neels has uploaded this change for review.
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)
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