Osmocom's Base Station Controller for 2G mobile networks https://osmocom.org/projects/osmobsc
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 
osmo-bsc/src/osmo-bsc/handover_decision_2.c

2075 lines
74 KiB

/* Handover Decision Algorithm 2 for intra-BSC (inter-BTS) handover, public API for OsmoBSC. */
/* (C) 2009 by Andreas Eversberg <jolly@eversberg.eu>
* (C) 2017-2018 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
*
* All Rights Reserved
*
* Author: Andreas Eversberg <jolly@eversberg.eu>
* Neels Hofmeyr <nhofmeyr@sysmocom.de>
*
* 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 <stdbool.h>
#include <errno.h>
#include <limits.h>
#include <math.h>
#include <osmocom/bsc/debug.h>
#include <osmocom/bsc/gsm_data.h>
#include <osmocom/bsc/assignment_fsm.h>
#include <osmocom/bsc/handover_fsm.h>
#include <osmocom/bsc/handover_decision.h>
#include <osmocom/bsc/handover_decision_2.h>
#include <osmocom/bsc/handover_cfg.h>
#include <osmocom/bsc/bsc_subscriber.h>
#include <osmocom/bsc/lchan_fsm.h>
#include <osmocom/bsc/signal.h>
#include <osmocom/bsc/penalty_timers.h>
#include <osmocom/bsc/neighbor_ident.h>
#include <osmocom/bsc/timeslot_fsm.h>
#include <osmocom/bsc/bts.h>
#include <osmocom/bsc/lchan_select.h>
#include <osmocom/bsc/chan_counts.h>
#define LOGPHOBTS(bts, level, fmt, args...) \
LOGP(DHODEC, level, "(BTS %u) " fmt, bts->nr, ## args)
#define LOGPHOLCHAN(lchan, level, fmt, args...) \
LOGP(DHODEC, level, "(lchan %u.%u%u%u %s %s) (subscr %s) " fmt, \
lchan->ts->trx->bts->nr, \
lchan->ts->trx->nr, \
lchan->ts->nr, \
lchan->nr, \
gsm_lchant_name(lchan->type), \
gsm48_chan_mode_name(lchan->current_ch_mode_rate.chan_mode), \
bsc_subscr_name(lchan->conn? lchan->conn->bsub : NULL), \
## args)
#define LOGPHOLCHANTOBTS(lchan, new_bts, level, fmt, args...) \
LOGP(DHODEC, level, "(lchan %u.%u%u%u %s %s)->(BTS %u) (subscr %s) " fmt, \
lchan->ts->trx->bts->nr, \
lchan->ts->trx->nr, \
lchan->ts->nr, \
lchan->nr, \
gsm_lchant_name(lchan->type), \
gsm48_chan_mode_name(lchan->current_ch_mode_rate.chan_mode), \
new_bts->nr, \
bsc_subscr_name(lchan->conn? lchan->conn->bsub : NULL), \
## args)
#define LOGPHOLCHANTOREMOTE(lchan, remote_cil, level, fmt, args...) \
LOGP(DHODEC, level, "(lchan %u.%u%u%u %s %s)->(remote-BSS %s) (subscr %s) " fmt, \
lchan->ts->trx->bts->nr, \
lchan->ts->trx->nr, \
lchan->ts->nr, \
lchan->nr, \
gsm_lchant_name(lchan->type), \
gsm48_chan_mode_name(lchan->current_ch_mode_rate.chan_mode), \
gsm0808_cell_id_list_name(remote_cil), \
bsc_subscr_name(lchan->conn? lchan->conn->bsub : NULL), \
## args)
#define LOGPHOCAND(candidate, level, fmt, args...) do {\
if ((candidate)->target.bts) \
LOGPHOLCHANTOBTS((candidate)->current.lchan, (candidate)->target.bts, level, fmt, ## args); \
else if ((candidate)->target.cell_ids.id_list_len) \
LOGPHOLCHANTOREMOTE((candidate)->current.lchan, &(candidate)->target.cell_ids, level, fmt, ## args); \
} while (0)
#define REQUIREMENT_A_TCHF 0x01
#define REQUIREMENT_B_TCHF 0x02
#define REQUIREMENT_C_TCHF 0x04
#define REQUIREMENT_A_TCHH 0x10
#define REQUIREMENT_B_TCHH 0x20
#define REQUIREMENT_C_TCHH 0x40
#define REQUIREMENT_TCHF_MASK (REQUIREMENT_A_TCHF | REQUIREMENT_B_TCHF | REQUIREMENT_C_TCHF)
#define REQUIREMENT_TCHH_MASK (REQUIREMENT_A_TCHH | REQUIREMENT_B_TCHH | REQUIREMENT_C_TCHH)
#define REQUIREMENT_A_MASK (REQUIREMENT_A_TCHF | REQUIREMENT_A_TCHH)
#define REQUIREMENT_B_MASK (REQUIREMENT_B_TCHF | REQUIREMENT_B_TCHH)
#define REQUIREMENT_C_MASK (REQUIREMENT_C_TCHF | REQUIREMENT_C_TCHH)
struct ho_candidate {
uint8_t requirements; /* what is fulfilled */
struct {
struct gsm_lchan *lchan;
struct gsm_bts *bts;
int rxlev;
/* free/min-free for the current TCH kind, same as either free_tch_f or free_tch_h below */
int free_tch;
int min_free_tch;
/* free/min-free for the two TCH kinds, to calculate F<->H cross effects for dynamic timeslots */
int free_tchf;
int min_free_tchf;
int free_tchh;
int min_free_tchh;
/* Effects of freeing a dynamic timeslot, i.e. turning it into PDCH mode and making available more free
* TCH: */
int lchan_frees_tchf;
int lchan_frees_tchh;
} current;
struct {
struct cell_ab ab; /* neighbor ARFCN+BSIC */
struct gsm0808_cell_id_list2 cell_ids; /* target cells in remote BSS */
struct gsm_bts *bts;
int rxlev;
int rxlev_afs_bias;
int free_tchf;
int min_free_tchf;
int free_tchh;
int min_free_tchh;
/* Effects of occupying a dynamic timeslot, i.e. turning from PDCH into a specific TCH kind, and
* reducing the number of free TCH for both TCH/F and TCH/H: */
int next_tchf_reduces_tchh;
int next_tchh_reduces_tchf;
} target;
};
enum ho_reason {
HO_REASON_INTERFERENCE,
HO_REASON_BAD_QUALITY,
HO_REASON_LOW_RXLEVEL,
HO_REASON_MAX_DISTANCE,
HO_REASON_BETTER_CELL,
HO_REASON_CONGESTION,
};
static const struct value_string ho_reason_names[] = {
{ HO_REASON_INTERFERENCE, "interference (bad quality)" },
{ HO_REASON_BAD_QUALITY, "bad quality" },
{ HO_REASON_LOW_RXLEVEL, "low rxlevel" },
{ HO_REASON_MAX_DISTANCE, "maximum allowed distance" },
{ HO_REASON_BETTER_CELL, "better cell" },
{ HO_REASON_CONGESTION, "congestion" },
{0, NULL}
};
static const char *ho_reason_name(int value)
{
return get_value_string(ho_reason_names, value);
}
static bool hodec2_initialized = false;
static enum ho_reason global_ho_reason;
static void congestion_check_cb(void *arg);
static bool is_upgrade_to_tchf(const struct ho_candidate *c, uint8_t for_requirement)
{
return c->current.lchan
&& (c->current.lchan->type == GSM_LCHAN_TCH_H)
&& ((c->requirements & for_requirement) & REQUIREMENT_TCHF_MASK);
}
static unsigned int ts_usage_count(struct gsm_bts_trx_ts *ts)
{
struct gsm_lchan *lchan;
unsigned int count = 0;
ts_for_n_lchans(lchan, ts, ts->max_lchans_possible) {
if (lchan_state_is(lchan, LCHAN_ST_ESTABLISHED))
count++;
}
return count;
}
/* This function gets called on ho2 init, whenever the congestion check interval is changed, and also
* when the timer has fired to trigger again after the next congestion check timeout. */
static void reinit_congestion_timer(struct gsm_network *net)
{
int congestion_check_interval_s;
bool was_active;
/* Don't setup timers from VTY config parsing before the main program has actually initialized
* the data structures. */
if (!hodec2_initialized)
return;
was_active = net->hodec2.congestion_check_timer.active;
if (was_active)
osmo_timer_del(&net->hodec2.congestion_check_timer);
congestion_check_interval_s = net->hodec2.congestion_check_interval_s;
if (congestion_check_interval_s < 1) {
if (was_active)
LOGP(DHODEC, LOGL_NOTICE, "HO algorithm 2: Disabling congestion check\n");
return;
}
LOGP(DHODEC, LOGL_DEBUG, "HO algorithm 2: next periodical congestion check in %u seconds\n",
congestion_check_interval_s);
osmo_timer_setup(&net->hodec2.congestion_check_timer,
congestion_check_cb, net);
osmo_timer_schedule(&net->hodec2.congestion_check_timer,
congestion_check_interval_s, 0);
}
void hodec2_on_change_congestion_check_interval(struct gsm_network *net, unsigned int new_interval)
{
net->hodec2.congestion_check_interval_s = new_interval;
reinit_congestion_timer(net);
}
/* did we get a RXLEV for a given cell in the given report? Mark matches as MRC_F_PROCESSED. */
static struct gsm_meas_rep_cell *cell_in_rep(struct gsm_meas_rep *mr, uint16_t arfcn, uint8_t bsic)
{
int i;
for (i = 0; i < mr->num_cell; i++) {
struct gsm_meas_rep_cell *mrc = &mr->cell[i];
if (mrc->arfcn != arfcn)
continue;
if (mrc->bsic != bsic)
continue;
return mrc;
}
return NULL;
}
static int current_rxlev(struct gsm_lchan *lchan)
{
struct gsm_bts *bts = lchan->ts->trx->bts;
return get_meas_rep_avg(lchan, TDMA_MEAS_FIELD_RXLEV, TDMA_MEAS_DIR_DL, ho_get_hodec2_tdma_meas_set(bts->ho),
ho_get_hodec2_rxlev_avg_win(bts->ho));
}
static int current_rxqual(struct gsm_lchan *lchan)
{
struct gsm_bts *bts = lchan->ts->trx->bts;
return get_meas_rep_avg(lchan, TDMA_MEAS_FIELD_RXQUAL, TDMA_MEAS_DIR_DL, ho_get_hodec2_tdma_meas_set(bts->ho),
ho_get_hodec2_rxqual_avg_win(bts->ho));
}
static bool is_low_rxlev(int rxlev_current, struct handover_cfg *neigh_cfg)
{
return rxlev_current >= 0
&& rxlev2dbm(rxlev_current) < ho_get_hodec2_min_rxlev(neigh_cfg);
}
static bool is_low_rxqual(int rxqual_current, struct handover_cfg *neigh_cfg)
{
/* min_rxqual is actually a bit of a misnomer, low quality is a high number. So the "min" refers to the minimum
* acceptable level of quality, and "min or better" here means "rxqual number must be SMALLER-or-equal than the
* min-rxqual setting". */
return rxqual_current >= 0
&& rxqual_current > ho_get_hodec2_min_rxqual(neigh_cfg);
}
/* obtain averaged rxlev for given neighbor */
static int neigh_meas_avg(struct neigh_meas_proc *nmp, int window)
{
unsigned int i, idx;
int avg = 0;
/* reduce window to the actual number of existing measurements */
if (window > nmp->rxlev_cnt)
window = nmp->rxlev_cnt;
/* this should never happen */
if (window <= 0)
return 0;
idx = calc_initial_idx(ARRAY_SIZE(nmp->rxlev),
nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev),
window);
for (i = 0; i < window; i++) {
int j = (idx+i) % ARRAY_SIZE(nmp->rxlev);
avg += nmp->rxlev[j];
}
return avg / window;
}
/* Find empty slot or the worst neighbor. */
static struct neigh_meas_proc *find_unused_or_worst_neigh(struct gsm_lchan *lchan)
{
struct neigh_meas_proc *nmp_worst = NULL;
int worst;
int j;
/* First try to find an empty/unused slot. */
for (j = 0; j < ARRAY_SIZE(lchan->neigh_meas); j++) {
struct neigh_meas_proc *nmp = &lchan->neigh_meas[j];
if (!nmp->arfcn)
return nmp;
}
/* No empty slot found. Return worst neighbor to be evicted. */
worst = 0; /* (overwritten on first loop, but avoid compiler warning) */
for (j = 0; j < ARRAY_SIZE(lchan->neigh_meas); j++) {
struct neigh_meas_proc *nmp = &lchan->neigh_meas[j];
int avg = neigh_meas_avg(nmp, MAX_WIN_NEIGH_AVG);
if (nmp_worst && avg >= worst)
continue;
worst = avg;
nmp_worst = nmp;
}
return nmp_worst;
}
/* process neighbor cell measurement reports */
static void process_meas_neigh(struct gsm_meas_rep *mr)
{
int i, j, idx;
/* For each reported cell, try to update measurements we already have from previous reports. */
for (j = 0; j < ARRAY_SIZE(mr->lchan->neigh_meas); j++) {
struct neigh_meas_proc *nmp = &mr->lchan->neigh_meas[j];
unsigned int idx;
struct gsm_meas_rep_cell *mrc;
/* skip unused entries */
if (!nmp->arfcn)
continue;
mrc = cell_in_rep(mr, nmp->arfcn, nmp->bsic);
idx = nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev);
if (mrc) {
nmp->rxlev[idx] = mrc->rxlev;
nmp->last_seen_nr = mr->nr;
mrc->flags |= MRC_F_PROCESSED;
} else {
nmp->rxlev[idx] = 0;
}
nmp->rxlev_cnt++;
}
/* Add cells that we don't know about yet, if necessary overwriting previous records that reflect
* cells with worse receive levels */
for (i = 0; i < mr->num_cell; i++) {
struct gsm_meas_rep_cell *mrc = &mr->cell[i];
struct neigh_meas_proc *nmp;
if (mrc->flags & MRC_F_PROCESSED)
continue;
nmp = find_unused_or_worst_neigh(mr->lchan);
nmp->arfcn = mrc->arfcn;
nmp->bsic = mrc->bsic;
nmp->rxlev_cnt = 0;
idx = nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev);
nmp->rxlev[idx] = mrc->rxlev;
nmp->rxlev_cnt++;
nmp->last_seen_nr = mr->nr;
LOGPHOLCHAN(mr->lchan, LOGL_DEBUG, "neigh %u new in report rxlev=%d last_seen_nr=%u\n",
nmp->arfcn, mrc->rxlev, nmp->last_seen_nr);
mrc->flags |= MRC_F_PROCESSED;
}
}
static bool codec_type_is_supported(struct gsm_subscriber_connection *conn,
enum gsm0808_speech_codec_type type)
{
int i;
struct gsm0808_speech_codec_list *clist = &conn->codec_list;
if (!conn->codec_list.len) {
/* We don't have a list of supported codecs. This should never happen. */
LOGPHOLCHAN(conn->lchan, LOGL_ERROR,
"No Speech Codec List present, accepting all codecs\n");
return true;
}
for (i = 0; i < clist->len; i++) {
if (clist->codec[i].type == type)
return true;
}
LOGPHOLCHAN(conn->lchan, LOGL_DEBUG, "Codec not supported by MS or not allowed by MSC: %s\n",
gsm0808_speech_codec_type_name(type));
return false;
}
#define LOAD_PRECISION 6
/* Return a number representing overload, i.e. the fraction of lchans used above the congestion threshold.
* Think of it as a percentage of used lchans above congestion, just represented in a fixed-point fraction with N
* decimal digits of fractional part. If there is no congestion (free_tch >= min_free_tch), return 0.
*/
static int32_t load_above_congestion(int free_tch, int min_free_tch)
{
int32_t v;
OSMO_ASSERT(free_tch >= 0);
/* Avoid division by zero when no congestion threshold is set, and return zero overload when there is no
* congestion. */
if (free_tch >= min_free_tch)
return 0;
v = min_free_tch - free_tch;
v *= pow(10, LOAD_PRECISION);
v /= min_free_tch;
return v;
}
/*
* Check what requirements the given cell fulfills.
* A bit mask of fulfilled requirements is returned.
*
* Target cell requirement A -- ability to service the call
*
* In order to successfully handover/assign to a better cell, the target cell
* must be able to continue the current call. Therefore the cell must fulfill
* the following criteria:
*
* * The handover must be enabled for the target cell, if it differs from the
* originating cell.
* * The assignment must be enabled for the cell, if it equals the current
* cell.
* * The handover penalty timer must not run for the cell.
* * If FR, EFR or HR codec is used, the cell must support this codec.
* * If FR or EFR codec is used, the cell must have a TCH/F slot type
* available.
* * If HR codec is used, the cell must have a TCH/H slot type available.
* * If AMR codec is used, the cell must have a TCH/F slot available, if AFS
* is supported by mobile and BTS.
* * If AMR codec is used, the cell must have a TCH/H slot available, if AHS
* is supported by mobile and BTS.
* * osmo-nitb with built-in MNCC application:
* o If AMR codec is used, the cell must support AMR codec with equal codec
* rate or rates. (not meaning TCH types)
* * If defined, the number of maximum unsynchronized handovers to this cell
* may not be exceeded. (This limits processing load for random access
* bursts.)
*
*
* Target cell requirement B -- avoid congestion
*
* In order to prevent congestion of a target cell, the cell must fulfill the
* requirement A, but also:
*
* * The minimum free channels, that are defined for that cell must be
* maintained after handover/assignment.
* * The minimum free channels are defined for TCH/F and TCH/H slot types
* individually.
*
*
* Target cell requirement C -- balance congestion
*
* In order to balance congested cells, the target cell must fulfill the
* requirement A, but also:
*
* * The target cell (which is congested also) must have more or equal free
* slots after handover/assignment.
* * The number of free slots are checked for TCH/F and TCH/H slot types
* individually.
*/
static void check_requirements(struct ho_candidate *c)
{
uint8_t requirement = 0;
unsigned int penalty_time;
int32_t current_overbooked;
struct gsm0808_cell_id target_cell_id;
c->requirements = 0;
/* Requirement A */
/* the handover/assignment must not be disabled */
if (c->current.bts == c->target.bts) {
if (!ho_get_hodec2_as_active(c->target.bts->ho)) {
LOGPHOLCHAN(c->current.lchan, LOGL_DEBUG, "Assignment disabled\n");
return;
}
} else {
if (!ho_get_ho_active(c->target.bts->ho)) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"not a candidate, handover is disabled in target BTS\n");
return;
}
}
/* the handover penalty timer must not run for this bts */
gsm_bts_cell_id(&target_cell_id, c->target.bts);
penalty_time = penalty_timers_remaining(&c->current.lchan->conn->hodec2.penalty_timers, &target_cell_id);
if (penalty_time) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG, "not a candidate, target BTS still in penalty time"
" (%u seconds left)\n", penalty_time);
return;
}
/* compatibility check for codecs.
* if so, the candidates for full rate and half rate are selected */
switch (gsm48_chan_mode_to_non_vamos(c->current.lchan->current_ch_mode_rate.chan_mode)) {
case GSM48_CMODE_SPEECH_V1:
switch (c->current.lchan->type) {
case GSM_LCHAN_TCH_F: /* mandatory */
requirement |= REQUIREMENT_A_TCHF;
break;
case GSM_LCHAN_TCH_H:
if (!c->target.bts->codec.hr) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"tch_mode='%s' type='%s' not supported\n",
get_value_string(gsm48_chan_mode_names,
c->current.lchan->current_ch_mode_rate.chan_mode),
gsm_lchant_name(c->current.lchan->type));
break;
}
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_HR1))
requirement |= REQUIREMENT_A_TCHH;
break;
default:
LOGPHOLCHAN(c->current.lchan, LOGL_ERROR, "Unexpected channel type: neither TCH/F nor TCH/H for %s\n",
get_value_string(gsm48_chan_mode_names,
c->current.lchan->current_ch_mode_rate.chan_mode));
return;
}
break;
case GSM48_CMODE_SPEECH_EFR:
if (!c->target.bts->codec.efr) {
LOGPHOBTS(c->target.bts, LOGL_DEBUG, "EFR not supported\n");
break;
}
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_FR2))
requirement |= REQUIREMENT_A_TCHF;
break;
case GSM48_CMODE_SPEECH_AMR:
if (!c->target.bts->codec.amr) {
LOGPHOBTS(c->target.bts, LOGL_DEBUG, "AMR not supported\n");
break;
}
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_FR3))
requirement |= REQUIREMENT_A_TCHF;
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_HR3))
requirement |= REQUIREMENT_A_TCHH;
break;
default:
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG, "Not even considering: src is not a SPEECH mode lchan\n");
/* FIXME: should allow handover of non-speech lchans */
return;
}
/* no candidate, because new cell is incompatible */
if (!requirement) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG, "not a candidate, because codec of MS and BTS are incompatible\n");
return;
}
/* remove slot types that are not available */
if (!c->target.free_tchf && (requirement & REQUIREMENT_A_TCHF)) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"removing TCH/F, since all TCH/F lchans are in use\n");
requirement &= ~(REQUIREMENT_A_TCHF);
}
if (!c->target.free_tchh && (requirement & REQUIREMENT_A_TCHH)) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"removing TCH/H, since all TCH/H lchans are in use\n");
requirement &= ~(REQUIREMENT_A_TCHH);
}
if (!requirement) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG, "not a candidate, because no suitable slots available\n");
return;
}
/* omit same channel type on same BTS (will not change anything) */
if (c->target.bts == c->current.bts) {
switch (c->current.lchan->type) {
case GSM_LCHAN_TCH_F:
requirement &= ~(REQUIREMENT_A_TCHF);
break;
case GSM_LCHAN_TCH_H:
requirement &= ~(REQUIREMENT_A_TCHH);
break;
default:
break;
}
if (!requirement) {
LOGPHOLCHAN(c->current.lchan, LOGL_DEBUG,
"Reassignment within cell not an option, no differing channel types available\n");
return;
}
}
#ifdef LEGACY
// This was useful in osmo-nitb. We're in osmo-bsc now and have no idea whether the osmo-msc does
// internal or external call control. Maybe a future config switch wants to add this behavior?
/* Built-in call control requires equal codec rates. Remove rates that are not equal. */
if (gsm48_chan_mode_to_non_vamos(c->current.lchan->tch_mode) == GSM48_CMODE_SPEECH_AMR
&& c->current.bts->network->mncc_recv != mncc_sock_from_cc) {
switch (c->current.lchan->type) {
case GSM_LCHAN_TCH_F:
if ((requirement & REQUIREMENT_A_TCHF)
&& !!memcmp(&c->current.bts->mr_full, &c->target.bts->mr_full,
sizeof(struct amr_multirate_conf)))
requirement &= ~(REQUIREMENT_A_TCHF);
if ((requirement & REQUIREMENT_A_TCHH)
&& !!memcmp(&c->current.bts->mr_full, &c->target.bts->mr_half,
sizeof(struct amr_multirate_conf)))
requirement &= ~(REQUIREMENT_A_TCHH);
break;
case GSM_LCHAN_TCH_H:
if ((requirement & REQUIREMENT_A_TCHF)
&& !!memcmp(&c->current.bts->mr_half, &c->target.bts->mr_full,
sizeof(struct amr_multirate_conf)))
requirement &= ~(REQUIREMENT_A_TCHF);
if ((requirement & REQUIREMENT_A_TCHH)
&& !!memcmp(&c->current.bts->mr_half, &c->target.bts->mr_half,
sizeof(struct amr_multirate_conf)))
requirement &= ~(REQUIREMENT_A_TCHH);
break;
default:
break;
}
if (!requirement) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"not a candidate, cannot provide identical codec rate\n");
return;
}
}
#endif
/* the maximum number of unsynchronized handovers must no be exceeded */
if (c->current.bts != c->target.bts
&& bts_handover_count(c->target.bts, HO_SCOPE_ALL) >= ho_get_hodec2_ho_max(c->target.bts->ho)) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"not a candidate, number of allowed handovers (%d) would be exceeded\n",
ho_get_hodec2_ho_max(c->target.bts->ho));
return;
}
/* Requirement B */
/* the minimum free timeslots that are defined for this cell must
* be maintained _after_ handover/assignment */
if (requirement & REQUIREMENT_A_TCHF) {
if ((c->target.free_tchf - 1) >= c->target.min_free_tchf
&& (!c->target.next_tchf_reduces_tchh
|| (c->target.free_tchh - c->target.next_tchf_reduces_tchh) >= c->target.min_free_tchh))
requirement |= REQUIREMENT_B_TCHF;
}
if (requirement & REQUIREMENT_A_TCHH) {
if ((c->target.free_tchh - 1) >= c->target.min_free_tchh
&& (!c->target.next_tchh_reduces_tchf
|| (c->target.free_tchf - c->target.next_tchh_reduces_tchf) >= c->target.min_free_tchf))
requirement |= REQUIREMENT_B_TCHH;
}
/* Requirement C */
/* the load percentage above congestion on the target cell *after* HO must be < the load percentage above
* congestion on the current cell, hence the - 1 on the target. */
current_overbooked = load_above_congestion(c->current.free_tch, c->current.min_free_tch);
if (requirement & REQUIREMENT_A_TCHF) {
bool ok;
int32_t target_overbooked;
int target_free_tchf_after_ho;
/* To evaluate whether a handover improves or worsens congestion on TCH/F, first figure out how many
* TCH/F lchans will be occupied on the target after the handover. If the target is a different cell,
* then we obviously reduce by one TCH/F. If source and target cell are the same (re-assignment), then
* the source lchan may also free a TCH/F at the same time. Add up all of these effects to figure out
* the congestion percentages before and after handover. */
target_free_tchf_after_ho = c->target.free_tchf - 1;
if (c->current.bts == c->target.bts)
target_free_tchf_after_ho += c->current.lchan_frees_tchf;
target_overbooked = load_above_congestion(target_free_tchf_after_ho, c->target.min_free_tchf);
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"current overbooked = %s%%, TCH/F target overbooked after HO = %s%%\n",
osmo_int_to_float_str_c(OTC_SELECT, current_overbooked, LOAD_PRECISION - 2),
osmo_int_to_float_str_c(OTC_SELECT, target_overbooked, LOAD_PRECISION - 2));
ok = target_overbooked < current_overbooked;
/* Look at dynamic timeslot effects on TCH/H: */
if (ok && c->target.next_tchf_reduces_tchh) {
/* Looking at the current TCH type and the target cell's TCH/F alone, congestion balancing
* should happen. However, what if the target TCH/F is a dynamic timeslot -- would that cause
* congestion on TCH/H above the current cell's TCH/H congestion? */
int32_t current_tchh_overbooked = load_above_congestion(c->current.free_tchh,
c->current.min_free_tchh);
int32_t target_tchh_overbooked;
int target_free_tchh_after_ho = c->target.free_tchh - c->target.next_tchf_reduces_tchh;
/* If this is a re-assignment within the same cell, and if the current candidate would free a
* dynamic timeslot, then the target-overbooking after HO is reduced again by the freed dynamic
* TS. */
if (c->current.bts == c->target.bts)
target_free_tchh_after_ho += c->current.lchan_frees_tchh;
target_tchh_overbooked = load_above_congestion(target_free_tchh_after_ho,
c->target.min_free_tchh);
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"dyn TS: current TCH/H overbooked = %s%%, TCH/H target overbooked after HO = %s%%\n",
osmo_int_to_float_str_c(OTC_SELECT, current_tchh_overbooked, LOAD_PRECISION - 2),
osmo_int_to_float_str_c(OTC_SELECT, target_tchh_overbooked, LOAD_PRECISION - 2));
/* For the current TCH kind, a handover should only happen if things actually get better
* (condition is '<'). For dynamic timeslot cross effects TCH/F->TCH/H, it is fine to not make
* it worse. Hence the smaller-or-equal condition. */
ok = target_tchh_overbooked <= current_tchh_overbooked;
}
if (ok)
requirement |= REQUIREMENT_C_TCHF;
}
if (requirement & REQUIREMENT_A_TCHH) {
bool ok;
int32_t target_overbooked;
int target_free_tchh_after_ho;
/* To evaluate whether a handover improves or worsens congestion on TCH/H, first figure out how many
* TCH/H lchans will be occupied on the target after the handover. If the target is a different cell,
* then we obviously reduce by one TCH/H. If source and target cell are the same (re-assignment), then
* the source lchan may also free one or two TCH/H at the same time. Add up all of these effects to
* figure out the congestion percentages before and after handover. */
target_free_tchh_after_ho = c->target.free_tchh - 1;
if (c->current.bts == c->target.bts)
target_free_tchh_after_ho += c->current.lchan_frees_tchh;
target_overbooked = load_above_congestion(target_free_tchh_after_ho, c->target.min_free_tchh);
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"current overbooked = %s%%, TCH/H target overbooked after HO = %s%%\n",
osmo_int_to_float_str_c(OTC_SELECT, current_overbooked, LOAD_PRECISION - 2),
osmo_int_to_float_str_c(OTC_SELECT, target_overbooked, LOAD_PRECISION - 2));
ok = target_overbooked < current_overbooked;
/* Look at dynamic timeslot effects on TCH/F: */
if (ok && c->target.next_tchh_reduces_tchf) {
/* Looking at the current TCH type and the target cell's TCH/H alone, congestion balancing
* should happen. However, what if the target TCH/H is a dynamic timeslot -- would that cause
* congestion on TCH/F above the current cell's TCH/F congestion? */
int32_t current_tchf_overbooked = load_above_congestion(c->current.free_tchf,
c->current.min_free_tchf);
int32_t target_tchf_overbooked;
int target_free_tchf_after_ho = c->target.free_tchf - c->target.next_tchh_reduces_tchf;
/* If this is a re-assignment within the same cell, and if the current candidate would free a
* dynamic timeslot, then the target-overbooking after HO is reduced again by the freed dynamic
* TS. */
if (c->current.bts == c->target.bts)
target_free_tchf_after_ho += c->current.lchan_frees_tchf;
target_tchf_overbooked = load_above_congestion(target_free_tchf_after_ho,
c->target.min_free_tchf);
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_DEBUG,
"dyn TS: current TCH/F overbooked = %s%%, TCH/F target overbooked after HO = %s%%\n",
osmo_int_to_float_str_c(OTC_SELECT, current_tchf_overbooked, LOAD_PRECISION - 2),
osmo_int_to_float_str_c(OTC_SELECT, target_tchf_overbooked, LOAD_PRECISION - 2));
/* For the current TCH kind, a handover should only happen if things actually get better
* (condition is '<'). For dynamic timeslot cross effects TCH/H->TCH/F, it is fine to not make
* it worse. Hence the smaller-or-equal condition. */
ok = target_tchf_overbooked <= current_tchf_overbooked;
}
if (ok)
requirement |= REQUIREMENT_C_TCHH;
}
/* return mask of fulfilled requirements */
c->requirements = requirement;
}
static void check_requirements_remote_bss(struct ho_candidate *c)
{
uint8_t requirement = 0;
unsigned int penalty_time;
c->requirements = 0;
/* Requirement A */
/* the handover penalty timer must not run for this bts */
penalty_time = penalty_timers_remaining_list(&c->current.lchan->conn->hodec2.penalty_timers, &c->target.cell_ids);
if (penalty_time) {
LOGPHOLCHANTOREMOTE(c->current.lchan, &c->target.cell_ids, LOGL_DEBUG,
"not a candidate, target BSS still in penalty time"
" (%u seconds left)\n", penalty_time);
return;
}
/* compatibility check for codecs -- we have no notion of what the remote BSS supports. We can
* only assume that a handover would work, and use only the local requirements. */
switch (gsm48_chan_mode_to_non_vamos(c->current.lchan->current_ch_mode_rate.chan_mode)) {
case GSM48_CMODE_SPEECH_V1:
switch (c->current.lchan->type) {
case GSM_LCHAN_TCH_F: /* mandatory */
requirement |= REQUIREMENT_A_TCHF;
break;
case GSM_LCHAN_TCH_H:
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_HR1))
requirement |= REQUIREMENT_A_TCHH;
break;
default:
LOGPHOLCHAN(c->current.lchan, LOGL_ERROR, "Unexpected channel type: neither TCH/F nor TCH/H for %s\n",
get_value_string(gsm48_chan_mode_names,
c->current.lchan->current_ch_mode_rate.chan_mode));
return;
}
break;
case GSM48_CMODE_SPEECH_EFR:
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_FR2))
requirement |= REQUIREMENT_A_TCHF;
break;
case GSM48_CMODE_SPEECH_AMR:
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_FR3))
requirement |= REQUIREMENT_A_TCHF;
if (codec_type_is_supported(c->current.lchan->conn, GSM0808_SCT_HR3))
requirement |= REQUIREMENT_A_TCHH;
break;
default:
LOGPHOLCHAN(c->current.lchan, LOGL_DEBUG, "Not even considering: src is not a SPEECH mode lchan\n");
/* FIXME: should allow handover of non-speech lchans */
return;
}
if (!requirement) {
LOGPHOLCHAN(c->current.lchan, LOGL_ERROR, "lchan doesn't fit its own requirements??\n");
return;
}
/* Requirement B and C */
/* We don't know how many timeslots are free in the remote BSS. We can only indicate that it
* would work out and hope for the best. */
if (requirement & REQUIREMENT_A_TCHF)
requirement |= REQUIREMENT_B_TCHF | REQUIREMENT_C_TCHF;
if (requirement & REQUIREMENT_A_TCHH)
requirement |= REQUIREMENT_B_TCHH | REQUIREMENT_C_TCHH;
/* return mask of fulfilled requirements */
c->requirements = requirement;
}
/* Trigger handover or assignment depending on the target BTS */
static int trigger_local_ho_or_as(struct ho_candidate *c, uint8_t requirements)
{
int afs_bias = 0;
bool full_rate = false;
/* afs_bias becomes > 0, if AFS is used and is improved */
if (gsm48_chan_mode_to_non_vamos(c->current.lchan->current_ch_mode_rate.chan_mode) == GSM48_CMODE_SPEECH_AMR)
afs_bias = ho_get_hodec2_afs_bias_rxlev(c->target.bts->ho);
/* select TCH rate, prefer TCH/F if AFS is improved */
switch (c->current.lchan->type) {
case GSM_LCHAN_TCH_F:
/* keep on full rate, if TCH/F is a candidate */
if ((requirements & REQUIREMENT_TCHF_MASK)) {
if (c->current.bts == c->target.bts) {
LOGPHOLCHAN(c->current.lchan, LOGL_INFO, "Not performing assignment: Already on target type\n");
return -EALREADY;
}
full_rate = true;
break;
}
/* change to half rate */
if (!(requirements & REQUIREMENT_TCHH_MASK)) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_ERROR,
"neither TCH/F nor TCH/H requested, aborting ho/as\n");
return -EINVAL;
}
break;
case GSM_LCHAN_TCH_H:
/* change to full rate if AFS is improved and a candidate */
if (afs_bias > 0 && (requirements & REQUIREMENT_TCHF_MASK)) {
full_rate = true;
break;
}
/* change to full rate if the only candidate */
if ((requirements & REQUIREMENT_TCHF_MASK)
&& !(requirements & REQUIREMENT_TCHH_MASK)) {
full_rate = true;
break;
}
/* keep on half rate */
if (!(requirements & REQUIREMENT_TCHH_MASK)) {
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_ERROR,
"neither TCH/F nor TCH/H requested, aborting ho/as\n");
return -EINVAL;
}
if (c->current.bts == c->target.bts) {
LOGPHOLCHAN(c->current.lchan, LOGL_INFO, "Not performing assignment: Already on target type\n");
return -EALREADY;
}
break;
default:
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_ERROR, "c->current.lchan is neither TCH/F nor TCH/H, aborting ho/as\n");
return -EINVAL;
}
/* trigger handover or assignment */
if (c->current.bts == c->target.bts) {
LOGPHOLCHAN(c->current.lchan, LOGL_NOTICE, "Triggering assignment to %s, due to %s\n",
full_rate ? "TCH/F" : "TCH/H",
ho_reason_name(global_ho_reason));
return reassignment_request_to_chan_type(ASSIGN_FOR_CONGESTION_RESOLUTION, c->current.lchan,
full_rate? GSM_LCHAN_TCH_F : GSM_LCHAN_TCH_H);
} else {
struct handover_out_req req = {
.from_hodec_id = HODEC2,
.old_lchan = c->current.lchan,
.new_lchan_type = full_rate? GSM_LCHAN_TCH_F : GSM_LCHAN_TCH_H,
};
bts_cell_ab(&req.target_cell_ab, c->target.bts);
LOGPHOLCHANTOBTS(c->current.lchan, c->target.bts, LOGL_INFO,
"Triggering handover to %s, due to %s\n",
full_rate ? "TCH/F" : "TCH/H",
ho_reason_name(global_ho_reason));
handover_request(&req);
/* Apply penalty timer hodec2_penalty_low_rxqual_ho */
if (global_ho_reason == HO_REASON_INTERFERENCE
|| global_ho_reason == HO_REASON_BAD_QUALITY) {
struct gsm0808_cell_id bts_id;
struct gsm_subscriber_connection *conn = c->current.lchan->conn;
int timeout = ho_get_hodec2_penalty_low_rxqual_ho(c->current.bts->ho);
gsm_bts_cell_id(&bts_id, c->current.bts);
LOGPHOCAND(c, LOGL_DEBUG, "Applying penalty-time low-rxqual-ho %d s on bts %u (%s), reason: %s\n",
timeout, c->current.bts->nr, gsm0808_cell_id_name_c(OTC_SELECT, &bts_id),
ho_reason_name(global_ho_reason));
penalty_timers_add(conn, &conn->hodec2.penalty_timers, &bts_id, timeout);
}
}
return 0;
}
static int trigger_remote_bss_ho(struct ho_candidate *c, uint8_t requirements)
{
struct handover_out_req req;
LOGPHOLCHANTOREMOTE(c->current.lchan, &c->target.cell_ids, LOGL_INFO,
"Triggering inter-BSC handover, due to %s\n",
ho_reason_name(global_ho_reason));
req = (struct handover_out_req){
.from_hodec_id = HODEC2,
.old_lchan = c->current.lchan,
.target_cell_ab = c->target.ab,
};
handover_request(&req);
return 0;
}
static int trigger_ho(struct ho_candidate *c, uint8_t requirements)
{
if (c->target.bts)
return trigger_local_ho_or_as(c, requirements);
else
return trigger_remote_bss_ho(c, requirements);
}
#define REQUIREMENTS_FMT "[%s%s%s]%s"
#define REQUIREMENTS_ARGS(REQUIREMENTS, TCHX) \
(REQUIREMENTS) & REQUIREMENT_A_TCH##TCHX ? "A" : \
((REQUIREMENTS) & REQUIREMENT_TCH##TCHX##_MASK) == 0? "-" : "", \
(REQUIREMENTS) & REQUIREMENT_B_TCH##TCHX ? "B" : "", \
(REQUIREMENTS) & REQUIREMENT_C_TCH##TCHX ? "C" : "", \
((REQUIREMENTS) & REQUIREMENT_TCH##TCHX##_MASK) == 0 ? " not a candidate" : \
(((REQUIREMENTS) & REQUIREMENT_TCH##TCHX##_MASK) == REQUIREMENT_A_TCH##TCHX ? \
" more congestion" : \
((REQUIREMENTS) & REQUIREMENT_B_TCH##TCHX ? \
" good" : \
/* now has to be (REQUIREMENTS) & REQUIREMENT_C_TCHX != 0: */ \
" less-or-equal congestion"))
/* verbosely log about a handover candidate */
static inline void debug_candidate(struct ho_candidate *candidate)
{
#define HO_CANDIDATE_FMT(tchx, TCHX) "TCH/" #TCHX "={free %d (want %d), " REQUIREMENTS_FMT "}"
#define HO_CANDIDATE_ARGS(tchx, TCHX) \
candidate->target.free_tch##tchx, candidate->target.min_free_tch##tchx, \
REQUIREMENTS_ARGS(candidate->requirements, TCHX)
if (!candidate->target.bts && !candidate->target.cell_ids.id_list_len)
LOGPHOLCHAN(candidate->current.lchan, LOGL_DEBUG, "Empty candidate\n");
if (candidate->target.bts && candidate->target.cell_ids.id_list_len)
LOGPHOLCHAN(candidate->current.lchan, LOGL_ERROR, "Invalid candidate: both local- and remote-BSS target\n");
if (candidate->target.cell_ids.id_list_len)
LOGPHOLCHANTOREMOTE(candidate->current.lchan, &candidate->target.cell_ids, LOGL_DEBUG,
"RX level %d dBm -> %d dBm\n",
rxlev2dbm(candidate->current.rxlev), rxlev2dbm(candidate->target.rxlev));
if (candidate->target.bts == candidate->current.bts)
LOGPHOLCHANTOBTS(candidate->current.lchan, candidate->target.bts, LOGL_DEBUG,
"RX level %d dBm; "
HO_CANDIDATE_FMT(f, F) "; " HO_CANDIDATE_FMT(h, H) "\n",
rxlev2dbm(candidate->current.rxlev),
HO_CANDIDATE_ARGS(f, F), HO_CANDIDATE_ARGS(h, H));
else if (candidate->target.bts)
LOGPHOLCHANTOBTS(candidate->current.lchan, candidate->target.bts, LOGL_DEBUG,
"RX level %d dBm -> %d dBm; "
HO_CANDIDATE_FMT(f, F) "; " HO_CANDIDATE_FMT(h, H) "\n",
rxlev2dbm(candidate->current.rxlev), rxlev2dbm(candidate->target.rxlev),
HO_CANDIDATE_ARGS(f, F), HO_CANDIDATE_ARGS(h, H));
}
static void candidate_set_free_tch(struct ho_candidate *c)
{
struct chan_counts *bts_counts;
struct gsm_lchan *next_lchan;
bts_counts = &c->current.bts->chan_counts;
c->current.free_tchf = bts_counts->val[CHAN_COUNTS1_ALL][CHAN_COUNTS2_FREE][GSM_LCHAN_TCH_F];
c->current.min_free_tchf = ho_get_hodec2_tchf_min_slots(c->current.bts->ho);
c->current.free_tchh = bts_counts->val[CHAN_COUNTS1_ALL][CHAN_COUNTS2_FREE][GSM_LCHAN_TCH_H];
c->current.min_free_tchh = ho_get_hodec2_tchh_min_slots(c->current.bts->ho);
switch (c->current.lchan->ts->pchan_is) {
case GSM_PCHAN_TCH_F:
c->current.free_tch = c->current.free_tchf;
c->current.min_free_tch = c->current.min_free_tchf;
c->current.lchan_frees_tchf = 1;
if (c->current.lchan->ts->pchan_on_init == GSM_PCHAN_OSMO_DYN)
c->current.lchan_frees_tchh = 2;
else
c->current.lchan_frees_tchh = 0;
break;
case GSM_PCHAN_TCH_H:
c->current.free_tch = c->current.free_tchh;
c->current.min_free_tch = c->current.min_free_tchh;
c->current.lchan_frees_tchh = 1;
/* Freeing one of two TCH/H does not free a dyn TS and would not free a TCH/F. It has to be the last
* TCH/H of a dynamic timeslot that is freed to get a new TCH/F in the current cell from the handover.
* Hence the ts_usage_count() condition. */
if (c->current.lchan->ts->pchan_on_init == GSM_PCHAN_OSMO_DYN
&& ts_usage_count(c->current.lchan->ts) == 1)
c->current.lchan_frees_tchf = 1;
else
c->current.lchan_frees_tchf = 0;
break;
default:
break;
}
/* For inter-BSC handover, the target BTS is in a different BSC and hence NULL here. */
if (c->target.bts) {
bts_counts = &c->target.bts->chan_counts;
c->target.free_tchf = bts_counts->val[CHAN_COUNTS1_ALL][CHAN_COUNTS2_FREE][GSM_LCHAN_TCH_F];
c->target.min_free_tchf = ho_get_hodec2_tchf_min_slots(c->target.bts->ho);
c->target.free_tchh = bts_counts->val[CHAN_COUNTS1_ALL][CHAN_COUNTS2_FREE][GSM_LCHAN_TCH_H];
c->target.min_free_tchh = ho_get_hodec2_tchh_min_slots(c->target.bts->ho);
/* Would the next TCH/F lchan occupy a dynamic timeslot that currently counts for free TCH/H timeslots?
*/
next_lchan = lchan_avail_by_type(c->target.bts, GSM_LCHAN_TCH_F,
SELECT_FOR_HANDOVER, NULL, false);
if (next_lchan && next_lchan->ts->pchan_on_init == GSM_PCHAN_OSMO_DYN)
c->target.next_tchf_reduces_tchh = 2;
else
c->target.next_tchf_reduces_tchh = 0;
/* Would the next TCH/H lchan occupy a dynamic timeslot that currently counts for free TCH/F timeslots?
* Note that a dyn TS already in TCH/H mode (half occupied) would not reduce free TCH/F. */
next_lchan = lchan_avail_by_type(c->target.bts, GSM_LCHAN_TCH_H,
SELECT_FOR_HANDOVER, NULL, false);
if (next_lchan && next_lchan->ts->pchan_on_init == GSM_PCHAN_OSMO_DYN
&& next_lchan->ts->pchan_is != GSM_PCHAN_TCH_H)
c->target.next_tchh_reduces_tchf = 1;
else
c->target.next_tchh_reduces_tchf = 0;
} else {
c->target.free_tchf = 0;
c->target.min_free_tchf = 0;
c->target.next_tchh_reduces_tchf = 0;
c->target.free_tchh = 0;
c->target.min_free_tchh = 0;
c->target.next_tchf_reduces_tchh = 0;
}
}
/* add candidate for re-assignment within the current cell */
static void collect_assignment_candidate(struct gsm_lchan *lchan, struct ho_candidate *clist,
unsigned int *candidates, int rxlev_current)
{
struct gsm_bts *bts = lchan->ts->trx->bts;
struct ho_candidate c;
c = (struct ho_candidate){
.current = {
.lchan = lchan,
.bts = bts,
.rxlev = rxlev_current,
},
.target = {
.bts = bts,
.rxlev = rxlev_current, /* same cell, same rxlev */
},
};
candidate_set_free_tch(&c);
check_requirements(&c);
debug_candidate(&c);
if (!c.requirements)
return;
clist[*candidates] = c;
(*candidates)++;
}
/* add candidates for handover to all neighbor cells */
static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_meas_proc *nmp,
struct ho_candidate *clist, unsigned int *candidates,
bool include_weaker_rxlev, int rxlev_current,
int *neighbors_count)
{
struct gsm_bts *bts = lchan->ts->trx->bts;
struct gsm_bts *neighbor_bts;
struct gsm0808_cell_id_list2 neighbor_cil;
struct cell_ab target_ab = {
.arfcn = nmp->arfcn,
.bsic = nmp->bsic,
};
struct ho_candidate c;
struct handover_cfg *neigh_cfg;
/* skip empty slots */
if (nmp->arfcn == 0)
return;
if (neighbors_count)
(*neighbors_count)++;
/* skip if measurement report is old */
if (nmp->last_seen_nr != lchan->meas_rep_last_seen_nr) {
LOGPHOLCHAN(lchan, LOGL_DEBUG, "neighbor ARFCN %u BSIC %u measurement report is old"
" (nmp->last_seen_nr=%u lchan->meas_rep_last_seen_nr=%u)\n",
nmp->arfcn, nmp->bsic, nmp->last_seen_nr, lchan->meas_rep_last_seen_nr);
return;
}
find_handover_target_cell(&neighbor_bts, &neighbor_cil,
lchan->conn, &target_ab, false);
if (!neighbor_bts && !neighbor_cil.id_list_len) {
LOGPHOBTS(bts, LOGL_DEBUG, "no neighbor ARFCN %u BSIC %u configured for this cell\n",
nmp->arfcn, nmp->bsic);
return;
}
/* in case we have measurements of our bts, due to misconfiguration */
if (neighbor_bts == bts) {
LOGPHOBTS(bts, LOGL_ERROR, "Configuration error: this BTS appears as its own neighbor\n");
return;
}
/* For cells in a remote BSS, we cannot query the target cell's handover config, and hence
* instead assume the local BTS' config to apply. */
neigh_cfg = (neighbor_bts ? : bts)->ho;
c = (struct ho_candidate){
.current = {
.lchan = lchan,
.bts = bts,
.rxlev = rxlev_current,
},
.target = {
.ab = target_ab,
.bts = neighbor_bts,
.cell_ids = neighbor_cil,
.rxlev = neigh_meas_avg(nmp, ho_get_hodec2_rxlev_neigh_avg_win(bts->ho)),
},
};
candidate_set_free_tch(&c);
/* Heed rxlev hysteresis only if the RXLEV/RXQUAL/TA levels of the MS aren't critically bad and
* we're just looking for an improvement. If levels are critical, we desperately need a handover
* and thus skip the hysteresis check. */
if (!include_weaker_rxlev) {
int pwr_hyst = ho_get_hodec2_pwr_hysteresis(bts->ho);
if ((c.target.rxlev - c.current.rxlev) <= pwr_hyst) {
LOGPHOCAND(&c, LOGL_DEBUG,
"Not a candidate, because RX level (%d dBm) is lower"
" or equal than current RX level (%d dBm) + hysteresis (%d)\n",
rxlev2dbm(c.target.rxlev), rxlev2dbm(c.current.rxlev), pwr_hyst);
return;
}
}
/* if the minimum level is not reached.
* In case of a remote-BSS, use the current BTS' configuration. */
if (is_low_rxlev(c.target.rxlev, neigh_cfg)) {
LOGPHOCAND(&c, LOGL_DEBUG,
"Not a candidate, because RX level (%d dBm) is lower"
" than the minimum required RX level (%d dBm)\n",
rxlev2dbm(c.target.rxlev), ho_get_hodec2_min_rxlev(neigh_cfg));
return;
}
if (neighbor_bts) {
check_requirements(&c);
} else
check_requirements_remote_bss(&c);
debug_candidate(&c);
if (!c.requirements)
return;
clist[*candidates] = c;
(*candidates)++;
}
static void collect_candidates_for_lchan(struct gsm_lchan *lchan,
struct ho_candidate *clist, unsigned int *candidates,
int *_rxlev_current, bool include_weaker_rxlev)
{
struct gsm_bts *bts = lchan->ts->trx->bts;
int rxlev_current;
bool assignment;
bool handover;
int neighbors_count = 0;
OSMO_ASSERT(candidates);
rxlev_current = current_rxlev(lchan);
if (_rxlev_current)
*_rxlev_current = rxlev_current;
/* in case there is no measurement report (yet) */
if (rxlev_current < 0) {
LOGPHOLCHAN(lchan, LOGL_DEBUG, "Not collecting candidates, not enough measurements"
" (got %d, want %u)\n",
lchan->meas_rep_count, ho_get_hodec2_rxlev_avg_win(bts->ho));
return;
}
assignment = ho_get_hodec2_as_active(bts->ho);
handover = ho_get_ho_active(bts->ho);
/* See if re-assignment within the same cell can resolve congestion.
* But: when TCH/F has low rxlev, do not re-assign. If a low rxlev TCH/F were re-assigned to TCH/H, we would
* subsequently oscillate back to TCH/F due to low rxlev. So skip TCH/F with low rxlev. */
if (assignment
&& !(lchan->type == GSM_LCHAN_TCH_F
&& (is_low_rxlev(rxlev_current, bts->ho) || is_low_rxqual(current_rxqual(lchan), bts->ho))))
collect_assignment_candidate(lchan, clist, candidates, rxlev_current);
if (handover) {
int i;
for (i = 0; i < ARRAY_SIZE(lchan->neigh_meas); i++) {
collect_handover_candidate(lchan, &lchan->neigh_meas[i],
clist, candidates,
include_weaker_rxlev, rxlev_current, &neighbors_count);
}
}
}
/*
* Search for a alternative / better cell.
*
* Do not trigger handover/assignment on slots which have already ongoing
* handover/assignment processes. If no AFS improvement offset is given, try to
* maintain the same TCH rate, if available.
* Do not perform this process, if handover and assignment are disabled for
* the current cell.
* Do not perform handover, if the minimum acceptable RX level
* is not reached for this cell.
*
* If one or more 'better cells' are available, check the current and neighbor
* cell measurements in descending order of their RX levels (down-link):
*
* * Select the best candidate that fulfills requirement B (no congestion
* after handover/assignment) and trigger handover or assignment.
* * If no candidate fulfills requirement B, select the best candidate that
* fulfills requirement C (less or equally congested cells after handover)
* and trigger handover or assignment.
* * If no candidate fulfills requirement C, do not perform handover nor
* assignment.
*
* If the RX level (down-link) or RX quality (down-link) of the current cell is
* below minimum acceptable level, or if the maximum allowed timing advance is
* reached or exceeded, check the RX levels (down-link) of the current and
* neighbor cells in descending order of their levels: (bad BTS case)
*
* * Select the best candidate that fulfills requirement B (no congestion after
* handover/assignment) and trigger handover or assignment.
* * If no candidate fulfills requirement B, select the best candidate that
* fulfills requirement C (less or equally congested cells after handover)
* and trigger handover or assignment.
* * If no candidate fulfills requirement C, select the best candidate that
* fulfills requirement A (ignore congestion after handover or assignment)
* and trigger handover or assignment.
* * If no candidate fulfills requirement A, do not perform handover nor
* assignment.
*
* RX levels (down-link) of current and neighbor cells:
*
* * The RX levels of the current cell and neighbor cells are improved by a
* given offset, if AFS (AMR on TCH/F) is used or is a candidate for
* handover/assignment.
* * If AMR is used, the requirement for handover is checked for TCH/F and
* TCH/H. Both results (if any) are used as a candidate.
* * If AMR is used, the requirement for assignment to a different TCH slot
* rate is checked. The result (if available) is used as a candidate.
*
* If minimum RXLEV, minimum RXQUAL or maximum TA are exceeded, the caller should pass
* include_weaker_rxlev=true so that handover is performed despite congestion.
*/
static int find_alternative_lchan(struct gsm_lchan *lchan, bool include_weaker_rxlev, bool request_upgrade_to_tch_f)
{
struct gsm_bts *bts = lchan->ts->trx->bts;
int ahs = (gsm48_chan_mode_to_non_vamos(lchan->current_ch_mode_rate.chan_mode) == GSM48_CMODE_SPEECH_AMR
&& lchan->type == GSM_LCHAN_TCH_H);
int rxlev_current;
struct ho_candidate clist[1 + ARRAY_SIZE(lchan->neigh_meas)];
unsigned int candidates = 0;
int i;
struct ho_candidate *best_cand = NULL;
unsigned int best_better_db;
bool best_applied_afs_bias = false;
int better;
/* check for disabled handover/assignment at the current cell */
if (!ho_get_hodec2_as_active(bts->ho)
&& !ho_get_ho_active(bts->ho)) {
LOGP(DHODEC, LOGL_INFO, "Skipping, Handover and Assignment both disabled in this cell\n");
return 0;
}
collect_candidates_for_lchan(lchan, clist, &candidates, &rxlev_current, include_weaker_rxlev);
/* If assignment is disabled and no neighbor cell report exists, or no neighbor cell qualifies,
* we may not even have any candidates. */
if (!candidates) {
LOGPHOLCHAN(lchan, LOGL_INFO, "No viable neighbor cells found\n");
return 0;
}
/* select best candidate that fulfills requirement B: no congestion after HO.
* Exclude remote-BSS neighbors: to avoid oscillation between neighboring BSS,
* rather keep subscribers in the local BSS unless there is critical RXLEV/TA. */
best_better_db = 0;
for (i = 0; i < candidates; i++) {
int afs_bias;
if (!(clist[i].requirements & REQUIREMENT_B_MASK))
continue;
/* Only consider Local-BSS cells */
if (!clist[i].target.bts)
continue;
better = clist[i].target.rxlev - clist[i].current.rxlev;
/* Apply AFS bias? Skip AFS bias for all intra-cell candidates. */
afs_bias = 0;
if (clist[i].target.bts != bts
&& ahs && (clist[i].requirements & REQUIREMENT_B_TCHF))
afs_bias = ho_get_hodec2_afs_bias_rxlev(clist[i].target.bts->ho);
better += afs_bias;
if (better > best_better_db) {
best_cand = &clist[i];
best_better_db = better;
best_applied_afs_bias = afs_bias? true : false;
}
}
/* perform handover, if there is a candidate */
if (best_cand) {
LOGPHOCAND(best_cand, LOGL_INFO, "Best candidate, RX level %d%s\n",
rxlev2dbm(best_cand->target.rxlev),
best_applied_afs_bias ? " (applied AHS -> AFS rxlev bias)" : "");
return trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_B_MASK);
}
/* select best candidate that fulfills requirement C: less or equal congestion after HO,
* again excluding remote-BSS neighbors. */
best_better_db = 0;
for (i = 0; i < candidates; i++) {
int afs_bias;
if (!(clist[i].requirements & REQUIREMENT_C_MASK))
continue;
/* Only consider Local-BSS cells */
if (!clist[i].target.bts)
continue;
better = clist[i].target.rxlev - clist[i].current.rxlev;
/* Apply AFS bias? Skip AFS bias for all intra-cell candidates. */
afs_bias = 0;
if (clist[i].target.bts != bts
&& ahs && (clist[i].requirements & REQUIREMENT_C_TCHF))
afs_bias = ho_get_hodec2_afs_bias_rxlev(clist[i].target.bts->ho);
better += afs_bias;
if (better > best_better_db) {
best_cand = &clist[i];
best_better_db = better;
best_applied_afs_bias = afs_bias? true : false;
}
}
/* perform handover, if there is a candidate */
if (best_cand) {
LOGPHOCAND(best_cand, LOGL_INFO, "Best candidate, RX level %d%s\n",
rxlev2dbm(best_cand->target.rxlev),
best_applied_afs_bias? " (applied AHS -> AFS rxlev bias)" : "");
return trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_C_MASK);
}
/* we are done in case the MS RXLEV/RXQUAL/TA aren't critical and we're avoiding congestion. */
if (!include_weaker_rxlev) {
LOGPHOLCHAN(lchan, LOGL_INFO, "No better/less congested neighbor cell found\n");
return 0;
}
/* Select best candidate that fulfills requirement A: can service the call.
* From above we know that there are no options that avoid congestion. Here we're trying to find
* *any* free lchan that has no critically low RXLEV and is able to handle the MS.
* We're also prepared to handover to remote BSS. */
best_better_db = 0;
for (i = 0; i < candidates; i++) {
int afs_bias;
if (!(clist[i].requirements & REQUIREMENT_A_MASK))
continue;
better = clist[i].target.rxlev - clist[i].current.rxlev;
/* Apply AFS bias? Skip AFS bias for all intra-cell candidates.
* (never to remote-BSS neighbors, since we will not change the lchan type for those.) */
afs_bias = 0;
if (ahs && (clist[i].requirements & REQUIREMENT_A_TCHF)
&& clist[i].target.bts && clist[i].target.bts != bts)
afs_bias = ho_get_hodec2_afs_bias_rxlev(clist[i].target.bts->ho);
better += afs_bias;
if (better > best_better_db
|| (better >= best_better_db /* Upgrade from TCH/H to TCH/F: allow for equal rxlev */
&& request_upgrade_to_tch_f
&& is_upgrade_to_tchf(&clist[i], REQUIREMENT_A_MASK))) {
best_cand = &clist[i];
best_better_db = better;
best_applied_afs_bias = afs_bias? true : false;
}
}
/* perform handover, if there is a candidate */
if (best_cand) {
int rc;
LOGPHOCAND(best_cand, LOGL_INFO, "Best candidate: RX level %d%s\n",
rxlev2dbm(best_cand->target.rxlev),
best_applied_afs_bias ? " (applied AHS -> AFS rxlev bias)" : "");
rc = trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_A_MASK);
/* After upgrading TCH/H to TCH/F due to bad RxQual, start penalty timer to avoid re-assignment within
* the same cell again, to avoid oscillation from RxQual noise combined with congestion resolution. */
if (!rc && best_cand->target.bts == best_cand->current.bts
&& is_upgrade_to_tchf(best_cand, REQUIREMENT_A_MASK)) {
struct gsm0808_cell_id bts_id;
gsm_bts_cell_id(&bts_id, best_cand->target.bts);
penalty_timers_add(lchan->conn, &lchan->conn->hodec2.penalty_timers, &bts_id,
ho_get_hodec2_penalty_low_rxqual_as(bts->ho));
}
return rc;
}
/* Damn, all is congested, has too low RXLEV or cannot service the voice call due to codec
* restrictions or because all lchans are taken. */
LOGPHOLCHAN(lchan, LOGL_INFO, "No alternative lchan found\n");
return 0;
}
/*
* Handover/assignment check, if measurement report is received
*
* Do not trigger handover/assignment on slots which have already ongoing
* handover/assignment processes.
*
* In case of handover triggered because maximum allowed timing advance is
* exceeded, the handover penalty timer is started for the originating cell.
*
*/
static void on_measurement_report(struct gsm_meas_rep *mr)
{
struct gsm_lchan *lchan = mr->lchan;
struct gsm_bts *bts = lchan->ts->trx->bts;
int av_rxlev = -EINVAL, av_rxqual = -EINVAL;
unsigned int pwr_interval;
/* we currently only do handover for TCH channels */
switch (mr->lchan->type) {
case GSM_LCHAN_TCH_F:
case GSM_LCHAN_TCH_H:
break;
default:
return;
}
if (log_check_level(DHODEC, LOGL_DEBUG)) {
int i;
LOGPHOLCHAN(lchan, LOGL_DEBUG, "MEASUREMENT REPORT (%d neighbors)\n",
mr->num_cell);
for (i = 0; i < mr->num_cell; i++) {
struct gsm_meas_rep_cell *mrc = &mr->cell[i];
LOGPHOLCHAN(lchan, LOGL_DEBUG,
" %d: arfcn=%u bsic=%u neigh_idx=%u rxlev=%u flags=%x\n",
i, mrc->arfcn, mrc->bsic, mrc->neigh_idx, mrc->rxlev, mrc->flags);
}
}
/* parse actual neighbor cell info */
if (mr->num_cell > 0 && mr->num_cell < 7)
process_meas_neigh(mr);
/* check for ongoing handover/assignment */
if (!lchan->conn) {
LOGPHOLCHAN(lchan, LOGL_ERROR, "Skipping, No subscriber connection???\n");
return;
}
if (lchan->conn->assignment.new_lchan) {
LOGPHOLCHAN(lchan, LOGL_INFO, "Skipping, Initial Assignment is still ongoing\n");
return;
}
if (lchan->conn->ho.fi) {
LOGPHOLCHAN(lchan, LOGL_INFO, "Skipping, Handover still ongoing\n");
return;
}
/* get average levels. if not enough measurements yet, value is < 0 */
av_rxlev = current_rxlev(lchan);
av_rxqual = current_rxqual(lchan);
if (av_rxlev < 0 && av_rxqual < 0) {
LOGPHOLCHAN(lchan, LOGL_INFO, "Skipping, Not enough recent measurements\n");
return;
}
/* improve levels in case of AFS, if defined */
if (lchan->type == GSM_LCHAN_TCH_F
&& gsm48_chan_mode_to_non_vamos(lchan->current_ch_mode_rate.chan_mode) == GSM48_CMODE_SPEECH_AMR) {
int av_rxlev_was = av_rxlev;
int av_rxqual_was = av_rxqual;
int rxlev_bias = ho_get_hodec2_afs_bias_rxlev(bts->ho);
int rxqual_bias = ho_get_hodec2_afs_bias_rxqual(bts->ho);
if (av_rxlev >= 0)
av_rxlev = av_rxlev + rxlev_bias;
if (av_rxqual >= 0)
av_rxqual = OSMO_MAX(0, av_rxqual - rxqual_bias);
LOGPHOLCHAN(lchan, LOGL_DEBUG,
"Avg RX level = %d dBm, %+d dBm AFS bias = %d dBm;"
" Avg RX quality = %d%s, %+d AFS bias = %d\n",
rxlev2dbm(av_rxlev_was), rxlev_bias, rxlev2dbm(av_rxlev),
OSMO_MAX(-1, av_rxqual_was), av_rxqual_was < 0 ? " (invalid)" : "",
-rxqual_bias, OSMO_MAX(-1, av_rxqual));
} else {
LOGPHOLCHAN(lchan, LOGL_DEBUG, "Avg RX level = %d dBm; Avg RX quality = %d%s\n",
rxlev2dbm(av_rxlev),
OSMO_MAX(-1, av_rxqual), av_rxqual < 0 ? " (invalid)" : "");
}
/* Bad Quality */
if (av_rxqual >= 0 && av_rxqual > ho_get_hodec2_min_rxqual(bts->ho)) {
if (rxlev2dbm(av_rxlev) > -85) {
global_ho_reason = HO_REASON_INTERFERENCE;
LOGPHOLCHAN(lchan, LOGL_INFO, "Trying handover/assignment"
" due to interference (bad quality)\n");
} else {
global_ho_reason = HO_REASON_BAD_QUALITY;
LOGPHOLCHAN(lchan, LOGL_INFO, "Trying handover/assignment due to bad quality\n");
}
find_alternative_lchan(lchan, true, true);
return;
}
/* Low Level */
if (is_low_rxlev(av_rxlev, bts->ho)) {
global_ho_reason = HO_REASON_LOW_RXLEVEL;
LOGPHOLCHAN(lchan, LOGL_NOTICE, "RX level is TOO LOW: %d < %d\n",
rxlev2dbm(av_rxlev), ho_get_hodec2_min_rxlev(bts->ho));
find_alternative_lchan(lchan, true, true);
return;
}
/* Max Distance */
if (lchan->meas_rep_count > 0
&& lchan->last_ta > ho_get_hodec2_max_distance(bts->ho)) {
struct gsm0808_cell_id bts_id;
global_ho_reason = HO_REASON_MAX_DISTANCE;
LOGPHOLCHAN(lchan, LOGL_NOTICE, "TA is TOO HIGH: %u > %d\n",
lchan->last_ta, ho_get_hodec2_max_distance(bts->ho));
/* start penalty timer to prevent coming back too
* early. it must be started before selecting a better cell,
* so there is no assignment selected, due to running
* penalty timer. */
gsm_bts_cell_id(&bts_id, bts);
penalty_timers_add(lchan->conn, &lchan->conn->hodec2.penalty_timers, &bts_id,
ho_get_hodec2_penalty_max_dist(bts->ho));
find_alternative_lchan(lchan, true, false);
return;
}
/* pwr_interval's range is 1-99, clarifying that no div-zero shall happen in modulo below: */
pwr_interval = ho_get_hodec2_pwr_interval(bts->ho);
OSMO_ASSERT(pwr_interval);
/* try handover to a better cell */
if (av_rxlev >= 0 && (mr->nr % pwr_interval) == 0) {
global_ho_reason = HO_REASON_BETTER_CELL;
find_alternative_lchan(lchan, false, false);
}
}
static bool lchan_is_on_dynamic_ts(struct gsm_lchan *lchan)
{
return lchan->ts->pchan_on_init == GSM_PCHAN_OSMO_DYN
|| lchan->ts->pchan_on_init == GSM_PCHAN_TCH_F_PDCH;
}
/* Given two candidates, pick the one that should rather be moved during handover.
* Return the better candidate in out-parameters best_cand and best_avg_db.
*/
static struct ho_candidate *pick_better_lchan_to_move(struct ho_candidate *a,
struct ho_candidate *b,
uint8_t for_requirement)
{
int a_rxlev_change;
int b_rxlev_change;
struct ho_candidate *ret = a;
if (!a)
return b;
if (!b)
return a;
a_rxlev_change = a->target.rxlev - a->current.rxlev;
b_rxlev_change = b->target.rxlev - b->current.rxlev;
/* Typically, a congestion related handover reduces RXLEV. If there is a candidate that actually improves RXLEV,
* prefer that, because it pre-empts a likely handover due to measurement results later. Also favor unchanged
* RXLEV over a loss of RXLEV (favor staying within the same cell over moving to a worse cell). */
if (a_rxlev_change >= 0 && a_rxlev_change > b_rxlev_change)
return a;
if (b_rxlev_change >= 0 && b_rxlev_change > a_rxlev_change)
return b;
if (a_rxlev_change < 0 && b_rxlev_change < 0) {
/* For handover that reduces RXLEV, favor the highest resulting RXLEV, AFS bias applied. */
int a_rxlev = a->target.rxlev + a->target.rxlev_afs_bias;
int b_rxlev = b->target.rxlev + b->target.rxlev_afs_bias;
if (a_rxlev > b_rxlev)
return a;
if (b_rxlev > a_rxlev)
return b;
/* There is no target RXLEV difference between the two candidates. Let other factors influence the
* choice. */
}
/* Prefer picking a dynamic timeslot: free PDCH and allow more timeslot type flexibility for further
* congestion resolution. */
if (lchan_is_on_dynamic_ts(b->current.lchan)) {
unsigned int ac, bc;
if (!lchan_is_on_dynamic_ts(a->current.lchan))
return b;
/* Both are dynamic timeslots. Prefer one that completely (or to a higher degree) frees its
* timeslot. */
ac = ts_usage_count(a->current.lchan->ts);
bc = ts_usage_count(b->current.lchan->ts);
if (bc < ac)
return b;
if (ac < bc)
return a;
/* (If both are dynamic timeslots, favor moving the later dynamic timeslot. That is a vague preference
* for later dynamic TS to become PDCH and join up with plain PDCH that follow it -- not actually clear
* whether that helps, and depends on user's TS config. No harm done either way.) */
ret = b;
}
/* When upgrading TCH/H to TCH/F, favor moving a TCH/H with lower current rxlev, because presumably that
* one benefits more from a higher bandwidth. */
if (is_upgrade_to_tchf(a, for_requirement) && is_upgrade_to_tchf(b, for_requirement)) {
if (b->current.rxlev < a->current.rxlev)
return b;
if (a->current.rxlev < b->current.rxlev)
return a;
}
return ret;
}
static struct ho_candidate *pick_best_candidate(struct ho_candidate *clist, int clist_len,
uint8_t for_requirement)
{
struct ho_candidate *result = NULL;
int i;
for (i = 0; i < clist_len; i++) {
struct ho_candidate *c = &clist[i];
/* For multiple passes of congestion resolution, already handovered candidates are marked by lchan =
* NULL. (though at the time of writing, multiple passes of congestion resolution are DISABLED.) */
if (!c->current.lchan)
continue;
/* Omit remote BSS */
if (!c->target.bts)
continue;
if (!(c->requirements & for_requirement))
continue;
/* improve AHS */
if (is_upgrade_to_tchf(c, for_requirement))
c->target.rxlev_afs_bias = ho_get_hodec2_afs_bias_rxlev(c->target.bts->ho);
else
c->target.rxlev_afs_bias = 0;
result = pick_better_lchan_to_move(result, c, for_requirement);
}
return result;
}
/*
* Handover/assignment check after timer timeout:
*
* Even if handover process tries to prevent a congestion, a cell might get
* congested due to new call setups or handovers to prevent loss of radio link.
* A cell is congested, if not the minimum number of free slots are available.
* The minimum number can be defined for TCH/F and TCH/H individually.
*
* Do not perform congestion check, if no minimum free slots are defined for
* a cell.
* Do not trigger handover/assignment on slots which have already ongoing
* handover/assignment processes. If no AFS improvement offset is given, try to
* maintain the same TCH rate, if available.
* Do not perform this process, if handover and assignment are disabled for
* the current cell.
* Do not perform handover, if the minimum acceptable RX level
* is not reached for this cell.
* Only check candidates that will solve/reduce congestion.
*
* If a cell is congested, all slots are checked for all their RX levels
* (down-link) of the current and neighbor cell measurements in descending
* order of their RX levels:
*
* * Select the best candidate that fulfills requirement B (no congestion after
* handover/assignment), trigger handover or assignment. Candidates that will
* cause an assignment from AHS (AMR on TCH/H) to AFS (AMR on TCH/F) are
* omitted.
* o This process repeated until the minimum required number of free slots
* are restored or if all cell measurements are checked. The process ends
* then, otherwise:
* * Select the worst candidate that fulfills requirement B, trigger
* assignment. Note that only assignment candidates for changing from AHS to
* AFS are left.
* o This process repeated until the minimum required number of free slots
* are restored or if all cell measurements are checked. The process ends
* then, otherwise:
* * Select the best candidates that fulfill requirement C (less or equally
* congested cells after handover/assignment), trigger handover or
* assignment. Candidates that will cause an assignment from AHS (AMR on
* TCH/H) to AFS (AMR on TCH/F) are omitted.
* o This process repeated until the minimum required number of free slots
* are restored or if all cell measurements are checked. The process ends
* then, otherwise:
* * Select the worst candidate that fulfills requirement C, trigger
* assignment. Note that only assignment candidates for changing from AHS to
* AFS are left.
* o This process repeated until the minimum required number of free slots
* are restored or if all cell measurements are checked.
*/
static int bts_resolve_congestion(struct gsm_bts *bts, int tchf_congestion, int tchh_congestion)
{
struct gsm_lchan *lc;
struct gsm_bts_trx *trx;
struct gsm_bts_trx_ts *ts;
int i, j;
struct ho_candidate *clist;
unsigned int candidates;
struct ho_candidate *best_cand = NULL;
int rc = 0;
int any_ho = 0;
if (tchf_congestion < 0)
tchf_congestion = 0;
if (tchh_congestion < 0)
tchh_congestion = 0;
LOGPHOBTS(bts, LOGL_INFO, "congested: %d TCH/F and %d TCH/H should be moved\n",
tchf_congestion, tchh_congestion);
/* allocate array of all bts */
clist = talloc_zero_array(tall_bsc_ctx, struct ho_candidate,
bts->num_trx * 8 * 2 * (1 + ARRAY_SIZE(lc->neigh_meas)));
if (!clist)
return 0;
candidates = 0;
/* loop through all active lchan and collect candidates */
llist_for_each_entry(trx, &bts->trx_list, list) {
if (!trx_is_usable(trx))
continue;
for (i = 0; i < 8; i++) {
ts = &trx->ts[i];
if (!ts_is_usable(ts))
continue;
/* (Do not consider dynamic TS that are in PDCH mode) */
switch (ts->pchan_is) {
case GSM_PCHAN_TCH_F:
/* No need to collect TCH/F candidates if no TCH/F needs to be moved. */
if (tchf_congestion == 0)
continue;
lc = &ts->lchan[0];
/* omit if channel not active */
if (lc->type != GSM_LCHAN_TCH_F
|| !lchan_state_is(lc, LCHAN_ST_ESTABLISHED))
break;
/* omit if there is an ongoing ho/as */
if (!lc->conn || lc->conn->assignment.new_lchan
|| lc->conn->ho.fi)
break;
/* We desperately want to resolve congestion, ignore rxlev when
* collecting candidates by passing include_weaker_rxlev=true. */
collect_candidates_for_lchan(lc, clist, &candidates, NULL, true);
break;
case GSM_PCHAN_TCH_H:
/* No need to collect TCH/H candidates if no TCH/H needs to be moved. */
if (tchh_congestion == 0)
continue;
for (j = 0; j < 2; j++) {
lc = &ts->lchan[j];
/* omit if channel not active */
if (lc->type != GSM_LCHAN_TCH_H
|| !lchan_state_is(lc, LCHAN_ST_ESTABLISHED))
continue;
/* omit of there is an ongoing ho/as */
if (!lc->conn
|| lc->conn->assignment.new_lchan
|| lc->conn->ho.fi)
continue;
/* We desperately want to resolve congestion, ignore rxlev when
* collecting candidates by passing include_weaker_rxlev=true. */
collect_candidates_for_lchan(lc, clist, &candidates, NULL, true);
}
break;
default:
break;
}
}
}
if (!candidates) {
LOGPHOBTS(bts, LOGL_DEBUG, "No neighbor cells qualify to solve congestion\n");
goto exit;
}
if (log_check_level(DHODEC, LOGL_DEBUG)) {
LOGPHOBTS(bts, LOGL_DEBUG, "Considering %u candidates to solve congestion:\n", candidates);
for (i = 0; i < candidates; i++) {
LOGPHOCAND(&clist[i], LOGL_DEBUG, "#%d: req={TCH/F:" REQUIREMENTS_FMT ", TCH/H:" REQUIREMENTS_FMT "} avg-rxlev=%d dBm\n",
i, REQUIREMENTS_ARGS(clist[i].requirements, F),
REQUIREMENTS_ARGS(clist[i].requirements, H),
rxlev2dbm(clist[i].target.rxlev));
}
}
#if 0
next_b1:
#endif
/* select best candidate that does not cause congestion in the target.
* Do not resolve congestion towards remote BSS, which would cause oscillation if the remote BSS is also
* congested.
* Treating specially below: upgrading TCH/H to TCH/F within the same cell, so omit here.
*/
/* TODO: attempt inter-BSC HO if no local cells qualify, and rely on the remote BSS to
* deny receiving the handover if it also considers itself congested. Maybe do that only
* when the cell is absolutely full, i.e. not only min-free-slots. (x) */
best_cand = pick_best_candidate(clist, candidates, REQUIREMENT_B_MASK);
if (best_cand) {
any_ho = 1;
LOGPHOCAND(best_cand, LOGL_DEBUG, "Best candidate: RX level %d%s\n",
rxlev2dbm(best_cand->target.rxlev),
best_cand->target.rxlev_afs_bias ? " (applied AHS->AFS bias)" : "");
trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_B_MASK);
#if 0
/* if there is still congestion, mark lchan as deleted
* and redo this process */
if (best_cand->lchan->type == GSM_LCHAN_TCH_H)
tchh_congestion--;
else
tchf_congestion--;
if (tchf_congestion > 0 || tchh_congestion > 0) {
delete_lchan = best_cand->lchan;
best_cand = NULL;
goto next_b1;
}
#else
/* must exit here, because triggering handover/assignment
* will cause change in requirements. more check for this
* bts is performed in the next iteration.
*/
#endif
goto exit;
}
#if 0
next_c1:
#endif
/* Select best candidate that balances congestion.
* Again no remote BSS.
* Again no TCH/H -> F upgrades within the same cell. */
best_cand = pick_best_candidate(clist, candidates, REQUIREMENT_C_MASK);
if (best_cand) {
any_ho = 1;
LOGPHOCAND(best_cand, LOGL_INFO, "Best candidate: RX level %d%s\n",
rxlev2dbm(best_cand->target.rxlev),
best_cand->target.rxlev_afs_bias ? " (applied AHS -> AFS rxlev bias)" : "");
trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_C_MASK);
#if 0
/* if there is still congestion, mark lchan as deleted
* and redo this process */
if (best_cand->lchan->type == GSM_LCHAN_TCH_H)
tchh_congestion--;
else
tchf_congestion--;
if (tchf_congestion > 0 || tchh_congestion > 0) {
delete_lchan = best_cand->lchan;
best_cand = NULL;
goto next_c1;
}
#else
/* must exit here, because triggering handover/assignment
* will cause change in requirements. more check for this
* bts is performed in the next iteration.
*/
#endif
goto exit;
}
LOGPHOBTS(bts, LOGL_DEBUG, "Did not find a best candidate that fulfills requirement C\n");
exit:
/* free array */
talloc_free(clist);
if (tchf_congestion <= 0 && tchh_congestion <= 0)
LOGP(DHODEC, LOGL_INFO, "Congestion at BTS %d solved!\n",
bts->nr);
else if (any_ho)
LOGP(DHODEC, LOGL_INFO, "Congestion at BTS %d reduced!\n",
bts->nr);
else
LOGP(DHODEC, LOGL_INFO, "Congestion at BTS %d can't be reduced/solved!\n", bts->nr);
return rc;
}
static void bts_congestion_check(struct gsm_bts *bts)
{
struct chan_counts *bts_counts;
int min_free_tchf, min_free_tchh;
int free_tchf, free_tchh;
global_ho_reason = HO_REASON_CONGESTION;
/* only check BTS if TRX 0 is usable */
if (!trx_is_usable(bts->c0)) {
LOGPHOBTS(bts, LOGL_DEBUG, "No congestion check: TRX 0 not usable\n");
return;
}
/* only check BTS if handover or assignment is enabled */
if (!ho_get_hodec2_as_active(bts->ho)
&& !ho_get_ho_active(bts->ho)) {
LOGPHOBTS(bts, LOGL_DEBUG, "No congestion check: Assignment and Handover both disabled\n");
return;
}
min_free_tchf = ho_get_hodec2_tchf_min_slots(bts->ho);
min_free_tchh = ho_get_hodec2_tchh_min_slots(bts->ho);
/* only check BTS with congestion level set */
if (!min_free_tchf && !min_free_tchh) {
LOGPHOBTS(bts, LOGL_DEBUG, "No congestion check: no minimum for free TCH/F nor TCH/H set\n");
return;
}
bts_counts = &bts->chan_counts;
free_tchf = bts_counts->val[CHAN_COUNTS1_ALL][CHAN_COUNTS2_FREE][GSM_LCHAN_TCH_F];
free_tchh = bts_counts->val[CHAN_COUNTS1_ALL][CHAN_COUNTS2_FREE][GSM_LCHAN_TCH_H];
LOGPHOBTS(bts, LOGL_INFO, "Congestion check: (free/want-free) TCH/F=%d/%d TCH/H=%d/%d\n",
free_tchf, min_free_tchf, free_tchh, min_free_tchh);
/* only check BTS if congested */
if (free_tchf >= min_free_tchf && free_tchh >= min_free_tchh) {
LOGPHOBTS(bts, LOGL_DEBUG, "Not congested\n");
return;
}
LOGPHOBTS(bts, LOGL_DEBUG, "Attempting to resolve congestion...\n");
bts_resolve_congestion(bts, min_free_tchf - free_tchf, min_free_tchh - free_tchh);
}
void hodec2_congestion_check(struct gsm_network *net)
{
struct gsm_bts *bts;
llist_for_each_entry(bts, &net->bts_list, list)
bts_congestion_check(bts);
}
static void congestion_check_cb(void *arg)
{
struct gsm_network *net = arg;
hodec2_congestion_check(net);
reinit_congestion_timer(net);
}
static void on_handover_end(struct gsm_subscriber_connection *conn, enum handover_result result)
{
struct gsm_bts *old_bts = NULL;
int penalty;
struct handover *ho = &conn->ho;
/* If all went fine, then there are no penalty timers to set. */
if (result == HO_RESULT_OK)
return;
if (conn->lchan)
old_bts = conn->lchan->ts->trx->bts;
/* Only interested in handovers within this BSS or going out into another BSS. Incoming handovers
* from another BSS are accounted for in the other BSS. */
if (!old_bts)
return;
if (conn->hodec2.failures < ho_get_hodec2_retries(old_bts->ho)) {
conn->hodec2.failures++;
LOG_HO(conn, LOGL_NOTICE, "Failed, allowing handover decision to try again"
" (%d/%d attempts)\n",
conn->hodec2.failures, ho_get_hodec2_retries(old_bts->ho));
return;
}
switch (ho->scope) {
case HO_INTRA_CELL:
penalty = ho_get_hodec2_penalty_failed_as(old_bts->ho);
break;
default:
/* TODO: separate penalty for inter-BSC HO? */
penalty = ho_get_hodec2_penalty_failed_ho(old_bts->ho);
break;
}
LOG_HO(conn, LOGL_NOTICE, "Failed, starting penalty timer (%d s)\n", penalty);
conn->hodec2.failures = 0;
penalty_timers_add_list(conn, &conn->hodec2.penalty_timers, &ho->target_cell_ids, penalty);
}
static struct handover_decision_callbacks hodec2_callbacks = {
.hodec_id = 2,
.on_measurement_report = on_measurement_report,
.on_handover_end = on_handover_end,
};
void hodec2_init(struct gsm_network *net)
{
handover_decision_callbacks_register(&hodec2_callbacks);
hodec2_initialized = true;
reinit_congestion_timer(net);
}