dyn TS: OS#1778 workaround: disable TCH/F on dyn TS for nitb
To avoid two phones picking mismatching TCH pchans, never pick TCH/F on dynamic
TS in osmo-nitb.
Add gsm_network flag dyn_ts_allow_tch_f, set to true by default in
gsm_network_init().
Set this flag to false in osmo-nitb's main().
See http://osmocom.org/issues/1778
Reasoning about ways to solve this:
* a compile time switch doesn't work because libbsc is first compiled and then
linked to both osmo-nitb and osmo-bsc.
* we could test net->bsc_api == msc_bsc_api(), but I have the so-called MSC
split waiting on branch sysmocom/cscn, which will result in msc_bsc_api() not
being linked in the osmo-bsc binary.
* have a function am_i_nitb() with different implementations in osmo-nitb and
osmo-bsc, but then we'd need to add implementations to all tests and other
binaries linking lchan_alloc().
* have a flag in struct bsc_api, but so far there are only function pointers
there.
Having a "global" flag in gsm_network allows to add a VTY command in case we
decide to keep this feature (#1781), has no linking implications and is nicely
explicit.
Tested that osmo-bsc still picks TCH/F on dyn TS indirectly, since I have no
standalone MSC available: when compiling osmo-nitb with the line that sets
dyn_ts_allow_tch_f = false commented out, TCH/F is picked as described in
OS#1778; and by printf-verifying that dyn_ts_allow_tch_f == true in osmo-bsc
main(), only osmo-nitb should have TCH/F disabled.
Related: OS#1778, OS#1781
Change-Id: If7e4797a72815fc6e2bbef27756ea5df69f4bde7
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index bdcd0e0..b9cb48d 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -296,6 +296,10 @@
/* control interface */
struct ctrl_handle *ctrl;
+
+ /* Allow or disallow TCH/F on dynamic TCH/F_TCH/H_PDCH; OS#1778 */
+ bool dyn_ts_allow_tch_f;
+ /* TODO: vty for this; related: OS#1781 */
};
struct osmo_esme;
diff --git a/openbsc/src/libbsc/chan_alloc.c b/openbsc/src/libbsc/chan_alloc.c
index 1e5dd74..c3a7e0f 100644
--- a/openbsc/src/libbsc/chan_alloc.c
+++ b/openbsc/src/libbsc/chan_alloc.c
@@ -309,8 +309,9 @@
if (lchan)
type = GSM_LCHAN_TCH_F;
}
+
/* Try fully dynamic TCH/F_TCH/H_PDCH as TCH/F... */
- if (!lchan) {
+ if (!lchan && bts->network->dyn_ts_allow_tch_f) {
lchan = _lc_dyn_find_bts(bts,
GSM_PCHAN_TCH_F_TCH_H_PDCH,
GSM_PCHAN_TCH_F);
diff --git a/openbsc/src/libbsc/net_init.c b/openbsc/src/libbsc/net_init.c
index ee0d445..6d03ee4 100644
--- a/openbsc/src/libbsc/net_init.c
+++ b/openbsc/src/libbsc/net_init.c
@@ -116,6 +116,8 @@
net->ext_max = GSM_MAX_EXTEN;
gsm_net_update_ctype(net);
+ net->dyn_ts_allow_tch_f = true;
+
return net;
}
diff --git a/openbsc/src/osmo-nitb/bsc_hack.c b/openbsc/src/osmo-nitb/bsc_hack.c
index 0b360dc..e3e8927 100644
--- a/openbsc/src/osmo-nitb/bsc_hack.c
+++ b/openbsc/src/osmo-nitb/bsc_hack.c
@@ -299,6 +299,19 @@
#endif
bsc_api_init(bsc_gsmnet, msc_bsc_api());
+ /*
+ * For osmo-nitb, skip TCH/F for now, because otherwise dyn TS
+ * always imply the possibility to have a mix of TCH/F and
+ * TCH/H channels; if two phones request a TCH/F and a TCH/H,
+ * respectively, they cannot call each other. If we deny TCH/F,
+ * they will both fall back to TCH/H, and dynamic channels are
+ * usable. See http://osmocom.org/issues/1778.
+ *
+ * A third-party MSC may well be able to handle a TCH/H TCH/F
+ * mismatch.
+ */
+ bsc_gsmnet->dyn_ts_allow_tch_f = false;
+
/* start control interface after reading config for
* ctrl_vty_get_bind_addr() */
LOGP(DNM, LOGL_NOTICE, "CTRL at %s %d\n",