diff --git a/tests/e1inp_hsl_bsc_test.c b/tests/e1inp_hsl_bsc_test.c
new file mode 100644
index 0000000..96749e3
--- /dev/null
+++ b/tests/e1inp_hsl_bsc_test.c
@@ -0,0 +1,232 @@
+#include <stdio.h>
+#include <talloc.h>
+#include <osmocom/abis/abis.h>
+#include <osmocom/abis/e1_input.h>
+#include <osmocom/core/application.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/gsm/protocol/gsm_12_21.h>
+
+static void *tall_test;
+static struct e1inp_sign_link *oml_sign_link, *rsl_sign_link;
+
+#define DBSCTEST 0
+
+struct log_info_cat bsc_test_cat[] = {
+	[DBSCTEST] = {
+		.name = "DBSCTEST",
+		.description = "BSC-mode test",
+		.color = "\033[1;35m",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
+};
+
+static struct e1inp_sign_link *
+sign_link_up(void *dev, struct e1inp_line *line, enum e1inp_sign_type type)
+{
+	struct e1inp_sign_link *sign_link = NULL;
+
+	LOGP(DBSCTEST, LOGL_NOTICE, "Signal link up request received.\n");
+	e1inp_ts_config_sign(&line->ts[E1INP_SIGN_OML - 1], line);
+	sign_link = oml_sign_link =
+		e1inp_sign_link_create(&line->ts[E1INP_SIGN_OML - 1],
+				       E1INP_SIGN_OML, NULL, 255, 0);
+	if (!oml_sign_link) {
+		LOGP(DBSCTEST, LOGL_ERROR, "OML link not yet set, giving up\n");
+		return NULL;
+	}
+	e1inp_ts_config_sign(&line->ts[E1INP_SIGN_RSL - 1], line);
+	sign_link = rsl_sign_link =
+	     e1inp_sign_link_create(&line->ts[E1INP_SIGN_RSL - 1],
+				    E1INP_SIGN_RSL, NULL, 0, 0);
+	if (sign_link)
+		LOGP(DBSCTEST, LOGL_NOTICE, "signal link has been set up.\n");
+
+	return sign_link;
+}
+
+static void sign_link_down(struct e1inp_line *line)
+{
+	LOGP(DBSCTEST, LOGL_NOTICE, "signal link has been closed\n");
+	if (oml_sign_link)
+		e1inp_sign_link_destroy(oml_sign_link);
+	if (rsl_sign_link)
+		e1inp_sign_link_destroy(rsl_sign_link);
+}
+
+static void fill_om_hdr(struct abis_om_hdr *oh, uint8_t len)
+{
+	oh->mdisc = ABIS_OM_MDISC_FOM;
+	oh->placement = ABIS_OM_PLACEMENT_ONLY;
+	oh->sequence = 0;
+	oh->length = len;
+}
+
+static void fill_om_fom_hdr(struct abis_om_hdr *oh, uint8_t len,
+                            uint8_t msg_type, uint8_t obj_class,
+                            uint8_t bts_nr, uint8_t trx_nr, uint8_t ts_nr)
+{
+	struct abis_om_fom_hdr *foh =
+		(struct abis_om_fom_hdr *) oh->data;
+
+	fill_om_hdr(oh, len+sizeof(*foh));
+	foh->msg_type = msg_type;
+	foh->obj_class = obj_class;
+	foh->obj_inst.bts_nr = bts_nr;
+	foh->obj_inst.trx_nr = trx_nr;
+	foh->obj_inst.ts_nr = ts_nr;
+}
+
+#define OM_ALLOC_SIZE           1024
+#define OM_HEADROOM_SIZE        128
+
+static struct msgb *nm_msgb_alloc(void)
+{
+	return msgb_alloc_headroom(OM_ALLOC_SIZE, OM_HEADROOM_SIZE, "OML");
+}
+
+
+static int abis_nm_sw_act_req_ack(struct e1inp_sign_link *sign_link,
+				  uint8_t obj_class,
+				  uint8_t i1, uint8_t i2, uint8_t i3,
+				  uint8_t *attr, int att_len)
+{
+	struct abis_om_hdr *oh;
+	struct msgb *msg = nm_msgb_alloc();
+	uint8_t msgtype = NM_MT_SW_ACT_REQ_ACK;
+
+	oh = (struct abis_om_hdr *) msgb_put(msg, ABIS_OM_FOM_HDR_SIZE);
+	fill_om_fom_hdr(oh, att_len, msgtype, obj_class, i1, i2, i3);
+
+	if (attr) {
+		uint8_t *ptr = msgb_put(msg, att_len);
+		memcpy(ptr, attr, att_len);
+	}
+	msg->dst = sign_link;
+	return abis_sendmsg(msg);
+}
+
+static int abis_nm_rx_sw_act_req(struct msgb *msg)
+{
+	struct abis_om_hdr *oh = msgb_l2(msg);
+	struct abis_om_fom_hdr *foh = msgb_l3(msg);
+	int ret;
+
+        ret = abis_nm_sw_act_req_ack(msg->dst,
+				     foh->obj_class,
+				     foh->obj_inst.bts_nr,
+				     foh->obj_inst.trx_nr,
+				     foh->obj_inst.ts_nr,
+				     foh->data, oh->length-sizeof(*foh));
+
+	return ret;
+}
+
+static int abis_nm_rcvmsg_fom(struct msgb *msg)
+{
+	struct abis_om_fom_hdr *foh = msgb_l3(msg);
+	uint8_t mt = foh->msg_type;
+	int ret = 0;
+
+	switch (mt) {
+	case NM_MT_SW_ACT_REQ:	/* Software activate request from BTS. */
+		ret = abis_nm_rx_sw_act_req(msg);
+		break;
+	default:
+		break;
+	}
+	return ret;
+}
+
+static int abis_nm_rcvmsg(struct msgb *msg)
+{
+	int ret = 0;
+	struct abis_om_hdr *oh = msgb_l2(msg);
+
+	msg->l3h = (unsigned char *)oh + sizeof(*oh);
+	switch (oh->mdisc) {
+	case ABIS_OM_MDISC_FOM:
+		ret = abis_nm_rcvmsg_fom(msg);
+		break;
+	default:
+		LOGP(DBSCTEST, LOGL_ERROR, "unknown OML message\n");
+		break;
+	}
+	return ret;
+}
+
+static int sign_link(struct msgb *msg)
+{
+	int ret = 0;
+	struct e1inp_sign_link *link = msg->dst;
+
+	switch(link->type) {
+	case E1INP_SIGN_RSL:
+		LOGP(DBSCTEST, LOGL_NOTICE, "RSL message received.\n");
+		break;
+	case E1INP_SIGN_OML:
+		LOGP(DBSCTEST, LOGL_NOTICE, "OML message received.\n");
+		ret = abis_nm_rcvmsg(msg);
+		break;
+	default:
+		LOGP(DBSCTEST, LOGL_ERROR, "Unknown signallin message.\n");
+		break;
+	}
+	return ret;
+}
+
+const struct log_info bsc_test_log_info = {
+        .filter_fn = NULL,
+        .cat = bsc_test_cat,
+        .num_cat = ARRAY_SIZE(bsc_test_cat),
+};
+
+int main(void)
+{
+	struct e1inp_line *line;
+
+	tall_test = talloc_named_const(NULL, 1, "e1inp_test");
+	libosmo_abis_init(tall_test);
+
+	osmo_init_logging(&bsc_test_log_info);
+
+	struct e1inp_line_ops ops = {
+		.addr		= "0.0.0.0",
+		.role		= E1INP_LINE_R_BSC,
+		.sign_link_up	= sign_link_up,
+		.sign_link_down	= sign_link_down,
+		.sign_link	= sign_link,
+	};
+
+#define LINENR 0
+
+	line = e1inp_line_create(LINENR, "hsl");
+	if (line == NULL) {
+		LOGP(DBSCTEST, LOGL_ERROR, "problem creating E1 line\n");
+		exit(EXIT_FAILURE);
+	}
+
+	e1inp_line_bind_ops(line, &ops);
+
+	/*
+	 * Depending if this is a real or virtual E1 lines:
+	 * - real (ISDN): create signal link for OML and RSL before line up.
+	 * - vitual (INET): we create it in signal_link_up(...) callback.
+	 *
+	 * The signal link is created via e1inp_sign_link_create(...)
+	 *
+	 * See e1_reconfig_trx and e1_reconfig_bts in libbsc/e1_config.c,
+	 * it explains how this is done with ISDN.
+	 */
+
+	if (e1inp_line_update(line) < 0) {
+		LOGP(DBSCTEST, LOGL_ERROR, "problem creating E1 line\n");
+		exit(EXIT_FAILURE);
+	}
+
+	LOGP(DBSCTEST, LOGL_NOTICE, "entering main loop\n");
+
+	while (1) {
+		osmo_select_main(0);
+	}
+	return 0;
+}
diff --git a/tests/e1inp_hsl_bts_test.c b/tests/e1inp_hsl_bts_test.c
new file mode 100644
index 0000000..c9e26f8
--- /dev/null
+++ b/tests/e1inp_hsl_bts_test.c
@@ -0,0 +1,274 @@
+#include <stdio.h>
+#include <talloc.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <osmocom/abis/abis.h>
+#include <osmocom/abis/e1_input.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/core/application.h>
+#include <osmocom/abis/ipaccess.h>
+#include <osmocom/gsm/protocol/gsm_12_21.h>
+
+static void *tall_test;
+static struct e1inp_sign_link *oml_sign_link, *rsl_sign_link;
+
+#define DBTSTEST 0
+
+struct log_info_cat bts_test_cat[] = {
+	[DBTSTEST] = {
+		.name = "DBTSTEST",
+		.description = "BTS-mode test",
+		.color = "\033[1;35m",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
+};
+
+const struct log_info bts_test_log_info = {
+	.filter_fn = NULL,
+	.cat = bts_test_cat,
+	.num_cat = ARRAY_SIZE(bts_test_cat),
+};
+
+enum bts_state_machine {
+	BTS_TEST_OML_SIGN_LINK_DOWN	= 0,
+	BTS_TEST_OML_SIGN_LINK_UP,
+	BTS_TEST_OML_WAIT_SW_ACT_ACK,
+};
+
+static struct osmo_fd bts_eventfd;
+static int eventfds[2];
+
+static enum bts_state_machine bts_state = BTS_TEST_OML_SIGN_LINK_DOWN;
+
+static struct e1inp_sign_link *
+sign_link_up(void *unit, struct e1inp_line *line, enum e1inp_sign_type type)
+{
+	struct e1inp_sign_link *sign_link = NULL;
+
+	LOGP(DBTSTEST, LOGL_NOTICE, "OML and RSL link up request received.\n");
+
+	e1inp_ts_config_sign(&line->ts[0], line);
+	sign_link = oml_sign_link =
+		e1inp_sign_link_create(&line->ts[0],
+					E1INP_SIGN_OML, NULL, 255, 0);
+	if (!oml_sign_link) {
+		LOGP(DBTSTEST, LOGL_ERROR, "cannot create OML sign link\n");
+		return NULL;
+	}
+	sign_link = rsl_sign_link =
+		e1inp_sign_link_create(&line->ts[0],
+					E1INP_SIGN_RSL, NULL, 0, 0);
+	if (!rsl_sign_link) {
+		LOGP(DBTSTEST, LOGL_ERROR, "cannot create RSL sign link\n");
+		return NULL;
+	}
+
+	if (sign_link) {
+		LOGP(DBTSTEST, LOGL_NOTICE, "signal link has been set up.\n");
+		/* Now we can send OML messages to the BSC. */
+		bts_state = BTS_TEST_OML_SIGN_LINK_UP;
+	}
+	/* tell GSM 12.21 that we're ready to proceed via our event fd. */
+	unsigned int event_type = 0;
+	if (write(eventfds[1], &event_type, sizeof(unsigned int)) < 0)
+		LOGP(DBTSTEST, LOGL_ERROR, "cannot write to event fd.\n");
+
+	return sign_link;
+}
+
+static void sign_link_down(struct e1inp_line *line)
+{
+	LOGP(DBTSTEST, LOGL_NOTICE, "signal link has been closed\n");
+	if (oml_sign_link)
+		e1inp_sign_link_destroy(oml_sign_link);
+	if (rsl_sign_link)
+		e1inp_sign_link_destroy(rsl_sign_link);
+}
+
+static int abis_nm_rcvmsg_fom(struct msgb *msg)
+{
+	struct abis_om_fom_hdr *foh = msgb_l3(msg);
+	uint8_t mt = foh->msg_type;
+	int ret = 0;
+
+	switch (mt) {
+	case NM_MT_SW_ACT_REQ_ACK:  /* SW activate request ACK from BSC. */
+		LOGP(DBTSTEST, LOGL_NOTICE, "Receive SW Act Req ACK\n");
+		break;
+	default:
+		LOGP(DBTSTEST, LOGL_ERROR, "unknown OML message\n");
+		break;
+	}
+	return ret;
+}
+
+static int abis_nm_rcvmsg(struct msgb *msg)
+{
+	int ret = 0;
+	struct abis_om_hdr *oh = msgb_l2(msg);
+
+	msg->l3h = (unsigned char *)oh + sizeof(*oh);
+	switch (oh->mdisc) {
+	case ABIS_OM_MDISC_FOM:
+		ret = abis_nm_rcvmsg_fom(msg);
+		break;
+	default:
+		LOGP(DBTSTEST, LOGL_ERROR, "unknown OML message\n");
+	break;
+	}
+	return ret;
+}
+
+static int sign_link(struct msgb *msg)
+{
+	int ret = 0;
+	struct e1inp_sign_link *link = msg->dst;
+
+	switch(link->type) {
+	case E1INP_SIGN_OML:
+		LOGP(DBTSTEST, LOGL_NOTICE, "OML message received.\n");
+		ret = abis_nm_rcvmsg(msg);
+		break;
+	case E1INP_SIGN_RSL:
+		LOGP(DBTSTEST, LOGL_NOTICE, "RSL message received.\n");
+		break;
+	default:
+		LOGP(DBTSTEST, LOGL_ERROR, "Unknown signalling message.\n");
+		break;
+	}
+	return ret;
+}
+
+static void fill_om_hdr(struct abis_om_hdr *oh, uint8_t len)
+{
+	oh->mdisc = ABIS_OM_MDISC_FOM;
+	oh->placement = ABIS_OM_PLACEMENT_ONLY;
+	oh->sequence = 0;
+	oh->length = len;
+}
+
+static void fill_om_fom_hdr(struct abis_om_hdr *oh, uint8_t len,
+			    uint8_t msg_type, uint8_t obj_class,
+			    uint8_t bts_nr, uint8_t trx_nr, uint8_t ts_nr)
+{
+	struct abis_om_fom_hdr *foh = (struct abis_om_fom_hdr *) oh->data;
+
+	fill_om_hdr(oh, len+sizeof(*foh));
+	foh->msg_type = msg_type;
+	foh->obj_class = obj_class;
+	foh->obj_inst.bts_nr = bts_nr;
+	foh->obj_inst.trx_nr = trx_nr;
+	foh->obj_inst.ts_nr = ts_nr;
+}
+
+#define OM_ALLOC_SIZE		1024
+#define OM_HEADROOM_SIZE	128
+
+static struct msgb *nm_msgb_alloc(void)
+{
+        return msgb_alloc_headroom(OM_ALLOC_SIZE, OM_HEADROOM_SIZE, "BTS/test");
+}
+
+static int abis_nm_sw_act_req(struct e1inp_sign_link *sign_link,
+			      uint8_t obj_class,
+			      uint8_t i1, uint8_t i2, uint8_t i3,
+			      uint8_t *attr, int att_len)
+{
+	struct abis_om_hdr *oh;
+	struct msgb *msg = nm_msgb_alloc();
+	uint8_t msgtype = NM_MT_SW_ACT_REQ;
+
+	oh = (struct abis_om_hdr *) msgb_put(msg, ABIS_OM_FOM_HDR_SIZE);
+	fill_om_fom_hdr(oh, att_len, msgtype, obj_class, i1, i2, i3);
+
+	if (attr) {
+		uint8_t *ptr = msgb_put(msg, att_len);
+		memcpy(ptr, attr, att_len);
+	}
+	msg->dst = sign_link;
+	return abis_sendmsg(msg);
+}
+
+static int test_bts_gsm_12_21_cb(struct osmo_fd *ofd, unsigned int what)
+{
+	int ret;
+	unsigned int event_type;
+
+	LOGP(DBTSTEST, LOGL_NOTICE, "event fd callback running\n");
+
+	if (read(ofd->fd, &event_type, sizeof(event_type)) == -1) {
+		LOGP(DBTSTEST, LOGL_ERROR, "problems with event fd\n");
+		return -EINVAL;
+	}
+	switch(bts_state) {
+	case BTS_TEST_OML_SIGN_LINK_DOWN:
+		/* Do nothing until OML link becomes ready. */
+		break;
+	case BTS_TEST_OML_SIGN_LINK_UP:
+		/* OML link is up, send SW ACT REQ. */
+		ret = abis_nm_sw_act_req(oml_sign_link, 0, 0, 0, 0, NULL, 0);
+		bts_state = BTS_TEST_OML_WAIT_SW_ACT_ACK;
+		break;
+	case BTS_TEST_OML_WAIT_SW_ACT_ACK:
+		/* ... things should continue after this. */
+		break;
+	}
+	return 0;
+}
+
+int main(void)
+{
+	struct hsl_unit bts_dev_info = {
+		.swversion	= 0xc0,
+		.serno		= 0x0123456789ABCDEF,
+	};
+	struct e1inp_line *line;
+
+	tall_test = talloc_named_const(NULL, 1, "e1inp_test");
+	libosmo_abis_init(tall_test);
+
+	osmo_init_logging(&bts_test_log_info);
+
+	struct e1inp_line_ops ops = {
+		.role		= E1INP_LINE_R_BTS,
+		.addr		= "127.0.0.1",
+		.data		= &bts_dev_info,
+		.sign_link_up	= sign_link_up,
+		.sign_link_down	= sign_link_down,
+		.sign_link	= sign_link,
+	};
+
+#define LINENR 0
+
+	line = e1inp_line_create(LINENR, "hsl");
+	if (line == NULL) {
+		LOGP(DBTSTEST, LOGL_ERROR, "problem enabling E1 line\n");
+		exit(EXIT_FAILURE);
+	}
+	e1inp_line_bind_ops(line, &ops);
+
+	if (e1inp_line_update(line) < 0) {
+		LOGP(DBTSTEST, LOGL_ERROR, "problem enabling E1 line\n");
+		exit(EXIT_FAILURE);
+	}
+
+	LOGP(DBTSTEST, LOGL_NOTICE, "entering main loop\n");
+
+	if (pipe(eventfds) < 0) {
+		LOGP(DBTSTEST, LOGL_ERROR, "cannot create pipe fds\n");
+		exit(EXIT_FAILURE);
+	}
+	bts_eventfd.fd = eventfds[0];
+	bts_eventfd.cb = test_bts_gsm_12_21_cb;
+	bts_eventfd.when = BSC_FD_READ;
+	if (osmo_fd_register(&bts_eventfd) < 0) {
+		LOGP(DBTSTEST, LOGL_ERROR, "could not register event fd\n");
+		exit(EXIT_FAILURE);
+	}
+
+	while (1) {
+		osmo_select_main(0);
+	}
+	return 0;
+}