diff --git a/include/osmocom/gsm/lapd_core.h b/include/osmocom/gsm/lapd_core.h
index 3f31881d3..6e6bff5b6 100644
--- a/include/osmocom/gsm/lapd_core.h
+++ b/include/osmocom/gsm/lapd_core.h
@@ -171,7 +171,7 @@ void lapd_dl_set_name(struct lapd_datalink *dl, const char *name);
 void lapd_dl_exit(struct lapd_datalink *dl);
 void lapd_dl_reset(struct lapd_datalink *dl);
 int lapd_set_mode(struct lapd_datalink *dl, enum lapd_mode mode);
-int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx);
+int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn);
 int lapd_recv_dlsap(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);
 
 /*! @} */
diff --git a/src/gsm/lapd_core.c b/src/gsm/lapd_core.c
index f552dbae7..d5737c8ce 100644
--- a/src/gsm/lapd_core.c
+++ b/src/gsm/lapd_core.c
@@ -812,7 +812,7 @@ static void lapd_acknowledge(struct lapd_msg_ctx *lctx)
 /* L1 -> L2 */
 
 /* Receive a LAPD U SABM(E) message from L1 */
-static int lapd_rx_u_sabm(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u_sabm(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	int length = lctx->length;
@@ -959,7 +959,7 @@ static int lapd_rx_u_sabm(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD U DM message from L1 */
-static int lapd_rx_u_dm(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u_dm(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	int rc = 0;
@@ -1041,7 +1041,7 @@ static int lapd_rx_u_dm(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD U UI message from L1 */
-static int lapd_rx_u_ui(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u_ui(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	int length = lctx->length;
@@ -1080,7 +1080,7 @@ static int lapd_rx_u_ui(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD U DISC message from L1 */
-static int lapd_rx_u_disc(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u_disc(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	int length = lctx->length;
@@ -1158,7 +1158,7 @@ static int lapd_rx_u_disc(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD U UA message from L1 */
-static int lapd_rx_u_ua(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u_ua(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	int length = lctx->length;
@@ -1251,7 +1251,7 @@ static int lapd_rx_u_ua(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD U FRMR message from L1 */
-static int lapd_rx_u_frmr(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u_frmr(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 
@@ -1267,22 +1267,22 @@ static int lapd_rx_u_frmr(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD U (Unnumbered) message from L1 */
-static int lapd_rx_u(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_u(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	switch (lctx->s_u) {
 	case LAPD_U_SABM:
 	case LAPD_U_SABME:
-		return lapd_rx_u_sabm(msg, lctx);
+		return lapd_rx_u_sabm(msg, lctx, fn);
 	case LAPD_U_DM:
-		return lapd_rx_u_dm(msg, lctx);
+		return lapd_rx_u_dm(msg, lctx, fn);
 	case LAPD_U_UI:
-		return lapd_rx_u_ui(msg, lctx);
+		return lapd_rx_u_ui(msg, lctx, fn);
 	case LAPD_U_DISC:
-		return lapd_rx_u_disc(msg, lctx);
+		return lapd_rx_u_disc(msg, lctx, fn);
 	case LAPD_U_UA:
-		return lapd_rx_u_ua(msg, lctx);
+		return lapd_rx_u_ua(msg, lctx, fn);
 	case LAPD_U_FRMR:
-		return lapd_rx_u_frmr(msg, lctx);
+		return lapd_rx_u_frmr(msg, lctx, fn);
 	default:
 		/* G.3.1 */
 		LOGDL(lctx->dl, LOGL_NOTICE, "Unnumbered frame not allowed\n");
@@ -1293,7 +1293,7 @@ static int lapd_rx_u(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD S (Supervisory) message from L1 */
-static int lapd_rx_s(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_s(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	int length = lctx->length;
@@ -1504,7 +1504,7 @@ static int lapd_rx_s(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD I (Information) message from L1 */
-static int lapd_rx_i(struct msgb *msg, struct lapd_msg_ctx *lctx)
+static int lapd_rx_i(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	struct lapd_datalink *dl = lctx->dl;
 	//uint8_t nr = lctx->n_recv;
@@ -1694,19 +1694,19 @@ static int lapd_rx_i(struct msgb *msg, struct lapd_msg_ctx *lctx)
 }
 
 /* Receive a LAPD message from L1 */
-int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx)
+int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx, uint32_t fn)
 {
 	int rc;
 
 	switch (lctx->format) {
 	case LAPD_FORM_U:
-		rc = lapd_rx_u(msg, lctx);
+		rc = lapd_rx_u(msg, lctx, fn);
 		break;
 	case LAPD_FORM_S:
-		rc = lapd_rx_s(msg, lctx);
+		rc = lapd_rx_s(msg, lctx, fn);
 		break;
 	case LAPD_FORM_I:
-		rc = lapd_rx_i(msg, lctx);
+		rc = lapd_rx_i(msg, lctx, fn);
 		break;
 	default:
 		LOGDL(lctx->dl, LOGL_NOTICE, "unknown LAPD format 0x%02x\n", lctx->format);
diff --git a/src/gsm/lapdm.c b/src/gsm/lapdm.c
index e7d46e631..5260aaad8 100644
--- a/src/gsm/lapdm.c
+++ b/src/gsm/lapdm.c
@@ -698,7 +698,7 @@ static int lapdm_rx_not_permitted(const struct lapdm_entity *le,
 }
 
 /* input into layer2 (from layer 1) */
-static int l2_ph_data_ind(struct msgb *msg, struct lapdm_entity *le,
+static int l2_ph_data_ind(struct msgb *msg, struct lapdm_entity *le, uint32_t fn,
 	uint8_t chan_nr, uint8_t link_id)
 {
 	uint8_t cbits = chan_nr >> 3;
@@ -835,7 +835,7 @@ static int l2_ph_data_ind(struct msgb *msg, struct lapdm_entity *le,
 			return -EINVAL;
 		}
 		/* send to LAPD */
-		rc = lapd_ph_data_ind(msg, &lctx);
+		rc = lapd_ph_data_ind(msg, &lctx, fn);
 		break;
 	case LAPDm_FMT_Bter:
 		/* FIXME */
@@ -907,7 +907,7 @@ int lapdm_phsap_up(struct osmo_prim_hdr *oph, struct lapdm_entity *le)
 			rc = -ENODEV;
 			goto free;
 		}
-		rc = l2_ph_data_ind(oph->msg, le, pp->u.data.chan_nr,
+		rc = l2_ph_data_ind(oph->msg, le, pp->u.data.fn, pp->u.data.chan_nr,
 				    pp->u.data.link_id);
 		break;
 	case PRIM_PH_RTS: