+	return 0;
+}
+
+static int iu_grnc_id_parse(struct iu_grnc_id *dst, struct RANAP_GlobalRNC_ID *src)
+{
+	/* The size is coming from arbitrary sender, check it gracefully */
+	if (src->pLMNidentity.size != 3) {
+		LOGPIU(LOGL_ERROR, "Invalid PLMN Identity size:"
+		       " should be 3, is %d\n", src->pLMNidentity.size);
+		return -1;
+	}
+	gsm48_mcc_mnc_from_bcd(&src->pLMNidentity.buf[0],
+			       &dst->mcc, &dst->mnc);
+	dst->rnc_id = (uint16_t)src->rNC_ID;
+	return 0;
+}
+
+#if 0
+ -- not used at present --
+static int iu_grnc_id_compose(struct iu_grnc_id *src, struct RANAP_GlobalRNC_ID *dst)
+{
+	/* The caller must ensure proper size */
+	OSMO_ASSERT(dst->pLMNidentity.size == 3);
+	gsm48_mcc_mnc_to_bcd(&dst->pLMNidentity.buf[0],
+			     src->mcc, src->mnc);
+	dst->rNC_ID = src->rnc_id;
+	return 0;
+}
+#endif
+
+struct new_ue_conn_ctx {
+	struct osmo_sccp_addr sccp_addr;
+	uint32_t conn_id;
+};
+
+static int ranap_handle_co_initial_ue(void *ctx, RANAP_InitialUE_MessageIEs_t *ies)
+{
+	struct new_ue_conn_ctx *new_ctx = ctx;
+	struct gprs_ra_id ra_id;
+	struct iu_grnc_id grnc_id;
+	uint16_t sai;
+	struct ranap_ue_conn_ctx *ue;
+	struct msgb *msg = msgb_alloc(256, "RANAP->NAS");
+	struct ranap_iu_rnc *rnc;
+
+	if (ranap_parse_lai(&ra_id, &ies->lai) != 0) {
+		LOGPIU(LOGL_ERROR, "Failed to parse RANAP LAI IE\n");
+		return -1;
+	}
+
+	if (ies->presenceMask & INITIALUE_MESSAGEIES_RANAP_RAC_PRESENT) {
+		ra_id.rac = asn1str_to_u8(&ies->rac);
+	}
+
+	if (iu_grnc_id_parse(&grnc_id, &ies->globalRNC_ID) != 0) {
+		LOGPIU(LOGL_ERROR,
+		       "Failed to parse RANAP Global-RNC-ID IE\n");
+		return -1;
+	}
+
+	sai = asn1str_to_u16(&ies->sai.sAC);
+	msgb_gmmh(msg) = msgb_put(msg, ies->nas_pdu.size);
+	memcpy(msgb_gmmh(msg), ies->nas_pdu.buf, ies->nas_pdu.size);
+
+	/* Make sure we know the RNC Id and LAC+RAC coming in on this connection. */
+	rnc = iu_rnc_register(grnc_id.rnc_id, ra_id.lac, ra_id.rac, &new_ctx->sccp_addr);
+
+	ue = ue_conn_ctx_alloc(rnc, new_ctx->conn_id);
+	OSMO_ASSERT(ue);
+	ue->ra_id = ra_id;
+
+	/* Feed into the MM layer */
+	msg->dst = ue;
+	global_iu_recv_cb(msg, &ra_id, &sai);
+
+	msgb_free(msg);
+
+	return 0;
+}
+
+static int ranap_handle_co_dt(void *ctx, RANAP_DirectTransferIEs_t *ies)
+{
+	struct gprs_ra_id _ra_id, *ra_id = NULL;
+	uint16_t _sai, *sai = NULL;
+	struct msgb *msg = msgb_alloc(256, "RANAP->NAS");
+
+	if (ies->presenceMask & DIRECTTRANSFERIES_RANAP_LAI_PRESENT) {
+		if (ranap_parse_lai(&_ra_id, &ies->lai) != 0) {
+			LOGPIU(LOGL_ERROR, "Failed to parse RANAP LAI IE\n");
+			return -1;
+		}
+		ra_id = &_ra_id;
+		if (ies->presenceMask & DIRECTTRANSFERIES_RANAP_RAC_PRESENT) {
+			_ra_id.rac = asn1str_to_u8(&ies->rac);
+		}
+		if (ies->presenceMask & DIRECTTRANSFERIES_RANAP_SAI_PRESENT) {
+			_sai = asn1str_to_u16(&ies->sai.sAC);
+			sai = &_sai;
+		}
+	}
+
+	msgb_gmmh(msg) = msgb_put(msg, ies->nas_pdu.size);
+	memcpy(msgb_gmmh(msg), ies->nas_pdu.buf, ies->nas_pdu.size);
+
+	/* Feed into the MM/CC/SMS-CP layer */
+	msg->dst = ctx;
+	global_iu_recv_cb(msg, ra_id, sai);
+
+	msgb_free(msg);
+
+	return 0;
+}
+
+static int ranap_handle_co_err_ind(void *ctx, RANAP_ErrorIndicationIEs_t *ies)
+{
+	if (ies->presenceMask & ERRORINDICATIONIES_RANAP_CAUSE_PRESENT)
+		LOGPIU(LOGL_ERROR, "Rx Error Indication (%s)\n",
+		       ranap_cause_str(&ies->cause));
+	else
+		LOGPIU(LOGL_ERROR, "Rx Error Indication\n");
+
+	return 0;
+}
+
+int ranap_iu_tx(struct msgb *msg_nas, uint8_t sapi)
+{
+	struct ranap_ue_conn_ctx *uectx = msg_nas->dst;
+	struct msgb *msg;
+	struct osmo_scu_prim *prim;
+
+	LOGPIU(LOGL_INFO, "Transmitting L3 Message as RANAP DT (SCCP conn_id %u)\n",
+	       uectx->conn_id);
+
+	msg = ranap_new_msg_dt(sapi, msg_nas->data, msgb_length(msg_nas));
+	msgb_free(msg_nas);
+	msg->l2h = msg->data;
+	prim = (struct osmo_scu_prim *) msgb_push(msg, sizeof(*prim));
+	prim->u.data.conn_id = uectx->conn_id;
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_DATA,
+			PRIM_OP_REQUEST, msg);
+	osmo_sccp_user_sap_down(g_scu, &prim->oph);
+	return 0;
+}
+
+/* Send Iu Release for the given UE connection.
+ * If cause is NULL, the standard "No remaining RAB" cause is sent, otherwise
+ * the provided cause. */
+int ranap_iu_tx_release(struct ranap_ue_conn_ctx *ctx, const struct RANAP_Cause *cause)
+{
+	struct msgb *msg;
+	struct osmo_scu_prim *prim;
+	static const struct RANAP_Cause default_cause = {
+		.present = RANAP_Cause_PR_radioNetwork,
+		.choice.radioNetwork = RANAP_CauseRadioNetwork_no_remaining_rab,
+	};
+
+	if (!cause)
+		cause = &default_cause;
+
+	msg = ranap_new_msg_iu_rel_cmd(cause);
+	msg->l2h = msg->data;
+	prim = (struct osmo_scu_prim *) msgb_push(msg, sizeof(*prim));
+	prim->u.data.conn_id = ctx->conn_id;
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_DATA,
+			PRIM_OP_REQUEST, msg);
+	return osmo_sccp_user_sap_down(g_scu, &prim->oph);
+}
+
+static int ranap_handle_co_iu_rel_req(struct ranap_ue_conn_ctx *ctx, RANAP_Iu_ReleaseRequestIEs_t *ies)
+{
+	LOGPIU(LOGL_INFO, "Received Iu Release Request, Sending Release Command\n");
+	ranap_iu_tx_release(ctx, &ies->cause);
+	return 0;
+}
+
+static int ranap_handle_co_rab_ass_resp(struct ranap_ue_conn_ctx *ctx, RANAP_RAB_AssignmentResponseIEs_t *ies)
+{
+	int rc = -1;
+
+	LOGPIU(LOGL_INFO,
+	       "Rx RAB Assignment Response for UE conn_id %u\n", ctx->conn_id);
+	if (ies->presenceMask & RAB_ASSIGNMENTRESPONSEIES_RANAP_RAB_SETUPORMODIFIEDLIST_PRESENT) {
+		/* TODO: Iterate over list of SetupOrModifiedList IEs and handle each one */
+		RANAP_IE_t *ranap_ie = ies->raB_SetupOrModifiedList.raB_SetupOrModifiedList_ies.list.array[0];
+		RANAP_RAB_SetupOrModifiedItemIEs_t setup_ies;
+
+		rc = ranap_decode_rab_setupormodifieditemies_fromlist(&setup_ies, &ranap_ie->value);
+		if (rc) {
+			LOGPIU(LOGL_ERROR, "Error in ranap_decode_rab_setupormodifieditemies()\n");
+			return rc;
+		}
+
+		rc = global_iu_event_cb(ctx, RANAP_IU_EVENT_RAB_ASSIGN, &setup_ies);
+
+		ranap_free_rab_setupormodifieditemies(&setup_ies);
+	}
+	/* FIXME: handle RAB Ass failure? */
+
+	return rc;
+}
+
+static void cn_ranap_handle_co_initial(void *ctx, ranap_message *message)
+{
+	int rc;
+
+	LOGPIU(LOGL_NOTICE, "handle_co_initial(dir=%u, proc=%u)\n", message->direction, message->procedureCode);
+
+	if (message->direction != RANAP_RANAP_PDU_PR_initiatingMessage
+	    || message->procedureCode != RANAP_ProcedureCode_id_InitialUE_Message) {
+		LOGPIU(LOGL_ERROR, "Expected direction 'InitiatingMessage',"
+		       " procedureCode 'InitialUE_Message', instead got %u and %u\n",
+		       message->direction, message->procedureCode);
+		rc = -1;
+	}
+	else
+		rc = ranap_handle_co_initial_ue(ctx, &message->msg.initialUE_MessageIEs);
+
+	if (rc) {
+		LOGPIU(LOGL_ERROR, "Error in %s (%d)\n", __func__, rc);
+		/* TODO handling of the error? */
+	}
+}
+
+/* Entry point for connection-oriented RANAP message */
+static void cn_ranap_handle_co(void *ctx, ranap_message *message)
+{
+	int rc;
+
+	LOGPIU(LOGL_NOTICE, "handle_co(dir=%u, proc=%u)\n", message->direction, message->procedureCode);
+
+	switch (message->direction) {
+	case RANAP_RANAP_PDU_PR_initiatingMessage:
+		switch (message->procedureCode) {
+		case RANAP_ProcedureCode_id_InitialUE_Message:
+			LOGPIU(LOGL_ERROR, "Got InitialUE_Message but this is not a new conn\n");
+			rc = -1;
+			break;
+		case RANAP_ProcedureCode_id_DirectTransfer:
+			rc = ranap_handle_co_dt(ctx, &message->msg.directTransferIEs);
+			break;
+		case RANAP_ProcedureCode_id_ErrorIndication:
+			rc = ranap_handle_co_err_ind(ctx, &message->msg.errorIndicationIEs);
+			break;
+		case RANAP_ProcedureCode_id_Iu_ReleaseRequest:
+			/* Iu Release Request */
+			rc = ranap_handle_co_iu_rel_req(ctx, &message->msg.iu_ReleaseRequestIEs);
+			break;
+		default:
+			LOGPIU(LOGL_ERROR, "Received Initiating Message: unknown Procedure Code %d\n",
+			       message->procedureCode);
+			rc = -1;
+			break;
+		}
+		break;
+	case RANAP_RANAP_PDU_PR_successfulOutcome:
+		switch (message->procedureCode) {
+		case RANAP_ProcedureCode_id_SecurityModeControl:
+			/* Security Mode Complete */
+			rc = global_iu_event_cb(ctx, RANAP_IU_EVENT_SECURITY_MODE_COMPLETE, NULL);
+			break;
+		case RANAP_ProcedureCode_id_Iu_Release:
+			/* Iu Release Complete */
+			rc = global_iu_event_cb(ctx, RANAP_IU_EVENT_IU_RELEASE, NULL);
+			if (rc) {
+				LOGPIU(LOGL_ERROR, "Iu Release event: Iu Event callback returned %d\n",
+				       rc);
+			}
+			break;
+		default:
+			LOGPIU(LOGL_ERROR, "Received Successful Outcome: unknown Procedure Code %d\n",
+			       message->procedureCode);
+			rc = -1;
+			break;
+		}
+		break;
+	case RANAP_RANAP_PDU_PR_outcome:
+		switch (message->procedureCode) {
+		case RANAP_ProcedureCode_id_RAB_Assignment:
+			/* RAB Assignment Response */
+			rc = ranap_handle_co_rab_ass_resp(ctx, &message->msg.raB_AssignmentResponseIEs);
+			break;
+		default:
+			LOGPIU(LOGL_ERROR, "Received Outcome: unknown Procedure Code %d\n",
+			       message->procedureCode);
+			rc = -1;
+			break;
+		}
+		break;
+	case RANAP_RANAP_PDU_PR_unsuccessfulOutcome:
+	default:
+		LOGPIU(LOGL_ERROR, "Received Unsuccessful Outcome: Procedure Code %d\n",
+		       message->procedureCode);
+		rc = -1;
+		break;
+	}
+
+	if (rc) {
+		LOGPIU(LOGL_ERROR, "Error in %s (%d)\n", __func__, rc);
+		/* TODO handling of the error? */
+	}
+}
+
+static int ranap_handle_cl_reset_req(void *ctx, RANAP_ResetIEs_t *ies)
+{
+	/* FIXME: send reset response */
+	return -1;
+}
+
+static int ranap_handle_cl_err_ind(void *ctx, RANAP_ErrorIndicationIEs_t *ies)
+{
+	if (ies->presenceMask & ERRORINDICATIONIES_RANAP_CAUSE_PRESENT)
+		LOGPIU(LOGL_ERROR, "Rx Error Indication (%s)\n",
+		       ranap_cause_str(&ies->cause));
+	else
+		LOGPIU(LOGL_ERROR, "Rx Error Indication\n");
+
+	return 0;
+}
+
+/* Entry point for connection-less RANAP message */
+static void cn_ranap_handle_cl(void *ctx, ranap_message *message)
+{
+	int rc;
+
+	switch (message->direction) {
+	case RANAP_RANAP_PDU_PR_initiatingMessage:
+		switch (message->procedureCode) {
+		case RANAP_ProcedureCode_id_Reset:
+			/* received reset.req, send reset.resp */
+			rc = ranap_handle_cl_reset_req(ctx, &message->msg.resetIEs);
+			break;
+		case RANAP_ProcedureCode_id_ErrorIndication:
+			rc = ranap_handle_cl_err_ind(ctx, &message->msg.errorIndicationIEs);
+			break;
+		default:
+			rc = -1;
+			break;
+		}
+		break;
+	case RANAP_RANAP_PDU_PR_successfulOutcome:
+	case RANAP_RANAP_PDU_PR_unsuccessfulOutcome:
+	case RANAP_RANAP_PDU_PR_outcome:
+	default:
+		rc = -1;
+		break;
+	}
+
+	if (rc) {
+		LOGPIU(LOGL_ERROR, "Error in %s (%d)\n", __func__, rc);
+		/* TODO handling of the error? */
+	}
+}
+
+/***********************************************************************
+ * Paging
+ ***********************************************************************/
+
+struct osmo_sccp_addr local_sccp_addr = {
+	.presence = OSMO_SCCP_ADDR_T_SSN | OSMO_SCCP_ADDR_T_PC,
+	.ri = OSMO_SCCP_RI_SSN_PC,
+	.ssn = OSMO_SCCP_SSN_RANAP,
+	.pc = 1,
+};
+
+/* Send a paging command down a given SCCP User. tmsi and paging_cause are
+ * optional and may be passed NULL and 0, respectively, to disable their use.
+ * See enum RANAP_PagingCause.
+ *
+ * If TMSI is given, the IMSI is not sent over the air interface. Nevertheless,
+ * the IMSI is still required for resolution in the HNB-GW and/or(?) RNC. */
+static int iu_tx_paging_cmd(struct osmo_sccp_addr *called_addr,
+			    const char *imsi, const uint32_t *tmsi,
+			    bool is_ps, uint32_t paging_cause)
+{
+	struct msgb *msg;
+	msg = ranap_new_msg_paging_cmd(imsi, tmsi, is_ps? 1 : 0, paging_cause);
+	msg->l2h = msg->data;
+	osmo_sccp_tx_unitdata_msg(g_scu, &local_sccp_addr, called_addr, msg);
+	return 0;
+}
+
+static int iu_page(const char *imsi, const uint32_t *tmsi_or_ptimsi,
+		   uint16_t lac, uint8_t rac, bool is_ps)
+{
+	struct ranap_iu_rnc *rnc;
+	int pagings_sent = 0;
+
+	if (tmsi_or_ptimsi) {
+		LOGPIU(LOGL_DEBUG, "%s: Looking for RNCs to page for IMSI %s"
+		       " (paging will use %s %x)\n",
+		       is_ps? "IuPS" : "IuCS",
+		       imsi,
+		       is_ps? "PTMSI" : "TMSI",
+		       *tmsi_or_ptimsi);
+	} else {
+		LOGPIU(LOGL_DEBUG, "%s: Looking for RNCs to page for IMSI %s"
+		       " (paging will use IMSI)\n",
+		       is_ps? "IuPS" : "IuCS",
+		       imsi
+		      );
+	}
+
+	llist_for_each_entry(rnc, &rnc_list, entry) {
+		if (rnc->lac != lac)
+			continue;
+		if (is_ps && rnc->rac != rac)
+			continue;
+
+		/* Found a match! */
+		if (iu_tx_paging_cmd(&rnc->sccp_addr, imsi, tmsi_or_ptimsi, is_ps, 0)
+		    == 0) {
+			LOGPIU(LOGL_DEBUG,
+			       "%s: Paged for IMSI %s on RNC %d, on SCCP addr %s\n",
+			       is_ps? "IuPS" : "IuCS",
+			       imsi, rnc->rnc_id, osmo_sccp_addr_dump(&rnc->sccp_addr));
+			pagings_sent ++;
+		}
+	}
+
+	/* Some logging... */
+	if (pagings_sent > 0) {
+		LOGPIU(LOGL_DEBUG,
+		       "%s: %d RNCs were paged for IMSI %s.\n",
+		       is_ps? "IuPS" : "IuCS",
+		       pagings_sent, imsi);
+	}
+	else {
+		if (is_ps) {
+			LOGPIU(LOGL_ERROR, "IuPS: Found no RNC to page for"
+			       " LAC %d RAC %d (would have paged IMSI %s)\n",
+			       lac, rac, imsi);
+		}
+		else {
+			LOGPIU(LOGL_ERROR, "IuCS: Found no RNC to page for"
+			       " LAC %d (would have paged IMSI %s)\n",
+			       lac, imsi);
+		}
+	}
+
+	return pagings_sent;
+}
+
+int ranap_iu_page_cs(const char *imsi, const uint32_t *tmsi, uint16_t lac)
+{
+	return iu_page(imsi, tmsi, lac, 0, false);
+}
+
+int ranap_iu_page_ps(const char *imsi, const uint32_t *ptmsi, uint16_t lac, uint8_t rac)
+{
+	return iu_page(imsi, ptmsi, lac, rac, true);
+}
+
+
+/***********************************************************************
+ *
+ ***********************************************************************/
+
+int tx_unitdata(struct osmo_sccp_user *scu);
+int tx_conn_req(struct osmo_sccp_user *scu, uint32_t conn_id);
+
+struct osmo_prim_hdr *make_conn_req(uint32_t conn_id);
+struct osmo_prim_hdr *make_dt1_req(uint32_t conn_id, const uint8_t *data, unsigned int len);
+
+static struct osmo_prim_hdr *make_conn_resp(struct osmo_scu_connect_param *param)
+{
+	struct msgb *msg = msgb_alloc(1024, "conn_resp");
+	struct osmo_scu_prim *prim;
+
+	prim = (struct osmo_scu_prim *) msgb_put(msg, sizeof(*prim));
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_CONNECT,
+			PRIM_OP_RESPONSE, msg);
+	memcpy(&prim->u.connect, param, sizeof(prim->u.connect));
+	return &prim->oph;
+}
+
+static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
+{
+	struct osmo_sccp_user *scu = _scu;
+	struct osmo_scu_prim *prim = (struct osmo_scu_prim *) oph;
+	struct osmo_prim_hdr *resp = NULL;
+	int rc;
+	struct ranap_ue_conn_ctx *ue;
+	struct new_ue_conn_ctx new_ctx = {};
+
+	LOGPIU(LOGL_DEBUG, "sccp_sap_up(%s)\n", osmo_scu_prim_name(oph));
+
+	switch (OSMO_PRIM_HDR(oph)) {
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_CONNECT, PRIM_OP_CONFIRM):
+		/* confirmation of outbound connection */
+		rc = -1;
+		break;
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_CONNECT, PRIM_OP_INDICATION):
+		/* indication of new inbound connection request*/
+		LOGPIU(LOGL_DEBUG, "N-CONNECT.ind(X->%u)\n", prim->u.connect.conn_id);
+		if (/*  prim->u.connect.called_addr.ssn != OSMO_SCCP_SSN_RANAP || */
+		    !msgb_l2(oph->msg) || msgb_l2len(oph->msg) == 0) {
+			LOGPIU(LOGL_NOTICE,
+			     "Received invalid N-CONNECT.ind\n");
+			return 0;
+		}
+		new_ctx.sccp_addr = prim->u.connect.calling_addr;
+		new_ctx.conn_id = prim->u.connect.conn_id;
+		/* first ensure the local SCCP socket is ACTIVE */
+		resp = make_conn_resp(&prim->u.connect);
+		osmo_sccp_user_sap_down(scu, resp);
+		/* then handle the RANAP payload */
+		rc = ranap_cn_rx_co(cn_ranap_handle_co_initial, &new_ctx, msgb_l2(oph->msg), msgb_l2len(oph->msg));
+		break;
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_DISCONNECT, PRIM_OP_INDICATION):
+		/* indication of disconnect */
+		LOGPIU(LOGL_DEBUG, "N-DISCONNECT.ind(%u)\n",
+		       prim->u.disconnect.conn_id);
+		ue = ue_conn_ctx_find(prim->u.disconnect.conn_id);
+		rc = ranap_cn_rx_co(cn_ranap_handle_co, ue, msgb_l2(oph->msg), msgb_l2len(oph->msg));
+		break;
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_DATA, PRIM_OP_INDICATION):
+		/* connection-oriented data received */
+		LOGPIU(LOGL_DEBUG, "N-DATA.ind(%u, %s)\n", prim->u.data.conn_id,
+		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+		/* resolve UE context */
+		ue = ue_conn_ctx_find(prim->u.data.conn_id);
+		rc = ranap_cn_rx_co(cn_ranap_handle_co, ue, msgb_l2(oph->msg), msgb_l2len(oph->msg));
+		break;
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_UNITDATA, PRIM_OP_INDICATION):
+		/* connection-less data received */
+		LOGPIU(LOGL_DEBUG, "N-UNITDATA.ind(%s)\n",
+		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+		rc = ranap_cn_rx_cl(cn_ranap_handle_cl, scu, msgb_l2(oph->msg), msgb_l2len(oph->msg));
+		break;
+	default:
+		rc = -1;
+		break;
+	}
+
+	msgb_free(oph->msg);
+	return rc;
+}
+
+int ranap_iu_init(void *ctx, int log_subsystem, const char *sccp_user_name, struct osmo_sccp_instance *sccp,
+		  ranap_iu_recv_cb_t iu_recv_cb, ranap_iu_event_cb_t iu_event_cb)
+{
+	iu_log_subsystem = log_subsystem;
+	talloc_iu_ctx = talloc_named_const(ctx, 1, "iu");
+	talloc_asn1_ctx = talloc_named_const(talloc_iu_ctx, 1, "asn1");
+
+	global_iu_recv_cb = iu_recv_cb;
+	global_iu_event_cb = iu_event_cb;
+	g_sccp = sccp;
+	g_scu = osmo_sccp_user_bind(g_sccp, sccp_user_name, sccp_sap_up, OSMO_SCCP_SSN_RANAP);
+
+	return 0;
+}
+