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MSC pooling: add 'no allow-attach' for MSC off-loading 

As in 3GPP TS 23.236, to offload an MSC, the BSC must be able to avoid
attaching new subscribers to it:

4.5a.1: "UEs being moved from one CN node are stopped from registering to the
same CN node again by an O&M command in BSCs and RNCs connected to the pool."

Change-Id: I6249201c15d0f6565aca643c21d2375c9ca58584
This commit is contained in:
Neels Hofmeyr 2020-06-11 02:36:29 +02:00
parent 343a8a1a1a
commit b69db82b1c
5 changed files with 55 additions and 1 deletions
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1
include/osmocom/bsc/bsc_msc_data.h
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@ -181,6 +181,7 @@ struct bsc_msc_data {
} mgcp_ipa;
struct osmo_nri_ranges *nri_ranges;
bool allow_attach;
};
int osmo_bsc_msc_init(struct bsc_msc_data *msc);

13
src/osmo-bsc/gsm_08_08.c
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@ -280,7 +280,18 @@ static struct bsc_msc_data *bsc_find_msc(struct gsm_subscriber_connection *conn,
/* 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. */
* 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 (!msc->allow_attach)
continue;
if (!msc_round_robin_first || msc->nr < msc_round_robin_first->nr)
msc_round_robin_first = msc;
if (msc->nr >= round_robin_next_nr

1
src/osmo-bsc/osmo_bsc_msc.c
View File

@ -230,6 +230,7 @@ struct bsc_msc_data *osmo_msc_data_alloc(struct gsm_network *net, int nr)
msc_data->mgcp_ipa.local_port = 0; /* dynamic */
msc_data->nri_ranges = osmo_nri_ranges_alloc(msc_data);
msc_data->allow_attach = true;
return msc_data;
}

27
src/osmo-bsc/osmo_bsc_vty.c
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@ -177,6 +177,9 @@ static void write_msc(struct vty *vty, struct bsc_msc_data *msc)
}
msc_write_nri(vty, msc, false);
if (!msc->allow_attach)
vty_out(vty, " no allow-attach%s", VTY_NEWLINE);
}
static int config_write_msc(struct vty *vty)
@ -860,6 +863,28 @@ DEFUN(cfg_msc_nri_del, cfg_msc_nri_del_cmd,
return CMD_SUCCESS;
}
DEFUN(cfg_msc_allow_attach, cfg_msc_allow_attach_cmd,
"allow-attach",
"Allow this MSC to attach new subscribers (default).\n")
{
struct bsc_msc_data *msc = bsc_msc_data(vty);
msc->allow_attach = true;
return CMD_SUCCESS;
}
DEFUN(cfg_msc_no_allow_attach, cfg_msc_no_allow_attach_cmd,
"no allow-attach",
NO_STR
"Do not assign new subscribers to this MSC."
" Useful if an MSC in an MSC pool is configured to off-load subscribers."
" The MSC will still be operational for already IMSI-Attached subscribers,"
" but the NAS node selection function will skip this MSC for new subscribers\n")
{
struct bsc_msc_data *msc = bsc_msc_data(vty);
msc->allow_attach = false;
return CMD_SUCCESS;
}
static void msc_write_nri(struct vty *vty, struct bsc_msc_data *msc, bool verbose)
{
struct osmo_nri_range *r;
@ -963,6 +988,8 @@ int bsc_vty_init_extra(void)
install_element(MSC_NODE, &cfg_msc_nri_add_cmd);
install_element(MSC_NODE, &cfg_msc_nri_del_cmd);
install_element(MSC_NODE, &cfg_msc_show_nri_cmd);
install_element(MSC_NODE, &cfg_msc_allow_attach_cmd);
install_element(MSC_NODE, &cfg_msc_no_allow_attach_cmd);
/* Deprecated: ping time config, kept to support legacy config files. */
install_element(MSC_NODE, &cfg_net_msc_no_ping_time_cmd);

14
tests/nri_cfg.vty
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@ -150,3 +150,17 @@ OsmoBSC(config-msc)# nri add 1000
OsmoBSC(config-msc)# show nri
msc 0
nri add 0 1000
OsmoBSC(config-msc)# show running-config
... ! no allow-attach
OsmoBSC(config-msc)# no allow-attach
OsmoBSC(config-msc)# show running-config
...
msc 0
...
nri add 0 1000
no allow-attach
... ! no allow-attach
OsmoBSC(config-msc)# allow-attach
OsmoBSC(config-msc)# show running-config
... ! no allow-attach