diff --git a/TODO-RELEASE b/TODO-RELEASE
index 0ae28c0..9f9f9d9 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -11,3 +11,4 @@
 libosmogsm	add struct member	Add codec_list_bss_supported to gsm0808_handover_request_ack (more_items flag ensures ABI compat)
 libosmogb	ABI BREAKAGE		Add reset_ack_notification function pointer to struct bssgp_bvc_fsm_ops
 libosmogsm      add API                 Add rach_tx_integer_raw2val() in gsm_utils.h
+libosmogsm      add API                 iuup.h
diff --git a/include/osmocom/gsm/iuup.h b/include/osmocom/gsm/iuup.h
index 1ea2b2e..db3d5e0 100644
--- a/include/osmocom/gsm/iuup.h
+++ b/include/osmocom/gsm/iuup.h
@@ -42,6 +42,14 @@
 	uint32_t t_ms;	/* time in ms */
 	uint32_t n_max;	/* max number of repetitions */
 };
+struct osmo_iuup_rfci {
+	uint8_t used:1,
+			spare1:1,
+			id:6;
+	uint8_t spare2:4,
+			IPTI:4; /* values range 0-15, 4 bits */;
+	uint16_t subflow_sizes[IUUP_MAX_SUBFLOWS];
+};
 struct osmo_iuup_rnl_config {
 	/* transparent (true) or SMpSDU (false): */
 	bool transparent;
@@ -56,9 +64,8 @@
 	uint16_t supported_versions_mask;
 	uint8_t num_rfci;
 	uint8_t num_subflows;
-	uint16_t subflow_sizes[IUUP_MAX_RFCIS][IUUP_MAX_SUBFLOWS];
 	bool IPTIs_present;
-	uint8_t IPTIs[IUUP_MAX_RFCIS]; /* values range 0-15, 4 bits */
+	struct osmo_iuup_rfci rfci[IUUP_MAX_RFCIS];
 
 	/* TODO: Indication of delivery of erroneous SDUs*/
 	struct osmo_iuup_rnl_config_timer t_init;
@@ -84,9 +91,8 @@
 			uint8_t data_pdu_type;
 			uint8_t num_rfci;
 			uint8_t num_subflows;
-			uint16_t subflow_sizes[IUUP_MAX_RFCIS][IUUP_MAX_SUBFLOWS];
 			bool IPTIs_present;
-			uint8_t IPTIs[IUUP_MAX_RFCIS]; /* values range 0-15, 4 bits */
+			struct osmo_iuup_rfci rfci[IUUP_MAX_RFCIS];
 		} initialization;
 		struct {
 		} rate_control;
diff --git a/src/gsm/iuup.c b/src/gsm/iuup.c
index eb595ce..edcea3b 100644
--- a/src/gsm/iuup.c
+++ b/src/gsm/iuup.c
@@ -286,13 +286,10 @@
 	struct iuup_ctrl_init_rfci_hdr *ihdr_rfci;
 	struct iuup_ctrl_init_tail *itail;
 	unsigned int i, j;
-	uint8_t num_subflows, num_rfci;
 	uint16_t payload_crc;
+	uint8_t rfci_cnt;
 	struct msgb *msg;
 
-	num_subflows = iui->config.num_subflows;
-	num_rfci = iui->config.num_rfci;
-
 	itp = osmo_iuup_tnl_prim_alloc(iui, OSMO_IUUP_TNL_UNITDATA, PRIM_OP_REQUEST, IUUP_MSGB_SIZE);
 	msg = itp->oph.msg;
 
@@ -307,42 +304,68 @@
 
 	ihdr = (struct iuup_ctrl_init_hdr *)msgb_put(msg, sizeof(*ihdr));
 	ihdr->chain_ind = 0; /* this frame is the last frame for the procedure. TODO: support several */
-	ihdr->num_subflows_per_rfci = num_subflows;
+	ihdr->num_subflows_per_rfci = iui->config.num_subflows;
 	ihdr->ti = iui->config.IPTIs_present ? 1 : 0;
 	ihdr->spare = 0;
 
 	/* RFCI + subflow size part: */
-	for (i = 0; i < num_rfci; i++) {
-		bool last = (i+1 == num_rfci);
-		uint8_t len_size = 1;
-		for (j = 0; j < num_subflows; j++) {
-			if (iui->config.subflow_sizes[i][j] > UINT8_MAX)
+	rfci_cnt = 0;
+	for (i = 0; i < ARRAY_SIZE(iui->config.rfci); i++) {
+		bool last;
+		uint8_t len_size;
+		struct osmo_iuup_rfci *rfci = &iui->config.rfci[i];
+		if (!rfci->used)
+			continue;
+		rfci_cnt++;
+		last = (rfci_cnt == iui->config.num_rfci);
+
+		len_size = 1;
+		for (j = 0; j < iui->config.num_subflows; j++) {
+			if (rfci->subflow_sizes[j] > UINT8_MAX)
 				len_size = 2;
 		}
-		ihdr_rfci = (struct iuup_ctrl_init_rfci_hdr *)msgb_put(msg, sizeof(*ihdr_rfci) + len_size * num_subflows);
-		ihdr_rfci->rfci = i;
+
+		ihdr_rfci = (struct iuup_ctrl_init_rfci_hdr *)msgb_put(msg, sizeof(*ihdr_rfci) + len_size * iui->config.num_subflows);
+		ihdr_rfci->rfci = rfci->id;
 		ihdr_rfci->li = len_size - 1;
 		ihdr_rfci->lri = last;
 		if (len_size == 2) {
 			uint16_t *buf = (uint16_t *)&ihdr_rfci->subflow_length[0];
-			for (j = 0; j < num_subflows; j++)
-				osmo_store16be(iui->config.subflow_sizes[i][j], buf++);
+			for (j = 0; j < iui->config.num_subflows; j++)
+				osmo_store16be(rfci->subflow_sizes[j], buf++);
 		} else {
-			for (j = 0; j < num_subflows; j++)
-				ihdr_rfci->subflow_length[j] = iui->config.subflow_sizes[i][j];
+			for (j = 0; j < iui->config.num_subflows; j++)
+				ihdr_rfci->subflow_length[j] = rfci->subflow_sizes[j];
 		}
+		/* early loop termination: */
+		if (last)
+			break;
+	}
+	/* Sanity check: */
+	if (rfci_cnt != iui->config.num_rfci) {
+		LOGP(DLIUUP, LOGL_ERROR, "rfci_cnt %u != num_rfci %u\n",
+			 rfci_cnt, iui->config.num_rfci);
+		msgb_free(msg);
+		return NULL;
 	}
 
 	if (iui->config.IPTIs_present) {
-		uint8_t num_bytes = (num_rfci + 1) / 2;
+		uint8_t num_bytes = (iui->config.num_rfci + 1) / 2;
 		uint8_t *buf = msgb_put(msg, num_bytes);
-		for (i = 0; i < num_bytes - 1; i++)
-			buf[i] = iui->config.IPTIs[i*2] << 4 |
-			      (iui->config.IPTIs[i*2 + 1] & 0x0f);
-		buf[i] = iui->config.IPTIs[i*2] << 4;
-		if (!(num_rfci & 0x01)) /* is even: */
-			buf[i] |= (iui->config.IPTIs[i*2 + 1] & 0x0f);
-
+		rfci_cnt = 0;
+		for (i = 0; i < ARRAY_SIZE(iui->config.rfci); i++) {
+			struct osmo_iuup_rfci *rfci = &iui->config.rfci[i];
+			if (!rfci->used)
+				continue;
+			if (!(rfci_cnt & 0x01)) /* is even: */
+				buf[rfci_cnt / 2] = (((uint8_t)rfci->IPTI) << 4);
+			else
+				buf[rfci_cnt / 2] |= (rfci->IPTI & 0x0F);
+			rfci_cnt++;
+			/* early loop termination: */
+			if (rfci_cnt == iui->config.num_rfci)
+				break;
+		}
 	}
 
 	itail = (struct iuup_ctrl_init_tail *)msgb_put(msg, sizeof(*itail));
@@ -368,12 +391,8 @@
 	irp->u.status.u.initialization.data_pdu_type = iui->config.data_pdu_type;
 	irp->u.status.u.initialization.num_subflows = iui->config.num_subflows;
 	irp->u.status.u.initialization.num_rfci = iui->config.num_rfci;
-	memcpy(irp->u.status.u.initialization.subflow_sizes, iui->config.subflow_sizes,
-	       IUUP_MAX_RFCIS * IUUP_MAX_SUBFLOWS * sizeof(iui->config.subflow_sizes[0][0]));
 	irp->u.status.u.initialization.IPTIs_present = iui->config.IPTIs_present;
-	if (iui->config.IPTIs_present)
-		memcpy(irp->u.status.u.initialization.IPTIs, iui->config.IPTIs,
-		       IUUP_MAX_RFCIS * sizeof(iui->config.IPTIs[0]));
+	memcpy(irp->u.status.u.initialization.rfci, iui->config.rfci, sizeof(iui->config.rfci));
 	return irp;
 }
 
@@ -530,24 +549,27 @@
 	ihdr_rfci = (struct iuup_ctrl_init_rfci_hdr *)ihdr->rfci_data;
 
 	do {
+		struct osmo_iuup_rfci *rfci = &iui->config.rfci[num_rfci];
 		uint8_t l_size_bytes = ihdr_rfci->li + 1;
 		is_last = ihdr_rfci->lri;
-		if (ihdr_rfci->rfci != num_rfci) {
-			LOGPFSML(iui->fi, LOGL_NOTICE, "Initialization: Unexpected RFCI %u at position %u received\n",
-				 ihdr_rfci->rfci, num_rfci);
+		if (num_rfci >= IUUP_MAX_RFCIS) {
+			LOGPFSML(iui->fi, LOGL_NOTICE, "Initialization: Too many RFCIs received (%u)\n",
+					 num_rfci);
 			err_cause = IUUP_ERR_CAUSE_UNEXPECTED_RFCI;
 			goto send_nack;
 		}
+		rfci->used = 1;
+		rfci->id = ihdr_rfci->rfci;
 		if (l_size_bytes == 2) {
 			uint16_t *subflow_size = (uint16_t *)ihdr_rfci->subflow_length;
 			for (i = 0; i < ihdr->num_subflows_per_rfci; i++) {
-				iui->config.subflow_sizes[ihdr_rfci->rfci][i] = osmo_load16be(subflow_size);
+				rfci->subflow_sizes[i] = osmo_load16be(subflow_size);
 				subflow_size++;
 			}
 		} else {
 			uint8_t *subflow_size = ihdr_rfci->subflow_length;
 			for (i = 0; i < ihdr->num_subflows_per_rfci; i++) {
-				iui->config.subflow_sizes[ihdr_rfci->rfci][i] = *subflow_size;
+				rfci->subflow_sizes[i] = *subflow_size;
 				subflow_size++;
 			}
 		}
@@ -561,19 +583,18 @@
 		uint8_t num_bytes = (num_rfci + 1) / 2;
 		iui->config.IPTIs_present = true;
 		for (i = 0; i < num_bytes - 1; i++) {
-			iui->config.IPTIs[i*2] = *buf >> 4;
-			iui->config.IPTIs[i*2 + 1] = *buf & 0x0f;
+			iui->config.rfci[i*2].IPTI = *buf >> 4;
+			iui->config.rfci[i*2 + 1].IPTI = *buf & 0x0f;
 			buf++;
 		}
-		iui->config.IPTIs[i*2] = *buf >> 4;
+		iui->config.rfci[i*2].IPTI = *buf >> 4;
 		if (!(num_rfci & 0x01)) /* is even: */
-			iui->config.IPTIs[i*2 + 1] = *buf & 0x0f;
+			iui->config.rfci[i*2 + 1].IPTI = *buf & 0x0f;
 		buf++;
 		itail = (struct iuup_ctrl_init_tail *)buf;
 	} else {
 		itail = (struct iuup_ctrl_init_tail *)ihdr_rfci;
 	}
-
 	if (itail->data_pdu_type > 1) {
 		LOGPFSML(iui->fi, LOGL_NOTICE, "Initialization: Unexpected Data PDU Type %u received\n", itail->data_pdu_type);
 		err_cause = IUUP_ERR_CAUSE_UNEXPECTED_VALUE;
diff --git a/tests/iuup/iuup_test.c b/tests/iuup/iuup_test.c
index a58481d..6e3d8ca 100644
--- a/tests/iuup/iuup_test.c
+++ b/tests/iuup/iuup_test.c
@@ -19,14 +19,14 @@
 	.supported_versions_mask = 0x0001,
 	.num_rfci = 3,
 	.num_subflows = 3,
-	.subflow_sizes = {
-		{81, 103, 60},
-		{39, 0, 0},
-		{0, 0, 0},
+	.IPTIs_present = true,
+	.rfci = {
+		{.used = 1, .id = 0, .IPTI = 1, .subflow_sizes = {81, 103, 60} },
+		{.used = 1, .id = 1, .IPTI = 7, .subflow_sizes = {39, 0, 0} },
+		{.used = 1, .id = 2, .IPTI = 1, .subflow_sizes = {0, 0, 0} },
 	},
 	/* .delivery_err_sdu = All set to 0 (YES) by default, */
 	.IPTIs_present = true,
-	.IPTIs = {1, 7, 1},
 	.t_init = { .t_ms = IUUP_TIMER_INIT_T_DEFAULT, .n_max = IUUP_TIMER_INIT_N_DEFAULT },
 	.t_ta = { .t_ms = IUUP_TIMER_TA_T_DEFAULT, .n_max = IUUP_TIMER_TA_N_DEFAULT },
 	.t_rc = { .t_ms = IUUP_TIMER_RC_T_DEFAULT, .n_max = IUUP_TIMER_RC_N_DEFAULT },