diff --git a/src/tbf_ul_ack_fsm.h b/src/tbf_ul_ack_fsm.h
new file mode 100644
index 0000000..aaee5a3
--- /dev/null
+++ b/src/tbf_ul_ack_fsm.h
@@ -0,0 +1,72 @@
+/* tbf_ul_ack_fsm.h
+ *
+ * Copyright (C) 2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * Author: Pau Espin Pedrol <pespin@sysmocom.de>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ */
+#pragma once
+
+#include <osmocom/core/fsm.h>
+#include <osmocom/core/tdef.h>
+
+#include <gprs_pcu.h>
+
+struct gprs_rlcmac_tbf;
+struct gprs_rlcmac_ul_tbf;
+
+enum tbf_ul_ack_fsm_event {
+	TBF_UL_ACK_EV_SCHED_ACK, /* Tx UL ACK/NACK is pending */
+	TBF_UL_ACK_EV_CREATE_RLCMAC_MSG, /* Scheduler wants to gen+Tx the Ass (rej): data=tbf_ul_ack_ev_create_rlcmac_msg_ctx */
+	TBF_UL_ACK_EV_RX_CTRL_ACK, /* Received CTRL ACK answering poll set on UL ACK/NACK */
+	TBF_UL_ACK_EV_POLL_TIMEOUT, /* Pdch Ul Controller signals timeout for poll set on UL ACK/NACK */
+};
+
+enum tbf_ul_ack_fsm_states {
+	TBF_UL_ACK_ST_NONE = 0,
+	TBF_UL_ACK_ST_SCHED_UL_ACK, /* send UL ACK/NACK on next RTS */
+	TBF_UL_ACK_ST_WAIT_ACK, /* wait for PACKET CONTROL ACK */
+};
+
+struct tbf_ul_ack_fsm_ctx {
+	struct osmo_fsm_inst *fi;
+	struct gprs_rlcmac_ul_tbf *tbf; /* back pointer */
+};
+
+extern const struct osmo_tdef_state_timeout tbf_ul_ack_fsm_timeouts[32];
+/* Transition to a state, using the T timer defined in tbf_ul_ack_fsm_timeouts.
+ * The actual timeout value is in turn obtained from conn->T_defs.
+ * Assumes local variable fi exists. */
+#define tbf_ul_ack_fsm_state_chg(fi, NEXT_STATE) \
+	osmo_tdef_fsm_inst_state_chg(fi, NEXT_STATE, \
+				     tbf_ul_ack_fsm_timeouts, \
+				     the_pcu->T_defs, \
+				     -1)
+
+extern struct osmo_fsm tbf_ul_ack_fsm;
+
+
+/* passed as data in TBF_UL_ACK_EV_CREATE_RLCMAC_MSG */
+struct tbf_ul_ack_ev_create_rlcmac_msg_ctx {
+	uint32_t fn; /* FN where the created DL ctrl block is to be sent */
+	uint8_t ts; /* TS where the created DL ctrl block is to be sent */
+	struct msgb *msg; /* to be filled by FSM during event processing */
+};
+
+
+struct msgb *tbf_ul_ack_create_rlcmac_msg(const struct gprs_rlcmac_tbf *tbf, uint32_t fn, uint8_t ts);
+bool tbf_ul_ack_rts(const struct gprs_rlcmac_tbf *tbf);
+bool tbf_ul_ack_waiting_cnf_final_ack(const struct gprs_rlcmac_tbf *tbf);
+bool tbf_ul_ack_exp_ctrl_ack(const struct gprs_rlcmac_tbf *tbf, uint32_t fn, uint8_t ts);