src/gb/gprs_ns.c

/* GPRS Networks Service (NS) messages on the Gb interface
 * 3GPP TS 08.16 version 8.0.1 Release 1999 / ETSI TS 101 299 V8.0.1 (2002-05) */

/* (C) 2009-2012 by Harald Welte <laforge@gnumonks.org>
 *
 * All Rights Reserved
 *
 * 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/>.
 *
 */

/*! \addtogroup libgb
 *  @{
 */

/*! \file gprs_ns.c */

/*!
 * GPRS Networks Service (NS) messages on the Gb interface
 * 3GPP TS 08.16 version 8.0.1 Release 1999 / ETSI TS 101 299 V8.0.1 (2002-05) 
 *
 * Some introduction into NS:  NS is used typically on top of frame relay,
 * but in the ip.access world it is encapsulated in UDP packets.  It serves
 * as an intermediate shim betwen BSSGP and the underlying medium.  It doesn't
 * do much, apart from providing congestion notification and status indication.
 *
 * Terms:
 * 	NS		Network Service
 *	NSVC		NS Virtual Connection
 *	NSEI		NS Entity Identifier
 *	NSVL		NS Virtual Link
 *	NSVLI		NS Virtual Link Identifier
 *	BVC		BSSGP Virtual Connection
 *	BVCI		BSSGP Virtual Connection Identifier
 *	NSVCG		NS Virtual Connection Goup
 *	Blocked		NS-VC cannot be used for user traffic
 *	Alive		Ability of a NS-VC to provide communication
 *
 *  There can be multiple BSSGP virtual connections over one (group of) NSVC's.  BSSGP will
 * therefore identify the BSSGP virtual connection by a BVCI passed down to NS.
 * NS then has to firgure out which NSVC's are responsible for this BVCI.
 * Those mappings are administratively configured.
 */

/* This implementation has the following limitations:
 *  o Only one NS-VC for each NSE: No load-sharing function
 *  o NSVCI 65535 and 65534 are reserved for internal use
 *  o Only UDP is supported as of now, no frame relay support
 *  o The IP Sub-Network-Service (SNS) as specified in 48.016 is not implemented
 *  o There are no BLOCK and UNBLOCK timers (yet?)
 */

#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <stdint.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#include <osmocom/core/msgb.h>
#include <osmocom/gsm/tlv.h>
#include <osmocom/core/talloc.h>
#include <osmocom/core/select.h>
#include <osmocom/core/rate_ctr.h>
#include <osmocom/core/socket.h>
#include <osmocom/core/signal.h>
#include <osmocom/gprs/gprs_ns.h>
#include <osmocom/gprs/gprs_bssgp.h>
#include <osmocom/gprs/gprs_ns_frgre.h>

#include "common_vty.h"

static const struct tlv_definition ns_att_tlvdef = {
	.def = {
		[NS_IE_CAUSE]	= { TLV_TYPE_TvLV, 0 },
		[NS_IE_VCI]	= { TLV_TYPE_TvLV, 0 },
		[NS_IE_PDU]	= { TLV_TYPE_TvLV, 0 },
		[NS_IE_BVCI]	= { TLV_TYPE_TvLV, 0 },
		[NS_IE_NSEI]	= { TLV_TYPE_TvLV, 0 },
	},
};

enum ns_ctr {
	NS_CTR_PKTS_IN,
	NS_CTR_PKTS_OUT,
	NS_CTR_BYTES_IN,
	NS_CTR_BYTES_OUT,
	NS_CTR_BLOCKED,
	NS_CTR_DEAD,
	NS_CTR_REPLACED,
	NS_CTR_NSEI_CHG,
	NS_CTR_INV_VCI,
	NS_CTR_INV_NSEI,
};

static const struct rate_ctr_desc nsvc_ctr_description[] = {
	{ "packets.in", "Packets at NS Level  ( In)" },
	{ "packets.out","Packets at NS Level  (Out)" },
	{ "bytes.in",	"Bytes at NS Level    ( In)" },
	{ "bytes.out",	"Bytes at NS Level    (Out)" },
	{ "blocked",	"NS-VC Block count         " },
	{ "dead",	"NS-VC gone dead count     " },
	{ "replaced",	"NS-VC replaced other count" },
	{ "nsei-chg",	"NS-VC changed NSEI count  " },
	{ "inv-nsvci",	"NS-VCI was invalid count  " },
	{ "inv-nsei",	"NSEI was invalid count    " },
};

static const struct rate_ctr_group_desc nsvc_ctrg_desc = {
	.group_name_prefix = "ns.nsvc",
	.group_description = "NSVC Peer Statistics",
	.num_ctr = ARRAY_SIZE(nsvc_ctr_description),
	.ctr_desc = nsvc_ctr_description,
};

#define CHECK_TX_RC(rc, nsvc) \
		if (rc < 0)							\
			LOGP(DNS, LOGL_ERROR, "TX failed (%d) to peer %s\n",	\
				rc, gprs_ns_ll_str(nsvc));


/*! \brief Lookup struct gprs_nsvc based on NSVCI
 *  \param[in] nsi NS instance in which to search
 *  \param[in] nsvci NSVCI to be searched
 *  \returns gprs_nsvc of respective NSVCI
 */
struct gprs_nsvc *gprs_nsvc_by_nsvci(struct gprs_ns_inst *nsi, uint16_t nsvci)
{
	struct gprs_nsvc *nsvc;
	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
		if (nsvc->nsvci == nsvci)
			return nsvc;
	}
	return NULL;
}

/*! \brief Lookup struct gprs_nsvc based on NSEI
 *  \param[in] nsi NS instance in which to search
 *  \param[in] nsei NSEI to be searched
 *  \returns first gprs_nsvc of respective NSEI
 */
struct gprs_nsvc *gprs_nsvc_by_nsei(struct gprs_ns_inst *nsi, uint16_t nsei)
{
	struct gprs_nsvc *nsvc;
	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
		if (nsvc->nsei == nsei)
			return nsvc;
	}
	return NULL;
}

static struct gprs_nsvc *gprs_active_nsvc_by_nsei(struct gprs_ns_inst *nsi,
						  uint16_t nsei)
{
	struct gprs_nsvc *nsvc;
	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
		if (nsvc->nsei == nsei) {
			if (!(nsvc->state & NSE_S_BLOCKED) &&
			    nsvc->state & NSE_S_ALIVE)
				return nsvc;
		}
	}
	return NULL;
}

/* Lookup struct gprs_nsvc based on remote peer socket addr */
static struct gprs_nsvc *nsvc_by_rem_addr(struct gprs_ns_inst *nsi,
					  struct sockaddr_in *sin)
{
	struct gprs_nsvc *nsvc;
	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
		if (nsvc->ip.bts_addr.sin_addr.s_addr ==
					sin->sin_addr.s_addr &&
		    nsvc->ip.bts_addr.sin_port == sin->sin_port)
			return nsvc;
	}
	return NULL;
}

static void gprs_ns_timer_cb(void *data);

struct gprs_nsvc *gprs_nsvc_create(struct gprs_ns_inst *nsi, uint16_t nsvci)
{
	struct gprs_nsvc *nsvc;

	LOGP(DNS, LOGL_INFO, "NSVCI=%u Creating NS-VC\n", nsvci);

	nsvc = talloc_zero(nsi, struct gprs_nsvc);
	nsvc->nsvci = nsvci;
	nsvc->nsvci_is_valid = 1;
	/* before RESET procedure: BLOCKED and DEAD */
	nsvc->state = NSE_S_BLOCKED;
	nsvc->nsi = nsi;
	nsvc->timer.cb = gprs_ns_timer_cb;
	nsvc->timer.data = nsvc;
	nsvc->ctrg = rate_ctr_group_alloc(nsvc, &nsvc_ctrg_desc, nsvci);

	llist_add(&nsvc->list, &nsi->gprs_nsvcs);

	return nsvc;
}

/*! \brief Delete given NS-VC
 *  \param[in] nsvc gprs_nsvc to be deleted
 */
void gprs_nsvc_delete(struct gprs_nsvc *nsvc)
{
	if (osmo_timer_pending(&nsvc->timer))
		osmo_timer_del(&nsvc->timer);
	llist_del(&nsvc->list);
	rate_ctr_group_free(nsvc->ctrg);
	talloc_free(nsvc);
}

static void ns_osmo_signal_dispatch(struct gprs_nsvc *nsvc, unsigned int signal,
			       uint8_t cause)
{
	struct ns_signal_data nssd = {0};

	nssd.nsvc = nsvc;
	nssd.cause = cause;

	osmo_signal_dispatch(SS_L_NS, signal, &nssd);
}

static void ns_osmo_signal_dispatch_mismatch(struct gprs_nsvc *nsvc,
					     struct msgb *msg,
					     uint8_t pdu_type, uint8_t ie_type)
{
	struct ns_signal_data nssd = {0};

	nssd.nsvc     = nsvc;
	nssd.pdu_type = pdu_type;
	nssd.ie_type  = ie_type;
	nssd.msg      = msg;

	osmo_signal_dispatch(SS_L_NS, S_NS_MISMATCH, &nssd);
}

static void ns_osmo_signal_dispatch_replaced(struct gprs_nsvc *nsvc, struct gprs_nsvc *old_nsvc)
{
	struct ns_signal_data nssd = {0};

	nssd.nsvc = nsvc;
	nssd.old_nsvc = old_nsvc;

	osmo_signal_dispatch(SS_L_NS, S_NS_REPLACED, &nssd);
}

/* Section 10.3.2, Table 13 */
static const struct value_string ns_cause_str[] = {
	{ NS_CAUSE_TRANSIT_FAIL,	"Transit network failure" },
	{ NS_CAUSE_OM_INTERVENTION, 	"O&M intervention" },
	{ NS_CAUSE_EQUIP_FAIL,		"Equipment failure" },
	{ NS_CAUSE_NSVC_BLOCKED,	"NS-VC blocked" },
	{ NS_CAUSE_NSVC_UNKNOWN,	"NS-VC unknown" },
	{ NS_CAUSE_BVCI_UNKNOWN,	"BVCI unknown" },
	{ NS_CAUSE_SEM_INCORR_PDU,	"Semantically incorrect PDU" },
	{ NS_CAUSE_PDU_INCOMP_PSTATE,	"PDU not compatible with protocol state" },
	{ NS_CAUSE_PROTO_ERR_UNSPEC,	"Protocol error, unspecified" },
	{ NS_CAUSE_INVAL_ESSENT_IE,	"Invalid essential IE" },
	{ NS_CAUSE_MISSING_ESSENT_IE,	"Missing essential IE" },
	{ 0, NULL }
};

/*! \brief Obtain a human-readable string for NS cause value */
const char *gprs_ns_cause_str(enum ns_cause cause)
{
	return get_value_string(ns_cause_str, cause);
}

static int nsip_sendmsg(struct gprs_nsvc *nsvc, struct msgb *msg);
extern int grps_ns_frgre_sendmsg(struct gprs_nsvc *nsvc, struct msgb *msg);

static int gprs_ns_tx(struct gprs_nsvc *nsvc, struct msgb *msg)
{
	int ret;

	log_set_context(GPRS_CTX_NSVC, nsvc);

	/* Increment number of Uplink bytes */
	rate_ctr_inc(&nsvc->ctrg->ctr[NS_CTR_PKTS_OUT]);
	rate_ctr_add(&nsvc->ctrg->ctr[NS_CTR_BYTES_OUT], msgb_l2len(msg));

	switch (nsvc->ll) {
	case GPRS_NS_LL_UDP:
		ret = nsip_sendmsg(nsvc, msg);
		break;
	case GPRS_NS_LL_FR_GRE:
		ret = gprs_ns_frgre_sendmsg(nsvc, msg);
		break;
	default:
		LOGP(DNS, LOGL_ERROR, "unsupported NS linklayer %u\n", nsvc->ll);
		msgb_free(msg);
		ret = -EIO;
		break;
	}
	return ret;
}

static int gprs_ns_tx_simple(struct gprs_nsvc *nsvc, uint8_t pdu_type)
{
	struct msgb *msg = gprs_ns_msgb_alloc();
	struct gprs_ns_hdr *nsh;

	log_set_context(GPRS_CTX_NSVC, nsvc);

	if (!msg)
		return -ENOMEM;

	msg->l2h = msgb_put(msg, sizeof(*nsh));
	nsh = (struct gprs_ns_hdr *) msg->l2h;

	nsh->pdu_type = pdu_type;

	return gprs_ns_tx(nsvc, msg);
}

/*! \brief Transmit a NS-RESET on a given NSVC
 *  \param[in] nsvc NS-VC used for transmission
 *  \paam[in] cause Numeric NS cause value
 */
int gprs_ns_tx_reset(struct gprs_nsvc *nsvc, uint8_t cause)
{
	struct msgb *msg = gprs_ns_msgb_alloc();
	struct gprs_ns_hdr *nsh;
	uint16_t nsvci = htons(nsvc->nsvci);
	uint16_t nsei = htons(nsvc->nsei);

	log_set_context(GPRS_CTX_NSVC, nsvc);

	if (!msg)
		return -ENOMEM;

	LOGP(DNS, LOGL_INFO, "NSEI=%u Tx NS RESET (NSVCI=%u, cause=%s)\n",
		nsvc->nsei, nsvc->nsvci, gprs_ns_cause_str(cause));

	nsvc->state |= NSE_S_RESET;

	msg->l2h = msgb_put(msg, sizeof(*nsh));
	nsh = (struct gprs_ns_hdr *) msg->l2h;
	nsh->pdu_type = NS_PDUT_RESET;

	msgb_tvlv_put(msg, NS_IE_CAUSE, 1, &cause);
	msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *) &nsvci);
	msgb_tvlv_put(msg, NS_IE_NSEI, 2, (uint8_t *) &nsei);

	return gprs_ns_tx(nsvc, msg);

}

/*! \brief Transmit a NS-STATUS on a given NSVC
 *  \param[in] nsvc NS-VC to be used for transmission
 *  \param[in] cause Numeric NS cause value
 *  \param[in] bvci BVCI to be reset within NSVC
 *  \param[in] orig_msg message causing the STATUS */
int gprs_ns_tx_status(struct gprs_nsvc *nsvc, uint8_t cause,
		      uint16_t bvci, struct msgb *orig_msg)
{
	struct msgb *msg = gprs_ns_msgb_alloc();
	struct gprs_ns_hdr *nsh;
	uint16_t nsvci = htons(nsvc->nsvci);

	log_set_context(GPRS_CTX_NSVC, nsvc);

	bvci = htons(bvci);

	if (!msg)
		return -ENOMEM;

	LOGP(DNS, LOGL_NOTICE, "NSEI=%u Tx NS STATUS (NSVCI=%u, cause=%s)\n",
		nsvc->nsei, nsvc->nsvci, gprs_ns_cause_str(cause));

	msg->l2h = msgb_put(msg, sizeof(*nsh));
	nsh = (struct gprs_ns_hdr *) msg->l2h;
	nsh->pdu_type = NS_PDUT_STATUS;

	msgb_tvlv_put(msg, NS_IE_CAUSE, 1, &cause);

	/* Section 9.2.7.1: Static conditions for NS-VCI */
	if (cause == NS_CAUSE_NSVC_BLOCKED ||
	    cause == NS_CAUSE_NSVC_UNKNOWN)
		msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *)&nsvci);

	/* Section 9.2.7.2: Static conditions for NS PDU */
	switch (cause) {
	case NS_CAUSE_SEM_INCORR_PDU:
	case NS_CAUSE_PDU_INCOMP_PSTATE:
	case NS_CAUSE_PROTO_ERR_UNSPEC:
	case NS_CAUSE_INVAL_ESSENT_IE:
	case NS_CAUSE_MISSING_ESSENT_IE:
		msgb_tvlv_put(msg, NS_IE_PDU, msgb_l2len(orig_msg),
			      orig_msg->l2h);
		break;
	default:
		break;
	}

	/* Section 9.2.7.3: Static conditions for BVCI */
	if (cause == NS_CAUSE_BVCI_UNKNOWN)
		msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *)&bvci);

	return gprs_ns_tx(nsvc, msg);
}

/*! \brief Transmit a NS-BLOCK on a tiven NS-VC
 *  \param[in] nsvc NS-VC on which the NS-BLOCK is to be transmitted
 *  \param[in] cause Numeric NS Cause value
 *  \returns 0 in case of success
 */
int gprs_ns_tx_block(struct gprs_nsvc *nsvc, uint8_t cause)
{
	struct msgb *msg = gprs_ns_msgb_alloc();
	struct gprs_ns_hdr *nsh;
	uint16_t nsvci = htons(nsvc->nsvci);

	log_set_context(GPRS_CTX_NSVC, nsvc);

	if (!msg)
		return -ENOMEM;

	LOGP(DNS, LOGL_INFO, "NSEI=%u Tx NS BLOCK (NSVCI=%u, cause=%s)\n",
		nsvc->nsei, nsvc->nsvci, gprs_ns_cause_str(cause));

	/* be conservative and mark it as blocked even now! */
	nsvc->state |= NSE_S_BLOCKED;
	rate_ctr_inc(&nsvc->ctrg->ctr[NS_CTR_BLOCKED]);

	msg->l2h = msgb_put(msg, sizeof(*nsh));
	nsh = (struct gprs_ns_hdr *) msg->l2h;
	nsh->pdu_type = NS_PDUT_BLOCK;

	msgb_tvlv_put(msg, NS_IE_CAUSE, 1, &cause);
	msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *) &nsvci);

	return gprs_ns_tx(nsvc, msg);
}

/*! \brief Transmit a NS-UNBLOCK on a given NS-VC
 *  \param[in] nsvc NS-VC on which the NS-UNBLOCK is to be transmitted
 *  \returns 0 in case of success
 */
int gprs_ns_tx_unblock(struct gprs_nsvc *nsvc)
{
	log_set_context(GPRS_CTX_NSVC, nsvc);
	LOGP(DNS, LOGL_INFO, "NSEI=%u Tx NS UNBLOCK (NSVCI=%u)\n",
		nsvc->nsei, nsvc->nsvci);

	return gprs_ns_tx_simple(nsvc, NS_PDUT_UNBLOCK);
}

/*! \brief Transmit a NS-ALIVE on a given NS-VC
 *  \param[in] nsvc NS-VC on which the NS-ALIVE is to be transmitted
 *  \returns 0 in case of success
 */
int gprs_ns_tx_alive(struct gprs_nsvc *nsvc)
{
	log_set_context(GPRS_CTX_NSVC, nsvc);
	LOGP(DNS, LOGL_DEBUG, "NSEI=%u Tx NS ALIVE (NSVCI=%u)\n",
		nsvc->nsei, nsvc->nsvci);

	return gprs_ns_tx_simple(nsvc, NS_PDUT_ALIVE);
}

/*! \brief Transmit a NS-ALIVE-ACK on a given NS-VC
 *  \param[in] nsvc NS-VC on which the NS-ALIVE-ACK is to be transmitted
 *  \returns 0 in case of success
 */
int gprs_ns_tx_alive_ack(struct gprs_nsvc *nsvc)
{
	log_set_context(GPRS_CTX_NSVC, nsvc);
	LOGP(DNS, LOGL_DEBUG, "NSEI=%u Tx NS ALIVE_ACK (NSVCI=%u)\n",
		nsvc->nsei, nsvc->nsvci);

	return gprs_ns_tx_simple(nsvc, NS_PDUT_ALIVE_ACK);
}

static const enum ns_timeout timer_mode_tout[_NSVC_TIMER_NR] = {
	[NSVC_TIMER_TNS_RESET]	= NS_TOUT_TNS_RESET,
	[NSVC_TIMER_TNS_ALIVE]	= NS_TOUT_TNS_ALIVE,
	[NSVC_TIMER_TNS_TEST]	= NS_TOUT_TNS_TEST,
};

static const struct value_string timer_mode_strs[] = {
	{ NSVC_TIMER_TNS_RESET, "tns-reset" },
	{ NSVC_TIMER_TNS_ALIVE, "tns-alive" },
	{ NSVC_TIMER_TNS_TEST, "tns-test" },
	{ 0, NULL }
};

static void nsvc_start_timer(struct gprs_nsvc *nsvc, enum nsvc_timer_mode mode)
{
	enum ns_timeout tout = timer_mode_tout[mode];
	unsigned int seconds = nsvc->nsi->timeout[tout];

	log_set_context(GPRS_CTX_NSVC, nsvc);
	DEBUGP(DNS, "NSEI=%u Starting timer in mode %s (%u seconds)\n",
		nsvc->nsei, get_value_string(timer_mode_strs, mode),
		seconds);
		
	if (osmo_timer_pending(&nsvc->timer))
		osmo_timer_del(&nsvc->timer);

	nsvc->timer_mode = mode;
	osmo_timer_schedule(&nsvc->timer, seconds, 0);
}

static void gprs_ns_timer_cb(void *data)
{
	struct gprs_nsvc *nsvc = data;
	enum ns_timeout tout = timer_mode_tout[nsvc->timer_mode];
	unsigned int seconds = nsvc->nsi->timeout[tout];

	log_set_context(GPRS_CTX_NSVC, nsvc);
	DEBUGP(DNS, "NSEI=%u Timer expired in mode %s (%u seconds)\n",
		nsvc->nsei, get_value_string(timer_mode_strs, nsvc->timer_mode),
		seconds);
		
	switch (nsvc->timer_mode) {
	case NSVC_TIMER_TNS_ALIVE:
		/* Tns-alive case: we expired without response ! */
		nsvc->alive_retries++;
		if (nsvc->alive_retries >
			nsvc->nsi->timeout[NS_TOUT_TNS_ALIVE_RETRIES]) {
			/* mark as dead and blocked */
			nsvc->state = NSE_S_BLOCKED;
			rate_ctr_inc(&nsvc->ctrg->ctr[NS_CTR_BLOCKED]);
			rate_ctr_inc(&nsvc->ctrg->ctr[NS_CTR_DEAD]);
			LOGP(DNS, LOGL_NOTICE,
				"NSEI=%u Tns-alive expired more then "
				"%u times, blocking NS-VC\n", nsvc->nsei,
				nsvc->nsi->timeout[NS_TOUT_TNS_ALIVE_RETRIES]);
			ns_osmo_signal_dispatch(nsvc, S_NS_ALIVE_EXP, 0);
			ns_osmo_signal_dispatch(nsvc, S_NS_BLOCK, NS_CAUSE_NSVC_BLOCKED);
			return;
		}
		/* Tns-test case: send NS-ALIVE PDU */
		gprs_ns_tx_alive(nsvc);
		/* start Tns-alive timer */
		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_ALIVE);
		break;
	case NSVC_TIMER_TNS_TEST:
		/* Tns-test case: send NS-ALIVE PDU */
		gprs_ns_tx_alive(nsvc);
		/* start Tns-alive timer (transition into faster
		 * alive retransmissions) */
		nsvc->alive_retries = 0;
		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_ALIVE);
		break;
	case NSVC_TIMER_TNS_RESET:
		/* Chapter 7.3: Re-send the RESET */
		gprs_ns_tx_reset(nsvc, NS_CAUSE_OM_INTERVENTION);
		/* Re-start Tns-reset timer */
		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_RESET);
		break;
	case _NSVC_TIMER_NR:
		break;
	}
}

/* Section 9.2.6 */
static int gprs_ns_tx_reset_ack(struct gprs_nsvc *nsvc)
{
	struct msgb *msg = gprs_ns_msgb_alloc();
	struct gprs_ns_hdr *nsh;
	uint16_t nsvci, nsei;

	log_set_context(GPRS_CTX_NSVC, nsvc);
	if (!msg)
		return -ENOMEM;

	nsvci = htons(nsvc->nsvci);
	nsei = htons(nsvc->nsei);

	msg->l2h = msgb_put(msg, sizeof(*nsh));
	nsh = (struct gprs_ns_hdr *) msg->l2h;

	nsh->pdu_type = NS_PDUT_RESET_ACK;

	LOGP(DNS, LOGL_INFO, "NSEI=%u Tx NS RESET ACK (NSVCI=%u)\n",
		nsvc->nsei, nsvc->nsvci);

	msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *)&nsvci);
	msgb_tvlv_put(msg, NS_IE_NSEI, 2, (uint8_t *)&nsei);

	return gprs_ns_tx(nsvc, msg);
}

/*! \brief High-level function for transmitting a NS-UNITDATA messsage
 *  \param[in] nsi NS-instance on which we shall transmit
 *  \param[in] msg struct msgb to be trasnmitted
 *
 * This function obtains the NS-VC by the msgb_nsei(msg) and then checks
 * if the NS-VC is ALIVEV and not BLOCKED.  After that, it adds a NS
 * header for the NS-UNITDATA message type and sends it off.
 *
 * Section 9.2.10: transmit side / NS-UNITDATA-REQUEST primitive 
 */
int gprs_ns_sendmsg(struct gprs_ns_inst *nsi, struct msgb *msg)
{
	struct gprs_nsvc *nsvc;
	struct gprs_ns_hdr *nsh;
	uint16_t bvci = msgb_bvci(msg);

	nsvc = gprs_active_nsvc_by_nsei(nsi, msgb_nsei(msg));
	if (!nsvc) {
		int rc;
		if (gprs_nsvc_by_nsei(nsi, msgb_nsei(msg))) {
		    LOGP(DNS, LOGL_ERROR,
			 "All NS-VCs for NSEI %u are either dead or blocked!\n",
			 msgb_nsei(msg));
		    rc = -EBUSY;
		} else {
		    LOGP(DNS, LOGL_ERROR, "Unable to resolve NSEI %u "
			 "to NS-VC!\n", msgb_nsei(msg));
		    rc = -EINVAL;
		}

		msgb_free(msg);
		return rc;
	}
	log_set_context(GPRS_CTX_NSVC, nsvc);

	msg->l2h = msgb_push(msg, sizeof(*nsh) + 3);
	nsh = (struct gprs_ns_hdr *) msg->l2h;
	if (!nsh) {
		LOGP(DNS, LOGL_ERROR, "Not enough headroom for NS header\n");
		msgb_free(msg);
		return -EIO;
	}

	nsh->pdu_type = NS_PDUT_UNITDATA;
	/* spare octet in data[0] */
	nsh->data[1] = bvci >> 8;
	nsh->data[2] = bvci & 0xff;

	return gprs_ns_tx(nsvc, msg);
}

/* Section 9.2.10: receive side */
static int gprs_ns_rx_unitdata(struct gprs_nsvc *nsvc, struct msgb *msg)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *)msg->l2h;
	uint16_t bvci;

	if (nsvc->state & NSE_S_BLOCKED)
		return gprs_ns_tx_status(nsvc, NS_CAUSE_NSVC_BLOCKED,
					 0, msg);

	/* spare octet in data[0] */
	bvci = nsh->data[1] << 8 | nsh->data[2];
	msgb_bssgph(msg) = &nsh->data[3];
	msgb_bvci(msg) = bvci;

	/* call upper layer (BSSGP) */
	return nsvc->nsi->cb(GPRS_NS_EVT_UNIT_DATA, nsvc, msg, bvci);
}

/* Section 9.2.7 */
static int gprs_ns_rx_status(struct gprs_nsvc *nsvc, struct msgb *msg)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
	struct tlv_parsed tp;
	uint8_t cause;
	int rc;

	LOGP(DNS, LOGL_NOTICE, "NSEI=%u Rx NS STATUS ", nsvc->nsei);

	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data,
			msgb_l2len(msg) - sizeof(*nsh), 0, 0);
	if (rc < 0) {
		LOGPC(DNS, LOGL_NOTICE, "Error during TLV Parse\n");
		LOGP(DNS, LOGL_ERROR, "NSEI=%u Rx NS STATUS: "
			"Error during TLV Parse\n", nsvc->nsei);
		return rc;
	}

	if (!TLVP_PRESENT(&tp, NS_IE_CAUSE)) {
		LOGPC(DNS, LOGL_INFO, "missing cause IE\n");
		return -EINVAL;
	}

	cause = *TLVP_VAL(&tp, NS_IE_CAUSE);
	LOGPC(DNS, LOGL_NOTICE, "cause=%s\n", gprs_ns_cause_str(cause));

	return 0;
}

/* Replace a nsvc object with another based on NSVCI.
 * This function replaces looks for a NSVC with the given NSVCI and replaces it
 * if possible and necessary. If replaced, the former value of *nsvc is
 * returned in *old_nsvc.
 * \return != 0 if *nsvc points to a matching NSVC.
 */
static int gprs_nsvc_replace_if_found(uint16_t nsvci,
				      struct gprs_nsvc **nsvc,
				      struct gprs_nsvc **old_nsvc)
{
	struct gprs_nsvc *matching_nsvc;

	if ((*nsvc)->nsvci == nsvci) {
		*old_nsvc = NULL;
		return 1;
	}

	matching_nsvc = gprs_nsvc_by_nsvci((*nsvc)->nsi, nsvci);

	if (!matching_nsvc)
		return 0;

	/* The NS-VCI is already used by this NS-VC */

	char *old_peer;

	/* Exchange the NS-VC objects */
	*old_nsvc = *nsvc;
	*nsvc     = matching_nsvc;

	/* Do logging */
	old_peer = talloc_strdup(*old_nsvc, gprs_ns_ll_str(*old_nsvc));
	LOGP(DNS, LOGL_INFO, "NS-VC changed link (NSVCI=%u) from %s to %s\n",
	     nsvci, old_peer, gprs_ns_ll_str(*nsvc));

	talloc_free(old_peer);

	return 1;
}

/* Section 7.3 */
static int gprs_ns_rx_reset(struct gprs_nsvc **nsvc, struct msgb *msg)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
	struct tlv_parsed tp;
	uint8_t cause;
	uint16_t nsvci, nsei;
	struct gprs_nsvc *orig_nsvc = NULL;
	int rc;

	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data,
			msgb_l2len(msg) - sizeof(*nsh), 0, 0);
	if (rc < 0) {
		LOGP(DNS, LOGL_ERROR, "NSEI=%u Rx NS RESET "
			"Error during TLV Parse\n", (*nsvc)->nsei);
		return rc;
	}

	if (!TLVP_PRESENT(&tp, NS_IE_CAUSE) ||
	    !TLVP_PRESENT(&tp, NS_IE_VCI) ||
	    !TLVP_PRESENT(&tp, NS_IE_NSEI)) {
		LOGP(DNS, LOGL_ERROR, "NS RESET Missing mandatory IE\n");
		gprs_ns_tx_status(*nsvc, NS_CAUSE_MISSING_ESSENT_IE, 0, msg);
		return -EINVAL;
	}

	cause = *(uint8_t  *) TLVP_VAL(&tp, NS_IE_CAUSE);
	nsvci = ntohs(*(uint16_t *) TLVP_VAL(&tp, NS_IE_VCI));
	nsei  = ntohs(*(uint16_t *) TLVP_VAL(&tp, NS_IE_NSEI));

	LOGP(DNS, LOGL_INFO, "NSVCI=%u%s Rx NS RESET (NSEI=%u, NSVCI=%u, cause=%s)\n",
	     (*nsvc)->nsvci, (*nsvc)->nsvci_is_valid ? "" : "(invalid)",
	     nsei, nsvci, gprs_ns_cause_str(cause));

	if ((*nsvc)->nsvci_is_valid && (*nsvc)->nsvci != nsvci) {
		if ((*nsvc)->persistent || (*nsvc)->remote_end_is_sgsn) {
			/* The incoming RESET doesn't match the NSVCI. Send an
			 * appropriate RESET_ACK and ignore the RESET.
			 * See 3GPP TS 08.16, 7.3.1, 2nd paragraph.
			 */
			ns_osmo_signal_dispatch_mismatch(*nsvc, msg,
							 NS_PDUT_RESET,
							 NS_IE_VCI);
			rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_INV_VCI]);
			gprs_ns_tx_reset_ack(*nsvc);
			return 0;
		}

		/* NS-VCI has changed */
		if (!gprs_nsvc_replace_if_found(nsvci, nsvc, &orig_nsvc)) {
			LOGP(DNS, LOGL_INFO, "Creating NS-VC %d replacing %d "
			     "at %s\n",
			     nsvci, (*nsvc)->nsvci,
			     gprs_ns_ll_str(*nsvc));
			orig_nsvc = *nsvc;
			*nsvc = gprs_nsvc_create((*nsvc)->nsi, nsvci);
			(*nsvc)->nsei  = nsei;
		}
	}

	if ((*nsvc)->nsvci_is_valid && (*nsvc)->nsei != nsei) {
		if ((*nsvc)->persistent || (*nsvc)->remote_end_is_sgsn) {
			/* The incoming RESET doesn't match the NSEI. Send an
			 * appropriate RESET_ACK and ignore the RESET.
			 * See 3GPP TS 08.16, 7.3.1, 3rd paragraph.
			 */
			ns_osmo_signal_dispatch_mismatch(*nsvc, msg,
							 NS_PDUT_RESET,
							 NS_IE_NSEI);
			rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_INV_NSEI]);
			rc = gprs_ns_tx_reset_ack(*nsvc);
			CHECK_TX_RC(rc, *nsvc);
			return 0;
		}

		/* NSEI has changed */
		rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_NSEI_CHG]);
		(*nsvc)->nsei = nsei;
	}

	/* Mark NS-VC as blocked and alive */
	(*nsvc)->state = NSE_S_BLOCKED | NSE_S_ALIVE;

	if (orig_nsvc) {
		rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_REPLACED]);
		ns_osmo_signal_dispatch_replaced(*nsvc, orig_nsvc);

		/* Update the ll info fields */
		gprs_ns_ll_copy(*nsvc, orig_nsvc);
		gprs_ns_ll_clear(orig_nsvc);
	} else {
		(*nsvc)->nsei  = nsei;
		(*nsvc)->nsvci = nsvci;
		(*nsvc)->nsvci_is_valid = 1;
	}

	/* inform interested parties about the fact that this NSVC
	 * has received RESET */
	ns_osmo_signal_dispatch(*nsvc, S_NS_RESET, cause);

	rc = gprs_ns_tx_reset_ack(*nsvc);

	/* start the test procedure */
	gprs_ns_tx_simple((*nsvc), NS_PDUT_ALIVE);
	nsvc_start_timer((*nsvc), NSVC_TIMER_TNS_TEST);

	return rc;
}

static int gprs_ns_rx_reset_ack(struct gprs_nsvc **nsvc, struct msgb *msg)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
	struct tlv_parsed tp;
	uint16_t nsvci, nsei;
	struct gprs_nsvc *orig_nsvc = NULL;
	int rc;

	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data,
			msgb_l2len(msg) - sizeof(*nsh), 0, 0);
	if (rc < 0) {
		LOGP(DNS, LOGL_ERROR, "NSEI=%u Rx NS RESET ACK "
			"Error during TLV Parse\n", (*nsvc)->nsei);
		return rc;
	}

	if (!TLVP_PRESENT(&tp, NS_IE_VCI) ||
	    !TLVP_PRESENT(&tp, NS_IE_NSEI)) {
		LOGP(DNS, LOGL_ERROR, "NS RESET ACK Missing mandatory IE\n");
		rc = gprs_ns_tx_status(*nsvc, NS_CAUSE_MISSING_ESSENT_IE, 0, msg);
		CHECK_TX_RC(rc, *nsvc);
		return -EINVAL;
	}

	nsvci = ntohs(*(uint16_t *) TLVP_VAL(&tp, NS_IE_VCI));
	nsei  = ntohs(*(uint16_t *) TLVP_VAL(&tp, NS_IE_NSEI));

	LOGP(DNS, LOGL_INFO, "NSVCI=%u%s Rx NS RESET ACK (NSEI=%u, NSVCI=%u)\n",
	     (*nsvc)->nsvci, (*nsvc)->nsvci_is_valid ? "" : "(invalid)",
	     nsei, nsvci);

	if (!((*nsvc)->state & NSE_S_RESET)) {
		/* Not waiting for a RESET_ACK on this NS-VC, ignore it.
		 * See 3GPP TS 08.16, 7.3.1, 5th paragraph.
		 */
		LOGP(DNS, LOGL_ERROR,
		     "NS RESET ACK Discarding unexpected message for "
		     "NS-VCI %d from SGSN NSEI=%d\n",
		     nsvci, nsei);
		return 0;
	}

	if (!(*nsvc)->nsvci_is_valid) {
		LOGP(DNS, LOGL_NOTICE,
		     "NS RESET ACK Uninitialised NS-VC (%u) for "
		     "NS-VCI %d, NSEI=%d from %s\n",
		     (*nsvc)->nsvci, nsvci, nsei, gprs_ns_ll_str(*nsvc));
		return -EINVAL;
	}

	if ((*nsvc)->nsvci != nsvci) {
		/* NS-VCI has changed */

		/* if !0, use another NSVC object that matches the NSVCI */
		int use_other_nsvc;

		/* Only do this with BSS peers */
		use_other_nsvc = !(*nsvc)->remote_end_is_sgsn &&
			!(*nsvc)->persistent;

		if (use_other_nsvc)
			/* Update *nsvc to point to the right NSVC object */
			use_other_nsvc = gprs_nsvc_replace_if_found(nsvci, nsvc,
								    &orig_nsvc);

		if (!use_other_nsvc) {
			/* The incoming RESET_ACK doesn't match the NSVCI.
			 * See 3GPP TS 08.16, 7.3.1, 4th paragraph.
			 */
			ns_osmo_signal_dispatch_mismatch(*nsvc, msg,
							 NS_PDUT_RESET_ACK,
							 NS_IE_VCI);
			rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_INV_VCI]);
			LOGP(DNS, LOGL_ERROR,
			     "NS RESET ACK Unknown NS-VCI %d (%s NSEI=%d) "
			     "from %s\n",
			     nsvci,
			     (*nsvc)->remote_end_is_sgsn ? "SGSN" : "BSS",
			     nsei, gprs_ns_ll_str(*nsvc));
			return -EINVAL;
		}

		/* Notify others */
		rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_REPLACED]);
		ns_osmo_signal_dispatch_replaced(*nsvc, orig_nsvc);

		/* Update the ll info fields */
		gprs_ns_ll_copy(*nsvc, orig_nsvc);
		gprs_ns_ll_clear(orig_nsvc);
	} else if ((*nsvc)->nsei != nsei) {
		if ((*nsvc)->persistent || (*nsvc)->remote_end_is_sgsn) {
			/* The incoming RESET_ACK doesn't match the NSEI.
			 * See 3GPP TS 08.16, 7.3.1, 4th paragraph.
			 */
			ns_osmo_signal_dispatch_mismatch(*nsvc, msg,
							 NS_PDUT_RESET_ACK,
							 NS_IE_NSEI);
			rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_INV_NSEI]);
			LOGP(DNS, LOGL_ERROR,
			     "NS RESET ACK Unknown NSEI %d (NS-VCI=%u) from %s\n",
			     nsei, nsvci, gprs_ns_ll_str(*nsvc));
			return -EINVAL;
		}

		/* NSEI has changed */
		rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_NSEI_CHG]);
		(*nsvc)->nsei = nsei;
	}

	/* Mark NS-VC as blocked and alive */
	(*nsvc)->state = NSE_S_BLOCKED | NSE_S_ALIVE;
	(*nsvc)->remote_state = NSE_S_BLOCKED | NSE_S_ALIVE;
	rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_BLOCKED]);
	if ((*nsvc)->persistent || (*nsvc)->remote_end_is_sgsn) {
		/* stop RESET timer */
		osmo_timer_del(&(*nsvc)->timer);
	}
	/* Initiate TEST proc.: Send ALIVE and start timer */
	rc = gprs_ns_tx_simple(*nsvc, NS_PDUT_ALIVE);
	nsvc_start_timer(*nsvc, NSVC_TIMER_TNS_TEST);

	return rc;
}

static int gprs_ns_rx_block(struct gprs_nsvc *nsvc, struct msgb *msg)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
	struct tlv_parsed tp;
	uint8_t *cause;
	int rc;

	LOGP(DNS, LOGL_INFO, "NSEI=%u Rx NS BLOCK\n", nsvc->nsei);

	nsvc->state |= NSE_S_BLOCKED;

	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data,
			msgb_l2len(msg) - sizeof(*nsh), 0, 0);
	if (rc < 0) {
		LOGP(DNS, LOGL_ERROR, "NSEI=%u Rx NS BLOCK "
			"Error during TLV Parse\n", nsvc->nsei);
		return rc;
	}

	if (!TLVP_PRESENT(&tp, NS_IE_CAUSE) ||
	    !TLVP_PRESENT(&tp, NS_IE_VCI)) {
		LOGP(DNS, LOGL_ERROR, "NS RESET Missing mandatory IE\n");
		gprs_ns_tx_status(nsvc, NS_CAUSE_MISSING_ESSENT_IE, 0, msg);
		return -EINVAL;
	}

	cause = (uint8_t *) TLVP_VAL(&tp, NS_IE_CAUSE);
	//nsvci = (uint16_t *) TLVP_VAL(&tp, NS_IE_VCI);

	ns_osmo_signal_dispatch(nsvc, S_NS_BLOCK, *cause);
	rate_ctr_inc(&nsvc->ctrg->ctr[NS_CTR_BLOCKED]);

	return gprs_ns_tx_simple(nsvc, NS_PDUT_BLOCK_ACK);
}

int gprs_ns_vc_create(struct gprs_ns_inst *nsi, struct msgb *msg,
		      struct gprs_nsvc *fallback_nsvc,
		      struct gprs_nsvc **new_nsvc);

int gprs_ns_process_msg(struct gprs_ns_inst *nsi, struct msgb *msg,
		      struct gprs_nsvc **nsvc);

/*! \brief Receive incoming NS message from underlying transport layer
 *  \param nsi NS instance to which the data belongs
 *  \param[in] msg message buffer containing newly-received data
 *  \param[in] saddr socketaddr from which data was received
 *  \param[in] ll link-layer type in which data was received
 *  \returns 0 in case of success, < 0 in case of error
 *
 * This is the main entry point int othe NS imlementation where frames
 * from the underlying transport (normally UDP) enter.
 */
int gprs_ns_rcvmsg(struct gprs_ns_inst *nsi, struct msgb *msg,
		   struct sockaddr_in *saddr, enum gprs_ns_ll ll)
{
	struct gprs_nsvc *nsvc;
	int rc = 0;

	/* look up the NSVC based on source address */
	nsvc = nsvc_by_rem_addr(nsi, saddr);

	if (!nsvc) {
		struct gprs_nsvc *fallback_nsvc;

		fallback_nsvc = nsi->unknown_nsvc;
		log_set_context(GPRS_CTX_NSVC, fallback_nsvc);
		fallback_nsvc->ip.bts_addr = *saddr;
		fallback_nsvc->ll = ll;

		rc = gprs_ns_vc_create(nsi, msg, fallback_nsvc, &nsvc);

		if (rc < 0)
			return rc;

		rc = 0;
	}

	if (nsvc)
		rc = gprs_ns_process_msg(nsi, msg, &nsvc);

	return rc;
}

const char *gprs_ns_ll_str(struct gprs_nsvc *nsvc)
{
	static char buf[80];
	snprintf(buf, sizeof(buf), "%s:%u",
		 inet_ntoa(nsvc->ip.bts_addr.sin_addr),
		 ntohs(nsvc->ip.bts_addr.sin_port));
	buf[sizeof(buf) - 1] = '\0';

	return buf;
}

void gprs_ns_ll_copy(struct gprs_nsvc *nsvc, struct gprs_nsvc *other)
{
	nsvc->ll = other->ll;

	switch (nsvc->ll) {
	case GPRS_NS_LL_UDP:
		nsvc->ip = other->ip;
		break;
	case GPRS_NS_LL_FR_GRE:
		nsvc->frgre = other->frgre;
		break;
	default:
		break;
	}
}

void gprs_ns_ll_clear(struct gprs_nsvc *nsvc)
{
	switch (nsvc->ll) {
	case GPRS_NS_LL_UDP:
		nsvc->ip.bts_addr.sin_addr.s_addr = INADDR_ANY;
		nsvc->ip.bts_addr.sin_port        = 0;
		break;
	case GPRS_NS_LL_FR_GRE:
		nsvc->frgre.bts_addr.sin_addr.s_addr = INADDR_ANY;
		nsvc->frgre.bts_addr.sin_port        = 0;
		break;
	default:
		break;
	}
}

/*! \brief Create/get NS-VC independently from underlying transport layer
 *  \param nsi NS instance to which the data belongs
 *  \param[in] msg message buffer containing newly-received data
 *  \param[in] fallback_nsvc is used to send error messages back to the peer
 *             and to initialise the ll info of a created NS-VC object
 *  \param[out] new_nsvc contains a pointer to a NS-VC object if one has
 *              been created or found
 *  \returns < 0 in case of error, GPRS_NS_CS_SKIPPED if a message has been
 *           skipped, GPRS_NS_CS_REJECTED if a message has been rejected and
 *           answered accordingly, GPRS_NS_CS_CREATED if a new NS-VC object
 *           has been created and registered, and GPRS_NS_CS_FOUND if an
 *           existing NS-VC object has been found with the same NSEI.
 *
 * This contains the initial NS automaton state (NS-VC not yet attached).
 */
int gprs_ns_vc_create(struct gprs_ns_inst *nsi, struct msgb *msg,
		      struct gprs_nsvc *fallback_nsvc,
		      struct gprs_nsvc **new_nsvc)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *)msg->l2h;
	struct gprs_nsvc *existing_nsvc;

	struct tlv_parsed tp;
	uint16_t nsvci;
	uint16_t nsei;

	int rc;

	if (nsh->pdu_type == NS_PDUT_STATUS) {
		/* Do not respond, see 3GPP TS 08.16, 7.5.1 */
		LOGP(DNS, LOGL_INFO, "Ignoring NS STATUS from %s "
		     "for non-existing NS-VC\n",
		     gprs_ns_ll_str(fallback_nsvc));
		return GPRS_NS_CS_SKIPPED;
	}

	if (nsh->pdu_type == NS_PDUT_ALIVE_ACK) {
		/* Ignore this, see 3GPP TS 08.16, 7.4.1 */
		LOGP(DNS, LOGL_INFO, "Ignoring NS ALIVE ACK from %s "
		     "for non-existing NS-VC\n",
		     gprs_ns_ll_str(fallback_nsvc));
		return GPRS_NS_CS_SKIPPED;
	}

	if (nsh->pdu_type == NS_PDUT_RESET_ACK) {
		/* Ignore this, see 3GPP TS 08.16, 7.3.1 */
		LOGP(DNS, LOGL_INFO, "Ignoring NS RESET ACK from %s "
		     "for non-existing NS-VC\n",
		     gprs_ns_ll_str(fallback_nsvc));
		return GPRS_NS_CS_SKIPPED;
	}

	/* Only the RESET procedure creates a new NSVC */
	if (nsh->pdu_type != NS_PDUT_RESET) {
		/* Since we have no NSVC, we have to use a fake */
		log_set_context(GPRS_CTX_NSVC, fallback_nsvc);
		LOGP(DNS, LOGL_INFO, "Rejecting NS PDU type 0x%0x "
		     "from %s for non-existing NS-VC\n",
		     nsh->pdu_type, gprs_ns_ll_str(fallback_nsvc));
		fallback_nsvc->nsvci = fallback_nsvc->nsei = 0xfffe;
		fallback_nsvc->nsvci_is_valid = 0;
		fallback_nsvc->state = NSE_S_ALIVE;

		rc = gprs_ns_tx_status(fallback_nsvc,
				       NS_CAUSE_PDU_INCOMP_PSTATE, 0, msg);
		if (rc < 0) {
			LOGP(DNS, LOGL_ERROR, "TX failed (%d) to peer %s\n",
				rc, gprs_ns_ll_str(fallback_nsvc));
			return rc;
		}
		return GPRS_NS_CS_REJECTED;
	}

	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data,
		       msgb_l2len(msg) - sizeof(*nsh), 0, 0);
	if (rc < 0) {
		LOGP(DNS, LOGL_ERROR, "Rx NS RESET Error %d during "
		     "TLV Parse\n", rc);
		return rc;
	}
	if (!TLVP_PRESENT(&tp, NS_IE_CAUSE) ||
	    !TLVP_PRESENT(&tp, NS_IE_VCI) || !TLVP_PRESENT(&tp, NS_IE_NSEI)) {
		LOGP(DNS, LOGL_ERROR, "NS RESET Missing mandatory IE\n");
		rc = gprs_ns_tx_status(fallback_nsvc, NS_CAUSE_MISSING_ESSENT_IE, 0,
				  msg);
		CHECK_TX_RC(rc, fallback_nsvc);
		return -EINVAL;
	}
	nsvci = ntohs(*(uint16_t *) TLVP_VAL(&tp, NS_IE_VCI));
	nsei  = ntohs(*(uint16_t *) TLVP_VAL(&tp, NS_IE_NSEI));
	/* Check if we already know this NSVCI, the remote end might
	 * simply have changed addresses, or it is a SGSN */
	existing_nsvc = gprs_nsvc_by_nsvci(nsi, nsvci);
	if (!existing_nsvc) {
		*new_nsvc = gprs_nsvc_create(nsi, 0xffff);
		(*new_nsvc)->nsvci_is_valid = 0;
		log_set_context(GPRS_CTX_NSVC, *new_nsvc);
		gprs_ns_ll_copy(*new_nsvc, fallback_nsvc);
		LOGP(DNS, LOGL_INFO, "Creating NS-VC for BSS at %s\n",
		     gprs_ns_ll_str(fallback_nsvc));

		return GPRS_NS_CS_CREATED;
	}

	/* Check NSEI */
	if (existing_nsvc->nsei != nsei) {
		LOGP(DNS, LOGL_NOTICE,
			"NS-VC changed NSEI (NSVCI=%u) from %u to %u\n",
			nsvci, existing_nsvc->nsei, nsei);

		/* Override old NSEI */
		existing_nsvc->nsei  = nsei;

		/* Do statistics */
		rate_ctr_inc(&existing_nsvc->ctrg->ctr[NS_CTR_NSEI_CHG]);
	}

	*new_nsvc = existing_nsvc;
	gprs_ns_ll_copy(*new_nsvc, fallback_nsvc);
	return GPRS_NS_CS_FOUND;
}

/*! \brief Process NS message independently from underlying transport layer
 *  \param nsi NS instance to which the data belongs
 *  \param[in] msg message buffer containing newly-received data
 *  \param[inout] nsvc refers to the virtual connection, may be modified when
 *                     processing a NS_RESET
 *  \returns 0 in case of success, < 0 in case of error
 *
 * This contains the main NS automaton.
 */
int gprs_ns_process_msg(struct gprs_ns_inst *nsi, struct msgb *msg,
			struct gprs_nsvc **nsvc)
{
	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
	int rc = 0;

	msgb_nsei(msg) = (*nsvc)->nsei;

	log_set_context(GPRS_CTX_NSVC, *nsvc);

	/* Increment number of Incoming bytes */
	rate_ctr_inc(&(*nsvc)->ctrg->ctr[NS_CTR_PKTS_IN]);
	rate_ctr_add(&(*nsvc)->ctrg->ctr[NS_CTR_BYTES_IN], msgb_l2len(msg));

	switch (nsh->pdu_type) {
	case NS_PDUT_ALIVE:
		/* If we're dead and blocked and suddenly receive a
		 * NS-ALIVE out of the blue, we might have been re-started
		 * and should send a NS-RESET to make sure everything recovers
		 * fine. */
		if ((*nsvc)->state == NSE_S_BLOCKED)
			rc = gprs_ns_tx_reset((*nsvc), NS_CAUSE_PDU_INCOMP_PSTATE);
		else
			rc = gprs_ns_tx_alive_ack(*nsvc);
		break;
	case NS_PDUT_ALIVE_ACK:
		/* stop Tns-alive and start Tns-test */
		nsvc_start_timer(*nsvc, NSVC_TIMER_TNS_TEST);
		if ((*nsvc)->remote_end_is_sgsn) {
			/* FIXME: this should be one level higher */
			if ((*nsvc)->state & NSE_S_BLOCKED)
				rc = gprs_ns_tx_unblock(*nsvc);
		}
		break;
	case NS_PDUT_UNITDATA:
		/* actual user data */
		rc = gprs_ns_rx_unitdata(*nsvc, msg);
		break;
	case NS_PDUT_STATUS:
		rc = gprs_ns_rx_status(*nsvc, msg);
		break;
	case NS_PDUT_RESET:
		rc = gprs_ns_rx_reset(nsvc, msg);
		break;
	case NS_PDUT_RESET_ACK:
		rc = gprs_ns_rx_reset_ack(nsvc, msg);
		break;
	case NS_PDUT_UNBLOCK:
		/* Section 7.2: unblocking procedure */
		LOGP(DNS, LOGL_INFO, "NSEI=%u Rx NS UNBLOCK\n", (*nsvc)->nsei);
		(*nsvc)->state &= ~NSE_S_BLOCKED;
		ns_osmo_signal_dispatch(*nsvc, S_NS_UNBLOCK, 0);
		rc = gprs_ns_tx_simple(*nsvc, NS_PDUT_UNBLOCK_ACK);
		break;
	case NS_PDUT_UNBLOCK_ACK:
		LOGP(DNS, LOGL_INFO, "NSEI=%u Rx NS UNBLOCK ACK\n", (*nsvc)->nsei);
		/* mark NS-VC as unblocked + active */
		(*nsvc)->state = NSE_S_ALIVE;
		(*nsvc)->remote_state = NSE_S_ALIVE;
		ns_osmo_signal_dispatch(*nsvc, S_NS_UNBLOCK, 0);
		break;
	case NS_PDUT_BLOCK:
		rc = gprs_ns_rx_block(*nsvc, msg);
		break;
	case NS_PDUT_BLOCK_ACK:
		LOGP(DNS, LOGL_INFO, "NSEI=%u Rx NS BLOCK ACK\n", (*nsvc)->nsei);
		/* mark remote NS-VC as blocked + active */
		(*nsvc)->remote_state = NSE_S_BLOCKED | NSE_S_ALIVE;
		break;
	default:
		LOGP(DNS, LOGL_NOTICE, "NSEI=%u Rx Unknown NS PDU type 0x%02x\n",
			(*nsvc)->nsei, nsh->pdu_type);
		rc = -EINVAL;
		break;
	}
	return rc;
}

/*! \brief Create a new GPRS NS instance
 *  \param[in] cb Call-back function for incoming BSSGP data
 *  \returns dynamically allocated gprs_ns_inst
 */
struct gprs_ns_inst *gprs_ns_instantiate(gprs_ns_cb_t *cb, void *ctx)
{
	struct gprs_ns_inst *nsi = talloc_zero(ctx, struct gprs_ns_inst);

	nsi->cb = cb;
	INIT_LLIST_HEAD(&nsi->gprs_nsvcs);
	nsi->timeout[NS_TOUT_TNS_BLOCK] = 3;
	nsi->timeout[NS_TOUT_TNS_BLOCK_RETRIES] = 3;
	nsi->timeout[NS_TOUT_TNS_RESET] = 3;
	nsi->timeout[NS_TOUT_TNS_RESET_RETRIES] = 3;
	nsi->timeout[NS_TOUT_TNS_TEST] = 30;
	nsi->timeout[NS_TOUT_TNS_ALIVE] = 3;
	nsi->timeout[NS_TOUT_TNS_ALIVE_RETRIES] = 10;

	/* Create the dummy NSVC that we use for sending
	 * messages to non-existant/unknown NS-VC's */
	nsi->unknown_nsvc = gprs_nsvc_create(nsi, 0xfffe);
	nsi->unknown_nsvc->nsvci_is_valid = 0;
	llist_del(&nsi->unknown_nsvc->list);
	INIT_LLIST_HEAD(&nsi->unknown_nsvc->list);

	return nsi;
}

void gprs_ns_close(struct gprs_ns_inst *nsi)
{
	struct gprs_nsvc *nsvc, *nsvc2;

	gprs_nsvc_delete(nsi->unknown_nsvc);

	/* delete all NSVCs and clear their timers */
	llist_for_each_entry_safe(nsvc, nsvc2, &nsi->gprs_nsvcs, list)
		gprs_nsvc_delete(nsvc);

	/* close socket and unregister */
	if (nsi->nsip.fd.data) {
		close(nsi->nsip.fd.fd);
		osmo_fd_unregister(&nsi->nsip.fd);
		nsi->nsip.fd.data = NULL;
	}
}

/*! \brief Destroy an entire NS instance
 *  \param nsi gprs_ns_inst that is to be destroyed
 *
 *  This function releases all resources associated with the
 *  NS-instance.
 */
void gprs_ns_destroy(struct gprs_ns_inst *nsi)
{
	gprs_ns_close(nsi);
	/* free the NSI */
	talloc_free(nsi);
}


/* NS-over-IP code, according to 3GPP TS 48.016 Chapter 6.2
 * We don't support Size Procedure, Configuration Procedure, ChangeWeight Procedure */

/* Read a single NS-over-IP message */
static struct msgb *read_nsip_msg(struct osmo_fd *bfd, int *error,
				  struct sockaddr_in *saddr)
{
	struct msgb *msg = gprs_ns_msgb_alloc();
	int ret = 0;
	socklen_t saddr_len = sizeof(*saddr);

	if (!msg) {
		*error = -ENOMEM;
		return NULL;
	}

	ret = recvfrom(bfd->fd, msg->data, NS_ALLOC_SIZE - NS_ALLOC_HEADROOM, 0,
			(struct sockaddr *)saddr, &saddr_len);
	if (ret < 0) {
		LOGP(DNS, LOGL_ERROR, "recv error %s during NSIP recv\n",
			strerror(errno));
		msgb_free(msg);
		*error = ret;
		return NULL;
	} else if (ret == 0) {
		msgb_free(msg);
		*error = ret;
		return NULL;
	}

	msg->l2h = msg->data;
	msgb_put(msg, ret);

	return msg;
}

static int handle_nsip_read(struct osmo_fd *bfd)
{
	int error;
	struct sockaddr_in saddr;
	struct gprs_ns_inst *nsi = bfd->data;
	struct msgb *msg = read_nsip_msg(bfd, &error, &saddr);

	if (!msg)
		return error;

	error = gprs_ns_rcvmsg(nsi, msg, &saddr, GPRS_NS_LL_UDP);

	msgb_free(msg);

	return error;
}

static int handle_nsip_write(struct osmo_fd *bfd)
{
	/* FIXME: actually send the data here instead of nsip_sendmsg() */
	return -EIO;
}

static int nsip_sendmsg(struct gprs_nsvc *nsvc, struct msgb *msg)
{
	int rc;
	struct gprs_ns_inst *nsi = nsvc->nsi;
	struct sockaddr_in *daddr = &nsvc->ip.bts_addr;

	rc = sendto(nsi->nsip.fd.fd, msg->data, msg->len, 0,
		  (struct sockaddr *)daddr, sizeof(*daddr));

	msgb_free(msg);

	return rc;
}

/* UDP Port 23000 carries the LLC-in-BSSGP-in-NS protocol stack */
static int nsip_fd_cb(struct osmo_fd *bfd, unsigned int what)
{
	int rc = 0;

	if (what & BSC_FD_READ)
		rc = handle_nsip_read(bfd);
	if (what & BSC_FD_WRITE)
		rc = handle_nsip_write(bfd);

	return rc;
}

/*! \brief Create a listening socket for GPRS NS/UDP/IP
 *  \param[in] nsi NS protocol instance to listen
 *  \returns >=0 (fd) in case of success, negative in case of error
 *
 *  A call to this function will create a UDP socket bound to the port
 *  number and IP address specified in the NS protocol instance. The
 *  file descriptor of the socket will be stored in nsi->nsip.fd.
 */
int gprs_ns_nsip_listen(struct gprs_ns_inst *nsi)
{
	struct in_addr in;
	int ret;

	in.s_addr = htonl(nsi->nsip.local_ip);

	nsi->nsip.fd.cb = nsip_fd_cb;
	nsi->nsip.fd.data = nsi;
	ret = osmo_sock_init_ofd(&nsi->nsip.fd, AF_INET, SOCK_DGRAM,
				 IPPROTO_UDP, inet_ntoa(in),
				 nsi->nsip.local_port, OSMO_SOCK_F_BIND);
	if (ret < 0)
		return ret;

	ret = setsockopt(nsi->nsip.fd.fd, IPPROTO_IP, IP_TOS,
				&nsi->nsip.dscp, sizeof(nsi->nsip.dscp));
	if (ret < 0)
		LOGP(DNS, LOGL_ERROR,
			"Failed to set the DSCP to %d with ret(%d) errno(%d)\n",
			nsi->nsip.dscp, ret, errno);


	return ret;
}

/*! \brief Initiate a RESET procedure
 *  \param[in] nsvc NS-VC in which to start the procedure
 *  \param[in] cause Numeric NS cause value
 *
 * This is a high-level function initiating a NS-RESET procedure. It
 * will not only send a NS-RESET, but also set the state to BLOCKED and
 * start the Tns-reset timer.
 */
void gprs_nsvc_reset(struct gprs_nsvc *nsvc, uint8_t cause)
{
	LOGP(DNS, LOGL_INFO, "NSEI=%u RESET procedure based on API request\n",
		nsvc->nsei);

	/* Mark NS-VC locally as blocked and dead */
	nsvc->state = NSE_S_BLOCKED;
	/* Send NS-RESET PDU */
	if (gprs_ns_tx_reset(nsvc, cause) < 0) {
		LOGP(DNS, LOGL_ERROR, "NSEI=%u, error resetting NS-VC\n",
			nsvc->nsei);
	}
	/* Start Tns-reset */
	nsvc_start_timer(nsvc, NSVC_TIMER_TNS_RESET);
}

/*! \brief Establish a NS connection (from the BSS) to the SGSN
 *  \param nsi NS-instance
 *  \param[in] dest Destination IP/Port
 *  \param[in] nsei NSEI of the to-be-established NS-VC
 *  \param[in] nsvci NSVCI of the to-be-established NS-VC
 *  \returns struct gprs_nsvc representing the new NS-VC
 *
 * This function will establish a single NS/UDP/IP connection in uplink
 * (BSS to SGSN) direction.
 */
struct gprs_nsvc *gprs_ns_nsip_connect(struct gprs_ns_inst *nsi,
				struct sockaddr_in *dest, uint16_t nsei,
				uint16_t nsvci)
{
	struct gprs_nsvc *nsvc;

	nsvc = nsvc_by_rem_addr(nsi, dest);
	if (!nsvc)
		nsvc = gprs_nsvc_create(nsi, nsvci);
	nsvc->ip.bts_addr = *dest;
	nsvc->nsei = nsei;
	nsvc->remote_end_is_sgsn = 1;

	gprs_nsvc_reset(nsvc, NS_CAUSE_OM_INTERVENTION);
	return nsvc;
}

void gprs_ns_set_log_ss(int ss)
{
	DNS = ss;
}

/*! }@ */