1 files changed, 561 insertions, 0 deletions

diff --git a/src/osmo-bsc/osmo_bsc_sigtran.c b/src/osmo-bsc/osmo_bsc_sigtran.c
new file mode 100644
index 000000000..0f6ca334f
--- /dev/null
+++ b/src/osmo-bsc/osmo_bsc_sigtran.c
@@ -0,0 +1,561 @@
+/* (C) 2017 by sysmocom s.f.m.c. GmbH
+ * All Rights Reserved
+ *
+ * Author: Philipp Maier
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/sigtran/osmo_ss7.h>
+#include <osmocom/sigtran/sccp_sap.h>
+#include <osmocom/sccp/sccp_types.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/gsm/gsm0808.h>
+#include <osmocom/core/msgb.h>
+#include <openbsc/bsc_msc_data.h>
+#include <openbsc/debug.h>
+#include <openbsc/osmo_bsc.h>
+#include <openbsc/osmo_bsc_grace.h>
+#include <openbsc/osmo_bsc_sigtran.h>
+#include <openbsc/a_reset.h>
+#include <openbsc/gsm_04_80.h>
+
+/* A pointer to a list with all involved MSCs
+ * (a copy of the pointer location submitted with osmo_bsc_sigtran_init() */
+static struct llist_head *msc_list;
+
+#define RESET_INTERVAL 1	/* sek */
+#define SCCP_MSG_MAXSIZE 1024
+#define CS7_POINTCODE_DEFAULT_OFFSET 2
+
+/* Internal list with connections we currently maintain. This
+ * list is of type struct osmo_bsc_sccp_con */
+static LLIST_HEAD(active_connections);
+
+/* The SCCP stack will not assign connection IDs to us automatically, we
+ * will do this ourselves using a counter variable, that counts one up
+ * for every new connection */
+static uint32_t conn_id_counter;
+
+/* Helper function to Check if the given connection id is already assigned */
+static struct osmo_bsc_sccp_con *get_bsc_conn_by_conn_id(int conn_id)
+{
+	conn_id &= 0xFFFFFF;
+	struct osmo_bsc_sccp_con *bsc_con;
+
+	llist_for_each_entry(bsc_con, &active_connections, entry) {
+		if (bsc_con->conn_id == conn_id)
+			return bsc_con;
+	}
+
+	return NULL;
+}
+
+/* Pick a free connection id */
+static int pick_free_conn_id(const struct bsc_msc_data *msc)
+{
+	int conn_id = conn_id_counter;
+	int i;
+
+	for (i = 0; i < 0xFFFFFF; i++) {
+		conn_id++;
+		conn_id &= 0xFFFFFF;
+		if (get_bsc_conn_by_conn_id(conn_id) == false) {
+			conn_id_counter = conn_id;
+			return conn_id;
+		}
+	}
+
+	return -1;
+}
+
+/* Send reset to MSC */
+static void osmo_bsc_sigtran_tx_reset(const struct bsc_msc_data *msc)
+{
+	struct osmo_ss7_instance *ss7;
+	struct msgb *msg;
+
+	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_NOTICE, "Sending RESET to MSC: %s\n", osmo_sccp_addr_name(ss7, &msc->a.msc_addr));
+	msg = gsm0808_create_reset();
+	osmo_sccp_tx_unitdata_msg(msc->a.sccp_user, &msc->a.bsc_addr,
+				  &msc->a.msc_addr, msg);
+}
+
+/* Send reset-ack to MSC */
+void osmo_bsc_sigtran_tx_reset_ack(const struct bsc_msc_data *msc)
+{
+	struct osmo_ss7_instance *ss7;
+	struct msgb *msg;
+	OSMO_ASSERT(msc);
+
+	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_NOTICE, "Sending RESET ACK to MSC: %s\n", osmo_sccp_addr_name(ss7, &msc->a.msc_addr));
+	msg = gsm0808_create_reset_ack();
+	osmo_sccp_tx_unitdata_msg(msc->a.sccp_user, &msc->a.bsc_addr,
+				  &msc->a.msc_addr, msg);
+}
+
+/* Find an MSC by its sigtran point code */
+static struct bsc_msc_data *get_msc_by_addr(const struct osmo_sccp_addr *msc_addr)
+{
+	struct osmo_ss7_instance *ss7;
+	struct bsc_msc_data *msc;
+	llist_for_each_entry(msc, msc_list, entry) {
+		if (memcmp(msc_addr, &msc->a.msc_addr, sizeof(*msc_addr)) == 0)
+			return msc;
+	}
+
+	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_ERROR, "Unable to find MSC data under address: %s\n", osmo_sccp_addr_name(ss7, msc_addr));
+	return NULL;
+}
+
+/* Send data to MSC, use the connection id which MSC it is */
+static int handle_data_from_msc(int conn_id, struct msgb *msg)
+{
+	struct osmo_bsc_sccp_con *bsc_con = get_bsc_conn_by_conn_id(conn_id);
+	int rc = -EINVAL;
+
+	if (bsc_con) {
+		msg->l3h = msgb_l2(msg);
+		rc = bsc_handle_dt(bsc_con, msg, msgb_l2len(msg));
+	} else
+		LOGP(DMSC, LOGL_NOTICE, "incoming data from unknown connection id: %i\n", conn_id);
+
+	return rc;
+}
+
+/* Sent unitdata to MSC, use the point code to determine which MSC it is */
+static int handle_unitdata_from_msc(const struct osmo_sccp_addr *msc_addr, struct msgb *msg,
+				    const struct osmo_sccp_user *scu)
+{
+	struct osmo_ss7_instance *ss7;
+	struct bsc_msc_data *msc = get_msc_by_addr(msc_addr);
+	int rc = -EINVAL;
+
+	if (msc) {
+		msg->l3h = msgb_l2(msg);
+		rc = bsc_handle_udt(msc, msg, msgb_l2len(msg));
+	} else {
+		ss7 = osmo_sccp_get_ss7(osmo_sccp_get_sccp(scu));
+		OSMO_ASSERT(ss7);
+		LOGP(DMSC, LOGL_NOTICE, "incoming unitdata data from unknown remote address: %s\n",
+		     osmo_sccp_addr_name(ss7, msc_addr));
+	}
+	return rc;
+}
+
+/* Callback function, called by the SSCP stack when data arrives */
+static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
+{
+	struct osmo_scu_prim *scu_prim = (struct osmo_scu_prim *)oph;
+	struct osmo_sccp_user *scu = _scu;
+	struct osmo_bsc_sccp_con *bsc_con;
+	int rc = 0;
+
+	switch (OSMO_PRIM_HDR(&scu_prim->oph)) {
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_UNITDATA, PRIM_OP_INDICATION):
+		/* Handle inbound UNITDATA */
+		DEBUGP(DMSC, "N-UNITDATA.ind(%s)\n", osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+		rc = handle_unitdata_from_msc(&scu_prim->u.unitdata.calling_addr, oph->msg, scu);
+		break;
+
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_CONNECT, PRIM_OP_INDICATION):
+		/* Handle (Reject) inbound connections */
+		DEBUGP(DMSC, "N-CONNECT.ind(X->%u)\n", scu_prim->u.connect.conn_id);
+		LOGP(DMSC, LOGL_DEBUG, "Rejecting inbound SCCP connection...\n");
+		rc = osmo_sccp_tx_disconn(scu, scu_prim->u.connect.conn_id, &scu_prim->u.connect.called_addr, 0);
+		break;
+
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_CONNECT, PRIM_OP_CONFIRM):
+		/* Handle outbound connection confirmation */
+		if (msgb_l2len(oph->msg) > 0) {
+			DEBUGP(DMSC, "N-CONNECT.cnf(%u, %s)\n", scu_prim->u.connect.conn_id,
+			       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+			rc = handle_data_from_msc(scu_prim->u.connect.conn_id, oph->msg);
+		} else
+			DEBUGP(DRANAP, "N-CONNECT.cnf(%u)\n", scu_prim->u.connect.conn_id);
+		break;
+
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_DATA, PRIM_OP_INDICATION):
+		/* Handle incoming connection oriented data */
+		DEBUGP(DMSC, "N-DATA.ind(%u, %s)\n", scu_prim->u.data.conn_id,
+		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+
+		/* Incoming data is a sign of a vital connection */
+		bsc_con = get_bsc_conn_by_conn_id(scu_prim->u.disconnect.conn_id);
+		if (bsc_con)
+			a_reset_conn_success(bsc_con->msc->a.reset);
+
+		rc = handle_data_from_msc(scu_prim->u.data.conn_id, oph->msg);
+		break;
+
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_DISCONNECT, PRIM_OP_INDICATION):
+		/* indication of disconnect */
+		if (msgb_l2len(oph->msg) > 0) {
+			DEBUGP(DMSC, "N-DISCONNECT.ind(%u, %s, cause=%i)\n", scu_prim->u.disconnect.conn_id,
+			       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)), scu_prim->u.disconnect.cause);
+			handle_data_from_msc(scu_prim->u.disconnect.conn_id, oph->msg);
+		} else
+			DEBUGP(DRANAP, "N-DISCONNECT.ind(%u, cause=%i)\n", scu_prim->u.disconnect.conn_id,
+			       scu_prim->u.disconnect.cause);
+
+		bsc_con = get_bsc_conn_by_conn_id(scu_prim->u.disconnect.conn_id);
+		if (bsc_con) {
+			/* We might have a connectivity problem. Maybe we need to go
+			 * through the reset procedure again? */
+			if (scu_prim->u.disconnect.cause == 0)
+				a_reset_conn_fail(bsc_con->msc->a.reset);
+
+			rc = osmo_bsc_sigtran_del_conn(bsc_con);
+		}
+		break;
+
+	default:
+		LOGP(DMSC, LOGL_ERROR, "Unhandled SIGTRAN primitive: %u:%u\n", oph->primitive, oph->operation);
+		break;
+	}
+
+	msgb_free(oph->msg);
+	return rc;
+}
+
+/* Allocate resources to make a new connection oriented sigtran connection
+ * (not the connection ittself!) */
+enum bsc_con osmo_bsc_sigtran_new_conn(struct gsm_subscriber_connection *conn, struct bsc_msc_data *msc)
+{
+	struct osmo_ss7_instance *ss7;
+	struct osmo_bsc_sccp_con *bsc_con;
+	int conn_id;
+
+	OSMO_ASSERT(conn);
+	OSMO_ASSERT(msc);
+
+	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_NOTICE, "Initializing resources for new SIGTRAN connection to MSC: %s...\n",
+	     osmo_sccp_addr_name(ss7, &msc->a.msc_addr));
+
+	if (a_reset_conn_ready(msc->a.reset) == false) {
+		LOGP(DMSC, LOGL_ERROR, "MSC is not connected. Dropping.\n");
+		return BSC_CON_REJECT_NO_LINK;
+	}
+
+	if (!bsc_grace_allow_new_connection(conn->bts->network, conn->bts)) {
+		LOGP(DMSC, LOGL_NOTICE, "BSC in grace period. No new connections.\n");
+		return BSC_CON_REJECT_RF_GRACE;
+	}
+
+	bsc_con = talloc_zero(conn->bts, struct osmo_bsc_sccp_con);
+	if (!bsc_con) {
+		LOGP(DMSC, LOGL_ERROR, "Failed to allocate new SIGTRAN connection.\n");
+		return BSC_CON_NO_MEM;
+	}
+
+	bsc_con->msc = msc;
+	bsc_con->conn = conn;
+	llist_add_tail(&bsc_con->entry, &active_connections);
+	conn->sccp_con = bsc_con;
+
+	/* Pick a free connection id */
+	conn_id = pick_free_conn_id(msc);
+	if (conn_id < 0)
+		return BSC_CON_REJECT_NO_LINK;
+	bsc_con->conn_id = conn_id;
+
+	LOGP(DMSC, LOGL_NOTICE, "Allocated new connection id: %i\n", conn_id);
+
+	return BSC_CON_SUCCESS;
+}
+
+/* Open a new connection oriented sigtran connection */
+int osmo_bsc_sigtran_open_conn(const struct osmo_bsc_sccp_con *conn, struct msgb *msg)
+{
+	struct osmo_ss7_instance *ss7;
+	struct bsc_msc_data *msc;
+	int conn_id;
+	int rc;
+
+	OSMO_ASSERT(conn);
+	OSMO_ASSERT(msg);
+	OSMO_ASSERT(conn->msc);
+
+	msc = conn->msc;
+
+	if (a_reset_conn_ready(msc->a.reset) == false) {
+		LOGP(DMSC, LOGL_ERROR, "MSC is not connected. Dropping.\n");
+		return -EINVAL;
+	}
+
+	conn_id = conn->conn_id;
+	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_NOTICE, "Opening new SIGTRAN connection (id=%i) to MSC: %s\n", conn_id,
+	     osmo_sccp_addr_name(ss7, &msc->a.msc_addr));
+
+	rc = osmo_sccp_tx_conn_req_msg(msc->a.sccp_user, conn_id, &msc->a.bsc_addr,
+				       &msc->a.msc_addr, msg);
+
+	return rc;
+}
+
+/* Send data to MSC */
+int osmo_bsc_sigtran_send(const struct osmo_bsc_sccp_con *conn, struct msgb *msg)
+{
+	struct osmo_ss7_instance *ss7;
+	int conn_id;
+	int rc;
+	struct bsc_msc_data *msc;
+
+	OSMO_ASSERT(conn);
+	OSMO_ASSERT(msg);
+	OSMO_ASSERT(conn->msc);
+
+	msc = conn->msc;
+
+	if (a_reset_conn_ready(msc->a.reset) == false) {
+		LOGP(DMSC, LOGL_ERROR, "MSC is not connected. Dropping.\n");
+		return -EINVAL;
+	}
+
+	conn_id = conn->conn_id;
+
+	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_DEBUG, "Sending connection (id=%i) oriented data to MSC: %si\n",
+	     conn_id, osmo_sccp_addr_name(ss7, &msc->a.msc_addr));
+
+	rc = osmo_sccp_tx_data_msg(msc->a.sccp_user, conn_id, msg);
+
+	return rc;
+}
+
+/* Delete a connection from the list with open connections
+ * (called by osmo_bsc_api.c on failing open connections and
+ * locally, when a connection is closed by the MSC */
+int osmo_bsc_sigtran_del_conn(struct osmo_bsc_sccp_con *conn)
+{
+	if (!conn)
+		return 0;
+
+	if (conn->conn) {
+		LOGP(DMSC, LOGL_ERROR,
+		     "sccp connection (id=%i) not cleared (gsm subscriber connection still active) -- forcefully clearing it now!\n",
+		     conn->conn_id);
+		bsc_subscr_con_free(conn->conn);
+		conn->conn = NULL;
+
+		/* This bahaviour might be caused by a bad connection. Maybe we
+		 * will have to go through the reset procedure again */
+		a_reset_conn_fail(conn->msc->a.reset);
+	}
+
+	llist_del(&conn->entry);
+	talloc_free(conn);
+
+	return 0;
+}
+
+/* Send an USSD notification in case we loose the connection to the MSC */
+static void bsc_notify_msc_lost(const struct osmo_bsc_sccp_con *conn)
+{
+	struct gsm_subscriber_connection *subscr_conn;
+
+	/* Check if sccp conn is still present */
+	if (!conn)
+		return;
+	subscr_conn = conn->conn;
+
+	/* send USSD notification if string configured and conn->data is set */
+	if (!subscr_conn)
+		return;
+
+	/* check for config string */
+	if (!conn->msc->ussd_msc_lost_txt)
+		return;
+	if (conn->msc->ussd_msc_lost_txt[0] == '\0')
+		return;
+
+	/* send USSD notification */
+	bsc_send_ussd_notify(subscr_conn, 1, subscr_conn->sccp_con->msc->ussd_msc_lost_txt);
+	bsc_send_ussd_release_complete(subscr_conn);
+}
+
+/* Close all open sigtran connections and channels */
+void osmo_bsc_sigtran_reset(const struct bsc_msc_data *msc)
+{
+	struct osmo_bsc_sccp_con *conn;
+	struct osmo_bsc_sccp_con *conn_temp;
+	OSMO_ASSERT(msc);
+
+	/* Close all open connections */
+	llist_for_each_entry_safe(conn, conn_temp, &active_connections, entry) {
+
+		/* We only may close connections which actually belong to this
+		 * MSC. All other open connections are left untouched */
+		if (conn->msc == msc) {
+			/* Notify active connection users via USSD that the MSC is down */
+			bsc_notify_msc_lost(conn);
+
+			/* Take down all occopied RF channels */
+			if (conn->conn)
+				gsm0808_clear(conn->conn);
+
+			/* Disconnect all Sigtran connections */
+			osmo_sccp_tx_disconn(msc->a.sccp_user, conn->conn_id, &msc->a.bsc_addr, 0);
+
+			/* Delete subscriber connection */
+			osmo_bsc_sigtran_del_conn(conn);
+		}
+	}
+}
+
+/* Callback function: Close all open connections */
+static void osmo_bsc_sigtran_reset_cb(const void *priv)
+{
+	struct bsc_msc_data *msc = (struct bsc_msc_data*) priv;
+
+	/* Shut down all ongoing traffic */
+	osmo_bsc_sigtran_reset(msc);
+
+	/* Send reset to MSC */
+	osmo_bsc_sigtran_tx_reset(msc);
+}
+
+/* Default point-code to be used as local address (BSC) */
+#define BSC_DEFAULT_PC "0.23.3"
+
+/* Default point-code to be used as remote address (MSC) */
+#define MSC_DEFAULT_PC "0.23.1"
+
+/* Initalize osmo sigtran backhaul */
+int osmo_bsc_sigtran_init(struct llist_head *mscs)
+{
+	bool free_attempt_used = false;
+	bool fail_on_next_invalid_cfg = false;
+
+	struct bsc_msc_data *msc;
+	char msc_name[32];
+	uint32_t default_pc;
+
+	OSMO_ASSERT(mscs);
+	msc_list = mscs;
+
+	llist_for_each_entry(msc, msc_list, entry) {
+		snprintf(msc_name, sizeof(msc_name), "msc-%u", msc->nr);
+		LOGP(DMSC, LOGL_NOTICE, "Initializing SCCP connection to MSC %s\n", msc_name);
+
+		/* Check if the VTY could determine a valid CS7 instance,
+		 * use safe default in case none is set */
+		if (msc->a.cs7_instance_valid == false) {
+			msc->a.cs7_instance = 0;
+			if (fail_on_next_invalid_cfg)
+				goto fail_auto_cofiguration;
+			free_attempt_used = true;
+		}
+		LOGP(DMSC, LOGL_NOTICE, "CS7 Instance identifier, A-Interface: %u\n", msc->a.cs7_instance);
+
+		/* Pre-Check if there is an ss7 instance present */
+		if (osmo_ss7_instance_find(msc->a.cs7_instance) == NULL) {
+			if (fail_on_next_invalid_cfg)
+				goto fail_auto_cofiguration;
+			free_attempt_used = true;
+		}
+
+		/* SS7 Protocol stack */
+		default_pc = osmo_ss7_pointcode_parse(NULL, BSC_DEFAULT_PC);
+		msc->a.sccp =
+		    osmo_sccp_simple_client_on_ss7_id(msc, msc->a.cs7_instance, msc_name, default_pc,
+						      OSMO_SS7_ASP_PROT_M3UA, 0, NULL, 0, NULL);
+		if (!msc->a.sccp)
+			return -EINVAL;
+
+		/* Check if the sccp-address fullfills minimum requirements (SSN+PC is present,
+		 * automatically recover addresses if the addresses are not set up properly) */
+		if (!osmo_sccp_check_addr(&msc->a.bsc_addr, OSMO_SCCP_ADDR_T_SSN | OSMO_SCCP_ADDR_T_PC)) {
+			if (fail_on_next_invalid_cfg)
+				goto fail_auto_cofiguration;
+			free_attempt_used = true;
+
+			LOGP(DMSC, LOGL_NOTICE,
+			     "A-interface: invalid or missing local (BSC) SCCP address (a.bsc_addr=%s)\n",
+			     osmo_sccp_addr_name(osmo_ss7_instance_find(msc->a.cs7_instance), &msc->a.bsc_addr));
+			osmo_sccp_local_addr_by_instance(&msc->a.bsc_addr, msc->a.sccp, SCCP_SSN_BSSAP);
+			LOGP(DMSC, LOGL_NOTICE,
+			     "A-interface: using automatically generated local (BSC) SCCP address (a.bsc_addr=%s)\n",
+			     osmo_sccp_addr_name(osmo_ss7_instance_find(msc->a.cs7_instance), &msc->a.bsc_addr));
+		} else {
+			LOGP(DMSC, LOGL_NOTICE,
+			     "A-interface: using local (BSC) automatically SCCP address (a.msc_addr=%s)\n",
+			     osmo_sccp_addr_name(osmo_ss7_instance_find(msc->a.cs7_instance), &msc->a.bsc_addr));
+		}
+
+		if (!osmo_sccp_check_addr(&msc->a.msc_addr, OSMO_SCCP_ADDR_T_SSN | OSMO_SCCP_ADDR_T_PC)) {
+			if (fail_on_next_invalid_cfg)
+				goto fail_auto_cofiguration;
+			free_attempt_used = true;
+
+			LOGP(DMSC, LOGL_NOTICE,
+			     "A-interface: invalid or missing remote (MSC) SCCP address for the MSC (a.msc_addr=%s)\n",
+			     osmo_sccp_addr_name(osmo_ss7_instance_find(msc->a.cs7_instance), &msc->a.msc_addr));
+			osmo_sccp_local_addr_by_instance(&msc->a.msc_addr, msc->a.sccp, SCCP_SSN_BSSAP);
+			msc->a.msc_addr.pc = osmo_ss7_pointcode_parse(NULL, MSC_DEFAULT_PC);
+			LOGP(DMSC, LOGL_NOTICE,
+			     "A-interface: using automatically generated remote (MSC) SCCP address (a.msc_addr=%s)\n",
+			     osmo_sccp_addr_name(osmo_ss7_instance_find(msc->a.cs7_instance), &msc->a.msc_addr));
+			free_attempt_used = true;
+		} else {
+			LOGP(DMSC, LOGL_NOTICE,
+			     "A-interface: using remote (MSC) automatically SCCP address (a.msc_addr=%s)\n",
+			     osmo_sccp_addr_name(osmo_ss7_instance_find(msc->a.cs7_instance), &msc->a.msc_addr));
+		}
+
+		/* Bind SCCP user */
+		msc->a.sccp_user = osmo_sccp_user_bind(msc->a.sccp, msc_name, sccp_sap_up, msc->a.bsc_addr.ssn);
+		if (!msc->a.sccp_user)
+			return -EINVAL;
+
+		/* Start MSC-Reset procedure */
+		msc->a.reset = a_reset_alloc(msc, msc_name, osmo_bsc_sigtran_reset_cb, msc);
+		if (!msc->a.reset)
+			return -EINVAL;
+
+		/* If we have detected that the SS7 configuration of the MSC we have just initalized
+		 * was incomplete or completely missing, we can not tolerate another incomplete
+		 * configuration. The reson for this is that we do only specify exactly one default
+		 * pointcode pair. We also specify localhost as default IP-Address. If we have wanted
+		 * to support multiple MSCs with automatic configuration we would be forced to invent
+		 * a complex ruleset how to allocate the pointcodes and respective IP-Addresses.
+		 * Furthermore, the situation where a single BSC is connected to multiple MSCs
+		 * is a very rare situation anyway. In this case we expect the user to experienced
+		 * enough to create a valid SS7/CS7 VTY configuration that does not lack any
+		 * components */
+		if (free_attempt_used)
+			fail_on_next_invalid_cfg = true;
+	}
+
+	return 0;
+
+fail_auto_cofiguration:
+	LOGP(DMSC, LOGL_ERROR,
+	     "A-interface: More than one invalid/inclomplete configuration detected, unable to revover - check config file!\n");
+	return -EINVAL;
+}