diff --git a/src/gprs/gprs_ranap.c b/src/gprs/gprs_ranap.c
new file mode 100644
index 0000000..e0470f6
--- /dev/null
+++ b/src/gprs/gprs_ranap.c
@@ -0,0 +1,231 @@
+/* Messages on the RANAP interface (Iu mode) */
+
+/* (C) 2009-2015 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2015 by Holger Hans Peter Freyther
+ * (C) 2019 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 "bscconfig.h"
+
+#ifdef BUILD_IU
+
+#include <gtp.h>
+
+#include <osmocom/core/rate_ctr.h>
+
+#include <osmocom/ranap/ranap_common.h>
+
+#include <osmocom/sgsn/gprs_gmm.h>
+#include <osmocom/sgsn/debug.h>
+#include <osmocom/sgsn/sgsn.h>
+#include <osmocom/sgsn/gprs_ranap.h>
+#include <osmocom/sgsn/gprs_gmm_attach.h>
+
+/* Send RAB activation requests for all PDP contexts */
+void activate_pdp_rabs(struct sgsn_mm_ctx *ctx)
+{
+	struct sgsn_pdp_ctx *pdp;
+	if (ctx->ran_type != MM_CTX_T_UTRAN_Iu)
+		return;
+	llist_for_each_entry(pdp, &ctx->pdp_list, list) {
+		iu_rab_act_ps(pdp->nsapi, pdp);
+	}
+}
+
+/* Callback for RAB assignment response */
+static int sgsn_ranap_rab_ass_resp(struct sgsn_mm_ctx *ctx, RANAP_RAB_SetupOrModifiedItemIEs_t *setup_ies)
+{
+	uint8_t rab_id;
+	bool require_pdp_update = false;
+	struct sgsn_pdp_ctx *pdp = NULL;
+	RANAP_RAB_SetupOrModifiedItem_t *item = &setup_ies->raB_SetupOrModifiedItem;
+
+	rab_id = item->rAB_ID.buf[0];
+
+	pdp = sgsn_pdp_ctx_by_nsapi(ctx, rab_id);
+	if (!pdp) {
+		LOGP(DRANAP, LOGL_ERROR, "RAB Assignment Response for unknown RAB/NSAPI=%u\n", rab_id);
+		return -1;
+	}
+
+	if (item->transportLayerAddress) {
+		LOGPC(DRANAP, LOGL_INFO, " Setup: (%u/%s)", rab_id, osmo_hexdump(item->transportLayerAddress->buf,
+								     item->transportLayerAddress->size));
+		switch (item->transportLayerAddress->size) {
+		case 7:
+			/* It must be IPv4 inside a X213 NSAP */
+			memcpy(pdp->lib->gsnlu.v, &item->transportLayerAddress->buf[3], 4);
+			break;
+		case 4:
+			/* It must be a raw IPv4 address */
+			memcpy(pdp->lib->gsnlu.v, item->transportLayerAddress->buf, 4);
+			break;
+		case 16:
+			/* TODO: It must be a raw IPv6 address */
+		case 19:
+			/* TODO: It must be IPv6 inside a X213 NSAP */
+		default:
+			LOGP(DRANAP, LOGL_ERROR, "RAB Assignment Resp: Unknown "
+				"transport layer address size %u\n",
+				item->transportLayerAddress->size);
+			return -1;
+		}
+		require_pdp_update = true;
+	}
+
+	/* The TEI on the RNC side might have changed, too */
+	if (item->iuTransportAssociation &&
+	    item->iuTransportAssociation->present == RANAP_IuTransportAssociation_PR_gTP_TEI &&
+	    item->iuTransportAssociation->choice.gTP_TEI.buf &&
+	    item->iuTransportAssociation->choice.gTP_TEI.size >= 4) {
+		uint32_t tei = osmo_load32be(item->iuTransportAssociation->choice.gTP_TEI.buf);
+		LOGP(DRANAP, LOGL_DEBUG, "Updating TEID on RNC side from 0x%08x to 0x%08x\n",
+			pdp->lib->teid_own, tei);
+		pdp->lib->teid_own = tei;
+		require_pdp_update = true;
+	}
+
+	if (require_pdp_update)
+		gtp_update_context(pdp->ggsn->gsn, pdp->lib, pdp, &pdp->lib->hisaddr0);
+
+	if (pdp->state != PDP_STATE_CR_CONF) {
+		send_act_pdp_cont_acc(pdp);
+		pdp->state = PDP_STATE_CR_CONF;
+	}
+	return 0;
+
+}
+
+int sgsn_ranap_iu_event(struct ranap_ue_conn_ctx *ctx, enum ranap_iu_event_type type, void *data)
+{
+	struct sgsn_mm_ctx *mm;
+	int rc = -1;
+
+	mm = sgsn_mm_ctx_by_ue_ctx(ctx);
+
+#define REQUIRE_MM \
+	if (!mm) { \
+		LOGIUP(ctx, LOGL_NOTICE, "Cannot find mm ctx for IU event %d\n", type); \
+		return rc; \
+	}
+
+	switch (type) {
+	case RANAP_IU_EVENT_RAB_ASSIGN:
+		REQUIRE_MM
+		rc = sgsn_ranap_rab_ass_resp(mm, (RANAP_RAB_SetupOrModifiedItemIEs_t *)data);
+		break;
+	case RANAP_IU_EVENT_IU_RELEASE:
+		/* fall thru */
+	case RANAP_IU_EVENT_LINK_INVALIDATED:
+		/* Clean up ranap_ue_conn_ctx here */
+		if (mm)
+			LOGMMCTXP(LOGL_INFO, mm, "IU release for imsi %s\n", mm->imsi);
+		else
+			LOGIUP(ctx, LOGL_INFO, "IU release\n");
+		if (mm && mm->pmm_state == PMM_CONNECTED)
+			mmctx_set_pmm_state(mm, PMM_IDLE);
+		rc = 0;
+		break;
+	case RANAP_IU_EVENT_SECURITY_MODE_COMPLETE:
+		REQUIRE_MM
+		/* Continue authentication here */
+		mm->iu.ue_ctx->integrity_active = 1;
+
+		/* FIXME: remove gmm_authorize */
+		if (mm->pending_req != GSM48_MT_GMM_ATTACH_REQ)
+			gsm48_gmm_authorize(mm);
+		else
+			osmo_fsm_inst_dispatch(mm->gmm_att_req.fsm, E_IU_SECURITY_CMD_COMPLETE, NULL);
+		break;
+	default:
+		if (mm)
+			LOGMMCTXP(LOGL_NOTICE, mm, "Unknown event received: %i\n", type);
+		else
+			LOGIUP(ctx, LOGL_NOTICE, "Unknown event received: %i\n", type);
+		rc = -1;
+		break;
+	}
+	return rc;
+}
+
+int iu_rab_act_ps(uint8_t rab_id, struct sgsn_pdp_ctx *pdp)
+{
+	struct msgb *msg;
+	struct sgsn_mm_ctx *mm = pdp->mm;
+	struct ranap_ue_conn_ctx *uectx;
+	uint32_t ggsn_ip;
+	bool use_x213_nsap;
+
+	uectx = mm->iu.ue_ctx;
+	use_x213_nsap = (uectx->rab_assign_addr_enc == RANAP_NSAP_ADDR_ENC_X213);
+
+	/* Get the IP address for ggsn user plane */
+	memcpy(&ggsn_ip, pdp->lib->gsnru.v, pdp->lib->gsnru.l);
+	ggsn_ip = htonl(ggsn_ip);
+
+	LOGP(DRANAP, LOGL_DEBUG, "Assigning RAB: rab_id=%d, ggsn_ip=%x,"
+	     " teid_gn=%x, use_x213_nsap=%d\n",
+	     rab_id, ggsn_ip, pdp->lib->teid_gn, use_x213_nsap);
+
+	msg = ranap_new_msg_rab_assign_data(rab_id, ggsn_ip,
+					    pdp->lib->teid_gn, use_x213_nsap);
+	msg->l2h = msg->data;
+	return ranap_iu_rab_act(uectx, msg);
+}
+
+
+/* Main entry point for incoming 04.08 GPRS messages from Iu */
+int gsm0408_gprs_rcvmsg_iu(struct msgb *msg, struct gprs_ra_id *ra_id,
+			   uint16_t *sai)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	uint8_t pdisc = gsm48_hdr_pdisc(gh);
+	struct sgsn_mm_ctx *mmctx;
+	int rc = -EINVAL;
+
+	mmctx = sgsn_mm_ctx_by_ue_ctx(MSG_IU_UE_CTX(msg));
+	if (mmctx) {
+		rate_ctr_inc(&mmctx->ctrg->ctr[GMM_CTR_PKTS_SIG_IN]);
+		if (ra_id)
+			memcpy(&mmctx->ra, ra_id, sizeof(mmctx->ra));
+	}
+
+	/* MMCTX can be NULL */
+
+	switch (pdisc) {
+	case GSM48_PDISC_MM_GPRS:
+		rc = gsm0408_rcv_gmm(mmctx, msg, NULL, false);
+#pragma message "set drop_cipherable arg for gsm0408_rcv_gmm() from IuPS?"
+		break;
+	case GSM48_PDISC_SM_GPRS:
+		rc = gsm0408_rcv_gsm(mmctx, msg, NULL);
+		break;
+	default:
+		LOGMMCTXP(LOGL_NOTICE, mmctx,
+			"Unknown GSM 04.08 discriminator 0x%02x: %s\n",
+			pdisc, osmo_hexdump((uint8_t *)gh, msgb_l3len(msg)));
+		/* FIXME: return status message */
+		break;
+	}
+
+	/* MMCTX can be invalid */
+
+	return rc;
+}
+#endif