Osmocom's Base Station Controller for 2G mobile networks https://osmocom.org/projects/osmobsc
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osmo-bsc/src/osmo-bsc/lchan_select.c

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14 KiB

/* Select a suitable lchan from a given cell.
*
* (C) 2008 by Harald Welte <laforge@gnumonks.org>
* (C) 2008, 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
* (C) 2018-2022 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
*
* All Rights Reserved
*
* 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 <stdlib.h>
#include <osmocom/bsc/debug.h>
#include <osmocom/bsc/gsm_data.h>
#include <osmocom/bsc/timeslot_fsm.h>
#include <osmocom/bsc/lchan_fsm.h>
#include <osmocom/bsc/lchan_select.h>
#include <osmocom/bsc/bts.h>
struct lchan_select_ts_list {
struct gsm_bts_trx_ts **list;
unsigned int num;
};
const struct value_string lchan_select_reason_names[] = {
OSMO_VALUE_STRING(SELECT_FOR_MS_CHAN_REQ),
OSMO_VALUE_STRING(SELECT_FOR_ASSIGNMENT),
OSMO_VALUE_STRING(SELECT_FOR_HANDOVER),
{0, NULL}
};
static struct gsm_lchan *pick_better_lchan(struct gsm_lchan *a, struct gsm_lchan *b)
{
if (!a)
return b;
if (!b)
return a;
/* comparing negative dBm values: smaller value means less interference. */
if (b->interf_dbm < a->interf_dbm)
return b;
return a;
}
static struct gsm_lchan *_lc_find(struct lchan_select_ts_list *ts_list,
enum gsm_phys_chan_config pchan,
enum gsm_phys_chan_config as_pchan,
bool allow_pchan_switch, bool log)
{
struct gsm_lchan *lchan;
struct gsm_lchan *found_lchan = NULL;
#define LOGPLCHANALLOC(fmt, args...) do { \
if (log) \
LOGP(DRLL, LOGL_DEBUG, "looking for lchan %s%s%s%s: " fmt, \
gsm_pchan_name(pchan), \
pchan == as_pchan ? "" : " as ", \
pchan == as_pchan ? "" : gsm_pchan_name(as_pchan), \
((pchan != as_pchan) && !allow_pchan_switch) ? " without pchan switch" : "", \
## args); \
} while (0)
for (unsigned int tn = 0; tn < ts_list->num; tn++) {
struct gsm_bts_trx_ts *ts = ts_list->list[tn];
int lchans_as_pchan;
/* The caller first selects what kind of TS to search in, e.g. looking for exact
* GSM_PCHAN_TCH_F, or maybe among dynamic GSM_PCHAN_OSMO_DYN... */
if (ts->pchan_on_init != pchan) {
LOGPLCHANALLOC("%s is != %s\n", gsm_ts_and_pchan_name(ts),
gsm_pchan_name(pchan));
continue;
}
/* Next, is this timeslot in or can it be switched to the pchan we want to use it for? */
if (!ts_usable_as_pchan(ts, as_pchan, allow_pchan_switch)) {
LOGPLCHANALLOC("%s is not usable as %s%s\n", gsm_ts_and_pchan_name(ts),
gsm_pchan_name(as_pchan),
allow_pchan_switch ? "" : " without pchan switch");
continue;
}
/* TS is (going to be) in desired pchan mode. Go ahead and check for an available lchan. */
lchans_as_pchan = pchan_subslots(as_pchan);
ts_for_n_lchans(lchan, ts, lchans_as_pchan) {
struct gsm_lchan *was = found_lchan;
if (lchan->fi->state != LCHAN_ST_UNUSED) {
LOGPLCHANALLOC("%s ss=%d in type=%s,state=%s not suitable\n",
gsm_ts_and_pchan_name(ts), lchan->nr,
gsm_lchant_name(lchan->type),
osmo_fsm_inst_state_name(lchan->fi));
continue;
}
found_lchan = pick_better_lchan(found_lchan, lchan);
if (found_lchan != was)
LOGPLCHANALLOC("%s ss=%d interf=%u=%ddBm is %s%s\n",
gsm_ts_and_pchan_name(ts), lchan->nr,
lchan->interf_band, lchan->interf_dbm,
was == NULL ? "available" : "better",
ts->pchan_is != as_pchan ? ", after dyn PCHAN change" : "");
else
LOGPLCHANALLOC("%s ss=%d interf=%u=%ddBm is also available but not better\n",
gsm_ts_and_pchan_name(ts), lchan->nr,
lchan->interf_band, lchan->interf_dbm);
/* When picking an lchan with least interference, continue to loop across all lchans. When
* ignoring interference levels, return the first match. */
if (found_lchan && !ts->trx->bts->chan_alloc_avoid_interf)
return found_lchan;
}
}
if (found_lchan)
LOGPLCHANALLOC("%s ss=%d interf=%ddBm%s is the best pick\n",
gsm_ts_and_pchan_name(found_lchan->ts), found_lchan->nr,
found_lchan->interf_dbm,
found_lchan->ts->pchan_is != as_pchan ? ", after dyn PCHAN change," : "");
else
LOGPLCHANALLOC("Nothing found\n");
return found_lchan;
#undef LOGPLCHANALLOC
}
static struct gsm_lchan *lc_dyn_find(struct lchan_select_ts_list *ts_list,
enum gsm_phys_chan_config pchan,
enum gsm_phys_chan_config dyn_as_pchan,
bool log)
{
struct gsm_lchan *lchan;
/* First find an lchan that needs no change in its timeslot pchan mode.
* In particular, this ensures that handover to a dynamic timeslot in TCH/H favors timeslots that are currently
* using only one of two TCH/H, so that we don't switch more dynamic timeslots to TCH/H than necessary.
* For non-dynamic timeslots, it is not necessary to do a second pass with allow_pchan_switch ==
* true, because they never switch anyway. */
if ((lchan = _lc_find(ts_list, pchan, dyn_as_pchan, false, log)))
return lchan;
if ((lchan = _lc_find(ts_list, pchan, dyn_as_pchan, true, log)))
return lchan;
return NULL;
}
static struct gsm_lchan *lc_find(struct lchan_select_ts_list *ts_list,
enum gsm_phys_chan_config pchan,
bool log)
{
return _lc_find(ts_list, pchan, pchan, false, log);
}
enum gsm_chan_t chan_mode_to_chan_type(enum gsm48_chan_mode chan_mode, enum channel_rate chan_rate)
{
switch (gsm48_chan_mode_to_non_vamos(chan_mode)) {
case GSM48_CMODE_SIGN:
switch (chan_rate) {
case CH_RATE_SDCCH:
return GSM_LCHAN_SDCCH;
case CH_RATE_HALF:
return GSM_LCHAN_TCH_H;
case CH_RATE_FULL:
return GSM_LCHAN_TCH_F;
default:
return GSM_LCHAN_NONE;
}
case GSM48_CMODE_SPEECH_EFR:
/* EFR works over FR channels only */
if (chan_rate != CH_RATE_FULL)
return GSM_LCHAN_NONE;
/* fall through */
case GSM48_CMODE_SPEECH_V1:
case GSM48_CMODE_SPEECH_AMR:
switch (chan_rate) {
case CH_RATE_HALF:
return GSM_LCHAN_TCH_H;
case CH_RATE_FULL:
return GSM_LCHAN_TCH_F;
default:
return GSM_LCHAN_NONE;
}
default:
return GSM_LCHAN_NONE;
}
}
static int qsort_func(const void *_a, const void *_b)
{
const struct gsm_bts_trx *trx_a = *(const struct gsm_bts_trx **)_a;
const struct gsm_bts_trx *trx_b = *(const struct gsm_bts_trx **)_b;
int pwr_a = trx_a->nominal_power - trx_a->max_power_red;
int pwr_b = trx_b->nominal_power - trx_b->max_power_red;
/* Sort in descending order */
return pwr_b - pwr_a;
}
static void populate_ts_list(struct lchan_select_ts_list *ts_list,
struct gsm_bts *bts,
bool chan_alloc_reverse,
bool sort_by_trx_power,
bool log)
{
struct gsm_bts_trx **trx_list;
struct gsm_bts_trx *trx;
unsigned int num = 0;
/* Allocate an array with pointers to all TRX instances of a BTS */
trx_list = talloc_array_ptrtype(bts, trx_list, bts->num_trx);
OSMO_ASSERT(trx_list != NULL);
llist_for_each_entry(trx, &bts->trx_list, list)
trx_list[trx->nr] = trx;
/* Sort by TRX power in descending order (if needed) */
if (sort_by_trx_power)
qsort(&trx_list[0], bts->num_trx, sizeof(trx), &qsort_func);
for (unsigned int trxn = 0; trxn < bts->num_trx; trxn++) {
trx = trx_list[trxn];
for (unsigned int tn = 0; tn < ARRAY_SIZE(trx->ts); tn++) {
struct gsm_bts_trx_ts *ts = &trx->ts[tn];
if (ts_is_usable(ts))
ts_list->list[num++] = ts;
else if (log)
LOGP(DRLL, LOGL_DEBUG, "%s is not usable\n", gsm_ts_name(ts));
}
}
talloc_free(trx_list);
ts_list->num = num;
/* Reverse the timeslot list if required */
if (chan_alloc_reverse) {
for (unsigned int tn = 0; tn < num / 2; tn++) {
struct gsm_bts_trx_ts *temp = ts_list->list[tn];
ts_list->list[tn] = ts_list->list[num - tn - 1];
ts_list->list[num - tn - 1] = temp;
}
}
}
static bool chan_alloc_ass_dynamic_reverse(struct gsm_bts *bts,
void *ctx, bool log)
{
const struct load_counter *ll = &bts->c0->lchan_load;
const struct gsm_lchan *old_lchan = ctx;
unsigned int lchan_load;
int avg_ul_rxlev;
OSMO_ASSERT(old_lchan != NULL);
OSMO_ASSERT(old_lchan->ts->trx->bts == bts);
#define LOG_COND(fmt, args...) do { \
if (log) \
LOG_LCHAN(old_lchan, LOGL_DEBUG, fmt, ## args); \
} while (0)
/* Condition a) Channel load on the C0 (BCCH carrier) */
lchan_load = ll->total ? ll->used * 100 / ll->total : 0;
if (lchan_load < bts->chan_alloc_dyn_params.c0_chan_load_thresh) {
LOG_COND("C0 Channel Load %u%% < thresh %u%% => using ascending order\n",
lchan_load, bts->chan_alloc_dyn_params.c0_chan_load_thresh);
return false;
}
/* Condition b) average Uplink RxLev */
avg_ul_rxlev = get_meas_rep_avg(old_lchan, TDMA_MEAS_FIELD_RXLEV,
TDMA_MEAS_DIR_UL, TDMA_MEAS_SET_AUTO,
bts->chan_alloc_dyn_params.ul_rxlev_avg_num);
if (avg_ul_rxlev < 0) {
LOG_COND("Unknown AVG UL RxLev => using ascending order\n");
return false;
}
if (avg_ul_rxlev < bts->chan_alloc_dyn_params.ul_rxlev_thresh) {
LOG_COND("AVG UL RxLev %u < thresh %u => using ascending order\n",
avg_ul_rxlev, bts->chan_alloc_dyn_params.ul_rxlev_thresh);
return false;
}
LOG_COND("C0 Channel Load %u%% >= thresh %u%% and "
"AVG UL RxLev %u >= thresh %u => using descending order\n",
lchan_load, bts->chan_alloc_dyn_params.c0_chan_load_thresh,
avg_ul_rxlev, bts->chan_alloc_dyn_params.ul_rxlev_thresh);
#undef LOG_COND
return true;
}
struct gsm_lchan *lchan_select_by_chan_mode(struct gsm_bts *bts,
enum gsm48_chan_mode chan_mode,
enum channel_rate chan_rate,
enum lchan_select_reason reason,
void *ctx)
{
enum gsm_chan_t type = chan_mode_to_chan_type(chan_mode, chan_rate);
if (type == GSM_LCHAN_NONE)
return NULL;
return lchan_select_by_type(bts, type, reason, ctx);
}
struct gsm_lchan *lchan_avail_by_type(struct gsm_bts *bts,
enum gsm_chan_t type,
enum lchan_select_reason reason,
void *ctx, bool log)
{
struct gsm_lchan *lchan = NULL;
enum gsm_phys_chan_config first, first_cbch, second, second_cbch;
struct lchan_select_ts_list ts_list;
bool sort_by_trx_power = false;
bool chan_alloc_reverse;
if (log) {
LOG_BTS(bts, DRLL, LOGL_DEBUG, "lchan_avail_by_type(type=%s, reason=%s)\n",
gsm_lchant_name(type), lchan_select_reason_name(reason));
}
switch (reason) {
case SELECT_FOR_MS_CHAN_REQ:
chan_alloc_reverse = bts->chan_alloc_chan_req_reverse;
break;
case SELECT_FOR_ASSIGNMENT:
if (bts->chan_alloc_assignment_dynamic) {
chan_alloc_reverse = chan_alloc_ass_dynamic_reverse(bts, ctx, log);
sort_by_trx_power = bts->chan_alloc_dyn_params.sort_by_trx_power;
} else {
chan_alloc_reverse = bts->chan_alloc_assignment_reverse;
}
break;
case SELECT_FOR_HANDOVER:
chan_alloc_reverse = bts->chan_alloc_handover_reverse;
break;
}
/* Allocate an array with pointers to all timeslots of a BTS */
ts_list.list = talloc_array_ptrtype(bts, ts_list.list, bts->num_trx * 8);
if (OSMO_UNLIKELY(ts_list.list == NULL))
return NULL;
/* Populate this array with the actual pointers */
populate_ts_list(&ts_list, bts, chan_alloc_reverse, sort_by_trx_power, log);
switch (type) {
case GSM_LCHAN_SDCCH:
if (chan_alloc_reverse) {
first = GSM_PCHAN_SDCCH8_SACCH8C;
first_cbch = GSM_PCHAN_SDCCH8_SACCH8C_CBCH;
second = GSM_PCHAN_CCCH_SDCCH4;
second_cbch = GSM_PCHAN_CCCH_SDCCH4_CBCH;
} else {
first = GSM_PCHAN_CCCH_SDCCH4;
first_cbch = GSM_PCHAN_CCCH_SDCCH4_CBCH;
second = GSM_PCHAN_SDCCH8_SACCH8C;
second_cbch = GSM_PCHAN_SDCCH8_SACCH8C_CBCH;
}
lchan = lc_find(&ts_list, first, log);
if (lchan == NULL)
lchan = lc_find(&ts_list, first_cbch, log);
if (lchan == NULL)
lchan = lc_find(&ts_list, second, log);
if (lchan == NULL)
lchan = lc_find(&ts_list, second_cbch, log);
/* No dedicated SDCCH available -- try fully dynamic
* TCH/F_TCH/H_SDCCH8_PDCH if BTS supports it: */
if (lchan == NULL && osmo_bts_has_feature(&bts->features, BTS_FEAT_DYN_TS_SDCCH8))
lchan = lc_dyn_find(&ts_list, GSM_PCHAN_OSMO_DYN,
GSM_PCHAN_SDCCH8_SACCH8C, log);
break;
case GSM_LCHAN_TCH_F:
lchan = lc_find(&ts_list, GSM_PCHAN_TCH_F, log);
/* If we don't have TCH/F available, try dynamic TCH/F_PDCH */
if (!lchan)
lchan = lc_dyn_find(&ts_list, GSM_PCHAN_TCH_F_PDCH,
GSM_PCHAN_TCH_F, log);
/* Try fully dynamic TCH/F_TCH/H_PDCH as TCH/F... */
if (!lchan && bts->network->dyn_ts_allow_tch_f)
lchan = lc_dyn_find(&ts_list, GSM_PCHAN_OSMO_DYN,
GSM_PCHAN_TCH_F, log);
break;
case GSM_LCHAN_TCH_H:
lchan = lc_find(&ts_list, GSM_PCHAN_TCH_H, log);
/* No dedicated TCH/x available -- try fully dynamic
* TCH/F_TCH/H_PDCH */
if (!lchan)
lchan = lc_dyn_find(&ts_list, GSM_PCHAN_OSMO_DYN,
GSM_PCHAN_TCH_H, log);
break;
default:
LOG_BTS(bts, DRLL, LOGL_ERROR, "Unknown gsm_chan_t %u\n", type);
}
talloc_free(ts_list.list);
return lchan;
}
/* Return a matching lchan from a specific BTS that is currently available. The next logical step is
* lchan_activate() on it, which would possibly cause dynamic timeslot pchan switching, taken care of by
* the lchan and timeslot FSMs. */
struct gsm_lchan *lchan_select_by_type(struct gsm_bts *bts,
enum gsm_chan_t type,
enum lchan_select_reason reason,
void *ctx)
{
struct gsm_lchan *lchan = NULL;
LOG_BTS(bts, DRLL, LOGL_DEBUG, "lchan_select_by_type(type=%s, reason=%s)\n",
gsm_lchant_name(type), lchan_select_reason_name(reason));
lchan = lchan_avail_by_type(bts, type, reason, ctx, true);
if (!lchan) {
LOG_BTS(bts, DRLL, LOGL_NOTICE, "Failed to select %s channel (%s)\n",
gsm_lchant_name(type), lchan_select_reason_name(reason));
return NULL;
}
lchan_select_set_type(lchan, type);
return lchan;
}
/* Set available lchan to given type. Usually used on lchan obtained with
* lchan_avail_by_type. The next logical step is lchan_activate() on it, which
* would possibly cause dynamic timeslot pchan switching, taken care of by the
* lchan and timeslot FSMs. */
void lchan_select_set_type(struct gsm_lchan *lchan, enum gsm_chan_t type)
{
lchan->type = type;
LOG_LCHAN(lchan, LOGL_INFO, "Selected\n");
}