diff options
| -rw-r--r-- | src/osmo-bsc/handover_decision_2.c | 213 |
1 files changed, 185 insertions, 28 deletions
diff --git a/src/osmo-bsc/handover_decision_2.c b/src/osmo-bsc/handover_decision_2.c index 457d57ae6..a8fff6319 100644 --- a/src/osmo-bsc/handover_decision_2.c +++ b/src/osmo-bsc/handover_decision_2.c @@ -98,8 +98,9 @@ struct ho_candidate { struct gsm_lchan *lchan; /* candidate for whom */ + struct neighbor_ident_key nik; /* neighbor ARFCN+BSIC */ struct gsm_bts *bts; /* target BTS in local BSS */ - struct gsm0808_cell_id_list2 *cil; /* target cells in remote BSS */ + const struct gsm0808_cell_id_list2 *cil; /* target cells in remote BSS */ uint8_t requirements; /* what is fulfilled */ int avg; /* average RX level */ }; @@ -619,6 +620,75 @@ static uint8_t check_requirements(struct gsm_lchan *lchan, struct gsm_bts *bts, return requirement; } +static uint8_t check_requirements_remote_bss(struct gsm_lchan *lchan, + const struct gsm0808_cell_id_list2 *cil) +{ + uint8_t requirement = 0; + unsigned int penalty_time; + + /* Requirement A */ + + /* the handover penalty timer must not run for this bts */ + penalty_time = conn_penalty_time_remaining(lchan->conn, cil); + if (penalty_time) { + LOGPHOLCHANTOREMOTE(lchan, cil, LOGL_DEBUG, + "not a candidate, target BSS still in penalty time" + " (%u seconds left)\n", penalty_time); + return 0; + } + + /* 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 (lchan->tch_mode) { + case GSM48_CMODE_SPEECH_V1: + switch (lchan->type) { + case GSM_LCHAN_TCH_F: /* mandatory */ + requirement |= REQUIREMENT_A_TCHF; + break; + case GSM_LCHAN_TCH_H: + if (codec_type_is_supported(lchan->conn, GSM0808_SCT_HR1)) + requirement |= REQUIREMENT_A_TCHH; + break; + default: + LOGPHOLCHAN(lchan, LOGL_ERROR, "Unexpected channel type: neither TCH/F nor TCH/H for %s\n", + get_value_string(gsm48_chan_mode_names, lchan->tch_mode)); + return 0; + } + break; + case GSM48_CMODE_SPEECH_EFR: + if (codec_type_is_supported(lchan->conn, GSM0808_SCT_FR2)) + requirement |= REQUIREMENT_A_TCHF; + break; + case GSM48_CMODE_SPEECH_AMR: + if (codec_type_is_supported(lchan->conn, GSM0808_SCT_FR3)) + requirement |= REQUIREMENT_A_TCHF; + if (codec_type_is_supported(lchan->conn, GSM0808_SCT_HR3)) + requirement |= REQUIREMENT_A_TCHH; + break; + default: + LOGPHOLCHAN(lchan, LOGL_DEBUG, "Not even considering: src is not a SPEECH mode lchan\n"); + /* FIXME: should allow handover of non-speech lchans */ + return 0; + } + + if (!requirement) { + LOGPHOLCHAN(lchan, LOGL_ERROR, "lchan doesn't fit its own requirements??\n"); + return 0; + } + + /* 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 */ + return requirement; +} + /* Trigger handover or assignment depending on the target BTS */ static int trigger_local_ho_or_as(struct ho_candidate *c, uint8_t requirements) { @@ -701,12 +771,29 @@ static int trigger_local_ho_or_as(struct ho_candidate *c, uint8_t requirements) return 0; } +static int trigger_remote_bss_ho(struct ho_candidate *c, uint8_t requirements) +{ + struct handover_out_req req; + + LOGPHOLCHANTOREMOTE(c->lchan, c->cil, 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->lchan, + .target_nik = c->nik, + }; + handover_request(&req); + return 0; +} + static int trigger_ho(struct ho_candidate *c, uint8_t requirements) { if (c->bts) return trigger_local_ho_or_as(c, requirements); else - return 0; /* TODO: remote candidates */ + return trigger_remote_bss_ho(c, requirements); } /* verbosely log about a handover candidate */ @@ -730,6 +817,16 @@ static inline void debug_candidate(struct ho_candidate *candidate, /* now has to be candidate->requirements & REQUIREMENT_C_TCHX != 0: */ \ " less-or-equal congestion")) + if (!candidate->bts && !candidate->cil) + LOGPHOLCHAN(lchan, LOGL_DEBUG, "Empty candidate\n"); + if (candidate->bts && candidate->cil) + LOGPHOLCHAN(lchan, LOGL_ERROR, "Invalid candidate: both local- and remote-BSS target\n"); + + if (candidate->cil) + LOGPHOLCHANTOREMOTE(lchan, candidate->cil, LOGL_DEBUG, + "RX level %d -> %d\n", + rxlev2dbm(rxlev), rxlev2dbm(candidate->avg)); + if (candidate->bts == lchan->ts->trx->bts) LOGPHOLCHANTOBTS(lchan, candidate->bts, LOGL_DEBUG, "RX level %d; " @@ -750,17 +847,20 @@ static void collect_assignment_candidate(struct gsm_lchan *lchan, struct ho_cand { struct gsm_bts *bts = lchan->ts->trx->bts; int tchf_count, tchh_count; - struct ho_candidate *c; + struct ho_candidate c; tchf_count = bts_count_free_ts(bts, GSM_PCHAN_TCH_F); tchh_count = bts_count_free_ts(bts, GSM_PCHAN_TCH_H); - c = &clist[*candidates]; - c->lchan = lchan; - c->bts = bts; - c->requirements = check_requirements(lchan, bts, tchf_count, tchh_count); - c->avg = av_rxlev; - debug_candidate(c, 0, tchf_count, tchh_count); + c = (struct ho_candidate){ + .lchan = lchan, + .bts = bts, + .requirements = check_requirements(lchan, bts, tchf_count, tchh_count), + .avg = av_rxlev, + }; + + debug_candidate(&c, 0, tchf_count, tchh_count); + clist[*candidates] = c; (*candidates)++; } @@ -771,7 +871,8 @@ static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_mea int *neighbors_count) { struct gsm_bts *bts = lchan->ts->trx->bts; - int tchf_count, tchh_count; + int tchf_count = 0; + int tchh_count = 0; struct gsm_bts *neighbor_bts; const struct gsm0808_cell_id_list2 *neighbor_cil; struct neighbor_ident_key ni = { @@ -782,6 +883,7 @@ static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_mea int avg; struct ho_candidate c; int min_rxlev; + struct handover_cfg *neigh_cfg; /* skip empty slots */ if (nmp->arfcn == 0) @@ -799,15 +901,19 @@ static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_mea } neighbor_bts = bts_by_neighbor_ident(bts->network, &ni); - if (!neighbor_bts) { - neighbor_cil = neighbor_ident_get(bts->network->neighbor_bss_cells, &ni); - if (neighbor_cil) { - LOGPHOBTS(bts, LOGL_ERROR, "would inter-BSC handover to ARFCN %u BSIC %u," - " but inter-BSC handover not implemented for ho decision 2\n", - nmp->arfcn, nmp->bsic); - return; - } + neighbor_cil = neighbor_ident_get(bts->network->neighbor_bss_cells, &ni); + + if (neighbor_bts && neighbor_cil) { + LOGPHOBTS(bts, LOGL_ERROR, "Configuration error: %s exists as both local" + " neighbor (bts %u) and remote-BSS neighbor (%s). Will consider only" + " the local-BSS neighbor.\n", + neighbor_ident_key_name(&ni), + neighbor_bts->nr, gsm0808_cell_id_list_name(neighbor_cil)); + neighbor_cil = NULL; + } + + if (!neighbor_bts && !neighbor_cil) { LOGPHOBTS(bts, LOGL_DEBUG, "no neighbor ARFCN %u BSIC %u configured for this cell\n", nmp->arfcn, nmp->bsic); return; @@ -819,13 +925,19 @@ static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_mea 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; + /* calculate average rxlev for this cell over the window */ avg = neigh_meas_avg(nmp, ho_get_hodec2_rxlev_neigh_avg_win(bts->ho)); c = (struct ho_candidate){ .lchan = lchan, .avg = avg, + .nik = ni, .bts = neighbor_bts, + .cil = neighbor_cil, }; /* Heed rxlev hysteresis only if the RXLEV/RXQUAL/TA levels of the MS aren't critically bad and @@ -842,8 +954,9 @@ static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_mea } } - /* if the minimum level is not reached */ - min_rxlev = ho_get_hodec2_min_rxlev(neighbor_bts->ho); + /* if the minimum level is not reached. + * In case of a remote-BSS, use the current BTS' configuration. */ + min_rxlev = ho_get_hodec2_min_rxlev(neigh_cfg); if (rxlev2dbm(avg) < min_rxlev) { LOGPHOCAND(&c, LOGL_DEBUG, "Not a candidate, because RX level (%d) is lower" @@ -852,9 +965,13 @@ static void collect_handover_candidate(struct gsm_lchan *lchan, struct neigh_mea return; } - tchf_count = bts_count_free_ts(neighbor_bts, GSM_PCHAN_TCH_F); - tchh_count = bts_count_free_ts(neighbor_bts, GSM_PCHAN_TCH_H); - c.requirements = check_requirements(lchan, neighbor_bts, tchf_count, tchh_count); + if (neighbor_bts) { + tchf_count = bts_count_free_ts(neighbor_bts, GSM_PCHAN_TCH_F); + tchh_count = bts_count_free_ts(neighbor_bts, GSM_PCHAN_TCH_H); + c.requirements = check_requirements(lchan, neighbor_bts, tchf_count, + tchh_count); + } else + c.requirements = check_requirements_remote_bss(lchan, neighbor_cil); debug_candidate(&c, av_rxlev, tchf_count, tchh_count); @@ -988,13 +1105,19 @@ static int find_alternative_lchan(struct gsm_lchan *lchan, bool include_weaker_r return 0; } - /* select best candidate that fulfills requirement B: no congestion after HO */ + /* 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].bts) + continue; + better = clist[i].avg - av_rxlev; /* Apply AFS bias? */ afs_bias = 0; @@ -1016,13 +1139,18 @@ static int find_alternative_lchan(struct gsm_lchan *lchan, bool include_weaker_r return trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_B_MASK); } - /* select best candidate that fulfills requirement C: less or equal congestion after HO */ + /* 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].bts) + continue; + better = clist[i].avg - av_rxlev; /* Apply AFS bias? */ afs_bias = 0; @@ -1052,7 +1180,8 @@ static int find_alternative_lchan(struct gsm_lchan *lchan, bool include_weaker_r /* 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. */ + * *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; @@ -1060,9 +1189,11 @@ static int find_alternative_lchan(struct gsm_lchan *lchan, bool include_weaker_r continue; better = clist[i].avg - av_rxlev; - /* Apply AFS bias? */ + /* Apply AFS bias? + * (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)) + if (ahs && (clist[i].requirements & REQUIREMENT_A_TCHF) + && clist[i].bts) afs_bias = ho_get_hodec2_afs_bias_rxlev(clist[i].bts->ho); better += afs_bias; if (better > best_better_db) { @@ -1385,6 +1516,14 @@ next_b1: if (!clist[i].lchan) continue; + /* Do not resolve congestion towards remote BSS, which would cause oscillation if the + * remote BSS is also congested. */ + /* 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) */ + if (!clist[i].bts) + continue; + if (!(clist[i].requirements & REQUIREMENT_B_MASK)) continue; /* omit assignment from AHS to AFS */ @@ -1462,6 +1601,12 @@ next_b2: if (!clist[i].lchan) continue; + /* Do not resolve congestion towards remote BSS, which would cause oscillation if + * the remote BSS is also congested. */ + /* TODO: see (x) above */ + if (!clist[i].bts) + continue; + if (!(clist[i].requirements & REQUIREMENT_B_MASK)) continue; /* omit all but assignment from AHS to AFS */ @@ -1524,6 +1669,12 @@ next_c1: if (!clist[i].lchan) continue; + /* Do not resolve congestion towards remote BSS, which would cause oscillation if + * the remote BSS is also congested. */ + /* TODO: see (x) above */ + if (!clist[i].bts) + continue; + if (!(clist[i].requirements & REQUIREMENT_C_MASK)) continue; /* omit assignment from AHS to AFS */ @@ -1602,6 +1753,12 @@ next_c2: if (!clist[i].lchan) continue; + /* Do not resolve congestion towards remote BSS, which would cause oscillation if + * the remote BSS is also congested. */ + /* TODO: see (x) above */ + if (!clist[i].bts) + continue; + if (!(clist[i].requirements & REQUIREMENT_C_MASK)) continue; /* omit all but assignment from AHS to AFS */ |