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prevent ARFCN+BSIC collisions in config

If multiple BTS are configured with identical ARFCN+BSIC, handover cannot
possibly work. Add warn_on_arfcn_bsic_collisions() and when collisions are

- exit right away on program startup.
- warn on vty bts node-exit (go_parent_cb()), i.e. when ARFCN+BSIC collide
  implicitly from default values.
- warn on vty bts/base_station_id_code cmd coming from telnet vty,
  i.e. when the user actively configures colliding BSIC.
- warn on vty trx/arfcn cmd coming from telnet vty,
  i.e. when the user actively configures colliding ARFCN.

When warning, warn on all of:
- DHO log,
- stderr,
- vty_out() in case a vty instance is passed (i.e. from interactive vty).
It's better to log this once too often than let the user miss it.

Rationale: when I started to implement ttcn3 tests for inter-bsc HO, I saw that
the new code based on ARFCN+BSIC would cause a handover request intended to go
from BTS 0 to BTS 1 to instead go from BTS 0 to back to BTS 0 -- because of
identical ARFCN+BSIC in the config of ttcn3-bsc-tests. Such a config badly
confuses handover: measurement reports interpreted to come from the wrong cell,
all handovers attempted to go to the first BTS (sometimes correctly, sometimes
wrongly), in short, non-obvious failure across the handover board. The network
would appear to work well, but occasionally a handover would kill a call
without apparent reason. It seems worthwhile to prevent such misconfiguration
as early as possible, and even allow previous ARFCN+BSIC misconfiguration that
used to work to instead break now (only upon reading config during program
startup, to not cause program exit just because a user introduces a temporary
collision in an interactive vty session).

Change-Id: Ia7c38188ccbad5d8b7398e3e5220015e62c08c8b
M include/osmocom/bsc/vty.h
M src/libbsc/bsc_vty.c
M src/osmo-bsc/osmo_bsc_main.c
3 files changed, 36 insertions(+), 0 deletions(-)

  git pull ssh:// refs/changes/14/7814/1

diff --git a/include/osmocom/bsc/vty.h b/include/osmocom/bsc/vty.h
index e632755..bfea69d 100644
--- a/include/osmocom/bsc/vty.h
+++ b/include/osmocom/bsc/vty.h
@@ -35,4 +35,6 @@
 struct gsm_network *gsmnet_from_vty(struct vty *vty);
+int warn_on_arfcn_bsic_collisions(struct gsm_network *net, struct vty *vty);
diff --git a/src/libbsc/bsc_vty.c b/src/libbsc/bsc_vty.c
index c8d1637..ddb6669 100644
--- a/src/libbsc/bsc_vty.c
+++ b/src/libbsc/bsc_vty.c
@@ -2071,6 +2071,30 @@
        return CMD_SUCCESS;
+int warn_on_arfcn_bsic_collisions(struct gsm_network *net, struct vty *vty)
+       struct gsm_bts *bts, *bts2;
+       int errors = 0;
+       llist_for_each_entry(bts, &net->bts_list, list) {
+               struct neighbor_ident_key *nik = bts_ident_key(bts);
+               bts2 = bts_by_neighbor_ident(net, nik);
+               if (bts != bts2) {
+                       LOGP(DHO, LOGL_ERROR, "CONFIG ERROR: Multiple BTS match 
%s: %d and %d\n",
+                            neighbor_ident_key_name(nik), bts->nr, bts2->nr);
+                       fprintf(stderr, "CONFIG ERROR: Multiple BTS match %s: 
%d and %d\n",
+                               neighbor_ident_key_name(nik), bts->nr, 
+                       if (vty)
+                               vty_out(vty, "%% CONFIG ERROR: Multiple BTS 
match %s: %d and %d%s",
+                                       neighbor_ident_key_name(nik), bts->nr, 
+                                       VTY_NEWLINE);
+                       errors ++;
+               }
+       }
+       return errors;
       "base_station_id_code <0-63>",
@@ -2086,6 +2110,9 @@
                return CMD_WARNING;
        bts->bsic = bsic;
+       if (vty->type != VTY_FILE)
+               warn_on_arfcn_bsic_collisions(bts->network, vty);
        return CMD_SUCCESS;
@@ -3836,6 +3863,9 @@
        /* FIXME: use OML layer to update the ARFCN */
        /* FIXME: use RSL layer to update SYSTEM INFORMATION */
+       if (vty->type != VTY_FILE)
+               warn_on_arfcn_bsic_collisions(trx->bts->network, vty);
        return CMD_SUCCESS;
diff --git a/src/osmo-bsc/osmo_bsc_main.c b/src/osmo-bsc/osmo_bsc_main.c
index 89d0d02..e6c085c 100644
--- a/src/osmo-bsc/osmo_bsc_main.c
+++ b/src/osmo-bsc/osmo_bsc_main.c
@@ -162,6 +162,8 @@
                        vty->index = bts->network;
                        vty->index_sub = NULL;
+               if (vty->type != VTY_FILE)
+                       warn_on_arfcn_bsic_collisions(bsc_gsmnet, vty);
        case TRX_NODE:
                vty->node = BTS_NODE;
@@ -456,6 +458,8 @@
                fprintf(stderr, "Bootstrapping the network failed. exiting.\n");
+       if (warn_on_arfcn_bsic_collisions(bsc_gsmnet, NULL))
+               exit(1);
        bsc_api_init(bsc_gsmnet, osmo_bsc_api());
        /* start control interface after reading config for

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Gerrit-MessageType: newchange
Gerrit-Change-Id: Ia7c38188ccbad5d8b7398e3e5220015e62c08c8b
Gerrit-PatchSet: 1
Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Owner: Neels Hofmeyr <>

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