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Introduce VTY option to forbid use of TCH for non-voicecall signalling 

Usual allocation mechansim, when some signalling channel is needed,
first tries to reserve an SDCCH, and if all of them are exhausted, then
attempts to reserve a TCH as a last resort.
This, however, may cause TCH starvation under certain situations, for
instance if there high load on other services (LU, SMS, etc.).
Hence, it may be desirable for the operator to forbid reservation
of TCH slots once SDCCH become exhausted. This commit is thus adding a
VTY command which allows forbidding it. The default behavior (allow using
TCH timeslots when SDCCHs are exhausted) is kept as before.

The above mentioned prohibition is applied only to non-voicecall related
signalling services. That's because voicecall services will end up
requiring a TCH anyway, and forbidding reservation of TCH straighaway
when SDCCHs are exhausted would mean no voice calls could be initiated
while still TCHs would be available.

Related: SYS#5548
Change-Id: Ib08027125145df26602069bfb51847063b0ccc0c
This commit is contained in:
Pau Espin 2021-07-22 13:25:05 +02:00
parent 8e3320ac48
commit 56eda35874
6 changed files with 67 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/osmocom/bsc/bts.h
View File

@ -454,6 +454,10 @@ struct gsm_bts {
* interference reported in RSL Resource Indication. */
bool chan_alloc_avoid_interf;
/* When true (default), TCH can be allocated to serve
* non-voicecall-related signalling services when SDCCHs are exhausted */
bool chan_alloc_allow_tch_for_signalling;
enum neigh_list_manual_mode neigh_list_manual_mode;
/* parameters from which we build SYSTEM INFORMATION */
struct {

5
include/osmocom/bsc/gsm_data.h
View File

@ -419,6 +419,11 @@ enum gsm_chreq_reason_t {
GSM_CHREQ_REASON_PDCH,
};
static inline bool gsm_chreq_reason_is_voicecall(enum gsm_chreq_reason_t reason)
{
return reason == GSM_CHREQ_REASON_EMERG || reason == GSM_CHREQ_REASON_CALL;
}
/* lchans 0..3 are SDCCH in combined channel configuration,
use 4 as magic number for BCCH hack - see osmo-bts-../oml.c:opstart_compl() */
#define CCCH_LCHAN 4

24
src/osmo-bsc/abis_rsl.c
View File

@ -2015,17 +2015,19 @@ void abis_rsl_chan_rqd_queue_poll(struct gsm_bts *bts)
* in the code below, all other channel requests will get an SDCCH first
* (if possible). */
if (!lchan) {
LOG_BTS(bts, DRSL, LOGL_NOTICE, "CHAN RQD[%s]: no resources for %s 0x%x, retrying with %s\n",
get_value_string(gsm_chreq_descs, rqd->reason), gsm_lchant_name(GSM_LCHAN_SDCCH),
rqd->ref.ra, gsm_lchant_name(GSM_LCHAN_TCH_H));
lchan = lchan_select_by_type(bts, GSM_LCHAN_TCH_H);
}
if (!lchan) {
LOG_BTS(bts, DRSL, LOGL_NOTICE, "CHAN RQD[%s]: no resources for %s 0x%x, retrying with %s\n",
get_value_string(gsm_chreq_descs, rqd->reason), gsm_lchant_name(GSM_LCHAN_SDCCH),
rqd->ref.ra, gsm_lchant_name(GSM_LCHAN_TCH_F));
lchan = lchan_select_by_type(bts, GSM_LCHAN_TCH_F);
if (gsm_chreq_reason_is_voicecall(rqd->reason) || bts->chan_alloc_allow_tch_for_signalling) {
if (!lchan) {
LOG_BTS(bts, DRSL, LOGL_NOTICE, "CHAN RQD[%s]: no resources for %s 0x%x, retrying with %s\n",
get_value_string(gsm_chreq_descs, rqd->reason), gsm_lchant_name(GSM_LCHAN_SDCCH),
rqd->ref.ra, gsm_lchant_name(GSM_LCHAN_TCH_H));
lchan = lchan_select_by_type(bts, GSM_LCHAN_TCH_H);
}
if (!lchan) {
LOG_BTS(bts, DRSL, LOGL_NOTICE, "CHAN RQD[%s]: no resources for %s 0x%x, retrying with %s\n",
get_value_string(gsm_chreq_descs, rqd->reason), gsm_lchant_name(GSM_LCHAN_SDCCH),
rqd->ref.ra, gsm_lchant_name(GSM_LCHAN_TCH_F));
lchan = lchan_select_by_type(bts, GSM_LCHAN_TCH_F);
}
}
if (!lchan) {
LOG_BTS(bts, DRSL, LOGL_NOTICE, "CHAN RQD[%s]: no resources for %s 0x%x\n",

1
src/osmo-bsc/bts.c
View File

@ -245,6 +245,7 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, struct gsm_bts_sm *bts_sm
bts->neigh_list_manual_mode = NL_MODE_AUTOMATIC;
bts->early_classmark_allowed_3g = true; /* 3g Early Classmark Sending controlled by bts->early_classmark_allowed param */
bts->si_unused_send_empty = true;
bts->chan_alloc_allow_tch_for_signalling = true;
bts->si_common.cell_sel_par.cell_resel_hyst = 2; /* 4 dB */
bts->si_common.cell_sel_par.rxlev_acc_min = 0;
bts->si_common.si2quater_neigh_list.arfcn = bts->si_common.data.earfcn_list;

22
src/osmo-bsc/bts_vty.c
View File

@ -565,6 +565,25 @@ DEFUN_ATTR(cfg_bts_chan_alloc_interf,
return CMD_SUCCESS;
}
DEFUN_ATTR(cfg_bts_chan_alloc_allow_tch_for_signalling,
cfg_bts_chan_alloc_allow_tch_for_signalling_cmd,
"channel allocator allow-tch-for-signalling (0|1)",
"Channel Allocator\n" "Channel Allocator\n"
"Configure whether TCH/H or TCH/F channels can be used to serve non-call-related signalling if SDCCHs are exhausted\n"
"Forbid use of TCH for non-call-related signalling purposes\n"
"Allow use of TCH for non-call-related signalling purposes (default)\n",
CMD_ATTR_IMMEDIATE)
{
struct gsm_bts *bts = vty->index;
if (!strcmp(argv[0], "0"))
bts->chan_alloc_allow_tch_for_signalling = false;
else
bts->chan_alloc_allow_tch_for_signalling = true;
return CMD_SUCCESS;
}
#define RACH_STR "Random Access Control Channel\n"
DEFUN_USRATTR(cfg_bts_rach_tx_integer,
@ -3736,6 +3755,8 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
VTY_NEWLINE);
if (bts->chan_alloc_avoid_interf)
vty_out(vty, " channel allocator avoid-interference 1%s", VTY_NEWLINE);
if (!bts->chan_alloc_allow_tch_for_signalling)
vty_out(vty, " channel allocator allow-tch-for-signalling 0%s", VTY_NEWLINE);
vty_out(vty, " rach tx integer %u%s",
bts->si_common.rach_control.tx_integer, VTY_NEWLINE);
vty_out(vty, " rach max transmission %u%s",
@ -4018,6 +4039,7 @@ int bts_vty_init(void)
install_element(BTS_NODE, &cfg_bts_oml_e1_tei_cmd);
install_element(BTS_NODE, &cfg_bts_challoc_cmd);
install_element(BTS_NODE, &cfg_bts_chan_alloc_interf_cmd);
install_element(BTS_NODE, &cfg_bts_chan_alloc_allow_tch_for_signalling_cmd);
install_element(BTS_NODE, &cfg_bts_rach_tx_integer_cmd);
install_element(BTS_NODE, &cfg_bts_rach_max_trans_cmd);
install_element(BTS_NODE, &cfg_bts_rach_max_delay_cmd);

25
tests/osmo-bsc.vty
View File

@ -163,14 +163,19 @@ OsmoBSC(config-net-bts)# channel ?
allocator Channel Allocator
OsmoBSC(config-net-bts)# channel allocator ?
ascending Allocate Timeslots and Transceivers in ascending order
descending Allocate Timeslots and Transceivers in descending order
avoid-interference Configure whether reported interference levels from RES IND are used in channel allocation
ascending Allocate Timeslots and Transceivers in ascending order
descending Allocate Timeslots and Transceivers in descending order
avoid-interference Configure whether reported interference levels from RES IND are used in channel allocation
allow-tch-for-signalling Configure whether TCH/H or TCH/F channels can be used to serve non-call-related signalling if SDCCHs are exhausted
OsmoBSC(config-net-bts)# channel allocator avoid-interference ?
0 Ignore interference levels (default). Always assign lchans in a deterministic order.
1 In channel allocation, prefer lchans with less interference.
OsmoBSC(config-net-bts)# channel allocator allow-tch-for-signalling ?
0 Forbid use of TCH for non-call-related signalling purposes
1 Allow use of TCH for non-call-related signalling purposes (default)
OsmoBSC(config-net-bts)# show running-config
... !channel allocator avoid-interference
OsmoBSC(config-net-bts)# channel allocator avoid-interference 1
@ -184,3 +189,17 @@ OsmoBSC(config-net-bts)# show running-config
OsmoBSC(config-net-bts)# channel allocator avoid-interference 0
OsmoBSC(config-net-bts)# show running-config
... !channel allocator avoid-interference
OsmoBSC(config-net-bts)# show running-config
... !channel allocator allow-tch-for-signalling
OsmoBSC(config-net-bts)# channel allocator allow-tch-for-signalling 0
OsmoBSC(config-net-bts)# show running-config
...
bts 0
...
channel allocator allow-tch-for-signalling 0
...
OsmoBSC(config-net-bts)# channel allocator allow-tch-for-signalling 1
OsmoBSC(config-net-bts)# show running-config
... !channel allocator allow-tch-for-signalling