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MSC pooling: implement NAS node selection by NRI from TMSI 

If applicable, choose MSC from NRI, extracted from TMSI MI.

Change-Id: Ifbdea197b26e88751a391c8a80c41f04e7d5e047
This commit is contained in:
Neels Hofmeyr 2020-05-26 16:53:44 +02:00
parent 4099f1db50
commit 2a366d9c25
1 changed files with 43 additions and 4 deletions
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47
src/osmo-bsc/gsm_08_08.c
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@ -33,6 +33,7 @@
#include <osmocom/gsm/gsm0808.h>
#include <osmocom/gsm/mncc.h>
#include <osmocom/gsm/gsm48.h>
#include <osmocom/gsm/gsm23236.h>
#include <osmocom/bsc/osmo_bsc_sigtran.h>
@ -152,6 +153,8 @@ static struct bsc_msc_data *bsc_find_msc(struct gsm_subscriber_connection *conn,
uint8_t round_robin_next_nr;
struct bsc_subscr *subscr;
bool is_emerg = false;
int16_t nri_v = -1;
bool is_null_nri = false;
if (msgb_l3len(msg) < sizeof(*gh)) {
LOGP(DRSL, LOGL_ERROR, "There is no GSM48 header here.\n");
@ -186,16 +189,45 @@ static struct bsc_msc_data *bsc_find_msc(struct gsm_subscriber_connection *conn,
}
}
/* TODO: extract NRI from MI */
#define LOG_NRI(LOGLEVEL, FORMAT, ARGS...) \
LOGP(DMSC, LOGLEVEL, "%s NRI(%d)=0x%x=%d: " FORMAT, osmo_mobile_identity_to_str_c(OTC_SELECT, &mi), \
net->nri_bitlen, nri_v, nri_v, ##ARGS)
/* Extract NRI bits from TMSI, possibly indicating which MSC is responsible */
if (mi.type == GSM_MI_TYPE_TMSI) {
if (osmo_tmsi_nri_v_get(&nri_v, mi.tmsi, net->nri_bitlen)) {
LOGP(DMSC, LOGL_ERROR, "Unable to retrieve NRI from TMSI, nri_bitlen == %u\n", net->nri_bitlen);
nri_v = -1;
} else {
is_null_nri = osmo_nri_v_matches_ranges(nri_v, net->null_nri_ranges);
if (is_null_nri)
LOG_NRI(LOGL_DEBUG, "this is a NULL-NRI\n");
}
}
/* Iterate MSCs 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 = (is_emerg ? net->mscs_round_robin_next_emerg_nr : net->mscs_round_robin_next_nr);
llist_for_each_entry(msc, &net->mscs, entry) {
if (!is_msc_usable(msc, is_emerg))
continue;
bool nri_matches_msc = (nri_v >= 0 && osmo_nri_v_matches_ranges(nri_v, msc->nri_ranges));
/* TODO: return msc when extracted NRI matches this MSC */
if (!is_msc_usable(msc, is_emerg)) {
if (nri_matches_msc)
LOG_NRI(LOGL_DEBUG, "matches msc %d, but this MSC is currently not connected\n",
msc->nr);
continue;
}
/* Return MSC if it matches this NRI, with some debug logging. */
if (nri_matches_msc) {
if (is_null_nri) {
LOG_NRI(LOGL_DEBUG, "matches msc %d, but this NRI is also configured as NULL-NRI\n",
msc->nr);
} else {
LOG_NRI(LOGL_DEBUG, "matches msc %d\n", msc->nr);
return msc;
}
}
/* 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
@ -207,6 +239,9 @@ static struct bsc_msc_data *bsc_find_msc(struct gsm_subscriber_connection *conn,
msc_round_robin_next = msc;
}
if (nri_v >= 0 && !is_null_nri)
LOG_NRI(LOGL_DEBUG, "No MSC found for this NRI, doing round-robin\n");
/* No dedicated MSC found. Choose by round-robin.
* If msc_round_robin_next is NULL, there are either no more MSCs at/after mscs_round_robin_next_nr, or none of
* them are usable -- wrap to the start. */
@ -217,12 +252,16 @@ static struct bsc_msc_data *bsc_find_msc(struct gsm_subscriber_connection *conn,
return NULL;
}
LOGP(DMSC, LOGL_DEBUG, "New subscriber %s: MSC round-robin selects msc %d\n",
osmo_mobile_identity_to_str_c(OTC_SELECT, &mi), msc_target->nr);
/* An MSC was picked by round-robin, so update the next round-robin nr to pick */
if (is_emerg)
net->mscs_round_robin_next_emerg_nr = msc_target->nr + 1;
else
net->mscs_round_robin_next_nr = msc_target->nr + 1;
return msc_target;
#undef LOG_NRI
}
static int handle_page_resp(struct gsm_subscriber_connection *conn, struct msgb *msg)