diff --git a/src/libmsc/a_iface.c b/src/libmsc/a_iface.c
index caf9d4b..93e8ab5 100644
--- a/src/libmsc/a_iface.c
+++ b/src/libmsc/a_iface.c
@@ -1,9 +1,8 @@
-/* A-interface implementation, from MSC to BSC */
-
-/* (C) 2016 by sysmocom s.m.f.c GmbH <info@sysmocom.de>
- *
+/* (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
@@ -19,35 +18,574 @@
  *
  */
 
+#include <osmocom/core/utils.h>
 #include <osmocom/core/msgb.h>
 #include <osmocom/core/logging.h>
-
+#include <osmocom/sigtran/sccp_helpers.h>
+#include <osmocom/sigtran/sccp_sap.h>
+#include <osmocom/sigtran/osmo_ss7.h>
+#include <osmocom/sigtran/protocol/m3ua.h>
+#include <osmocom/gsm/gsm0808.h>
+#include <osmocom/gsm/protocol/gsm_08_08.h>
+#include <osmocom/gsm/protocol/gsm_04_08.h>
+#include <osmocom/gsm/gsm0808_utils.h>
 #include <openbsc/debug.h>
-
-#include <openbsc/gsm_data.h>
 #include <openbsc/msc_ifaces.h>
-#include <openbsc/debug.h>
+#include <openbsc/a_iface.h>
+#include <openbsc/a_iface_bssap.h>
+#include <openbsc/transaction.h>
+#include <openbsc/mgcpgw_client.h>
+#include <osmocom/core/byteswap.h>
+#include <osmocom/sccp/sccp_types.h>
+#include <openbsc/a_reset.h>
+#include <openbsc/osmo_msc.h>
 
-int a_tx(struct msgb *msg)
+/* A pointer to the GSM network we work with. By the current paradigm,
+ * there can only be one gsm_network per MSC. The pointer is set once
+ * when calling a_init() */
+static struct gsm_network *gsm_network = NULL;
+
+/* A struct to track currently active connections. We need that information
+ * to handle failure sitautions. In case of a problem, we must know which
+ * connections are currently open and which BSC is responsible. We also need
+ * the data to perform our connection checks (a_reset). All other logic will
+ * look at the connection ids and addresses that are supplied by the
+ * primitives */
+struct bsc_conn {
+	struct llist_head list;
+	uint32_t conn_id;			/* Connection identifier */
+};
+
+/* Internal list with connections we currently maintain. This
+ * list is of type struct bsc_conn (see above) */
+static LLIST_HEAD(active_connections);
+
+/* Record info of a new active connection in the active connection list */
+static void record_bsc_con(const void *ctx, uint32_t conn_id)
 {
-	LOGP(DMSC, LOGL_ERROR, "message to be sent to BSC, but A-interface"
-	     " not implemented.\n%s\n", osmo_hexdump(msg->data, msg->len));
-	return -1;
+	struct bsc_conn *conn;
+
+	conn = talloc_zero(ctx, struct bsc_conn);
+	OSMO_ASSERT(conn);
+
+	conn->conn_id = conn_id;
+
+	llist_add_tail(&conn->list, &active_connections);
 }
 
-int a_page(const char *imsi, uint32_t tmsi, uint16_t lac)
+/* Delete info of a closed connection from the active connection list */
+void a_delete_bsc_con(uint32_t conn_id)
 {
-	LOGP(DMSC, LOGL_ERROR, "Paging to be sent to BSC, but A-interface"
-	     " not implemented: IMSI %s TMSI 0x%08x LAC %u\n",
-	     imsi, tmsi, lac);
-	return -1;
+	struct bsc_conn *conn;
+	struct bsc_conn *conn_temp;
+
+	LOGP(DMSC, LOGL_DEBUG,
+	     "Removing connection from active sccp-connection list (conn_id=%i)\n",
+	     conn_id);
+
+	llist_for_each_entry_safe(conn, conn_temp, &active_connections, list) {
+		if (conn->conn_id == conn_id) {
+			llist_del(&conn->list);
+			talloc_free(conn);
+		}
+	}
 }
 
-int msc_gsm0808_tx_cipher_mode(struct gsm_subscriber_connection *conn, int cipher,
-			       const uint8_t *key, int len, int include_imeisv)
+/* Check if a specified connection id has an active SCCP connection */
+static bool check_connection_active(uint32_t conn_id)
+{
+	struct bsc_conn *conn;
+
+	/* Find the address for the current connection id */
+	llist_for_each_entry(conn, &active_connections, list) {
+		if (conn->conn_id == conn_id) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/* Get the reset context for a specifiec calling (BSC) address */
+static struct a_reset_ctx *get_reset_ctx_by_sccp_addr(const struct osmo_sccp_addr *addr)
+{
+	struct bsc_context *bsc_ctx;
+	struct osmo_ss7_instance *ss7;
+
+	if (!addr)
+		return NULL;
+
+	llist_for_each_entry(bsc_ctx, &gsm_network->a.bscs, list) {
+		if (memcmp(&bsc_ctx->bsc_addr, addr, sizeof(*addr)) == 0)
+			return bsc_ctx->reset;
+	}
+
+	ss7 = osmo_ss7_instance_find(gsm_network->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_ERROR, "The calling BSC (%s) is unknown to this MSC ...\n",
+	     osmo_sccp_addr_name(ss7, addr));
+	return NULL;
+}
+
+/* Send DTAP message via A-interface */
+int a_iface_tx_dtap(struct msgb *msg)
+{
+	struct gsm_subscriber_connection *conn;
+	struct msgb *msg_resp;
+
+	/* FIXME: Set this to some meaninful value! */
+	uint8_t link_id = 0x00;
+	OSMO_ASSERT(msg);
+	conn = (struct gsm_subscriber_connection *)msg->dst;
+	OSMO_ASSERT(conn);
+	OSMO_ASSERT(conn->a.scu);
+
+	LOGP(DMSC, LOGL_DEBUG, "Passing DTAP message from MSC to BSC (conn_id=%i)\n", conn->a.conn_id);
+
+	msg->l3h = msg->data;
+	msg_resp = gsm0808_create_dtap(msg, link_id);
+	if (!msg_resp) {
+		LOGP(DMSC, LOGL_ERROR, "Unable to generate BSSMAP DTAP message!\n");
+		return -EINVAL;
+	} else
+		LOGP(DMSC, LOGL_DEBUG, "Massage will be sent as BSSMAP DTAP message!\n");
+
+	LOGP(DMSC, LOGL_DEBUG, "N-DATA.req(%u, %s)\n", conn->a.conn_id, osmo_hexdump(msg_resp->data, msg_resp->len));
+	return osmo_sccp_tx_data_msg(conn->a.scu, conn->a.conn_id, msg_resp);
+}
+
+/* Send Cipher mode command via A-interface */
+int a_iface_tx_cipher_mode(const struct gsm_subscriber_connection *conn,
+			   int cipher, const const uint8_t *key, int len, int include_imeisv)
 {
 	/* TODO generalize for A- and Iu interfaces, don't name after 08.08 */
-	LOGP(DMSC, LOGL_ERROR, "gsm0808_cipher_mode(): message to be sent to"
-	     " BSC, but A interface not yet implemented.\n");
-	return -1;
+	struct msgb *msg_resp;
+	struct gsm0808_encrypt_info ei;
+
+	OSMO_ASSERT(conn);
+
+	LOGP(DMSC, LOGL_DEBUG, "Passing Cipher mode command message from MSC to BSC (conn_id=%i)\n", conn->a.conn_id);
+	uint8_t crm = 0x01;
+	uint8_t *crm_ptr = NULL;
+
+	/* Setup encryption information */
+	if (len > ENCRY_INFO_KEY_MAXLEN || !key) {
+		LOGP(DMSC, LOGL_ERROR,
+		     "Cipher mode command message could not be generated due to invalid key! (conn_id=%i)\n",
+		     conn->a.conn_id);
+		return -EINVAL;
+	} else {
+		memcpy(&ei.key, key, len);
+		ei.key_len = len;
+	}
+
+	if (include_imeisv)
+		crm_ptr = &crm;
+
+	ei.perm_algo[0] = (uint8_t) (1 << cipher);
+	ei.perm_algo_len = 1;
+
+	msg_resp = gsm0808_create_cipher(&ei, crm_ptr);
+	LOGP(DMSC, LOGL_DEBUG, "N-DATA.req(%u, %s)\n", conn->a.conn_id, osmo_hexdump(msg_resp->data, msg_resp->len));
+
+	return osmo_sccp_tx_data_msg(conn->a.scu, conn->a.conn_id, msg_resp);
+}
+
+/* Page a subscriber via A-interface */
+int a_iface_tx_paging(const char *imsi, uint32_t tmsi, uint16_t lac)
+{
+	struct bsc_context *bsc_ctx;
+	struct gsm0808_cell_id_list cil;
+	struct msgb *msg;
+	int page_count = 0;
+	struct osmo_ss7_instance *ss7;
+
+	OSMO_ASSERT(imsi);
+
+	cil.id_discr = CELL_IDENT_LAC;
+	cil.id_list_lac[0] = lac;
+	cil.id_list_len = 1;
+
+	ss7 = osmo_ss7_instance_find(gsm_network->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+
+	/* Deliver paging request to all known BSCs */
+	llist_for_each_entry(bsc_ctx, &gsm_network->a.bscs, list) {
+		if (a_reset_conn_ready(bsc_ctx->reset)) {
+			LOGP(DMSC, LOGL_DEBUG,
+			     "Passing paging message from MSC %s to BSC %s (imsi=%s, tmsi=0x%08x, lac=%u)\n",
+			     osmo_sccp_addr_name(ss7, &bsc_ctx->msc_addr),
+			     osmo_sccp_addr_name(ss7, &bsc_ctx->bsc_addr), imsi, tmsi, lac);
+			msg = gsm0808_create_paging(imsi, &tmsi, &cil, NULL);
+			osmo_sccp_tx_unitdata_msg(bsc_ctx->sccp_user,
+						  &bsc_ctx->msc_addr, &bsc_ctx->bsc_addr, msg);
+			page_count++;
+		} else {
+			LOGP(DMSC, LOGL_DEBUG,
+			     "Connection down, dropping paging from MSC %s to BSC %s (imsi=%s, tmsi=0x%08x, lac=%u)\n",
+			     osmo_sccp_addr_name(ss7, &bsc_ctx->msc_addr),
+			     osmo_sccp_addr_name(ss7, &bsc_ctx->bsc_addr), imsi, tmsi, lac);
+		}
+	}
+
+	if (page_count <= 0)
+		LOGP(DMSC, LOGL_ERROR, "Could not deliver paging because none of the associated BSCs is available!\n");
+
+	return page_count;
+}
+
+/* Convert speech version field */
+static uint8_t convert_Abis_sv_to_A_sv(int speech_ver)
+{
+	/* The speech versions that are transmitted in the Bearer capability
+	 * information element, that is transmitted on the Abis interfece
+	 * use a different encoding than the permitted speech version
+	 * identifier, that is signalled in the channel type element on the A
+	 * interface. (See also 3GPP TS 48.008, 3.2.2.1 and 3GPP TS 24.008,
+	 * 10.5.103 */
+
+	switch (speech_ver) {
+	case GSM48_BCAP_SV_FR:
+		return GSM0808_PERM_FR1;
+		break;
+	case GSM48_BCAP_SV_HR:
+		return GSM0808_PERM_HR1;
+		break;
+	case GSM48_BCAP_SV_EFR:
+		return GSM0808_PERM_FR2;
+		break;
+	case GSM48_BCAP_SV_AMR_F:
+		return GSM0808_PERM_FR3;
+		break;
+	case GSM48_BCAP_SV_AMR_H:
+		return GSM0808_PERM_HR3;
+		break;
+	case GSM48_BCAP_SV_AMR_OFW:
+		return GSM0808_PERM_FR4;
+		break;
+	case GSM48_BCAP_SV_AMR_OHW:
+		return GSM0808_PERM_HR4;
+		break;
+	case GSM48_BCAP_SV_AMR_FW:
+		return GSM0808_PERM_FR5;
+		break;
+	case GSM48_BCAP_SV_AMR_OH:
+		return GSM0808_PERM_HR6;
+		break;
+	}
+
+	/* If nothing matches, tag the result as invalid */
+	LOGP(DMSC, LOGL_ERROR, "Invalid permitted speech version / rate detected, discarding.\n");
+	return 0xFF;
+}
+
+/* Convert speech preference field */
+static uint8_t convert_Abis_prev_to_A_pref(int radio)
+{
+	/* The Radio channel requirement field that is transmitted in the
+	 * Bearer capability information element, that is transmitted on the
+	 * Abis interfece uses a different encoding than the Channel rate and
+	 * type field that is signalled in the channel type element on the A
+	 * interface. (See also 3GPP TS 48.008, 3.2.2.1 and 3GPP TS 24.008,
+	 * 10.5.102 */
+
+	switch (radio) {
+	case GSM48_BCAP_RRQ_FR_ONLY:
+		return GSM0808_SPEECH_FULL_BM;
+	case GSM48_BCAP_RRQ_DUAL_FR:
+		return GSM0808_SPEECH_FULL_PREF;
+	case GSM48_BCAP_RRQ_DUAL_HR:
+		return GSM0808_SPEECH_HALF_PREF;
+	}
+
+	LOGP(DMSC, LOGL_ERROR, "Invalid speech version / rate combination preference, defaulting to full rate.\n");
+	return GSM0808_SPEECH_FULL_BM;
+}
+
+/* Assemble the channel type field */
+static int enc_channel_type(struct gsm0808_channel_type *ct, const struct gsm_mncc_bearer_cap *bc)
+{
+	unsigned int i;
+	uint8_t sv;
+	unsigned int count = 0;
+	bool only_gsm_hr = true;
+
+	OSMO_ASSERT(ct);
+	OSMO_ASSERT(bc);
+
+	ct->ch_indctr = GSM0808_CHAN_SPEECH;
+
+	for (i = 0; i < ARRAY_SIZE(bc->speech_ver); i++) {
+		if (bc->speech_ver[i] == -1)
+			break;
+		sv = convert_Abis_sv_to_A_sv(bc->speech_ver[i]);
+		if (sv != 0xFF) {
+			/* Detect if something else than
+			 * GSM HR V1 is supported */
+			if (sv == GSM0808_PERM_HR2 ||
+			    sv == GSM0808_PERM_HR3 || sv == GSM0808_PERM_HR4 || sv == GSM0808_PERM_HR6)
+				only_gsm_hr = false;
+
+			ct->perm_spch[count] = sv;
+			count++;
+		}
+	}
+	ct->perm_spch_len = count;
+
+	if (only_gsm_hr)
+		/* Note: We must avoid the usage of GSM HR1 as this
+		 * codec only offers very poor audio quality. If the
+		 * MS only supports GSM HR1 (and full rate), and has
+		 * a preference for half rate. Then we will ignore the
+		 * preference and assume a preference for full rate. */
+		ct->ch_rate_type = GSM0808_SPEECH_FULL_BM;
+	else
+		ct->ch_rate_type = convert_Abis_prev_to_A_pref(bc->radio);
+
+	if (count)
+		return 0;
+	else
+		return -EINVAL;
+}
+
+/* Assemble the speech codec field */
+static int enc_speech_codec_list(struct gsm0808_speech_codec_list *scl, const struct gsm0808_channel_type *ct)
+{
+	unsigned int i;
+	int rc;
+
+	memset(scl, 0, sizeof(*scl));
+	for (i = 0; i < ct->perm_spch_len; i++) {
+		rc = gsm0808_speech_codec_from_chan_type(&scl->codec[i], ct->perm_spch[i]);
+		if (rc != 0)
+			return -EINVAL;
+	}
+	scl->len = i;
+
+	return 0;
+}
+
+/* Send assignment request via A-interface */
+int a_iface_tx_assignment(const struct gsm_trans *trans)
+{
+	struct gsm_subscriber_connection *conn;
+	struct gsm0808_channel_type ct;
+	struct gsm0808_speech_codec_list scl;
+	uint32_t *ci_ptr = NULL;
+	struct msgb *msg;
+	struct sockaddr_storage rtp_addr;
+	struct sockaddr_in rtp_addr_in;
+	int rc;
+
+	OSMO_ASSERT(trans);
+	conn = trans->conn;
+	OSMO_ASSERT(conn);
+
+	LOGP(DMSC, LOGL_ERROR, "Sending assignment command to BSC (conn_id %u)\n", conn->a.conn_id);
+
+	/* Channel type */
+	rc = enc_channel_type(&ct, &trans->bearer_cap);
+	if (rc < 0) {
+		LOGP(DMSC, LOGL_ERROR, "Faild to generate channel type -- assignment not sent!\n");
+		return -EINVAL;
+	}
+
+	/* Speech codec list */
+	rc = enc_speech_codec_list(&scl, &ct);
+	if (rc < 0) {
+		LOGP(DMSC, LOGL_ERROR, "Faild to generate Speech codec list -- assignment not sent!\n");
+		return -EINVAL;
+	}
+
+	/* Package RTP-Address data */
+	memset(&rtp_addr_in, 0, sizeof(rtp_addr_in));
+	rtp_addr_in.sin_family = AF_INET;
+	rtp_addr_in.sin_port = osmo_htons(conn->rtp.port_subscr);
+	rtp_addr_in.sin_addr.s_addr = osmo_htonl(mgcpgw_client_remote_addr_n(gsm_network->mgcpgw.client));
+
+	memset(&rtp_addr, 0, sizeof(rtp_addr));
+	memcpy(&rtp_addr, &rtp_addr_in, sizeof(rtp_addr_in));
+
+	msg = gsm0808_create_ass(&ct, NULL, &rtp_addr, &scl, ci_ptr);
+
+	LOGP(DMSC, LOGL_DEBUG, "N-DATA.req(%u, %s)\n", conn->a.conn_id, osmo_hexdump(msg->data, msg->len));
+	return osmo_sccp_tx_data_msg(conn->a.scu, conn->a.conn_id, msg);
+}
+
+/* Send clear command via A-interface */
+int a_iface_tx_clear_cmd(struct gsm_subscriber_connection *conn)
+{
+	struct msgb *msg;
+
+	LOGP(DMSC, LOGL_NOTICE, "Sending clear command to BSC (conn_id=%u)\n", conn->a.conn_id);
+
+	msg = gsm0808_create_clear_command(GSM0808_CAUSE_CALL_CONTROL);
+	return osmo_sccp_tx_data_msg(conn->a.scu, conn->a.conn_id, msg);
+}
+
+/* Callback function: Close all open connections */
+static void a_reset_cb(const void *priv)
+{
+	struct msgb *msg;
+	struct bsc_context *bsc_ctx = (struct bsc_context*) priv;
+	struct osmo_ss7_instance *ss7;
+
+	/* Skip if the A interface is not properly initalized yet */
+	if (!gsm_network)
+		return;
+
+	/* Clear all now orphaned subscriber connections */
+	a_clear_all(bsc_ctx->sccp_user, &bsc_ctx->bsc_addr);
+
+	/* Send reset to the remote BSC */
+	ss7 = osmo_ss7_instance_find(gsm_network->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_NOTICE, "Sending RESET to BSC %s\n", osmo_sccp_addr_name(ss7, &bsc_ctx->bsc_addr));
+	msg = gsm0808_create_reset();
+	osmo_sccp_tx_unitdata_msg(bsc_ctx->sccp_user, &bsc_ctx->msc_addr,
+				  &bsc_ctx->bsc_addr, msg);
+}
+
+/* Add a new BSC connection to our internal list with known BSCs */
+static void add_bsc(const struct osmo_sccp_addr *msc_addr, const struct osmo_sccp_addr *bsc_addr,
+		    struct osmo_sccp_user *scu)
+{
+	struct bsc_context *bsc_ctx;
+	struct osmo_ss7_instance *ss7;
+
+	OSMO_ASSERT(bsc_addr);
+	OSMO_ASSERT(msc_addr);
+	OSMO_ASSERT(scu);
+
+	/* Check if we already know this BSC, if yes, skip adding it. */
+	if (get_reset_ctx_by_sccp_addr(bsc_addr))
+		return;
+
+	ss7 = osmo_ss7_instance_find(gsm_network->a.cs7_instance);
+	OSMO_ASSERT(ss7);
+	LOGP(DMSC, LOGL_NOTICE, "Adding new BSC connection for BSC %s...\n", osmo_sccp_addr_name(ss7, bsc_addr));
+
+	/* Generate and fill up a new bsc context */
+	bsc_ctx = talloc_zero(gsm_network, struct bsc_context);
+	OSMO_ASSERT(bsc_ctx);
+	memcpy(&bsc_ctx->bsc_addr, bsc_addr, sizeof(*bsc_addr));
+	memcpy(&bsc_ctx->msc_addr, msc_addr, sizeof(*msc_addr));
+	bsc_ctx->sccp_user = scu;
+	llist_add_tail(&bsc_ctx->list, &gsm_network->a.bscs);
+
+	/* Start reset procedure to make the new connection active */
+	bsc_ctx->reset = a_reset_alloc(bsc_ctx, osmo_sccp_addr_name(ss7, bsc_addr), a_reset_cb, bsc_ctx);
+}
+
+/* Callback function, called by the SSCP stack when data arrives */
+static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
+{
+	struct osmo_sccp_user *scu = _scu;
+	struct osmo_scu_prim *scu_prim = (struct osmo_scu_prim *)oph;
+	int rc = 0;
+	struct a_conn_info a_conn_info;
+	memset(&a_conn_info, 0, sizeof(a_conn_info));
+	a_conn_info.network = gsm_network;
+	a_conn_info.reset = NULL;
+
+	switch (OSMO_PRIM_HDR(&scu_prim->oph)) {
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_CONNECT, PRIM_OP_INDICATION):
+		/* Handle inbound connection indication */
+		add_bsc(&scu_prim->u.connect.called_addr, &scu_prim->u.connect.calling_addr, scu);
+		a_conn_info.conn_id = scu_prim->u.connect.conn_id;
+		a_conn_info.msc_addr = &scu_prim->u.connect.called_addr;
+		a_conn_info.bsc_addr = &scu_prim->u.connect.calling_addr;
+		a_conn_info.reset = get_reset_ctx_by_sccp_addr(&scu_prim->u.unitdata.calling_addr);
+
+		if (a_reset_conn_ready(a_conn_info.reset) == false) {
+			rc = osmo_sccp_tx_disconn(scu, a_conn_info.conn_id, a_conn_info.msc_addr,
+						  SCCP_RETURN_CAUSE_UNQUALIFIED);
+			break;
+		}
+
+		osmo_sccp_tx_conn_resp(scu, scu_prim->u.connect.conn_id, &scu_prim->u.connect.called_addr, NULL, 0);
+		if (msgb_l2len(oph->msg) > 0) {
+			LOGP(DMSC, LOGL_DEBUG, "N-CONNECT.ind(%u, %s)\n",
+			     scu_prim->u.connect.conn_id, osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+			rc = sccp_rx_dt(scu, &a_conn_info, oph->msg);
+		} else
+			LOGP(DMSC, LOGL_DEBUG, "N-CONNECT.ind(%u)\n", scu_prim->u.connect.conn_id);
+
+		record_bsc_con(scu, scu_prim->u.connect.conn_id);
+		break;
+
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_DATA, PRIM_OP_INDICATION):
+		/* Handle incoming connection oriented data */
+		a_conn_info.conn_id = scu_prim->u.data.conn_id;
+		LOGP(DMSC, LOGL_DEBUG, "N-DATA.ind(%u, %s)\n",
+		     scu_prim->u.data.conn_id, osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+		sccp_rx_dt(scu, &a_conn_info, oph->msg);
+		break;
+
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_UNITDATA, PRIM_OP_INDICATION):
+		/* Handle inbound UNITDATA */
+		add_bsc(&scu_prim->u.unitdata.called_addr, &scu_prim->u.unitdata.calling_addr, scu);
+		a_conn_info.msc_addr = &scu_prim->u.unitdata.called_addr;
+		a_conn_info.bsc_addr = &scu_prim->u.unitdata.calling_addr;
+		a_conn_info.reset = get_reset_ctx_by_sccp_addr(&scu_prim->u.unitdata.calling_addr);
+		DEBUGP(DMSC, "N-UNITDATA.ind(%s)\n", osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
+		sccp_rx_udt(scu, &a_conn_info, oph->msg);
+		break;
+
+	default:
+		LOGP(DMSC, LOGL_ERROR, "Unhandled SIGTRAN primitive: %u:%u\n", oph->primitive, oph->operation);
+		break;
+	}
+
+	return rc;
+}
+
+/* Clear all subscriber connections on a specified BSC */
+void a_clear_all(struct osmo_sccp_user *scu, const struct osmo_sccp_addr *bsc_addr)
+{
+	struct gsm_subscriber_connection *conn;
+	struct gsm_subscriber_connection *conn_temp;
+	struct gsm_network *network = gsm_network;
+
+	OSMO_ASSERT(scu);
+	OSMO_ASSERT(bsc_addr);
+
+	llist_for_each_entry_safe(conn, conn_temp, &network->subscr_conns, entry) {
+		/* Clear only A connections and connections that actually
+		 * belong to the specified BSC */
+		if (conn->via_ran == RAN_GERAN_A && memcmp(bsc_addr, &conn->a.bsc_addr, sizeof(conn->a.bsc_addr)) == 0) {
+			LOGP(DMSC, LOGL_NOTICE, "Dropping orphaned subscriber connection (conn_id %i)\n",
+			     conn->a.conn_id);
+			msc_clear_request(conn, GSM48_CC_CAUSE_SWITCH_CONG);
+
+			/* If there is still an SCCP connection active, remove it now */
+			if (check_connection_active(conn->a.conn_id)) {
+				osmo_sccp_tx_disconn(scu, conn->a.conn_id, bsc_addr,
+						     SCCP_RELEASE_CAUSE_END_USER_ORIGINATED);
+				a_delete_bsc_con(conn->a.conn_id);
+			}
+		}
+	}
+}
+
+/* Initalize A interface connection between to MSC and BSC */
+int a_init(struct osmo_sccp_instance *sccp, struct gsm_network *network)
+{
+	OSMO_ASSERT(sccp);
+	OSMO_ASSERT(network);
+
+	/* FIXME: Remove hardcoded parameters, use parameters in parameter list */
+	LOGP(DMSC, LOGL_NOTICE, "Initalizing SCCP connection to stp...\n");
+
+	/* Set GSM network variable, there can only be
+	 * one network by design */
+	if (gsm_network != NULL) {
+		OSMO_ASSERT(gsm_network == network);
+	} else
+		gsm_network = network;
+
+	/* SCCP Protocol stack */
+	osmo_sccp_user_bind(sccp, "OsmoMSC-A", sccp_sap_up, SCCP_SSN_BSSAP);
+
+	return 0;
 }