Gb: add a second NS implementation

Reimplement NS with FSM.

Change-Id: I3525beef205588dfab9d3880a34115f1a2676e48

1 files changed, 675 insertions, 0 deletions

diff --git a/src/gb/gprs_ns2_vc_fsm.c b/src/gb/gprs_ns2_vc_fsm.c
new file mode 100644
index 00000000..7487ecde
--- /dev/null
+++ b/src/gb/gprs_ns2_vc_fsm.c
@@ -0,0 +1,675 @@
+/*! \file gprs_ns2_vc_fsm.c
+ * NS virtual circuit FSM implementation
+ * 3GPP TS 08.16 version 8.0.1 Release 1999 / ETSI TS 101 299 V8.0.1 (2002-05)
+ * as well as its successor 3GPP TS 48.016 */
+
+/* (C) 2020 sysmocom - s.f.m.c. GmbH
+ * Author: Alexander Couzens <lynxis@fe80.eu>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/* The BSS NSE only has one SGSN IP address configured, and it will use the SNS procedures
+ * to communicated its local IPs/ports as well as all the SGSN side IPs/ports and
+ * associated weights.  In theory, the BSS then uses this to establish a full mesh
+ * of NSVCs between all BSS-side IPs/ports and SGSN-side IPs/ports */
+
+#include <errno.h>
+
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <osmocom/core/fsm.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/rate_ctr.h>
+#include <osmocom/core/socket.h>
+#include <osmocom/core/stat_item.h>
+#include <osmocom/gsm/prim.h>
+#include <osmocom/gsm/tlv.h>
+#include <osmocom/gprs/gprs_msgb.h>
+#include <osmocom/gprs/protocol/gsm_08_16.h>
+
+#include "gprs_ns2_internal.h"
+
+#define S(x)	(1 << (x))
+
+#define DNS 10
+
+struct gprs_ns2_vc_priv {
+	struct gprs_ns2_vc *nsvc;
+	/* how often the timer was triggered */
+	int N;
+	/* The initiater is responsible to UNBLOCK the VC. The BSS is usually the initiater.
+	 * It can change while runtime. The side which blocks an unblocked side.*/
+	bool initiater;
+
+	/* the alive counter is present in all states */
+	struct {
+		struct osmo_timer_list timer;
+		enum ns2_timeout mode;
+		int N;
+		struct timeval timer_started;
+	} alive;
+};
+
+
+/* The FSM covers both the VC with RESET/BLOCK and without RESET/BLOCK procedure..
+ *
+ * With RESET/BLOCK, the state should follow:
+ * - UNCONFIGURED -> RESET -> BLOCK -> UNBLOCKED
+ *
+ * Without RESET/BLOCK, the state should follow:
+ * - UNCONFIGURED -> ALIVE -> UNBLOCKED
+ *
+ * The UNBLOCKED and TEST states are used to send ALIVE PDU using the timeout Tns-test and Tns-alive.
+ * UNBLOCKED -> TEST: on expire of Tns-Test, send Alive PDU.
+ * TEST -> UNBLOCKED: on receive of Alive_Ack PDU, go into UNBLOCKED.
+ *
+ * The ALIVE state is used as intermediate, because a VC is only valid if it received an Alive ACK when
+ * not using RESET/BLOCK procedure.
+ */
+
+enum gprs_ns2_vc_state {
+	GPRS_NS2_ST_UNCONFIGURED,
+	GPRS_NS2_ST_RESET,
+	GPRS_NS2_ST_BLOCKED,
+	GPRS_NS2_ST_UNBLOCKED, /* allows sending NS_UNITDATA */
+
+	GPRS_NS2_ST_ALIVE, /* only used when not using RESET/BLOCK procedure */
+};
+
+enum gprs_ns2_vc_event {
+	GPRS_NS2_EV_START,
+
+	/* received messages */
+	GPRS_NS2_EV_RESET,
+	GPRS_NS2_EV_RESET_ACK,
+	GPRS_NS2_EV_UNBLOCK,
+	GPRS_NS2_EV_UNBLOCK_ACK,
+	GPRS_NS2_EV_BLOCK,
+	GPRS_NS2_EV_BLOCK_ACK,
+	GPRS_NS2_EV_ALIVE,
+	GPRS_NS2_EV_ALIVE_ACK,
+	GPRS_NS2_EV_STATUS,
+
+	GPRS_NS2_EV_UNITDATA,
+};
+
+static const struct value_string gprs_ns2_vc_event_names[] = {
+	{ GPRS_NS2_EV_START, 		"START" },
+	{ GPRS_NS2_EV_RESET,		"RESET" },
+	{ GPRS_NS2_EV_RESET_ACK,	"RESET_ACK" },
+	{ GPRS_NS2_EV_UNBLOCK,		"UNBLOCK" },
+	{ GPRS_NS2_EV_UNBLOCK_ACK,	"UNBLOCK_ACK" },
+	{ GPRS_NS2_EV_BLOCK,		"BLOCK" },
+	{ GPRS_NS2_EV_BLOCK_ACK,	"BLOCK_ACK" },
+	{ GPRS_NS2_EV_ALIVE,		"ALIVE" },
+	{ GPRS_NS2_EV_ALIVE_ACK,	"ALIVE_ACK" },
+	{ GPRS_NS2_EV_STATUS,		"STATUS" },
+	{ GPRS_NS2_EV_UNITDATA,		"UNITDATA" },
+	{ 0, NULL }
+};
+
+static inline struct gprs_ns2_inst *ns_inst_from_fi(struct osmo_fsm_inst *fi)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+	return priv->nsvc->nse->nsi;
+}
+
+static void start_test_procedure(struct gprs_ns2_vc_priv *priv)
+{
+	struct gprs_ns2_inst *nsi = priv->nsvc->nse->nsi;
+
+	if (osmo_timer_pending(&priv->alive.timer))
+		return;
+
+	priv->alive.mode = NS_TOUT_TNS_ALIVE;
+	priv->alive.N = 0;
+
+	osmo_gettimeofday(&priv->alive.timer_started, NULL);
+	ns2_tx_alive(priv->nsvc);
+	osmo_timer_schedule(&priv->alive.timer, nsi->timeout[NS_TOUT_TNS_ALIVE], 0);
+}
+
+static void stop_test_procedure(struct gprs_ns2_vc_priv *priv)
+{
+	osmo_timer_del(&priv->alive.timer);
+}
+
+static int alive_timer_elapsed_ms(struct gprs_ns2_vc_priv *priv)
+{
+	struct timeval now, elapsed;
+	osmo_gettimeofday(&now, NULL);
+	timersub(&now, &priv->alive.timer_started, &elapsed);
+
+	return 1000 * elapsed.tv_sec + elapsed.tv_usec / 1000;
+}
+
+static void recv_test_procedure(struct osmo_fsm_inst *fi)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+	struct gprs_ns2_vc *nsvc = priv->nsvc;
+
+	/* ignoring ACKs without sending an ALIVE */
+	if (priv->alive.mode != NS_TOUT_TNS_ALIVE)
+		return;
+
+	priv->alive.mode = NS_TOUT_TNS_TEST;
+	osmo_timer_schedule(&priv->alive.timer, nsi->timeout[NS_TOUT_TNS_TEST], 0);
+	osmo_stat_item_set(nsvc->statg->items[NS_STAT_ALIVE_DELAY],
+		alive_timer_elapsed_ms(priv));
+}
+
+
+static void alive_timeout_handler(void *data)
+{
+	struct osmo_fsm_inst *fi = data;
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	switch (priv->alive.mode) {
+	case NS_TOUT_TNS_TEST:
+		priv->alive.mode = NS_TOUT_TNS_ALIVE;
+		ns2_tx_alive(priv->nsvc);
+		osmo_timer_schedule(&priv->alive.timer, nsi->timeout[NS_TOUT_TNS_ALIVE], 0);
+		break;
+	case NS_TOUT_TNS_ALIVE:
+		priv->alive.N++;
+
+		if (priv->alive.N <= nsi->timeout[NS_TOUT_TNS_ALIVE_RETRIES]) {
+			/* retransmission */
+			ns2_tx_alive(priv->nsvc);
+			osmo_timer_schedule(&priv->alive.timer, nsi->timeout[NS_TOUT_TNS_ALIVE], 0);
+		} else {
+			/* lost connection */
+			if (priv->nsvc->mode == NS2_VC_MODE_BLOCKRESET) {
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_RESET, nsi->timeout[NS_TOUT_TNS_RESET], 0);
+			} else {
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_ALIVE, nsi->timeout[NS_TOUT_TNS_ALIVE], 0);
+			}
+		}
+		break;
+	default:
+		break;
+	}
+}
+
+static void gprs_ns2_st_unconfigured(struct osmo_fsm_inst *fi, uint32_t event, void *data)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+	struct gprs_ns2_inst *nsi = priv->nsvc->nse->nsi;
+
+	switch (event) {
+	case GPRS_NS2_EV_START:
+		switch (priv->nsvc->mode) {
+		case NS2_VC_MODE_ALIVE:
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_ALIVE, nsi->timeout[NS_TOUT_TNS_ALIVE], NS_TOUT_TNS_ALIVE);
+			break;
+		case NS2_VC_MODE_BLOCKRESET:
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_RESET, nsi->timeout[NS_TOUT_TNS_RESET], NS_TOUT_TNS_RESET);
+			break;
+		}
+
+		break;
+	default:
+		OSMO_ASSERT(0);
+	}
+}
+
+
+static void gprs_ns2_st_reset_onenter(struct osmo_fsm_inst *fi, uint32_t old_state)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	if (old_state != GPRS_NS2_ST_RESET)
+		priv->N = 0;
+
+	if (priv->initiater)
+		ns2_tx_reset(priv->nsvc, NS_CAUSE_OM_INTERVENTION);
+
+	stop_test_procedure(priv);
+	ns2_nse_notify_unblocked(priv->nsvc, false);
+}
+
+static void gprs_ns2_st_reset(struct osmo_fsm_inst *fi, uint32_t event, void *data)
+{
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	if (priv->initiater) {
+		switch (event) {
+		case GPRS_NS2_EV_RESET_ACK:
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_BLOCKED,
+						nsi->timeout[NS_TOUT_TNS_BLOCK], NS_TOUT_TNS_BLOCK);
+			break;
+		}
+	} else {
+		/* we are on the receiving end */
+		switch (event) {
+		case GPRS_NS2_EV_RESET:
+			ns2_tx_reset_ack(priv->nsvc);
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_BLOCKED,
+						0, 0);
+			break;
+		}
+	}
+}
+
+static void gprs_ns2_st_blocked_onenter(struct osmo_fsm_inst *fi, uint32_t old_state)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	if (old_state != GPRS_NS2_ST_BLOCKED)
+		priv->N = 0;
+
+	if (priv->initiater)
+		ns2_tx_unblock(priv->nsvc);
+
+	start_test_procedure(priv);
+}
+
+static void gprs_ns2_st_blocked(struct osmo_fsm_inst *fi, uint32_t event, void *data)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	if (priv->initiater) {
+		switch (event) {
+		case GPRS_NS2_EV_BLOCK:
+			/* TODO: BLOCK is a UNBLOCK_NACK */
+			ns2_tx_block_ack(priv->nsvc);
+			break;
+		case GPRS_NS2_EV_UNBLOCK:
+			ns2_tx_unblock_ack(priv->nsvc);
+			/* fall through */
+		case GPRS_NS2_EV_UNBLOCK_ACK:
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_UNBLOCKED,
+						0, NS_TOUT_TNS_TEST);
+			break;
+		}
+	} else {
+		/* we are on the receiving end. The initiator who sent RESET is responsible to UNBLOCK! */
+		switch (event) {
+		case GPRS_NS2_EV_UNBLOCK:
+			ns2_tx_unblock_ack(priv->nsvc);
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_UNBLOCKED,
+						0, 0);
+			break;
+		}
+	}
+}
+
+static void gprs_ns2_st_unblocked_on_enter(struct osmo_fsm_inst *fi, uint32_t old_state)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	ns2_nse_notify_unblocked(priv->nsvc, true);
+}
+
+static void gprs_ns2_st_unblocked(struct osmo_fsm_inst *fi, uint32_t event, void *data)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	switch (event) {
+	case GPRS_NS2_EV_BLOCK:
+		priv->initiater = false;
+		ns2_tx_block_ack(priv->nsvc);
+		osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_BLOCKED,
+					0, 2);
+		break;
+	}
+}
+
+static void gprs_ns2_st_alive(struct osmo_fsm_inst *fi, uint32_t event, void *data)
+{
+	switch (event) {
+	case GPRS_NS2_EV_ALIVE_ACK:
+		osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_UNBLOCKED, 0, 0);
+		break;
+	}
+}
+
+static void gprs_ns2_st_alive_onenter(struct osmo_fsm_inst *fi, uint32_t old_state)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+
+	priv->alive.mode = NS_TOUT_TNS_TEST;
+	osmo_timer_schedule(&priv->alive.timer, nsi->timeout[NS_TOUT_TNS_TEST], 0);
+
+	if (old_state != GPRS_NS2_ST_ALIVE)
+		priv->N = 0;
+
+	ns2_tx_alive(priv->nsvc);
+	ns2_nse_notify_unblocked(priv->nsvc, false);
+}
+
+static void gprs_ns2_st_alive_onleave(struct osmo_fsm_inst *fi, uint32_t next_state)
+{
+	start_test_procedure(fi->priv);
+}
+
+static const struct osmo_fsm_state gprs_ns2_vc_states[] = {
+	[GPRS_NS2_ST_UNCONFIGURED] = {
+		.in_event_mask = S(GPRS_NS2_EV_START),
+		.out_state_mask = S(GPRS_NS2_ST_RESET) | S(GPRS_NS2_ST_ALIVE),
+		.name = "UNCONFIGURED",
+		.action = gprs_ns2_st_unconfigured,
+	},
+	[GPRS_NS2_ST_RESET] = {
+		.in_event_mask = S(GPRS_NS2_EV_RESET_ACK) | S(GPRS_NS2_EV_RESET),
+		.out_state_mask = S(GPRS_NS2_ST_RESET) |
+				  S(GPRS_NS2_ST_BLOCKED),
+		.name = "RESET",
+		.action = gprs_ns2_st_reset,
+		.onenter = gprs_ns2_st_reset_onenter,
+	},
+	[GPRS_NS2_ST_BLOCKED] = {
+		.in_event_mask = S(GPRS_NS2_EV_BLOCK) | S(GPRS_NS2_EV_BLOCK_ACK) |
+		S(GPRS_NS2_EV_UNBLOCK) | S(GPRS_NS2_EV_UNBLOCK_ACK),
+		.out_state_mask = S(GPRS_NS2_ST_RESET) |
+				  S(GPRS_NS2_ST_UNBLOCKED) |
+				  S(GPRS_NS2_ST_BLOCKED),
+		.name = "BLOCKED",
+		.action = gprs_ns2_st_blocked,
+		.onenter = gprs_ns2_st_blocked_onenter,
+	},
+	[GPRS_NS2_ST_UNBLOCKED] = {
+		.in_event_mask = S(GPRS_NS2_EV_BLOCK),
+		.out_state_mask = S(GPRS_NS2_ST_RESET) | S(GPRS_NS2_ST_ALIVE) |
+				  S(GPRS_NS2_ST_BLOCKED),
+		.name = "UNBLOCKED",
+		.action = gprs_ns2_st_unblocked,
+		.onenter = gprs_ns2_st_unblocked_on_enter,
+	},
+
+	/* ST_ALIVE is only used on VC without RESET/BLOCK */
+	[GPRS_NS2_ST_ALIVE] = {
+		.in_event_mask = S(GPRS_NS2_EV_ALIVE_ACK),
+		.out_state_mask = S(GPRS_NS2_ST_RESET) |
+				  S(GPRS_NS2_ST_UNBLOCKED),
+		.name = "ALIVE",
+		.action = gprs_ns2_st_alive,
+		.onenter = gprs_ns2_st_alive_onenter,
+		.onleave = gprs_ns2_st_alive_onleave,
+	},
+};
+
+static int gprs_ns2_vc_fsm_timer_cb(struct osmo_fsm_inst *fi)
+{
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+
+	if (priv->initiater) {
+		/* PCU timeouts */
+		switch (fi->state) {
+		case GPRS_NS2_ST_RESET:
+			priv->N++;
+			if (priv->N <= nsi->timeout[NS_TOUT_TNS_RESET_RETRIES]) {
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_RESET, nsi->timeout[NS_TOUT_TNS_RESET], 0);
+			} else {
+				priv->N = 0;
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_RESET, nsi->timeout[NS_TOUT_TNS_RESET], 0);
+			}
+			break;
+		case GPRS_NS2_ST_BLOCKED:
+			priv->N++;
+			if (priv->N <= nsi->timeout[NS_TOUT_TNS_BLOCK_RETRIES]) {
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_BLOCKED, nsi->timeout[NS_TOUT_TNS_BLOCK], 0);
+			} else {
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_RESET, nsi->timeout[NS_TOUT_TNS_RESET], 0);
+			}
+			break;
+		case GPRS_NS2_ST_ALIVE:
+			priv->N++;
+			if (priv->N <= nsi->timeout[NS_TOUT_TNS_ALIVE_RETRIES]) {
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_ALIVE, 0, 0);
+			} else {
+				priv->N = 0;
+				osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_ALIVE, 0, 0);
+			}
+			break;
+		}
+	}
+	return 0;
+}
+
+static void gprs_ns2_recv_unitdata(struct osmo_fsm_inst *fi,
+				   struct msgb *msg)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct osmo_gprs_ns2_prim nsp = {};
+	uint16_t bvci;
+
+	if (msgb_l2len(msg) < sizeof(*nsh) + 3)
+		return;
+
+	/* TODO: 7.1: For an IP sub-network, an NS-UNITDATA PDU
+	 * for a PTP BVC may indicate a request to change the IP endpoint
+	 * and/or a response to a change in the IP endpoint. */
+
+	/* TODO: nsh->data[0] -> C/R only valid in IP SNS */
+	bvci = nsh->data[1] << 8 | nsh->data[2];
+
+	msgb_bssgph(msg) = &nsh->data[3];
+	msgb_bvci(msg) = nsp.bvci = bvci;
+	msgb_nsei(msg) = nsp.nsei = priv->nsvc->nse->nsei;
+
+	if (nsh->data[0])
+		nsp.u.unitdata.change = NS_ENDPOINT_REQUEST_CHANGE;
+
+	osmo_prim_init(&nsp.oph, SAP_NS, PRIM_NS_UNIT_DATA,
+			PRIM_OP_INDICATION, msg);
+	nsi->cb(&nsp.oph, nsi->cb_data);
+}
+
+static void gprs_ns2_vc_fsm_allstate_action(struct osmo_fsm_inst *fi,
+					    uint32_t event,
+					    void *data)
+{
+	struct gprs_ns2_vc_priv *priv = fi->priv;
+	struct gprs_ns2_inst *nsi = ns_inst_from_fi(fi);
+
+	switch (event) {
+	case GPRS_NS2_EV_RESET:
+		if (priv->nsvc->mode != NS2_VC_MODE_BLOCKRESET)
+			break;
+
+		/* move the FSM into reset */
+		if (fi->state != GPRS_NS2_ST_RESET) {
+			priv->initiater = false;
+			osmo_fsm_inst_state_chg(fi, GPRS_NS2_ST_RESET, nsi->timeout[NS_TOUT_TNS_RESET], NS_TOUT_TNS_RESET);
+		}
+		/* pass the event down into FSM action */
+		gprs_ns2_st_reset(fi, event, data);
+		break;
+	case GPRS_NS2_EV_ALIVE:
+		switch (fi->state) {
+		case GPRS_NS2_ST_UNCONFIGURED:
+		case GPRS_NS2_ST_RESET:
+			/* ignore ALIVE */
+			break;
+		default:
+			ns2_tx_alive_ack(priv->nsvc);
+		}
+		break;
+	case GPRS_NS2_EV_ALIVE_ACK:
+		/* for VCs without RESET/BLOCK/UNBLOCK, the connections comes after ALIVE_ACK unblocked */
+		if (fi->state == GPRS_NS2_ST_ALIVE)
+			gprs_ns2_st_alive(fi, event, data);
+		else
+			recv_test_procedure(fi);
+		break;
+	case GPRS_NS2_EV_UNITDATA:
+		switch (fi->state) {
+		case GPRS_NS2_ST_BLOCKED:
+			/* 7.2.1: the BLOCKED_ACK might be lost */
+			if (priv->initiater)
+				gprs_ns2_recv_unitdata(fi, data);
+			else
+				ns2_tx_status(priv->nsvc,
+					      NS_CAUSE_NSVC_BLOCKED,
+					      0, data);
+			break;
+		/* ALIVE can receive UNITDATA if the ALIVE_ACK is lost */
+		case GPRS_NS2_ST_ALIVE:
+		case GPRS_NS2_ST_UNBLOCKED:
+			gprs_ns2_recv_unitdata(fi, data);
+			break;
+		}
+		break;
+	}
+}
+
+static struct osmo_fsm gprs_ns2_vc_fsm = {
+	.name = "GPRS-NS2-VC",
+	.states = gprs_ns2_vc_states,
+	.num_states = ARRAY_SIZE(gprs_ns2_vc_states),
+	.allstate_event_mask = S(GPRS_NS2_EV_UNITDATA) |
+			S(GPRS_NS2_EV_RESET) |
+			       S(GPRS_NS2_EV_ALIVE) |
+			       S(GPRS_NS2_EV_ALIVE_ACK),
+	.allstate_action = gprs_ns2_vc_fsm_allstate_action,
+	.cleanup = NULL,
+	.timer_cb = gprs_ns2_vc_fsm_timer_cb,
+	/* .log_subsys = DNS, "is not constant" */
+	.event_names = gprs_ns2_vc_event_names,
+	.pre_term = NULL,
+	.log_subsys = DLNS,
+};
+
+/*!
+ * \brief gprs_ns2_vc_fsm_alloc
+ * \param ctx
+ * \param vc
+ * \param id a char representation of the virtual curcuit
+ * \param initiater initiater is the site which starts the connection. Usually the BSS.
+ * \return NULL on error, otherwise the fsm
+ */
+struct osmo_fsm_inst *gprs_ns2_vc_fsm_alloc(struct gprs_ns2_vc *nsvc,
+					    const char *id, bool initiater)
+{
+	struct osmo_fsm_inst *fi;
+	struct gprs_ns2_vc_priv *priv;
+
+	fi = osmo_fsm_inst_alloc(&gprs_ns2_vc_fsm, nsvc, NULL, LOGL_DEBUG, id);
+	if (!fi)
+		return fi;
+
+	nsvc->fi = fi;
+	priv = fi->priv = talloc_zero(fi, struct gprs_ns2_vc_priv);
+	priv->nsvc = nsvc;
+	priv->initiater = initiater;
+
+	osmo_timer_setup(&priv->alive.timer, alive_timeout_handler, fi);
+
+	return fi;
+}
+
+/*!
+ * \brief gprs_ns2_vc_fsm_start start the FSM
+ * \param vc the virtual circuit
+ * \return 0 on success
+ */
+int gprs_ns2_vc_fsm_start(struct gprs_ns2_vc *nsvc)
+{
+	/* allows to call this function even for started nsvc by gprs_ns2_start_alive_all_nsvcs */
+	if (nsvc->fi->state == GPRS_NS2_ST_UNCONFIGURED)
+		return osmo_fsm_inst_dispatch(nsvc->fi, GPRS_NS2_EV_START, NULL);
+	return 0;
+}
+
+/*!
+ * \brief gprs_ns2_vc_rx entry point for messages from the driver/VL
+ * \param vc the virtual circuit on which is recived
+ * \param msg the message
+ * \param tp the parsed TLVs
+ * \return 0 on success
+ */
+int gprs_ns2_vc_rx(struct gprs_ns2_vc *nsvc, struct msgb *msg, struct tlv_parsed *tp)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct osmo_fsm_inst *fi = nsvc->fi;
+	uint8_t cause;
+
+	/* TODO: 7.2: on UNBLOCK/BLOCK: check if NS-VCI is correct,
+	 *  if not answer STATUS with "NS-VC unknown" */
+	/* TODO: handle RESET with different VCI */
+	/* TODO: handle BLOCK/UNBLOCK/ALIVE with different VCI */
+
+	if (gprs_ns2_validate(nsvc, nsh->pdu_type, msg, tp, &cause)) {
+		if (nsh->pdu_type != NS_PDUT_STATUS) {
+			return ns2_tx_status(nsvc, cause, 0, msg);
+		}
+	}
+
+	switch (nsh->pdu_type) {
+	case NS_PDUT_RESET:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_RESET, tp);
+		break;
+	case NS_PDUT_RESET_ACK:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_RESET_ACK, tp);
+		break;
+	case NS_PDUT_BLOCK:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_BLOCK, tp);
+		break;
+	case NS_PDUT_BLOCK_ACK:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_BLOCK_ACK, tp);
+		break;
+	case NS_PDUT_UNBLOCK:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_UNBLOCK, tp);
+		break;
+	case NS_PDUT_UNBLOCK_ACK:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_UNBLOCK_ACK, tp);
+		break;
+	case NS_PDUT_ALIVE:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_ALIVE, tp);
+		break;
+	case NS_PDUT_ALIVE_ACK:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_ALIVE_ACK, tp);
+		break;
+	case NS_PDUT_UNITDATA:
+		osmo_fsm_inst_dispatch(fi, GPRS_NS2_EV_UNITDATA, msg);
+		break;
+	default:
+		LOGP(DLNS, LOGL_ERROR, "NSEI=%u Rx unknown NS PDU type %s\n", nsvc->nse->nsei,
+			get_value_string(gprs_ns_pdu_strings, nsh->pdu_type));
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*!
+ * \brief gprs_ns2_vc_is_alive says if this
+ * \param vc
+ * \return
+ */
+int gprs_ns2_vc_is_unblocked(struct gprs_ns2_vc *nsvc)
+{
+	return (nsvc->fi->state == GPRS_NS2_ST_UNBLOCKED);
+}
+
+/* initialize osmo_ctx on main tread */
+static __attribute__((constructor)) void on_dso_load_ctx(void)
+{
+	OSMO_ASSERT(osmo_fsm_register(&gprs_ns2_vc_fsm) == 0);
+}