neels has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-hnbgw/+/33136 )

Change subject: cnpool: select CN link from pool by NRI or round robin ......................................................................

cnpool: select CN link from pool by NRI or round robin

This is the bulk of the CN pooling logic but is not working properly without these future patches:

- detect in/active CN links by RANAP RESET Id3eefdea889a736fd5957b80280fa45b9547b792

- return Paging Resp to the exact CN link that Paged I907dbcaeb442ca5630146f8cad40601c448fc40e

Change-Id: I66fba27cfbe6e2b27ee3443718846ecfbbd8a974 --- M src/osmo-hnbgw/hnbgw_cn.c 1 file changed, 162 insertions(+), 10 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/osmo-hnbgw refs/changes/36/33136/1

diff --git a/src/osmo-hnbgw/hnbgw_cn.c b/src/osmo-hnbgw/hnbgw_cn.c index 486d30a..f33023e 100644 --- a/src/osmo-hnbgw/hnbgw_cn.c +++ b/src/osmo-hnbgw/hnbgw_cn.c @@ -702,21 +702,155 @@ return NULL; }

+static bool is_cnlink_usable(struct hnbgw_cnlink *cnlink, bool is_emerg) +{ + if (is_emerg && !cnlink->allow_emerg) + return false; + if (!cnlink->hnbgw_sccp_user || !cnlink->hnbgw_sccp_user->sccp_user) + return false; + // TODO indicator whether the CN link is actually active, akin to bssmap_reset_is_conn_ready() + return true; +} + +/* Decide which MSC/SGSN to forward this Complete Layer 3 request to. The current Layer 3 Info is passed in map->l3. + * a) If the subscriber was previously paged from a particular CN link, that CN link shall receive the Paging Response. + * b) If the message contains an NRI indicating a particular CN link that is currently connected, that CN link shall + * handle this conn. + * c) All other cases distribute the messages across connected CN links in a round-robin fashion. + */ struct hnbgw_cnlink *hnbgw_cnlink_select(struct hnbgw_context_map *map) { struct hnbgw_cnpool *cnpool = map->is_ps ? &g_hnbgw->sccp.cnpool_iups : &g_hnbgw->sccp.cnpool_iucs; struct hnbgw_cnlink *cnlink; - /* FUTURE: soon we will pick one of many configurable CN peers from a pool. There will be more input arguments - * (MI, or TMSI, or NRI decoded from RANAP) and this function will do round robin for new subscribers. */ - llist_for_each_entry(cnlink, &cnpool->cnlinks, entry) { - if (!cnlink->hnbgw_sccp_user || !cnlink->hnbgw_sccp_user->sccp_user) - continue; - LOG_MAP(map, DCN, LOGL_INFO, "Selected %s / %s\n", - cnlink->name, - cnlink->hnbgw_sccp_user->name); - return cnlink; + struct hnbgw_cnlink *round_robin_next = NULL; + struct hnbgw_cnlink *round_robin_first = NULL; + unsigned int round_robin_next_nr; + int16_t nri_v = -1; + bool is_null_nri = false; + uint8_t nri_bitlen = cnpool->use.nri_bitlen; + +#define LOG_NRI(LOGLEVEL, FORMAT, ARGS...) \ + LOG_MAP(map, DCN, LOGLEVEL, "%s NRI(%dbit)=0x%x=%d: " FORMAT, osmo_mobile_identity_to_str_c(OTC_SELECT, &map->l3.mi), \ + nri_bitlen, nri_v, nri_v, ##ARGS) + + /* Get the NRI bits either from map->l3.nri, or extract NRI bits from TMSI. + * The NRI possibly indicates which MSC is responsible. */ + if (map->l3.gmm_nri_container >= 0) { + nri_v = map->l3.gmm_nri_container; + /* The 'TMSI based NRI container' is always 10 bits long. If the relevant NRI length is configured to be + * less than that, ignore the lower bits. */ + if (nri_bitlen < 10) + nri_v >>= 10 - nri_bitlen; + } else if (map->l3.mi.type == GSM_MI_TYPE_TMSI) { + if (osmo_tmsi_nri_v_get(&nri_v, map->l3.mi.tmsi, nri_bitlen)) { + LOG_NRI(LOGL_ERROR, "Unable to retrieve NRI from TMSI 0x%x, nri_bitlen == %u\n", map->l3.mi.tmsi, + nri_bitlen); + nri_v = -1; + } } - return NULL; + + if (map->l3.from_other_plmn && nri_v >= 0) { + /* If a subscriber was previously attached to a different PLMN, it might still send the other + * PLMN's TMSI identity in an IMSI Attach. The LU sends a LAI indicating the previous PLMN. If + * it mismatches our PLMN, ignore the NRI. */ + LOG_NRI(LOGL_DEBUG, + "This Complete Layer 3 message indicates a switch from another PLMN. Ignoring the NRI.\n"); + nri_v = -1; + } + + if (nri_v >= 0) + is_null_nri = osmo_nri_v_matches_ranges(nri_v, cnpool->use.null_nri_ranges); + if (is_null_nri) + LOG_NRI(LOGL_DEBUG, "this is a NULL-NRI\n"); + + /* Iterate CN links to find one that matches the extracted NRI, and the next round-robin target for the case no + * NRI match is found. */ + round_robin_next_nr = (map->l3.is_emerg ? cnpool->round_robin_next_emerg_nr : cnpool->round_robin_next_nr); + llist_for_each_entry(cnlink, &cnpool->cnlinks, entry) { + bool nri_matches_cnlink = (nri_v >= 0 && osmo_nri_v_matches_ranges(nri_v, cnlink->use.nri_ranges)); + + if (!is_cnlink_usable(cnlink, map->l3.is_emerg)) { + if (nri_matches_cnlink) { + LOG_NRI(LOGL_DEBUG, "NRI matches %s %d, but this %s is currently not connected\n", + cnpool->peer_name, cnlink->nr, cnpool->peer_name); + rate_ctr_inc(rate_ctr_group_get_ctr(cnlink->ctrs, CNLINK_CTR_CNPOOL_SUBSCR_ATTACH_LOST)); + } + continue; + } + + /* Return CN link if it matches this NRI, with some debug logging. */ + if (nri_matches_cnlink) { + if (is_null_nri) { + LOG_NRI(LOGL_DEBUG, "NRI matches %s %d, but this NRI is also configured as NULL-NRI\n", + cnpool->peer_name, cnlink->nr); + } else { + LOG_NRI(LOGL_INFO, "NRI match selects %s %d\n", cnpool->peer_name, cnlink->nr); + rate_ctr_inc(rate_ctr_group_get_ctr(cnlink->ctrs, CNLINK_CTR_CNPOOL_SUBSCR_KNOWN)); + if (map->l3.is_emerg) { + rate_ctr_inc(rate_ctr_group_get_ctr(cnlink->ctrs, CNLINK_CTR_CNPOOL_EMERG_FORWARDED)); + rate_ctr_inc(rate_ctr_group_get_ctr(cnpool->ctrs, CNPOOL_CTR_EMERG_FORWARDED)); + } + return cnlink; + } + } + + /* Figure out the next round-robin MSC. The MSCs may appear unsorted in net->mscs. Make sure to linearly + * round robin the MSCs by number: pick the lowest msc->nr >= round_robin_next_nr, and also remember the + * lowest available msc->nr to wrap back to that in case no next MSC is left. + * + * MSCs configured with `no allow-attach` do not accept new subscribers and hence must not be picked by + * round-robin. Such an MSC still provides service for already attached subscribers: those that + * successfully performed IMSI-Attach and have a TMSI with an NRI pointing at that MSC. We only avoid + * adding IMSI-Attach of new subscribers. The idea is that the MSC is in a mode of off-loading + * subscribers, and the MSC decides when each subscriber is off-loaded, by assigning the NULL-NRI in a + * new TMSI (at the next periodical LU). So until the MSC decides to offload, an attached subscriber + * remains attached to that MSC and is free to use its services. + */ + if (!cnlink->allow_attach) + continue; + /* Find the allowed cnlink with the lowest nr */ + if (!round_robin_first || cnlink->nr < round_robin_first->nr) + round_robin_first = cnlink; + /* Find the allowed cnlink with the lowest nr >= round_robin_next_nr */ + if (cnlink->nr >= round_robin_next_nr + && (!round_robin_next || cnlink->nr < round_robin_next->nr)) + round_robin_next = cnlink; + } + + if (nri_v >= 0 && !is_null_nri) + LOG_NRI(LOGL_DEBUG, "No %s found for this NRI, doing round-robin\n", cnpool->peer_name); + + /* No dedicated CN link found. Choose by round-robin. + * If round_robin_next is NULL, there are either no more CN links at/after round_robin_next_nr, or none of + * them are usable -- wrap to the start. */ + cnlink = round_robin_next ? : round_robin_first; + if (!cnlink) { + rate_ctr_inc(rate_ctr_group_get_ctr(cnpool->ctrs, CNPOOL_CTR_SUBSCR_NO_CNLINK)); + if (map->l3.is_emerg) + rate_ctr_inc(rate_ctr_group_get_ctr(cnpool->ctrs, CNPOOL_CTR_EMERG_LOST)); + return NULL; + } + + LOGP(DCN, LOGL_DEBUG, "New subscriber MI=%s: CN link round-robin selects %s %d\n", + osmo_mobile_identity_to_str_c(OTC_SELECT, &map->l3.mi), cnpool->peer_name, cnlink->nr); + + if (is_null_nri) + rate_ctr_inc(rate_ctr_group_get_ctr(cnlink->ctrs, CNLINK_CTR_CNPOOL_SUBSCR_REATTACH)); + else + rate_ctr_inc(rate_ctr_group_get_ctr(cnlink->ctrs, CNLINK_CTR_CNPOOL_SUBSCR_NEW)); + + if (map->l3.is_emerg) { + rate_ctr_inc(rate_ctr_group_get_ctr(cnlink->ctrs, CNLINK_CTR_CNPOOL_EMERG_FORWARDED)); + rate_ctr_inc(rate_ctr_group_get_ctr(cnpool->ctrs, CNPOOL_CTR_EMERG_FORWARDED)); + } + + /* A CN link was picked by round-robin, so update the next round-robin nr to pick */ + if (map->l3.is_emerg) + cnpool->round_robin_next_emerg_nr = cnlink->nr + 1; + else + cnpool->round_robin_next_nr = cnlink->nr + 1; + return cnlink; +#undef LOG_NRI }

char *cnlink_sccp_addr_to_str(struct hnbgw_cnlink *cnlink, const struct osmo_sccp_addr *addr)