Implement AoIP, port to M3UA SIGTRAN (large addition and refactoring)

This was originally a long series of commits converging to the final result
seen in this patch. It does not make much sense to review the smaller steps'
trial and error, we need to review this entire change as a whole.

Implement AoIP in osmo-msc and osmo-bsc.

Change over to the new libosmo-sigtran API with support for proper
SCCP/M3UA/SCTP stacking, as mandated by 3GPP specifications for the IuCS and
IuPS interfaces.

From here on, a separate osmo-stp process is required for SCCP routing between
OsmoBSC / OsmoHNBGW <-> OsmoMSC / OsmoSGSN

jenkins.sh: build from libosmo-sccp and osmo-iuh master branches now for new
M3UA SIGTRAN.

Patch-by: pmaier, nhofmeyr, laforge
Change-Id: I5ae4e05ee7c57cad341ea5e86af37c1f6b0ffa77

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;
+}