bsc: Enable force-combined-si on nanoBTS by default

Some nanoBTS firmwares (if not all) are known to not work properly with
SI2ter. If BSC enables SI2ter through RSL, SI3 bit announcing SI2ter
available will be forwarded by nanoBTS to MS, but will still only send
SI2 message instead of expected SI2ter during TC=5 (see GSM 05.02 sec 6.3.4 "Mapping
of BCCH data"). As a result, some MS won't allow registering to the
network.

To avoid this kind of scenario, enable force-combined-si by default on
nanoBTS while still allowing to overwrite the feature through VTY. Other
BTS models are kept with force-combined-si disabled by default as
usually, since they seems to be working fine when SI2ter is enabled.

Related: OS#3063
Change-Id: Ide6e8967de0eedc9e2bcaf4414aaa537b009d72d

4 files changed, 15 insertions, 4 deletions

diff --git a/src/osmo-bsc/bsc_vty.c b/src/osmo-bsc/bsc_vty.c
index 3ac592c66..931db5b34 100644
--- a/src/osmo-bsc/bsc_vty.c
+++ b/src/osmo-bsc/bsc_vty.c
@@ -985,8 +985,9 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
 	if (bts->excl_from_rf_lock)
 		vty_out(vty, "  rf-lock-exclude%s", VTY_NEWLINE);
 
-	vty_out(vty, "  %sforce-combined-si%s",
-		bts->force_combined_si ? "" : "no ", VTY_NEWLINE);
+	if (bts->force_combined_si_set)
+		vty_out(vty, "  %sforce-combined-si%s",
+			bts->force_combined_si ? "" : "no ", VTY_NEWLINE);
 
 	for (i = 0; i < ARRAY_SIZE(bts->depends_on); ++i) {
 		int j;
@@ -3411,6 +3412,7 @@ DEFUN(cfg_bts_force_comb_si,
 {
 	struct gsm_bts *bts = vty->index;
 	bts->force_combined_si = 1;
+	bts->force_combined_si_set = true;
 	return CMD_SUCCESS;
 }
 
@@ -3421,6 +3423,7 @@ DEFUN(cfg_bts_no_force_comb_si,
 {
 	struct gsm_bts *bts = vty->index;
 	bts->force_combined_si = 0;
+	bts->force_combined_si_set = true;
 	return CMD_SUCCESS;
 }
 
diff --git a/src/osmo-bsc/bts_ipaccess_nanobts.c b/src/osmo-bsc/bts_ipaccess_nanobts.c
index 1fffd89c4..cf81a22c6 100644
--- a/src/osmo-bsc/bts_ipaccess_nanobts.c
+++ b/src/osmo-bsc/bts_ipaccess_nanobts.c
@@ -63,7 +63,12 @@ struct gsm_bts_model bts_model_nanobts = {
 	.start = bts_model_nanobts_start,
 	.oml_rcvmsg = &abis_nm_rcvmsg,
 	.oml_status = &get_oml_status,
-	.e1line_bind_ops = bts_model_nanobts_e1line_bind_ops, 
+	.e1line_bind_ops = bts_model_nanobts_e1line_bind_ops,
+	/* Some nanoBTS firmwares (if not all) don't support SI2ter and cause
+	 * problems on some MS if it is enabled, see OS#3063. Disable it by
+	 * default, can still be enabled through VTY cmd with same name.
+	 */
+	.force_combined_si = true,
 	.nm_att_tlvdef = {
 		.def = {
 			/* ip.access specifics */
diff --git a/src/osmo-bsc/bts_sysmobts.c b/src/osmo-bsc/bts_sysmobts.c
index 91d1118c5..253786428 100644
--- a/src/osmo-bsc/bts_sysmobts.c
+++ b/src/osmo-bsc/bts_sysmobts.c
@@ -48,6 +48,9 @@ int bts_model_sysmobts_init(void)
 	model_sysmobts.name = "sysmobts";
 	model_sysmobts.type = GSM_BTS_TYPE_OSMOBTS;
 
+	/* Unlike nanoBTS, sysmoBTS supports SI2bis and SI2ter fine */
+	model_sysmobts.force_combined_si = false;
+
 	model_sysmobts.features.data = &model_sysmobts._features_data[0];
 	model_sysmobts.features.data_len =
 				sizeof(model_sysmobts._features_data);
diff --git a/src/osmo-bsc/system_information.c b/src/osmo-bsc/system_information.c
index 0148ac389..0a441dc46 100644
--- a/src/osmo-bsc/system_information.c
+++ b/src/osmo-bsc/system_information.c
@@ -327,7 +327,7 @@ int bts_uarfcn_add(struct gsm_bts *bts, uint16_t arfcn, uint16_t scramble, bool
 static inline int use_arfcn(const struct gsm_bts *bts, const bool bis, const bool ter,
 			const bool pgsm, const int arfcn)
 {
-	if (bts->force_combined_si)
+	if (bts->force_combined_si_set ? bts->force_combined_si : bts->model->force_combined_si)
 		return !bis && !ter;
 	if (!bis && !ter && band_compatible(bts, arfcn))
 		return 1;