HO prep: introduce per-BTS handover config, with defaults on net node

It is desirable to allow configuring handover for each individual network cell.
At the same time, it is desirable to set global defaults.

Treat the 'network' node handover parameters as global defaults, add another
set of parameters for each individual BTS.

This raises questions on how the 'network' node should affect the individual
BTS. The simplistic solution would have been: on creating a BTS in the config,
just copy the current defaults; with serious drawbacks:
- tweaking any parameter in the telnet VTY on network node will never affect
  any running BTS.
- network node defaults *must* be issued before the bts sections in the config
  file.
- when writing a config back to file, we would copy all net node defaults to
  each BTS node, making the network node configs pointless.

Instead, add a handover_cfg API that tracks whether a given node has a value
set or not. A bts node ho_cfg gets a pointer to the network node config and
returns those values if locally unset. If no value is set on any node, use the
"factory" defaults, which are hardcoded in the API. Only write back exactly
those config items that were actually issued in a config file / on the telnet
VTY. (ho_cfg API wise, we could trivially add another ho_cfg level per TRX if
we so desire in the future.)

Implement ho parameters as an opaque config struct with getters and setters to
ensure the tracking is always heeded. Opaqueness dictates allocating instead of
direct embedding in gsm_network and gsm_bts structs, ctx is gsm_net / bts.

This is 100% backwards compatible to
old configs.
- No VTY command syntax changes (only the online help).
- If a 'bts' sets nothing, it will use the 'network' defaults.
- The 'show network' output only changes in presence of individual BTS configs.

On 'show network', say "Handover: On|Off" as before, iff all BTS reflect
identical behavior. Otherwise, output BTS counts of handover being enabled or
not.

Use the same set of VTY commands (same VTY cmd syntax as before) on network and
BTS nodes, i.e. don't duplicate VTY code. From the current vty->node, figure
out which ho_cfg to modify.

For linking, add handover_cfg.c (the value API) in libcommon, while the
handover_vty.c is in libbsc. This is mainly because some utility programs use
gsm_network and hence suck in the ho stuff, but don't need the VTY commands.

Review the VTY online help strings.

Add VTY transcript test for handover options, testing config propagation from
network to bts nodes, 'show network' output and VTY online help strings.
(Needs recent addition of '... !' wildcard to osmo_interact_common.py.)

I considered leaving parts of this more readable, but in the end decided for
heavy use of macros to define and declare the API, because more values will be
added in upcoming patches and I want to prevent myself from messing them up.

Inspired-by: jolly/new_handover branch, which moves the config to 'bts' level
Depends: I7c1ebb2e7f059047903a53de26a0ec1ce7fa9b98 (osmo-python-tests)
Change-Id: I79d35f6d3c0fbee67904378ad7f216df34fde79a

9 files changed, 239 insertions, 134 deletions

diff --git a/src/libbsc/Makefile.am b/src/libbsc/Makefile.am
index 3ac1c0b80..d118f443b 100644
--- a/src/libbsc/Makefile.am
+++ b/src/libbsc/Makefile.am
@@ -57,5 +57,6 @@ libbsc_a_SOURCES = \
 	net_init.c \
 	bsc_dyn_ts.c \
 	bts_ipaccess_nanobts_omlattr.c \
+	handover_vty.c \
 	$(NULL)
 
diff --git a/src/libbsc/bsc_vty.c b/src/libbsc/bsc_vty.c
index 75b0b9a5c..b4a8e2ddc 100644
--- a/src/libbsc/bsc_vty.c
+++ b/src/libbsc/bsc_vty.c
@@ -58,6 +58,8 @@
 #include <osmocom/bsc/pcu_if.h>
 #include <osmocom/bsc/common_cs.h>
 #include <osmocom/bsc/handover.h>
+#include <osmocom/bsc/handover_cfg.h>
+#include <osmocom/bsc/handover_vty.h>
 #include <osmocom/bsc/gsm_04_08_utils.h>
 
 #include <inttypes.h>
@@ -178,8 +180,27 @@ static void net_dump_vty(struct vty *vty, struct gsm_network *net)
 		VTY_NEWLINE);
 	vty_out(vty, "  Use TCH for Paging any: %d%s", net->pag_any_tch,
 		VTY_NEWLINE);
-	vty_out(vty, "  Handover: %s%s", net->handover.active ? "On" : "Off",
-		VTY_NEWLINE);
+
+	{
+		struct gsm_bts *bts;
+		unsigned int ho_active_count = 0;
+		unsigned int ho_inactive_count = 0;
+
+		llist_for_each_entry(bts, &net->bts_list, list) {
+			if (ho_get_ho_active(bts->ho))
+				ho_active_count ++;
+			else
+				ho_inactive_count ++;
+		}
+
+		if (ho_active_count && ho_inactive_count)
+			vty_out(vty, "  Handover: On at %u BTS, Off at %u BTS%s",
+				ho_active_count, ho_inactive_count, VTY_NEWLINE);
+		else
+			vty_out(vty, "  Handover: %s%s", ho_active_count ? "On" : "Off",
+				VTY_NEWLINE);
+	}
+
 	network_chan_load(&pl, net);
 	vty_out(vty, "  Current Channel Load:%s", VTY_NEWLINE);
 	dump_pchan_load_vty(vty, "    ", &pl);
@@ -778,6 +799,8 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
 	if (bts->pcu_sock_path)
 		vty_out(vty, "  pcu-socket %s%s", bts->pcu_sock_path, VTY_NEWLINE);
 
+	ho_vty_write(vty, "  ", bts->ho);
+
 	config_write_bts_model(vty, bts);
 }
 
@@ -807,19 +830,9 @@ static int config_write_net(struct vty *vty)
 	vty_out(vty, " encryption a5 %u%s", gsmnet->a5_encryption, VTY_NEWLINE);
 	vty_out(vty, " neci %u%s", gsmnet->neci, VTY_NEWLINE);
 	vty_out(vty, " paging any use tch %d%s", gsmnet->pag_any_tch, VTY_NEWLINE);
-	vty_out(vty, " handover %u%s", gsmnet->handover.active, VTY_NEWLINE);
-	vty_out(vty, " handover window rxlev averaging %u%s",
-		gsmnet->handover.win_rxlev_avg, VTY_NEWLINE);
-	vty_out(vty, " handover window rxqual averaging %u%s",
-		gsmnet->handover.win_rxqual_avg, VTY_NEWLINE);
-	vty_out(vty, " handover window rxlev neighbor averaging %u%s",
-		gsmnet->handover.win_rxlev_avg_neigh, VTY_NEWLINE);
-	vty_out(vty, " handover power budget interval %u%s",
-		gsmnet->handover.pwr_interval, VTY_NEWLINE);
-	vty_out(vty, " handover power budget hysteresis %u%s",
-		gsmnet->handover.pwr_hysteresis, VTY_NEWLINE);
-	vty_out(vty, " handover maximum distance %u%s",
-		gsmnet->handover.max_distance, VTY_NEWLINE);
+
+	ho_vty_write(vty, " ", gsmnet->ho);
+
 	VTY_OUT_TIMER(3101);
 	VTY_OUT_TIMER(3103);
 	VTY_OUT_TIMER(3105);
@@ -1649,100 +1662,6 @@ DEFUN(cfg_net_neci,
 	return CMD_SUCCESS;
 }
 
-#define HANDOVER_STR	"Handover Options\n"
-
-DEFUN(cfg_net_handover, cfg_net_handover_cmd,
-      "handover (0|1)",
-	HANDOVER_STR
-	"Don't perform in-call handover\n"
-	"Perform in-call handover\n")
-{
-	int enable = atoi(argv[0]);
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-
-	if (enable && ipacc_rtp_direct) {
-		vty_out(vty, "%% Cannot enable handover unless RTP Proxy mode "
-			"is enabled by using the -P command line option%s",
-			VTY_NEWLINE);
-		return CMD_WARNING;
-	}
-	gsmnet->handover.active = enable;
-
-	return CMD_SUCCESS;
-}
-
-#define HO_WIN_STR HANDOVER_STR "Measurement Window\n"
-#define HO_WIN_RXLEV_STR HO_WIN_STR "Received Level Averaging\n"
-#define HO_WIN_RXQUAL_STR HO_WIN_STR "Received Quality Averaging\n"
-#define HO_PBUDGET_STR HANDOVER_STR "Power Budget\n"
-#define HO_AVG_COUNT_STR "Amount to use for Averaging\n"
-
-DEFUN(cfg_net_ho_win_rxlev_avg, cfg_net_ho_win_rxlev_avg_cmd,
-      "handover window rxlev averaging <1-10>",
-	HO_WIN_RXLEV_STR
-	"How many RxLev measurements are used for averaging\n"
-	HO_AVG_COUNT_STR)
-{
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-	gsmnet->handover.win_rxlev_avg = atoi(argv[0]);
-	return CMD_SUCCESS;
-}
-
-DEFUN(cfg_net_ho_win_rxqual_avg, cfg_net_ho_win_rxqual_avg_cmd,
-      "handover window rxqual averaging <1-10>",
-	HO_WIN_RXQUAL_STR
-	"How many RxQual measurements are used for averaging\n"
-	HO_AVG_COUNT_STR)
-{
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-	gsmnet->handover.win_rxqual_avg = atoi(argv[0]);
-	return CMD_SUCCESS;
-}
-
-DEFUN(cfg_net_ho_win_rxlev_neigh_avg, cfg_net_ho_win_rxlev_avg_neigh_cmd,
-      "handover window rxlev neighbor averaging <1-10>",
-	HO_WIN_RXLEV_STR "Neighbor\n"
-	"How many RxQual measurements are used for averaging\n"
-	HO_AVG_COUNT_STR)
-{
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-	gsmnet->handover.win_rxlev_avg_neigh = atoi(argv[0]);
-	return CMD_SUCCESS;
-}
-
-DEFUN(cfg_net_ho_pwr_interval, cfg_net_ho_pwr_interval_cmd,
-      "handover power budget interval <1-99>",
-	HO_PBUDGET_STR
-	"How often to check if we have a better cell (SACCH frames)\n"
-	"Interval\n" "Number\n")
-{
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-	gsmnet->handover.pwr_interval = atoi(argv[0]);
-	return CMD_SUCCESS;
-}
-
-DEFUN(cfg_net_ho_pwr_hysteresis, cfg_net_ho_pwr_hysteresis_cmd,
-      "handover power budget hysteresis <0-999>",
-	HO_PBUDGET_STR
-	"How many dB does a neighbor to be stronger to become a HO candidate\n"
-	"Hysteresis\n" "Number\n")
-{
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-	gsmnet->handover.pwr_hysteresis = atoi(argv[0]);
-	return CMD_SUCCESS;
-}
-
-DEFUN(cfg_net_ho_max_distance, cfg_net_ho_max_distance_cmd,
-      "handover maximum distance <0-9999>",
-	HANDOVER_STR
-	"How big is the maximum timing advance before HO is forced\n"
-	"Distance\n" "Number\n")
-{
-	struct gsm_network *gsmnet = gsmnet_from_vty(vty);
-	gsmnet->handover.max_distance = atoi(argv[0]);
-	return CMD_SUCCESS;
-}
-
 DEFUN(cfg_net_pag_any_tch,
       cfg_net_pag_any_tch_cmd,
       "paging any use tch (0|1)",
@@ -4387,13 +4306,6 @@ int bsc_vty_init(struct gsm_network *network)
 	logging_vty_add_cmds(NULL);
 
 	install_element(GSMNET_NODE, &cfg_net_neci_cmd);
-	install_element(GSMNET_NODE, &cfg_net_handover_cmd);
-	install_element(GSMNET_NODE, &cfg_net_ho_win_rxlev_avg_cmd);
-	install_element(GSMNET_NODE, &cfg_net_ho_win_rxqual_avg_cmd);
-	install_element(GSMNET_NODE, &cfg_net_ho_win_rxlev_avg_neigh_cmd);
-	install_element(GSMNET_NODE, &cfg_net_ho_pwr_interval_cmd);
-	install_element(GSMNET_NODE, &cfg_net_ho_pwr_hysteresis_cmd);
-	install_element(GSMNET_NODE, &cfg_net_ho_max_distance_cmd);
 	install_element(GSMNET_NODE, &cfg_net_T3101_cmd);
 	install_element(GSMNET_NODE, &cfg_net_T3103_cmd);
 	install_element(GSMNET_NODE, &cfg_net_T3105_cmd);
@@ -4408,6 +4320,7 @@ int bsc_vty_init(struct gsm_network *network)
 	install_element(GSMNET_NODE, &cfg_net_T3141_cmd);
 	install_element(GSMNET_NODE, &cfg_net_dtx_cmd);
 	install_element(GSMNET_NODE, &cfg_net_pag_any_tch_cmd);
+	/* See also handover commands added on net level from handover_vty.c */
 
 	install_element(GSMNET_NODE, &cfg_bts_cmd);
 	install_node(&bts_node, config_write_bts);
@@ -4513,6 +4426,7 @@ int bsc_vty_init(struct gsm_network *network)
 	install_element(BTS_NODE, &cfg_bts_amr_hr_hyst3_cmd);
 	install_element(BTS_NODE, &cfg_bts_amr_hr_start_mode_cmd);
 	install_element(BTS_NODE, &cfg_bts_pcu_sock_cmd);
+	/* See also handover commands added on bts level from handover_vty.c */
 
 	install_element(BTS_NODE, &cfg_trx_cmd);
 	install_node(&trx_node, dummy_config_write);
@@ -4551,6 +4465,8 @@ int bsc_vty_init(struct gsm_network *network)
 	e1inp_vty_init();
 	osmo_fsm_vty_add_cmds();
 
+	ho_vty_init();
+
 	bsc_vty_init_extra();
 
 	return 0;
diff --git a/src/libbsc/handover_decision.c b/src/libbsc/handover_decision.c
index 3bca05fa0..a2abb391a 100644
--- a/src/libbsc/handover_decision.c
+++ b/src/libbsc/handover_decision.c
@@ -30,9 +30,11 @@
 #include <osmocom/bsc/meas_rep.h>
 #include <osmocom/bsc/signal.h>
 #include <osmocom/core/talloc.h>
-#include <osmocom/bsc/handover.h>
 #include <osmocom/gsm/gsm_utils.h>
 
+#include <osmocom/bsc/handover.h>
+#include <osmocom/bsc/handover_cfg.h>
+
 /* Get reference to a neighbor cell on a given BCCH ARFCN */
 static struct gsm_bts *gsm_bts_neighbor(const struct gsm_bts *bts,
 					uint16_t arfcn, uint8_t bsic)
@@ -187,7 +189,7 @@ static void process_meas_neigh(struct gsm_meas_rep *mr)
 /* attempt to do a handover */
 static int attempt_handover(struct gsm_meas_rep *mr)
 {
-	struct gsm_network *net = mr->lchan->ts->trx->bts->network;
+	struct gsm_bts *bts = mr->lchan->ts->trx->bts;
 	struct neigh_meas_proc *best_cell = NULL;
 	unsigned int best_better_db = 0;
 	int i, rc;
@@ -204,10 +206,10 @@ static int attempt_handover(struct gsm_meas_rep *mr)
 			continue;
 
 		/* caculate average rxlev for this cell over the window */
-		avg = neigh_meas_avg(nmp, net->handover.win_rxlev_avg_neigh);
+		avg = neigh_meas_avg(nmp, ho_get_rxlev_neigh_avg_win(bts->ho));
 
 		/* check if hysteresis is fulfilled */
-		if (avg < mr->dl.full.rx_lev + net->handover.pwr_hysteresis)
+		if (avg < mr->dl.full.rx_lev + ho_get_pwr_hysteresis(bts->ho))
 			continue;
 
 		better = avg - mr->dl.full.rx_lev;
@@ -222,7 +224,7 @@ static int attempt_handover(struct gsm_meas_rep *mr)
 
 	LOGP(DHO, LOGL_INFO, "%s: Cell on ARFCN %u is better: ",
 		gsm_ts_name(mr->lchan->ts), best_cell->arfcn);
-	if (!net->handover.active) {
+	if (!ho_get_ho_active(bts->ho)) {
 		LOGPC(DHO, LOGL_INFO, "Skipping, Handover disabled\n");
 		return 0;
 	}
@@ -248,9 +250,10 @@ static int attempt_handover(struct gsm_meas_rep *mr)
  * attempt a handover */
 static int process_meas_rep(struct gsm_meas_rep *mr)
 {
-	struct gsm_network *net = mr->lchan->ts->trx->bts->network;
+	struct gsm_bts *bts = mr->lchan->ts->trx->bts;
 	enum meas_rep_field dlev, dqual;
 	int av_rxlev;
+	unsigned int pwr_interval;
 
 	/* we currently only do handover for TCH channels */
 	switch (mr->lchan->type) {
@@ -274,7 +277,7 @@ static int process_meas_rep(struct gsm_meas_rep *mr)
 		process_meas_neigh(mr);
 
 	av_rxlev = get_meas_rep_avg(mr->lchan, dlev,
-				    net->handover.win_rxlev_avg);
+				    ho_get_rxlev_avg_win(bts->ho));
 
 	/* Interference HO */
 	if (rxlev2dbm(av_rxlev) > -85 &&
@@ -297,14 +300,15 @@ static int process_meas_rep(struct gsm_meas_rep *mr)
 	}
 
 	/* Distance */
-	if (mr->ms_l1.ta > net->handover.max_distance) {
-		LOGPC(DHO, LOGL_INFO, "HO cause: Distance av_rxlev=%d dBm ta=%u\n",
-		      rxlev2dbm(av_rxlev), mr->ms_l1.ta);
+	if (mr->ms_l1.ta > ho_get_max_distance(bts->ho)) {
+		LOGPC(DHO, LOGL_INFO, "HO cause: Distance av_rxlev=%d dBm ta=%d \n",
+					rxlev2dbm(av_rxlev), mr->ms_l1.ta);
 		return attempt_handover(mr);
 	}
 
 	/* Power Budget AKA Better Cell */
-	if ((mr->nr % net->handover.pwr_interval) == net->handover.pwr_interval - 1)
+	pwr_interval = ho_get_pwr_interval(bts->ho);
+	if ((mr->nr % pwr_interval) == pwr_interval - 1)
 		return attempt_handover(mr);
 
 	return 0;
diff --git a/src/libbsc/handover_vty.c b/src/libbsc/handover_vty.c
new file mode 100644
index 000000000..225e9a909
--- /dev/null
+++ b/src/libbsc/handover_vty.c
@@ -0,0 +1,101 @@
+/* OsmoBSC interface to quagga VTY for handover parameters */
+/* (C) 2017 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * 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 <osmocom/bsc/gsm_data.h>
+#include <osmocom/bsc/vty.h>
+#include <osmocom/bsc/handover_cfg.h>
+
+static struct handover_cfg *ho_cfg_from_vty(struct vty *vty)
+{
+	switch (vty->node) {
+	case GSMNET_NODE:
+		return gsmnet_from_vty(vty)->ho;
+	case BTS_NODE:
+		OSMO_ASSERT(vty->index);
+		return ((struct gsm_bts *)vty->index)->ho;
+	default:
+		OSMO_ASSERT(false);
+	}
+}
+
+
+#define HO_CFG_ONE_MEMBER(TYPE, NAME, DEFAULT_VAL, \
+			  VTY_CMD, VTY_CMD_ARG, VTY_ARG_EVAL, \
+			  VTY_WRITE_FMT, VTY_WRITE_CONV, \
+			  VTY_DOC) \
+DEFUN(cfg_ho_##NAME, cfg_ho_##NAME##_cmd, \
+      VTY_CMD " (" VTY_CMD_ARG "|default)", \
+      VTY_DOC \
+      "Use default (" #DEFAULT_VAL "), remove explicit setting on this node\n") \
+{ \
+	struct handover_cfg *ho = ho_cfg_from_vty(vty); \
+	const char *val = argv[0]; \
+	if (!strcmp(val, "default")) { \
+		const char *msg; \
+		if (ho_isset_##NAME(ho)) {\
+			ho_clear_##NAME(ho); \
+			msg = "setting removed, now is"; \
+		} else \
+			msg = "already was unset, still is"; \
+		vty_out(vty, "%% '" VTY_CMD "' %s " VTY_WRITE_FMT "%s%s", \
+			msg, VTY_WRITE_CONV( ho_get_##NAME(ho) ), \
+			ho_isset_on_parent_##NAME(ho)? " (set on higher level node)" : "", \
+			VTY_NEWLINE); \
+	} \
+	else \
+		ho_set_##NAME(ho, VTY_ARG_EVAL(val)); \
+	return CMD_SUCCESS; \
+}
+
+HO_CFG_ALL_MEMBERS
+#undef HO_CFG_ONE_MEMBER
+
+
+void ho_vty_write(struct vty *vty, const char *indent, struct handover_cfg *ho)
+{
+#define HO_CFG_ONE_MEMBER(TYPE, NAME, DEFAULT_VAL, \
+			  VTY_CMD, VTY_CMD_ARG, VTY_ARG_EVAL, \
+			  VTY_WRITE_FMT, VTY_WRITE_CONV, \
+			  VTY_DOC) \
+	if (ho_isset_##NAME(ho)) \
+		vty_out(vty, "%s" VTY_CMD " " VTY_WRITE_FMT "%s", indent, \
+			VTY_WRITE_CONV( ho_get_##NAME(ho) ), VTY_NEWLINE);
+
+	HO_CFG_ALL_MEMBERS
+#undef HO_CFG_ONE_MEMBER
+}
+
+static void ho_vty_init_cmds(int parent_node)
+{
+#define HO_CFG_ONE_MEMBER(TYPE, NAME, DEFAULT_VAL, VTY1, VTY2, VTY3, VTY4, VTY5, VTY6) \
+	install_element(parent_node, &cfg_ho_##NAME##_cmd);
+
+	HO_CFG_ALL_MEMBERS
+#undef HO_CFG_ONE_MEMBER
+}
+
+void ho_vty_init()
+{
+	ho_vty_init_cmds(GSMNET_NODE);
+	ho_vty_init_cmds(BTS_NODE);
+}
+
diff --git a/src/libbsc/net_init.c b/src/libbsc/net_init.c
index 30de0cce9..57d824156 100644
--- a/src/libbsc/net_init.c
+++ b/src/libbsc/net_init.c
@@ -21,6 +21,7 @@
 #include <osmocom/bsc/osmo_bsc.h>
 #include <osmocom/bsc/bsc_msc_data.h>
 #include <osmocom/bsc/gsm_04_08_utils.h>
+#include <osmocom/bsc/handover_cfg.h>
 
 struct gsm_network *bsc_network_init(void *ctx,
 				     uint16_t country_code,
@@ -55,13 +56,7 @@ struct gsm_network *bsc_network_init(void *ctx,
 	net->T3122 = GSM_T3122_DEFAULT;
 	net->T3141 = GSM_T3141_DEFAULT;
 
-	/* default set of handover parameters */
-	net->handover.win_rxlev_avg = 10;
-	net->handover.win_rxqual_avg = 1;
-	net->handover.win_rxlev_avg_neigh = 10;
-	net->handover.pwr_interval = 6;
-	net->handover.pwr_hysteresis = 3;
-	net->handover.max_distance = 9999;
+	net->ho = ho_cfg_init(net, NULL);
 
 	INIT_LLIST_HEAD(&net->bts_list);
 
diff --git a/src/libcommon/Makefile.am b/src/libcommon/Makefile.am
index c66cbcdcd..9f7e7b9e9 100644
--- a/src/libcommon/Makefile.am
+++ b/src/libcommon/Makefile.am
@@ -27,4 +27,5 @@ libcommon_a_SOURCES = \
 	gsm_data_shared.c \
 	socket.c \
 	talloc_ctx.c \
+	handover_cfg.c \
 	$(NULL)
diff --git a/src/libcommon/gsm_data.c b/src/libcommon/gsm_data.c
index 87d954ad8..92ebbfe0c 100644
--- a/src/libcommon/gsm_data.c
+++ b/src/libcommon/gsm_data.c
@@ -37,6 +37,7 @@
 #include <osmocom/bsc/gsm_data.h>
 #include <osmocom/bsc/bsc_msc_data.h>
 #include <osmocom/bsc/abis_nm.h>
+#include <osmocom/bsc/handover_cfg.h>
 
 void *tall_bsc_ctx;
 
diff --git a/src/libcommon/gsm_data_shared.c b/src/libcommon/gsm_data_shared.c
index c14047d49..e4ec594f8 100644
--- a/src/libcommon/gsm_data_shared.c
+++ b/src/libcommon/gsm_data_shared.c
@@ -33,6 +33,7 @@
 #include <osmocom/core/statistics.h>
 
 #include <osmocom/bsc/gsm_data.h>
+#include <osmocom/bsc/handover_cfg.h>
 
 void gsm_abis_mo_reset(struct gsm_abis_mo *mo)
 {
@@ -374,6 +375,8 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, uint8_t bts_num)
 	/* si handling */
 	bts->bcch_change_mark = 1;
 
+	bts->ho = ho_cfg_init(bts, net->ho);
+
 	return bts;
 }
 
diff --git a/src/libcommon/handover_cfg.c b/src/libcommon/handover_cfg.c
new file mode 100644
index 000000000..8c208f669
--- /dev/null
+++ b/src/libcommon/handover_cfg.c
@@ -0,0 +1,83 @@
+/* OsmoBSC handover configuration implementation */
+/* (C) 2017 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * 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 <stdbool.h>
+#include <talloc.h>
+
+#include <osmocom/bsc/vty.h>
+#include <osmocom/bsc/handover_cfg.h>
+#include <osmocom/bsc/gsm_data.h>
+
+struct handover_cfg {
+	struct handover_cfg *higher_level_cfg;
+
+#define HO_CFG_ONE_MEMBER(TYPE, NAME, DEFAULT_VAL, VTY1, VTY2, VTY3, VTY4, VTY5, VTY6) \
+	TYPE NAME; \
+	bool has_##NAME;
+
+	HO_CFG_ALL_MEMBERS
+#undef HO_CFG_ONE_MEMBER
+};
+
+struct handover_cfg *ho_cfg_init(void *ctx, struct handover_cfg *higher_level_cfg)
+{
+	struct handover_cfg *ho = talloc_zero(ctx, struct handover_cfg);
+	OSMO_ASSERT(ho);
+	ho->higher_level_cfg = higher_level_cfg;
+	return ho;
+}
+
+#define HO_CFG_ONE_MEMBER(TYPE, NAME, DEFAULT_VAL, VTY1, VTY2, VTY_ARG_EVAL, VTY4, VTY5, VTY6) \
+TYPE ho_get_##NAME(struct handover_cfg *ho) \
+{ \
+	if (ho->has_##NAME) \
+		return ho->NAME; \
+	if (ho->higher_level_cfg) \
+		return ho_get_##NAME(ho->higher_level_cfg); \
+	return VTY_ARG_EVAL(#DEFAULT_VAL); \
+} \
+\
+void ho_set_##NAME(struct handover_cfg *ho, TYPE value) \
+{ \
+	ho->NAME = value; \
+	ho->has_##NAME = true; \
+} \
+\
+bool ho_isset_##NAME(struct handover_cfg *ho) \
+{ \
+	return ho->has_##NAME; \
+} \
+\
+void ho_clear_##NAME(struct handover_cfg *ho) \
+{ \
+	ho->has_##NAME = false; \
+} \
+\
+bool ho_isset_on_parent_##NAME(struct handover_cfg *ho) \
+{ \
+	return ho->higher_level_cfg \
+		&& (ho_isset_##NAME(ho->higher_level_cfg) \
+		    || ho_isset_on_parent_##NAME(ho->higher_level_cfg)); \
+}
+
+HO_CFG_ALL_MEMBERS
+#undef HO_CFG_ONE_MEMBER