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support "empty" SCCP N-Connect from MSC 

Teach osmo-bsc to handle empty N-Connect. So far we were always
expecting user data in an SCCP N-Connect from an MSC. However, it is
perfectly valid for an initial BSSMAP request to follow later.

This is relevant for:
- Handover Request (incoming inter-BSC handover)
- Perform Location Request (query physical location of the MS)

Add state WAIT_INITIAL_USER_DATA with new timeout net X25. Always enter
this state so that we don't have two separate code paths for handling
initial user data.

Related: SYS#5864
Change-Id: I535c791fa01e99a2226392eb05f676ba6c3cc16e
This commit is contained in:
Neels Hofmeyr 2022-03-03 01:50:50 +01:00
parent bdead6e87a
commit 908f014f09
5 changed files with 135 additions and 37 deletions
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1
include/osmocom/bsc/bsc_subscr_conn_fsm.h
View File

@ -9,6 +9,7 @@
enum gscon_fsm_event {
/* local SCCP stack tells us incoming conn from MSC */
GSCON_EV_A_CONN_IND,
GSCON_EV_A_INITIAL_USER_DATA,
/* RSL side requests CONNECT to MSC */
GSCON_EV_MO_COMPL_L3,
/* MSC confirms the SCCP connection */

146
src/osmo-bsc/bsc_subscr_conn_fsm.c
View File

@ -60,6 +60,8 @@
enum gscon_fsm_states {
ST_INIT,
/* wait for initial BSSMAP after the MSC opened a new SCCP connection */
ST_WAIT_INITIAL_USER_DATA,
/* waiting for CC from MSC */
ST_WAIT_CC,
/* active connection */
@ -73,6 +75,7 @@ enum gscon_fsm_states {
static const struct value_string gscon_fsm_event_names[] = {
{GSCON_EV_A_CONN_IND, "MT-CONNECT.ind"},
{GSCON_EV_A_INITIAL_USER_DATA, "A_INITIAL_USER_DATA"},
{GSCON_EV_MO_COMPL_L3, "MO_COMPL_L3"},
{GSCON_EV_A_CONN_CFM, "MO-CONNECT.cfm"},
{GSCON_EV_A_CLEAR_CMD, "CLEAR_CMD"},
@ -95,6 +98,7 @@ static const struct value_string gscon_fsm_event_names[] = {
};
struct osmo_tdef_state_timeout conn_fsm_timeouts[32] = {
[ST_WAIT_INITIAL_USER_DATA] = { .T = -25 },
[ST_WAIT_CC] = { .T = -3210 },
[ST_WAIT_CLEAR_CMD] = { .T = -4 },
[ST_WAIT_SCCP_RLSD] = { .T = -4 },
@ -258,23 +262,21 @@ void gscon_release_lchans(struct gsm_subscriber_connection *conn, bool do_rr_rel
gscon_release_lchan(conn, conn->lchan, do_rr_release, false, cause_rr);
}
static void handle_bssap_n_connect(struct osmo_fsm_inst *fi, struct osmo_scu_prim *scu_prim)
static int validate_initial_user_data(struct osmo_fsm_inst *fi, struct msgb *msg)
{
struct gsm_subscriber_connection *conn = fi->priv;
struct msgb *msg = scu_prim->oph.msg;
struct bssmap_header *bs;
uint8_t bssmap_type;
enum BSS_MAP_MSG_TYPE bssmap_type;
msg->l3h = msgb_l2(msg);
if (!msgb_l3(msg)) {
LOGPFSML(fi, LOGL_ERROR, "internal error: no l3 in msg\n");
goto refuse;
return -EINVAL;
}
if (msgb_l3len(msg) < sizeof(*bs)) {
LOGPFSML(fi, LOGL_ERROR, "message too short for BSSMAP header (%u < %zu)\n",
msgb_l3len(msg), sizeof(*bs));
goto refuse;
return -EINVAL;
}
bs = (struct bssmap_header*)msgb_l3(msg);
@ -282,7 +284,7 @@ static void handle_bssap_n_connect(struct osmo_fsm_inst *fi, struct osmo_scu_pri
LOGPFSML(fi, LOGL_ERROR,
"message too short for length indicated in BSSMAP header (%u < %u)\n",
msgb_l3len(msg), bs->length);
goto refuse;
return -EINVAL;
}
switch (bs->type) {
@ -290,36 +292,42 @@ static void handle_bssap_n_connect(struct osmo_fsm_inst *fi, struct osmo_scu_pri
break;
default:
LOGPFSML(fi, LOGL_ERROR,
"message type not allowed for N-CONNECT: %s\n", gsm0808_bssap_name(bs->type));
goto refuse;
"message type not allowed for initial BSSMAP: %s\n", gsm0808_bssap_name(bs->type));
return -EINVAL;
}
msg->l4h = &msg->l3h[sizeof(*bs)];
/* Validate initial message type. See also BSC_Tests.TC_outbound_connect. */
bssmap_type = msg->l4h[0];
LOGPFSML(fi, LOGL_DEBUG, "Rx N-CONNECT: %s: %s\n", gsm0808_bssap_name(bs->type),
gsm0808_bssmap_name(bssmap_type));
switch (bssmap_type) {
case BSS_MAP_MSG_HANDOVER_RQST:
case BSS_MAP_MSG_PERFORM_LOCATION_RQST:
break;
return 0;
default:
LOGPFSML(fi, LOGL_ERROR, "No support for N-CONNECT: %s: %s\n",
LOGPFSML(fi, LOGL_ERROR, "No support for initial BSSMAP: %s: %s\n",
gsm0808_bssap_name(bs->type), gsm0808_bssmap_name(bssmap_type));
goto refuse;
return -EINVAL;
}
}
/* First off, accept the new conn. */
if (osmo_sccp_tx_conn_resp(conn->sccp.msc->a.sccp_user, scu_prim->u.connect.conn_id,
&scu_prim->u.connect.called_addr, NULL, 0)) {
LOGPFSML(fi, LOGL_ERROR, "Cannot send SCCP CONN RESP\n");
goto refuse;
}
static void handle_initial_user_data(struct osmo_fsm_inst *fi, struct msgb *msg)
{
struct gsm_subscriber_connection *conn = fi->priv;
struct bssmap_header *bs;
enum BSS_MAP_MSG_TYPE bssmap_type;
/* Make sure the conn FSM will osmo_sccp_tx_disconn() on term */
conn->sccp.state = SUBSCR_SCCP_ST_CONNECTED;
/* validate_initial_user_data() must be called before this */
OSMO_ASSERT(msgb_l4(msg));
bs = msgb_l3(msg);
bssmap_type = msg->l4h[0];
/* FIXME: Extract optional IMSI and update FSM using osmo_fsm_inst_set_id() (OS#2969) */
LOGPFSML(fi, LOGL_DEBUG, "Rx initial BSSMAP: %s: %s\n", gsm0808_bssap_name(bs->type),
gsm0808_bssmap_name(bssmap_type));
switch (bssmap_type) {
case BSS_MAP_MSG_HANDOVER_RQST:
@ -336,13 +344,51 @@ static void handle_bssap_n_connect(struct osmo_fsm_inst *fi, struct osmo_scu_pri
return;
default:
OSMO_ASSERT(false);
LOGPFSML(fi, LOGL_ERROR, "No support for initial BSSMAP: %s: %s\n",
gsm0808_bssap_name(bs->type), gsm0808_bssmap_name(bssmap_type));
osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
return;
}
}
static void handle_sccp_n_connect(struct osmo_fsm_inst *fi, struct osmo_scu_prim *scu_prim)
{
struct gsm_subscriber_connection *conn = fi->priv;
struct msgb *msg = scu_prim->oph.msg;
/* Make sure the conn FSM will osmo_sccp_tx_disconn() on term */
conn->sccp.state = SUBSCR_SCCP_ST_CONNECTED;
msg->l3h = msgb_l2(msg);
/* If (BSSMAP) user data is included, validate it before accepting the connection */
if (msgb_l3(msg) && msgb_l3len(msg)) {
if (validate_initial_user_data(fi, msg)) {
osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
return;
}
}
refuse:
osmo_sccp_tx_disconn(conn->sccp.msc->a.sccp_user, scu_prim->u.connect.conn_id,
&scu_prim->u.connect.called_addr, 0);
osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
/* accept the new conn. */
if (osmo_sccp_tx_conn_resp(conn->sccp.msc->a.sccp_user, scu_prim->u.connect.conn_id,
&scu_prim->u.connect.called_addr, NULL, 0)) {
LOGPFSML(fi, LOGL_ERROR, "Cannot send SCCP CONN RESP\n");
osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
return;
}
/* The initial user data may already be included in this N-Connect, or it may come later in a separate message.
* If it is already included, also go to ST_WAIT_INITIAL_USER_DATA now, so that we don't have to tend to two
* separate code paths doing the same thing (handling of HANDOVER_END). */
OSMO_ASSERT(conn_fsm_state_chg(ST_WAIT_INITIAL_USER_DATA) == 0);
/* It is usually a bad idea to continue using a fi after a state change, because the fi might terminate during
* the state change. In this case it is certain that the fi stays around for the initial user data. */
if (msgb_l3(msg) && msgb_l3len(msg)) {
handle_initial_user_data(fi, msg);
} else {
LOGPFSML(fi, LOGL_DEBUG, "N-Connect does not contain user data (no BSSMAP message included)\n");
}
}
static void gscon_fsm_init(struct osmo_fsm_inst *fi, uint32_t event, void *data)
@ -351,7 +397,6 @@ static void gscon_fsm_init(struct osmo_fsm_inst *fi, uint32_t event, void *data)
struct osmo_scu_prim *scu_prim = NULL;
struct msgb *msg = NULL;
int rc;
enum handover_result ho_result;
switch (event) {
case GSCON_EV_MO_COMPL_L3:
@ -379,11 +424,28 @@ static void gscon_fsm_init(struct osmo_fsm_inst *fi, uint32_t event, void *data)
osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
return;
}
/* FIXME: Extract optional IMSI and update FSM using osmo_fsm_inst_set_id()
* related: OS2969 (same as above) */
handle_bssap_n_connect(fi, scu_prim);
handle_sccp_n_connect(fi, scu_prim);
break;
default:
OSMO_ASSERT(false);
}
}
static void gscon_fsm_wait_initial_user_data(struct osmo_fsm_inst *fi, uint32_t event, void *data)
{
struct gsm_subscriber_connection *conn = fi->priv;
struct msgb *msg = data;
enum handover_result ho_result;
switch (event) {
case GSCON_EV_A_INITIAL_USER_DATA:
if (validate_initial_user_data(fi, msg)) {
osmo_fsm_inst_term(fi, OSMO_FSM_TERM_REGULAR, NULL);
return;
}
handle_initial_user_data(fi, msg);
break;
case GSCON_EV_HANDOVER_END:
ho_result = HO_RESULT_ERROR;
if (data)
@ -715,10 +777,20 @@ bool gscon_connect_mgw_to_msc(struct gsm_subscriber_connection *conn,
static const struct osmo_fsm_state gscon_fsm_states[] = {
[ST_INIT] = {
.name = "INIT",
.in_event_mask = S(GSCON_EV_MO_COMPL_L3) | S(GSCON_EV_A_CONN_IND)
| S(GSCON_EV_HANDOVER_END),
.out_state_mask = S(ST_WAIT_CC) | S(ST_ACTIVE) | S(ST_WAIT_CLEAR_CMD) | S(ST_WAIT_SCCP_RLSD),
.in_event_mask = S(GSCON_EV_MO_COMPL_L3) | S(GSCON_EV_A_CONN_IND),
.out_state_mask = 0
| S(ST_WAIT_INITIAL_USER_DATA)
| S(ST_WAIT_CC) | S(ST_ACTIVE) | S(ST_WAIT_CLEAR_CMD) | S(ST_WAIT_SCCP_RLSD),
.action = gscon_fsm_init,
},
[ST_WAIT_INITIAL_USER_DATA] = {
.name = "WAIT_INITIAL_USER_DATA",
.in_event_mask = 0
| S(GSCON_EV_A_INITIAL_USER_DATA)
| S(GSCON_EV_HANDOVER_END)
,
.out_state_mask = S(ST_WAIT_CC) | S(ST_ACTIVE) | S(ST_WAIT_CLEAR_CMD) | S(ST_WAIT_SCCP_RLSD),
.action = gscon_fsm_wait_initial_user_data,
},
[ST_WAIT_CC] = {
.name = "WAIT_CC",

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

@ -71,6 +71,7 @@ static struct osmo_tdef gsm_network_T_defs[] = {
.desc = "Forget-sum period for all_allocated:* rate counters:"
" after this amount of idle time, forget internally cumulated time remainders. Zero to always"
" keep remainders. See also X16, X17." },
{ .T=-25, .default_val=5, .desc="Timeout for initial user data after an MSC initiated an SCCP connection to the BSS" },
{ .T=-3111, .default_val=4, .desc="Wait time after lchan was released in error (should be T3111 + 2s)" },
{ .T=-3210, .default_val=20, .desc="After L3 Complete, wait for MSC to confirm" },
{}

22
src/osmo-bsc/osmo_bsc_bssap.c
View File

@ -981,6 +981,24 @@ reject:
return -1;
}
/* Handle Handover Request message, part of inter-BSC handover:
* The MSC opened a new SCCP connection and is asking this BSS to accept an inter-BSC incoming handover.
* If we accept, we'll send a Handover Request Acknowledge.
* This function is only called when the Handover Request is *not* included in the initial SCCP N-Connect message, but
* follows an "empty" N-Connect in a separate DT1 message.
*/
static int bssmap_handle_handover_request(struct gsm_subscriber_connection *conn, struct msgb *msg)
{
if (osmo_fsm_inst_dispatch(conn->fi, GSCON_EV_A_INITIAL_USER_DATA, msg)) {
/* A Handover Request message should come in on a newly opened SCCP conn. Apparently the MSC has sent a
* Handover Request on an already busy SCCP conn, and naturally we cannot accept another subscriber
* here. This is unlikely to ever happen in practice. Respond in the only possible way: */
bsc_tx_bssmap_ho_failure(conn);
return -EINVAL;
}
return 0;
}
/* Handle Handover Command message, part of inter-BSC handover:
* This BSS sent a Handover Required message.
* The MSC contacts the remote BSS and receives from it an RR Handover Command; this BSSMAP Handover
@ -1165,6 +1183,10 @@ static int bssmap_rcvmsg_dt1(struct gsm_subscriber_connection *conn,
rate_ctr_inc(&ctrs[MSC_CTR_BSSMAP_RX_DT1_LCLS_CONNECT_CTRL]);
ret = bssmap_handle_lcls_connect_ctrl(conn, msg, length);
break;
case BSS_MAP_MSG_HANDOVER_RQST:
rate_ctr_inc(&ctrs[MSC_CTR_BSSMAP_RX_DT1_HANDOVER_RQST]);
ret = bssmap_handle_handover_request(conn, msg);
break;
case BSS_MAP_MSG_HANDOVER_CMD:
rate_ctr_inc(&ctrs[MSC_CTR_BSSMAP_RX_DT1_HANDOVER_CMD]);
ret = bssmap_handle_handover_cmd(conn, msg, length);

2
tests/timer.vty
View File

@ -33,6 +33,7 @@ net: X14 = 5 s Timeout for RSL Channel Mode Modify ACK (BSC <-> BTS) (default: 5
net: X16 = 1000 ms Granularity for all_allocated:* rate counters: amount of milliseconds that one counter increment represents. See also X17, X18 (default: 1000 ms)
net: X17 = 0 ms Rounding threshold for all_allocated:* rate counters: round up to the next counter increment after this many milliseconds. If set to half of X16 (or 0), employ the usual round() behavior: round up after half of a granularity period. If set to 1, behave like ceil(): already increment the counter immediately when all channels are allocated. If set >= X16, behave like floor(): only increment after a full X16 period of all channels being occupied. See also X16, X18 (default: 0 ms)
net: X18 = 60000 ms Forget-sum period for all_allocated:* rate counters: after this amount of idle time, forget internally cumulated time remainders. Zero to always keep remainders. See also X16, X17. (default: 60000 ms)
net: X25 = 5 s Timeout for initial user data after an MSC initiated an SCCP connection to the BSS (default: 5 s)
net: X3111 = 4 s Wait time after lchan was released in error (should be T3111 + 2s) (default: 4 s)
net: X3210 = 20 s After L3 Complete, wait for MSC to confirm (default: 20 s)
mgw: X2427 = 5 s timeout for MGCP response from MGW (default: 5 s)
@ -86,6 +87,7 @@ net: X14 = 5 s Timeout for RSL Channel Mode Modify ACK (BSC <-> BTS) (default: 5
net: X16 = 1000 ms Granularity for all_allocated:* rate counters: amount of milliseconds that one counter increment represents. See also X17, X18 (default: 1000 ms)
net: X17 = 0 ms Rounding threshold for all_allocated:* rate counters: round up to the next counter increment after this many milliseconds. If set to half of X16 (or 0), employ the usual round() behavior: round up after half of a granularity period. If set to 1, behave like ceil(): already increment the counter immediately when all channels are allocated. If set >= X16, behave like floor(): only increment after a full X16 period of all channels being occupied. See also X16, X18 (default: 0 ms)
net: X18 = 60000 ms Forget-sum period for all_allocated:* rate counters: after this amount of idle time, forget internally cumulated time remainders. Zero to always keep remainders. See also X16, X17. (default: 60000 ms)
net: X25 = 5 s Timeout for initial user data after an MSC initiated an SCCP connection to the BSS (default: 5 s)
net: X3111 = 4 s Wait time after lchan was released in error (should be T3111 + 2s) (default: 4 s)
net: X3210 = 20 s After L3 Complete, wait for MSC to confirm (default: 20 s)
mgw: X2427 = 5 s timeout for MGCP response from MGW (default: 5 s)