diff --git a/src/libbsc/acc_ramp.c b/src/libbsc/acc_ramp.c
new file mode 100644
index 0000000..7cace4b
--- /dev/null
+++ b/src/libbsc/acc_ramp.c
@@ -0,0 +1,235 @@
+/* (C) 2018 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * Author: Stefan Sperling <ssperling@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <strings.h>
+#include <errno.h>
+#include <stdbool.h>
+
+#include <osmocom/bsc/debug.h>
+#include <osmocom/bsc/acc_ramp.h>
+#include <osmocom/bsc/gsm_data.h>
+
+/*
+ * Check if an ACC has been permanently barred for a BTS,
+ * e.g. with the 'rach access-control-class' VTY command.
+ */
+static bool acc_is_enabled(struct gsm_bts *bts, unsigned int acc)
+{
+	OSMO_ASSERT(acc >= 0 && acc <= 9);
+	if (acc == 8 || acc == 9)
+		return (bts->si_common.rach_control.t2 & (1 << (acc - 8))) == 0;
+	return (bts->si_common.rach_control.t3 & (1 << (acc))) == 0;
+}
+
+static void allow_one_acc(struct acc_ramp *acc_ramp, unsigned int acc)
+{
+	OSMO_ASSERT(acc >= 0 && acc <= 9);
+	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: allowing Access Control Class %u\n", acc_ramp->bts->nr, acc);
+	acc_ramp->barred_accs &= ~(1 << acc);
+}
+
+static void barr_one_acc(struct acc_ramp *acc_ramp, unsigned int acc)
+{
+	OSMO_ASSERT(acc >= 0 && acc <= 9);
+	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: barring Access Control Class %u\n", acc_ramp->bts->nr, acc);
+	acc_ramp->barred_accs |= (1 << acc);
+}
+
+static void barr_all_enabled_accs(struct acc_ramp *acc_ramp)
+{
+	unsigned int acc;
+	for (acc = 0; acc < 10; acc++) {
+		if (acc_is_enabled(acc_ramp->bts, acc))
+			barr_one_acc(acc_ramp, acc);
+	}
+}
+
+static void allow_all_enabled_accs(struct acc_ramp *acc_ramp)
+{
+	unsigned int acc;
+	for (acc = 0; acc < 10; acc++) {
+		if (acc_is_enabled(acc_ramp->bts, acc))
+			allow_one_acc(acc_ramp, acc);
+	}
+}
+
+static unsigned int get_next_step_interval(struct acc_ramp *acc_ramp)
+{
+	struct gsm_bts *bts = acc_ramp->bts;
+	uint64_t load;
+
+	if (acc_ramp->step_interval_is_fixed)
+		return acc_ramp->step_interval_sec;
+
+	/* Scale the step interval to current channel load average. */
+	load = (bts->chan_load_avg << 8); /* convert to fixed-point */
+	acc_ramp->step_interval_sec = ((load * ACC_RAMP_STEP_INTERVAL_MAX) / 100) >> 8;
+	if (acc_ramp->step_interval_sec < ACC_RAMP_STEP_SIZE_MIN)
+		acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MIN;
+	else if (acc_ramp->step_interval_sec > ACC_RAMP_STEP_INTERVAL_MAX)
+		acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MAX;
+
+	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: step interval set to %u seconds based on %u%% channel load average\n",
+	     bts->nr, acc_ramp->step_interval_sec, bts->chan_load_avg);
+	return acc_ramp->step_interval_sec;
+}
+
+static void do_acc_ramping_step(void *data)
+{
+	struct acc_ramp *acc_ramp = data;
+	int i;
+
+	/* Shortcut in case we only do one ramping step. */
+	if (acc_ramp->step_size == ACC_RAMP_STEP_SIZE_MAX) {
+		allow_all_enabled_accs(acc_ramp);
+		gsm_bts_set_system_infos(acc_ramp->bts);
+		return;
+	}
+
+	/* Allow 'step_size' ACCs, starting from ACC0. ACC9 will be allowed last. */
+	for (i = 0; i < acc_ramp->step_size; i++) {
+		int idx = ffs(acc_ramp_get_barred_t3(acc_ramp));
+		if (idx > 0) {
+			/* One of ACC0-ACC7 is still bared. */
+			unsigned int acc = idx - 1;
+			if (acc_is_enabled(acc_ramp->bts, acc))
+				allow_one_acc(acc_ramp, acc);
+		} else {
+			idx = ffs(acc_ramp_get_barred_t2(acc_ramp));
+			if (idx == 1 || idx == 2) {
+				/* ACC8 or ACC9 is still barred. */
+				unsigned int acc = idx - 1 + 8;
+				if (acc_is_enabled(acc_ramp->bts, acc))
+					allow_one_acc(acc_ramp, acc);
+			} else {
+				/* All ACCs are now allowed. */
+				break;
+			}
+		}
+	}
+
+	gsm_bts_set_system_infos(acc_ramp->bts);
+
+	/* If we have not allowed all ACCs yet, schedule another ramping step. */
+	if (acc_ramp_get_barred_t2(acc_ramp) != 0x00 ||
+	    acc_ramp_get_barred_t3(acc_ramp) != 0x00)
+		osmo_timer_schedule(&acc_ramp->step_timer, get_next_step_interval(acc_ramp), 0);
+}
+
+/*!
+ * Initialize an acc_ramp data structure.
+ * Storage for this structure must be provided by the caller.
+ *
+ * If ACC ramping is enabled, all ACCs are denied by default.
+ * A subsequent call to acc_ramp_start() will begin the ramping process.
+ * If ACC ramping is disabled, all ACCs will be allowed by default,
+ * and there is no need to do anything else.
+ *
+ * \param[in] acc_ramp Pointer to acc_ramp structure to be initialized.
+ * \param[in] enable Indicates whether ACC ramping should be enabled or disabled.
+ * \param[in] bts BTS which uses this ACC ramp data structure.
+ */
+void acc_ramp_init(struct acc_ramp *acc_ramp, bool enable, struct gsm_bts *bts)
+{
+	acc_ramp->bts = bts;
+	acc_ramp->acc_ramping_enabled = enable;
+	acc_ramp->step_size = ACC_RAMP_STEP_SIZE_DEFAULT;
+	acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MIN;
+	acc_ramp->step_interval_is_fixed = false;
+	osmo_timer_setup(&acc_ramp->step_timer, do_acc_ramping_step, acc_ramp);
+
+	if (acc_ramp->acc_ramping_enabled)
+		barr_all_enabled_accs(acc_ramp);
+	else
+		allow_all_enabled_accs(acc_ramp);
+}
+
+/*!
+ * Change the ramping step size which controls how many ACCs will be allowed per ramping step.
+ * Returns negative on error (step_size out of range), else zero.
+ * \param[in] acc_ramp Pointer to acc_ramp structure.
+ * \param[in] step_size The new step size value.
+ */
+int acc_ramp_set_step_size(struct acc_ramp *acc_ramp, unsigned int step_size)
+{
+	if (step_size < ACC_RAMP_STEP_SIZE_MIN || step_size > ACC_RAMP_STEP_SIZE_MAX)
+		return -ERANGE;
+
+	acc_ramp->step_size = step_size;
+	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: ramping step size set to %u\n", acc_ramp->bts->nr, step_size);
+	return 0;
+}
+
+/*!
+ * Change the ramping step interval to a fixed value. Unless this function is called,
+ * the interval is automatically scaled to the BTS channel load average.
+ * \param[in] acc_ramp Pointer to acc_ramp structure.
+ * \param[in] step_interval The new fixed step interval in seconds.
+ */
+int acc_ramp_set_step_interval(struct acc_ramp *acc_ramp, unsigned int step_interval)
+{
+	if (step_interval < ACC_RAMP_STEP_INTERVAL_MIN || step_interval > ACC_RAMP_STEP_INTERVAL_MAX)
+		return -ERANGE;
+
+	acc_ramp->step_interval_sec = step_interval;
+	acc_ramp->step_interval_is_fixed = true;
+	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: ramping step interval set to %u seconds\n",
+	     acc_ramp->bts->nr, step_interval);
+	return 0;
+}
+
+/*!
+ * Clear a previously set fixed ramping step interval, so that the interval
+ * is again automatically scaled to the BTS channel load average.
+ * \param[in] acc_ramp Pointer to acc_ramp structure.
+ */
+void acc_ramp_set_step_interval_dynamic(struct acc_ramp *acc_ramp)
+{
+	acc_ramp->step_interval_is_fixed = false;
+	LOGP(DRSL, LOGL_DEBUG, "(bts=%d) ACC RAMP: ramping step interval set to 'dynamic'\n",
+	     acc_ramp->bts->nr);
+}
+
+/*!
+ * Begin the ramping process. Perform at least one ramping step to allow 'step_size' ACCs.
+ * If 'step_size' is ACC_RAMP_STEP_SIZE_MAX, all ACCs will be allowed immediately.
+ * \param[in] acc_ramp Pointer to acc_ramp structure.
+ */
+void acc_ramp_start(struct acc_ramp *acc_ramp)
+{
+	/* Abort any previously running ramping process. */
+	acc_ramp_abort(acc_ramp);
+
+	/* Set all availble ACCs to barred and start ramping up. */
+	barr_all_enabled_accs(acc_ramp);
+	do_acc_ramping_step(acc_ramp);
+}
+
+/*!
+ * Abort the ramping process. If ramping is disabled or has already finished,
+ * then this function has no effect.
+ * \param[in] acc_ramp Pointer to acc_ramp structure.
+ */
+void acc_ramp_abort(struct acc_ramp *acc_ramp)
+{
+	if (osmo_timer_pending(&acc_ramp->step_timer))
+		osmo_timer_del(&acc_ramp->step_timer);
+}