diff --git a/src/libosmo-mgcp/iuup_cn_node.c b/src/libosmo-mgcp/iuup_cn_node.c
index 390dc1c..f555e36 100644
--- a/src/libosmo-mgcp/iuup_cn_node.c
+++ b/src/libosmo-mgcp/iuup_cn_node.c
@@ -39,12 +39,13 @@
 #include <osmocom/mgcp/debug.h>
 
 #define LOG_IUUP_CN(cn, level, fmt, args...) \
-		LOGP(DRTP, level, "(%s) " fmt, (cn)->name, ## args)
+		LOGP(DIUUP, level, "(%s) " fmt, (cn)->name, ## args)
 
 struct osmo_iuup_cn {
 	struct osmo_iuup_cn_cfg cfg;
 	char *name;
 	uint8_t next_frame_nr;
+	int rtp_payload_type;
 };
 
 struct osmo_iuup_cn *osmo_iuup_cn_init(void *ctx, struct osmo_iuup_cn_cfg *cfg,
@@ -63,8 +64,10 @@
 	cn->name = talloc_vasprintf(cn, name_fmt, ap);
 	va_end(ap);
 
+	LOGP(DIUUP, LOGL_INFO, "(%s) Initializing IuUP node\n", cn->name);
+
 	if (!osmo_identifier_valid(cn->name)) {
-		LOGP(DLGLOBAL, LOGL_ERROR, "Attempting to set illegal id for IuUP CN instance: %s\n",
+		LOGP(DIUUP, LOGL_ERROR, "Attempting to set illegal id for IuUP CN instance: %s\n",
 		     osmo_quote_str(cn->name, -1));
 		talloc_free(cn);
 		return NULL;
@@ -79,7 +82,7 @@
 }
 
 static int rx_data(struct osmo_iuup_cn *cn, struct msgb *pdu,
-		   struct osmo_iuup_hdr_data *hdr, void *pdu_priv)
+		   struct osmo_iuup_hdr_data *hdr)
 {
 	/* 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;
@@ -87,42 +90,72 @@
 
 	msgb_pull(pdu, sizeof(*hdr));
 
-	cn->cfg.rx_payload(pdu, cn->cfg.node_priv, pdu_priv);
+	LOGP(DIUUP, LOGL_DEBUG, "(%s) IuUP stripping IuUP header from RTP data\n", cn->name);
+	cn->cfg.rx_payload(pdu, cn->cfg.node_priv);
 
 	return 0;
 }
 
-static int tx_init_ack(struct osmo_iuup_cn *cn, void *pdu_priv)
+static int tx_init_ack(struct osmo_iuup_cn *cn, struct msgb *src_pdu)
 {
 	/* Send Initialization Ack PDU back to the sender */
+	int rc;
 	struct msgb *ack = msgb_alloc(4096, "IuUP Initialization Ack");
 	OSMO_ASSERT(ack);
+	ack->dst = src_pdu->dst;
+
+	/* Just copy the RTP header that was sent... TODO: tweak some RTP values?? */
+	memcpy(msgb_put(ack, sizeof(struct rtp_hdr)), src_pdu->data, sizeof(struct rtp_hdr));
+
 	osmo_iuup_make_init_ack(ack);
-	return cn->cfg.tx_msg(ack, cn->cfg.node_priv, pdu_priv);
+
+	LOGP(DIUUP, LOGL_DEBUG, "(%s) Sending Initialization ACK %p\n", cn->name, cn->cfg.node_priv);
+	rc = cn->cfg.tx_msg(ack, cn->cfg.node_priv);
+	msgb_free(ack);
+	return rc;
 }
 
 static int rx_control(struct osmo_iuup_cn *cn, struct msgb *pdu,
-		      struct osmo_iuup_hdr_ctrl *hdr, void *pdu_priv)
+		      struct osmo_iuup_hdr_ctrl *hdr)
 {
 	switch (hdr->procedure) {
 	case OSMO_IUUP_PROC_INITIALIZATION:
 		switch (hdr->ack_nack) {
 		case OSMO_IUUP_ACKNACK_PROCEDURE:
-			return tx_init_ack(cn, pdu_priv);
+			LOGP(DIUUP, LOGL_INFO, "(%s) Rx IuUP Initialization, sending ACK\n", cn->name);
+			cn->rtp_payload_type = ((struct rtp_hdr*)pdu->data)->payload_type;
+			return tx_init_ack(cn, pdu);
 
 		default:
+			LOGP(DIUUP, LOGL_DEBUG, "(%s) Rx IuUP Initialization, unhandled ack_nack = %d\n",
+			     cn->name, hdr->ack_nack);
 			break;
 		}
-		/* fall thru */
+		/* Continue to log "unexpected procedure" below. */
+		break;
+
+	case OSMO_IUUP_PROC_ERROR_EVENT:
+		{
+			union osmo_iuup_hdr_ctrl_payload *p = (void*)hdr->payload;
+			LOGP(DIUUP, LOGL_ERROR,
+			     "(%s) Rx IuUP Error Event: distance=%u, cause=%u=\"%s\"\n",
+			     cn->name, p->error_event.error_distance, p->error_event.error_cause,
+			     osmo_iuup_error_cause_name(p->error_event.error_cause));
+			return 0;
+		}
+
 	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;
+		break;
 	}
+	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)
+/* Feed a received PDU to the IuUP CN node. This function takes ownership of the msgb, it must not be
+ * freed by the caller. */
+int osmo_iuup_cn_rx_pdu(struct osmo_iuup_cn *cn, struct msgb *pdu)
 {
 	struct osmo_iuup_hdr_ctrl *is_ctrl;
 	struct osmo_iuup_hdr_data *is_data;
@@ -133,20 +166,23 @@
 		return rc;
 
 	if (is_ctrl)
-		return rx_control(cn, pdu, is_ctrl, pdu_priv);
+		return rx_control(cn, pdu, is_ctrl);
 	if (is_data)
-		return rx_data(cn, pdu, is_data, pdu_priv);
+		return rx_data(cn, pdu, is_data);
 	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;
+	cn->next_frame_nr = (frame_nr + 1) & 0x0f;
 	return frame_nr;
 }
 
-int osmo_iuup_cn_tx_payload(struct osmo_iuup_cn *cn, struct msgb *pdu, void *pdu_priv)
+/* Send this RTP packet to the IuUP peer: add IuUP header and call the tx_msg() to transmit the resulting
+ * message to the IuUP peer.
+ * Returns 0 on success, negative on error. */
+int osmo_iuup_cn_tx_payload(struct osmo_iuup_cn *cn, struct msgb *pdu)
 {
 	struct rtp_hdr *rtp_was, *rtp;
 	struct osmo_iuup_hdr_data *iuup_hdr;
@@ -157,6 +193,10 @@
 	/* 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));
+
+	/* Send the same payload type to the peer (erm...) */
+	rtp->payload_type = cn->rtp_payload_type;
+
 	iuup_hdr = (void*)rtp->data;
 
 	*iuup_hdr = (struct osmo_iuup_hdr_data){
@@ -166,6 +206,8 @@
 	};
 
 	osmo_iuup_set_checksums((uint8_t*)iuup_hdr, pdu->tail - (uint8_t*)iuup_hdr);
+	LOGP(DIUUP, LOGL_DEBUG, "(%s) IuUP inserting IuUP header in RTP data (frame nr %u)\n",
+	     cn->name, iuup_hdr->frame_nr);
 
-	return cn->cfg.tx_msg(pdu, cn->cfg.node_priv, pdu_priv);
+	return cn->cfg.tx_msg(pdu, cn->cfg.node_priv);
 }