diff --git a/src/libosmo-mgcp/iuup_cn_node.c b/src/libosmo-mgcp/iuup_cn_node.c
new file mode 100644
index 0000000..390dc1c
--- /dev/null
+++ b/src/libosmo-mgcp/iuup_cn_node.c
@@ -0,0 +1,171 @@
+/* A Media Gateway Control Protocol Media Gateway: RFC 3435 */
+/* IuUP Core Network side protocol handling, minimal implementation */
+
+/*
+ * (C) 2018 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <neels@hofmeyr.de>
+ *
+ * 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 <talloc.h>
+#include <errno.h>
+#include <string.h>
+#include <arpa/inet.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/core/msgb.h>
+
+#include <osmocom/netif/rtp.h>
+
+#include <osmocom/mgcp/iuup_cn_node.h>
+#include <osmocom/mgcp/iuup_protocol.h>
+
+#include <osmocom/mgcp/debug.h>
+
+#define LOG_IUUP_CN(cn, level, fmt, args...) \
+		LOGP(DRTP, level, "(%s) " fmt, (cn)->name, ## args)
+
+struct osmo_iuup_cn {
+	struct osmo_iuup_cn_cfg cfg;
+	char *name;
+	uint8_t next_frame_nr;
+};
+
+struct osmo_iuup_cn *osmo_iuup_cn_init(void *ctx, struct osmo_iuup_cn_cfg *cfg,
+				       const char *name_fmt, ...)
+{
+	va_list ap;
+	struct osmo_iuup_cn *cn = talloc_zero(ctx, struct osmo_iuup_cn);
+	OSMO_ASSERT(cn);
+
+	cn->cfg = *cfg;
+
+	if (!name_fmt)
+		name_fmt = "-";
+
+	va_start(ap, name_fmt);
+	cn->name = talloc_vasprintf(cn, name_fmt, ap);
+	va_end(ap);
+
+	if (!osmo_identifier_valid(cn->name)) {
+		LOGP(DLGLOBAL, LOGL_ERROR, "Attempting to set illegal id for IuUP CN instance: %s\n",
+		     osmo_quote_str(cn->name, -1));
+		talloc_free(cn);
+		return NULL;
+	}
+
+	return cn;
+}
+
+void osmo_iuup_cn_free(struct osmo_iuup_cn *cn)
+{
+	talloc_free(cn);
+}
+
+static int rx_data(struct osmo_iuup_cn *cn, struct msgb *pdu,
+		   struct osmo_iuup_hdr_data *hdr, void *pdu_priv)
+{
+	/* Remove the IuUP bit from the middle of the buffer by writing the RTP header forward. */
+	unsigned int pre_hdr_len = ((uint8_t*)hdr) - pdu->data;
+	memmove(pdu->data + sizeof(*hdr), pdu->data, pre_hdr_len);
+
+	msgb_pull(pdu, sizeof(*hdr));
+
+	cn->cfg.rx_payload(pdu, cn->cfg.node_priv, pdu_priv);
+
+	return 0;
+}
+
+static int tx_init_ack(struct osmo_iuup_cn *cn, void *pdu_priv)
+{
+	/* Send Initialization Ack PDU back to the sender */
+	struct msgb *ack = msgb_alloc(4096, "IuUP Initialization Ack");
+	OSMO_ASSERT(ack);
+	osmo_iuup_make_init_ack(ack);
+	return cn->cfg.tx_msg(ack, cn->cfg.node_priv, pdu_priv);
+}
+
+static int rx_control(struct osmo_iuup_cn *cn, struct msgb *pdu,
+		      struct osmo_iuup_hdr_ctrl *hdr, void *pdu_priv)
+{
+	switch (hdr->procedure) {
+	case OSMO_IUUP_PROC_INITIALIZATION:
+		switch (hdr->ack_nack) {
+		case OSMO_IUUP_ACKNACK_PROCEDURE:
+			return tx_init_ack(cn, pdu_priv);
+
+		default:
+			break;
+		}
+		/* fall thru */
+	default:
+		LOG_IUUP_CN(cn, LOGL_ERROR,
+			    "Rx control PDU with unexpected procedure: 0x%x acknack=0x%x\n",
+			    hdr->procedure, hdr->ack_nack);
+		return -EINVAL;
+	}
+}
+
+int osmo_iuup_cn_rx_pdu(struct osmo_iuup_cn *cn, struct msgb *pdu, void *pdu_priv)
+{
+	struct osmo_iuup_hdr_ctrl *is_ctrl;
+	struct osmo_iuup_hdr_data *is_data;
+	int rc;
+
+	rc = osmo_iuup_classify(true, cn->name, pdu, &is_ctrl, &is_data);
+	if (rc)
+		return rc;
+
+	if (is_ctrl)
+		return rx_control(cn, pdu, is_ctrl, pdu_priv);
+	if (is_data)
+		return rx_data(cn, pdu, is_data, pdu_priv);
+	return rc;
+}
+
+static uint8_t next_frame_nr(struct osmo_iuup_cn *cn)
+{
+	uint8_t frame_nr = cn->next_frame_nr;
+	cn->next_frame_nr = (cn->next_frame_nr + 1) % 0x0f;
+	return frame_nr;
+}
+
+int osmo_iuup_cn_tx_payload(struct osmo_iuup_cn *cn, struct msgb *pdu, void *pdu_priv)
+{
+	struct rtp_hdr *rtp_was, *rtp;
+	struct osmo_iuup_hdr_data *iuup_hdr;
+
+	/* Splice an IuUP header in between RTP header and payload data */
+	rtp_was = (void*)pdu->data;
+
+	/* copy the RTP header part backwards by the size needed for the IuUP header */
+	rtp = (void*)msgb_push(pdu, sizeof(*iuup_hdr));
+	memmove(rtp, rtp_was, sizeof(*rtp));
+	iuup_hdr = (void*)rtp->data;
+
+	*iuup_hdr = (struct osmo_iuup_hdr_data){
+		.pdu_type = OSMO_IUUP_PDU_DATA_WITH_CRC,
+		.frame_nr = next_frame_nr(cn),
+		.frame_good = OSMO_IUUP_FRAME_GOOD,
+	};
+
+	osmo_iuup_set_checksums((uint8_t*)iuup_hdr, pdu->tail - (uint8_t*)iuup_hdr);
+
+	return cn->cfg.tx_msg(pdu, cn->cfg.node_priv, pdu_priv);
+}