diff --git a/src/bts.h b/src/bts.h
index fae3c5e..4b7f7e8 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -119,6 +119,7 @@
 	uint8_t force_cs;	/* 0=use from BTS 1=use from VTY */
 	uint16_t force_llc_lifetime; /* overrides lifetime from SGSN */
 	uint32_t llc_discard_csec;
+	uint32_t llc_idle_ack_csec;
 	uint8_t t3142;
 	uint8_t t3169;
 	uint8_t t3191;
diff --git a/src/pcu_vty.c b/src/pcu_vty.c
index 3d9c79a..00cd6fc 100644
--- a/src/pcu_vty.c
+++ b/src/pcu_vty.c
@@ -100,6 +100,9 @@
 	if (bts->llc_discard_csec)
 		vty_out(vty, " queue hysteresis %d%s", bts->llc_discard_csec,
 			VTY_NEWLINE);
+	if (bts->llc_idle_ack_csec)
+		vty_out(vty, " queue idle-ack-delay %d%s", bts->llc_idle_ack_csec,
+			VTY_NEWLINE);
 	if (bts->alloc_algorithm == alloc_algorithm_a)
 		vty_out(vty, " alloc-algorithm a%s", VTY_NEWLINE);
 	if (bts->alloc_algorithm == alloc_algorithm_b)
@@ -217,7 +220,7 @@
 
 DEFUN(cfg_pcu_queue_hysteresis,
       cfg_pcu_queue_hysteresis_cmd,
-      "queue hysteresis <1-65534>",
+      "queue hysteresis <1-65535>",
       QUEUE_STR QUEUE_HYSTERESIS_STR "Hysteresis in centi-seconds")
 {
 	struct gprs_rlcmac_bts *bts = bts_main_data();
@@ -240,6 +243,33 @@
 	return CMD_SUCCESS;
 }
 
+#define QUEUE_IDLE_ACK_STR "Request an ACK after the last DL LLC frame in centi-seconds\n"
+
+DEFUN(cfg_pcu_queue_idle_ack_delay,
+      cfg_pcu_queue_idle_ack_delay_cmd,
+      "queue idle-ack-delay <1-65535>",
+      QUEUE_STR QUEUE_IDLE_ACK_STR "Idle ACK delay in centi-seconds")
+{
+	struct gprs_rlcmac_bts *bts = bts_main_data();
+	uint8_t csec = atoi(argv[0]);
+
+	bts->llc_idle_ack_csec = csec;
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_pcu_no_queue_idle_ack_delay,
+      cfg_pcu_no_queue_idle_ack_delay_cmd,
+      "no queue idle-ack-delay",
+      NO_STR QUEUE_STR QUEUE_IDLE_ACK_STR)
+{
+	struct gprs_rlcmac_bts *bts = bts_main_data();
+
+	bts->llc_idle_ack_csec = 0;
+
+	return CMD_SUCCESS;
+}
+
 
 DEFUN(cfg_pcu_alloc,
       cfg_pcu_alloc_cmd,
@@ -400,6 +430,8 @@
 	install_element(PCU_NODE, &cfg_pcu_no_queue_lifetime_cmd);
 	install_element(PCU_NODE, &cfg_pcu_queue_hysteresis_cmd);
 	install_element(PCU_NODE, &cfg_pcu_no_queue_hysteresis_cmd);
+	install_element(PCU_NODE, &cfg_pcu_queue_idle_ack_delay_cmd);
+	install_element(PCU_NODE, &cfg_pcu_no_queue_idle_ack_delay_cmd);
 	install_element(PCU_NODE, &cfg_pcu_alloc_cmd);
 	install_element(PCU_NODE, &cfg_pcu_two_phase_cmd);
 	install_element(PCU_NODE, &cfg_pcu_fc_interval_cmd);
diff --git a/src/tbf.cpp b/src/tbf.cpp
index 2c7bd94..9869ff4 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -128,6 +128,7 @@
 	if (tbf->direction == GPRS_RLCMAC_DL_TBF) {
 		gprs_rlcmac_dl_tbf *dl_tbf = static_cast<gprs_rlcmac_dl_tbf *>(tbf);
 		gprs_rlcmac_lost_rep(dl_tbf);
+		dl_tbf->cleanup();
 	}
 
 	LOGP(DRLCMAC, LOGL_INFO, "%s free\n", tbf_name(tbf));
diff --git a/src/tbf.h b/src/tbf.h
index 17ba980..e835ab6 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -311,6 +311,8 @@
 }
 
 struct gprs_rlcmac_dl_tbf : public gprs_rlcmac_tbf {
+	void cleanup();
+
 	/* dispatch Unitdata.DL messages */
 	static int handle(struct gprs_rlcmac_bts *bts,
 		const uint32_t tlli, const char *imsi, const uint8_t ms_class,
@@ -365,6 +367,9 @@
 	int maybe_start_new_window();
 	bool dl_window_stalled() const;
 	void reuse_tbf(const uint8_t *data, const uint16_t len);
+	void start_llc_timer();
+
+	struct osmo_timer_list m_llc_timer;
 };
 
 struct gprs_rlcmac_ul_tbf : public gprs_rlcmac_tbf {
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index aeec23f..e8c5dfe 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -62,6 +62,38 @@
 		tbf->ms_class = ms_class;
 }
 
+static void llc_timer_cb(void *_tbf)
+{
+	struct gprs_rlcmac_dl_tbf *tbf = (struct gprs_rlcmac_dl_tbf *)_tbf;
+
+	if (tbf->state_is_not(GPRS_RLCMAC_FLOW))
+		return;
+
+	LOGP(DRLCMAC, LOGL_DEBUG,
+		"%s LLC receive timeout, requesting DL ACK\n", tbf_name(tbf));
+
+	tbf->request_dl_ack();
+}
+
+void gprs_rlcmac_dl_tbf::cleanup()
+{
+	osmo_timer_del(&m_llc_timer);
+}
+
+void gprs_rlcmac_dl_tbf::start_llc_timer()
+{
+	if (bts_data()->llc_idle_ack_csec > 0) {
+		struct timeval tv;
+
+		/* TODO: this ought to be within a constructor */
+		m_llc_timer.data = this;
+		m_llc_timer.cb = &llc_timer_cb;
+
+		csecs_to_timeval(bts_data()->llc_idle_ack_csec, &tv);
+		osmo_timer_schedule(&m_llc_timer, tv.tv_sec, tv.tv_usec);
+	}
+}
+
 int gprs_rlcmac_dl_tbf::append_data(const uint8_t ms_class,
 				const uint16_t pdu_delay_csec,
 				const uint8_t *data, const uint16_t len)
@@ -80,7 +112,9 @@
 		/* it is no longer drained */
 		m_last_dl_drained_fn = -1;
 		tbf_update_ms_class(this, ms_class);
+		start_llc_timer();
 	} else {
+		/* TODO: put this path into an llc_enqueue method */
 		/* the TBF exists, so we must write it in the queue
 		 * we prepend lifetime in front of PDU */
 		struct timeval *tv;
@@ -95,6 +129,7 @@
 		memcpy(msgb_put(llc_msg, len), data, len);
 		m_llc.enqueue(llc_msg);
 		tbf_update_ms_class(this, ms_class);
+		start_llc_timer();
 	}
 
 	return 0;