Implement M3UA-over-TCP (in addition to SCTP)

RFC 4666 section 1.3.1 states that "TCP MAY be used as the underlying
common transport protocol" under certain scenarios.  There is even
IANA-allocated TCP port 2905 for that purpose (see section 1.4.8).

Since TCP is a stream oriented protocol, so we need to handle message
boundaries ourselves by reading the M3UA header to know the PDU length.

Change-Id: I8c76d271472befacbeb998a93bbdc9e8660d9b5d
Related: SYS#5424

10 files changed, 575 insertions, 110 deletions

diff --git a/TODO-RELEASE b/TODO-RELEASE
index 25eeb6e..7785711 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -12,3 +12,8 @@ libosmo-netif >1.4.0	osmo_stream_{srv,cli}_get_fd()
 libosmocore >1.9.0  osmo_sock_multiaddr_get_ip_and_port(), osmo_multiaddr_ip_and_port_snprintf()
 libosmocore >1.9.0  osmo_sock_sctp_get_peer_addr_info()
 libosmo-netif >1.4.0    osmo_sctp_spinfo_state_str(), osmo_sctp_sstat_state_str()
+libosmo-sigtran	ABI change	struct osmo_ss7_asp: new field(s) at the end
+libosmo-sigtran	ABI change	struct osmo_xua_server: new field(s) at the end
+libosmo-sigtran	API added	osmo_ss7_asp_get_trans_proto()
+libosmo-sigtran	API added	osmo_ss7_asp_{find2,find_or_create2}()
+libosmo-sigtran	API added	osmo_ss7_xua_server_{find2,create2}()
diff --git a/include/osmocom/sigtran/osmo_ss7.h b/include/osmocom/sigtran/osmo_ss7.h
index fc323a8..2324532 100644
--- a/include/osmocom/sigtran/osmo_ss7.h
+++ b/include/osmocom/sigtran/osmo_ss7.h
@@ -453,6 +453,9 @@ struct osmo_ss7_asp {
 			uint16_t max_attempts_value;
 			uint16_t max_init_timeo_value; /* ms */
 		} sctp_init;
+
+		/*! The underlaying transport protocol (one of IPPROTO_*) */
+		int trans_proto;
 	} cfg;
 };
 
@@ -482,11 +485,21 @@ osmo_ss7_asp_find_by_proto(struct osmo_ss7_as *as,
 struct osmo_ss7_asp *
 osmo_ss7_asp_find(struct osmo_ss7_instance *inst, const char *name,
 		  uint16_t remote_port, uint16_t local_port,
-		  enum osmo_ss7_asp_protocol proto);
+		  enum osmo_ss7_asp_protocol proto)
+	OSMO_DEPRECATED("Use osmo_ss7_asp_find2() instead");
+struct osmo_ss7_asp *
+osmo_ss7_asp_find2(struct osmo_ss7_instance *inst, const char *name,
+		   uint16_t remote_port, uint16_t local_port,
+		   int trans_proto, enum osmo_ss7_asp_protocol proto);
 struct osmo_ss7_asp *
 osmo_ss7_asp_find_or_create(struct osmo_ss7_instance *inst, const char *name,
 			    uint16_t remote_port, uint16_t local_port,
-			    enum osmo_ss7_asp_protocol proto);
+			    enum osmo_ss7_asp_protocol proto)
+	OSMO_DEPRECATED("Use osmo_ss7_asp_find_or_create2() instead");
+struct osmo_ss7_asp *
+osmo_ss7_asp_find_or_create2(struct osmo_ss7_instance *inst, const char *name,
+			     uint16_t remote_port, uint16_t local_port,
+			     int trans_proto, enum osmo_ss7_asp_protocol proto);
 void osmo_ss7_asp_destroy(struct osmo_ss7_asp *asp);
 int osmo_ss7_asp_send(struct osmo_ss7_asp *asp, struct msgb *msg);
 int osmo_ss7_asp_restart(struct osmo_ss7_asp *asp);
@@ -495,6 +508,7 @@ bool osmo_ss7_asp_active(const struct osmo_ss7_asp *asp);
 int osmo_ss7_asp_get_log_subsys(const struct osmo_ss7_asp *asp);
 const char *osmo_ss7_asp_get_name(const struct osmo_ss7_asp *asp);
 enum osmo_ss7_asp_protocol osmo_ss7_asp_get_proto(const struct osmo_ss7_asp *asp);
+int osmo_ss7_asp_get_trans_proto(const struct osmo_ss7_asp *asp);
 
 /*! Weak function to handle payload for unknown/unsupported PPID or IPA StreamID.
  *  This function can be overridden by application code to implement whatever handling
@@ -543,16 +557,32 @@ struct osmo_xua_server {
 			uint16_t num_ostreams_value;
 			uint16_t max_instreams_value;
 		} sctp_init;
+
+		/*! The underlaying transport protocol (one of IPPROTO_*) */
+		int trans_proto;
 	} cfg;
 };
 
 struct osmo_xua_server *
-osmo_ss7_xua_server_find(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_protocol proto,
-			 uint16_t local_port);
+osmo_ss7_xua_server_find(struct osmo_ss7_instance *inst,
+			 enum osmo_ss7_asp_protocol proto,
+			 uint16_t local_port)
+	OSMO_DEPRECATED("Use osmo_ss7_xua_server_find2() instead");
+struct osmo_xua_server *
+osmo_ss7_xua_server_find2(struct osmo_ss7_instance *inst,
+			  int trans_proto,
+			  enum osmo_ss7_asp_protocol proto,
+			  uint16_t local_port);
 
 struct osmo_xua_server *
-osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_protocol proto,
-			   uint16_t local_port, const char *local_host);
+osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst,
+			   enum osmo_ss7_asp_protocol proto,
+			   uint16_t local_port, const char *local_host)
+	OSMO_DEPRECATED("Use osmo_ss7_xua_server_create2() instead");
+struct osmo_xua_server *
+osmo_ss7_xua_server_create2(struct osmo_ss7_instance *inst,
+			    int trans_proto, enum osmo_ss7_asp_protocol proto,
+			    uint16_t local_port, const char *local_host);
 
 int
 osmo_ss7_xua_server_bind(struct osmo_xua_server *xs);
diff --git a/src/osmo_ss7.c b/src/osmo_ss7.c
index 50ad172..74b0f50 100644
--- a/src/osmo_ss7.c
+++ b/src/osmo_ss7.c
@@ -1017,9 +1017,9 @@ osmo_ss7_asp_find_by_proto(struct osmo_ss7_as *as,
 }
 
 struct osmo_ss7_asp *
-osmo_ss7_asp_find(struct osmo_ss7_instance *inst, const char *name,
-		  uint16_t remote_port, uint16_t local_port,
-		  enum osmo_ss7_asp_protocol proto)
+osmo_ss7_asp_find2(struct osmo_ss7_instance *inst, const char *name,
+		   uint16_t remote_port, uint16_t local_port,
+		   int trans_proto, enum osmo_ss7_asp_protocol proto)
 {
 	struct osmo_ss7_asp *asp;
 
@@ -1028,47 +1028,107 @@ osmo_ss7_asp_find(struct osmo_ss7_instance *inst, const char *name,
 	if (!asp)
 		return NULL;
 
-	if ((asp->cfg.remote.port != remote_port || asp->cfg.local.port != local_port || asp->cfg.proto != proto))
+	if (asp->cfg.remote.port != remote_port || asp->cfg.local.port != local_port)
+		return NULL;
+	if (asp->cfg.trans_proto != trans_proto)
+		return NULL;
+	if (asp->cfg.proto != proto)
 		return NULL;
 
 	return asp;
 }
 
 struct osmo_ss7_asp *
-osmo_ss7_asp_find_or_create(struct osmo_ss7_instance *inst, const char *name,
-			    uint16_t remote_port, uint16_t local_port,
-			    enum osmo_ss7_asp_protocol proto)
+osmo_ss7_asp_find(struct osmo_ss7_instance *inst, const char *name,
+		  uint16_t remote_port, uint16_t local_port,
+		  enum osmo_ss7_asp_protocol proto)
+{
+	const int trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+
+	return osmo_ss7_asp_find2(inst, name,
+				  remote_port, local_port,
+				  trans_proto, proto);
+}
+
+struct osmo_ss7_asp *
+osmo_ss7_asp_find_or_create2(struct osmo_ss7_instance *inst, const char *name,
+			     uint16_t remote_port, uint16_t local_port,
+			     int trans_proto, enum osmo_ss7_asp_protocol proto)
 {
 	struct osmo_ss7_asp *asp;
 
 	OSMO_ASSERT(ss7_initialized);
 	asp = osmo_ss7_asp_find_by_name(inst, name);
 	if (asp) {
-		if (asp->cfg.remote.port != remote_port ||
-		    asp->cfg.local.port != local_port ||
-		    asp->cfg.proto != proto)
+		if (asp->cfg.remote.port != remote_port || asp->cfg.local.port != local_port)
+			return NULL;
+		if (asp->cfg.trans_proto != trans_proto)
+			return NULL;
+		if (asp->cfg.proto != proto)
 			return NULL;
 		return asp;
 	}
 
-	return ss7_asp_alloc(inst, name, remote_port, local_port, proto);
+	return ss7_asp_alloc(inst, name, remote_port, local_port, trans_proto, proto);
 }
 
+struct osmo_ss7_asp *
+osmo_ss7_asp_find_or_create(struct osmo_ss7_instance *inst, const char *name,
+			    uint16_t remote_port, uint16_t local_port,
+			    enum osmo_ss7_asp_protocol proto)
+{
+	const int trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+
+	return osmo_ss7_asp_find_or_create2(inst, name,
+					    remote_port, local_port,
+					    trans_proto, proto);
+}
+
+/*! \brief find an xUA server with the given parameters
+ *  \param[in] inst SS7 Instance on which we operate
+ *  \param[in] trans_proto transport protocol in use (one of IPPROTO_*)
+ *  \param[in] proto protocol (xUA variant) in use
+ *  \param[in] local_port local port of the server
+ *  \returns \ref osmo_xua_server or NULL (not found)
+ */
 struct osmo_xua_server *
-osmo_ss7_xua_server_find(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_protocol proto,
-			 uint16_t local_port)
+osmo_ss7_xua_server_find2(struct osmo_ss7_instance *inst,
+			  int trans_proto,
+			  enum osmo_ss7_asp_protocol proto,
+			  uint16_t local_port)
 {
 	struct osmo_xua_server *xs;
 
 	OSMO_ASSERT(ss7_initialized);
 	llist_for_each_entry(xs, &inst->xua_servers, list) {
-		if (proto == xs->cfg.proto &&
-		    local_port == xs->cfg.local.port)
-			return xs;
+		if (trans_proto != xs->cfg.trans_proto)
+			continue;
+		if (proto != xs->cfg.proto)
+			continue;
+		if (local_port != xs->cfg.local.port)
+			continue;
+		return xs;
 	}
+
 	return NULL;
 }
 
+/*! \brief find an xUA server with the given parameters
+ *  \param[in] inst SS7 Instance on which we operate
+ *  \param[in] proto protocol (xUA variant) in use
+ *  \param[in] local_port local port of the server
+ *  \returns \ref osmo_xua_server or NULL (not found)
+ */
+struct osmo_xua_server *
+osmo_ss7_xua_server_find(struct osmo_ss7_instance *inst,
+			 enum osmo_ss7_asp_protocol proto,
+			 uint16_t local_port)
+{
+	const int trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+
+	return osmo_ss7_xua_server_find2(inst, trans_proto, proto, local_port);
+}
+
 bool osmo_ss7_pc_is_local(struct osmo_ss7_instance *inst, uint32_t pc)
 {
 	OSMO_ASSERT(ss7_initialized);
diff --git a/src/osmo_ss7_asp.c b/src/osmo_ss7_asp.c
index a36d385..f211872 100644
--- a/src/osmo_ss7_asp.c
+++ b/src/osmo_ss7_asp.c
@@ -127,7 +127,32 @@ const struct value_string osmo_ss7_asp_role_names[] = {
 	{ 0, NULL }
 };
 
-int ss7_asp_proto_to_ip_proto(enum osmo_ss7_asp_protocol proto)
+/* check if the given transport and ASP protocols are compatible (and implemented) */
+bool ss7_asp_protocol_check_trans_proto(enum osmo_ss7_asp_protocol proto, int trans_proto)
+{
+	switch (proto) {
+	case OSMO_SS7_ASP_PROT_IPA:
+		if (trans_proto == IPPROTO_TCP)
+			return true;
+		return false;
+	case OSMO_SS7_ASP_PROT_SUA:
+		if (trans_proto == IPPROTO_SCTP)
+			return true;
+		return false;
+	case OSMO_SS7_ASP_PROT_M3UA:
+		if (trans_proto == IPPROTO_SCTP)
+			return true;
+		if (trans_proto == IPPROTO_TCP)
+			return true;
+		return false;
+	case OSMO_SS7_ASP_PROT_NONE:
+	default:
+		return false;
+	}
+}
+
+/* get _default_ transport protocol for the given ASP protocol */
+int ss7_default_trans_proto_for_asp_proto(enum osmo_ss7_asp_protocol proto)
 {
 	switch (proto) {
 	case OSMO_SS7_ASP_PROT_IPA:
@@ -503,9 +528,18 @@ ss7_asp_find_by_socket_addr(int fd)
 
 struct osmo_ss7_asp *ss7_asp_alloc(struct osmo_ss7_instance *inst, const char *name,
 				   uint16_t remote_port, uint16_t local_port,
-				   enum osmo_ss7_asp_protocol proto)
+				   int trans_proto, enum osmo_ss7_asp_protocol proto)
 {
-	struct osmo_ss7_asp *asp = talloc_zero(inst, struct osmo_ss7_asp);
+	struct osmo_ss7_asp *asp;
+
+	if (!ss7_asp_protocol_check_trans_proto(proto, trans_proto)) {
+		LOGP(DLSCCP, LOGL_ERROR,
+		     "ASP protocol '%s' with transport protocol %d is not supported",
+		     osmo_ss7_asp_protocol_name(proto), trans_proto);
+		return NULL;
+	}
+
+	asp = talloc_zero(inst, struct osmo_ss7_asp);
 	asp->ctrg = rate_ctr_group_alloc(asp, &ss7_asp_rcgd, g_ss7_asp_rcg_idx++);
 	if (!asp->ctrg) {
 		talloc_free(asp);
@@ -517,6 +551,7 @@ struct osmo_ss7_asp *ss7_asp_alloc(struct osmo_ss7_instance *inst, const char *n
 	asp->cfg.remote.port = remote_port;
 	osmo_ss7_asp_peer_init(&asp->cfg.local);
 	asp->cfg.local.port = local_port;
+	asp->cfg.trans_proto = trans_proto;
 	asp->cfg.proto = proto;
 	asp->cfg.name = talloc_strdup(asp, name);
 
@@ -566,6 +601,7 @@ void osmo_ss7_asp_destroy(struct osmo_ss7_asp *asp)
 
 static int xua_cli_read_cb(struct osmo_stream_cli *conn);
 static int ipa_cli_read_cb(struct osmo_stream_cli *conn);
+static int m3ua_tcp_cli_read_cb(struct osmo_stream_cli *conn);
 static int xua_cli_connect_cb(struct osmo_stream_cli *cli);
 
 int osmo_ss7_asp_restart(struct osmo_ss7_asp *asp)
@@ -601,13 +637,27 @@ int osmo_ss7_asp_restart(struct osmo_ss7_asp *asp)
 		osmo_stream_cli_set_port(asp->client, asp->cfg.remote.port);
 		osmo_stream_cli_set_local_addrs(asp->client, (const char **)asp->cfg.local.host, asp->cfg.local.host_cnt);
 		osmo_stream_cli_set_local_port(asp->client, asp->cfg.local.port);
-		osmo_stream_cli_set_proto(asp->client, ss7_asp_proto_to_ip_proto(asp->cfg.proto));
+		osmo_stream_cli_set_proto(asp->client, asp->cfg.trans_proto);
 		osmo_stream_cli_set_reconnect_timeout(asp->client, 5);
 		osmo_stream_cli_set_connect_cb(asp->client, xua_cli_connect_cb);
-		if (asp->cfg.proto == OSMO_SS7_ASP_PROT_IPA)
+		switch (asp->cfg.proto) {
+		case OSMO_SS7_ASP_PROT_IPA:
+			OSMO_ASSERT(asp->cfg.trans_proto == IPPROTO_TCP);
 			osmo_stream_cli_set_read_cb(asp->client, ipa_cli_read_cb);
-		else
+			break;
+		case OSMO_SS7_ASP_PROT_M3UA:
+			if (asp->cfg.trans_proto == IPPROTO_SCTP)
+				osmo_stream_cli_set_read_cb(asp->client, xua_cli_read_cb);
+			else if (asp->cfg.trans_proto == IPPROTO_TCP)
+				osmo_stream_cli_set_read_cb(asp->client, m3ua_tcp_cli_read_cb);
+			else
+				OSMO_ASSERT(0);
+			break;
+		default:
+			OSMO_ASSERT(asp->cfg.trans_proto == IPPROTO_SCTP);
 			osmo_stream_cli_set_read_cb(asp->client, xua_cli_read_cb);
+			break;
+		}
 		osmo_stream_cli_set_data(asp->client, asp);
 		byte = 1; /*AUTH is needed by ASCONF. enable, don't abort socket creation if AUTH can't be enabled */
 		osmo_stream_cli_set_param(asp->client, OSMO_STREAM_CLI_PAR_SCTP_SOCKOPT_AUTH_SUPPORTED, &byte, sizeof(byte));
@@ -838,6 +888,78 @@ out:
 	return rc;
 }
 
+/* netif code tells us we can read something from the socket */
+int ss7_asp_m3ua_tcp_srv_conn_cb(struct osmo_stream_srv *conn)
+{
+	struct osmo_ss7_asp *asp = osmo_stream_srv_get_data(conn);
+	int fd = osmo_stream_srv_get_fd(conn);
+	struct msgb *msg = asp->pending_msg;
+	const struct xua_common_hdr *hdr;
+	size_t msg_length;
+	int rc;
+
+	OSMO_ASSERT(fd >= 0);
+
+	if (msg == NULL) {
+		msg = m3ua_msgb_alloc(__func__);
+		asp->pending_msg = msg;
+	}
+
+	/* read message header first */
+	if (msg->len < sizeof(*hdr)) {
+		errno = 0;
+		rc = recv(fd, msg->tail, sizeof(*hdr) - msg->len, 0);
+		if (rc <= 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 0; /* need more data */
+			osmo_stream_srv_destroy(conn);
+			asp->pending_msg = NULL;
+			msgb_free(msg);
+			return rc;
+		}
+
+		msgb_put(msg, rc);
+		if (msg->len < sizeof(*hdr))
+			return 0; /* need more data */
+	}
+
+	hdr = (const struct xua_common_hdr *)msg->data;
+	msg_length = ntohl(hdr->msg_length); /* includes sizeof(*hdr) */
+
+	/* read the rest of the message */
+	if (msg->len < msg_length) {
+		errno = 0;
+		rc = recv(fd, msg->tail, msg_length - msg->len, 0);
+		if (rc <= 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 0; /* need more data */
+			osmo_stream_srv_destroy(conn);
+			asp->pending_msg = NULL;
+			msgb_free(msg);
+			return rc;
+		}
+
+		msgb_put(msg, rc);
+		if (msg->len < msg_length)
+			return 0; /* need more data */
+	}
+
+	msg->dst = asp;
+	rate_ctr_inc2(asp->ctrg, SS7_ASP_CTR_PKT_RX_TOTAL);
+
+	/* spoof SCTP Stream ID */
+	if (hdr->msg_class == M3UA_MSGC_XFER)
+		msgb_sctp_stream(msg) = 1;
+	else
+		msgb_sctp_stream(msg) = 0;
+
+	rc = m3ua_rx_msg(asp, msg);
+	asp->pending_msg = NULL;
+	msgb_free(msg);
+
+	return rc;
+}
+
 /* client has established SCTP connection to server */
 static int xua_cli_connect_cb(struct osmo_stream_cli *cli)
 {
@@ -858,7 +980,7 @@ static int xua_cli_connect_cb(struct osmo_stream_cli *cli)
 	 * fed and the local port is known for sure. Apply SCTP Primary addresses
 	 * if needed:
 	 */
-	if (asp->cfg.proto != OSMO_SS7_ASP_PROT_IPA) {
+	if (asp->cfg.trans_proto == IPPROTO_SCTP) {
 		rc = ss7_asp_apply_peer_primary_address(asp);
 		rc = ss7_asp_apply_primary_address(asp);
 	}
@@ -926,6 +1048,78 @@ static int ipa_cli_read_cb(struct osmo_stream_cli *conn)
 	return ipa_rx_msg(asp, msg, fd & 0xf);
 }
 
+/* read call-back for M3UA-over-TCP socket */
+static int m3ua_tcp_cli_read_cb(struct osmo_stream_cli *conn)
+{
+	struct osmo_ss7_asp *asp = osmo_stream_cli_get_data(conn);
+	int fd = osmo_stream_cli_get_fd(conn);
+	struct msgb *msg = asp->pending_msg;
+	const struct xua_common_hdr *hdr;
+	size_t msg_length;
+	int rc;
+
+	OSMO_ASSERT(fd >= 0);
+
+	if (msg == NULL) {
+		msg = m3ua_msgb_alloc(__func__);
+		asp->pending_msg = msg;
+	}
+
+	/* read message header first */
+	if (msg->len < sizeof(*hdr)) {
+		errno = 0;
+		rc = recv(fd, msg->tail, sizeof(*hdr) - msg->len, 0);
+		if (rc <= 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 0; /* need more data */
+			xua_cli_close_and_reconnect(conn);
+			asp->pending_msg = NULL;
+			msgb_free(msg);
+			return rc;
+		}
+
+		msgb_put(msg, rc);
+		if (msg->len < sizeof(*hdr))
+			return 0; /* need more data */
+	}
+
+	hdr = (const struct xua_common_hdr *)msg->data;
+	msg_length = ntohl(hdr->msg_length); /* includes sizeof(*hdr) */
+
+	/* read the rest of the message */
+	if (msg->len < msg_length) {
+		errno = 0;
+		rc = recv(fd, msg->tail, msg_length - msg->len, 0);
+		if (rc <= 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 0; /* need more data */
+			xua_cli_close_and_reconnect(conn);
+			asp->pending_msg = NULL;
+			msgb_free(msg);
+			return rc;
+		}
+
+		msgb_put(msg, rc);
+		if (msg->len < msg_length)
+			return 0; /* need more data */
+	}
+
+	msg->dst = asp;
+	rate_ctr_inc2(asp->ctrg, SS7_ASP_CTR_PKT_RX_TOTAL);
+
+	/* spoof SCTP Stream ID */
+	if (hdr->msg_class == M3UA_MSGC_XFER)
+		msgb_sctp_stream(msg) = 1;
+	else
+		msgb_sctp_stream(msg) = 0;
+
+	rc = m3ua_rx_msg(asp, msg);
+	asp->pending_msg = NULL;
+	msgb_free(msg);
+
+	return rc;
+}
+
 static int xua_cli_read_cb(struct osmo_stream_cli *conn)
 {
 	struct osmo_ss7_asp *asp = osmo_stream_cli_get_data(conn);
@@ -1135,6 +1329,15 @@ enum osmo_ss7_asp_protocol osmo_ss7_asp_get_proto(const struct osmo_ss7_asp *asp
 	return asp->cfg.proto;
 }
 
+/*! \brief Get the transport proto of a given ASP
+ *  \param[in] asp The ASP for which the transport proto is requested
+ *  \returns The transport proto of the ASP (one of IPPROTO_*)
+ */
+int osmo_ss7_asp_get_trans_proto(const struct osmo_ss7_asp *asp)
+{
+	return asp->cfg.trans_proto;
+}
+
 /*! \brief Get the fd of a given ASP
  *  \param[in] asp The ASP for which the fd is requested
  *  \returns The fd of the ASP if acailable, negative otherwise
diff --git a/src/osmo_ss7_vty.c b/src/osmo_ss7_vty.c
index 33e6e56..42a3383 100644
--- a/src/osmo_ss7_vty.c
+++ b/src/osmo_ss7_vty.c
@@ -62,6 +62,11 @@
 	"MTP3 User Adaptation\n"	\
 	"IPA Multiplex (SCCP Lite)\n"
 
+#define IPPROTO_VAR_STR "(sctp|tcp)"
+#define IPPROTO_VAR_HELP_STR \
+	"SCTP (Stream Control Transmission Protocol)\n" \
+	"TCP (Transmission Control Protocol)\n"
+
 /* netinet/tcp.h */
 static const struct value_string tcp_info_state_values[] = {
 	{ TCP_ESTABLISHED,	"ESTABLISHED" },
@@ -465,6 +470,17 @@ DEFUN(show_cs7_route, show_cs7_route_cmd,
  * xUA Listener Configuration (SG)
  ***********************************************************************/
 
+static const struct value_string ipproto_vals[] = {
+	{ IPPROTO_SCTP,		"sctp" },
+	{ IPPROTO_TCP,		"tcp" },
+	{ 0, NULL },
+};
+
+static int parse_trans_proto(const char *protocol)
+{
+	return get_string_value(ipproto_vals, protocol);
+}
+
 static enum osmo_ss7_asp_protocol parse_asp_proto(const char *protocol)
 {
 	return get_string_value(osmo_ss7_asp_protocol_vals, protocol);
@@ -477,19 +493,29 @@ static struct cmd_node xua_node = {
 };
 
 DEFUN_ATTR(cs7_xua, cs7_xua_cmd,
-	   "listen " XUA_VAR_STR " <0-65534>",
+	   "listen " XUA_VAR_STR " <0-65534> [" IPPROTO_VAR_STR "]",
 	   "Configure/Enable xUA Listener\n"
-	   XUA_VAR_HELP_STR "SCTP Port number\n",
+	   XUA_VAR_HELP_STR
+	   "Port number\n"
+	   IPPROTO_VAR_HELP_STR,
 	   CMD_ATTR_IMMEDIATE)
 {
 	struct osmo_ss7_instance *inst = vty->index;
 	struct osmo_xua_server *xs;
 	enum osmo_ss7_asp_protocol proto = parse_asp_proto(argv[0]);
 	uint16_t port = atoi(argv[1]);
+	int trans_proto;
 
-	xs = osmo_ss7_xua_server_find(inst, proto, port);
+	if (argc > 2)
+		trans_proto = parse_trans_proto(argv[2]);
+	else /* default transport protocol */
+		trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+	if (trans_proto < 0)
+		return CMD_WARNING;
+
+	xs = osmo_ss7_xua_server_find2(inst, trans_proto, proto, port);
 	if (!xs) {
-		xs = osmo_ss7_xua_server_create(inst, proto, port, NULL);
+		xs = osmo_ss7_xua_server_create2(inst, trans_proto, proto, port, NULL);
 		if (!xs)
 			return CMD_WARNING;
 		/* Drop first dummy address created automatically by _create(): */
@@ -502,17 +528,27 @@ DEFUN_ATTR(cs7_xua, cs7_xua_cmd,
 }
 
 DEFUN_ATTR(no_cs7_xua, no_cs7_xua_cmd,
-	   "no listen " XUA_VAR_STR " <0-65534>",
-	   NO_STR "Disable xUA Listener on given SCTP Port\n"
-	   XUA_VAR_HELP_STR "SCTP Port number\n",
+	   "no listen " XUA_VAR_STR " <0-65534> [" IPPROTO_VAR_STR "]",
+	   NO_STR "Disable xUA Listener on given port\n"
+	   XUA_VAR_HELP_STR
+	   "Port number\n"
+	   IPPROTO_VAR_HELP_STR,
 	   CMD_ATTR_IMMEDIATE)
 {
 	struct osmo_ss7_instance *inst = vty->index;
 	struct osmo_xua_server *xs;
 	enum osmo_ss7_asp_protocol proto = parse_asp_proto(argv[0]);
 	uint16_t port = atoi(argv[1]);
+	int trans_proto;
 
-	xs = osmo_ss7_xua_server_find(inst, proto, port);
+	if (argc > 2)
+		trans_proto = parse_trans_proto(argv[2]);
+	else /* default transport protocol */
+		trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+	if (trans_proto < 0)
+		return CMD_WARNING;
+
+	xs = osmo_ss7_xua_server_find2(inst, trans_proto, proto, port);
 	if (!xs) {
 		vty_out(vty, "No xUA server for port %u found%s", port, VTY_NEWLINE);
 		return CMD_WARNING;
@@ -616,9 +652,13 @@ DEFUN_ATTR(xua_no_sctp_param_init, xua_no_sctp_param_init_cmd,
 static void write_one_xua(struct vty *vty, struct osmo_xua_server *xs)
 {
 	int i;
-	vty_out(vty, " listen %s %u%s",
+
+	vty_out(vty, " listen %s %u",
 		get_value_string(osmo_ss7_asp_protocol_vals, xs->cfg.proto),
-		xs->cfg.local.port, VTY_NEWLINE);
+		xs->cfg.local.port);
+	if (xs->cfg.trans_proto != ss7_default_trans_proto_for_asp_proto(xs->cfg.proto))
+		vty_out(vty, " %s", get_value_string(ipproto_vals, xs->cfg.trans_proto));
+	vty_out(vty, "%s", VTY_NEWLINE);
 
 	for (i = 0; i < xs->cfg.local.host_cnt; i++) {
 		if (xs->cfg.local.host[i])
@@ -646,7 +686,7 @@ static void vty_dump_xua_server(struct vty *vty, struct osmo_xua_server *xs)
 		size_t num_hostbuf = ARRAY_SIZE(hostbuf);
 		char portbuf[6];
 		int rc;
-		rc = osmo_sock_multiaddr_get_ip_and_port(fd, ss7_asp_proto_to_ip_proto(xs->cfg.proto),
+		rc = osmo_sock_multiaddr_get_ip_and_port(fd, xs->cfg.trans_proto,
 							 &hostbuf[0][0], &num_hostbuf, sizeof(hostbuf[0]),
 							 portbuf, sizeof(portbuf), true);
 		if (rc < 0) {
@@ -659,37 +699,60 @@ static void vty_dump_xua_server(struct vty *vty, struct osmo_xua_server *xs)
 							    portbuf);
 		}
 	}
-	vty_out(vty, "xUA server for %s on %s is %s%s",
-		proto, buf, fd >= 0 ? "listening" : "inactive", VTY_NEWLINE);
+	vty_out(vty, "xUA server for %s/%s on %s is %s%s",
+		proto, get_value_string(ipproto_vals, xs->cfg.trans_proto),
+		buf, fd >= 0 ? "listening" : "inactive", VTY_NEWLINE);
 }
 
-DEFUN(show_cs7_xua, show_cs7_xua_cmd,
-      "show cs7 "XUA_VAR_STR" [<0-65534>]",
-      SHOW_STR CS7_STR XUA_VAR_HELP_STR "Port Number")
+static int _show_cs7_xua(struct vty *vty,
+			 enum osmo_ss7_asp_protocol proto,
+			 int trans_proto, int local_port)
 {
-	struct osmo_ss7_instance *inst;
-	struct osmo_xua_server *xs;
-	enum osmo_ss7_asp_protocol proto = parse_asp_proto(argv[0]);
+	const struct osmo_ss7_instance *inst;
 
 	llist_for_each_entry(inst, &osmo_ss7_instances, list) {
-		if (argc > 1) {
-			int port = atoi(argv[1]);
-			xs = osmo_ss7_xua_server_find(inst, proto, port);
-			if (!xs) {
-				vty_out(vty, "%% No matching server found%s", VTY_NEWLINE);
-				return CMD_WARNING;
-			}
+		struct osmo_xua_server *xs;
+
+		llist_for_each_entry(xs, &inst->xua_servers, list) {
+			if (xs->cfg.proto != proto)
+				continue;
+			if (local_port >= 0 && xs->cfg.local.port != local_port) /* optional */
+				continue;
+			if (trans_proto >= 0 && xs->cfg.trans_proto != trans_proto) /* optional */
+				continue;
 			vty_dump_xua_server(vty, xs);
-		} else {
-			llist_for_each_entry(xs, &inst->xua_servers, list) {
-				if (xs->cfg.proto == proto)
-					vty_dump_xua_server(vty, xs);
-			}
 		}
 	}
+
 	return CMD_SUCCESS;
 }
 
+#define SHOW_CS7_XUA_CMD \
+	"show cs7 " XUA_VAR_STR
+#define SHOW_CS7_XUA_CMD_HELP \
+	SHOW_STR CS7_STR XUA_VAR_HELP_STR
+
+DEFUN(show_cs7_xua, show_cs7_xua_cmd,
+      SHOW_CS7_XUA_CMD " [<0-65534>]",
+      SHOW_CS7_XUA_CMD_HELP "Local Port Number\n")
+{
+	enum osmo_ss7_asp_protocol proto = parse_asp_proto(argv[0]);
+	int local_port = (argc > 1) ? atoi(argv[1]) : -1;
+
+	return _show_cs7_xua(vty, proto, -1, local_port);
+}
+
+DEFUN(show_cs7_xua_trans_proto, show_cs7_xua_trans_proto_cmd,
+      SHOW_CS7_XUA_CMD " " IPPROTO_VAR_STR " [<0-65534>]",
+      SHOW_CS7_XUA_CMD_HELP IPPROTO_VAR_HELP_STR "Local Port Number\n")
+{
+	enum osmo_ss7_asp_protocol proto = parse_asp_proto(argv[0]);
+	int trans_proto = parse_trans_proto(argv[1]);
+	int local_port = (argc > 2) ? atoi(argv[2]) : -1;
+
+	return _show_cs7_xua(vty, proto, trans_proto, local_port);
+}
+
 DEFUN(show_cs7_config, show_cs7_config_cmd,
       "show cs7 config",
       SHOW_STR CS7_STR "Currently running cs7 configuration")
@@ -738,8 +801,8 @@ DEFUN_ATTR(cs7_asp, cs7_asp_cmd,
 	   "asp NAME <0-65535> <0-65535> " XUA_VAR_STR,
 	   "Configure Application Server Process\n"
 	   "Name of ASP\n"
-	   "Remote SCTP port number\n"
-	   "Local SCTP port number\n"
+	   "Remote port number\n"
+	   "Local port number\n"
 	   XUA_VAR_HELP_STR,
 	   CMD_ATTR_NODE_EXIT)
 {
@@ -747,17 +810,30 @@ DEFUN_ATTR(cs7_asp, cs7_asp_cmd,
 	const char *name = argv[0];
 	uint16_t remote_port = atoi(argv[1]);
 	uint16_t local_port = atoi(argv[2]);
-	enum osmo_ss7_asp_protocol protocol = parse_asp_proto(argv[3]);
+	enum osmo_ss7_asp_protocol proto = parse_asp_proto(argv[3]);
 	struct osmo_ss7_asp *asp;
+	int trans_proto;
 
-	if (protocol == OSMO_SS7_ASP_PROT_NONE) {
+	if (proto == OSMO_SS7_ASP_PROT_NONE) {
 		vty_out(vty, "invalid protocol '%s'%s", argv[3], VTY_NEWLINE);
 		return CMD_WARNING;
 	}
 
-	asp = osmo_ss7_asp_find(inst, name, remote_port, local_port, protocol);
+	/* argv[4] can be supplied by an alias (see below) */
+	if (argc > 4)
+		trans_proto = parse_trans_proto(argv[4]);
+	else /* default transport protocol */
+		trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+	if (trans_proto < 0)
+		return CMD_WARNING;
+
+	asp = osmo_ss7_asp_find2(inst, name,
+				 remote_port, local_port,
+				 trans_proto, proto);
 	if (!asp) {
-		asp = osmo_ss7_asp_find_or_create(inst, name, remote_port, local_port, protocol);
+		asp = osmo_ss7_asp_find_or_create2(inst, name,
+						   remote_port, local_port,
+						   trans_proto, proto);
 		if (!asp) {
 			vty_out(vty, "cannot create ASP '%s'%s", name, VTY_NEWLINE);
 			return CMD_WARNING;
@@ -772,6 +848,18 @@ DEFUN_ATTR(cs7_asp, cs7_asp_cmd,
 	return CMD_SUCCESS;
 }
 
+/* XXX: workaround for https://osmocom.org/issues/6360, can be removed once it's fixed.
+ * Currently we hit an assert if we make the IPPROTO_VAR_STR optional in cs7_asp_cmd. */
+ALIAS_ATTR(cs7_asp, cs7_asp_trans_proto_cmd,
+	   "asp NAME <0-65535> <0-65535> " XUA_VAR_STR " " IPPROTO_VAR_STR,
+	   "Configure Application Server Process\n"
+	   "Name of ASP\n"
+	   "Remote port number\n"
+	   "Local port number\n"
+	   XUA_VAR_HELP_STR
+	   IPPROTO_VAR_HELP_STR,
+	   CMD_ATTR_NODE_EXIT);
+
 DEFUN_ATTR(no_cs7_asp, no_cs7_asp_cmd,
 	   "no asp NAME",
 	   NO_STR "Disable Application Server Process\n"
@@ -1217,10 +1305,10 @@ static void show_one_asp(struct vty *vty, struct osmo_ss7_asp *asp)
 
 	int fd = ss7_asp_get_fd(asp);
 	if (fd > 0) {
-		int proto = ss7_asp_proto_to_ip_proto(asp->cfg.proto);
-		if (!get_sockname_buf(buf_loc, sizeof(buf_loc), fd, proto, true))
+		const int trans_proto = asp->cfg.trans_proto;
+		if (!get_sockname_buf(buf_loc, sizeof(buf_loc), fd, trans_proto, true))
 			OSMO_STRLCPY_ARRAY(buf_loc, "<sockname-error>");
-		if (!get_sockname_buf(buf_rem, sizeof(buf_rem), fd, proto, false))
+		if (!get_sockname_buf(buf_rem, sizeof(buf_rem), fd, trans_proto, false))
 			OSMO_STRLCPY_ARRAY(buf_rem, "<sockname-error>");
 	} else {
 		osmo_ss7_asp_peer_snprintf(buf_loc, sizeof(buf_loc), &asp->cfg.local);
@@ -1374,9 +1462,7 @@ static void show_one_asp_remaddr_sctp(struct vty *vty, struct osmo_ss7_asp *asp)
 
 static void show_one_asp_remaddr(struct vty *vty, struct osmo_ss7_asp *asp)
 {
-	int proto = ss7_asp_proto_to_ip_proto(asp->cfg.proto);
-
-	switch (proto) {
+	switch (asp->cfg.trans_proto) {
 	case IPPROTO_TCP:
 		show_one_asp_remaddr_tcp(vty, asp);
 		break;
@@ -1386,7 +1472,8 @@ static void show_one_asp_remaddr(struct vty *vty, struct osmo_ss7_asp *asp)
 		break;
 #endif
 	default:
-		vty_out(vty, "%-12s  %-46s  unknown proto %u%s", asp->cfg.name, "", proto, VTY_NEWLINE);
+		vty_out(vty, "%-12s  %-46s  unknown proto %d%s",
+			asp->cfg.name, "", asp->cfg.trans_proto, VTY_NEWLINE);
 		break;
 	}
 }
@@ -1530,9 +1617,7 @@ static void show_one_asp_assoc_status_sctp(struct vty *vty, struct osmo_ss7_asp
 
 static void show_one_asp_assoc_status(struct vty *vty, struct osmo_ss7_asp *asp)
 {
-	int proto = ss7_asp_proto_to_ip_proto(asp->cfg.proto);
-
-	switch (proto) {
+	switch (asp->cfg.trans_proto) {
 	case IPPROTO_TCP:
 		show_one_asp_assoc_status_tcp(vty, asp);
 		break;
@@ -1542,7 +1627,8 @@ static void show_one_asp_assoc_status(struct vty *vty, struct osmo_ss7_asp *asp)
 		break;
 #endif
 	default:
-		vty_out(vty, "%-12s  unknown proto %u%s", asp->cfg.name, proto, VTY_NEWLINE);
+		vty_out(vty, "%-12s  unknown proto %d%s",
+			asp->cfg.name, asp->cfg.trans_proto, VTY_NEWLINE);
 		break;
 	}
 }
@@ -1611,9 +1697,12 @@ static void write_one_asp(struct vty *vty, struct osmo_ss7_asp *asp, bool show_d
 	    && !show_dyn_config)
 		return;
 
-	vty_out(vty, " asp %s %u %u %s%s",
+	vty_out(vty, " asp %s %u %u %s",
 		asp->cfg.name, asp->cfg.remote.port, asp->cfg.local.port,
-		osmo_ss7_asp_protocol_name(asp->cfg.proto), VTY_NEWLINE);
+		osmo_ss7_asp_protocol_name(asp->cfg.proto));
+	if (asp->cfg.trans_proto != ss7_default_trans_proto_for_asp_proto(asp->cfg.proto))
+		vty_out(vty, " %s", get_value_string(ipproto_vals, asp->cfg.trans_proto));
+	vty_out(vty, "%s", VTY_NEWLINE);
 	if (asp->cfg.description)
 		vty_out(vty, "  description %s%s", asp->cfg.description, VTY_NEWLINE);
 	for (i = 0; i < asp->cfg.local.host_cnt; i++) {
@@ -2862,6 +2951,7 @@ static void vty_init_shared(void *ctx)
 
 	install_lib_element_ve(&show_cs7_user_cmd);
 	install_lib_element_ve(&show_cs7_xua_cmd);
+	install_lib_element_ve(&show_cs7_xua_trans_proto_cmd);
 	install_lib_element_ve(&show_cs7_config_cmd);
 	install_lib_element(ENABLE_NODE, &cs7_asp_disconnect_cmd);
 
@@ -2885,6 +2975,7 @@ static void vty_init_shared(void *ctx)
 	install_lib_element_ve(&show_cs7_asp_assoc_status_cmd);
 	install_lib_element_ve(&show_cs7_asp_assoc_status_name_cmd);
 	install_lib_element(L_CS7_NODE, &cs7_asp_cmd);
+	install_lib_element(L_CS7_NODE, &cs7_asp_trans_proto_cmd);
 	install_lib_element(L_CS7_NODE, &no_cs7_asp_cmd);
 	install_lib_element(L_CS7_ASP_NODE, &cfg_description_cmd);
 	install_lib_element(L_CS7_ASP_NODE, &asp_remote_ip_cmd);
diff --git a/src/osmo_ss7_xua_srv.c b/src/osmo_ss7_xua_srv.c
index 32266ff..0b83b19 100644
--- a/src/osmo_ss7_xua_srv.c
+++ b/src/osmo_ss7_xua_srv.c
@@ -67,19 +67,32 @@ static int xua_accept_cb(struct osmo_stream_srv_link *link, int fd)
 	struct osmo_ss7_asp *asp;
 	char *sock_name = osmo_sock_get_name(link, fd);
 	const char *proto_name = get_value_string(osmo_ss7_asp_protocol_vals, oxs->cfg.proto);
+	int (*read_cb)(struct osmo_stream_srv *conn) = NULL;
 	int rc = 0;
 
 	LOGP(DLSS7, LOGL_INFO, "%s: New %s connection accepted\n", sock_name, proto_name);
 
-	if (oxs->cfg.proto == OSMO_SS7_ASP_PROT_IPA) {
-		srv = osmo_stream_srv_create(oxs, link, fd,
-					     ss7_asp_ipa_srv_conn_cb,
-					     ss7_asp_xua_srv_conn_closed_cb, NULL);
-	} else {
-		srv = osmo_stream_srv_create(oxs, link, fd,
-					     ss7_asp_xua_srv_conn_cb,
-					     ss7_asp_xua_srv_conn_closed_cb, NULL);
+	switch (oxs->cfg.proto) {
+	case OSMO_SS7_ASP_PROT_IPA:
+		OSMO_ASSERT(oxs->cfg.trans_proto == IPPROTO_TCP);
+		read_cb = &ss7_asp_ipa_srv_conn_cb;
+		break;
+	case OSMO_SS7_ASP_PROT_M3UA:
+		if (oxs->cfg.trans_proto == IPPROTO_SCTP)
+			read_cb = &ss7_asp_xua_srv_conn_cb;
+		else if (oxs->cfg.trans_proto == IPPROTO_TCP)
+			read_cb = &ss7_asp_m3ua_tcp_srv_conn_cb;
+		else
+			OSMO_ASSERT(0);
+		break;
+	default:
+		OSMO_ASSERT(oxs->cfg.trans_proto == IPPROTO_SCTP);
+		read_cb = &ss7_asp_xua_srv_conn_cb;
+		break;
 	}
+
+	srv = osmo_stream_srv_create(oxs, link, fd, read_cb,
+				     &ss7_asp_xua_srv_conn_closed_cb, NULL);
 	if (!srv) {
 		LOGP(DLSS7, LOGL_ERROR, "%s: Unable to create stream server "
 		     "for connection\n", sock_name);
@@ -112,8 +125,9 @@ static int xua_accept_cb(struct osmo_stream_srv_link *link, int fd)
 			char namebuf[32];
 			static uint32_t dyn_asp_num = 0;
 			snprintf(namebuf, sizeof(namebuf), "asp-dyn-%u", dyn_asp_num++);
-			asp = osmo_ss7_asp_find_or_create(oxs->inst, namebuf, 0, 0,
-							  oxs->cfg.proto);
+			asp = osmo_ss7_asp_find_or_create2(oxs->inst, namebuf, 0, 0,
+							   oxs->cfg.trans_proto,
+							   oxs->cfg.proto);
 			if (asp) {
 				char hostbuf[INET6_ADDRSTRLEN];
 				const char *hostbuf_ptr = &hostbuf[0];
@@ -157,7 +171,7 @@ static int xua_accept_cb(struct osmo_stream_srv_link *link, int fd)
 	 * data */
 	osmo_stream_srv_set_data(srv, asp);
 
-	if (oxs->cfg.proto != OSMO_SS7_ASP_PROT_IPA) {
+	if (oxs->cfg.trans_proto == IPPROTO_SCTP) {
 		rc = ss7_asp_apply_peer_primary_address(asp);
 		rc = ss7_asp_apply_primary_address(asp);
 	}
@@ -170,19 +184,29 @@ static int xua_accept_cb(struct osmo_stream_srv_link *link, int fd)
 }
 
 /*! \brief create a new xUA server configured with given ip/port
- *  \param[in] ctx talloc allocation context
+ *  \param[in] inst SS7 Instance on which we operate
+ *  \param[in] trans_proto transport protocol to use (one of IPPROTO_*)
  *  \param[in] proto protocol (xUA variant) to use
  *  \param[in] local_port local SCTP port to bind/listen to
  *  \param[in] local_host local IP address to bind/listen to (optional)
  *  \returns callee-allocated \ref osmo_xua_server in case of success
  */
 struct osmo_xua_server *
-osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_protocol proto,
-			   uint16_t local_port, const char *local_host)
+osmo_ss7_xua_server_create2(struct osmo_ss7_instance *inst,
+			    int trans_proto, enum osmo_ss7_asp_protocol proto,
+			    uint16_t local_port, const char *local_host)
 {
-	struct osmo_xua_server *oxs = talloc_zero(inst, struct osmo_xua_server);
+	struct osmo_xua_server *oxs;
+
+	if (!ss7_asp_protocol_check_trans_proto(proto, trans_proto)) {
+		LOGP(DLSCCP, LOGL_ERROR,
+		     "ASP protocol '%s' with transport protocol %d is not supported",
+		     osmo_ss7_asp_protocol_name(proto), trans_proto);
+		return NULL;
+	}
 
 	OSMO_ASSERT(ss7_initialized);
+	oxs = talloc_zero(inst, struct osmo_xua_server);
 	if (!oxs)
 		return NULL;
 
@@ -191,6 +215,7 @@ osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_pro
 
 	INIT_LLIST_HEAD(&oxs->asp_list);
 
+	oxs->cfg.trans_proto = trans_proto;
 	oxs->cfg.proto = proto;
 	oxs->cfg.local.port = local_port;
 
@@ -201,7 +226,7 @@ osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_pro
 
 	osmo_stream_srv_link_set_nodelay(oxs->server, true);
 	osmo_stream_srv_link_set_port(oxs->server, oxs->cfg.local.port);
-	osmo_stream_srv_link_set_proto(oxs->server, ss7_asp_proto_to_ip_proto(proto));
+	osmo_stream_srv_link_set_proto(oxs->server, trans_proto);
 
 	osmo_ss7_xua_server_set_local_host(oxs, local_host);
 
@@ -218,6 +243,24 @@ osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst, enum osmo_ss7_asp_pro
 	return oxs;
 }
 
+/*! \brief create a new xUA server configured with given ip/port
+ *  \param[in] ctx talloc allocation context
+ *  \param[in] proto protocol (xUA variant) to use
+ *  \param[in] local_port local SCTP port to bind/listen to
+ *  \param[in] local_host local IP address to bind/listen to (optional)
+ *  \returns callee-allocated \ref osmo_xua_server in case of success
+ */
+struct osmo_xua_server *
+osmo_ss7_xua_server_create(struct osmo_ss7_instance *inst,
+			   enum osmo_ss7_asp_protocol proto,
+			   uint16_t local_port, const char *local_host)
+{
+	const int trans_proto = ss7_default_trans_proto_for_asp_proto(proto);
+
+	return osmo_ss7_xua_server_create2(inst, trans_proto, proto,
+					   local_port, local_host);
+}
+
 /*! \brief Set the xUA server to bind/listen to the currently configured ip/port
  *  \param[in] xs xUA server to operate
  *  \returns 0 on success, negative value on error.
diff --git a/src/sccp_user.c b/src/sccp_user.c
index 94b6d02..b72b2a6 100644
--- a/src/sccp_user.c
+++ b/src/sccp_user.c
@@ -515,6 +515,9 @@ osmo_sccp_simple_client_on_ss7_id(void *ctx, uint32_t ss7_id, const char *name,
 	struct osmo_ss7_asp *asp;
 	bool asp_created = false;
 	char *as_name, *asp_name = NULL;
+	int trans_proto;
+
+	trans_proto = ss7_default_trans_proto_for_asp_proto(prot);
 
 	/*! The function will examine the given CS7 instance and its sub
 	 *  components (as, asp, etc.). If necessary it will allocate
@@ -625,11 +628,10 @@ osmo_sccp_simple_client_on_ss7_id(void *ctx, uint32_t ss7_id, const char *name,
 			asp_name = talloc_asprintf(ctx, "asp-clnt-%s", name);
 			LOGP(DLSCCP, LOGL_NOTICE, "%s: No unassociated ASP for %s, creating new ASP %s\n",
 			     name, osmo_ss7_asp_protocol_name(prot), asp_name);
-			asp =
-			    osmo_ss7_asp_find_or_create(ss7, asp_name,
-							default_remote_port,
-							default_local_port,
-							prot);
+			asp = osmo_ss7_asp_find_or_create2(ss7, asp_name,
+							   default_remote_port,
+							   default_local_port,
+							   trans_proto, prot);
 			talloc_free(asp_name);
 			if (!asp)
 				goto out_rt;
@@ -678,7 +680,9 @@ osmo_sccp_simple_client_on_ss7_id(void *ctx, uint32_t ss7_id, const char *name,
 			LOGP(DLSCCP, LOGL_NOTICE,
 			     "%s: Requesting an SCCP simple client on ASP %s configured with 'sctp-role server'\n",
 			     name, asp->cfg.name);
-			xs = osmo_ss7_xua_server_find(ss7, prot, asp->cfg.local.port);
+			xs = osmo_ss7_xua_server_find2(ss7,
+						       asp->cfg.trans_proto, prot,
+						       asp->cfg.local.port);
 			if (!xs) {
 				LOGP(DLSCCP, LOGL_ERROR, "%s: Requesting an SCCP simple client on ASP %s configured "
 				     "with 'sctp-role server' but no matching xUA server was configured!\n",
@@ -755,8 +759,11 @@ osmo_sccp_simple_server_on_ss7_id(void *ctx, uint32_t ss7_id, uint32_t pc,
 {
 	struct osmo_ss7_instance *ss7;
 	struct osmo_xua_server *xs;
+	int trans_proto;
 	int rc;
 
+	trans_proto = ss7_default_trans_proto_for_asp_proto(prot);
+
 	if (local_port < 0)
 		local_port = osmo_ss7_asp_protocol_port(prot);
 
@@ -766,7 +773,7 @@ osmo_sccp_simple_server_on_ss7_id(void *ctx, uint32_t ss7_id, uint32_t pc,
 		return NULL;
 	ss7->cfg.primary_pc = pc;
 
-	xs = osmo_ss7_xua_server_create(ss7, prot, local_port, local_ip);
+	xs = osmo_ss7_xua_server_create2(ss7, trans_proto, prot, local_port, local_ip);
 	if (!xs)
 		goto out_ss7;
 
@@ -811,6 +818,9 @@ osmo_sccp_simple_server_add_clnt(struct osmo_sccp_instance *inst,
 	struct osmo_ss7_asp *asp;
 	struct osmo_xua_server *oxs;
 	char *as_name, *asp_name;
+	int trans_proto;
+
+	trans_proto = ss7_default_trans_proto_for_asp_proto(prot);
 
 	if (local_port < 0)
 		local_port = osmo_ss7_asp_protocol_port(prot);
@@ -831,10 +841,12 @@ osmo_sccp_simple_server_add_clnt(struct osmo_sccp_instance *inst,
 	if (!rt)
 		goto out_as;
 
-	asp = osmo_ss7_asp_find_or_create(ss7, asp_name, remote_port, local_port, prot);
+	asp = osmo_ss7_asp_find_or_create2(ss7, asp_name,
+					   remote_port, local_port,
+					   trans_proto, prot);
 	if (!asp)
 		goto out_rt;
-	oxs = osmo_ss7_xua_server_find(ss7, prot, local_port);
+	oxs = osmo_ss7_xua_server_find2(ss7, asp->cfg.trans_proto, prot, local_port);
 	if (!oxs)
 		goto out_asp;
 	if (osmo_ss7_asp_peer_set_hosts(&asp->cfg.local, asp,
diff --git a/src/ss7_internal.h b/src/ss7_internal.h
index fd01ca4..ed4fae7 100644
--- a/src/ss7_internal.h
+++ b/src/ss7_internal.h
@@ -16,15 +16,17 @@ struct osmo_ss7_as *ss7_as_alloc(struct osmo_ss7_instance *inst, const char *nam
 
 struct osmo_ss7_asp *ss7_asp_alloc(struct osmo_ss7_instance *inst, const char *name,
 				   uint16_t remote_port, uint16_t local_port,
-				   enum osmo_ss7_asp_protocol proto);
+				   int trans_proto, enum osmo_ss7_asp_protocol proto);
 bool ss7_asp_set_default_peer_hosts(struct osmo_ss7_asp *asp);
 bool ss7_asp_is_started(const struct osmo_ss7_asp *asp);
 int ss7_asp_get_fd(const struct osmo_ss7_asp *asp);
 struct osmo_ss7_asp *ss7_asp_find_by_socket_addr(int fd);
 
-int ss7_asp_proto_to_ip_proto(enum osmo_ss7_asp_protocol proto);
+bool ss7_asp_protocol_check_trans_proto(enum osmo_ss7_asp_protocol proto, int trans_proto);
+int ss7_default_trans_proto_for_asp_proto(enum osmo_ss7_asp_protocol proto);
 int ss7_asp_ipa_srv_conn_cb(struct osmo_stream_srv *conn);
 int ss7_asp_xua_srv_conn_cb(struct osmo_stream_srv *conn);
+int ss7_asp_m3ua_tcp_srv_conn_cb(struct osmo_stream_srv *conn);
 int ss7_asp_xua_srv_conn_closed_cb(struct osmo_stream_srv *srv);
 int ss7_asp_apply_peer_primary_address(const struct osmo_ss7_asp *asp);
 int ss7_asp_apply_primary_address(const struct osmo_ss7_asp *asp);
diff --git a/tests/ss7/ss7_test.c b/tests/ss7/ss7_test.c
index cf48b89..ad8dc77 100644
--- a/tests/ss7/ss7_test.c
+++ b/tests/ss7/ss7_test.c
@@ -248,7 +248,8 @@ static void test_as(void)
 	OSMO_ASSERT(osmo_ss7_as_find_by_rctx(s7i, 2342) == as);
 	OSMO_ASSERT(osmo_ss7_as_add_asp(as, "asp1") == -ENODEV);
 
-	asp = osmo_ss7_asp_find_or_create(s7i, "asp1", 0, M3UA_PORT, OSMO_SS7_ASP_PROT_M3UA);
+	asp = osmo_ss7_asp_find_or_create2(s7i, "asp1", 0, M3UA_PORT,
+					   IPPROTO_SCTP, OSMO_SS7_ASP_PROT_M3UA);
 	OSMO_ASSERT(asp);
 
 	OSMO_ASSERT(osmo_ss7_as_has_asp(as, asp) == false);
diff --git a/tests/vty/ss7_asp_test.vty b/tests/vty/ss7_asp_test.vty
index d91df24..7b36009 100644
--- a/tests/vty/ss7_asp_test.vty
+++ b/tests/vty/ss7_asp_test.vty
@@ -2,6 +2,7 @@ ss7_asp_vty_test> list
 ... !show cs7
   show cs7 instance <0-15> users
   show cs7 (sua|m3ua|ipa) [<0-65534>]
+  show cs7 (sua|m3ua|ipa) (sctp|tcp) [<0-65534>]
   show cs7 config
   show cs7 instance <0-15> asp
   show cs7 instance <0-15> asp name ASP_NAME
@@ -23,6 +24,7 @@ ss7_asp_vty_test# list
 ... !show cs7
   show cs7 instance <0-15> users
   show cs7 (sua|m3ua|ipa) [<0-65534>]
+  show cs7 (sua|m3ua|ipa) (sctp|tcp) [<0-65534>]
   show cs7 config
   cs7 instance <0-15> asp NAME disconnect
   show cs7 instance <0-15> asp
@@ -53,7 +55,18 @@ ss7_asp_vty_test# show cs7 ?
   config    Currently running cs7 configuration
 
 ss7_asp_vty_test# show cs7 m3ua ?
-  [<0-65534>]  Port Number
+  [<0-65534>]  Local Port Number
+  sctp         SCTP (Stream Control Transmission Protocol)
+  tcp          TCP (Transmission Control Protocol)
+
+ss7_asp_vty_test# show cs7 m3ua 2905 ?
+  <cr>  
+
+ss7_asp_vty_test# show cs7 m3ua sctp ?
+  [<0-65534>]  Local Port Number
+
+ss7_asp_vty_test# show cs7 m3ua sctp 2905 ?
+  <cr>  
 
 ss7_asp_vty_test# show cs7 instance ?
   <0-15>  An instance of the SS7 stack
@@ -96,6 +109,7 @@ ss7_asp_vty_test(config-cs7)# list
   point-code delimiter (default|dash)
   xua rkm routing-key-allocation (static-only|dynamic-permitted)
   asp NAME <0-65535> <0-65535> (sua|m3ua|ipa)
+  asp NAME <0-65535> <0-65535> (sua|m3ua|ipa) (sctp|tcp)
   no asp NAME
   as NAME (sua|m3ua|ipa)
   no as NAME
@@ -154,13 +168,17 @@ ss7_asp_vty_test(config-cs7)# xua rkm routing-key-allocation ?
 ss7_asp_vty_test(config-cs7)# asp ?
   NAME  Name of ASP
 ss7_asp_vty_test(config-cs7)# asp foo ?
-  <0-65535>  Remote SCTP port number
+  <0-65535>  Remote port number
 ss7_asp_vty_test(config-cs7)# asp foo 0 ?
-  <0-65535>  Local SCTP port number
+  <0-65535>  Local port number
 ss7_asp_vty_test(config-cs7)# asp foo 0 0 ?
   sua   SCCP User Adaptation
   m3ua  MTP3 User Adaptation
   ipa   IPA Multiplex (SCCP Lite)
+ss7_asp_vty_test(config-cs7)# asp foo 0 0 m3ua ?
+  sctp  SCTP (Stream Control Transmission Protocol)
+  tcp   TCP (Transmission Control Protocol)
+  <cr>  
 
 ss7_asp_vty_test(config-cs7)# as ?
   NAME  Name of the Application Server